NBSIR 76-1008

Energy Conservation Through

the Facilitation of Increased

Blended Cement Use

Paul Wencil Brown

James R. Clifton

Geoffrey Frohnsdorff

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

February 1 976

Interim Report

July 1 - December 1, 1975

Prepared for

Energy Research and Development Administration

20 Massachusetts Avenue

Washington, D. C. 20545

NBSIR 76-1008

ENERGY CONSERVATION THROUGH

THE FACILITATION OF INCREASED

BLENDED CEMENT USE

Paul Wencil Brown

James R. Clifton

Geoffrey Frohnsdorff

Institute for Applied Technology

National Bureau of Standards

Washington, D. C. 20234

February 1 976

Interim Report

July 1- December 1, 1975

Prepared for

Energy Research and Development Administration

20 Massachusetts Avenue

Washington, D. c. 20545

U.S. DEPARTMENT OF COMMERCE, Elliot L. Richardson, Secretary

James A. Baker, III, Under Secretary

Dr. Betsy Ancker-Johnson, Assistant Secretary for Science and Technology

NATIONAL BUREAU OF STANDARDS, Ernest Ambler, Acting Director

TABLE OF CONTENTS

Page

ABSTRACT iv

1. INTRODUCTION 1

2. BLENDED CEMENT PRODUCTION AND UTILIZATION 4

3. OBSTACLES TO THE INCREASED USE OF BLENDED CHyiENT 6

3.1 Geographical Limitations to the Utilization of Slag and Fly Ash in Cement.. 7

3.2 Specification Limitations to Slag and Fly Ash Utilization in Cement 9

3.3 Standard Tests for Blended Cements 12

3.3.1 Soundness 13

3.3.2 Resistance to Attack by Sulfates 14

3.3.3 Reactivity with Alkali-Susceptible Aggregates 15

3.3.4 Freeze-Thaw Durability 16

3.3.5 Admixture Performance 16

3.3.6 Fly Ash and Slag Contents of Blended Cements 17

3.3.7 Strength Gains of Blended Cement Concretes 17

3.3.8 Pozzolan and Slag Reactivity 18

3.3.9 Protection of Reinforcing Bars from Corrosion 18

4. BASIC RESEARCH REQUIREVENTS 19

5. SUMMARY 20

6. REFERENCES 21

iii
ABSTRACT

About 95% of the cement produced in the United States is portland cement and its

manufactiire requires about 2% of the energy consumed annually in the nation's indust|:ial

processes. The production of blended cements containing substantial amounts of fly ash or

blast furnace slag and their substitution for portland cement appears attractive frccn the

standpoint of energy caiservation. While prodi;«:tion and utilizsatifai of blended cements in

other industrialized countries is extensive, blended cements account for less than 1% of the

total cement production in tbe U.S. The reasons for the small production of blended

cements are discussed in the contexts of standards revision and the need for the dsvelopnent

of additional data as a basis for this revision.

Keywords: Blast furnace slag; blended cements; energy conservation; fly ash.

iv
1. INTRDDUCTION

Hydraulic cement concrete is the most widely lased man-made building material in the

world. About 700 million tons (6.5 x 10"^^ kg) are used annually in the United States alone*.

The binder in most concrete placed in the U.S. is portland cement. Its manufacture uses

17 about 564 trillion Btu (6 x 10 J) [2] or about 2% of the energy consumed directly m the

nation's industrial processes**. Although the energy lased per unit weight of portland pement

is low cotpared to most other building materials (table 1) , the cost of energy to produce

cement as a percentage of its market value is high (table 2) . Because the large quantity of

cement produced annually in the U.S., 85 million tons [4] , requires a large energy consurtption, it is in the national interest to reduce the energy requirement for cement manufacture.

For most purposes, portland cements can be substituted by blended cements v^ich require

less energy to maniifacture . Blended cements are made by intergrinding reactive additives

such as certain industrial wastes or by-products with portland cement clinker***. The most

ijTportant of these reactive additives are fly ash from coal bxaming pcwer plants and granulated

blast furnace slag.

About 95% of the cements used in the U.S. fall into 5 main types v*iich are defined by

ASIM standard specification C150-74 [5] . Table 3 lists the estimated amounts of each of

these types produced annually in the U.S. and indicates the suitability for extensive substitution by a blended cement if appropriate standards were available to ensure satisfactory

performance. As may be seen, blended cements may potentially be extensively substituted for

each type of portland cement listed with the exception of type III, high early strength

cement. This belief is based largely on successful foreign experience and considerations of

cement chemistry. However, as will be discussed later, there is a need for additional data

with regard to certain specific properties or applications before the full potential uses of

blended cements can be achieved in the U.S.

* Calculation based on concrete with an average cement content of 12% [1]

.

** Calculation based on a national energy consultation of 72,200 trillion Btu (7.3 x 10 J)

in 1972 [3]

.

***For the purposes of this paper, blended cements are considered to contain significant

amoiants, at least 10%, of these additives, but their catpositions are not restricted to

the types defined by ASIM specifications [5]

.

1
TABLE 1. Energy Requironents for Manufacture of

Sate Basic Building Materials [6]

Material Tons (kg) of Oil/Ton (kg) of Basic Material

Aluminum 5 .

6

Copper 1.2

Steel 1.0

Polystyrene 3.2

PVC 2.0

Paper and Board 1.4

Glass 0.5

Cenent* 0.18

Concrete* 0.02

*Calculated assuming an average energy requirement of 7,400,000 Btu/ton (8.2 x 10^ JAg) of

cement produced [1]

.

TABLE 2. Cost of Purchased Energy as a Percentage of the Value of

Shipments of Selected Building Materials [7]

Product Energy Cost % of Value

Hydraulic Canent 15.6 j

Building Paper and Board 7..6

Structural Clay Products 7.4'

Flat Glass 4.3

Plastics 3.1

Concrete, Gypsum & Plaster Products 2.7

Roofing Materials 2.6

Cut Stone 2.2

2
TABLE 3. Portland Ceannent Types, Characteristics and Possibilities

for Substitution by Blended Cements

..AS1M

Cement

Purpose or

Distinguishing

Characteristics

Estirtiated

Amount Used,

tons X lO^/year

May be Substituted by a

Blended Cement Containing

Slag Fly Ash

T 70 y yes

II Moderate Sxilfate Resistance yes [8] yes

Moderate Heat of Hydration 10 yes [8] yes

Low Alkali Content yes yes

III High Early Strength 2.9 no no

IV Low Heat of Hydration <1 yes yes

V High Sulfate Resistance <1 yes yes

*Qne ton is equivalent to about 907 kg.

3
The cement manufacturing process may be divic3ed into 3 parts: raw materials processing,

pyroprocessing and finish grinding. Table 4 lists the approximate energy requirements for

each of these. The introduction of suitable reactive waste materials, such as fly ash or

blast furnace slag, into the cement making process can resiolt in large energy savings. Fly

ash is produced as finely divided particles, therefore little grinding is required. Because

fly ash is pozzolanic, no further pyroprocessing is necessary, and this material may be

mixed with portland cement clinker in the final grinding phase of the cement manufacturing

process. Like fly ash, many slags are reactive in the presence of water and portland

cement and only require grinding to cement fineness. Slags, however, tend to be sanevdiat

more difficult to grind than portland cement clinker making final grinding more energy

intensive. Nevertheless, conpared with the manufacture of portland cements, the manufacture

of blended cements requires less energy roughly in proportion to the amount of the interground

fly ash or blast furnace slag. -

2. BLE3SDED CEMENT PRODUCTION AND UTILIZATION

Although the cements used in the U.S. are almost exclusively portland cements, many

other industrialized countries use large quantities of blended cements. For example,

approximately 60% of the weight of cements produced in France is blended cements [9] . The

Soviet Union produces about 30 million tons of slag portland cement annually accounting for

about 1/3 of its cement production [10] . About 20% of the cement produced in South Africa

is slag cement with its production limited only by the amount of slag produced v\Aiile in

Japan a similar situation exists with regard to fly ash. Table 5 lists the amounts of cement

and concrete and the amounts of slag and fly ash produced and used in cement and concrete in

the U.S. each year. While the building practices in the United States sometimes require the

use of relatively rapidly hardening portland cements, blended cements could, as table 3

indicates, be si±)stituted for portland cements in most areas of general use with a significant

saving in energy. For example. Type II portland cement, v^ether selected for its moderate

resistance to sulfate attack or its moderately low heat of hydration, could probably be

replaced almost carpletely by blended cements. Fiarther, some blended cements produce concretes

*Pozzolanic reactivity is the ability of a material to react with lime in the presence of

water at ordinary tenperatures to form cementitious connpounds. Materials vdiich react in

this manner are referred to as pozzolans.

4
TABLE 4. Energy Consijrrption in Portland Cement Maniafacture [1]

Process Percent of Total Energy

Raw Materials Processing:

Quarrying and Crushing 1.5

Drying 4 .

3

Initial Grinding 3.8 - 4.3

Pyroprocessing (kiln fuel) 79.7

Finish Grinding 7.0

TABLE 5. Annual U.S. Concrete, Cement, Fly Ash and Slag

Production and Utilization

Material Production or Utilization Reference

in tons x 106*

Portland Cement Concrete 700 [1]

Portland Cement (U.S. Production) 85 [4]

Portland Cement (Iitported) 8 [4]

Fly Ash Collected 40 [17]

Fly Ash Used in ASTM Type IP Blended Cement 4 [17]

Type IP Blended Cement Containing Fly Ash** <1 ***

Blast Furnace Slag 25 [3]

Type IS Blended Cement Containing Slag • 1 ****

Slag as Aggregate in Concrete 2. 3 [3]

* One ton is equivalent to about 907 kg.

** Exclusive of cement produced by mixing fly ash with portland cement at the construction

site.

*** Estimated output of the cement conpanies v^ich produce type IP cement.

****Estimated output of the cement catpanies vdxLch produce type IS cement.

5
with higher ultimate strengths than otherwise similar concrete with portland cenent [11]

Published information [12-16] on blended cements also suggests they can bring irrprovement in

other irtportant properties of concrete (e.g. permeability, acid resistance, sulfate resistance,

etc.)

.

3. OBSTACLES TO THE INCREASED USE OF BLEJSTOED CEMENTS

Considering the widespread use of blended cements in Europe and Japan, it is important

to ask v^y more blended cements are not produced and used in the United States. The reasons

for the limited production of blended cannents in the U.S. probably include:

a) Ccxnbination of low fuel costs and high labor costs have not provided a

strong incentive for fuel savings in the past.

b) Abundant supplies of raw materials and relative ease of solid waste disposal

have not provided incentives for by-product utilization.

c) Lack of technical information on specific aspects of engineering performance

of blended cements based on U.S. materials.

d) Corrpositional restrictions posed by the ASTM and related standards for blended

cements and the limited range of performance tests for cements.

e) Uncertainty about the sustained availability, uniformity and quality of

the additives,

f ) Capital equipment costs required to produce a more complex product.

Reasons a, b, f and, to some extent, e are essentially econcmic and will be weakened

by the increasing cost of energy. Reasons c, d and, to some extent, e are essentially

technical and the development of appropriate technical data is needed to overcone them and

facilitate blended cement production and utilization. For example, with regard to reason

e, the hydraulic activity of many slags could be substantially upgraded by the introduction

of more effective quenching processes. This is because differences in the rates of cooling

after molten slag is tapped from a blast furnace at the usual tenperature of about 1450 to

1500°C result in slags with substantially different reactivities. Slowly cooled slag, called

air cooled slag, solidifies into a dense material with a crystalline structiore much like that

6
of a natural igneous rock [18] . This material, which usually has a high degree of crystallinity,

is of little value as a constituent of blended cement. It is, hcwever, useful as aggregate.

If the molten slag is cooled more rapidly in the presence of a controlled airount of water,

foamed or ej^anded slag results. This has a high porosity and, because its bulk density is

low, it is used as lightweight aggregate. Slag which is very rapidly quenched in a large

excess of water solidifies into small glassy granules. Rapid quenching inhibits crystallization and the slag usually retains sufficient reactivity to be a valuable constituent of

blended cements . Granulated slag is the only suitable form of slag for use in the manufacture of slag blended cements. Although its use in cement represents a high value use

o of slag, less than 0.5 million tons (4.54 x 10 kg) of slag are granulated for this purpose

in the U.S. per year [3] . It appears that steel producers have been reluctant to invest in

granulation facilities, perhaps because of the small and uncertain market which presently

exists for this product.

In the following sections, the geographical limitations on the availability of fly ash

and slags for use in blended cement manufacture will be discussed, as will the limitations

due to ASIM standards. Steps which might be taken to overcone the latter will then be

explained.

3.1 Geographical Limitations to the Utilization of Slag and Fly Ash in Cement

ClearIv. increased manufacture of blended cements will require the reactive additives

to be shipped econcmically to the cement plants^

Thus, table 6 indicates the geographic distribution of the coal burned by utilities in 1965

[19] . The amount of ash produced in each area may be assumed to be about 10% of the weight

of coal burned. As this table shews, the amount of ash produced is widely distributed

suggesting that transportation costs frcm the utilities to the cement producers will often

be low. Of course, not all cement producers are in a position to benefit equally frcan the

fly ash produced, nor are all utilities in a position to benefit from ash utilization in

cement manufacture. However, many are and the quantity of fly ash blended cement produced

could probably be si±)stantially increased before serious transportation limitations occurred.

7
TABLE 6. Regional Distribution of Coal Burned in the United States [19]

Geographical Coal Bu^^ed,

Area States tons x 10 /year

New England (ME, NH, VI, MA, RI, CT) 8,207

Middle Atlantic (NY, NJ, PA) 40,553

East North Central (OH, IN, IL, MI, WI) 83,570

West North Central (MN, lA, MO, KS, NE, SD, ND) 13,749

South Atlantic (MD, DE, VA, WV, NC, SC, GA, FL) 39,502

East South Central (MS, AL, TN, KY) 33,902

West South Central (LA, AR, TX, OK) 10

Mountain (NM, AZ, NV, CO, UT, WY, MT, ID) 6,644

Pacific (CA, OR, WA) None

One ton is equivalent to approximately 907 kg.
The production of blast furnace slag is much more localized than that of fly ash. Of

10 9

the 25 million tons (2.3 x 10 kg) produced in 1972, about 5.3 million (4.8 x 10 kg) were

9 produced in Ohio, 6 million (5.4 x 10 kg) in Pennsylvania, and a total of 5.3 million

9 9

(4.8 X 10 kg) in Illinois, Indiana and Michigan. The remaining 8.4 million tons (7.6 x 10

kg) were produced in 11 other states [3] . Figure 1 shows the distribution of cement plants

and blast furnaces. With only a few exceptions slag is produced within a relatively short

distance (150 miles or less) fron a cement plant. This seems to indicate that the minimal

utilization of slag by the cement industry is not a result of excessive transpoirtation

distances

.

3.2 Specification Limitations to Slag and Fly Ash Utilization in Cement

Even if there are no major technical problems in making blended cements v\^ich perform

well, the lack of appropriate standard tests and specifications would hinder the acceptance

of these materials. As one example, ASIM specifications for blended canents, specifically

ASIM C595-74 [5] tend to be restrictive with regard to the quantities of fly ash pozzolans

or blast furnace slag which can be used. This standard only provides for blended

certents containing 15 to 40% fly ash or a minimum of 25% blast furnace slag, even though

experience in other countries has shown that greater or lesser quantities of these materials

could be added depending on the engineering performance desired from the blended cement.

For example, a blended cement containing relatively snail amounts, perhaps 5-15%, of fly

ash or ground slag, may give a concrete of higher early strength than one made with a portland

cement. The slag or fly ash, because of their reactivity, might also contribute additional

strength to the system at later ages. In spite of this, the present lack of standard

specifications for such cements provides an obstacle to their irianufacture and use. While

there is discussion about the possibility of modifying the ASIM blended cement specifications,

to permit addition levels outside the presently specified ranges, no action has yet been

taken.

9
FIGURE 1. The geographic distribution of blast furnaces and cement production

facilities [1]

.

10
As an exanple of the need for new standard tests, the need for a standard test to

determine hydraulic reactivity of slags may be nentioned. The reactivity of a slag, hence

its siiitability for incorporation into a blended cement, depends on its chemical coiiposition

and the rate at which it was quenched from the molten state. The quenching rate influences

both the ccnposition and the fraction of the amorphous or glassy material present. Judged

by the ccnpressive strengths of slag-portland cement mixtures, there may be an optimum

coiposition of slag glass of about 52% CaO, 33% Si02 and 15% Al20^ [20] . While ASIM Standard

C595-74 does not place cotpositional requirements on slags for use in cement [5] , foreign

specifications generally contain formulas, such as (CaO + MgO + Al202)/Si02-1 [21] , by

v^iich the suitability of a particular slag may be judged. While convenient to use, a

specification of this type will usually be more restrictive than a performance based specification such as the pozzolanic activity index [5] which may be applied to fly ash. However,

present ASTM standards do not provide either type of specification for slag. Thus, a

potential user does not have an accepted method by which slag may be evaluated for suitability

for use in cement manufacture.

Fly ashes to be used in blended cements are, however, subject to ccnpositional restrictions. ASTM Standard C618-73 requires that the minimum combined amounts of Si02, ^2'^3

Fe202 be at least 70% of the weight of the ash [22] . This precludes utilization of many fly

ashes even though it has not been adequately demonstrated that those which do not conform

to these catpositional requirements will necessarily result in unsatisfactory blended

canents. For exaitple, this coitpositional requirertent precludes the use of many fly ashes

from the lav sulfur western coals which are being used in rapidly increasing amounts due

to environmental limitations on SO2 emissions. Ash fron these coals is high in CaO, with

contents often exceeding 30%. While the performance of blended cements containing these

ashes must be shown to be satisfactory before their use is allowed, the ashes should not be

unnecessarily precluded by the 70% carposition requireinent alone.

While the oxide cctrposition requirement may be too restrictive on the loss, ignition

requirement for fly ash may not be sufficiently restrictive. Because unbumed carbon always

occurs in intimate mixture with fly ash, a maximum weight loss on ignition of 12% fly ash is

specified by ASTM Standard C618-73 [22] . However, this requirement does not ensure the

11
exclusion of carbon contents v\fcLch may result in a large or variable consunption of chemical

admixtxares for concrete. These admixtures, which are losually organic, are used for set

regulation, air entrainment, or water reduction. Apparently, these admixtures are adsorbed

oh the surfaces of the carbon particles thereby reducing their effectiveness. Frcm an

esthetic standpoint, high carbon ash nay impart an undesirable color to concrete. Decreasing

permitted ignition losses to a lower level could aid in the elimination of this problem.

This could be done directly by specifying a Icwer maximum ignition loss or, indirectly,

through the development of appropriate performance criteria for admixture consurrption.

Fran these exanples, it can be seen that new standard tests and specifications could

facilitate the selection of materials for lose in blended cements and contribute to confidence

in the performance of the blended cement themselves. In the following section, consideration

is given to specific perfomance tests.

3.3 Standard Tests for Blended Cements

Most of the performance tests and specifications currently applied to blended cements

were originally developed for portland cements. In many cases, they provide adequate basis

for the evaluation of blended cements. However, in other cases, they are unduly restrictive

and do not adequately consider the differences between these types of materials. The development of tests v^ch objectively evaluate the performance of blended cements is crucial to

the facilitation of the acceptance of -diese materials.

Inportant areas in which new or improved standard tests, specifications and/or research

data are needed are:

1) soundness

2) resistance to attack by sulfates

3) reactivity with alkali-susceptible aggregates

4) freeze-thaw durabilitY

5) admixture performance

6) fly ash or slag content of blended cement

12
7) strength gain

8) pozzolan and slag reactivity

9) protection of reinforcing steel against corrosion.

Brief outlines of the reasons v^y new or irtproved perfortiance tests and specifications

are needed are given in the following sections.

3.3.1 Soundness

Soundness is the ability of a cement paste, mortar or concrete to withstand internal

stresses generated during the cement hydration without cracking. Unsoundness, v^en it occurs,

is usually due to slow hydration of dead-burned CaO and MgO in the cement after the cement

paste matrix has hardened. The products of both hydration reactions have significantly larger

volumes than the cctrpounds from which they are formed. These increases in volume result in

internal stresses v\^ich may be reflected as an expansion or, if sufficiently large, a total

disruption of the paste.

The autoclave expansion test developed for detecting unsoundness in portland canents,

ASIM Cl51-74a [5] , is a good, though perhaps overly severe, test for this property. This

test is also applied to blended cements although in this case there is some uncertainty as

to viiiether it provides adequate protection against unsoundness occurring in use. This is

because there are indications that the hydration of MgO in the presence of fly ash under

autoclave conditions may result in smaller expansions than occur under field conditions.

This may be attributed to the formation of comoounds v^iich do not occur in field conditions

[23] . Further study in this area is warranted to assess the validity of this test. Alternatively, if blended cements do exhibit diminished expansive tendencies, an increase in the

allowable MgO limit above the current 5% (ASTM C595-74 [5]) may be jiostified. This could

permit the use of readily available higher MgO limestones with possible savings in mining

and transportation costs and conserve lav magnesium limestones for purposes for vMch they

are essential.

The results of the autoclave tests on any cement are probably effected by the strength

developed in the specimen during the prescribed curing prior to initiating the test. This

13
may cause an unnecessary bias against blended cements containing high percentages of pozzolan

or slag since the strengths of these materials are usually lower than those of portland

cements after the standard one day cure. The influence of preautoclave strength on autoclave

expansion should also be investigated. The expansion vAiich takes place in the autoclave is

a result of internal stresses v\^ch exceed the strength of the material, and autoclaving

probably accelerates the reactions causing developsnent of internal stresses more than those

responsible for strength development. It may therefore be beneficial to permit a given

strength to be attained prior to test initiation.

3.3.2 Resistance to Attack by Sulfates

There is strong evidence that blended cements tend to show higher resistance to sulfate

attack than portland ceitients [14, 15] . Sulfate attack of concrete may lead to disruptive

expansion of the hardened cement paste matrix of the concrete and reduce the useful life of

concrete structures exposed to sulfate conditions. Sources of sulfate include drainage

water, ground water and sea water. While the actual mechanism is not fully understood,

attack may result from reaction of soluble sulfates with the calciimi hydroxide and hydrated

alumina-containing phases formed during cement hydration to form gypsum and highly hydrated

calcium aluminosulfate conpounds having large specific volumes. Susceptibility to these

reactions appears to be reduced in blended cements, possibly because of reactions between

the calciijm hydroxide and pozzolan or slag. In spite of their probably advantages, the use

of blended cements, rather than Type V portland canent, where high sulfate resistance is

required is virtually excluded since there is no standard tests for establishing sulfate

resistance.

i

The only standard sulfate resistance test currently available, AS1M C452-68 [5] , involves

the measurement of expansion of mortar. In this test, calcium sulfate is mixed with dry

cement prior to the addition of water. Because a substantial degree of reaction occurs at

early ages before the mortar has developed its full strength, this test is not representative

of field conditions. Under normal exposure conditions, sulfate attack probably occurs by the

slow diffusion of sulfate-containing water into the concrete after the cement has undergone a

substantial degree of hydration. A test v^ich more closely simulates this behavior would

14
ije more realistic as a basis for selection of sulfate resistant cements. The availability

of such a test would facilitate the selection of any suitable cement, whether blended or

Portland, for use where sulfate resistance is iirportant.

.3.3.3 Reactivity with Alkali-Susceptible Aggregates

The reaction between alkalis present in cement and certain types of stone aggregate used

in concrete sometimes leads to the formation of highly hydrated alkali silicates. The

formation of these conpounds can result in a dismaptive expansion of concrete. The mechanism

and kinetics of these reactions are not well understood and, depending on the nature of the

aggregate and the exposure conditions, expansion may manifest itself at an early age or only

after several years. Additions of pozzolanic fly ash to a canent or concrete can reduce the

expansive potential of this reaction between alkalis and aggregate [24] . However, the usual

approach to reducing the likelihood of alkali-aggregate reaction is to specify low alkali

Portland canents.

Current specifications, ASTM C441-69 and C227-71 [22] , for cements to be used with

reactive aggregates appear to be unnecessarily restrictive in that they apply only to portland

cement and do not permit beneficial interactions between the ingredients of the concrete to

be taken into account. It would be beneficial if performance specifications could be

developed v±iich would take into account txDth the alkali absorption capacity of the pozzolan

and the alkali content of the cement. Such a specification could provide flexibility in the

use of each conponent in a composite such as concrete. This could be of value to the cement

industry in that it would make it possible for the alkali contents of seme cements to be

increased. This would allow the use of readily available raw materials with alkali contents

higher than those currently permitted and reduce the need to discard large quantities of high

alkali kiln dust. These changes would aid in the conservation of both materials and energy.

Energy would be conserved since kiln dust already has a significant energy input fran the

grinding and heat requirements of cement production and its reintroduction into the system

would alleviate a substantial disposal problem.

15
3.3.4 Freeze-Thaw Durability

In many areas of the country, concrete is subject to damage by freezing and thawing.

This must be taken into account when designing the concrete and it may influence the

.selection of the concrete. Thus, when blended cements are tested according to ASTM C666-73

[22] ,the standard method for measuring the freeze-thaw diirability of portland cement

concretes, inferior resistance is usually observed [25] . This is probably because test

initiation after only a short curing period does not make proper allcwance for the generally

lower rate of strength development of blended cements. Freeze-thaw studies, when initiated

after longer curing periods, have indicated that blended cements, due to development of

strengths equivalent or superior to those of portland cements, also develop superior

resistance to freezing and thawing [26]

.

Studies are needed to determine the rate of development of freeze-thaw resistance in

blended cement as this directly relates to seasonal concrete placement practices. If substitution between them is to be facilitated, comparison of portland and blended cements on

the basis of equivalent age should be supplanted or supplemented by the development of more

realistic basis of conparison, such as equivalent strength or predicted strength at time of

first freeze.

3.3.5 Admixture Performance

A sx±)stantial and increasing fraction of the concrete placed in the U.S. contains

chemical admixtures which are used to regulate set times, entrain air or reduce water

requirements. Set regulation is used to delay initial set times extending the time available

for finishing; air entrainment, the entrapment of small air voids in the cement paste, is used

to improve resistance to freeze-thaw damage; water requirement reduction leads to a reduction

in the porosity of the matrix of the hardened concrete with attendent benefits of increased

strength and chemical resistance. Blended cements containing fly ash contain small but

variable amounts of active carbon which is present in fly ash due to inccsnnplete ccmbustion

of coal from which it was formed. This carbon absorbs chemical admixtures and tends to

diminish their effectiveness. Since this effect does not vary in a consistent way with the

16
absolute carbon content of the cement, admixture response is difficult to predict. Methods

for determining the absolute amount and surface area of the carbon in fly ash may need to be

developed in order to more fully understand this phencanenon and, if possible, to establish a

standard testing procedure.

3.3.6 Fly Ash and Slag Contents of Blended Cements

The uniformity of a conent is important to the user. Uniformity of a blended cement

depends on both cement content and the fineness and conposition of the additive material.

At present no standard tests are available for the analysis of a blended cement for its

constituents. Tests for the determination of the portland cement clinker and additive

contents and their coitpositions are therefore needed. The availability of such tests would

make it possible to assess the uniformity of blended cements both from the standpoint of

cement composition and additive characteristics. This information could be inportant to the

manufacturer and the user in alerting them to changes in quality and in establishing the

causes of unexpected variations in performance.

3.3.7 Strength Gains of Blended Cement Concretes

In considering the substitution of a blended cement for a portland cement, it must be

recognized that the two cements may have different rates of strength gain and that the differences in the effects of tenperature on strength gain may be substantial. One approach

that holds promise in the development of criteria to predict strength gain in cement in general and

blended cement in particular is that represented by the maturity concept. Development of

this concept involves modeling the cement curing process by relating the time-temperature

history to strength gain while including such variables as humidity, cement cotposition and

section thickness. An approach of this type is needed in considering for possibilities for

substitution of blended cements for portland cerrents since blended cements shew strength development characteristics which have a higher dependence on curing conditions. This approach

would be of practical benefit to the construction industry by providing a rational basis for

choosing the proper cement for a given application and in aiding the prediction of form

removal times on the work site.

17
3.3.8 Pozzolan and Slag Reactivity

Pozzolanic reactivity is a ineasure of the ability of a pozzolan to ccdbine with calcium

hydroxide, such as that liberated by hydrating cement, to form products with cementing

value. An irtproved test by v*u.ch this reactivity may be measured requires development.

While tests v^ch measure the rate of lime consunption by fly ash and other pozzolans exist,

a test which allows correlation of reactivity with strength does not. A lime consunption

test may not always be valid because calcium hydroxide may react with cortpounds present in

a pozzolan to form products v^ch do not contribute appreciably to strength development. In

general, it appears that improved methods for assessing the pozzolanic value of fly ashes

could assist in the selection of fly ashes for use in blended cements. The development of a

suitable means by v^ich slag reactivity may be measured also requires development as was

discussed in section 3.2.

3.3.9 Protection of Reinforcing Bars from Corrosion

The effectiveness of blended canent concretes in protecting steel reinforcing bars fran

corrosion must be taken into account in the s\±)Stitution of blended canents for portland

cements. Normally steel is passive towards corrosion v^en in portland cement concrete because

of the highly basic environment (pH of about 12.5 [27]); however, aggressive agents, such as

chloride ions, are able to depassivate steel and thereby promote its active corrosion [28]

.

A small amount of corrosion of the steel may cause the spalling and cracking of concrete and

result in the need for expensive repairs. For exanple, the annual national cost of repairing

and replacing concrete bridge decks because of such damage has recently been estimated by the

Federal Highway Administration to be more than $200 million. Furthemnore, other reinforced

concrete structures, particularly parking garages, piers, and buildings located near the ocean,

are si±)ject to damage due to corrosion of embedded steel reinforcement.

In the next two decades, the amount of shoreline and offshore concrete construction,

especially for nuclear reactors and oil wells, will substantially increase. Therefore, it

is anticipated that prevention of corrosion of steel reinforcanent in concrete will become

increasingly inportant.

18
The extent of the use of blended cements in reinforced concrete construction will, to

scjT^ extent, depend on the ability of blended canent concretes to protect steel reinforcement

from corrosion. More information is needed about this ability since there appear to be at

least two opposing factors: blended cement concretes containing fly ash may have lower

pH's than concretes with normal portland cements [30] , but they also tend to be less permeable

to the migration of chloride ions and, on this account, tend to provide better protection to

the reinforcing steel than portland conent concretes [31] . Better protection may also be

provided because fly ash blended cement concretes seem to be less susceptible to shrinkage

cracking than portland cement concretes [32]

.

Many of the environmental factors v^ich accelerate the corrosion of steel in concrete

have been studied. However, the relative effects of different types of cements on the rates

of corrosion have received little attention. Furthermore, no ASTM or other standard test

method exists for catparing the corrosion protection provided by different concrete including those containing different cements. The development of a standard corrosion test would

be beneficial in evaluating the corrosion protective qualities of all types of hydraulic

cements and, specifically, in comparing blended and portland cements.

4. BASIC RESEARCH REQUIREMENTS

Additional research will be required to provide a sound basis for the development of the

standard tests and specifications needed to facilitate substitution between blended and

portland cements. For the most part these areas relate to understanding the reactivity of

the additives in blended cements and the mechanisms of degradation of portland and blended

cement concretes. These areas are:

1) Mechanisms of fly ash and/or slag-cement interaction

2) Influence of absolute fly ash coitposition and of catposition variability within the individual ash particles

3) Methods of accelerating and/or activating fly ash and slag to produce cements

exhibiting more rapid gains in strength.

19
4) Methods of modifying slag crystallization through cortposition and/or

nucleation inhibitors

5) Mechanisms of sulfate attack

6) Mechanisms of alkali-aggregate reaction

7) Influence of microstructure including porosity, surface area, morphology,

and distribution of reaction products on strength and durability

8) Determination of the tenperature dependence on the reactivity of blended

cements and their engineering properties.

5. SUMMARY

The substitution of blended cements for portland cements appears to be attractive frem

the standpoint of energy conservation. The materials most suitable for use with portland

cement clinker in blended cement manufacture are fly ash and blast furnace slags. Fly ash

is generated as fine particles and requires little or no processing prior to its introduction

into the cement manufacturing process. Blast furnace slag, on the other hand, does require

special processing such as granulation to develop its full reactivity. Both blast furnace

slag and fly ash are generated in large quantities and the availability of these materials

to cement plants does not appear to be a factor which would severely limit their use in this

way. Hcwever, a more detailed analysis would be required to properly assess these limitations .

The limitations of the cxirrent AS1M and related standard specifications covering

blended cements along with the need for additional durability and engineering performance

data on these materials appears to present significant obstacles to their production and

utilization. Standard specifications should be modified to include slag and fly ash

addition levels not currently covered by the standards. Coirposition requirements could

in many cases be supplanted by performance based specifications. Durability and performance

data for blended cements need to be developed as a basis for standard tests and specifications

to further define the advantages and limitation to the utilization of blended cements, and to

allow for their appropriate substitution for portland cements.

20
6. REFERENCES

1. Energy Conservation Potential in the Cement Industry, FEA Conservation Paper #26, 1975.

2. The Conference Board, Energy Consurtption in Maniafacturing, Ballinger Publ., Cambridge,

Mass., 1974.

3. Bureau of Mines Minerals Yearbook, 1972.

4. U.S. Industrial Outlook 1975, Dept. of Ccrtit^ce, 1975.

5. "1974 Annual Book of ASIM Standards", Part 13, ASIM, Philadelphia, Pa.

6. All values are from Plastics and Rubber Weekly, Septeniber 6, 1974 ^cept vd:iere noted.

7. "The Costs of Purchased Fuels and Electric Energy by Industry", Econonic Stabilization

Program, Cost of Living Council, December 26, 1973.

8. W. Gutt, The Use of By-Products in Concrete, Building Research Establishment Current

Paper 53/74 (1974)

.

9. Cembuream, Bull. No. 57, 1974.

10. V. I. Satarin, "Slag Portland Cement", Proc. of the Sixth International Synposium on

the Chemistry of Cement, Moscow 1974.

11. Bu. Reclamation Concrete Lab Rept. No. C-980, 1961.

12. K. Guida, Ash Utilization, Bu. Mines IC 8640, 1974, p. 58.

13. R. J. Elfert, Ash Utilization, Bu. Mines IC 8640, 1974, p. 88.

21
14. F. M. Lea, The Chemistry of Cement and Concrete, Chem. Publ. Co., N.Y. 1971.

15. G. L. Kalousek, L. C. Porter and E. J. Benton, Cement and Concrete Research 2, 79

(1972)

.

16. E. A. Abdun-Nur, Fly Ash in Concrete, Chicago Fly Ash Co., Oct. 1959.

17. Ash Collection and Utilization 1974, Ash at Work, Vol. 7, No. 3, 1975.

18. A. R. Lee, "Blast Furnace and Steel Slag", John Wiley, N.Y., 1975.

19. C. E. Bracket, in Fly Ash Utilization, Bu. Mines IC 8348 (1967) p. 20.

20. T. Tanaka and J. Jamani, Zement-Kalk-Gips 11, 50 (1968)

.

21. German Specification DIN 1164, 1967.

22. Annual Book of ASTM Standards, Part 14 Concrete and Mineral Aggregates, ASIM

Philadelphia (1974).

23. J. Rosa, Zanent-Galk-Gips 9, 460 (1965).

24. U. S. ArrriY Engineers Waterways Expt. Station Tech. Rept. 6-627, June 1963.

25. A. G. Tirims and W. E. Grieb, Public Roads 29, 142 (1957) .

26. R. E. Davis, et al, J. Am. Concrete Inst. 37, 281 (1941).

27. J. D. MDzer, A. C. Bianchini and C. E. Kesler, J. Am. Concrete Inst. 62^, No. 8, 90

(1965)

.

28. J. E. O. Mayne, J. W. Menter, and M. J. Pryor, J. Chem. Soc. 3229 (1960).

22
29. H. Abe, S. Nagatabi and R. Tusbayama, Discussion of Fly Ash and Fly Ash Cement by

M. Koki±)u, p. 105, Volume IV, Proceedings of the Fifth International Syitposium on the

Chemistry of Cement, Tokyo, 1968.

30. R. E. Davis, J. Amer. Concrete Inst. 46, No. 1, 377 (1950).

31. R, F. Blanks, J. Amer. Concrete Inst., 46, No. 5, 701 (1950).

USCOMM-NBS-DC

23

NBS-114A (REV. 7-73)

U.S. d:".pt. of comm. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR RHPORT NO.

NBSIR 76-1008

2. Gov't Acces.sion

No.

3. Rcc ipient ',s Acces.sion No.

4. TITLE AND SUBTITLL

Energy Conservation Through the Faciliation of Increased

Blended Cement Use

5. Publication Date

February 1976

6. Performing Organization Code

7. AUTHOR{S). , ^ . ^ Paul Wencil Brown, James R. Clifton, Geoffrey Frohnsdorff

8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

Energy Research and Development Administration

20 Massachusetts Avenue

Washington, DC 20545

13. Type of Report & Period

Covered Interim

Jjuly 1 - December 1975

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

About 95% of the cement produced in the United States is portland cement and its

manufacture requires about 2% of the energy consumed annually in the nation's industrial

processes. The production of blended cements containing substantial amounts of fly ash

or blast furnace slag and their substitution for portland cement appears attractive from

the standpoint of energy conservation. While production and utilization of blended

cements in other industrialized countries is extensive, blended cements account for less

than 1% of the total cement production in the U.S. The reasons for the small U.S.

production of blended cements are discussed in the contexts of standards revision and

the need for the development of additional data as a basis for this revision.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper

name; separated by semicolons)

Blast furnace slag; blended cements; energy conservation; fly ash;

18. AVAILABILITY Unlimited

I

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^ Order From Sup. of Doc, U.S. Government Printing Office

Washington, D.C. 20402, SD Cat. No. C13

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(THIS REPORT)

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UNCLASSIFIED

21. NO. OF PAGES

27

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USCOMM-DC 29042-P74