Front Cover

Draft 2/22/96

**MANUAL OF PRACTICE**

**FOR AN EFFECTIVE**

**ANTI-ICING PROGRAM**

A Guide For Highway

Winter Maintenance Personnel

Prepared for the Federal Highway Administration

by

**US Army Cold Regions Research and**

**Engineering Laboratory**

**Corps of Engineers**

**Hanover, New Hampshire**

R&D Foreword and Disclaimer Notice

Technical Report Documentation Page

4\. Title and Subtitle

MANUAL OF PRACTICE FOR AN EFFECTIVE ANTI-ICING PROGRAM

A Guide For Highway Winter Maintenance Personnel

7\. Authors

Stephen A. Ketcham, L. David Minsk, Robert R. Blackburn, Edward J.
Fleege

9\. Performing Organization Name and Address

US Army Cold Regions Research and Engineering Laboratory

72 Lyme Road

Hanover, New Hampshire 03755-1290

15\. Supplementary Notes

Contracting Officer's Technical Representative (COTR) - Brian Chollar

16\. Abstract

Highway anti-icing is the snow and ice control practice of preventing
the formation or development of bonded snow and ice by timely
applications of a chemical freezing-point depressant. It provides a
maintenance manager with two major capabilities: the capability for
maintaining roads in the best conditions possible during a winter storm,
and the capability to do so in an efficient manner. As a consequence,
anti-icing has the potential to provide the benefit of increased traffic
safety at the lowest cost. However, to achieve this benefit the
maintenance manager must adopt a systematic approach to snow and ice
control and must ensure that the performance of the operations is
consistent with the objective of preventing the formation or development
of bonded snow and ice. Such an approach requires use of considerable
judgment in making decisions, requires that available information
sources be utilized methodically, and requires that the operations be
anticipatory or prompt in nature.

This manual provides information for successful implementation of an
effective highway anti-icing program. It is written to guide the
maintenance manager in developing a systematic and efficient practice
for maintaining roads in the best conditions possible during a winter
storm. It describes the significant factors that should be understood
and must be addressed in an anti-icing program, with the recognition
that the development of the program must be based on the specific needs
of the site or region within its reach. The manual includes
recommendations for anti-icing practices and guidance for conducting
anti-icing operations during specific precipitation and weather events.

17\. Key Words

highways, anti-icing, snow and ice control, preventive strategy, bonded
snow and ice, application timing, chemical freezing point depressant,
deicing

Metric Conversion Chart

**TABLE OF CONTENTS**

**[Section]{.underline} [Page]{.underline}**

1\. INTRODUCTION

1.1 PURPOSE OF THE MANUAL

1.2 SCOPE AND ORGANIZATION OF THE MANUAL

2\. ANTI-ICING IN THE CONTEXT OF A WINTER MAINTENANCE PROGRAM

2.1 LEVEL OF SERVICE

2.2 CLIMATIC CONDITIONS

2.3 DEICING AND ANTI-ICING

2.4 ANTI-ICING AS A SYSTEMATIC PRACTICE

2.5 ABRASIVES USE

3\. ANTI-ICING PROGRAM TOOLBOXES

3.1 OPERATIONS TOOLBOX

3.1.1 Solid chemical application capability

3.1.1.1 Solid materials and gradation

3.1.1.2 Equipment

Solid material spreaders

Solid chemical storage facilities

3.1.2 Liquid chemical (chemical solution) application capability

3.1.2.1 Chemical solutions

3.1.2.2 Equipment

Liquid application equipment

Chemical solution production facilities; salt brine

Chemical solution production facilities; liquid CMA

Chemical solution storage facilities

3.1.3 Prewetted solid chemical application capability

3.1.3.1 Materials

Solid materials and gradation

Prewetting solutions

3.1.3.2 Prewetting techniques and equipment

Prewetting of stockpile

Prewetting of a load or while loading

Prewetting by spreader spray systems

Chemical solution production and chemical storage facilities

TABLE OF CONTENTS (Continued)

3.1.4 Plowing capability

3.1.4.1 Types of snowplows

3.1.4.2 Cutting edges

3.1.4.3 Slush blades

3.2 DECISION-MAKING TOOLBOX

3.2.1 Weather forecast information

3.2.2 Road and road weather information

3.2.2.1 Road information

3.2.2.2 Road Weather Information Systems (RWIS) and their components

3.2.2.3 Role of thermal mapping

3.2.3 Nowcasting

3.2.4 Traffic information

3.2.5 Patrols

3.2.6 Evaluations of treatment effectiveness

3.3 PERSONNEL TOOLBOX

3.3.1 Trained personnel for anti-icing decision making and operations

3.3.2 Deployment of personnel

4\. RECOMMENDED ANTI-ICING PRACTICES

4.1 INITIAL OPERATION

4.1.1 Information assembly

4.1.2 Decision point

4.1.3 Action

4.1.3.1 Apply chemical

Recommendations for use of liquid chemicals

Recommendations for use of solid and prewetted solid chemicals

4.1.3.2 Plow

4.1.3.3 Do nothing

4.2 SUBSEQUENT OPERATIONS

4.2.1 Monitoring of conditions

4.2.2 Action

4.2.2.1 Apply chemical

4.2.2.2 Plow

4.2.2.3 Do nothing

4.3 SPECIAL CONSIDERATIONS

4.3.1 Traffic condition

4.3.2 Wind

4.3.3 Hybrid precipitation events

4.3.4 Prewetting quantities

4.3.5 Development of snowpack and bond

4.3.6 Use of abrasives

TABLE OF CONTENTS (Continued)

4.4 POST-STORM ASSESSMENT OF OPERATIONS

APPENDIX A. SELECTED CHEMICALS AND THEIR PROPERTIES

A.1 CALCIUM CHLORIDE, CaCl~2~

A.1.1 Introduction

A.1.2 Preparation of liquid CaCl~2~

A.1.2.1 Method 1 (Known mixing container volume)

A.1.2.2 Method 2 (Unknown mixing container volume)

A.1.2.3. Additional comments

A.2 SODIUM CHLORIDE, NaCl

A.2.1 Solid NaCl

A.2.2 Preparation of liquid NaCl

A.2.2.1 Method 1 (Known mixing container volume)

A.2.2.2 Method 2 (Unknown mixing container volume)

A.2.2.3 Additional comments

A.3 MAGNESIUM CHLORIDE, MgCl~2~

A.4 CALCIUM MAGNESIUM ACETATE, \[CaMg~2~ (CH~3~COO)~2~\]~6~

A.4.1 Introduction

A.4.2 Preparation of liquid CMA

A.5 POTASSIUM ACETATE, KC~2~H~3~O~2~

APPENDIX B. FREEZING-POINT OF CHEMICAL SOLUTIONS

B.1 INTRODUCTION

B.2 NaCl AND CaCl~2~

B.3 MgCl~2~

B.4 CMA AND KAc

APPENDIX C. OPERATIONS GUIDE FOR MAINTENANCE FIELD PERSONNEL

C.1 INTRODUCTION

C.2 GUIDANCE FOR ANTI-ICING OPERATIONS

C.3 GLOSSARY OF TERMS

REFERENCES

**LIST OF FIGURES**

**[Figure]{.underline} [Page]{.underline}**

1\. Outline of the components of an anti-icing program in the context of
a winter maintenance\
program.

2\. Hopper type spreader.

3\. Under-tailgate spreader with prewetting equipment.

4\. Simple roof over stockpile.

5\. Enclosed structure for chemical storage.

6\. Single disk liquid spreader.

7\. Liquid spreader using a distributor bar with nozzles.

8\. Chassis-mounted liquid spreader.

9\. Slip-in liquid spreader.

10\. Tow-behind liquid spreader.

11\. Kansas DOT salt brine production facility.

12\. Testing of salt brine concentration with a hydrometer.

13\. Outside CMA mixing facility operated by Washington DOT.

14\. Overhead spraybar for prewetting chemical load in truck.

15\. RWIS roadside installation.

16\. Phase diagrams of NaCl and CaCl~2~ solutions.

17\. Phase diagrams of five chemical solutions.

**LIST OF TABLES**

**[Table]{.underline} [Page]{.underline}**

1\. Pure salt concentration and corresponding specific gravity (measured
by a hydrometer) at\
15°C (59°F).

2\. Calcium chloride mixing proportions.

3\. Gradation of salt specified by ASTM D 632.

4\. Salt gradation specified by British Standard BS 3247 *Specification
for salt for spreading\
in highways for winter maintenance*.

5\. Swedish gradation for salt.

6\. Finnish gradation for salt.

7\. Proportions for preparing sodium chloride solutions from commercial
grade salt (i.e., up\
to 5 percent impurities).

8\. Weather event: light snow storm.

9\. Weather event: light snow storm with period(s) of moderate or heavy
snow.

10\. Weather event: moderate or heavy snow storm.

11\. Weather event: frost or black ice.

12\. Weather event: freezing rain storm.

13\. Weather event: sleet storm.

# introduction

Application of a chemical freezing-point depressant onto a highway
pavement at the start of a winter storm, or even prior to the beginning
of precipitation, inhibits the development of a bond between the snow or
ice and the pavement surface. Furthermore, moderate and periodic
reapplications of the chemical during the storm can continue this
effect. Such preventive operations are the core of an anti-icing
program.

Anti-icing is the snow and ice control practice of *preventing* the
formation or development of bonded snow and ice by timely applications
of a chemical freezing-point depressant. It provides a maintenance
manager with two major capabilities: the capability for maintaining
roads in the best conditions possible during a winter storm, and the
capability to do so in an efficient manner. As a consequence, anti-icing
has the potential to provide the benefit of increased traffic safety at
the lowest cost. However, to achieve this benefit the maintenance
manager must adopt a systematic approach to snow and ice control and
must ensure that the performance of the operations is consistent with
the objective of preventing the formation or development of bonded snow
and ice. Such an approach requires use of considerable judgment in
making decisions, requires that available information sources be
utilized methodically, and requires that the operations be anticipatory
or prompt in nature.

In contrast to anti-icing operations, a common procedure of traditional
snow and ice control practice is to wait until an inch or more of snow
accumulates on the pavement before beginning to plow and treat the
highway with chemicals or abrasives. While this procedure is
straight-forward, it frequently leads to a compacted snow layer (pack)
that is tightly bonded to the pavement surface. A subsequent "deicing"
of the pavement is then necessary, usually requiring a large quantity of
chemical to work its way through the pack to reach the snow/pavement
interface and destroy or weaken the bond. Because this operation is
reactionary, it requires less judgment than anti-icing. Yet as a result
of its inherent delay, it often provides less safety, at higher cost,
than anti-icing. Nonetheless the reactive technique of deicing will
remain important for snow and ice control, as there will always be lower
priority service levels that preclude preventive operations.

Anti-icing is well suited to routes with a higher level of service. This
is because the vigilance and timeliness of successful anti-icing
operations are most compatible with service levels requiring earlier and
higher frequency winter maintenance operations. It is also because the
preventive nature of anti-icing can support higher service level
objectives such as maintaining bare pavement throughout a storm or
returning to bare pavement as soon as possible following pack formation.
In fact, because of the demanding requirements of higher service levels,
many maintenance forces in the United States have been instinctively
implementing elements of anti-icing practices for years. Sufficient
evidence has accumulated from 2 years of Strategic Highway Research
Program (SHRP) and 2 years of Federal Highway Administration (FHWA)
anti-icing testing to demonstrate the effectiveness of US anti-icing
practices, which has culminated in this manual.

## Purpose of the manual

This manual provides information for successful implementation of an
effective anti-icing program. It is intended for use by highway agency
maintenance managers at headquarters and subareas as well as field
personnel.

The manual is written to guide the maintenance manager in developing a
systematic and efficient practice for maintaining roads in the best
conditions possible during a winter storm. It describes the significant
factors that should be understood and must be addressed in an anti-icing
program, with the recognition that the development of the program must
be based on the specific needs of the site or region within its reach.
It focuses on the weather information, materials, and methods that will
best address site conditions such as level of service, highway agency
resources, climatological conditions, and traffic.

## Scope and organization of the manual

Following the Introduction, this manual is divided in three sections
plus appendixes:

-   Section 2 presents an introduction to anti-icing in the context of
    an agency's winter maintenance program.

-   Section 3 describes the operational, decision making, and personnel
    management capabilities needed to support an anti-icing program. It
    contains three major components: operations toolbox, decision-making
    toolbox, and personnel toolbox.

-   Section 4 describes the operations and practices of anti-icing. It
    includes recommendations for successful anti-icing practices that
    can be employed for various combinations of precipitation,
    temperature, traffic volumes, and mandated levels of service. It
    complements the information provided in section 3, and serves as a
    companion and background document for the specific and concise
    guidance in Appendix C. The Section contains four major components:
    initial operations, subsequent operations, special considerations,
    and post-storm assessment of operations. It and the guidance of
    Appendix C are based on analysis of data obtained during the winters
    of 1993/94 and 1994/95 in the 15 States participating in the FHWA
    Test and Evaluation Project 28 (T&E 28) ([1]{.underline})[^1], and
    also on the relevant experience and review of anti-icing practices
    from SHRP Project H-208 ([2]{.underline}).

-   Supporting and auxiliary material regarding chemicals is presented
    in the Appendixes A and B. Appendix C presents guidance for
    conducting anti-icing operations during specific precipitation and
    weather events.

# anti-icing in the context of a winter maintenance program

A winter maintenance program consists of several elements with varying
degrees of importance depending on the size of the operational
jurisdiction it covers and the complexity of its road network. One
element, level of service (LOS), is important for all jurisdictions. It
must be considered, along with the climatic conditions, in the design of
any snow and ice control program. This Section describes how the level
of service and climatic conditions influence an anti-icing program, and
how anti-icing fits into the context of an overall winter maintenance
program and level of service.

## Level of service

The extent to which maintenance services will be provided to a road
section is determined by management by the assignment of a level of
service. In the case of winter maintenance, this will require
establishing a prescribed end-of-storm road condition, what intermediate
conditions will be acceptable while obtaining that condition, or the
frequency of snow and ice control maintenance operations. Some examples
of LOS are: maintain 24-h coverage until near normal surface conditions
are restored with coverage at a rate of 2 to 4 cycles (passes one
vehicle would make over a given point on the road) per shift (however
defined) as conditions and resources allow; bare pavement during
daylight hours; center bare at all times; or snow-covered to a maximum
of 12 mm (1/2 in) during daylight hours. The LOS will largely be
determined by the importance of the road, and hence the average daily
traffic. As a reflection of the desired bare pavement condition, high
winter maintenance service levels are often generically called "bare
pavement policies."

As defined in the Introduction, anti-icing is the snow and ice control
practice of preventing the formation or development of bonded snow and
ice by timely applications of a chemical freezing-point depressant. A
winter maintenance crew that is persistent in this practice is best able
to support demanding road condition requirements set forth by a higher
LOS. If the LOS requirements are in terms of operational frequency
rather than road condition, a crew operating at higher frequency would
find anti-icing practices to provide the best road conditions possible
within a given set of operational constraints. Because of the proven
compatibility between anti-icing and higher LOS, this manual presents
anti-icing as a strategy for support of high service levels.

Figure 1 depicts the components of an anti-icing program in the context
of a winter maintenance program and the LOS assignment. It shows
anti-icing as a support strategy for "bare pavement" service levels.

## Climatic conditions

In addition to the service level, maintenance effort will vary with
climatic conditions. A factor of great importance is pavement
temperature. Pavement temperature directly influences the formation,
development, and breaking of a bond between fallen or compacted
precipitation and the road surface as well as the effectiveness of
chemical treatments. It is also important when high humidity levels are
accompanied by low dew point temperatures. Under these conditions there
will be a greater potential for formation of frost and black ice. Unless
some external source of heat is provided, the pavement temperature will
generally track air temperature with a time delay. For road sections
without obstructions to a clear sky view, solar radiation during the day
and exposure to the clear night sky will affect the road surface
temperature to a greater extent than on sections influenced by air
contact only.

Other important climatic factors are type and rate of precipitation.
Together with pavement temperature, they are the most important
variables to consider when performing anti-icing operations. The
operational guidance described later in this manual is presented in
terms of these variables.

Figure 1. Outline of the components of an anti-icing program in the
context of a winter maintenance program.

## Deicing and anti-icing

There are two distinct snow and ice control strategies that make use of
chemical freezing-point depressants: deicing and anti-icing. They differ
in their fundamental objective. Whereas anti-icing operations are
conducted to prevent the formation or development of bonded snow and ice
for easy removal, deicing operations are performed to break the bond of
already-bonded snow and ice. Deicing is familiar to most agencies since
it has been the most widely used strategy in the past. The design of
deicing operations as a bond-breaking operation stems from its timing:
it is commonly initiated only after 25 mm (1 in) or more of snow has
accumulated and bonded to the road.

A distinction between anti-icing and deicing has not always been clear.
This is because anti-icing is a relatively new term. Some agencies that
have instinctively adopted anti-icing practices over the years have used
the term deicing to describe their operations, even when they were
intended to prevent a strong ice-pavement bond. In this manual a
distinction between a primarily-*preventive* and a primarily-*reactive*
strategy is intended when referring to anti-icing and deicing,
respectively.

There are other strategies and techniques that can and have been used in
snow and ice control operations. These include such approaches to a bare
pavement policy as use of heated pavements, structural covering of a
road to protect it from precipitation (e.g., covered bridges or
avalanche sheds), and the use of a modified pavement surface in
conjunction with plowing, to name a few. These are not covered in this
manual.

## Anti-icing as a systematic practice

As illustrated in Figure 1, both deicing and anti-icing can be used to
support higher service level objectives. However, because deicing is
reactionary, it cannot support strict requirements for safe road
conditions *during* a winter storm. Anti-icing can meet such
requirements, but to successfully and efficiently do so the maintenance
manager must ensure that the *timing* of the operations is consistent
with the objective of preventing the formation or development of bonded
snow and ice. This is not an easy task. It requires use of much more
judgment in making decisions, requires that available information
sources be utilized methodically, and requires that the operations be
anticipatory or prompt in nature. In short it requires a systematic
approach.

The elements of a systematic anti-icing program are shown in Figure 1.
As indicated, support of an anti-icing strategy is divided into *tools*
and *operations*. The supporting tools can be organized according to
*operations*, *decision-making*, and *personnel* "toolboxes," which are
further broken down according to capabilities, information sources, and
procedures that may be available for a given operation. A toolbox
analogy is followed to suggest that managers should use their available
resources systematically as they would use mechanical tools in the
course of a methodical repair job. Operations are broken down into
*initial* and *subsequent* operations in order to convey the importance
of the initial chemical treatment in anti-icing operations, and to
signal that subsequent operations throughout a storm or weather event
should follow the anti-icing strategy as well.

While the outline of Figure 1 indicates the underlying complexity of
anti-icing practices, it also reveals that what may initially be thought
of as an overly demanding practice is actually an organized set of
preparations, decisions, and operations. Such a methodical program can
be designed for an agency's unique conditions using tools that are
generally available to agencies today and using operational guidance
provided later in this manual. The tools are described in Section 3, and
the operational guidance is presented in Section 4 and Appendix C.

## abrasives use

Common to many snow and ice control operations is the use of abrasives.
It is recognized that abrasives may be necessary when a rapid increase
in friction coefficient is required, particularly at temperatures so low
that chemical action is slow, and in conditions where snow or ice is
strongly bonded to the pavement and cannot easily be removed. As these
latter conditions are more likely to occur in the course of deicing,
abrasives treatments can be an important tool for deicing operations.
Abrasives are not ice-control chemicals, however, and will not support
the fundamental objective of either anti-icing or deicing. Their sole
function is to increase the coefficient of friction. This increase may
be short lived, because traffic will rapidly disperse abrasives.

There is generally no advantage gained from the routine use of abrasives
in an anti-icing program. When anti-icing operations have successfully
prevented or mitigated the hazards of packed snow, for example, straight
abrasives applications will provide no significant increase in friction
or improvement in pavement condition. Further, a mix of abrasives and
chemical will usually be no more effective as an anti-icing treatment
during snowstorms than the same amount of chemical placed alone. It even
appears that the use of abrasives in the mix can be detrimental to the
effectiveness of the chemical. Because of the cost associated with both
application and clean-up of roads and drainage facilities, and because
of the potential airborne dust problem accompanying their use, abrasives
applications should not be a routine operation of an anti-icing program.

Although this manual does not present abrasives application capability
as a tool for anti-icing, Section 4 and Appendix C do provide guidance
for conditions under which abrasives use may be appropriate during
operations. Recommended practice for abrasives applications, or for
deicing, is not provided in this manual.

# Anti-icing program toolboxes

As indicated in Figure 1, the supporting tools of an anti-icing strategy
are organized into an operations toolbox, a decision-making toolbox, and
a personnel toolbox. Each comprises a combination of new, conventional,
and traditional technologies, and contains capabilities, information
sources, or procedures that address the toolbox function.

The operations toolbox includes capabilities for applying solid
chemicals, "liquid" chemicals (i.e., chemical solutions), or prewetted
solid chemicals, and for plowing. The decision-making toolbox includes
long- and mid-term weather forecasts, road and road weather information,
nowcasting, traffic information, patrols providing information on
weather and pavement conditions, and evaluations of treatment
effectiveness. The personnel toolbox consists of personnel trained in
anti-icing practices and use of information sources for decision making,
and stand-by and call-out procedures.

In the development of an anti-icing program, each toolbox should be
viewed as a critical component of a systematic operation or practice.
The required elements of the toolboxes will differ from site to site,
jurisdiction to jurisdiction, or agency to agency, depending primarily
on levels of service, highway agency resources, and climatic conditions,
and so the selection of the tools will differ in each program design. In
addition, as newer technologies become available, as more effective
operational techniques are identified, and as a program is accordingly
developed over the course of time, the toolboxes will expand and their
elements improve. However, it will always be important that the
maintenance manager select and maintain effective anti-icing support
tools in the subject areas of the outline: operations, decision making,
and personnel. The discussion below is written as an initial guide to
assist the maintenance manager in this process.

## Operations toolbox

This discussion of the operations toolbox is divided into four major
categories: solid chemical application capability, chemical solution
application capability, prewetted solid chemical application capability,
and plowing capability. Each of these is described below. Material and
equipment requirements, and discussions of techniques, are included in
the descriptions.

### Solid chemical application capability

The use of dry solid chemicals as an anti-icing treatment can be
effective in many circumstances, but only those where there is
sufficient moisture or accumulation on the pavement. Moisture must be
available for two reasons: to prevent loss of material off a dry
pavement, and to trigger the solution of the salt. For initial
operations, solid chemicals will be effective when a maintenance team
has the operational resources to apply the chemical as soon as possible
after sufficient precipitation has fallen, but before snowpack or ice
bonds to the pavement. For subsequent operations, solid chemical
treatments will usually be effective as there is typically adequate
moisture or accumulation during later periods of storms. Nonetheless,
for either initial or subsequent operations, when there is not enough
moisture or accumulation on the pavement there is likely to be loss of
the chemical from the pavement. This may be caused by the blowing action
of traffic, especially from high speed and commercial vehicles, or by
the bouncing of particles off the pavement during spreading. It is not
uncommon to see dry solid chemicals rebound up to 1/2 m (2 ft) from a
dry pavement after being distributed from a conventional spreader
spinner, although recently-introduced zero-velocity spreaders have
enabled the placement of solid chemicals on the pavement with minimum
bounce.

The material and equipment requirements for solid chemical applications
are similar or identical to those used conventionally or well known by
most agencies. These are discussed here.

#### Solid materials and gradation

The solid chemical most commonly used for anti-icing treatments is salt,
or sodium chloride. A mix of solid sodium chloride and solid calcium
chloride has been used by some agencies, and in some instances straight
calcium chloride has been used. In fact, almost any solid chemical that
has been used for deicing also can be used for anti-icing depending on
operating conditions. Information on solid chemicals and solubility can
be found in Appendixes A and B.

The gradations of salt used for anti-icing treatments have mostly been
particle size distributions designed for deicing operations, which is
appropriate in the absence of prewetting. A discussion of gradation is
presented in Appendix A.

#### Equipment

##### Solid material spreaders

Originally salt was spread during snow and ice control operations by
shoveling it onto the road from the truck bed. Control of application
rate was not possible, and the physical exertion required over long
stretches of the road was demanding.

Later, salt spreaders which could be attached to a truck were developed
along the line of the fertilizer distributors used in agriculture. This
was the beginning of attempts to achieve a more uniform method of
applying salt to the road. Rate control of the material, however, was
still not satisfactory because the spreading rate was not varied as a
function of truck speed. Over-spreading occurred when the truck came to
a stop, and under-spreading when the truck accelerated. When the
economic and environmental demands became evident, manufacturers of
spreading equipment modified their equipment to distribute snow and ice
control materials at controlled flow rates and at speeds higher than
were used for agricultural purposes.

Nowadays dry chemicals are applied to the roadway by means of either a
hopper type spreader (Figure 2) or a dump body with an under-tailgate
spreader (Figure 3). These spreaders are capable of spreading
free-flowing granular materials from a minimum width of 1 m (3 ft) to a
maximum of 12 m (40 ft). Generally the hopper spreaders are
self-contained units mounted in dump-trucks in winter, then removed and
stored in other seasons so that the trucks may be used for other
maintenance work. These units consist of a steel V-box body,
discharge/feed conveyer, spinner disc, power drive, and other necessary
components. The V-box spreaders have hopper capacities of 3.4 to 13.2
m^3^ (4.5 to 17.2 yd^3^). At the hopper's base is a full-length feed
system whose speed is controlled from the truck cab. This feed system
can be either a full-length belt, chain-drag belt, or a longitudinal
auger. These systems feed material into a chute where it falls onto a
spinner that spreads it laterally across the road.

The under-tailgate spreader is also a self-contained unit that slips
into a dump body and is easily removed and hooked up. These devices
consist of a small hopper, an auger feed mechanism, hydraulic driver
system, and a spinner disc. Both under-tailgate and hopper spreaders
have been used successfully for anti-icing operations.

The variables affecting application rate of a given material are 1) area
of the gate opening on a hopper box or the opening in the bottom of the
tailgate hopper, 2) feed-belt or auger speed, and 3) truck speed. The
gate opening height is an adjustment made at the time of calibration and
generally is not changed during spreading operations. Thus, to control
the actual spreading rate, the speed of the feed belt or auger needs to
be considered along with truck speed. The methods that can be used to
control the spreading rate of spreaders fall into three categories: 1)
no control, 2) manual control, and 3) automatic control.

Figure 2. Hopper type spreader.

Figure 3. Under-tailgate spreader with prewetting equipment.

Automatic control of material application rates is achieved with
ground-speed-oriented controllers. These units automatically adjust a
pressure-compensation valve. A truck operator with an automatic
controller is able to maintain a constant application rate of material
on the road without having to adjust the valve opening to conform to the
changing speed of the truck. To spread a constant amount of material
along a road, a truck operator need only select an application rate.
With some controllers, the spreading width can also be selected. Changes
can be made at any time during operation - the automatic controller does
the rest. Manual control, however, requires continual adjustment of the
valve to maintain a constant application rate.

Automatic controllers use a truck-speed sensor for adjusting the opening
of the pressure-compensation valve which in turn controls the operating
speed of the feed mechanism. Various types of truck-speed sensors are
available. Most are connected to the speedometer cable, while some
measure the rotation of the drive shaft or a wheel. There is not enough
information in the literature to suggest which type of sensor is the
most durable, reliable, or appropriate for anti-icing operations.
However, all commercially available units appear to be equally suitable.

There are two types of automatic controllers: the open-loop system and
the closed-loop system. Both types require a speed sensor. The open-loop
controller uses only this sensor to adjust the hydraulic valve opening.
In the closed-loop system, a second sensor detects the operating speed
of the feed-belt or auger. The closed-loop controller integrates the two
signals to adjust the hydraulic valve opening automatically.

Many maintenance managers believe that an open-loop controller with its
single truck-speed sensor provides adequate control of the application
rate. They feel that annual equipment maintenance and calibration avoid
the need for the second sensor provided with the closed-loop system.
Some also believe that, because much material is not uniform but lumpy,
very close control of the feed-belt or auger speed is not necessary.

Other users prefer the multiple control provided by closed-loop
controller systems. They feel the second sensor is needed to correct
changes which occur during snow and ice control operations such as wear
of spreader equipment and variations in performance of the spreader's
hydraulic fluid. Wear can change the calibration of the equipment. Also,
the variable operating temperature and aging of the spreader's hydraulic
fluid change the operation of the feed-belt, auger and the spinner
motors.

Regardless of the type of spreader, it is extremely important to
calibrate it to ensure that the desired quantity of material is really
being applied. All equipment should be calibrated before winter
operations begin. Though most agencies do this, they are less likely to
check the manufacturer's calibration on new equipment delivered from the
factory. It is good practice to do so. Also, many agencies assume
calibration is necessary only before the season begins and don't realize
that settings may change with use. Changes in mechanical linkages and
components may occur, and hydraulic systems perform differently as the
season progresses. It is also good practice to recalibrate the spreader
equipment after any maintenance is performed on the spreader/truck
system.

Anti-icing operations generally require applying a controlled quantity
of chemical (often as little as 30 kg/lane-km (100 lb/lane-mi), and in
some cases even less) uniformly across the road. To determine a
spreader's capability to control application rate and the distribution
pattern, the equipment can be evaluated and calibrated following the
"Proposed American Testing Protocol for Winter Maintenance Spreaders."
This protocol is reported in SHRP H-385 report *Development of
Anti-Icing Technology* ([2]{.underline}). Another procedure for
calibrating application rate is outlined in the Salt Institute's *The
Snowfighter's Handbook* ([3]{.underline}).

##### Solid chemical storage facilities

Solid chemicals should be stored under cover or inside a building.
Chemicals stored in the open pick up moisture, produce leachate which
drains into water sources, and develop a waste outer crust. When loaded
into a spreader, the crust breaks into lumps that may clog the spreading
equipment or will at least interrupt the feeding of the spinner.

Many types of barns or silos are in use for chemical storage, ranging
from a simple roof over the stockpile (Figure 4) to a complete building
(Figure 5). These facilities may also house the spreader(s) under the
same or appended roof.

The number of storage loading points for a given roadway system is
determined by the following considerations: 1) the maximum cycle time
allowed for a spreading operation; 2) the level of service of the road
segments to be treated; 3) special features such as bridges, tunnels,
and intersections; and 4) the route length of the spreaders. The route
length determines the number of material storage locations (sheds) and
the way they are distributed geographically. It is possible that the
route length or range of operation of a spreader used in anti-icing
operations can be expanded over that used for conventional practices. As
such, the important factors in determining the number of storage
locations are the first three enumerated above. It is possible that the
number of storage loading points can be consolidated through the use of
anti-icing operations.

### Liquid chemical (chemical solution) application capability

Though solid or prewetted solid chemicals can be used as anti-icing
treatments, there are advantages to use of liquids in small amounts for
some conditions at pavement temperatures of about -5^o^C (23^o^F) and
above. These include the ability to place chemical uniformly over the
pavement at relatively fast spreading speeds, and the ability to place
chemical onto dry pavement as a pre-storm treatment to avert delays that
may lead to bonded snow or ice. However, this means putting the chemical
down before enough snow has accumulated to keep the chemical from
reaching the pavement or from being excessively diluted. In some
situations it may be beneficial to remove snow and slush from the road
using methods that are more thorough than conventional techniques. This
will be discussed later in Section 3.1.4 on plowing. Liquids can be used
at pavement temperatures below -5^o^C (23^o^F) by increasing the
application rate over the levels recommended for -5^o^C (23^o^F) and
above. The cost effectiveness of using higher liquid chemical
application rates at lower pavement temperatures needs to be evaluated
on a case-by-case basis.

#### Chemical solutions

Five chemicals have been used for liquid anti-icing treatments: sodium
chloride (NaCl), magnesium chloride (MgCl~2~), calcium chloride
(CaCl~2~), calcium magnesium acetate (CMA), and potassium acetate (KAc).
Appendix A presents information on the properties of these chemicals and
instructions for preparing various liquid concentrations. Appendix B
contains information on the freezing-point of these five brines as a
function of the solution concentrations.

#### Equipment

##### Liquid application equipment

There are two principal types of liquid application equipment for
highway use. One uses spinners consisting of either multiple rotating
disks or a single disk (Figure 6). The other type uses nozzles on a
distributor bar (Figure 7). Either spreader may be chassis-mounted
(fixed on the frame) (Figure 8); be a "slip-in" unit that can be placed
temporarily in the bed of a dump truck or on the frame and removed
during the off-season (Figure 9); or it can be a trailer, or
"tow-behind" unit (Figure 10).

Until recently, most liquid applicators were made in Europe and
Scandinavia. Several United States firms now provide highway spreader
equipment and spreader components for distributing liquid chemicals (and
prewetted solids).

Figure 4. Simple roof over stockpile.

Figure 5. Enclosed structure for chemical storage.

Figure 6. Single disk liquid spreader.

Figure 7. Liquid spreader using a distributor bar with nozzles.

Figure 8. Chassis-mounted liquid spreader.

Figure 9. Slip-in liquid spreader.

Figure 10. Tow-behind liquid spreader.

Descriptions of the capabilities of a nozzle-type and a spinner-type
spreader are presented here. They are provided only as examples for
discussion purposes, and are not to be taken as endorsements or as
recommended specifications.

*Nozzle-type spreader*. This spreader, shown in Figure 10, sprays the
liquid from nozzles at a low height above the road to reduce the
influence of air turbulence behind the vehicle that can cause the liquid
to disperse before hitting the pavement. The unit is designed to be
towed by a truck equipped with a liquid tank. The spreader is powered by
its own traction-driven wheel and also has a ground-speed control.

In this particular unit, the liquid chemical flows by gravity through a
clear 75 mm (3 in) plastic hose from the tank to the spreader, where two
liquid pumps provide an adequate supply of liquid chemical to an array
of nozzles. The two diaphragm pumps share a common inlet filter. The
spraybar is 2.3 m (89 in) long and is equipped with six nozzles\--three
large and three small. The large nozzles spray over a 3.5 m (11.5 ft)
width. At low speeds, the smaller nozzles are used. As the truck's speed
increases and the need for liquid volume increases, the smaller nozzles
are shut off automatically and the larger nozzles are supplied without a
break in spray pattern. As the truck slows down, the reverse process
occurs.

Three additional stainless steel nozzles are mounted on the left end of
the spray bar. These apply liquid to the left lane. A total width of 7 m
(23 ft) can be sprayed with the spraybar and side nozzles. Each side
nozzle is pressure regulated to ensure an even flow at all speeds.

*Spinner-type spreader*. This unit, shown in Figure 6, attaches to the
rear of a truck equipped with liquid tanks. The unit can be powered
either by the vehicle's hydraulic system or by a separate road wheel.

In this unit, the liquid chemical is pumped by two impeller pumps to a
specially designed stainless steel spinner. This is slightly convex with
10 curved vanes, and the spinner mechanism is manually adjustable to
give asymmetric or symmetric spread patterns. The unit can apply liquid
over a spread width of 2 to 8 m (7 to 26 ft) while traveling between 10
and 60 km/h (5 and 40 mph).

There is not enough information in the literature to suggest which type
of liquid spreader is the most reliable or effective for anti-icing
operations. The nozzle type can have problems with nozzles plugging or
can dispense such a fine mist that it disperses before hitting the
pavement surface. Some nozzle type designs incorporate large size (6 mm
(0.25 in) or larger) spray nozzles that increase the reliability of
spray equipment because they require less liquid filtration and are less
likely to clog. Spinner disks can dispense liquid droplets that are too
large for uniform coating of the pavement surface. A highway agency
interested in using a liquid spreader for anti-icing operations needs to
review the spreader manufacturer's claims carefully.

Highway agencies interested in beginning or experimenting with an
anti-icing program might consider modifying some existing spreader
equipment before investing in new equipment. Asphalt distributor trucks,
liquid fertilizer spreaders, and spreaders used to spray for weed
control have been modified and successfully used by some highway
agencies (Nevada Department of Transportation and Colorado Department of
Transportation to name only two) in their initial anti-icing programs.
California Department of Transportation (Caltrans) has built a
customized spray bar that is capable of applying 100 L (25 gal) of
solution per lane mile at speeds up to 50 km/h (30 mph). Based on just 1
year's positive experience with the spray bar, Caltrans decided to build
two additional liquid spreaders.

Regardless of the type of liquid spreader used, it is extremely
important to calibrate it to ensure that the desired quantity of
material is actually being applied. All equipment should be calibrated
before winter operations begin. Though most agencies do this, they are
less likely to check the manufacturer's calibration on new equipment
delivered from the factory. It is a good practice to perform this
calibration. Also, many agencies assume calibration is necessary only
before the season begins and don't realize that settings may change with
use. Changes in mechanical linkages and components may occur, and
hydraulic systems perform differently as the season progresses. As a
check, compare the controller application rate setting against the
volume remaining in the tank several times during the winter for any
deviation. It is a simple matter with most liquid applicators to use a
dipstick for a check.

An application that leaves the surface merely damp will be sufficient in
many conditions. Since these applications do not result in flow of
liquid on the pavement, the uniformity of spread must be achieved at
time of application. If a nozzle or filter is plugged, that part of the
road the spray normally "sees" will remain untreated. [Nozzles and
filters need to be checked frequently]{.underline}.

Spreader speed must be evaluated for the particular conditions.
Turbulence will affect spread coverage uniformity. It would be desirable
to have a spreader that could perform adequately at speeds close to
those of the traveling public in order to reduce the speed differential
and improve the safety of the operation.

Generally, experience has shown that liquid chemicals can be
successfully applied at speeds up to 40 to 55 km/h (25 to 35 mph) for
spinner type spreaders and at speeds up to 65 to 80 km/h (40 to 50 mph)
for spray bar type spreaders. Turbulence behind the spreader truck
prevents a uniform distribution pattern at higher application speeds.

The liquid supply tanks used on spreader vehicles should be made of
non-corrosive material such as polyethylene. Some States have used
stainless steel tanks but this adds to the weight of the system. A
number of highway agencies have installed 11 m^3^ (3000 gal)
truck-mounted tanks for use on the spreaders. They soon discovered, due
to weight limitations and density of the liquid chemicals used, only 7.5
m^3^ (2000 gal) of liquid could be carried on the standard size truck.
Also, they experienced problems with the liquid sloshing in a tank
without internal baffles. It is recommended that truck-mounted tanks
larger than 5.5 m^3^ (1500 gal) be equipped with internal baffles.

##### Chemical solution production facilities; salt brine

Simple NaCl brine manufacturing plants that can operate relatively
trouble-free became a necessity with the use of salt brine or prewetted
salt for anti-icing treatments. Highway agencies working with private
companies have designed a number of salt brine production plants. As a
result, there are several companies that manufacture brine production
systems.

Two types of manufacturing plants are currently in use for preparation
of saturated brine: batch and continuous flow. Simple batch units for
temporary or small scale production can be assembled using small tanks.
Water passed through a bed of rock salt by gravity will produce a
solution saturated at the water temperature. Production involves loading
a tank with salt and running water through it, collecting the brine in a
holding tank. From there the brine is passed through a 10 µm filter or
pumped into a storage tank or directly into a spreader truck. Production
rates are somewhat low with this process, about 8 L/s (600 gal/h).
Several agencies have assembled their own simple plants like this. The
plant used by Kansas DOT is shown in Figure 11.

The concentration should be checked during production with a hydrometer
(Figure 12). This device measures the specific gravity of the solution
which will increase as the concentration increases. Table 1 lists
hydrometer readings and the corresponding salt concentration for a
solution temperature of 15°C (59°F). More efficient continuous flow
units have been developed for high capacity production. These plants
force water under pressure through a bed of salt. The saturated solution
then flows into a storage receptacle. Salt and water are metered
automatically and continuously.

The following items should be considered in specifying or designing a
brine manufacturing plant:

-   Future needs for additional capacity

-   Adequate water inlet capacity

-   Suitability of the proposed site from an operational and
    environmental standpoint

-   Pump capacity requirement

-   Possibility of using earth heat for storage tanks

-   Overflow control requirement

-   Containment of spills

-   Use of noncorrosive material in the plant construction

##### Chemical solution production facilities; liquid CMA

A CMA solution is prepared by dissolving solid CMA in water, resulting
in a murky solution that settles over time to produce a clear CMA
solution on top and insoluble waste on the bottom. It is recommended
that the solution concentration not exceed about 25 percent. The
solution tends to be stable at this concentration. If the concentration
exceeds 28.5 percent, the dissolved CMA will tend to recrystallize which
will clog the spray nozzles on the liquid spreaders. The recommended 25
percent concentration is prepared by mixing 1.36 kg (3.00 lb) of CMA per
3.78 L (1 gal) water. For example, 1000 kg (2205 lb) of CMA mixed with
2.78 m^3^ (735 gal) of water will produce 3.31 m^3^ (875 gal) of a 25
percent solution.

Table 1. Pure salt concentration and corresponding specific gravity
(measured by a hydrometer)\
at 15°C (59°F).

+-----------+---------------------+--------------+--------------------+
| **        | **Specific          | **Percent    | **\*Weight of      |
| Percent** | gravity**           | of**         | salt**             |
|           |                     |              |                    |
| **salt**  | **at 15°C (59°F)**  | **           | **kg/m^3^          |
|           |                     | saturation** | (lb/gal)**         |
+-----------+---------------------+--------------+--------------------+
| 0         | 1.000               | 0            | 0 (0)              |
+-----------+---------------------+--------------+--------------------+
| 5         | 1.035               | 20           | 51.8 (0.432)       |
+-----------+---------------------+--------------+--------------------+
| 6         | 1.043               | 24           | 62.7 (0.523)       |
+-----------+---------------------+--------------+--------------------+
| 7         | 1.050               | 28           | 73.5 (0.613)       |
+-----------+---------------------+--------------+--------------------+
| 8         | 1.057               | 32           | 84.6 (0.706)       |
+-----------+---------------------+--------------+--------------------+
| 9         | 1.065               | 36           | 95.9 (0.800)       |
+-----------+---------------------+--------------+--------------------+
| 10        | 1.072               | 40           | 107.2 (0.895)      |
+-----------+---------------------+--------------+--------------------+
| 11        | 1.080               | 44           | 118.9 (0.992)      |
+-----------+---------------------+--------------+--------------------+
| 12        | 1.087               | 48           | 119.8 (1.000)      |
+-----------+---------------------+--------------+--------------------+
| 13        | 1.095               | 52           | 131.8 (1.100)      |
+-----------+---------------------+--------------+--------------------+
| 14        | 1.103               | 56           | 154.7 (1.291)      |
+-----------+---------------------+--------------+--------------------+
| 15        | 1.111               | 60           | 166.8 (1.392)      |
+-----------+---------------------+--------------+--------------------+
| 16        | 1.118               | 63           | 178.9 (1.493)      |
+-----------+---------------------+--------------+--------------------+
| 17        | 1.126               | 67           | 191.5 (1.598)      |
+-----------+---------------------+--------------+--------------------+
| 18        | 1.134               | 71           | 204.3 (1.705)      |
+-----------+---------------------+--------------+--------------------+
| 19        | 1.142               | 75           | 217.2 (1.813)      |
+-----------+---------------------+--------------+--------------------+
| 20        | 1.150               | 79           | 230.1 (1.920)      |
+-----------+---------------------+--------------+--------------------+
| 21        | 1.158               | 83           | 243.4 (2.031)      |
+-----------+---------------------+--------------+--------------------+
| 22        | 1.166               | 87           | 256.8 (2.143)      |
+-----------+---------------------+--------------+--------------------+
| 23        | 1.175               | 91           | 270.3 (2.256)      |
+-----------+---------------------+--------------+--------------------+
| 24        | 1.183               | 95           | 284.1 (2.371)      |
+-----------+---------------------+--------------+--------------------+
| 25        | 1.191               | 99           | 293.3 (2.448)      |
+-----------+---------------------+--------------+--------------------+
| 25.2      | 1.200               | 100          |                    |
+-----------+---------------------+--------------+--------------------+

\*Note: Weight of commercial salt required = (weight of pure NaCl from
table) ÷ (purity in percent)

CMA will go into solution relatively quickly if vigorously agitated, and
especially if warm water is used. Two methods have been used to agitate
the solution in a batch system. One method uses paddle mixers in
dedicated mixing tanks. For simpler installations, a flat-bottom, 7.5
m^3^ (2000 gal) polyethylene tank can be fitted with a small electric
paddle mixer. This arrangement will provide the necessary agitation.
Another method is to keep the CMA particles suspended in the water and
in constant motion by the force of moving water. This is accomplished by
using a high volume, high pressure pump to recirculate the water until
the CMA particles are fully dissolved. This has been successfully used,
but the return leg should be submerged in order to minimize the
introduction of air. Too much air injection can cause foaming and
premature biodegradation.

Washington DOT (WSDOT) has found that the addition of a surfactant
(liquid car washing soap) to the solution is effective in suspending
insoluble material for weeks. Only about 10 mL (2 teaspoons) are needed
per 1000 kg (2205 lb) of solid CMA.

Figure 11. Kansas DOT salt brine production facility.

Figure 12. Testing of salt brine concentration with a hydrometer.

CMA contains about 4 percent by weight of water-insoluble material.
These are impurities in the limestone used to make CMA. The particles
range in size from 1 to 100 µm (40 to 4000 µin), and most will settle
within 24 h after agitation is stopped. The particles are easily
suspended by further agitation, and are not prone to caking.

The user needs to determine if the particles will affect performance of
pumps and nozzles in the spreader equipment. If so, particles may be
removed either by decanting the clear CMA liquid, or by filtering.
Decanting can be avoided if a coarse mesh filter that will still prevent
clogging of pumps and nozzles is used. Particles removed from the
solution are not hazardous. Spreading the residue on sand piles to keep
it from freezing has been recommended by some users.

The user needs to evaluate the quantity of liquid CMA needed, and what
size batches are appropriate depending on storage capacity, storm
frequency, and available personnel resources. This is needed in
determining what mixing facilities will be required. An outside CMA
mixing facility operated by WSDOT is shown in Figure 13.

##### Chemical solution storage facilities

The decision whether to use inside or outside storage facilities depends
on the freezing temperature of the solution and the lowest air
temperature expected in the area. If the lowest air temperature is at or
below the freezing-point of the solution, then inside storage should be
used. However, if that is not possible, heat can be applied either with
heat tapes or immersion heaters in the outside storage vessel to
maintain the solution temperature above the freezing-point. Some highway
agencies have buried the storage vessels and used the earth heat to
maintain the temperature above freezing. Buried tanks must meet all code
requirements.

The type and kind of storage vessel depends on the solution it contains
and whether a secondary containment (e.g., double-walled tank or
containment dike) is used. Secondary containment may be required to
protect against leakage and pollution: this should be determined from
the appropriate regulatory agency. If the solution is corrosive, or if
the vessel will ever be used to contain a corrosive solution, the vessel
should be made of a noncorrosive material such as stainless steel, glass
fiber, or polyethylene.

Depending on the type of chemical solution, agitation or circulation may
be required before loading material from the storage vessels to the tank
on the spreader. This is especially true of solutions which have
additives to reduce corrosion. Agitation can be provided either by
paddles within the storage vessel or by circulation using pumps.
Generally it is sufficient if this is done approximately 15 min before
loading. There are some materials on the market that, if not circulated
on a regular basis, will settle to the bottom of the tank. If this
occurs, it is very hard to get them back into suspension.

### Prewetted solid chemical application capability

The wetting of a solid chemical prior to spreading can improve the
effectiveness of the solid chemical in many situations. As described in
Appendix B, a solid chemical requires energy to go into solution, and a
dry solid chemical particle will remain inert until a liquid film forms.
The process of going into solution will be accelerated if a liquid is
added to the solid surface. This is only one of the benefits of
prewetting. Other advantages include: the solid chemical is spread more
uniformly because of less waste from bouncing or traffic action
(although not all waste is eliminated); granules adhere to the road
surface better; there is a faster and longer-lasting effect; spreading
speed can be increased; and in some cases the road surface dries more
quickly. The practical result is a reduction in the resources necessary
for maintaining the highway since a lower application rate translates
into a spreader load covering more area, oftentimes requiring less
deadheading (returning to the garage empty) to obtain material.

Figure 13. Outside CMA mixing facility operated by Washington DOT.

#### Materials

##### Solid materials and gradation

Sodium chloride (salt) has been the solid material most commonly used
when applying prewetted chemicals in anti-icing operations. The material
gradations, however, have ranged from coarse particle size distributions
intended for deicing operations to finer sizes more appropriate for
anti-icing. In deicing the aim is to get the salt particle to move
rapidly through an ice or snow layer to the pavement surface. A large
particle will have greater weight and therefore greater success in
penetrating this layer. Since it is recommended that an anti-icing
treatment be made on pavement with a minimal amount of frozen
precipitation, the weight of the particles, and thus the coarse
gradation, may not be an advantage. Fine particles have more surface
area for an equivalent load weight and will go into solution faster.
Their use will decrease the time for a solution to form and cover the
entire road surface, and, if the road is clear or well plowed prior to
the application, they may be more effective. However, care must be taken
to plow ahead of an application when needed, to ensure that the spinner
speed is adequate for spreading over the desired road width, and to
ensure that the truck speed is not so high that turbulence adversely
affects the uniformity of the fine particle spread.

It may be beneficial to have a gradation available at a specific site
which is a compromise between those used for deicing and anti-icing in
order to reduce the need for multiple stockpiles. The gradation must be
selected based on individual site conditions. Several specifications for
salt gradation are listed in Appendix A.

##### Prewetting solutions

The prewetting solutions can be made from sodium chloride (NaCl, salt
brine), calcium chloride (CaCl~2~), magnesium chloride (MgCl~2~),
potassium acetate (KAc), or CMA. Since CaCl~2~ solutions have a lower
freezing-point than salt brine at the recommended concentrations, the
possibility of freezing in the storage tank may make its use desirable
for very cold sites. Water alone has been used as the prewetting
solution, a practical approach for the load-wetting method, but only
when used at higher temperatures. Since there may be a risk of freezing
in the truck-mounted storage tank or in the supply line to the nozzles
or at the nozzles themselves, it is generally better to use a chemical
solution. Information on freezing-points of various solution
concentrations is given in Appendix B.

CaCl~2~ has been used as a freeze-proofing additive to salt since the
1940s. Experience has shown the use of CaCl~2~ to have an advantage over
NaCl because it is hygroscopic; i.e., it will absorb moisture from air
at a relative humidity (RH) of 42 percent and higher. This serves to
keep the salt crystals on the pavement after the bulk of the water has
evaporated or been removed by traffic. In contrast, salt by itself will
dry up and much will blow away. However, retaining the moisture may also
increase tire pick-up. It has been found in field tests that a 20
percent CaCl~2~ solution applied to salt at the rate of 30 percent by
weight of the total mixture is effective. Liquid CMA can be used as a
prewetting agent and has the advantage of being essentially
non-corrosive and non-polluting. Tests by Minnesota DOT have
demonstrated some reduction in corrosion rate of salt when CMA is added.
One practice based on several years of experience is to add 30 percent
by weight saturated NaCl solution (about 25 percent) to dry salt.
Although the chemical used for prewetting will be influential to an
extent, it may not be as important as the prewetting/application rate.

Further discussions of solid chemicals, solubility, and chemical
solutions pertinent to application of prewetted solids are presented in
Appendixes A and B.

#### Prewetting techniques and equipment

Prewetting can be accomplished by either of three methods. First, a
prewetting chemical can be injected into material stock pile at a
specified dosage. Second, a liquid chemical can be sprayed onto a loaded
spreader or on the material as it is being loaded into the spreader.
Third, an on-board spray system mounted on the spreader and/or the dump
body can add a liquid chemical to the dry chemical at the time of
spreading.

##### Prewetting of stockpile

Wetting of stockpiled salt is performed in the late fall when the
temperature of the stockpile drops to approximately 0^o^C (32^o^F). The
prewetting liquid is usually calcium chloride. One method uses a 42 or
45 percent solution liquid calcium chloride, heated to over 32^o^C
(90^o^F), hauled to the site by tanker truck and injected vertically
into the stockpile at 0.4 to 0.6 m (1.5 to 2 ft) spacing using special
spray nozzles which penetrate deep into the pile. The recommended
application rate is 30 L (8 gal) of liquid calcium chloride per 1000 kg
(ton) of salt. When pumped from the tank truck, the heated liquid
calcium chloride flows freely through parts of the stockpile, coating
the particles in contact with the liquid within the stockpile with a
thin film. The degree of coating and completeness of coverage depends on
the injection operator. As the solution is dispensed into the cool
stockpile, its temperature rapidly drops. At about 21^o^C (69^o^F),
crystallization of the solution begins. Deeper into the stockpile,
crystal growth continues. As long as the temperature of the stockpile
remains well below 21^o^C (69^o^F), little runoff of the solution will
occur.

The stockpile wetting is performed by the vendor of the liquid calcium
chloride. Therefore, the advantages of this method are 1) there is no
spray equipment to purchase or maintain, 2) no installation of liquid
storage tanks, 3) no training of employees on application procedures.
However, there are some known disadvantages to this method of
prewetting. Rain or snow on a wetted stockpile will dilute the calcium
chloride and cause migration through the pile. Therefore it is essential
that stockpiles be covered and placed on impervious asphalt or concrete
floors. If the stockpile was built by loader equipment which traveled on
top of the material, the injection process may not distribute the
solution uniformly through the stockpile. The degree of coating the dry
salt during the injection process is highly operator dependent. Frequent
working of the pile may be required to keep the pile manageable.
Finally, the material cannot be readily carried through a warm season
without the solution migrating from the pile. Some highway agencies have
abandoned this approach to prewetting because of these disadvantages.

##### Prewetting of a load or while loading

The second method of prewetting consists of spraying liquid chemical
onto a loaded spreader or on the material as it is loaded into the
spreader. Application on the load is accomplished by an overhead sprayer
with nozzles that dispense the liquid (Figure 14). The driver pulls his
truck loaded with dry chemical beneath a timer-controlled overhead spray
bar system. A timer button activates a pump which sprays the loaded
spreader with a solution. The recommended application rate for a 32
percent CaCl~2~ concentration is 45 L (12 gal) per 1000 kg (ton) of
salt.

There are other variations to this second method. For example, the
liquid can be sprayed onto each bucketful of salt as it is placed in the
truck. Some highway agencies employ a conveyor system, spraying liquid
calcium chloride on the salt as it travels up the belt to the truck.

Despite their differences, these variations on the truck-load
application method have one important feature in common. First, the
equipment is very modest. The basic components for all truck-load
systems are a storage tank, a centrifugal pump, piping, an open spray
area, a metering device, and the necessary wiring. The cost of a basic
truck-load application system with all new components is between \$8,000
to \$10,000.

The one notable disadvantage of this second method is that it has a very
high corrosive effect on the truck equipment. Another drawback is the
loaded material has to be completely discharged. The unused portion
cannot be left in the truck box or mingled with non-prewetted material.
Finally, it is very difficult to get uniform particle coating with this
method. Liquid sometimes channels through the load to the truck bed
without coating segments of the dry chemical. Other times, too much
liquid is used in an attempt to achieve reasonable particle coating.

##### Prewetting by spreader spray systems

The most common method of prewetting is through the use of on-board
spreader spray systems. A spreader equipped for prewetting can apply
liquids directly to the material being spread. The prewetting equipment
can be an integral part of the spreader design or it can be a system
that is added to an existing dry-material spreader. An existing spreader
can be modified relatively simply and inexpensively. Both electric and
hydraulic spray systems are used. An electric system consists of a 12 V
DC electric pump rated at up to 11 L/min (3 gal/min), in-cab controls,
one or two nozzles, hoses, spray tank(s) and necessary fittings. The cab
controls are generally of two types. The simple type has an on/off
switch and a variable speed pump control for increasing or decreasing
the liquid material flow rate. Typically, this controller is not
ground-speed oriented. The other type of control monitors the amount of
granular material being applied and automatically adjusts the liquid
flow rate to maintain a constant gallons/ton ratio. The second
controller also monitors and displays overall total gallons of liquid
pumped and tons of granular material spread per trip and for the entire
season. These latter controllers are equipped with their own
conveyor/auger sensor. They can generally be used in conjunction with
any type of ground-speed control system. Both control systems operate
independently of the spread width control.

Figure 14. Overhead spraybar for prewetting chemical load in truck.

The hydraulic sprayer is in-line with the conveyor/auger motor which
provides a constant relationship with the amount of material being
spread. The system includes a liquid spray pump, hydraulic motor, cab
controls, nozzle kit, spray tank(s), and necessary hoses and fittings.
Generally, a small hydraulic motor is used to drive the product pump and
is coupled in series with the conveyor/auger motor. An electrical
solenoid valve built into the motor housing is connected to an on/off
(system) switch in the cab. An adjustable pressure regulator is located
in-line between the pump and nozzles to control the liquid flow rate. An
on/off, cab-mounted light displays when the solenoid is engaged. There
is also a low pressure sensor to indicate when the liquid level is low
or if a problem exists in the system. The system generally includes
between two and four brass spray nozzles. Some nozzles have variable
orifice openings which provide an extended range of liquid material
output.

Generally the on-board spreader tanks are made of molded polyethylene
and are provided with a replaceable output-line screen strainer and
shut-off valves. Tank capacity is between 0.25 and 0.5 m^3^ (60 and 125
gal). Some manufacturers can provide stainless steel tanks in lieu of
the polyethylene.

The prewetting equipment available from Scandinavian/European sources
includes designs that automatically maintain a constant liquid-to-solid
ratio regardless of variations in truck speed, spread quantity, or
spread width. These prewetting systems are also equipped with hydraulic
controls that automatically reduce the solid quantity exiting the
conveyor belt 30 percent by weight when the liquid system is engaged.
The liquid is pumped through a check valve, then flows by gravity onto
the spinner. The dry material and liquid mix as they travel along the
curved vanes of the spinner. Nozzles are not used to prewet the material
in these designs.

As with all spreaders, periodic calibrations should be made, and any
radical deviation in the spreader output compared to the control setting
(e.g., running out before the route is completed, or having material
remaining) should be investigated. Of some concern is spread uniformity.
Although spinner spreaders leave "waves" of material on the road,
traffic should distribute a solid or prewetted chemical over the road in
both anti-icing and deicing applications. Although a maximum spreading
speed of about 64 km/h (40 mph) is achievable, the actual speed used
must be selected to ensure uniform material distribution. Also, in order
to achieve as uniform a distribution as possible, ground-speed-oriented
controls should be used. These modulate the material flow rate as a
function of vehicle speed to obtain a constant area coverage.

The prewetting equipment in use by highway agencies is not trouble free.
Frequent failures of electric pumps have been reported along with spray
nozzle clogging. Also, in some designs, the add-on hydraulic system is
not totally compatible with the truck's hydraulic system. The more
sophisticated foreign prewetting equipment also has experienced
operational problems. Ruptures have occurred in the liquid chemical feed
lines and liquid line couplings have broken or come loose during
anti-icing operations.

##### Chemical solution production and chemical storage facilities

The chemical solution production and storage facilities needed for
prewetting operations are generally the same as those needed for liquid
applications. However, smaller production/storage facilities may be
adequate because of the lesser volumes of the chemical solution that
will be required. Storage facilities needed for the solid chemicals are
the same as those required for solid chemical applications. If stockpile
prewetting techniques are used, storage techniques described above
should be used.

### Plowing capability

The primary role of snowplowing in an anti-icing operation is to remove
as much snow or loose ice as appropriate before applying chemicals in
order that excessive dilution is avoided and the applied chemical can be
effective. Because the initial chemical treatment should be placed
before a significant accumulation, this is generally more important for
subsequent operations. However, prior to liquid applications, it is
essential that the pavement be cleared of as much snow or loose ice as
possible, which may be important even for the initial operation.

If the pavement and snow are cold and dry, and it is apparent that the
snow in tire tracks is not adhering to the pavement, then plowing is all
that will be necessary.

#### Types of snowplows

There are many types of snowplows. These include one-way front plows,
reversible plows, deformable moldboard plows, underbody plows, side
wings, and plows specifically designed for slush removal. All plows are
hydraulically controlled. In most cases, it takes only a short while to
mount and dismount the plows using a quick-change buffer system.

Hydraulically extendible plows have recently been developed. The width
of the plow can be extended to the left or right hand side, depending on
the manufacturer. These plows are best suited to roads that vary in
width. The extendible plows typically allow width adjustment between 3
and 4 m (9 and 12 ft).

Side wing plows can be attached to trucks and motor graders. The one-way
front plow and underbody plow can be used simultaneously with the side
wing plows.

#### Cutting edges

Cutting edges are available that are made of synthetic polymers, rubber,
steel, and carbide inserts. Their performance is dependent on highway
and snow and ice conditions. Some highway agencies have experimented to
establish the effectiveness of different edges for different conditions.
For example, Washington State Department of Transportation has
demonstrated that polymer edges are effective for removing slush.

During anti-icing operations the cutting edge should be kept as close to
the pavement as possible in an attempt to remove all the snow and slush.
Thus, the use of casters or shoes on the plow is not recommended.

#### Slush blades

So-called slush plows have been developed in Sweden and Finland that use
two blades, the leading blade having a cutting edge of steel and the
trailing blade having an edge of rubber. This design is more effective
over a wider range of conditions than is possible with either blade
alone. The double blade plows are very good when the consistency of
slush varies. Rubber blades are effective only in the removal of wet
slush. The wetter the slush, the thicker the rubber blade can be. The
slush blades are either spring loaded or hydraulically controlled to
maintain pressure on the road surface. These blades cannot remove wet or
compacted snow because of their flexibility; they will fold back and
become ineffective.

## Decision-making toolbox

The discussion of the tools in the decision-making toolbox is divided
into six major categories: weather forecast information, road and road
weather information, nowcasting, traffic information, patrols, and
evaluations of treatment effectiveness. Each of these categories is
described below.

### Weather forecast information

The decision whether or not to initiate a treatment, when to start and
what treatment to apply, can only be made if good weather information is
available. This includes forecasts for each geographical region of when
precipitation is expected to start, what form it will be, the probable
air temperatures and the temperature trend during and after the storm,
and the wind direction and speed. One source of this information on a
regional and national basis is the National Weather Service. Its
products must cover the entire gamut of weather users, from agricultural
to marine and aviation interests. As a consequence, NWS forecasts are
not generally specific enough for maintenance managers to use for
decision making for an effective anti-icing program. A good source of
locally-specific, timely forecasts is a contract forecast service.
Guidelines for selecting a VAMS (Value Added Meteorological Service)
along with a sample Request for Proposal for services are included in
the report SHRP-H-351 *Road Weather Information Systems, Volume 2:
Implementation Guide* ([4]{.underline}).

### Road and road weather information 

#### Road information

Real-time knowledge of the pavement surface state is necessary for
making an informed decision on treatment: the pavement temperature,
whether it is wet or dry, and some indication of the concentration of a
freezing-point depressant. The most important is pavement temperature.
The solubility of all chemicals varies with temperature. The lower the
temperature the less the solubility. An ice-control chemical must form a
solution in water in order to depress the freezing-point. The pavement
temperature will determine if it will form an ice-melting interface at
the pavement surface. Air temperature is less important at the critical
time of application and immediately following since there is usually a
lag between air temperature change and the response of the pavement
surface. Nonetheless, the air temperature trend is important to track
because pavement temperature will usually follow the air temperature
within a few hours depending on the difference in the air temperatures,
the amount of solar radiation, wind, and the characteristics of the
road.

Pavement sensors accomplish this monitoring and warning function. In
addition to their real-time monitoring function, pavement temperature
sensors can be used to generate a forecast of pavement temperature trend
and warn when it will drop below freezing. This warning can occur
several hours before the event, providing sufficient time to plan
operations and avoid unnecessary costs.

In addition to measuring temperature most pavement sensors give a
relative value of the chemical concentration on the sensor surface based
on conductivity measurement. It will serve as a guide to whether some
chemical remains on the road and help in making the decision whether or
not to retreat. Another capability is available on some of the newest
types of pavement sensors: measurement of the freezing-point of the
solution on the detector. Its value lies in warning of the refreeze of a
chemical treatment which has been diluted by melted snow or ice.

Remote measurement of amount and type of precipitation will guide the
maintenance manager in deploying available resources most effectively.
It is not unusual for part of a region to be receiving freezing rain,
another part snow, and still another no precipitation.

Using the most appropriate chemical and application rate for the
condition, scheduling only plowing, or choosing to do nothing can all be
informed decisions based on road and weather information (see Section 4
for guidance on operational options).

#### Road Weather Information Systems (RWIS) and their components

Road weather information systems (RWIS) are networks of weather
data-gathering and road condition monitoring systems and their
associated communications, processing, and display facilities which
provide decision information to maintenance managers. The most visible
components of RWIS are the roadside installations of system components
(Figure 15). A single site, which may have many sensors, is referred to
as a remote processing unit (RPU) station. The RPU station typically
consists of atmospheric sensors mounted on some form of a tower, sensors
embedded in the pavement surface and beneath the surface, and an
enclosure which contains data processing capability and communications
equipment.

Data from the sensors are formatted at the RPU. They are transmitted to
a central processing unit (CPU) where they may be stored, retransmitted
to other workstations or locations, or accessed directly. The CPU can be
a separate computer or a workstation.

Another component of a RWIS is the data processing and display
capability used by the maintenance personnel. The actual system
configuration depends on the management structure of the maintenance
organization. This component can be a computer workstation in a
maintenance facility or at a District or Area headquarters. It can also
be a portable computer a manager, supervisor or foreman takes home.

Whoever makes the decisions for allocating resources for snow and ice
control should have access to the latest weather and road information.
If decisions are made from a central office, perhaps one workstation
allocated with the CPU will suffice. If decision making is
decentralized, workstations and/or portable computers should be
available to the local decision makers for them to access data.

Additional information about RWIS, their selection, procurement, siting,
use, maintenance, and calibration can be obtained in the two-volume SHRP
report *Road Weather Information Systems, Volume 1: Research Report
(SHRP-H-350)* and *Volume 2: Implementation Guide (SHRP-H-351)
([5]{.underline}), ([4]{.underline}).*

#### Role of thermal mapping

Thermal mapping, or thermography, is the process of determining thermal
profiles of road surfaces using infrared sensors. The measurements are
typically made in the early morning hours, when there is the least
change in the pavement temperature during the measurement process. They
are also made under different atmospheric conditions, since the
radiation balance at the surface is related to the atmospheric
conditions, including cloud cover, wind speed, and precipitation.

A variation of thermal mapping is called road climatology. Additional
data are acquired when measuring pavement temperature, including air
temperature, relative humidity, and climatological characteristics of
the pavement environment. The additional data are input to a short-range
(up to 4 h) forecasting model for pavement temperature.

Thermal mapping of highway segments has been conducted in several
States, including Washington, Nevada, and Minnesota. The data from
thermal mapping have assisted in siting RPU stations, forecasting
pavement temperatures for locations where no RWIS sensors exist, and for
developing snow- and ice-control strategies. Other potential locations
for thermal mapping include those areas where anti-icing operations are
used, where reduced chemical areas exist, or where a significant number
of different microclimates exist in a given area. Thermal mapping may
also point to representative RPU locations that can eliminate the need
for one or more sites.

Thermal mapping profiles can be used to infer pavement temperatures
between sensor locations where the temperatures are known. An extension
of this process is to forecast temperatures along the roadway based on
the forecasts of temperatures at known points. This approach has been
used in the United Kingdom in areas where frost or ice formation on the
roads is a concern.

Better routing or allocation of maintenance resources and personnel is
possible based on thermal mapping. The data can allow staging of
responses to only those road segments expected to be below freezing. It
can also indicate certain areas or locations that may not need
attention.

Research has indicated that thermal information from the road
environment can be obtained using relatively inexpensive hand-held
radiometers ([2]{.underline}, [5]{.underline}). Vehicle-mounted
instruments for measuring pavement temperatures are already used by some
State highway agencies.

There is some thought that thermal mapping should be considered when
variations of pavement temperature greater than 5^o^C (9^o^F) are
possible, or when the road elevation changes more than about 200 m (650
ft) over the segment length of interest. These "rules of thumb" are for
general guidance and have not been validated by research data.

### Nowcasting

Nowcasting refers to the use of real-time data for short-term
forecasting. It relies on the rapid transmittal of data from RWIS
installations, radar, patrols (see Section 3.2.5), and any other
information source for making a judgment of the probable weather and
pavement condition/temperature over the next hour or two. Nowcasting is
one important tool for making the decision of when to call in personnel.
Mobilization timing may vary among sites, therefore the frequency of
weather information updating required for a nowcast will also vary with
the site. Nowcasts can be provided by a weather service or performed by
the maintenance manager. Specially trained maintenance managers in some
highway agencies already perform this duty using the necessary
information available from a variety of sources.

### Traffic information

Vehicles can affect the pavement surface in several ways: tires compact
snow, abrade it, displace or disperse it; heat from tire friction,
engine, and the exhaust system can add measurable heat to the pavement
surface. As described previously, they can also result in applied
chemical being blown from the pavement. As a consequence, they can
influence, both positively and negatively, the effectiveness of
anti-icing treatments, and should be considered in the decision-making
process. The traffic information most important for making operational
decisions is the variation of traffic rate throughout a 24 h period.

Figure 15. RWIS roadside installation.

### Patrols

There is no substitute for visual observation of weather conditions and
conditions of the pavement surface. Observations remain an important
tool for making operational decisions even when an agency has access to
and experience with new technology such as RWIS. Use of patrols for this
purpose can be highly effective. Though the State or local highway
patrol can fulfill this role, trained maintenance personnel are better
prepared to judge the severity of conditions and to make or recommend
corrective action.

### Evaluations of treatment effectiveness

Maintenance decisions should not be based on a rigid, automatic basis
but rather on the assessment of a need. In contrast to prescribing that
chemicals be applied, or plow runs be made every hour or two or other
fixed interval, decision on treatment need can be based on a number of
information sources. The first and most obvious is the visual
observations of precipitation/weather and pavement conditions from
patrols, as discussed above, and from operators. The second is an
indication or the measurement of chemical concentration on the pavement.
The third is the measurement of frictional resistance to sliding.

The availability of chemical concentration indicators appears to enhance
the timing of subsequent applications by providing indications of the
dilution of the chemical. A manager can time the reapplication of
chemicals so that the operation is complete before the freezing-point of
the brine on the pavement surface starts to climb and, especially,
before it reaches 0^o^C (32^o^F). Where decision makers have confidence
in these data, they can be used as a basis for establishing cycle times
of the repeat applications for different conditions.

Measurement of friction was used successfully in the SHRP and FHWA
anti-icing projects. An agency may find it reasonable to establish this
as a technique used during patrols. There are many devices for measuring
friction. Skid trailers are commonly used for the measurement of the
coefficient of friction, but for various reasons related to safety and
equipment deterioration, they are not normally used on snow-covered
pavements. Specialized vehicles incorporating a fifth wheel, which
measures the increase in force when braked at a controlled slip rate,
are available, but high cost has limited their use mainly to airports. A
low-cost device was used in both the SHRP and FHWA test programs because
it can be installed in most any vehicle and can produce reliable
measurements. It gives a direct readout of friction coefficient when the
vehicle is hard-braked from 65 km/h (40 mph). Its repeatability is
acceptable for treatment analysis and decision support purposes,
provided the device is calibrated and operated in accordance with the
manufacturer's specifications. Because it requires hard braking,
however, it is not suitable for use in heavy traffic.

In addition to evaluations during a storm, it is beneficial for the
personnel of each maintenance area to conduct a post-storm evaluation of
the treatment effectiveness. This can help identify areas needing
improvement and changes that can be made in the treatment strategy. A
post-season review of treatment effectiveness is likewise helpful. It
can help identify where changes are needed in equipment, material, and
route configurations, and can begin a process of engineering an
anti-icing program to fit the exact needs of a site or agency. It can
also help identify where changes in personnel procedures and training
are needed to improve the effectiveness of the winter maintenance
program.

## Personnel toolbox

The discussion of the tools in the personnel toolbox is divided into two
major categories: trained personnel for anti-icing decision making and
operations, and deployment of personnel. Each of these is described
below.

### Trained personnel for anti-icing decision making and operations

It is essential for effective implementation of an anti-icing program
that personnel be trained in the details of the workings of the program.
Anti-icing techniques and operations may be so foreign to many operators
and managers that old ideas must be banished before a workable program
can be started. Everybody resists change, but change in most cases is
what is required for an anti-icing program to be successful. An
anti-icing program will necessitate more information for making an
informed decision and may involve different methods and materials than
do conventional methods. This will require an emphasis on training. This
training can be accomplished by a consultant or highway agency staff
using this manual and other material developed under FHWA and SHRP
studies ([1]{.underline},[2]{.underline}). Workshop material being
produced under a current FHWA study ([6]{.underline}) can be used also
during the training.

### Deployment of personnel 

Deployment of personnel for anti-icing operations involves improved
standby and call-out procedures. Use of modern weather forecasting
information will provide more time in advance of a storm to plan
operations. With better information, personnel can be advised of standby
status with more certainty of need. Personnel on standby must abide by
agency requirements regarding alcohol consumption, availability, and
rest. Since many agencies may pay personnel for standby time, reducing
unproductive call-outs and standby time will represent large savings.

Once the decision has been made that a snow and ice control operation is
necessary based on accurate and timely weather information, crews must
be called out. The necessary weather information needed to make the
decision to initiate call-out procedures must be provided in a timely
manner to ensure adequate lead time for mobilization of resources. Lead
time may vary by site, thus weather information needs may also vary by
site. This is especially important for anti-icing operations as the
timing of the initial treatment is critical. By minimizing the
mobilization time, total crew time may be reduced or crew availability
may be extended. A well-organized call-out system must be in place to
mobilize crews within the required time. Automated telephone calling
systems can assist in streamlining the call-out process.

#   {#section .unnumbered}

# Recommended Anti-icing PRACTICES

This section presents general recommendations for successful anti-icing
practices that can be employed for various combinations of
precipitation, pavement temperature, traffic volumes, and mandated
levels of service. It presents information that will assist in the
development of a systematic anti-icing program, and complements Section
3 on the capabilities, information sources, and procedures that make up
the tools of an anti-icing program. It contains four major components:
initial operations, subsequent operations, special considerations, and
post-storm assessment of operations.

The section is intended as a companion and background document to
Appendix C, which presents specific and concise recommendations for
anti-icing operations for six weather events. These are:

-   Light Snow Storm

-   Light Snow Storm with Period(s) of Moderate or Heavy Snow

-   Moderate or Heavy Snow Storm

-   Frost or Black Ice

-   Freezing Rain Storm

-   Sleet Storm

Guidance on maintenance actions for each event is provided in the
Appendix C tables for several pavement temperature ranges and for
initial and subsequent operations. Temperature trend, an important
factor, is also indicated. Solid, liquid, and prewetted solid chemical
application rates are suggested where appropriate. These rates are not
to be considered as fixed values but rather the middle of a range to be
selected by an agency according to its local conditions and experience.
Traffic volumes have not been found to have a consistent or dominant
influence on pavement condition or traction to suggest varying chemical
application rates except in the case of frost and black ice, and that
category is the only one incorporating traffic as an operational
consideration. Special considerations associated with maintenance
actions are listed in the Comments and Notes given on the tables.

The guidance presented in this section and in Appendix C is based upon
the results of 4 years of anti-icing field testing conducted by 15 State
highway agencies and supported by the Strategic Highway Research Program
(SHRP) and the Federal Highway Administration (FHWA). It has been
augmented with practices developed outside the U.S., where necessary,
for completeness. However, no short discussion or list of
recommendations can completely cover the range of conditions facing
agencies continent wide. Therefore every agency is encouraged to use the
guidance of this document as a starting point for developing its own
anti-icing program, and to modify the recommendations when necessary in
order to accommodate local experience, specific site concerns, and
agency objectives. Careful recording of conditions and the operations
made in response will provide the basis for fine-tuning the program for
specific service levels and conditions.

## Initial operation

The initial anti-icing operation is most often the application of a
chemical freezing-point depressant to the pavement before enough snow
has accumulated to keep the chemical from reaching the pavement.
However, before this action is taken, information about the nature and
characteristics of the anticipated storm should be assembled and a
decision made concerning the action. Each of these steps is discussed
next.

### Information assembly

Several pieces of information need to be assembled upon first notice
that a winter storm or frost/black ice event may affect the maintenance
area. This information includes weather forecasts, weather radar data,
satellite data, local road condition and RWIS data, pavement temperature
forecasts, and any RWIS data from areas outside the immediate
maintenance jurisdiction that might have already have been affected by
the approaching storm. The information must be reviewed to estimate when
and where the event will begin, its extent, and severity.

### Decision point

The decision on whether or not to initiate a treatment, when to start it
and what type of treatment to apply can be made after the review is made
of the information assembled. The decision is based on when
precipitation is expected to start, what form it will be, the probable
air and pavement temperatures, the anticipated trend of the
temperatures, the expected sky conditions, the wind speed and direction,
and the intended timing of the treatment.

### Action

#### Apply chemical

Either dry solid chemicals, liquid chemicals, or prewetted solid
chemicals can be used as an initial anti-icing treatment. Whichever is
used, the timing of the application should be consistent with the
underlying objective of preventing the formation or development of
bonded snow or ice, and should reflect an underlying readiness
consistent with a preventive strategy. That is, it should be made in
anticipation of or in prompt response to worsening pavement conditions.
Applications in advance of snowfall are not necessary for preventing
bonded snowpack, but early applications when the pavement condition is
no worse than wet, slushy, or lightly snow covered are for the most part
necessary for anti-icing success. As this may not always be possible,
for example because of a limited fleet or heavy traffic, pretreating the
road before a snowstorm may be the only way to ensure that all areas are
treated before conditions deteriorate.

Residual chemical from previous operations has a short-lived effect on
highway conditions at the beginning of storms, and should not be relied
upon for timing of initial anti-icing operations without independent
indications of adequate chemical concentration.

##### Recommendations for use of liquid chemicals

Guidance for initial liquid treatments is given in Appendix C for four
events: light snow storm; light snow storm with period(s) of moderate or
heavy snow; moderate or heavy snow storm; and frost or black ice. The
use of a liquid is not recommended during either a freezing rain or
sleet storm because of the large quantity needed to retain an effective
concentration. The suggested application rates are the equivalent dry
chemical rates. All are given only for pavement temperatures at -5^o^C
(23^o^F) and above because of the ineffectiveness of the indicated rates
at pavement temperatures below -5^o^C (23^o^F).

For snowstorms, initial liquid applications can be made either as a
"pretreatment" in advance of the storm or as an "early-storm treatment,"
i.e., soon after snowfall has begun and/or when the pavement temperature
is dropping toward freezing. A pretreatment can be made well ahead of a
storm as long as the storm does not start out with above freezing
temperatures and rain, washing the chemical away. In the case of
early-storm treatment, the application may be made onto dry, wet, light
slush, or lightly snow covered pavement. Late applications onto
pavements with more than a light covering of slush or snow can result in
excessive dilution of the chemical, and risk failure. These should
always be coordinated with plowing.

Relative to conventional practices in which surfaces are not treated
until later in a storm, benefits from liquid pretreatments can include
higher friction and better pavement conditions early in a storm. These
benefits are generally short-lived, however, and should not be expected
over a long period. Subsequent chemical applications should be made as
soon as conditions begin to deteriorate. In essence, pretreatments can
be thought of as "buying time" in the earliest stages of a storm until
subsequent chemical applications become effective.

For preventing the formation of frost or black ice \-- caused by
radiational cooling of the pavement in the presence of high humidity \--
the chemical should be applied in advance of the expected time of ice
formation so that the water component of the brine will evaporate or be
removed by traffic action. This will leave only the chemical on the road
surface, and thus result in the greatest concentration when frost or
black ice conditions occur. Of the recommended frost or black ice
treatments given in Appendix C, traffic condition is a dominant factor
only in the temperature range of -2 to 2^o^C (28 to 35^o^F).

As an example of frost prevention, one agency has found that a solution
of 27 percent MgCl~2~ can be applied to bridge decks in valley areas to
prevent preferential icing (frosting) conditions. The liquid is applied
at the rate of 100 L (25 gal) per lane-mile at speeds up to 50 km/h (30
mph). Depending on traffic and weather conditions, the residual chemical
can prevent frosting conditions for about one week on low-volume roads
and 3 to 4 days on higher volume freeways. Appendix C includes this
experience as guidance, presenting the application rate in terms of the
weight of the dry chemical in the applied solution.

##### Recommendations for use of solid and prewetted solid chemicals

Guidance for initial prewetted solid chemical applications is given in
Appendix C for all of the events. Guidance for initial dry solid
chemical treatments is given for three events only: light snow storm;
light snow storm with period(s) of moderate or heavy snow; and moderate
or heavy snow storm (dry solid chemical is referred to as solid chemical
in the Appendix C tables). The differences in the recommendations for
solid and prewetted solids are primarily a result of the additional
benefits that prewetting provides and the limitations on the use of
solid chemicals when insufficient moisture or accumulation is present on
the road. These have been discussed in Sections 3.1.1 and 3.1.3. For
some conditions identified in the Appendix C tables, prewetting is not
listed as a recommended maintenance action even though dry solid
chemicals are. These are cases where sufficient moisture is present to
trigger the effectiveness of the dry chemical. Under such conditions,
however, there would be no loss of effectiveness in applying prewetted
solids.

For precipitation events, prewetted solid applications, like liquid
treatments, can be made either in advance of the storm or as an
early-storm treatment. In the latter case, the application can be made
onto dry, wet, slush, or lightly snow covered pavement. It should be
completed before accumulation or pack bonds to the pavement.
Applications onto dry pavement, either as a pretreatment or early-storm
treatment, should be monitored to avoid excessive loss of material. Late
applications onto pavements with more than a light covering of slush or
snow can result in excessive dilution of the chemical, and should be
coordinated with plowing. Where there is sufficient moisture after
snowfall has begun, dry solid chemicals can be applied.

Application of dry solid chemical onto dry pavement is not recommended,
and therefore should not be used as a pretreatment. Timing of an initial
dry solid chemical application for snowstorm events is therefore
critical; it should be made as soon as possible after sufficient
precipitation has fallen to prevent loss, but before snowpack or ice
bonds to the pavement.

#### Plow

If the pavement and snow are cold and dry, and it is apparent that snow
in tire tracks is not adhering to the pavement, plowing is all that will
be necessary to remove accumulation. If residual chemical or pavement
temperature is high enough to form some liquid, wetting the snow or
causing slush, then plowing with an appropriate cutting edge or slush
blade is recommended (see Section 3.1.4).

#### Do nothing

When the pavement is cold (below -9.5^o^C (15^o^F)) and new or blowing
snow are light and cold, traffic and wind (speeds of 25 km/h (15 mph) or
higher) may be sufficient to prevent accumulation and compaction in tire
tracks. In this case, application of any chemical, even that added as
freeze-proofing to an abrasive, may create rather than cure a problem.
Once a wet surface develops where before it was cold and dry, the dry
snow can adhere and begin to build up. Prompt removal with a plow may
prevent pack from developing, but this situation may have been avoided
by refraining from chemical application. If the weather forecast is for
rising temperatures, however, chemical should be applied before snow
becomes wet with the potential of forming pack. Application should be
made when the temperature rises high enough for the chemical to act
rapidly, usually above about -5^o^C (23^o^F). Application can be made at
temperatures as low as -9.5^o^C (15^o^F) if a rapid rise in temperature
is forecast.

## Subsequent operations

An initial application of chemical may suffice for some conditions and
short duration events, but it is far more likely that further treatments
will be required during a storm. In many cases these do not differ from
initial treatments, although other considerations become very important
such as the coordination of the application with plowing.

### Monitoring of conditions

It is important that roadway and weather conditions, weather forecast
updates, and RWIS data be closely monitored once the initial anti-icing
operation has taken place. Special attention should be paid to pavement
temperature and trend and to changes in precipitation type and
intensity. This information, plus observations of precipitation,
observations of pavement conditions, and evaluations of treatment
effectiveness (as discussed in Section 3.2.6) are needed to determine
when, or if, additional anti-icing treatments are necessary. Only by the
systematic use of available information can the most efficient
anti-icing actions be taken over the course of a storm.

### Action

#### Apply chemical

As for the initial operation, guidance for solid, liquid, and prewetted
solid chemical applications is given in Appendix C for subsequent
operations that may be necessary. Again the guidance for liquid
applications is limited to four events: light snow storm; light snow
storm with period(s) of moderate or heavy snow; moderate or heavy snow
storm; and frost or black ice. Also, guidance for prewetted solid
chemical applications is given for all of the events, whereas guidance
for dry solid chemical treatments is given for three events only: light
snow storm; light snow storm with period(s) of moderate or heavy snow;
and moderate or heavy snow storm. Much of the discussion above for the
initial chemical application is pertinent to the subsequent application.

Whichever treatment is used, the timing of subsequent applications, like
the initial application, should be consistent with the underlying
objective of preventing the formation or development of bonded snow or
ice, and should reflect an operational readiness consistent with a
preventive strategy. That is, they should be made in anticipation of or
in prompt response to worsening pavement conditions.

For snowfalls, an initial anti-icing treatment may be all that is
necessary to cope with a light or short duration event. There will be
little dilution of the chemical, so the freezing-point may not reach the
pavement temperature. When snowfall continues, and pavement temperature
is about -9.5^o^C (15^o^F) or higher, subsequent treatments may be
required to prevent the formation or development of pack or bonded pack.
In such a case, the snow should be plowed off as completely as possible
before chemical is reapplied, allowing the necessary small amount of
chemical to reach the pavement surface.

In snow storms with generally steady precipitation and pavement
temperature conditions, subsequent chemical operations made at regular
intervals are generally adequate. However, in storms with significant
changes in precipitation and pavement temperature conditions, operations
will likely be at irregular intervals. In either case, systematic
operations using all available decision-making tools should be
conducted. Subsequent chemical applications that are made in prompt
response to changing conditions can improve friction and pavement
conditions. Subsequent chemical applications that are made in
anticipation of changing conditions can prevent deteriorating conditions
or mitigate their effects.

A limited period of heavier snow in an otherwise light snow storm should
be treated as "a storm within a storm." That is, chemical operations
should be conducted just prior to or at the beginning of the intense
snow period to reduce the likelihood that snowpack will develop or be
sustained by a strong bond, and to increase the likelihood that plowing
operations can readily remove any packed snow that may develop. Use of
reliable short-term forecasting tools would facilitate the timing of
these operations, but they would otherwise be routine extensions of the
responses to heavy snow seen in current snow and ice control practice.
The result may not only be the prevention of a strong bond between the
packed snow and the pavement, but also the prevention of excessive
reductions in friction that precede the development of snowpack.
Guidance for the weather event "Light Snow Storm with Period(s) of
Moderate or Heavy Snow" was developed specifically to underscore the
importance of being ready for these heavy snow periods and the poor road
conditions that often result.

Although subsequent liquid applications can be successful, operational
constraints such as the capacities of truck tanks and storage
facilities, as well as operational preferences, may lead to anti-icing
chemical operations that include transitions from liquid to solid
applications. In such cases, the transition should be anticipated to
allow continuous anti-icing operations and to avoid operational delays,
and the solid chemical operations should be performed according to
anti-icing practices.

#### Plow

Plowing passes should be made as necessary to prevent build-up of a
compacted snow layer. *Before applying any more chemical*, the pavement
surface should be cleared of frozen precipitation as best as possible to
allow the small amount of chemical to reach the pavement surface. This
is very important for the application of liquids.

As described for the initial operation, if the pavement and snow are
cold and dry, and it is apparent that snow in tire tracks is not
adhering to the pavement, plowing is all that will be necessary to
remove accumulation.

#### Do nothing

If the initial or previous anti-icing treatments have done their job,
the pavement temperature is around\
-2^o^C (28^o^F) and holding steady or rising, and there is no additional
precipitation coming down or forecast, there may be no need for further
action. This is especially the case when the pavement temperature is
above 0^o^C (32^o^F) and steady or rising, whether it is during or after
precipitation. Recognition of such conditions, and communication of
these conditions to operators, can result in significant material
savings. However, it is important to monitor conditions closely when
pavement temperature is below or slightly above 0^o^C (32^o^F), and to
be aware of the potential for surprise freeze-ups.

## SPECIAL CONSIDERATIONS

Several special factors influence choice or timing of an operational
treatment. These are introduced or amplified here.

### Traffic condition

Other than the influence that traffic volume has on the assignment of
level of service, the influence of traffic on anti-icing storm
operations comes primarily from the variation of traffic rate throughout
the period of a storm or icing event. Although traffic density has an
effect on friction, this is less important and not as direct or
consistent as the effects of precipitation type and rate and pavement
temperature. In fact, anti-icing snowstorm operations have been shown to
be successful in high volume rush hour traffic as well as low volume
middle-of-night traffic. Because of this, and because traffic can have
both positive and detrimental effects on road condition during
anti-icing operations, traffic rate has not been included as a variable
in the anti-icing guidance provided in Appendix C, except in the table
for frost or black ice. The routine use of traffic information should be
mostly to ensure that storm operations are completed ahead of rush
periods in order to avoid delays which can lead to bonded pack or ice.
This is reflected in the Notes provided in the Appendix C tables. Local
experience or level of service may warrant further incorporation of
traffic information within the anti-icing operational guidance. If so,
the Appendix C tables can be appropriately modified.

### Wind

Experience has shown that crosswind speeds in excess of about 24 km/h
(15 mph) may cause local drifting across a pavement and retention of
snow if, for example, the pavement is wet. The threshold wind speed at
which this becomes a problem will vary widely with road siting and other
conditions. Maintenance personnel should be alert to the conditions that
may cause this interception of snow and incorporate the information in
operating procedures. For liquid applications, when a decision is made
to apply chemical during windy conditions, experience has shown that
adjusting the sprayer closer to the pavement can be successful in
avoiding loss and achieving the desired application.

### Hybrid precipitation events

Few storms will fit neatly into specific classifications based on
intensity, duration, and type of precipitation. The operational
treatment used early in a storm may have to be modified during the
course of the event or operation. This is particularly critical when a
light snowfall is interspersed with one or more periods of heavy
snowfall. "Light Snow Storm with Period(s) of Moderate or Heavy Snow"
has been defined for this case in Appendix C. However, other "hybrid"
events are not specified in the remaining Appendix C tables, which are
organized according to the type of storm or event. In the occurrence of
changing precipitation conditions, maintenance managers should be
prepared to base operational decisions on more than one of the tables.

### Prewetting quantities

In theory, only sufficient liquid to wet every particle of dry solid
chemical is required for prewetting. The actual rate to achieve this
wetting will vary with the particle size distribution. In practice it
has been found, for example, that 37 L (10 gal) of 23 percent
concentration sodium chloride solution will be sufficient for a 1000 kg
(1 ton) of dry chemical of coarse gradation. Some agencies have used
three times this quantity so that the material is applied as a slurry in
order to reduce losses by traffic action.

### Development of snowpack and bond

Even when anti-icing operations are performed successfully, a snowpack
may still develop and a bond may form between the pack and pavement.
Technically this generally implies that deicing is necessary. However it
is often observed in practice that the previous anti-icing treatments
have inhibited the development of a bond, resulting in a weak bond that
is easily broken, leading to a rapid return to acceptable pavement
conditions. Those charged with developing anti-icing programs should
recognize that bonded snowpack can occur even when anti-icing is
"successful," but that it will not usually have the strength of bonded
pack observed during traditional deicing operations. Indeed, the stated
objective of anti-icing is not only to prevent *formation* of a bond,
but to prevent *development* if one does form.

If during anti-icing operations rapidly changing climatic conditions or
delays in operations lead to *strongly* bonded snow or ice, maintenance
managers should be prepared (1) to utilize deicing techniques to break
the bond to return the road to acceptable conditions, and (2) to apply
abrasives if a rapid increase in friction coefficient is required in the
interim. However, once acceptable road conditions are recovered, a
return to preventive anti-icing operations would be appropriate.

### Use of abrasives

Abrasives may be necessary when a rapid increase in friction coefficient
is required, particularly at pavement temperatures so low that chemical
action is slow, and, as discussed above, in conditions where snow or ice
is strongly bonded to the pavement and cannot be removed rapidly.
Several tables in Appendix C contain low pavement temperature conditions
that may warrant abrasives use, most directly in the tables for
frost/black ice events and freezing rain storms. However, abrasives are
not ice-control chemicals, and will not support the fundamental
objective of anti-icing when applied either straight or in a mix with
chemicals. Because of this, and because of evidence that they are
generally ineffective when used routinely in anti-icing operations, they
should not be a customary operation of an anti-icing program outside of
the low pavement temperature conditions presented in Appendix C.
However, even in these conditions, chemical typically added as
freeze-proofing to abrasives may create a problem by causing a wet
pavement surface. As described previously in Section 4.1.3.3, once a wet
surface develops where before it was cold and dry, the dry snow can
adhere and begin to build up. Maintenance crews should be aware of this
possibility.

## Post-storm assessment of operations

Lessons can be learned from both the successes and failures of any
winter maintenance operation. Anti-icing operations are no exception.
Improvements in operations, and even in equipment, can be identified and
implemented through a post-storm assessment of the practices and
treatments used. It is important that all levels of maintenance
personnel, from district level supervisors to equipment operators, be
involved in these evaluations. Many times, what is witnessed during a
storm by a supervisor is not readily seen by an operator, and vice
versa. As part of the post-storm assessment, it is suggested that the
highway agency track the cost and effectiveness of the anti-icing
program, and, if possible, do the same for conventional snow and ice
control operations in comparable areas. This process should include
evaluations of treatment effectiveness, as discussed in Section 3.2.6,
and examinations of costs. Techniques for these evaluations can be based
upon an agency's current storm data collection practice, or upon those
used for FHWA T&E 28 ([1]{.underline}).

The cost data of a storm or weather event can be organized according to
the total costs for materials (chemicals and abrasives), labor, and
equipment employed in operations. For chemicals, this includes the
purchase price, transportation to storage site, storage, truck loading,
handling and mixing of solid chemicals, and solution preparation. For
abrasives it should include both material costs and any clean-up costs.
Labor costs should be fully burdened and include overtime, while
equipment costs would be the agency's hourly rates times the hours used.
Other costs can be considered, if appropriate. These include the cost of
dispatchers, costs of specialized equipment, cost of patrols, etc.

The costs and effectiveness measures of the anti-icing and conventional
operations need to be recorded separately for each highway section or
route considered. The cost per lane mile can then be calculated for each
type of operation, effectiveness measures can be evaluated, and the
relative success of the two operations compared.

While the implementation of systematic anti-icing practices can be
thought of as a means for maintaining roads in the best conditions
possible during a winter storm, and a way to do so in an efficient
manner, it should not be thought of as an improvement that will
automatically result in reduced overall costs. Most importantly,
anti-icing techniques provide the potential for maintaining roads in the
best conditions possible during winter storms. Cost savings will depend
on the current practice: for example, what level of service governs,
what materials it uses, whether it is more deicing than anti-icing, and
what information sources it uses. Examples of success include providing
the same level of maintenance effectiveness at less total cost, and
providing a higher level of maintenance effectiveness at the same cost.
As these examples illustrate, for those examining the costs or success
of anti-icing operations, an examination of both costs *and* level of
maintenance effectiveness is important.

# APPENDIX A. SELECTED CHEMICALS AND THEIR PROPERTIES {#appendix-a.-selected-chemicals-and-their-properties .HeadingA1}

Information is presented in this appendix on the properties of five
chemicals used for anti-icing treatments and instructions for preparing
various liquid concentrations. The five chemicals are calcium chloride,
sodium chloride, magnesium chloride, calcium magnesium acetate, and
potassium acetate. They are listed here with their eutectic temperatures
and concentrations:

  ----------------------------- ------------------- ---------------------
  **Chemical**                  **Eutectic          **Eutectic
                                temperature\        concentration\
                                ^o^C (°F)**         %**

  calcium chloride (CaCl~2~)    -51 (-60)           29.8

  sodium chloride (NaCl)        -21 (-5.8)          23.3

  magnesium chloride (MgCl~2~)  -33 (-28)           21.6

  calcium magnesium acetate     -27.5 (-17.5)       32.5
  (CMA)                                             

  potassium acetate (KAc)       -60 (-76)           49
  ----------------------------- ------------------- ---------------------

No information is provided on the corrosive properties or environmental
aspects of the chemicals. Discussions of these items can be found in the
literature. Likewise no cost data for the chemicals are given. These
data can be obtained readily from distributors.

## A.1 Calcium Chloride, CaCl~2~ {#a.1-calcium-chloride-cacl2 .HeadingA2}

### A.1.1 Introduction {#a.1.1-introduction .HeadingA3}

Two methods are used to manufacture commercial CaCl~2~: extraction from
natural brines obtained from deep wells, principally in Michigan; and by
a chemical process, the Solvay process, in which sodium chloride is
reacted with calcium carbonate to produce sodium carbonate (soda ash)
and calcium chloride.

The American Society for Testing and Materials (ASTM) has prepared two
standards for calcium chloride: D 98 *Specification for Calcium
Chloride,* and E 449 *Standard Test Method of Analysis of Calcium
Chloride.*

### A.1.2 Preparation of liquid CaCl~2~ {#a.1.2-preparation-of-liquid-cacl2 .HeadingA3}

Solid calcium chloride dissolves readily in water with little agitation
required. Considerable heat is given off when it dissolves. Two methods
of mixing can be used to obtain a specific concentration of liquid
CaCl~2~. Method 1 is used if the volume of the mixing container is
known. Use Method 2 if the volume of the mixing container is not known.
Each of these methods is described below. For both, the water
temperature should be below 20^o^C (68^o^F).

#### A.1.2.1 Method 1 (Known mixing container volume) {#a.1.2.1-method-1-known-mixing-container-volume .HeadingA4}

1.  From the "per volume solution" column of Table 2 determine the
    weight in kg (or lb) of solid calcium chloride required to make 1
    m^3^ (or 1 gal) of solution at the desired concentration level. This
    value, multiplied by the volume of the container in m^3^ (or gal),
    gives the total weight of calcium chloride required.

2.  Fill the container approximately 2/3 full of water, then add the
    required calcium chloride gradually while stirring carefully with a
    paddle by hand, with a mechanical agitator, or with an air bubbler.

3.  After the calcium chloride has completely dissolved, add water to
    the container to bring the level to the working volume and then
    agitate the solution slowly until a uniform mixture is obtained.

Table 2. Calcium chloride mixing proportions.

+-----------+-----------+----------+------------------+---------------+
| *         | **Weight  |          | **C              | **Weight per  |
| *%CaCl~2~ | CaCl~2~   |          | rystallization** | unit**        |
| actual**  | 77%       |          |                  |               |
|           | flake**   |          |                  |               |
+-----------+-----------+----------+------------------+---------------+
|           | **per     | **per    | **temperature\   | **volume of   |
|           | volume    | volume   | ^o^C (°F)**      | solution\     |
|           | s         | water**  |                  | kg/m^3^       |
|           | olution** |          |                  | (lb/gal)**    |
|           |           | *        |                  |               |
|           | **kg/m^3^ | *kg/m^3^ |                  |               |
|           | (         | (l       |                  |               |
|           | lb/gal)** | b/gal)** |                  |               |
+-----------+-----------+----------+------------------+---------------+
| 10        | 139       | 146      | -5.4 (22.3)      | 1085 (9.06)   |
|           | (1.16)    | (1.22)   |                  |               |
+-----------+-----------+----------+------------------+---------------+
| 15        | 218       | 238      | -10.3 (13.5)     | 1133 (9.46)   |
|           | (1.82)    | (1.99)   |                  |               |
+-----------+-----------+----------+------------------+---------------+
| 20        | 303       | 344      | -18.0 (-0.4)     | 1185 (9.89)   |
|           | (2.53)    | (2.87)   |                  |               |
+-----------+-----------+----------+------------------+---------------+
| 25        | 397       | 471      | -29.4 (-21)      | 1234 (10.3)   |
|           | (3.31)    | (3.93)   |                  |               |
+-----------+-----------+----------+------------------+---------------+
| 29.8\*    | 491 (4.1) | 621      | -55.0 (-67)      | 1288 (10.75)  |
|           |           | (5.18)   |                  |               |
+-----------+-----------+----------+------------------+---------------+
| 30        | 498       | 627      | -46.0 (-50.8)    | 1294 (10.8)   |
|           | (4.16)    | (5.23)   |                  |               |
+-----------+-----------+----------+------------------+---------------+

\*Note: this is the "eutectic" point, i.e., the concentration that
results in the lowest temperature\
(-55^o^C (-67°F)) at which a solution can exist while remaining
completely liquid.

#### A.1.2.2 Method 2 (Unknown mixing container volume) {#a.1.2.2-method-2-unknown-mixing-container-volume .HeadingA4}

1.  Put a measured volume of water in the container to no more than 2/3
    of the container capacity.

2.  Dissolve in it the required weight of calcium chloride given in the
    "per volume water" column of Table 2 for each cubic meter (or
    gallon) of water used. Add the calcium chloride slowly to the water
    with agitation.

3.  When completely dissolved, the solution will have the desired
    concentration.

#### A.1.2.3. Additional comments {#a.1.2.3.-additional-comments .HeadingA4}

For those mathematically inclined, the following formula can be used to
determine the volume of water required for a given level of
concentration.

m^3^ of water required to kg dry CaCl~2~ x %CaCl~2~

make a solution of a = -- kg dry CaCl~2~ ÷ 1000 kg/m^3^ water

desired concentration desired % solution

Example: to make a 20 percent solution from 500 kg of flake CaCl~2~
(this is typically 78 percent concentration),

500 x 78

-- 500 ÷ 1000 = 1.45 m^3^ water

20

(In English units:

gal of water required to lb dry CaCl~2~ x %CaCl~2~

make a solution of a = -- lb dry CaCl~2~ ÷ 8.34 lb/gal water

desired concentration desired % solution

Example: to make a 20 percent solution from 1000 lb of flake CaCl~2~
(this is typically 78 percent concentration),

1000 x 78

-- 1000 ÷ 8.34 = 348 gal water )

20

**A word of caution.** Calcium chloride when dissolved gives off heat.
This heat of solution causes the brine to expand and occupy more space
than it will after it cools. That's why the container in Method 2 is
filled to no more than 2/3 capacity. For example, additional tank
capacity of approximately 90 L (23 gal) for every\
4 m^3^ (1000 gal) of 20 percent solution is required. This will increase
slightly to 100 L (26 gal) for every\
4 m^3^ (1000 gal) of a 34 percent solution.

Always add the calcium chloride to the water. If you put the calcium
chloride in the container first and then add water, the chemical may
form a solid mass which is difficult to dissolve completely.

## A.2 Sodium Chloride, NaCl {#a.2-sodium-chloride-nacl .HeadingA2}

### A.2.1 Solid NaCl {#a.2.1-solid-nacl .HeadingA3}

Sodium chloride has been used as an ice-control chemical on roads since
early in this century. It is produced by three processes: *rock salt* is
mined by conventional hard rock mining equipment and techniques; *solar
salt* is produced by the evaporation of sea water and may contain only a
small amount of impurities; and *evaporated* or *solution* or *vacuum
salt*, a very pure form made by drying under vacuum the solution
resulting from injection of water into deep underground deposits. Most
salt used for highway applications in the United States is rock salt,
though some solar salt is produced in several western states and some is
imported into the eastern US. Naturally occurring rock salt is the
mineral halite, and usually contains between 1 percent and 4 percent
impurities, mostly gypsum, shale, dolomite, and quartz.

The ASTM designation for salt used for highway ice control is D 632
*Standard Specification for Sodium Chloride.*

Two gradations of salt are designated by the ASTM standard as shown in
Table 3. Similar but slightly different gradations are used by the
British. These along with the Swedish and Finnish gradations are shown
below, in Tables 4, 5 and 6, respectively.

Table 3. Gradation of salt specified by ASTM D 632.

+------------------------------+-------------------+------------------+
| **Sieve size**               | **Weight %        |                  |
|                              | passing**         |                  |
+------------------------------+-------------------+------------------+
|                              | **Grade 1**       | **Grade 2**      |
+------------------------------+-------------------+------------------+
| 19.0 mm (3/4 in)             | . . .             | 100              |
|                              |                   |                  |
| 12.5 mm (1/2 in)             | 100               | . . .            |
|                              |                   |                  |
| 9.5 mm (3/8 in)              | 95 to 100         | . . .            |
|                              |                   |                  |
| 4.75 mm (No. 4)              | 20 to 90          | 20 to 100        |
|                              |                   |                  |
| 2.36 mm (No. 8)              | 10 to 60          | 10 to 60         |
|                              |                   |                  |
| 600 µm (No. 30)              | 0 to 15           | 0 to 15          |
+------------------------------+-------------------+------------------+

Note: grade 1 is the most commonly used gradation in the U.S.

Table 4. Salt gradation specified by British Standard BS 3247
*Specification for salt for spreading in highways for winter
maintenance*.

+------------------+-------------+----------------+-------------------+
| **Type and grade |             | **BS 410 test  | **Percentage**    |
| of salt**        |             | sieve**        |                   |
|                  |             |                | **passing**       |
|                  |             |                |                   |
|                  |             |                | **test sieve**    |
+------------------+-------------+----------------+-------------------+
| Rock salt        | Coarse      | 10 mm          | 100               |
|                  |             |                |                   |
|                  |             | 6.3 mm         | 75 to 95          |
|                  |             |                |                   |
|                  |             | 2.36 mm        | 30 to 70          |
|                  |             |                |                   |
|                  |             | 300 μm         | 0 to 20           |
+------------------+-------------+----------------+-------------------+
|                  | Fine        | 6.3 mm         | 100               |
|                  |             |                |                   |
|                  |             | 2.36 mm        | 30 to 80          |
|                  |             |                |                   |
|                  |             | 300 μm         | 0 to 20           |
+------------------+-------------+----------------+-------------------+
| Vacuum salt and  | Coarse      | 10 mm          | 100               |
| marine salt      |             |                |                   |
|                  |             | 1.18 mm        | 0 to 80           |
|                  |             |                |                   |
|                  |             | 150 μm         | 0 to 10           |
+------------------+-------------+----------------+-------------------+
|                  | Fine        | 1.18 mm        | 100               |
|                  |             |                |                   |
|                  |             | 150 μm         | 0 to 30           |
+------------------+-------------+----------------+-------------------+

Table 5. Swedish gradation for salt.

+--------------------------------+-------------------------------------+
| **Sieve size,mm**              | **Weight % passing**                |
+--------------------------------+-------------------------------------+
| 3                              | 95-100                              |
|                                |                                     |
| 2                              | 65-100                              |
|                                |                                     |
| 1                              | 26-50                               |
|                                |                                     |
| 0.5                            | 5-26                                |
|                                |                                     |
| 0.16                           | 0-5                                 |
+--------------------------------+-------------------------------------+

Table 6. Finnish gradation for salt.

+--------------------------------+-------------------------------------+
| **Sieve size, mm**             | **Weight % passing**                |
+--------------------------------+-------------------------------------+
| 5                              | 100                                 |
|                                |                                     |
| 4                              | 90-100                              |
|                                |                                     |
| 3                              | 70-100                              |
|                                |                                     |
| 2                              | 40-90                               |
|                                |                                     |
| 1                              | 15-55                               |
|                                |                                     |
| 0.5                            | 3-25                                |
+--------------------------------+-------------------------------------+

### A.2.2 Preparation of liquid NaCl {#a.2.2-preparation-of-liquid-nacl .HeadingA3}

Two methods of mixing can be used to obtain a specific concentration of
liquid NaCl. Method 1 is used if the volume of the mixing container is
known and a desired volume of salt brine is to be produced. Use method 2
if the volume of the mixing container is not known. Each of these
methods is described below.

#### A.2.2.1 Method 1 (Known mixing container volume) {#a.2.2.1-method-1-known-mixing-container-volume .HeadingA4}

1.  From the "per volume solution" column of Table 7, determine the
    determine the weight in kg (or lb) of dry salt required to make 1
    m^3^ (or 1 gal) of solution at the desired concentration level. This
    value, multiplied by the volume of the container, gives the total
    weight of dry salt required.

2.  Fill the container approximately 2/3 full of water, then add the
    required dry salt gradually while stirring with a paddle by hand,
    with a mechanical agitator, or with an air bubbler.

3.  After the salt has dissolved, add water to the container to bring
    the level to the working volume and then agitate the solution slowly
    until a uniform mixture is obtained. Some insoluble precipitate from
    the impurities will remain in the bottom of the tank until
    physically removed.

4.  Finally, the salt brine should be tested with a hydrometer to
    determine the percentage of concentration that has been produced.
    For anti-icing operations, the concentration of the salt brine
    should be as close to 23.3 percent as possible, but no more than 25
    percent. If the concentration is more than 25 percent, some water
    should be added to the mixture to reduce the concentration to the
    desired level. If the concentration is less than 23 percent some
    salt should be added to the mixture to raise the concentration to
    the desired level. The table of hydrometer readings versus percent
    concentration of salt given in Section 3.1.2.2 can be used for these
    tests.

Table 7. Proportions for preparing sodium chloride solutions from
commercial grade salt (i.e., up to\
5 percent impurities).

+-----------+-----------+----------+------------------+---------------+
| **% NaCl  | **Weight  |          | **C              | **Weight per  |
| actual**  | NaCl**    |          | rystallization** | unit**        |
+-----------+-----------+----------+------------------+---------------+
|           | **per     | **per    | **temperature\   | **volume of   |
|           | volume    | volume   | ^o^C (°F)**      | solution\     |
|           | s         | water**  |                  | kg/m^3^       |
|           | olution** |          |                  | (lb/gal)**    |
|           |           | *        |                  |               |
|           | **kg/m^3^ | *kg/m^3^ |                  |               |
|           | (         | (l       |                  |               |
|           | lb/gal)** | b/gal)** |                  |               |
+-----------+-----------+----------+------------------+---------------+
| 10        | 108 (0.9) | 96 (0.8) | -6.7 (20)        | 1072 (8.95)   |
+-----------+-----------+----------+------------------+---------------+
| 15        | 168 (1.4) | 156      | -11.1 (12)       | 1112 (9.28)   |
|           |           | (1.3)    |                  |               |
+-----------+-----------+----------+------------------+---------------+
| 20        | 228 (1.9) | 204      | -17.8 (0)        | 1150 (9.6)    |
|           |           | (1.7)    |                  |               |
+-----------+-----------+----------+------------------+---------------+
| 23\*      | 276 (2.3) | 228      | -21.1 (-6)       | 1169 (9.76)   |
|           |           | (1.9)    |                  |               |
+-----------+-----------+----------+------------------+---------------+
| 25        | 300 (2.5) | 252      | -8.9 (16)        | 1234 (10.3)   |
|           |           | (2.1)    |                  |               |
+-----------+-----------+----------+------------------+---------------+

\*Note. This is the approximate eutectic composition (see explanation in
calcium chloride entry above).

#### A.2.2.2 Method 2 (Unknown mixing container volume) {#a.2.2.2-method-2-unknown-mixing-container-volume .HeadingA4}

1.  Fill a hopper tank with dry salt and let water slowly run through
    the salt by gravity action to the bottom of the tank.

2.  Discharge the brine at the bottom of the hopper tank into a holding
    tank below the hopper tank. Pump the brine from the holding tank
    into a larger storage tank. Stir the mixture in the larger storage
    tank with a mechanical agitator or with an air bubbler.

3.  Continue to add salt and water to the hopper tank until the large
    storage tank is almost full.

4.  Determine the percentage of concentration of the salt brine using a
    hydrometer and the table in Section 3.1.2.2. Method 2 will produce
    up to a 100 percent saturated brine solution depending on the rate
    of water flow through the salt. A 100 percent saturated brine
    solution corresponds to a 27 percent concentration level. Water
    should be added now to the storage tank to reduce the concentration
    of the mixture to the 23 to 25 percent level.

5.  Finally, the required number of pounds of salt used in Method 2 can
    be roughly calculated by multiplying the total volume of water by
    the weight of sodium chloride per volume of water given in the "per
    volume water" column of Table 7 that corresponds to the percent
    concentration level achieved. This estimate of the amount of salt
    used can be used to generate subsequent volumes of mixture to fill
    the storage tank when it is completely empty.

#### A.2.2.3 Additional comments {#a.2.2.3-additional-comments .HeadingA4}

Method 2 above has been used successfully by several States to generate
a salt brine for anti-icing operations. In practice, the brine
generation process operates continuously during a storm. This is because
liquid brine is drawn from the storage tank throughout the storm to fill
the tanks on the spreader vehicles. In this situation, it is important
to frequently monitor the percentage concentration level of the mixture
in the storage tank. Adjustments should be made to mixture when
necessary to achieve the desired level of concentration.

## A.3 Magnesium Chloride, MgCl~2~ {#a.3-magnesium-chloride-mgcl2 .HeadingA2}

The principal source of this ice control chemical is brines from Great
Salt Lake. Though it is available in solid (flake) form, it is used in
liquid form for ice control. Eutectic temperature is about -33^o^C
(-28^o^F) at a concentration of 21.6 percent. Its ice melting capacity
is about 40 percent greater than CaCl~2~. Proprietary mixtures are
available containing 20 to 25 percent MgCl~2~ with various corrosion
inhibitor additives. One proprietary compound reportedly has an eutectic
temperature of -20^o^C (-4^o^F). These solutions are effective
ice-melting agents at temperatures above -7^o^C (19^o^F).

## A.4 Calcium Magnesium Acetate, \[CaMg~2~ (CH~3~COO)~2~\]~6~  {#a.4-calcium-magnesium-acetate-camg2-ch3coo26 .HeadingA2}

### A.4.1 Introduction {#a.4.1-introduction .HeadingA3}

Currently there is only one commercial source for CMA, using the
reaction of acetic acid with dolomitic limestone for production. The
acetic acid, the costly component of the compound, is manufactured from
natural gas or petroleum, though small quantities have been produced by
biodegradation of agricultural wastes. The compound is available as
pellets. Though not as soluble in water as NaCl and CaCl~2~, solutions
can be made at point of use for use as a prewetting agent or straight
chemical application. It is not a highly effective deicing chemical in
solid form because of its affinity for water and its light particle
mass. Its benefit is that snow is made mealy and will not compact. CMA
is primarily a mixture of calcium and magnesium acetates, produced with
a 3/7 Ca/Mg ratio which was found to be optimum in previous FHWA
studies. The eutectic temperature is about -28^o^C (-18^o^F) at a
concentration of 32.5 percent.

### A.4.2 Preparation of liquid CMA {#a.4.2-preparation-of-liquid-cma .HeadingA3}

Liquid CMA is prepared by dissolving pelletized CMA in water. This
process results in a murky solution that settles in time to produce a
clear liquid CMA on top and discardable insolubles on the bottom. A 25
percent concentration of liquid CMA is recommended for anti-icing
operations. Specifics of liquid CMA production are given in Section
3.1.2.2.

## A.5 Potassium Acetate, KC~2~H~3~O~2~ {#a.5-potassium-acetate-kc2h3o2 .HeadingA2}

Potassium acetate, or KAc as it is commonly known, is produced by the
reaction of acetic acid with potassium carbonate. The sources of acetic
acid are the same as are used in the production of CMA. Potassium
carbonate is one of the group of salts commercially known as potash.
Potassium carbonate was originally obtained by running water through
wood ashes and boiling the resulting solution in large iron pots. The
substance that formed was called potash. Potassium carbonate is
currently produced by one of several processes that use potassium
chloride, another salt of the potash family. The compound, potassium
acetate, is a white, crystalline, deliquescent powder that has a saline
taste. It is soluble in water and alcohol. Solutions are alkaline under
a litmus test. The dry compound is combustible but is used as a
dehydrating agent, a reagent in analytical chemistry, and in the
production of synthetic flavors, in addition to other uses. The eutectic
temperature of a KAc and water solution is -60^o^C (-76^o^F) at a
concentration of 49 percent. A commercial form of liquid KAc, containing
a 50 percent concentration by weight plus corrosion inhibitors, has been
used as a prewetting agent with dry salt or as a straight chemical
application. Some experience has been gained with the straight liquid
form during anti-icing experiments ([1]{.underline}).

#   {#section-1 .HeadingA1 .unnumbered}

# APPENDIX B. FREEZING-POINT OF chemical solutions {#appendix-b.-freezing-point-of-chemical-solutions .HeadingA1}

## B.1 INTRODUCTION {#b.1-introduction .HeadingA2}

In order for a chemical to act as a freezing-point depressant, it must
go into solution. A solid chemical applied as an anti-icing treatment
must cover the highway pavement surface as rapidly as possible in
solution form to act as a barrier to the formation of a bonded snow or
ice layer anywhere on the road. The dissolution of two common chemicals
used in snow and ice control operations, sodium chloride (salt) and
calcium chloride, will be used as examples to help explain the brine
generation process.

Energy is required to initiate the solution process and to continue it.
The solution process, in the case of salt, will take place very slowly.
A dry particle of salt placed on a dry surface will just sit there for a
time until it can absorb enough thermal energy from the surrounding
environment to a point where a liquid film is formed on the surface of
the particle. This initial brine then triggers the solution of the rest
of the salt. As the particle dissolves, it continues to absorb thermal
energy from its surroundings. This type of absorption process is called
an endothermic reaction.

The rate at which salt goes into solution can be accelerated by several
means. It can find free moisture or liquid on the pavement surface to
start the brine generation process. Or, a liquid can be added to the
surface of the salt particles before they are placed on the pavement
surface. This second means of applying a liquid to dry salt is
accomplished by a prewetting process.

The solution process of calcium chloride takes place much faster than
that of salt. This is because calcium chloride is both hygroscopic and
deliquescent (CaCl~2~ will absorb moisture at a relative humidity (RH)
of 42 percent and higher; NaCl will not begin to absorb moisture until a
RH of 76 percent is reached). Thus, solid calcium chloride will absorb
moisture from the air until it dissolves. The brine solution will
continue to absorb moisture until an equilibrium is reached between the
vapor pressure of the solution and that of the air. If the humidity of
the air increases, more moisture is absorbed by the solution. If the
humidity of the air decreases, water evaporates from the solution to the
air. As the particle of calcium chloride dissolves, it releases a
considerable amount of heat. This type of process is called an
exothermic reaction.

When calcium chloride and salt are combined, they complement each other
as snow and ice control chemicals. When combined, the deliquescent
calcium chloride absorbs moisture from its surroundings releasing heat
and thereby increasing the rate of solution of sodium chloride. These
reactions produce brine quickly which sustains the continued brine
generation of the two chemicals.

The solubility of all chemicals varies with temperature. The lower the
temperature, the less the solubility. This decrease in solubility has a
limit, a point where no more of the chemical can dissolve and depress
the freezing-point.

The freezing-point of a brine can best be described by reference to the
phase diagram of a generic salt-water solution shown in the small plot
inserted in the lower left of Figure 16. The solid curve is a plot of
concentration of a salt (X-axis) versus temperature (Y-axis). The solid
curve separates the phases of the solution. Above this curve, the salt
is totally in solution. The lowest temperature on the curve is called
the temperature at the eutectic point, or eutectic temperature. Below
this temperature (and below the dashed line), no solution exists, only a
mixture of ice and solid salt. A mixture of ice and salt solution exists
to the left of the solid curve and above the dashed line. A mixture of
solid salt and salt solution exists to the right of the solid curve and
above the dashed line. Thus, the solid curve describes the
freezing-point of a brine as a function of the concentration of the salt
solution.

Some comments are given below about the important characteristics of the
generic phase diagram.

1.  The freezing-point of the brine solution decreases with increasing
    concentration up to the eutectic composition. The freezing-point of
    the brine solution will increase as the concentration increases
    beyond the eutectic composition.

2.  Brine solutions having a concentration less than the eutectic
    composition have a freezing-point lower than the melting temperature
    of pure ice or 0^o^C (32^o^F).

3.  In snow and ice control operations and particularly during
    anti-icing treatments, it is necessary to operate with brine
    solutions as close as possible to, but less than, the eutectic
    composition. The brine solution concentration will decrease as it is
    diluted with water from either the melting of snow/ice or falling
    rain/freezing rain. Consequently, it is important to monitor the
    dilution process so that the solution concentration does not
    decrease to a value which corresponds to a temperature in the
    freezing temperature range above the pavement temperature. When this
    occurs, a refreeze of the solution will take place.

## B.2 NaCl and CaCl~2~ {#b.2-nacl-and-cacl2 .HeadingA2}

The phase diagrams of NaCl and CaCl~2~ solutions are also presented in
Figure 16. As can be seen, the eutectic temperature of the calcium
chloride-water system is lower than the eutectic temperature of the
sodium chloride-water system. The eutectic composition of the calcium
chloride-water system is approximately 30 percent CaCl~2~ and 70 percent
H~2~0 by weight which remains a solution as low as -51^o^C (-60^o^F).
The eutectic composition of the sodium chloride (common road salt)-water
system is 23 percent NaCl and 77 percent H~2~0 by weight, which freezes
at about -21^o^C (-6^o^F).

The 30 percent concentration of calcium chloride shown in Figure 16 at
the eutectic temperature is higher than the corresponding concentration
of a commercially available pelletized form of calcium chloride (29.6 to
29.8 percent). Some differences can occur between individual phase
diagrams of commercially available calcium chloride-water systems
because of the presence and amounts of other chemical elements.

Some evidence suggest that anti-icing operations should not be conducted
(using liquid, prewetted, or dry salt) when the pavement temperature is
at or below about -9.5^o^C (15^o^F) ([2]{.underline}). Some highway
agencies also believe that it is not practical to use salt below -9^o^C
(15^o^F) for general snow and ice control operations, at least not
without calcium chloride. This experience has convinced them that salt's
action is too slow at these lower temperatures. An inspection of Figure
16 shows that the phase diagrams of NaCl and CaCl~2~ are not too
dissimilar in the temperature range of 0^o^C (32^o^F) down to -10^o^C
(15^o^F) or even down to about -15^o^C (5^o^F). Thus, the two chemical
brines have about the same solidification (freezing) characteristics in
this temperature range. The fact that calcium chloride has a much lower
eutectic temperature than sodium chloride is not of importance for
anti-icing operations.

Figure 16. Phase diagrams of NaCl and CaCl~2~ solutions.

## B.3 MgCl~2~ {#b.3-mgcl2 .HeadingA2}

The phase diagram of magnesium chloride, MgCl~2~, solutions is presented
in Figure 17 together with those of CMA, KAc, and the chloride solutions
discussed above. The eutectic temperature of the magnesium
chloride-water system is between that of NaCl and CaCl~2~. The eutectic
composition for the magnesium chloride-water system in this figure is
21.6 percent MgCl~2~ and 78.4 percent H~2~0 by weight which freezes at
about -33^o^C (-28^o^F). The density and chemical composition of MgCl~2~
brines can vary somewhat with the source of MgCl~2~ and with seasonal
weather fluctuations which affect the solar evaporation process used in
the production of flake MgCl~2~. The chemical composition of MgCl~2~
brines can include, in addition to magnesium and chloride, such
components as sulfates, sodium, potassium, lithium, bromine, and iron.
Consequently, some differences can occur between individual phase
diagrams of commercially available magnesium chloride-water systems.

It is necessary to check the percent concentration of MgCl~2~ brines
before use in anti-icing treatments either as a prewetting agent for a
solid chemical or as a straight liquid. It is important that the percent
concentration not be too high above that at the eutectic temperature. If
it is, there is the possibility that the solution might clog the
spreader spray nozzles and/or burn out electric pumps.

An interesting comparison of the freezing-point of the three chloride
solutions can be made by reference to Figure 17. For a given pavement
temperature below 0^o^C (32^o^F) but above the eutectic temperature of
NaCl, a MgCl~[2]{.underline}~ solution will refreeze at a lower
concentration than the corresponding concentrations of either CaCl~2~ or
NaCl at that temperature. For example, the refreeze concentration of
MgCl~2~ at -10^o^C (15^o^F) is about 11 percent while the refreeze
concentrations of CaCl~2~ and NaCl at that temperature are about 12.5
percent and 13.5 percent, respectively. This means that MgCl~2~ brines
can be diluted more than CaCl~2~ and NaCl before refreezing at a given
temperature. However, once the dilution process starts, the refreeze
temperature of MgCl~2~ rises faster than do the refreeze temperatures of
both CaCl~2~ and NaCl. The slope of the MgCl~2~ curve to the left of its
eutectic concentration is steeper than the slope of either the CaCl~2~
or NaCl curves until the three brine concentrations reach about 5
percent or a corresponding temperature of about -3^o^C (27^o^F). Between
this temperature and 0^o^C (32^o^F), all three brines have about the
same refreeze characteristics.

One final comment about the chloride solution curves in Figure 17. The
refreeze temperature of NaCl solutions rises slower with dilution than
do the refreeze temperatures of either CaCl~2~ or MgCl~2~. However, a
slightly higher concentration of a NaCl solution (slightly more salt) is
needed than the corresponding concentration of CaCl~2~ at a given
temperature to keep the two brine solutions from refreezing. A much
higher concentration of NaCl is needed than the corresponding
concentration of MgCl~2~ at the same temperature to keep the two brine
solutions from refreezing.

## B.4 CMA AND KAc {#b.4-cma-and-kac .HeadingA2}

The curve for CMA (Figure 17) was determined from different percent
concentration solutions made by dissolving commercially available CMA
supplied in a dry pellet form. The curve for KAc was determined using a
commercially available liquid form of KAc. The eutectic temperature for
the CMA-water system in Figure 17 is -27.5^o^C (-17.5^o^F) at a
concentration of 32.5 percent. The eutectic temperature for the
KAc-water system is -60^o^C (-76^o^F) at a concentration of 49 percent.
The curves for CMA and KAc almost coincide with each other. Also, they
have a much flatter slope than the other three curves. This is an
important feature of both CMA and KAc solutions. The refreeze
temperature of both CMA and KAc solutions rises slower with dilution
than do the refreeze temperatures of either NaCl, CaCl~2~, or MgCl~2~.
This feature makes them well suited for being used in a liquid form
during anti-icing treatments. This is especially true for their use in a
liquid form for the pretreatment of bridge decks in anticipation of
frosting, or localized icing conditions.

Figure 17. Phase diagrams of five chemical solutions.

All is not favorable with the use of CMA or KAc over that of, say, NaCl.
A much higher concentration of either CMA or KAc solution is needed than
the corresponding concentration of NaCl at a given temperature to keep
the solutions from refreezing. The solution concentration of CMA must be
1.41 times higher than the NaC1 solution concentration at -9.4^o^C
(15^o^F) (19 percent for CMA versus 13.5 percent for NaCl) to keep both
solutions from refreezing. This factor increases to 1.54 at -3.9^o^C
(25^o^F). The solution concentration of KAc must be about 1.37 and 1.38
higher than the NaCl solution concentrations at -9.4^o^C (15^o^F) and
-3.9^o^C (25^o^F), respectively. These differences in concentrations
needed for both CMA and KAc translate into considerably higher costs per
application treatment for both chemicals than NaCl.

#   {#section-2 .HeadingA1 .unnumbered}

# Appendix C. Operations guide for Maintenance Field PERSONNEL {#appendix-c.-operations-guide-for-maintenance-field-personnel .HeadingA1}

## C.1 Introduction {#c.1-introduction .HeadingA2}

This appendix is a guide to highway anti-icing operations for
maintenance field personnel. Its purpose is to suggest maintenance
actions for *preventing* the formation or development of packed and
bonded snow or bonded ice during a variety of winter weather events. It
is intended to complement the decision-making and management practices
of a systematic anti-icing program so that roads can be efficiently
maintained in the best possible condition.

The guidance is based upon the results of four years of anti-icing field
testing conducted by 15 State highway agencies and supported by the
Strategic Highway Research Program (SHRP) and the Federal Highway
Administration (FHWA). It has been augmented with practices developed
outside the U.S., where necessary, for completeness. The recommendations
are subject to refinement as U.S. highway agencies gain additional
experience with anti-icing operations. Final decisions for their
implementation rests with management personnel.

## C.2 Guidance for anti-ICING operations {#c.2-guidance-for-anti-icing-operations .HeadingA2}

Guidance for anti-icing operations is presented in Tables 8 to 13 for
six distinctive winter weather events. The six events are:

-   Light Snow Storm

-   Light Snow Storm with Period(s) of Moderate or Heavy Snow

-   Moderate or Heavy Snow Storm

-   Frost or Black Ice

-   Freezing Rain Storm

-   Sleet Storm

The tables suggest the appropriate maintenance action to take during an
initial or subsequent (follow-up) anti-icing operation for a given
precipitation or icing event. Each action is defined for a range of
pavement temperatures and an associated temperature trend. For some
events the operation is dependent not only on the pavement temperature
and trend, but also upon the pavement surface or the traffic condition
at the time of the action. Most of the maintenance actions involve the
application of a chemical in either a dry solid, liquid, or prewetted
solid form. Application rates ("spread rates") are given for each
chemical form where appropriate. These are suggested values and should
be adjusted, if necessary to achieve increased effectiveness or
efficiency, for local conditions. *The rates given for liquid chemicals
are the equivalent dry chemical rates*. Application rates in volumetric
units such as L/lane-km (or gal/lane-mi) must be calculated from these
dry chemical rates for each chemical and concentration.

Comments and notes are given in each table where appropriate to further
guide the maintenance field personnel in their anti-icing operations.

## C.3 Glossary of terms {#c.3-glossary-of-terms .HeadingA2}

**Black ice**. Popular term for a very thin coating of clear,
bubble-free, homogeneous ice which forms on a pavement with a
temperature at or slightly above 0^o^C (32^o^F) when the temperature of
the air in contact with the ground is below the freezing-point of water
and small slightly supercooled water droplets deposit on the surface and
coalesce (flow together) before freezing.

**Dry chemical spread rate**. The chemical application rate. For solid
applications it is simply the weight of the chemical applied per lane
kilometer (or mile). For liquid applications it is the weight of the dry
chemical in solution applied per lane kilometer (or mile).

**Freezing rain**. Supercooled droplets of liquid precipitation falling
on a surface whose temperature is below or slightly above freezing,
resulting in a hard, slick, generally thick coating of ice commonly
called glaze or clear ice. Non-supercooled raindrops falling on a
surface whose temperature is well below freezing will also result in
glaze.

**Frost**. Also called hoarfrost. Ice crystals in the form of scales,
needles, feathers or fans deposited on surfaces cooled by radiation or
by other processes. The deposit may be composed of drops of dew frozen
after deposition and of ice formed directly from water vapor at a
temperature below 0^o^C (32^o^F) (sublimation).

**Light snow**. Snow falling at the rate of less than 12 mm (1/2 in) per
hour; visibility is not affected adversely.

**Liquid chemical**. A chemical solution; the weight of the dry chemical
in solution applied per lane kilometer (or mile) is the chemical
application rate -- the "dry chemical spread rate" -- used in this
appendix.

**Moderate or heavy snow**. Snow falling at a rate of 12 mm (1/2 in) per
hour or greater; visibility may be reduced.

**Sleet**. A mixture of rain and of snow which has been partially melted
by falling through an atmosphere with a temperature slightly above
freezing.

**Slush**. Accumulation of snow which lies on an impervious base and is
saturated with water in excess of its freely drained capacity. It will
not support any weight when stepped or driven on but will "squish" until
the base support is reached.

Table 8. Weather event: light snow storm.

+-------+----+------+---+-----+------+---+----+--------------------+
| **    | *  |      |   |     | **SU |   |    | **COMMENTS**       |
| PAVEM | *I |      |   |     | BSEQ |   |    |                    |
| ENT** | NI |      |   |     | UENT |   |    |                    |
|       | TI |      |   |     | OPER |   |    |                    |
|       | AL |      |   |     | ATIO |   |    |                    |
|       | O  |      |   |     | NS** |   |    |                    |
|       | PE |      |   |     |      |   |    |                    |
|       | RA |      |   |     |      |   |    |                    |
|       | TI |      |   |     |      |   |    |                    |
|       | ON |      |   |     |      |   |    |                    |
|       | ** |      |   |     |      |   |    |                    |
+-------+----+------+---+-----+------+---+----+--------------------+
| **T   | ** | *    | * |     | *    | * |    |                    |
| EMPER | pa | *mai | * |     | *mai | * |    |                    |
| ATURE | ve | nten | d |     | nten | d |    |                    |
| RA    | me | ance | r |     | ance | r |    |                    |
| NGE,\ | nt | acti | y |     | acti | y |    |                    |
| AND   | s  | on** | c |     | on** | c |    |                    |
| TR    | ur |      | h |     |      | h |    |                    |
| END** | fa |      | e |     |      | e |    |                    |
|       | ce |      | m |     |      | m |    |                    |
|       | at |      | i |     |      | i |    |                    |
|       | ti |      | c |     |      | c |    |                    |
|       | me |      | a |     |      | a |    |                    |
|       | of |      | l |     |      | l |    |                    |
|       | ** |      | s |     |      | s |    |                    |
|       |    |      | p |     |      | p |    |                    |
|       |    |      | r |     |      | r |    |                    |
|       |    |      | e |     |      | e |    |                    |
|       |    |      | a |     |      | a |    |                    |
|       |    |      | d |     |      | d |    |                    |
|       |    |      | r |     |      | r |    |                    |
|       |    |      | a |     |      | a |    |                    |
|       |    |      | t |     |      | t |    |                    |
|       |    |      | e |     |      | e |    |                    |
|       |    |      | , |     |      | , |    |                    |
|       |    |      | k |     |      | k |    |                    |
|       |    |      | g |     |      | g |    |                    |
|       |    |      | / |     |      | / |    |                    |
|       |    |      | l |     |      | l |    |                    |
|       |    |      | a |     |      | a |    |                    |
|       |    |      | n |     |      | n |    |                    |
|       |    |      | e |     |      | e |    |                    |
|       |    |      | - |     |      | - |    |                    |
|       |    |      | k |     |      | k |    |                    |
|       |    |      | m |     |      | m |    |                    |
|       |    |      | ( |     |      | ( |    |                    |
|       |    |      | l |     |      | l |    |                    |
|       |    |      | b |     |      | b |    |                    |
|       |    |      | / |     |      | / |    |                    |
|       |    |      | l |     |      | l |    |                    |
|       |    |      | a |     |      | a |    |                    |
|       |    |      | n |     |      | n |    |                    |
|       |    |      | e |     |      | e |    |                    |
|       |    |      | - |     |      | - |    |                    |
|       |    |      | m |     |      | m |    |                    |
|       |    |      | i |     |      | i |    |                    |
|       |    |      | ) |     |      | ) |    |                    |
|       |    |      | * |     |      | * |    |                    |
|       |    |      | * |     |      | * |    |                    |
+-------+----+------+---+-----+------+---+----+--------------------+
|       | *  |      | * | *   |      | * | *  |                    |
|       | *i |      | * | *so |      | * | *s |                    |
|       | ni |      | l | lid |      | l | ol |                    |
|       | ti |      | i | or  |      | i | id |                    |
|       | al |      | q | pre |      | q | or |                    |
|       | o  |      | u | wet |      | u | p  |                    |
|       | pe |      | i | ted |      | i | re |                    |
|       | ra |      | d | s   |      | d | we |                    |
|       | ti |      | * | oli |      | * | tt |                    |
|       | on |      | * | d** |      | * | ed |                    |
|       | ** |      |   |     |      |   | s  |                    |
|       |    |      |   |     |      |   | ol |                    |
|       |    |      |   |     |      |   | id |                    |
|       |    |      |   |     |      |   | ** |                    |
+-------+----+------+---+-----+------+---+----+--------------------+
| **    | Dr | N    |   |     | N    |   |    | 1\) Monitor        |
| Above | y, | one, |   |     | one, |   |    | pavement           |
| 0^o^C | we | see  |   |     | see  |   |    | temperature        |
| (     | t, | comm |   |     | comm |   |    | closely for drops  |
| 32^o^ | sl | ents |   |     | ents |   |    | toward 0^o^C       |
| F)**, | us |      |   |     |      |   |    | (32^o^F) and below |
|       | h, |      |   |     |      |   |    |                    |
| s     | or |      |   |     |      |   |    | 2\) Treat icy      |
| teady | l  |      |   |     |      |   |    | patches if needed  |
| or    | ig |      |   |     |      |   |    | with chemical at\  |
| r     | ht |      |   |     |      |   |    | 28 kg/lane-km (100 |
| ising | sn |      |   |     |      |   |    | lb/lane-mi); plow  |
|       | ow |      |   |     |      |   |    | if needed          |
|       | c  |      |   |     |      |   |    |                    |
|       | ov |      |   |     |      |   |    |                    |
|       | er |      |   |     |      |   |    |                    |
+-------+----+------+---+-----+------+---+----+--------------------+
| **    | D  | A    | 2 | 28\ | Plow | 2 | 2  | 1\) Applications   |
| Above | ry | pply | 8 | (1  | as   | 8 | 8\ | will need to be    |
| 0^o^C |    | li   | \ | 00) | nee  | \ | (  | more frequent at   |
| (     |    | quid | ( |     | ded; | ( | 10 | lower temperatures |
| 32^o^ |    | or   | 1 |     | rea  | 1 | 0) | and higher         |
| F)**, |    | p    | 0 |     | pply | 0 |    | snowfall rates     |
|       |    | rewe | 0 |     | li   | 0 |    |                    |
| 0^o^C |    | tted | ) |     | quid | ) |    | 2\) It is not      |
| (32   |    | s    |   |     | or   |   |    | advisable to apply |
| ^o^F) |    | olid |   |     | s    |   |    | a liquid chemical  |
| or    |    | chem |   |     | olid |   |    | at the indicated   |
| below |    | ical |   |     | chem |   |    | spread rate when   |
| is    |    |      |   |     | ical |   |    | the pavement       |
| immi  |    |      |   |     | when |   |    |                    |
| nent; |    |      |   |     | ne   |   |    |                    |
|       |    |      |   |     | eded |   |    |                    |
+-------+----+------+---+-----+------+---+----+--------------------+
| *     | We | A    | 2 | 28\ |      |   |    | temperature drops  |
| ALSO* | t, | pply | 8 | (1  |      |   |    | below -5^o^C       |
|       | sl | li   | \ | 00) |      |   |    | (23^o^F)           |
| **-7  | us | quid | ( |     |      |   |    |                    |
| to    | h, | or   | 1 |     |      |   |    | 3\) Do not apply   |
| 0^    | or | s    | 0 |     |      |   |    | liquid chemical    |
| o^C** | l  | olid | 0 |     |      |   |    | onto heavy snow    |
|       | ig | chem | ) |     |      |   |    | accumulation or    |
| **(20 | ht | ical |   |     |      |   |    | packed snow        |
| to    | sn |      |   |     |      |   |    |                    |
| 32^o^ | ow |      |   |     |      |   |    |                    |
| F)**, | c  |      |   |     |      |   |    |                    |
|       | ov |      |   |     |      |   |    |                    |
| rema  | er |      |   |     |      |   |    |                    |
| ining |    |      |   |     |      |   |    |                    |
| in    |    |      |   |     |      |   |    |                    |
| range |    |      |   |     |      |   |    |                    |
+-------+----+------+---+-----+------+---+----+--------------------+
| **-10 | Dr | A    |   | 55\ | Plow |   | 5  | If sufficient      |
| to    | y, | pply |   | (2  | as   |   | 5\ | moisture is        |
| -7^   | we | p    |   | 00) | nee  |   | (  | present, solid     |
| o^C** | t, | rewe |   |     | ded; |   | 20 | chemical without   |
|       | sl | tted |   |     | rea  |   | 0) | prewetting can be  |
| **(15 | us | s    |   |     | pply |   |    | applied            |
| to    | h, | olid |   |     | p    |   |    |                    |
| 20^o^ | or | chem |   |     | rewe |   |    |                    |
| F)**, | l  | ical |   |     | tted |   |    |                    |
|       | ig |      |   |     | s    |   |    |                    |
| rema  | ht |      |   |     | olid |   |    |                    |
| ining | sn |      |   |     | chem |   |    |                    |
| in    | ow |      |   |     | ical |   |    |                    |
| range | c  |      |   |     | when |   |    |                    |
|       | ov |      |   |     | ne   |   |    |                    |
|       | er |      |   |     | eded |   |    |                    |
+-------+----+------+---+-----+------+---+----+--------------------+
| **    | D  | Plow |   |     | Plow |   |    | 1\) It is not      |
| Below | ry | as   |   |     | as   |   |    | recommended that   |
| -1    | or | ne   |   |     | ne   |   |    | chemicals be       |
| 0^o^C | l  | eded |   |     | eded |   |    | applied in this    |
| (     | ig |      |   |     |      |   |    | temperature range  |
| 15^o^ | ht |      |   |     |      |   |    |                    |
| F)**, | sn |      |   |     |      |   |    | 2\) Abrasives can  |
|       | ow |      |   |     |      |   |    | be applied to      |
| s     | c  |      |   |     |      |   |    | enhance traction   |
| teady | ov |      |   |     |      |   |    |                    |
| or    | er |      |   |     |      |   |    |                    |
| fa    |    |      |   |     |      |   |    |                    |
| lling |    |      |   |     |      |   |    |                    |
+-------+----+------+---+-----+------+---+----+--------------------+

***Notes***

**CHEMICAL APPLICATIONS**. (1) Time initial and subsequent chemical
applications to *prevent* deteriorating conditions or development of
packed and bonded snow. (2) Apply chemical ahead of traffic rush periods
occurring during storm.

**PLOWING**. If needed, *plow before chemical applications* so that
excess snow, slush, or ice is removed and pavement is wet, slushy, or
lightly snow covered when treated.

Table 9. Weather event: light snow storm with period(s) of moderate or
heavy snow.

<table style="width:100%;">
<colgroup>
<col style="width: 12%" />
<col style="width: 7%" />
<col style="width: 9%" />
<col style="width: 5%" />
<col style="width: 8%" />
<col style="width: 9%" />
<col style="width: 4%" />
<col style="width: 6%" />
<col style="width: 4%" />
<col style="width: 6%" />
<col style="width: 25%" />
</colgroup>
<tbody>
<tr class="odd">
<td><strong>PAVEMENT</strong></td>
<td colspan="4"><strong>INITIAL OPERATION</strong></td>
<td colspan="5"><strong>SUBSEQUENT OPERATIONS</strong></td>
<td><strong>COMMENTS</strong></td>
</tr>
<tr class="even">
<td><strong>TEMPERATURE RANGE,<br />
AND TREND</strong></td>
<td><strong>pavement surface at time of</strong></td>
<td><strong>maintenance action</strong></td>
<td colspan="2"><strong>dry chemical spread rate, kg/lane-km
(lb/lane-mi)</strong></td>
<td><strong>maintenance action</strong></td>
<td colspan="4"><strong>dry chemical spread<br />
rate, kg/lane-km<br />
(lb/lane-mi)</strong></td>
<td></td>
</tr>
<tr class="odd">
<td></td>
<td><strong>initial operation</strong></td>
<td></td>
<td><strong>liquid</strong></td>
<td><strong>solid or prewetted</strong></td>
<td></td>
<td colspan="2"><strong>liquid</strong></td>
<td colspan="2"><strong>solid or prewetted solid</strong></td>
<td></td>
</tr>
<tr class="even">
<td></td>
<td></td>
<td></td>
<td></td>
<td><strong>solid</strong></td>
<td></td>
<td><strong>light snow</strong></td>
<td><strong>heavier snow</strong></td>
<td><strong>light snow</strong></td>
<td><strong>heavier snow</strong></td>
<td></td>
</tr>
<tr class="odd">
<td><p><strong>Above 0<sup>o</sup>C (32<sup>o</sup>F)</strong>,</p>
<p>steady or rising</p></td>
<td>Dry, wet, slush, or light snow cover</td>
<td>None, see comments</td>
<td></td>
<td></td>
<td>None, see comments</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td><p>1) Monitor pavement temperature closely for drops toward
0<sup>o</sup>C (32<sup>o</sup>F) and below</p>
<p>2) Treat icy patches if needed with chemical at 28 kg/lane-km<br />
(100 lb/lane-mi); plow if needed</p></td>
</tr>
<tr class="even">
<td><p><strong>Above 0<sup>o</sup>C (32<sup>o</sup>F)</strong>,</p>
<p>0<sup>o</sup>C (32<sup>o</sup>F) or below is imminent;</p></td>
<td>Dry</td>
<td>Apply liquid or prewetted solid chemical</td>
<td>28<br />
(100)</td>
<td>28<br />
(100)</td>
<td>Plow as needed; reapply liquid or solid</td>
<td>28<br />
(100)</td>
<td>55<br />
(200)</td>
<td>28<br />
(100)</td>
<td>55<br />
(200)</td>
<td><p>1) Applications will need to be more frequent at lower
temperatures and higher snowfall rates</p>
<p>2) Do not apply liquid chemical onto</p></td>
</tr>
<tr class="odd">
<td><p><em>ALSO</em></p>
<p><strong>-4 to 0<sup>o</sup>C</strong></p>
<p><strong>(25 to 32<sup>o</sup>F)</strong>,</p>
<p>remaining in range</p></td>
<td>Wet, slush, or light snow cover</td>
<td>Apply liquid or solid chemical</td>
<td>28<br />
(100)</td>
<td>28<br />
(100)</td>
<td>chemical when needed</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td><p>heavy snow accumulation or packed snow</p>
<p>3) After heavier snow periods and during light snow fall, reduce
chemical rate to<br />
28 kg/lane-km (100 lb/lane-mi); continue to plow and apply chemicals as
needed</p></td>
</tr>
<tr class="even">
<td><p><strong>-10 to -4<sup>o</sup>C</strong></p>
<p><strong>(15 to 25<sup>o</sup>F)</strong>,</p>
<p>remaining in range</p></td>
<td>Dry, wet, slush, or light snow cover</td>
<td>Apply prewetted solid chemical</td>
<td></td>
<td>55<br />
(200)</td>
<td>Plow as needed; reapply prewetted solid chemical when needed</td>
<td></td>
<td></td>
<td>55<br />
(200)</td>
<td>70<br />
(250)</td>
<td><p>1) If sufficient moisture is present, solid chemical without
prewetting can be applied</p>
<p>2) Reduce chemical rate to 55 kg/lane-km (200 lb/lane-mi) after
heavier snow periods and during light snow fall; continue to plow and
apply chemicals as needed</p></td>
</tr>
<tr class="odd">
<td><p><strong>Below -10<sup>o</sup>C (15<sup>o</sup>F)</strong>,</p>
<p>steady or falling</p></td>
<td>Dry or light snow cover</td>
<td>Plow as needed</td>
<td></td>
<td></td>
<td>Plow as needed</td>
<td></td>
<td></td>
<td></td>
<td></td>
<td><p>1) It is not recommended that chemicals be applied in this
temperature range</p>
<p>2) Abrasives can be applied to enhance traction</p></td>
</tr>
</tbody>
</table>

***Notes***

**CHEMICAL APPLICATIONS**. (1) Time initial and subsequent chemical
applications to *prevent* deteriorating conditions or development of
packed and bonded snow. (2) *Anticipate increases in snowfall intensity.
Apply higher rate treatments prior to or at the beginning of heavier
snowfall periods to prevent development of packed and bonded snow*. (3)
Apply chemical ahead of traffic rush periods occurring during storm.

**PLOWING**. If needed, *plow before chemical applications* so that
excess snow, slush, or ice is removed and pavement is wet, slushy, or
lightly snow covered when treated.

Table 10. Weather event: moderate or heavy snow storm.

+-------+----+-----+---+----+-----+---+----+-----------------------+
| **    | *  |     |   |    | **S |   |    | **COMMENTS**          |
| PAVEM | *I |     |   |    | UBS |   |    |                       |
| ENT** | NI |     |   |    | EQU |   |    |                       |
|       | TI |     |   |    | ENT |   |    |                       |
|       | AL |     |   |    | OPE |   |    |                       |
|       | O  |     |   |    | RAT |   |    |                       |
|       | PE |     |   |    | ION |   |    |                       |
|       | RA |     |   |    | S** |   |    |                       |
|       | TI |     |   |    |     |   |    |                       |
|       | ON |     |   |    |     |   |    |                       |
|       | ** |     |   |    |     |   |    |                       |
+-------+----+-----+---+----+-----+---+----+-----------------------+
| **T   | ** | *   | * |    | *   | * |    |                       |
| EMPER | pa | *ma | * |    | *ma | * |    |                       |
| ATURE | ve | int | d |    | int | d |    |                       |
| RA    | me | ena | r |    | ena | r |    |                       |
| NGE,\ | nt | nce | y |    | nce | y |    |                       |
| AND   | s  | ac  | c |    | ac  | c |    |                       |
| TR    | ur | tio | h |    | tio | h |    |                       |
| END** | fa | n** | e |    | n** | e |    |                       |
|       | ce |     | m |    |     | m |    |                       |
|       | at |     | i |    |     | i |    |                       |
|       | ti |     | c |    |     | c |    |                       |
|       | me |     | a |    |     | a |    |                       |
|       | of |     | l |    |     | l |    |                       |
|       | ** |     | s |    |     | s |    |                       |
|       |    |     | p |    |     | p |    |                       |
|       |    |     | r |    |     | r |    |                       |
|       |    |     | e |    |     | e |    |                       |
|       |    |     | a |    |     | a |    |                       |
|       |    |     | d |    |     | d |    |                       |
|       |    |     | r |    |     | r |    |                       |
|       |    |     | a |    |     | a |    |                       |
|       |    |     | t |    |     | t |    |                       |
|       |    |     | e |    |     | e |    |                       |
|       |    |     | , |    |     | , |    |                       |
|       |    |     | k |    |     | k |    |                       |
|       |    |     | g |    |     | g |    |                       |
|       |    |     | / |    |     | / |    |                       |
|       |    |     | l |    |     | l |    |                       |
|       |    |     | a |    |     | a |    |                       |
|       |    |     | n |    |     | n |    |                       |
|       |    |     | e |    |     | e |    |                       |
|       |    |     | - |    |     | - |    |                       |
|       |    |     | k |    |     | k |    |                       |
|       |    |     | m |    |     | m |    |                       |
|       |    |     | ( |    |     | ( |    |                       |
|       |    |     | l |    |     | l |    |                       |
|       |    |     | b |    |     | b |    |                       |
|       |    |     | / |    |     | / |    |                       |
|       |    |     | l |    |     | l |    |                       |
|       |    |     | a |    |     | a |    |                       |
|       |    |     | n |    |     | n |    |                       |
|       |    |     | e |    |     | e |    |                       |
|       |    |     | - |    |     | - |    |                       |
|       |    |     | m |    |     | m |    |                       |
|       |    |     | i |    |     | i |    |                       |
|       |    |     | ) |    |     | ) |    |                       |
|       |    |     | * |    |     | * |    |                       |
|       |    |     | * |    |     | * |    |                       |
+-------+----+-----+---+----+-----+---+----+-----------------------+
|       | *  |     | * | *  |     | * | *  |                       |
|       | *i |     | * | *s |     | * | *s |                       |
|       | ni |     | l | ol |     | l | ol |                       |
|       | ti |     | i | id |     | i | id |                       |
|       | al |     | q | or |     | q | or |                       |
|       | o  |     | u | p  |     | u | p  |                       |
|       | pe |     | i | re |     | i | re |                       |
|       | ra |     | d | we |     | d | we |                       |
|       | ti |     | * | tt |     | * | tt |                       |
|       | on |     | * | ed |     | * | ed |                       |
|       | ** |     |   | s  |     |   | s  |                       |
|       |    |     |   | ol |     |   | ol |                       |
|       |    |     |   | id |     |   | id |                       |
|       |    |     |   | ** |     |   | ** |                       |
+-------+----+-----+---+----+-----+---+----+-----------------------+
| **    | Dr | No  |   |    | No  |   |    | 1\) Monitor pavement  |
| Above | y, | ne, |   |    | ne, |   |    | temperature closely   |
| 0^o^C | we | see |   |    | see |   |    | for drops toward      |
| (     | t, | co  |   |    | co  |   |    | 0^o^C (32^o^F) and    |
| 32^o^ | sl | mme |   |    | mme |   |    | below                 |
| F)**, | us | nts |   |    | nts |   |    |                       |
|       | h, |     |   |    |     |   |    | 2\) Treat icy patches |
| s     | or |     |   |    |     |   |    | if needed with        |
| teady | l  |     |   |    |     |   |    | chemical at\          |
| or    | ig |     |   |    |     |   |    | 28 kg/lane-km (100    |
| r     | ht |     |   |    |     |   |    | lb/lane-mi); plow if  |
| ising | sn |     |   |    |     |   |    | needed                |
|       | ow |     |   |    |     |   |    |                       |
|       | c  |     |   |    |     |   |    |                       |
|       | ov |     |   |    |     |   |    |                       |
|       | er |     |   |    |     |   |    |                       |
+-------+----+-----+---+----+-----+---+----+-----------------------+
| **    | D  | Ap  | 2 | 2  | P   | 2 | 2  | 1\) If the desired    |
| Above | ry | ply | 8 | 8\ | low | 8 | 8\ | plowing/treatment     |
| 0^o^C |    | liq | \ | (  | acc | \ | (  | frequency cannot be   |
| (     |    | uid | ( | 10 | umu | ( | 10 | maintained, the       |
| 32^o^ |    | or  | 1 | 0) | lat | 1 | 0) | spread rate can be    |
| F)**, |    | pre | 0 |    | ion | 0 |    | increased to\         |
|       |    | wet | 0 |    | and | 0 |    | 55 kg/lane-km (200    |
| 0^o^C |    | ted | ) |    | r   | ) |    | lb/lane-mi) to        |
| (32   |    | so  |   |    | eap |   |    | accommodate longer    |
| ^o^F) |    | lid |   |    | ply |   |    | operational cycles    |
| or    |    | ch  |   |    | liq |   |    |                       |
| below |    | emi |   |    | uid |   |    |                       |
| is    |    | cal |   |    | or  |   |    |                       |
| immi  |    |     |   |    | so  |   |    |                       |
| nent; |    |     |   |    | lid |   |    |                       |
+-------+----+-----+---+----+-----+---+----+-----------------------+
| *     | We | Ap  | 2 | 2  | ch  |   |    | 2\) Do not apply      |
| ALSO* | t, | ply | 8 | 8\ | emi |   |    | liquid chemical onto  |
|       | sl | liq | \ | (  | cal |   |    | heavy snow            |
| **-1  | us | uid | ( | 10 | as  |   |    | accumulation or       |
| to    | h, | or  | 1 | 0) | nee |   |    | packed snow           |
| 0^    | or | so  | 0 |    | ded |   |    |                       |
| o^C** | l  | lid | 0 |    |     |   |    |                       |
|       | ig | ch  | ) |    |     |   |    |                       |
| **(30 | ht | emi |   |    |     |   |    |                       |
| to    | sn | cal |   |    |     |   |    |                       |
| 32^o^ | ow |     |   |    |     |   |    |                       |
| F)**, | c  |     |   |    |     |   |    |                       |
|       | ov |     |   |    |     |   |    |                       |
| rema  | er |     |   |    |     |   |    |                       |
| ining |    |     |   |    |     |   |    |                       |
| in    |    |     |   |    |     |   |    |                       |
| range |    |     |   |    |     |   |    |                       |
+-------+----+-----+---+----+-----+---+----+-----------------------+
| **-4  | D  | Ap  | 5 | 42 | P   | 5 | 5  | 1\) If the desired    |
| to    | ry | ply | 5 | -5 | low | 5 | 5\ | plowing/treatment     |
| -1^   |    | liq | \ | 5\ | acc | \ | (  | frequency cannot be   |
| o^C** |    | uid | ( | (  | umu | ( | 20 | maintained, the       |
|       |    | or  | 2 | 15 | lat | 2 | 0) | spread rate can be    |
| **(25 |    | pre | 0 | 0- | ion | 0 |    | increased to\         |
| to    |    | wet | 0 | 20 | and | 0 |    | 110 kg/lane-km (400   |
| 30^o^ |    | ted | ) | 0) | r   | ) |    | lb/lane-mi) to        |
| F)**, |    | so  |   |    | eap |   |    | accommodate longer    |
|       |    | lid |   |    | ply |   |    |                       |
| rema  |    | ch  |   |    |     |   |    |                       |
| ining |    | emi |   |    |     |   |    |                       |
| in    |    | cal |   |    |     |   |    |                       |
| range |    |     |   |    |     |   |    |                       |
+-------+----+-----+---+----+-----+---+----+-----------------------+
|       | We | Ap  | 5 | 42 | liq |   |    | operational cycles    |
|       | t, | ply | 5 | -5 | uid |   |    |                       |
|       | sl | liq | \ | 5\ | or  |   |    | 2\) Do not apply      |
|       | us | uid | ( | (  | so  |   |    | liquid chemical onto  |
|       | h, | or  | 2 | 15 | lid |   |    | heavy snow            |
|       | or | so  | 0 | 0- | ch  |   |    | accumulation or       |
|       | l  | lid | 0 | 20 | emi |   |    | packed snow           |
|       | ig | ch  | ) | 0) | cal |   |    |                       |
|       | ht | emi |   |    | as  |   |    |                       |
|       | sn | cal |   |    | nee |   |    |                       |
|       | ow |     |   |    | ded |   |    |                       |
|       | c  |     |   |    |     |   |    |                       |
|       | ov |     |   |    |     |   |    |                       |
|       | er |     |   |    |     |   |    |                       |
+-------+----+-----+---+----+-----+---+----+-----------------------+
| **-10 | Dr | Ap  |   | 5  | P   |   | 7  | 1\) If the desired    |
| to    | y, | ply |   | 5\ | low |   | 0\ | plowing/treatment     |
| -4^   | we | pre |   | (  | acc |   | (  | frequency cannot be   |
| o^C** | t, | wet |   | 20 | umu |   | 25 | maintained, the       |
|       | sl | ted |   | 0) | lat |   | 0) | spread rate can be    |
| **(15 | us | so  |   |    | ion |   |    | increased to\         |
| to    | h, | lid |   |    | and |   |    | 140 kg/lane-km (500   |
| 25^o^ | or | ch  |   |    | r   |   |    | lb/lane-mi) to        |
| F)**, | l  | emi |   |    | eap |   |    | accommodate longer    |
|       | ig | cal |   |    | ply |   |    | operational cycles    |
| rema  | ht |     |   |    | pre |   |    |                       |
| ining | sn |     |   |    | wet |   |    | 2\) If sufficient     |
| in    | ow |     |   |    | ted |   |    | moisture is present,  |
| range | c  |     |   |    | so  |   |    | solid chemical        |
|       | ov |     |   |    | lid |   |    | without prewetting    |
|       | er |     |   |    | ch  |   |    | can be applied        |
|       |    |     |   |    | emi |   |    |                       |
|       |    |     |   |    | cal |   |    |                       |
|       |    |     |   |    | as  |   |    |                       |
|       |    |     |   |    | nee |   |    |                       |
|       |    |     |   |    | ded |   |    |                       |
+-------+----+-----+---+----+-----+---+----+-----------------------+
| **    | D  | P   |   |    | P   |   |    | 1\) It is not         |
| Below | ry | low |   |    | low |   |    | recommended that      |
| -1    | or | as  |   |    | acc |   |    | chemicals be applied  |
| 0^o^C | l  | nee |   |    | umu |   |    | in this temperature   |
| (     | ig | ded |   |    | lat |   |    | range                 |
| 15^o^ | ht |     |   |    | ion |   |    |                       |
| F)**, | sn |     |   |    | as  |   |    | 2\) Abrasives can be  |
|       | ow |     |   |    | nee |   |    | applied to enhance    |
| s     | c  |     |   |    | ded |   |    | traction              |
| teady | ov |     |   |    |     |   |    |                       |
| or    | er |     |   |    |     |   |    |                       |
| fa    |    |     |   |    |     |   |    |                       |
| lling |    |     |   |    |     |   |    |                       |
+-------+----+-----+---+----+-----+---+----+-----------------------+

***Notes***

**CHEMICAL APPLICATIONS**. (1) Time initial and subsequent chemical
applications to *prevent* deteriorating conditions or development of
packed and bonded snow \-- *timing and frequency of subsequent
applications will be determined primarily by plowing requirements*. (2)
Apply chemical ahead of traffic rush periods occurring during storm.

**PLOWING**. *Plow before chemical applications* so that excess snow,
slush, or ice is removed and pavement is wet, slushy, or lightly snow
covered when treated.

Table 11. Weather event: frost or black ice.

<table style="width:100%;">
<colgroup>
<col style="width: 12%" />
<col style="width: 10%" />
<col style="width: 9%" />
<col style="width: 6%" />
<col style="width: 7%" />
<col style="width: 10%" />
<col style="width: 7%" />
<col style="width: 7%" />
<col style="width: 0%" />
<col style="width: 28%" />
</colgroup>
<tbody>
<tr class="odd">
<td><strong>PAVEMENT</strong></td>
<td><strong>TRAFFIC</strong></td>
<td colspan="3"><strong>INITIAL OPERATION</strong></td>
<td colspan="3"><strong>SUBSEQUENT OPERATIONS</strong></td>
<td colspan="2"><strong>COMMENTS</strong></td>
</tr>
<tr class="even">
<td><strong>TEMPERATURE RANGE,<br />
TREND, AND</strong></td>
<td><strong>CONDITION</strong></td>
<td><strong>maintenance action</strong></td>
<td colspan="2"><strong>dry chemical spread rate, kg/lane-km
(lb/lane-mi)</strong></td>
<td><strong>maintenance action</strong></td>
<td colspan="2"><strong>dry chemical spread rate, kg/lane-km
(lb/lane-mi)</strong></td>
<td colspan="2"></td>
</tr>
<tr class="odd">
<td><strong>RELATION TO DEW POINT</strong></td>
<td></td>
<td></td>
<td><strong>liquid</strong></td>
<td><strong>solid or prewetted solid</strong></td>
<td></td>
<td><strong>liquid</strong></td>
<td colspan="2"><strong>solid or prewetted solid</strong></td>
<td></td>
</tr>
<tr class="even">
<td><p><strong>Above 0<sup>o</sup>C (32<sup>o</sup>F)</strong>,</p>
<p>steady or rising</p></td>
<td>Any level</td>
<td>None, see comments</td>
<td></td>
<td></td>
<td>None, see comments</td>
<td></td>
<td colspan="2"></td>
<td>Monitor pavement temperature closely; begin treatment if temperature
starts to fall to 0<sup>o</sup>C (32<sup>o</sup>F) or below and is at or
below dew point</td>
</tr>
<tr class="odd">
<td><p><strong>-2 to 2<sup>o</sup>C</strong></p>
<p><strong>(28 to 35<sup>o</sup>F)</strong>,</p>
<p>remaining in range or falling to 0<sup>o</sup>C</p></td>
<td>Traffic rate less than 100 vehicles per h</td>
<td>Apply prewetted solid chemical</td>
<td></td>
<td>7-18<br />
(25-65)</td>
<td>Reapply prewetted solid chemical as needed</td>
<td></td>
<td colspan="2">7-18<br />
(25-65)</td>
<td><p>1) Monitor pavement closely; if pavement becomes wet or if thin
ice forms, reapply chemical at higher indicated rate</p>
<p>2) Do not apply liquid chemical on ice so thick</p></td>
</tr>
<tr class="even">
<td>(32<sup>o</sup>F) or below, <em>and</em> equal to or below dew
point</td>
<td>Traffic rate greater than 100 vehicles per h</td>
<td>Apply liquid or prewetted solid chemical</td>
<td>7-18<br />
(25-65)</td>
<td>7-18<br />
(25-65)</td>
<td>Reapply liquid or prewetted solid chemical as needed</td>
<td>11-32<br />
(40-115)</td>
<td colspan="2">7-18<br />
(25-65)</td>
<td>that the pavement can not be seen</td>
</tr>
<tr class="odd">
<td><p><strong>-7 to -2<sup>o</sup>C</strong></p>
<p><strong>(20 to 28<sup>o</sup>F)</strong>,</p>
<p>remaining in range, <em>and</em> equal to or below dew point</p></td>
<td>Any level</td>
<td>Apply liquid or prewetted solid chemical</td>
<td>18-36<br />
(65-130)</td>
<td>18-36<br />
(65-130)</td>
<td>Reapply liquid or prewetted solid chemical when needed</td>
<td>18-36<br />
(65-130)</td>
<td colspan="2">18-36<br />
(65-130)</td>
<td><p>1) Monitor pavement closely; if thin ice forms, reapply chemical
at higher indicated rate</p>
<p>2) Applications will need to be more frequent at higher levels of
condensation; if traffic volumes are not enough to disperse
condensation, it may be necessary to increase frequency</p>
<p>3) It is not advisable to apply a liquid chemical at the indicated
spread rate when the pavement temperature drops below -5<sup>o</sup>C
(23<sup>o</sup>F)</p></td>
</tr>
<tr class="even">
<td><p><strong>-10 to -7<sup>o</sup>C</strong></p>
<p><strong>(15 to 20<sup>o</sup>F)</strong>,</p>
<p>remaining in range, <em>and</em> equal to or below dew point</p></td>
<td>Any level</td>
<td>Apply prewetted solid chemical</td>
<td></td>
<td>36-55<br />
(130-200)</td>
<td>Reapply prewetted solid chemical when needed</td>
<td></td>
<td colspan="2">36-55<br />
(130-200)</td>
<td><p>1) Monitor pavement closely; if thin ice forms, reapply chemical
at higher indicated rate</p>
<p>2) Applications will need to be more frequent at higher levels of
condensation; if traffic volumes are not enough to disperse
condensation, it may be necessary to increase frequency</p></td>
</tr>
<tr class="odd">
<td><p><strong>Below -10<sup>o</sup>C (15<sup>o</sup>F)</strong>,</p>
<p>steady or falling</p></td>
<td>Any level</td>
<td>Apply abrasives</td>
<td></td>
<td></td>
<td>Apply abrasives as needed</td>
<td></td>
<td colspan="2"></td>
<td>It is not recommended that chemicals be applied in this temperature
range</td>
</tr>
</tbody>
</table>

***Notes***

**TIMING**. (1) Conduct initial operation in advance of freezing. Apply
liquid chemical up to 3 h in advance. Use longer advance times in this
range to effect drying when traffic volume is low. Apply prewetted solid
1 to 2 h in advance. (2) In the absence of precipitation, liquid
chemical at 21 kg/lane-km (75 lb/lane-mi) has been successful in
preventing bridge deck icing when placed up to 4 days before freezing on
higher volume roads and 7 days before on lower volume roads.

Table 12. Weather event: freezing rain storm.

+-------+------+-----+------+-----+---------------------------------+
| **    | *    |     | **SU |     | **COMMENTS**                    |
| PAVEM | *INI |     | BSEQ |     |                                 |
| ENT** | TIAL |     | UENT |     |                                 |
|       | OPE  |     | OPER |     |                                 |
|       | RATI |     | ATIO |     |                                 |
|       | ON** |     | NS** |     |                                 |
+-------+------+-----+------+-----+---------------------------------+
| **T   | *    | *   | *    | *   |                                 |
| EMPER | *mai | *ch | *mai | *ch |                                 |
| ATURE | nten | emi | nten | emi |                                 |
| RA    | ance | cal | ance | cal |                                 |
| NGE,\ | acti | spr | acti | spr |                                 |
| AND   | on** | ead | on** | ead |                                 |
| TR    |      | ra  |      | rat |                                 |
| END** |      | te, |      | e,\ |                                 |
|       |      | k   |      | k   |                                 |
|       |      | g/l |      | g/l |                                 |
|       |      | ane |      | ane |                                 |
|       |      | -km |      | -km |                                 |
|       |      | (l  |      | (l  |                                 |
|       |      | b/l |      | b/l |                                 |
|       |      | ane |      | ane |                                 |
|       |      | -mi |      | -mi |                                 |
|       |      | )** |      | )** |                                 |
+-------+------+-----+------+-----+---------------------------------+
| **    | N    |     | N    |     | 1\) Monitor pavement            |
| Above | one, |     | one, |     | temperature closely for drops   |
| 0^o^C | see  |     | see  |     | toward 0^o^C (32^o^F) and below |
| (     | comm |     | comm |     |                                 |
| 32^o^ | ents |     | ents |     | 2\) Treat icy patches if needed |
| F)**, |      |     |      |     | with prewetted solid chemical   |
|       |      |     |      |     | at 21-28 kg/lane-km (75-100     |
| s     |      |     |      |     | lb/lane-mi)                     |
| teady |      |     |      |     |                                 |
| or    |      |     |      |     |                                 |
| r     |      |     |      |     |                                 |
| ising |      |     |      |     |                                 |
+-------+------+-----+------+-----+---------------------------------+
| **    | A    | 21  | Rea  | 21  | Monitor pavement temperature    |
| Above | pply | -28 | pply | -28 | and precipitation closely       |
| 0^o^C | p    |     | p    |     |                                 |
| (     | rewe | (7  | rewe | (7  |                                 |
| 32^o^ | tted | 5-1 | tted | 5-1 |                                 |
| F)**, | s    | 00) | s    | 00) |                                 |
|       | olid |     | olid |     |                                 |
| 0^o^C | chem |     | chem |     |                                 |
| (32   | ical |     | ical |     |                                 |
| ^o^F) |      |     | as   |     |                                 |
| or    |      |     | ne   |     |                                 |
| below |      |     | eded |     |                                 |
| is    |      |     |      |     |                                 |
| imm   |      |     |      |     |                                 |
| inent |      |     |      |     |                                 |
+-------+------+-----+------+-----+---------------------------------+
| **-7  | A    | 21- | Rea  | 21- | 1\) Monitor pavement            |
| to    | pply | 70\ | pply | 70\ | temperature and precipitation   |
| 0^    | p    | (7  | p    | (7  | closely                         |
| o^C** | rewe | 5-2 | rewe | 5-2 |                                 |
|       | tted | 50) | tted | 50) | 2\) Increase spread rate toward |
| **(20 | s    |     | s    |     | *higher indicated rate* with    |
| to    | olid |     | olid |     | decrease in pavement            |
| 32^o^ | chem |     | chem |     | temperature or increase in      |
| F)**, | ical |     | ical |     | intensity of freezing rainfall  |
|       |      |     | as   |     |                                 |
| rema  |      |     | ne   |     | 3\) Decrease spread rate toward |
| ining |      |     | eded |     | *lower indicated rate* with     |
| in    |      |     |      |     | increase in pavement            |
| range |      |     |      |     | temperature or decrease in      |
|       |      |     |      |     | intensity of freezing rainfall  |
+-------+------+-----+------+-----+---------------------------------+
| **-10 | A    | 7   | Rea  | 7   | 1\) Monitor precipitation       |
| to    | pply | 0-1 | pply | 0-1 | closely                         |
| -7^   | p    | 10\ | p    | 10\ |                                 |
| o^C** | rewe | (25 | rewe | (25 | 2\) Increase spread rate toward |
|       | tted | 0-4 | tted | 0-4 | *higher indicated rate* with    |
| **(15 | s    | 00) | s    | 00) | increase in intensity of        |
| to    | olid |     | olid |     | freezing rainfall               |
| 20^o^ | chem |     | chem |     |                                 |
| F)**, | ical |     | ical |     | 3\) Decrease spread rate toward |
|       |      |     | as   |     | *lower indicated rate* with     |
| rema  |      |     | ne   |     | decrease in intensity of        |
| ining |      |     | eded |     | freezing rainfall               |
| in    |      |     |      |     |                                 |
| range |      |     |      |     |                                 |
+-------+------+-----+------+-----+---------------------------------+
| **    | A    |     | A    |     | It is not recommended that      |
| Below | pply |     | pply |     | chemicals be applied in this    |
| -1    | a    |     | a    |     | temperature range               |
| 0^o^C | bras |     | bras |     |                                 |
| (     | ives |     | ives |     |                                 |
| 15^o^ |      |     | as   |     |                                 |
| F)**, |      |     | ne   |     |                                 |
|       |      |     | eded |     |                                 |
| s     |      |     |      |     |                                 |
| teady |      |     |      |     |                                 |
| or    |      |     |      |     |                                 |
| fa    |      |     |      |     |                                 |
| lling |      |     |      |     |                                 |
+-------+------+-----+------+-----+---------------------------------+

***Notes***

**CHEMICAL APPLICATIONS**. (1) Time initial and subsequent chemical
applications to *prevent* glaze ice conditions. (2) Apply chemical ahead
of traffic rush periods occurring during storm.

Table 13. Weather event: sleet storm.

+-------+------+------+-------+------+------------------------------+
| **    | *    |      | **    |      | **COMMENTS**                 |
| PAVEM | *INI |      | SUBSE |      |                              |
| ENT** | TIAL |      | QUENT |      |                              |
|       | OPE  |      | OP    |      |                              |
|       | RATI |      | ERATI |      |                              |
|       | ON** |      | ONS** |      |                              |
+-------+------+------+-------+------+------------------------------+
| **T   | *    | **   | **m   | **   |                              |
| EMPER | *mai | chem | ainte | chem |                              |
| ATURE | nten | ical | nance | ical |                              |
| RA    | ance | sp   | act   | sp   |                              |
| NGE,\ | acti | read | ion** | read |                              |
| AND   | on** | r    |       | ra   |                              |
| TR    |      | ate, |       | te,\ |                              |
| END** |      | kg   |       | kg   |                              |
|       |      | /lan |       | /lan |                              |
|       |      | e-km |       | e-km |                              |
|       |      | (l   |       | (l   |                              |
|       |      | b/la |       | b/la |                              |
|       |      | ne-m |       | ne-m |                              |
|       |      | i)** |       | i)** |                              |
+-------+------+------+-------+------+------------------------------+
| **    | N    |      | None, |      | 1\) Monitor pavement         |
| Above | one, |      | see   |      | temperature closely for      |
| 0^o^C | see  |      | com   |      | drops toward 0^o^C (32^o^F)  |
| (     | comm |      | ments |      | and below                    |
| 32^o^ | ents |      |       |      |                              |
| F)**, |      |      |       |      | 2\) Treat icy patches if     |
|       |      |      |       |      | needed with prewetted solid  |
| s     |      |      |       |      | chemical at 35 kg/lane-km    |
| teady |      |      |       |      | (125 lb/lane-mi)             |
| or    |      |      |       |      |                              |
| r     |      |      |       |      |                              |
| ising |      |      |       |      |                              |
+-------+------+------+-------+------+------------------------------+
| **    | A    | 35\  | Plow  | 35\  | Monitor pavement temperature |
| Above | pply | (    | as    | (    | and precipitation closely    |
| 0^o^C | p    | 125) | ne    | 125) |                              |
| (     | rewe |      | eded, |      |                              |
| 32^o^ | tted |      | re    |      |                              |
| F)**, | s    |      | apply |      |                              |
|       | olid |      | prew  |      |                              |
| 0^o^C | chem |      | etted |      |                              |
| (32   | ical |      | solid |      |                              |
| ^o^F) |      |      | che   |      |                              |
| or    |      |      | mical |      |                              |
| below |      |      | when  |      |                              |
| is    |      |      | n     |      |                              |
| imm   |      |      | eeded |      |                              |
| inent |      |      |       |      |                              |
+-------+------+------+-------+------+------------------------------+
| **-2  | A    | 35   | Plow  | 35   | 1\) Monitor pavement         |
| to    | pply | -90\ | as    | -90\ | temperature and              |
| 0^    | p    | (    | ne    | (    | precipitation closely        |
| o^C** | rewe | 125- | eded, | 125- |                              |
|       | tted | 325) | re    | 325) | 2\) Increase spread rate     |
| **(28 | s    |      | apply |      | toward *higher indicated     |
| to    | olid |      | prew  |      | rate* with increase in sleet |
| 32^o^ | chem |      | etted |      | intensity                    |
| F)**, | ical |      | solid |      |                              |
|       |      |      | che   |      | 3\) Decrease spread rate     |
| rema  |      |      | mical |      | toward *lower indicated      |
| ining |      |      | when  |      | rate* with decrease in sleet |
| in    |      |      | n     |      | intensity                    |
| range |      |      | eeded |      |                              |
+-------+------+------+-------+------+------------------------------+
| **-10 | A    | 70-  | Plow  | 70-  | 1\) Monitor precipitation    |
| to    | pply | 110\ | as    | 110\ | closely                      |
| -2^   | p    | (    | ne    | (    |                              |
| o^C** | rewe | 250- | eded, | 250- | 2\) Increase spread rate     |
|       | tted | 400) | re    | 400) | toward *higher indicated     |
| **(15 | s    |      | apply |      | rate* with decrease in       |
| to    | olid |      | prew  |      | pavement temperature or      |
| 28^o^ | chem |      | etted |      | increase in sleet intensity  |
| F)**, | ical |      | solid |      |                              |
|       |      |      | che   |      | 3\) Decrease spread rate     |
| rema  |      |      | mical |      | toward *lower indicated      |
| ining |      |      | when  |      | rate* with increase in       |
| in    |      |      | n     |      | pavement temperature or      |
| range |      |      | eeded |      | decrease in sleet intensity  |
+-------+------+------+-------+------+------------------------------+
| **    | Plow |      | Plow  |      | 1\) It is not recommended    |
| Below | as   |      | as    |      | that chemicals be applied in |
| -1    | ne   |      | n     |      | this temperature range       |
| 0^o^C | eded |      | eeded |      |                              |
| (     |      |      |       |      | 2\) Abrasives can be applied |
| 15^o^ |      |      |       |      | to enhance traction          |
| F)**, |      |      |       |      |                              |
|       |      |      |       |      |                              |
| s     |      |      |       |      |                              |
| teady |      |      |       |      |                              |
| or    |      |      |       |      |                              |
| fa    |      |      |       |      |                              |
| lling |      |      |       |      |                              |
+-------+------+------+-------+------+------------------------------+

***Notes***

**CHEMICAL APPLICATIONS**. (1) Time initial and subsequent chemical
applications to *prevent* the sleet from bonding to the pavement. (2)
Apply chemical ahead of traffic rush periods occurring during storm.

# References {#references .Heading-0}

1\. U.S. Army Cold Regions Research and Engineering Laboratory. *FHWA
Test and Evaluation Project No. 28, "Anti-Icing Technology," Field
Evaluation Report*. Hanover, New Hampshire, 1996.

2\. Blackburn R.R., E.J. McGrane, C.C. Chappelow, D.W. Harwood, and E.
J. Fleege. *Development of Anti-Icing Technology*. Report SHRP-H-385,
National Research Council, Washington, DC, 1994.

3\. *The Snowfighter's Handbook*. The Salt Institute, Alexandria,
Virginia, 1991.

4\. Boselly, S.E. and D. Ernst. *Road Weather Information Systems,
Volume 2: Implementation Guide*. Report SHRP-H-351, SHRP, National
Research council, Washington, DC, 1993.

5\. Boselly, S.E., J.E. Thornes, C. Ulberg, and D. Ernst. *Road Weather
Information Systems, Volume 1: Research Report*. Report SHRP-H-350,
SHRP, National Research Council, Washington, DC, 1993.

6\. SHRP Snow and Ice Control Showcasing and Implementation, FHWA
Contract No. DTFH61-94-C-00177, Federal Highway Administration,
Washington, DC.

[^1]: ^\*^ Underlined numbers in parentheses refer to references at the
    end of this document.