Report No. DOT-TST-74-21

TRUCK NOISE l-A

NOISE EVALUATION TESTS OF MILITARY TRUCK TIRES

William A. Leasure, Jr.

Denzil E. Mathews

William J. Rinkinen

FINAL REPORT

FEBRUARY 1974

Availability is unlimited. Document may be released to

the National Technical Information Service, Operations

Division, Springfield, Virginia 22151, for sale to the public.

Prepared for

DEPARTMENT OF TRANSPORTATION

Office of the Secretary

Office of Noise Abatement

Washington, D.C. 20590
This document is disseminated under the sponsorship of the Department of Transportation in the interest of information

exchange. The United States Government assumes no liability for its contents or use thereof. Specific commercial products

are identified in this report in order to adequately specify the tasks performed. In no case does such identification imply

recommendation or endorsement by the Department of Transportation.
TECHNICAL REPORT STANDARD TITLE PAGE

1. Report No. DOT-TST-74-21

2. Government Accession No. 3. Recipient's Cotalog No.

f V —-'^ / ^ t / f f 4. Title and Subtitle Truck Noise I-A: Noise Evaluation Tests of

Military Truck Tires

5. Report Date February 1974

6. Performing Organization Code

7. Authorfs) William A. Leasure, Jr., Danzil E. Mathews, and

William J. Rinkinen

8. Performing Orgonization Report No.

9. Performing Organization Name and Address National Bureau of Standards

Mechanics Division

US Department of Commerce

Washington , DC

10. Work Unit No.

1 1 . Controct or Grant No. DOT-AS-10004

13. Type of Report and Period Covered

Final Report

12. Sponsoring Agency Name and Address US Department of Transportation, Office of the

Secretary, Office of Noise Abatement,

Washington, DC 20590 14. Sponsoring Agency Code

15. Supplementary Notes This is a special report within a series of reports emanating from an interagency

agreement with NBS to perform a wide variety of truck and passenger car tire

noise research.

16. Abstract This report presents the A-weighted sound level and one-third octave band

spectral data resulting from a study conducted to characterize the noise

generated by military truck tires. The study was conducted by the National

Bureau of Standards in cooperation with the U.S. Department of Transportation

under the sponsorship of the U.S. Army Tank-Automotive Command. The data base

established will allow for comparison of the tire noise generated by military

and commercial truck tires.

The study investigated the influence of load and speed on the noise generated

by tires with four different tread designs: the standard Army tire, a retread

of Army design and commercial tires with rib and cross-bar type tread patterns.

Army and commercial trucks were utilized as test vehicles.

In addition, the report includes a discussion of the measurement and analysis

techniques utilized for the establishment of this data base.

17. Key Words noise, tire noise, truck tires,

acoustics, sound, military vehicles

18. Distribution Statement Availability is unlimited. Dociiment may be

released to the National Technical Information Service, Operations Division,

Springfield, Virginia 22151, for sale to

the public

19. Security Clossif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages

52

22. Pr

Form DOT F 1700.7 (s-es)

Table of Contents

1. Introduction 1

2. Field Test Program 2

2.1. Field Test Site 2

2.2. Test Tires 5 a. Tire Preparation and Warmup 5 b. Tire Characteristic Measurements 6

2.3. Test Vehicles 6

2.4 Test Procedure 12

3. Parametric Study 18

4. Appendix A. Parametric Study Results 32

5. Appendix B. Instrumentation Descriptions 41

6. Appendix C. Test Section Substrate Details 45

4. References 51

i

1. Introduction

The U. S. Army Tank-Automotive Command is presently establishing data

bases on the performance characteristics, including noise, of their vehicles

and components, such as tires. Noise data are especially important since

military vehicles frequently operate on public roads and therefore contribute

to community noise levels.

The U. S. Department of Transportation and the National Bureau of Standards

have been working in the tire noise area since 1970 and have established an extensive data base on commercial tire noise [1,2].!./ Tread design, wear, load,

speed and pavement surface were the major parameters investigated in these

studies. On the basis of this experience and expertise in the tire noise area,

the Army sponsored a study with DOT/NBS to investigate the noise generation

characteristics of the standard Army tire, a retread of Army design and two

commercial truck tires

i

The test program was designed to be of optimum benefit to the Army and

of necessity considered operational variables which are peculiar to realworld Army use as compared to nominal commercial use practices.

Briefly the testing included the following:

Noise measurements were made at 25 and 50 feet as measured from the

centerline of vehicle travel. These distances correspond to the

standard European and American measurement locations.

A 2-1/2 ton military vehicle (M35-A2C) equipped with 10 test tires was operated under the following conditions: (1) speeds of 35, 40,

and 45 mph, vehicle loaded as per Army axle load recommendations,

(2) speeds of 40 and 45 mph unloaded, (3) at each test condition both

coast-by (engine shut-off) and powered drive-by runs. A commercial single-chassis truck equipped with 4 test tires on the

drive axle and 2 quiet tires on the steering axle was tested. The

truck was loaded (axle loading comparable to that for the loaded

military vehicle) and operated at speeds of 40, 50, and 60 mph.

A minimum of two test runs was made at each operational condition.

It was anticipated that such a program would provide the Army with tire

noise data as presently reported in the public domain (4 test tires) , the

total tire noise output for a typical military vehicle (10 test tires), and

the data to define the power plant/drive line (transmission/differential)

noise characteristics for this type military vehicle.

—Figures in brackets indicate the literature references at the end of this

report

.

1
2. Field Test Program

To ensure that the Army would derive maximum benefit from the existing

tire noise data base, this test program was patterned after the previous

DOT/NBS field test programs. The exceptions, of course, were in those areas where the standard operating procedures differed between the military and

commercial applications. A discussion of the details associated with the

test program for the evaluation of a sample of four specific tire types of

interest to the Army follows.

2.1 Field Test Site

The research runway at the Wallops Island, Virginia, facility of the

National Aeronautics and Space Administration was chosen as the test site

for the road testing phase of the program. This location provided an adequate stretch of pavement (8750 feet) and a flat terrain providing a well-defined reflecting surface without any unusual reflection and attenuation effects. An agreement was reached with NASA for utilization of this

facility for the data acquisition phase of the program.

On the 8750 foot length of research runway 4-22 (bearing 040° and 220°),

a 600 foot test section was established. This test area was designated as the concrete test section. The nominal runway width was 150 feet with a center section (50 foot wide located at the center of the runway) of

specially constructed substrates including some grooved sections. Although

no lanes, such as one thinks of as being present on highways, were marked

on the runway, the concrete on either side of the special pavement area was

laid in sections 12 feet wide and 20 feet long. For this test program, the

truck ran in one of these 12 foot lanes. Due to the deteriorated condition

of the pavement surface near the edge of the runway, the truck ran one lane

in from the edge. Figure 1 shows an overall view of the research runway

with the location of the test section noted. Appendix C contains a detailed

discussion of the composition of the test section.

The concrete test section began 2850 feet from the northeast end of

runway 4-22 and extended to 3450 feet. It consisted of a substrate of

reinforced, air-entrained Portland Cement concrete with a "C" finish

(smooth concrete) . The "C" finish section of pavement was smoothed with

a belt of canvas composition. Figure 2 is a detailed layout of the concrete

test area while Figure 3 shows the actual surface in the smooth concrete

section.

As is evident from Figure 2, a grooved pavement section existed along the

centerline of the runway in a portion of the concrete test section. However,

only a small corner of this grooved section was in the line of sight path from

the test vehicle to the microphone array. The effect of the grooves on re- flection of sound was not established during this study; however, the width

and spacing of the grooves (1/4 inch and 1 inch respectively) appear to be

such that only high frequencies would be affected. It is felt that the

grooves would have little or no effect at those frequencies (200-2000 Hz)

where most of the tire noise is concentrated.

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4
2.2. Test Tires

For this study, the Army selected a total of four tire types for

evaluation. A photograph of each tire showing the tread design is shown

in Appendix A. The test tires were size 9.00 x 20 and included the

standard military tire, two commercial tires and a retread of Army design.

The Army retread (tire-C) and one of the commercial tires (tire-D)

utilized a radial unisteel carcass.

a. Tire Preparation, Break-In and Warmup

In accordance with standard operating procedure the tires utilized

during this test program were not balanced.

When new tires are installed on a truck, balancing is not performed

unless there is a definite handling problem or severe vibration reported

which might jeopardize the safety of the vehicle. When such a problem

arises, the entire front end assembly, not just the tires, is checked.

Unlike the normal practice with automobile tires, only front (steering)

tires are ever balanced on trucks.

A tire was not considered acceptable as a test specimen for the tire

noise investigation until it had undergone a break-in period of sufficient

mileage under actual driving conditions to ensure the removal of all mold

marks and manufacturing irregularities.

In addition, a warm-up procedure was followed immediately prior to the

actual testing of a given set of tires. This was done to eliminate the

periodic vibrations caused by flatspots typically present on cold tires.

Flat-spotting is a phenomena caused by a thermal shrinkage property common

to some fabric-cord materials. The cord material shortens slightly

when hot and as the loaded tire cools while stationary, the cords temporarily "set" at the shorter length in the road-contact area (flatspot)

and do not equalize until their temperature has again been raised.

The normal procedure required a minimum of five round trips over the

length of the research runway at the field test site (a total of approximately 10 miles). If the driver could sense any "thumping" or heavy

vibration, as could be expected if the tires were cold, he then would

continue the procedure until he felt that the vibration had been eliminated.

5
b. Tire Characteristic Measurements

Two measurements were made for each test tire — tread depth and

Shore hardness. The resulting data are tabulated in Appendix A.

Tread depth measurements were taken at four equally spaced locations

around the tire circumference. The device utilized for this measurement

was simply a depth gage with 1/32 inch graduations. The operator located

the depth gage over a major groove (not over sipes or other small grooves),

depressed the probe into the groove, and noted the tread depth directly

from the instrument.

The Shore hardness of the tread rubber was determined by ASTM test

method D-2240-68 [3] . A type A durometer (for soft materials) was utilized in the following manner: the durometer was held in a vertical

position with the point of the indentor at the center of the tread face.

The presser foot was applied to the specimen as rapidly as possible

without shock, keeping the foot parallel to the specimen surface. The

scale was read five seconds after the presser foot was in firm contact

with the specimen. The reported values represent the average for

readings taken at approximately the same four locations as the tread

depth measurements.

' 2.3. Test Vehicles

Two. types of vehicles were utilized throughout this program —

a 4 X 2—' single-chassis commercial vehicle and a 6 x 6 single-chassis

military vehicle.

The military vehicles — two M35A2C 2-1/2 ton trucks with a gross

vehicle weight capacity of 25,530 pounds — were loaned to the research

program for test purposes by the U. S. Army. The test tires (9.00 x 20)

were mounted at all wheel positions; however, only the rear axles were driven (i.e., the truck was operated in a 6 x 4 configuration). One

truck (Figure 4) was operated in an unloaded condition, while the other

carried 10,510 pounds of load. Figure 5 shows the loading arrangement.

Two concrete slabs and four sand bags were appropriately located such

that maximum loading was attained on all tires. The test vehicles were weighed at the official scale of the State of Virginia near the

Wallops Station test site resulting in the following weight breakdown:

— The nomenclature 4x2 relates to the number of wheel positions —

4, and the number of driven positions —2, but has no relationship to

the number of tires — 6. Thus, a 6 x 4 would have 10 tires

mounted at 6 wheel positions, 4 of which are driven.

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16,660 pounds

(3,425 pounds/tire)

(2,082 pounds/tire)

gross vehicle weight 23,510 pounds

Truck #2 (unloaded)

front axle

rear axles

5,930 pounds

7,070 pounds

(2,965 pounds/tire)

( 884 pounds/tire)

gross vehicle weight 13,000 pounds

The 4x2 commercial single-chassis vehicle (similar to that utilized

in the DOT/NBS [1,2] truck tire noise program) was an International— Model

1600 chassis equipped with a 20-foot stake body which was rented from

Ryder Truck Rental, Inc., Baltimore, Maryland. The vehicle was equipped

with a 7,500 pound front axle, V-345 gasoline engine, 5-speed transmission,

2-speed, 17,000 pound rear axle and 10.00 x 20 tires (9.00 x 20 tires can also be mounted on this vehicle) . The truck had a gross vehicle weight

capacity of 25,000 pounds. Figure 6 gives an overall view of this

vehicle.

This truck was operated in a loaded condition. Figure 7 shows the

loading arrangement. Eleven 500 pound weights were distributed to develop

loading per tire comparable to that for the loaded military vehicle. The

resulting weight distribution was as follows:

front axle 6,830 pounds (3,415 pounds/ tire) rear axle 8,570 pounds (2,142 pounds/tire)

gross vehicle weight 15,400 pounds

For this vehicle, the test tires were always mounted on the drive

axle and rib tires whose characteristic tire noise level was known to be

low were always mounted on the steering axle.

Tires on the loaded test vehicles were inflated to an air pressure

of 50 pounds per square inch as specified by the Tire and Rim Association

recommendations for the above loading conditions. The tires on the unloaded

— The commercial vehicles utilized are identified in this report in order

to adequately describe the vehicles on xizhich the test tires were mounted

throughout this program. In no case does such identification imply

recommendation or endorsement by the National Bureau of Standards, nor

does it imply that these vehicles were necessarily the best available

for the purpose.

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vehicle also were inflated to 50 pounds per square inch even though the

loading was significantly less. This follows standard operating procedure

since the driver of an unloaded truck would not lower the air pressure in

his tires simply because he had no load.

2.4. Test Procedure

Prior to a discussion of the test procedure, a few words of description are necessary to establish the placement of all instrumentation

within the test section. Figure 8 shows the placement of the microphones,

radio transmitters, and the path of the test vehicle.

The two microphones were located at 25 and 50 feet as measured from

the centerline of the lane in which the vehicle travelled along a line

perpendicular to the path of travel of the test vehicle. Radio transmitters,

activiated by the truck running over a tape switch, were located along

the test lane parallel to the path of the vehicle. Although not shown in

Figure 8, the mobile instrumentation van was located 500 feet back from

the edge of the runway. Coaxial cables connected the microphones

with the tape recording and monitoring equipment housed in the instrumentation van.

For a nominal 40 mph run (the vehicle should be travelling 40

mph as it passed the microphone array) the driver of the test vehicle

either maintained a constant speed (during powered drive-bys) or accelerated the truck to slightly more than the desired speed to com- pensate for the deceleration characteristics of the particular vehicle

(during coast-bys with the engine off)

.

As the truck passed over the initial tape switch, the tape recorder

in the instrumentation van was remotely commanded to turn on via the

signal from the radio transmitters. The initial tape switch/radio

transmitter system was located such that the tape recorder was up to

speed by the time that the test vehicle entered the test section.

(The location was selected based on the maximum test speed of the vehicle

during the program.) Following a time delay a signal was recorded

on the FM channel of the tape recorder which designated the start of

data. As the truck left the test section, a second tape switch was

activated, the radio transmitter sent a signal to the tape recorder,

a signal identifying the end of data was recorded and then the tape

recorder was remotely turned off. The data start and data end signals were transmitted to the receiver in the instrumentation van at different

frequencies. An elapsed time clock indicated the time it took for the

vehicle to cover the known distance between the tape switches from

which the average speed of the vehicle was calculated.

Figure 9 identifies the components that constituted the data

acquisition system. To describe the workings of the system, the following

example is cited with the contribution of each component discussed.

12
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Consider a truck passing an array of microphones (Figure 10). As

the truck moved forward, it caused pressure fluctuations which travelled

as waves and activated the microphone's diaphragm into vibration. These

variations were transduced into an AC voltage which could be recorded

for analysis at a later time. The microphone itself was a four-part

subsystem comprised of a one-inch, free-field condenser microphone

cartridge, protecting grid, dehumidif ier , and a microphone preamplifier.

The polarization voltage was supplied to the microphone by a batteryoperated microphone power supply. Prior to recording the signal on

the tape, there existed a need for signal conditioning. The step attenuator

provided the capability for selection of attenuation over a range of 60

dB in 10 dB steps. The linear hold circuitry provided an indication

as to whether or not a tape channel had become saturated (i.e., signal

had exceeded the dynamic range of the recorder) . Once saturation was detected, that particular data run was repeated. The signal was then

recorded on one track of the tape recorder. In addition, the system

included an A-weighting network and associated hold circuitry which

provided a direct reading, in the field, of the maximum A-weighted sound

level observed during a oassby without having to return to the laboratory

for the analysis of the tapes. The measurements were performed out-of-doors;

therefore, windscreens were placed over the microphones to minimize the

noise produced by wind passing over the microphone. A single point calibration utilizing a pistonphone which produced a 124 dB sound pressure level

(re 20M.Pa) at a frequency of 250 Hz was used for system calibration in the

field. Calibration tones were recorded on the data tape once each hour as well as at the beginning and end of each data tape..

Once the data had been recorded, the analog tapes were returned

to the National Bureau of Standards for reduction and analysis. Figure 11

identifies the equipment which was utilized for analysis purposes. Each

tape was played back a channel at a time through the real-time analyzer.

An interface-coupler was necessary to make the real-time analyzer com- patible with a mini-computer. When a timing signal appeared on the

analog tape, the real-time analyzer was commanded to begin analysis.

A time constant of .2 second above 2kHz and one which below 2kHz followed

a straight line to 3.15 seconds at 12.5Hz was utilized to obtain the rootmean-square (rms) value of the level in each one-third octave band at

the output of the analyzer. Once all data had been analyzed in one-third

octave bands, the computer stored the data and dumped it onto digital

magnetic tape. This tape was formated to be acceptable to the large NBS

computer which was utilized for further analysis. This instrumentation

system provided for efficient data acquisition and data handling for

the thousands of data points generated for each truck passby.

Appendix B contains a brief description of the instruments utilized

for data acquisition, reduction and analysis.

15
Figure 10. Overall view of the microphone array with the test vehicle.

The array consisted of two tripod -mounted microphones located

at 25 and 50 feet from the centerline of vehicle travel

along a line perpendicular to the vehicle path.

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3. Parametric Study

The data acquisition program was designed to address the following

questions

:

B What are the noise generation characteristics of these tires?

What is the effect of parameters such as speed and load on the

noise level for these tires?

Is a 6 X 6 military truck suitable as a vehicle for tire noise

testing?

In order to develop the data base necessary to answer these questions

the test matrix shown in Table 1 was established. The data acquisition

program followed this well-defined test plan.

The extensive data base on truck tire noise existing in the public

domain is based primarily on testing with a 4 x 2 vehicle with four

test tires on the drive axle and quiet rib tires on the steering axle.

To provide the necessary tie to this data base, the tires of interest

to the Army were tested on a commercial 4x2 single-chassis vehicle

over a speed range of 40-60 mph. Obviously, one is also quite interested in determining the total tire noise contribution for the

6x6 military vehicle, i.e., the noise generated when the test tires are mounted at all ten wheel positions. It is also important to define

the total vehicle noise over the speed range which is representative

of typical operational speeds of the vehicle. Such information provides

some insight as to the importance of tire noise relative to other sources such as engine/ exhaust noise. For this reason the military

vehicle was operated in a powered drive-by in addition to the coast-by

mode typically utilized for tire noise testing.

One Army vehicle was loaded to its maximum gross vehicle weight

capacity, while the second vehicle was operated in the unloaded condition. The commercial vehicle was loaded such that the load per drive

axle tire corresponded to the load per drive-axle tire observed for

the loaded Army truck.

For each operational mode, a minimum of two runs was made. The maximum A-weighted sound level data for all test runs are tabulated in

Appendix A. Also included are photographs showing characteristic tread

design patterns of the four test tires and the associated tread depth and

rubber hardness. In this section summary plots of the detailed A-weighted

sound level data are presented to show the effect of tread design, speed

and load on the noise level generated by these tires. Also presented are selected spectral data which provide additional insight into the tire

noise problem.

18
Truck/Operational Tire Type Load Speed

Mode

35 40 45 50 60

A.jruiy iruCrv ul J-Vfci uy T ir e - A T.opid pd X X X

Unloaded X X

TJL i

-L ri- pC - RU T±J,n^iCI. rlVJ. pHV_l X X X

Unloaded X X

Tire-C T .o^i d pH X X X

Unloaded X X

Tire-D Loaded X X X

Unloaded X X

A T"m\7 TtiipW Pope:*- — K\7 Tire-A T , Orl d pd X X X

Unloaded X X

Tire-B T .n^3 d pd X X X

Unloaded X X

Tire-C T .o;^ d pd X X X

Unloaded X X

Tire-D Loaded X X X

Unloaded X X

Ryder Truck Coast-by Tire-A Loaded X X X

Tire-B Loaded X X X

Tire-C Loaded X X X

Tire-D Loaded X X X

Table 1. Test matrix for the noise evaluation tests of military truck

tires. A minimum of two test runs were made for each operational

condition.

19
Figures 12-15 show characteristic frequency spectra for each of the

four tire types tested. Each figure contains three plots corresponding

to: (1) test tires mounted at all ten wheel positions during a powered

drive-by with the Army vehicle, (2) test tires mounted at all ten wheel

positions during a coast-by (engine shut off) with the Army vehicle, and

(3) a coast-by with the commercial vehicle with test tires at the four

wheel positions on the drive axle and quiet rib tires on the steering

axle. In all cases the vehicles were loaded and operated at a speed of

40 mph while running on a concrete surface.

A maximum exists in all the drive-by spectra at 100-125 Hz. This

is the fundamental associated with the vehicle exhaust noise. In general,

this peak is approximately 30 dB above the sound pressure level observed

in this frequency band during the coast-by mode. A harmonic of the

exhaust noise fundamental is also observed.

Maxima observed in the coast-by spectra, regardless of whether the

test vehicle was a 6 x 6 military truck or a 4 x 2 commercial truck, appear

to be attributable to the major tread element spacing and the rotational

rate of the tire. The fundamental frequency in the one-third octave band

spectra can be predicted on the basis of tread spacing and vehicle velocity

according to the following relationship:

£ = (1) a where, f = fundamental frequency, Hz

V = vehicle speed, mph

a = tread element spacing, in.

Table 2 shows the major tread spacing for each tire, the predicted frequency

of the fundamental based on major tread spacing, and the one-third octave

frequency band in which the fundamental was actually measured. The calculations are based on a vehicle speed of 40 mph. All of the test tires,

with the exception of tire-A, had randomized tread-pattern pitch lengths

as evidenced by the range in values for the tread spacing for these tires

shown in Table 2. In all cases the maximum in the one-third octave band

spectra was predictable on the basis of the tread spacing. This does not

imply, however, that other noise generation mechanisms are not also major

contributors to the overall noise levels observed. Our knowledge of tire

noise generation mechanisms is limited at present and, therefore, we must

be cautious in drawing any far-reaching conclusions.

A comparison of coast-by spectral data from the 4x2 commercial truck

and the 6x6 military truck seems to indicate that the 6x6 Army truck can serve as a test vehicle during tire tests. At the onset of this program,

there was some question as to the suitability of this 6x6 vehicle as a test truck due to the suspicion that the drive train/differential noise

was much higher for military vehicles than for comparable commercial

vehicles. Thus, even in a coast-by mode, the tire noise would be masked

by the inherent vehicle noise.

20
CD

CM

as

CD

GO

00

UJ

CC

QO

<

CO

o

o

100

90

80

70

60

50

40

30

1—r—i—r-|

TIRE A

T—

I—r~i—I

n—

r

1—r~r-i—rn—i—r~r T

0.1

• ARMY DRIVE-BY

A ARMY COAST-BY

o RYDER COAST-BY

1.0

FREQUENCY, kHz

10.0

Figure 12. One-third octave band frequency spectra for tire-A as measured at 50 feet corresponding to operation of the

Army vehicle (10 test tires) in drive-by and coast-by

modes and the commercial vehicle (4 test tires) in a coast-by mode. The vehicles were loaded and operated

at a speed of 40 mph while running on a concrete surface.

21
Figure 13. One-third octave band frequency spectra for tire-B as measured at 50 feet corresponding to operation of the

Army vehicle (10 test tires) in drive-by and coast-by

modes and the commercial vehicle (4 test tires) in a coast-by node. The vehicles were loaded and operated

at a speed of 40 mph while running on a concrete surface.

22
100 I I I t

I

I I I I II TIRE C

90 -

80

70

60

50 -

40

I I

! I I I

I I I I I t

I

• ARMY DRIVE-BY

A ARMY COAST-BY

o RYDER COAST-BY

30 MM I I I I I I I I I I I I I I I I I I M I

0.1 1.0

FREQUENCY, kHz

10.0

Figure 14. One-third octave band frequency spectra for tire-C as measured at 50 feet corresponding to operation of the

Army vehicle (10 test tires) in drive-by and coast-by

modes and the commercial vehicle (4 test tires) in a coast-by mode. The vehicles were loaded and operated

at a speed of 40 mph while running on a concrete surface.

23
CO o

CD

CD

CO

GO

UJ

OC

Q-

<

CO

CJ) o

o

OC

100

90

80

70

60

50

40

30

TIRE D

• ARMY DRIVE-BY

A ARMY COAST-BY

o RYDER COAST-BY

II I I I I I I I I I I I I I I M I I I I I I I 0.1 1.0 10.0

FREQUENCY, kHz

Figure 15. One-third octave band frequency spectra for tire-D as measured at 50 feet corresponding to operation of the

Army vehicle (10 test tires) in drive-by and coast-by

modes and the commercial vehicle (4 test tires) in a coast-by mode. The vehicles were loaded and operated

at a speed of 40 mph while running on a concrete surface.

24
Major Tread

Spacing, in.

Predicted

Fundamental

Frequency, Hz

•Center Frequency

of One-third Octave

Band Containing the

Measured Fundamental

Frequency, Hz

Tire-A 3.250 217 200

Tire-B 2.000-2.375 296-352 315

Tire-C 2.437-2.875 245-289 315

Tire-D 2.875-3.375 209-245 250

Table 2. Predicted and measured fundamental tire noise frequencies

based on major tread spacing considerations corresponding

to a vehicle speed of 40 mph.

In order to investigate the effect of tread design and speed on generated

noise levels a plot of maximum A-weighted sound level versus speed with tread

design as a variable was developed (Figure 16) . These data represent

measurements at 50 feet for coast-by runs of the loaded 4x2 single-chassis

vehicle on a concrete surface. In every case, an increase in speed resulted

in an increase in the maximum A-weighted sound level. In general, the

increases were on the order of 6-8 dB for speed changes from 40 to 60 mph.

This corresponds to sound level increasing as the third to fourth power

of speed. The obvious exception to this general statement is tire-A which

exhibited an increase of approximately 11 dB over the same speed range.

Tire-A is approximately 2 dB higher than the next noisiest tire (tire-B)

at a speed of 40 mph; however, the difference increases to 6 dB at 60 mph.

Tire-B is approximately 2-2.5 dB noisier than tires-C and -D over the speed

range studied. Tires-C and -D have nearly identical A-weighted sound level versus speed curves, with tire-D being slightly quieter at higher speeds.

It is obvious that the choice of tires based on noise considerations is

dependent on the speed range over which the vehicles are expected to

operate. For well maintained trucks equipped with reasonable exhaust

mufflers, tire noise can become a significant contributor to overall

vehicle noise at speeds as low as 35-40 mph and the predominate contributor at speeds of 50 mph and higher. Also, these data are for new

tires and in general an increase in the noise level is observed between

the new and half-worn states of tire wear. Depending on the tire type,

the increase can be significant. At this time no knowledge of the

magnitude of the increase which could be expected for these tires exists.

25
SPEED, MPH

50

CO

cvias

CQ

CD

CO

CD

X

<

60 70 80 90

SPEED, KM/HR

100

Figure 16. Maximum A-weighted sound level, as measured at 50 feet, versus speed for a loaded 4x2 single-chassis vehicle

coast-by on a concrete surface. Various types of new

tires were mounted on the drive axle.

26
Since Army vehicles are operated on public roads at typical highway

speeds (when not in convoy) , there exists a need to establish the high speed

tire noise contribution to overall vehicle noise levels. Ideally, one would

like to test the Army vehicle (10 test tires) under full load at speeds of

50 - 60 mph. Practical limitations did not allow such a test. The maximum

attainable speed for the Army vehicle under full load in the available

runway length (slightly greater than one mile) was 45 mph. For this reason,

all of the high speed data in this report are based on tests utilizing the

commercial single-chassis vehicle which was capable of attaining speeds of

60 mph within the available space limitations.

The impact of these practical constraints is shown by the data in

Figures 17 and 18 where the maximum A-weighted sound levels versus speed

as measured at the 50 foot microphone are plotted for tires-C and-D under

the following test conditions: (1) driven Army vehicle (10 test tires)

(2) coasting Army vehicle (10 test tires), and (3) coasting commercial

vehicle (4 test tires). The vehicles were loaded and ran on a concrete

surface.

The difference in sound level between the coasting Army truck and the

coasting commercial truck is approximately 3 dB which is to be expected

since the Army truck has an additional rear axle and therefore has twice the

number of rear tires. It should be further noted that all tires are not

characterized by a linear relationship between noise level and vehicle speed.

For instance, the characteristic noise level versus speed curve for tire-C

is linear over the speed range from 40 - 60 mph (a 3.5 dB increase in sound

level is observed for each 10 mph increase in speed) , while tire-D does not

possess such a characteristic. Noise levels for tire-D increase at a given

rate (5 dB/10 mph) between 40 and 50 mph and at a different rate (1 dB/10 mph)

between 50 and 60 mph. The fact that a slope is defined over a limited

speed range at lower speeds, does not allow one to extrapolate that trend in

order to predict the noise level expected at higher speeds.

Load is another important parameter which influences tire noise levels.

Past studies [1,2] have shown that changes in load can significantly affect

the noise level generated by tires with cross-bar tread patterns while noise

from tires with rib type tread patterns were relatively unaffected by load

changes. In the case of cross-bar tires, as the load is increased, more of

the tire load is carried on the outer edges of the tread where more drastic

interruptions in tread pattern exist. Since the rib pattern is the same across the width of the tire, it may not be as important- how much load is

carried on the outer edges of the tire.

Figure 19 shows the effect of load on tire noise observed during this

study based on 40 mph coast-by data for 6x6 military vehicle. A wide

variation in noise level for nominally identical test conditions was observed

in the data for tire-B. Thus the slope of the A-weighted sound level versus

tire load curve is questionable for this tire. Tire-A (the standard Army

tire), which is cross-bar in nature, behaved as would be expected on the

basis of the existing tire noise data base.

27
90

40

SPEED, MPH

50 60

CD

CD

CM

O)

CQ

80

o

CO

CD

70

X

<

60

I r TIRE C

o DRIVEN (ARMY)

A COAST-BY (ARMY)

• COAST-BY (RYDER)

60 70 80 90

SPEED, KM/HR

100

Figure 17. Maximum A-weighted sound level, as measured at 50 feet, versus speed for tire-C corresponding to operation of

the Army vehicle (10 test tires) in drive-by and coast-

. : by modes and the commercial vehicle (4 test tires) in a coast-by mode. The vehicles were loaded and ran on a concrete surface.

28
90

40

SPEED, MPH

50

CO Q.

CD

CVJ

CL>

CO

-a 80

o

CO

CD

70

X

<

60

—1

1 1 1 r TIRE D

o DRIVEN (ARMY)

A COAST-BY (ARMY)

• COAST-BY (RYDER)

60

~r60 70 80 90

SPEED, KM/HR

100

Figure 18. Maximum A-weighted sound level, as measured at 50 feet, versus speed for tire-D corresponding to operation of

the Army vehicle (10 test tires) in drive-by and coastby modes and the commercial vehicle (4 test tires) in a coast-by mode. The vehicles were loaded and ran on a concrete surface.

29
90

CO Ocu

CO

80

o

CO

CD

70

X

<

60

LOAD PER TIRE, Ibf

1000 2000 3000

1 1 1

1 1 1 1 I 1

o TIRE A

TIRE B • TIRE C

A TIRF 1 1 n L nu

— A

A ^^^^^

1 1 1 4000 8000 12000

LOAD PER TIRE, N

16000

ure 19. Maximum A-weighted sound level, as measured at 50 feet versus the load per drive axle tire for a 40 mph coast

of the 6x6 military vehicle on a concrete surface.

30
An increase in sound level was observed with increasing load. Of special

interest is the fact that tire-A is the quietest tire when unloaded and even when loaded is only 1-2 dB noisier than tires-C and -D (at a speed of

40 mph) . As noted earlier (Figure 16) , on the basis of coast-by data

utilizing the commercial vehicle, tire-A was the noisiest tire over the speed

range 40-60 mph. A decrease in sound level was observed with an increase

in load for tires-C and -D (Figure 19) . The decrease was small (less than

1 dB) and is probably attributable to the fact that under load the drive

train noise is slightly lower. It should further be pointed out that the

tires in this study were not loaded in the same manner as in previous

studies. As discussed previously in this report, the commercial vehicle

was loaded such that the load per drive axle tire corresponded to the load

per drive axle tire observed for the loaded Army truck. The military and

commercial test vehicles had the same gross vehicle weight capacity (approximately

25,000 pounds), but since the military vehicle had an additional drive axle,

the load per tire was about one-half the load that would be typical in

normal commercial usage. This difference in loading explains the apparent

discrepency between the data of Figures 16 and 19.

Based on the data obtained during the conduct of this test program,

the following conclusions can be drawn:

The data base established during this study provides the basis

for comparison of the tire noise generated by military and

commercial truck tires. There is a need to do some testing with a 4x2 single-chassis vehicle to ensure a tie with the extensive

data base on tire noise which now exists in the public domain.

It is possible to select tires which produce lower noise levels

than the standard Army tire. Since the magnitude of the tire

noise problem increases with spaed, it is important to consider

the typical operating cycle of these vehicles. Tires acceptable

from a noise level standpoint at low speeds may be totally

unacceptable at typical highway speeds.

The 6x6 military truck can serve as a test vehicle for coasting tire

tests; however, under full tire load an extremely long test site

would be necessary to allow for the vehicle to attain speeds of

50-60 mph.

For these particular military vehicles the engine/exhaust noise

is such that tire noise is not a problem (at present) over the

speed range studied (35-45 mph) . It must be noted that the

test tires in this study were all new. No knowledge exists at this time

to predict the expected noise level for these tires over their wear

cycle.

Load is also a factor in the choice of tires, for instance the

standard military tire which is the noisiest tire under load at

higher speed, is actually the quietest tire under no-load conditions

at a vehicle speed of 40 mph.

31
4. Appendix A

$ Parametric Study Results

The tabulated values of A-weighted sound level (maximum rms value

of the A-weighted sound level during a passby) as measured at the

two microphone locations are reported. The data are assembled according

to tread design and loading of the test tires and the speed and

operation mode of the test vehicle. A photograph showing the characteristic tread element pattern is presented for each of the tire types

tested. Also included are the average tread depth and Shore hardness

values characteristic of these tires.

32
Figure A-1. Characteristic tread element pattern of tire

A (standard Army tire) . The nominal new tread

depth for this tire was 21/32 inch. Shore

hardness values ranging from 51-60 were observed

with the average being 57.

33
TIRE A (STANDARD ARl-IY TIRE)

Army Truck Loaded - Drive-by

A-weighted Sound Levels, dB

Microphone

Location, ft. 35 35

Nominal

35

Speed, mph

40 40 45 45 45

25

50

85.4

78.8

84.8

78.8

86.8 85.8 86.2

82.2 81.8

89.0

84.2

87.8

82.4 83.8

Army Truck Unloaded - Drive-By

A-Weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed, mph

40 40 45 45

25

50

87.4 86.8 88.4 88.4

81.4 80.8 82.8 82.8

Army Truck Loaded - Coast-by

A-Weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed, mph

35 35 40 40 45 45 45

25

50

76.0 75.8 77.2 77.6 82.0 81.4 80.4

71.2 71.8 73.0 74.6 75.0 77.0 76.8

Army Truck Unloaded - Coast-by

A-Weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed, mph

40 40 45 45

25

50

74.0 74.2 76.0 78.6

69.2 69.6 74.0 73.6

Ryder Truck Loaded - Coast-By

A-Weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed , mph

40 40 40 50 50 50 60 60

25

50

75.8 78.2 77.2 87.0 84.8 86.0 89.0 85.8

70.8 72.8 73.4 82.4 82.6 82.6 82.4 84.2

34
Figure A-2. Characteristic tread element pattern of tire

B (commercial rib tire) . The nominal new

tread depth for this tire was 16/32 inch.

Shore hardness values ranging from 60-64 were observed with the average being 61.

35

I
TIRE B (COMMERCIAL RIB TIRE)

Army Truck Loaded - Drive-by

A-Weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed , mph

35 35 40 40 45 45

25

50

85.0 85.8 86.0 86.2 88.8 87.2

80.4 80.8 81.0 81.2 83.2 82.2

Army Truck Unloaded - Drive-by

A-Weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed, mph

40 40 45 45

25

50_

86.0 85.8 88.4 87.2

81.0 81.2 82.8 83.0

Army Truck Loaded - Coast-by

A-Weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed, mph

35 35 40 40 45 45

25

50

79.0 79.0 81.6 80.0 83.4 81.0

73.6 73.2 78.6 75.2 75.4 76.8

Army Truck Unloaded - Coast-by

A-Weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed, mph

40 40 45 45

25

50

78.0 79.6 80.8 80.4

73.6 76.8 74.6 75.8

Ryder Truck Loaded - Coast-by

A-Weighted Sound Levels, dB

Microphone

Location, ft.

«i _ —

Nominal Speed, mph

40 40 50 50 60 60

25

50

75.4 75.8 78.6 79.4 80.6 81.0

71.6 70.8 73.4 75.8 77.8 77.0

36
Figure A-3. Characteristic tread element pattern of tire

C (Army. retread tire) . The nominal new tread

depth for this tire was 20/32 inch. Shore

hardness values ranging from 58-64 were observed

with the average being 62.

37
TIRE C (ARl^ RETREAD TIRE)

Army Truck Loaded - Drive-by

A-weighted Sound Levels , dB

Microphone

Location, ft.

Nominal Speed, mph

35 35 40 40 45 45

25

50

83.4 82.8 85.8 84.8 86.0 87.2

77.4 77.6 80.6 80.6 81.4 81.8

Army Truck Unloaded - Drive-by

A-Weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed, mph

40 40 45 45

25

50

85.8 85.2 37.2 89.0

81.0 80.6 83.8 83.4

Army Truck Loaded - Coast-by

A-Weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed, mph

35 35 40 40 45 45

25

50

76.6 75.4 79.2 78.4 76.4 76.6

71.4 71.4 71.4 71.4 72.6 73.2

Army Truck Unloaded - Coast-by

A-Weighted Sound Levels, dB

Microphone

Locat ion , ft.

Nominal Speed, mph

40 40 45 45

25

50

75.4 74.6 76.4 77.2

72.0 71.6 73.2 72.0

Ryder Truck Loaded - Coast-by

A-weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed , mph

40 40 50 50 60 60

25

50

72.2 73.0 75.6 76.6 79.0 79.2

68.2 69.2 72.4 71.6 75.6 75.0

38
Figure A-4. Characteristic tread element pattern of tire

D (commercial cross-bar tire) . The nominal new tread depth for this tire was 19/32 inch.

Shore hardness values ranging from 61-66 were observed with the average being 64.

39
TIRE D (COMMERCIAL CROSS-BAR TIRE)

Army Truck Loaded - Drive-by

A-Weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed, mph

35 35 40 40 45 45

25

50

83.6 81.8 84.8 83.8 85.6 85.6

77.6 76.2 80.8 78.6 81.4 80.0

Army Truck Unloaded - Drive-by

A-Weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed, mph

40 40 45 45

25

50

85.6 86.4 88.2 88.4

80.6 80.8 83.2 82.4

Army Truck Loaded - Coast-by

A-Weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed, mph

35 35 40 40 45 45

25

50

76.0 75.6 77.8 78.6 80.6 81.6

71.2 71.6 73.0 72.4 75.6 73.0

Army Truck Unloaded - Coast-by

A-Weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed, mph

40 40 45 45

25

50

78.0 77.8 79.4 78.2

73.2 72.8 74.6 74.2

Ryder Truck Loaded - Coast-by

A-Weighted Sound Levels, dB

Microphone

Location, ft.

Nominal Speed, mph

40 40 50 50 * 60 60

25

50

73.2

68.6

72.6

68.0

78.0

73.0

77.6

73.6

80.0

74.6

79.0

73.4

40
5. Appendix B

Instrument Descriptions

Unless otherwise stated, all instruments are Brliel and Kjaer^^

(B & K).

Type UA 0207 Windscreen : When a microphone is exposed to wind, the

turbulence created around the microphone and wind velocity

variations cause a noise to be generated due to a variation of

air pressure on the diaphragm. To reduce this extraneous wind

noise, a spherical windscreen constructed of specially prepared

porous polyurethane sponge was utilized.

Type 4220 Pistonphone : This instrument is a small, battery-operated

precision sound source which provides quick and accurate direct

calibration of sound measuring equipment. When fitted to a B & K

microphone, the pistonphone produces a sound pressure level of

124 +0.2 dB, re 20 yPa, at a frequency of 250 Hz + 1% (controlled by means of a transistor circuit) . Maximum stability

and a very low distortion (less than 3% at 250 Hz) result from

the piston arrangement consisting of two pistons moving in

opposite phase. The calibration of the pistonphone is performed

at normal atmospheric pressure. Ambient pressure corrections

are necessary for pressures other than 760 mm Hg. This calibration

is not influenced by relative humidities up to 100% or temperatures

within the range of 0 - 60°C (32 - 140°F)

.

IHcrophone : When one speaks of a microphone, a three part minimum

system is implied: (1) a protecting grid; (2) a condenser

microphone cartridge; and (3) a microphone preamplifier or cathode follower. For this testing the following components were utilized.

Type 4161 One-inch Condenser Microphone : The one-inch free-field

condenser microphone is a type possessing relatively high

sensitivity and covering a range of applicability from 2 Hz to

18 kHz (frequency range) and 15 dB to 140 dB (dynamic range)

.

A feature of these microphones is long-term stability under a varie

of environmental conditions and insensitivity to temperature

variations. Condenser microphones, in addition.

— Commercial instruments are identified in this report in order to

adequately specify the experimental procedure. In no case does such

identification imply recommendation or endorsement by the National

Bureau of Standards, nor does it imply that the equipment identified

is necessarily the best available for the purpose.

41
were chosen because of their higher dynamic range, ease in calibration, and uniform frequency response. The cartridge which

houses the microphone diaphragm is protected by the grid on one side and on the other is normally screwed onto the preamplifier.

This particular microphone vents into a dehumidifier (which is

located between the microphone and the preamplifier) rather than

air. The silica gel drys the air used by the microphone for

pressure equalization.

Type UA 0310 Dehumidifier : The dehumidifier is designed to be mounted

between the 4161 condenser microphone and its amplifier. It

contains silica gel to dry the air used by the microphone for

pressure equalization. When used in 100% relative humidity

situations, the silica gel requires drying approximately once a month. The drying is accomplished by heating the silica gel for some hours at a temperature of 100°C.

Type 2619 Half-inch FET Preamplifier : This preamplifier features a very high input impedance field-effect transistor, which represents

virtually no load to the microphone cartridge. To mate the 2619

with the 4161 a suitable adapter must be utilized (model DB-0375)

.

Built into the preamplifier itself is a 6.3V heating coil to prevent

condensation when operation must be carried out in cold or humid

environments

.

The above described microphone subassembly provides reliable

operation over a wide range of temperature, humidity, and vibration

and allows precision sound pressure measurements to be made over a wide frequency and dynamic range.

Type 2804 Two Channel Power Supply : This unit is a portable, batterydriven supply unit designed to provide the necessary polarization

voltage for condenser microphones and their accompanying preamplifiers.

NBS Field Instrumentation : To facilitate data acquisition in the field,

this battery-powered instrumentation system was designed and fabricated by NBS specifically for application to passby noise measurements. The unit contains a 60 dB variable gain amplifier which

provides the needed signal conditioning (amplification/attenuation)

prior to recording. In addition to recording the signal, weighting

networks and hold circuitry are included to allow for direct reading

of the linear and A-weighted fast response sound level observed

during the passby. The hold circuitry and weighting networks meet

42
the Type 1 requirements for the fast dynamic characteristic and

the A-weighting response respectively of American National Standard

Specification for Sound Level Meters, SI. 4-1971. The linear hold

circuitry provides an indication as to whether or not a tape channel

had become saturated (i.e., the signal had exceeded the dynamic

range of the recorder) and thus the data were not acceptable.

The A-weighted hold circuitry allowfed for direct-reading of the

A-weighted sound level observed during a passby without the necessity

for returning the tape recordings to the laboratory for reduction

and analysis.

Nagra Model SJ Tape Recorder : This unit is a portable 3- track (1/4

inch magnetic) tape recorder with two high quality amplitude

modulated sound tracks (25 Hz to 35 kHz), plus a third FM track

for recording very low frequencies (dc to 4 kHz), commentary,

synchronization signals or timing information. The instrument

records and reproduces at four speeds — 15, 7-1/2, 3-3/4 and 1-1/2

ips. The two- amplitude modulated channels can be fed from separate

microphone inputs. The volume is controlled by separate step

attenuators.

Type 3347 Real Time Analyzer : The real time analyzer is composed of

two basic units: (1) type 2130 frequency analyzer and (2) type

4710 control and display unit.

The 2130 contains a measuring amplifier, filter channels with 1/3-

octave bandwidth, a linear channel, weighting channels, true RMS

detectors, and the synchronization system for scanning the channels.

The analyzer contains 38 parallel channels. 33 of these channels

contain 1/3-octave filters with center frequencies from 12.5 Hz to

20 kHz. The remaining five channels are reserved for the four

weighting network filters — A, B, C, and D — and one linear

response channel.

The 4710 contains the circuitry for the 12-inch cathode ray tube

(CRT), the Nixie displays, digital readout, and the logic control.

The logic control section controls the analog/digital conversion and

the communication sequence for external systems, as well as the

internal synchronization in the 3347 during display or read-out

modes.

The level in each channel can be read in dB directly on the

screen, while a Nixie display shows the output level of any

selected channel. This channel is indicated on the CRT as a brighter trace. The complete channel display is renewed every

20 msec.

43
Outputs are provided for both analog instruments (X-Y or level

recorders) as well as digital (on-line computer or tape puncher)

.

The digital output is in binary coded decimal (BCD) code.

Time constants may be selected from 20 msec to 20 sec so that

confidence limits can be maintained throughout the frequency

range.

Model 704 Raytheon Computer System : The Raytheon 704 computer system

is a general purpose digital system that provides a 16-bit central

processor unit with 900 nanosecond cycle time for on-line, real

time applications.

The hardware configuration includes an 8K (expandable to 32K)

memory system, direct input/output bus, automatic priority interrupt,

direct and indexed addressing, and byte and word addressing and

instructions. Standard peripherals such as high speed paper tape,

ASR-33 teletype, card equipment, and a magnetic tape unit are also

included

.

44
6. Appendix C

Concrete Test Section Substrate Details^'

Substrate details discussed in this appendix are not the exact details

of the test pavements; however, they represent the specifications followed

in the construction of the pavements. Since surface details are most

important when considering the effect of the pavement on noise generation

characteristics of tires, special note should be taken of the discussion

of surface finishing techniques.

The surface utilized for these tests consists of a wearing surface

of reinforced air-entrained Portland Cement concrete pavement with two

types of finishes on a suitably prepared subbase.

1. Materials

The cement used in this work was a standard brand of Portland cement

with air-entraining properties. The air-entrained cement conformed to

A.S.T.M. designation C-175.

In no case was the use of pit run or naturally mixed coarse aggregates permitted. Naturally mixed aggregates were in every case

screened and washed and all fine and coarse aggregates were stored

separately and kept clean. In no case were aggregates containing

lumps of frozen or partially cemented material used.

The coarse aggregate conformed to the requirements of A.A.S.H.O.

Specification M-80. Also, at least sixty percent of the gravel aggregate

had at least one fractured face. The coarse aggregate had no more than

one percent of material removable by the decantation test, using

A.A.S.H.O. Method T-11 nor more than one percent of shale, nor more

than one percent of clay lumps. Chert did not exceed one percent. The

total of shale, coal clay lumps, chert, soft fragments, and other

deleterious materials did not exceed five percent. The coarse aggregate did not show evidence of disintegration nor show a total loss

greater than twelve percent when subjected to five cycles of the sodium

sulfate soundness test using A.A.S.H.O. Method T-104.

— Details of the composition of this test section were taken from a National Aeronautics and Space Administration, Wallops Station, Virginia,

Specification numbered P-1643, entitled "Modification to Runway 4-22", and

dated April 18, 1967.

45
The coarse aggregate conformed to the following gradations:

Sieve Size

Square Mesh

Percent Passing by Weight

Gradation A Gradation B

2 inch

11/2 inch

1 inch

100

90-100

20-55

0-15

0-15

100

90-100

20-55

0-10

0-5

3/4 inch

3/8 inch

No. 4

No. 8

The coarse aggregate were batched in two separate sizes which

could be varied within a range from forty to sixty percent by weight

to secure the most desirable and uniform gradation of the combined mix.

The fine aggregates conformed to the requirements of A.A.S.H.O.

Specification M-6.

When subjected to five cycles of the sodium sulfate soundness test

using A.A.S.H.O. Method T-104, the fine aggregate had a total loss less

than ten percent by weight. It also contained less than three percent

of material removable by the decantation test, using A.A.S.H.O. Method

T-11. Permissible percentages of shale, clay lumps, etc. were the same

as for the coarse aggregate.

The fine aggregate was well graded from fine to coarse and met

the following gradation requirements, using A.A.S.H.O. Method T-27.

Sieve Designation (Square Mesh) Percentage Passing by Weight

The water used in the concrete and for curing was clean, clear, and

free of injurious amounts of sewage, oil, acid, strong alkalies, or vegetable matter, and, also, free of clay and loam.

2. Composition of Mixture

The weights of fine and coarse aggregate and the quantity of water

bag of cement were determined from the weights given in the following

table:

3/8 inch 100

No. 4

No. 16

No. 30

No. 50

No. 100

95-100

45-80

25-55

10-30

2-10

46
Type of

) Minimum Cement

|

Maximum

1 Weights in pounds of dry

t Slump ! Aggregate Content Per \ Net Water ) Aggregate per bag of cement Range, i Cubic Yard of ; Concrete

I

Content

,

Gallons

Per Bag

1 Fine

; Aggregate

I

Coarse

Aggregate

Total Inches j

i

j -

Gravel

j 5.8 bags 5 1/2 ' 169 394 563

j 1 1/2 j

Crushed

j

Stone 5.8 bags 5 3/4 195 366 561 ; 1 1/2 I

Yield tests in accordance with ASTM Specification C-138 were made to

determine the cement content per cubic yard of concrete. If at any time,

the content was found to be less than that specified, the batch weights

were reduced until the requirements were met.

Air-entrained Portland cement concrete causes a bulking of the mortar

of the concrete due to the amount of entrained air . To keep the cement

factor specified at the correct amount, the weight of the fine aggregate

was reduced as required. The air content of the fresh concrete was determined by ASTM Designation C-231.

The proportions in the above table produced a concrete of satisfactory

plasticity and workability which attained, after fourteen days, a minimum

compressive strength of 3000 pounds per square inch and a modulus of

rupture of 700 pounds per square inch after twenty-one days. The specimens were cured and tested in accordance with A.A.S.H.O. Methods T-22, T-23

and T-97.

3. Placing and Finishing

The concrete was deposited and spread so that any segregation would

be corrected and a uniform layer of concrete would be produced whose thickness was approximately one inch greater than that required for the finished

pavement

.

After the first operation of the finishing machine, additional

concrete was added to all low places and the concrete rescreeded.

After the final pass of the finishing machine, the placing of

all joints longitudinal and transverse, and before the concrete had

started to dry, the surface of the pavement was finished with a longitudinal float.

After the concrete was brought to the required grade, contour, and

smoothness, it was finished by means of a finishing belt. The belt was

eight to twelve inches in width and at least two feet longer than the

47
width of the pavement section to be finished. On the "C" (smooth)

finish section of pavement a belt of canvas composition was

used

.

48
References for Appendix C

American Society for Testing and Materials, C-175-69> Standard

Specification for Air-Entraining Portland Cement in Part 10 , Book

of ASTM Standards, 1970 (ASTM, Philadelphia, Pennsylvania).

American Association of State H:tghway Officials, M-80-51, Standard

Specification for Portland Cement Concrete , Standard

Specifications for Highway Materials and Methods of Sampling and

Testing, Ninth Edition, 1966 (AASHO, Washington, D. C).

American Association of State Highway Officials, T-104-65, Standard

Method of Test for Soundness of Aggregates by Use of Sodium Sulfate or Magnesium Sulfate , Standard Specifications for Highway Materials and

Methods of Sampling and Testing, Ninth Edition, 1966 (AASHO,

Washington, D. C.)«

American Association of State Highway Officials, M-6-65, Standard

Specification for Fine Aggregate for Portland Cement Concrete , Standard Specifications for Highway Materials and Methods of Sampling

and Testing, Ninth Edition, 1966 (AASHO, Washington, D. C.)-

American Association of State Highway Officials, T-11-60, Standard

Method of Test for the Amount of Material Finer than No. 200 Sieve

in Aggregate , Standard Specifications for Highway Materials and

Methods of Sampling and Testing, Ninth Edition, 1966 (AASHO,

Washington, D. C).

American Association of State Highway Officials, T-27-60, Standard

Method of Test for Sieve Analysis of Fine and Coarse Aggregates , Standard Specifications for Highway Materials and Methods of Sampling

and Testing, Ninth Edition, 1966 (AASHO, Washington, D. C).

American Society of Testing and Materials, C-138-63 (1969 ),

Standard Method of Test for Weight per Cubic Foot, Yield, and Air

Content (Gravimetric) of Concrete in Part 10 , Book of ASTM Standards,

1970, (ASTM, Philadelphia, Pennsylvania).

American Society for Testing and Materials, C-231-68, Standard Method

of Test for the Air Content of Freshly Mixed Concrete by the Pressure

Method , Book of ASTM Standards, 1970 (ASTM, Philadelphia, Pennsylvania)

American Association of State Highway Officials, T-22-64, Standard

Method of Test for Compressive Strength of Molded Concrete Cylinders

(ASTM designation: C-39-66) , Standard Specifications for Highway

Materials and Methods of Sampling and Testing, Ninth Edition,

1966 (AASHO, Washington, D. C).

49
[10] American Association of State Highway Officials, T-23-65, Standard

Method for Making and Curing Concrete Compression and Flexural Test

Specimens in the Field , Standard Specifications for Highway

Materials and Methods of Sampling and Testing, Ninth Edition, 1966

(AASHO, Washington, D.C.).

[11] American Association of State Highway Officials, T-97-64, Standard

Method of Test for Flexural Strength of Concrete (Using Simple

Beam with Third-Point Loading) (ASTM designation: C-78-64)

,

Standard Specifications for Highway Materials and Methods of Sampling

and Testing, Ninth Edition, 1966 (AASHO, Washington, D.C.).

50
7. References

Anon., Truck noise-I, peak A-weighted sound levels due to truck

tires, (National Bureau of Standards, Washington, D. C, 1970)

Department of Transportation Report OST-ONA-71-9

.

Leasure, Jr., W. A., Corley, D. M. , Flynn, D. R. and Forrer, J. S.

Addendum truck noise-I, peak A-weighted sound levels due to truck

tires, (National Bureau of Standards, Washington, D. C, 1972),

Department of Transportation Report OST/TST-72-1

.

American Society for Testing and Materials, D 2240-68, Standard

Method of Test for Indentation Hardness of Rubber and Plastics by

Means of a Durometer in Part 27, 28 , Book of ASTM Standards, 1970

(ASTM, Philadelphia, Pe.insylvania) .

51
Acknowledgement s

The authors would like to recognize the contributions made by the

following organizations which have greatly aided this research program:

The U. S- Army Tank-Automotive Command, especially Mr. D. W. Rees and

Mr. W. Bremerkamp, and the staff of the Wallops Station Facility of the

National Aeronautics and Space Administration. Special thanks go to

Mr. G. Godwin who was our liaison at Wallops Station.

The authors also express appreciation to the following members of the

staff of the Applied Acoustics Section: Mrs. Mary L. Friend and Mrs. Marilyn A.

Cadoff for their assistance in the assembly of the report, Mr. D. S. Blomquist

and Mr. C. 0. Shoemaker for instrumentation design and fabrication, and

Mr. D. R. Flynn and Mr. W. H. Close (Office of Noise Abatement, U.S., Department of Transportation) for their review and comments.

52
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