Mineral Fillers in Asphalt Paving Mixtures B . F . KALLAS, V. P. PUZINAUSKAS, and H . C. KRIEGER, The Asphalt Institute, College Park, Maryland

This paper describes a continuation of investigations on effects of various mineral f i l l e r s on properties of asphalt paving mijctures. Previous studies indicated that introduction of varying amounts and types of mineral f i l l e r s into a paving mixture may greatly influence compaction characteristics and therefore resultant volu­metric proportions and test properties of mixtures compacted with a constant compactive ef for t .

Mechanical gyratory compaction procedures using variable compactive efforts were developed to compact laboratory test specimens containing constant volume proportions of mineral aggregates and air regardless of types and amounts of mineral f i l l e r s and asphalt used. The procedures permitted an evalu­ation of the effects of mineral f i l l e r s and asphalt on compaction characteristics of the paving mixtures. The relative effects of mineral f i l l e r and asphalt on properties of paving mixtures containing constant volume proportions of mixture components were then determined.

Both sand asphalt and asphalt concrete paving mixtures were studied. Mixtures were prepared with no added mineral f i l l e r , and with varying amounts of limestone dust, hydrated l ime, kaolin clay, asbestos, and fu l l e r ' s earth. Varying amounts of different viscosity asphalts were used in the mixtures.

Test results presented and discussed indicate pronounced and varying effects which mineral f i l l e r s and asphalts have on paving mixture properties.

•MINERAL f i l l e r s f o r asphalt paving mixtures consist of fme mineral particles that are added to or are naturally present in the mineral aggregate, and that predominantly pass U. S. Standard Sieve No. 200. As such, they may normally be viewed as a con­tinuation or extension of the mineral aggregate which usually is well-graded and larger than the opening of sieve No. 200. Jn this sense, mineral f i l l e r s are part of the aggregate skeleton of the pavement. They provide contact points between individual particles and, therefore, are generally considered to per form the same function as the coarser particles in resisting stresses imposed on the pavement.

However, the fine particles of mineral f i l l e r may sometimes assume a dual role . Extremely fine particles may be located in the asphalt f i lms that coat the coarser aggregate particles. In this case, mineral f i l l e r s may alter and have an appreciable effect on the apparent viscosity characteristics of the asphalt used in the pavement.

Previous Asphalt Institute Studies (l) exammed a large number of mineral f i l l e r s , and i t was demonstrated that different f i l l e r s affect the properties of asphalt paving mixtures different ly. It was si^gested that such changes in test properties can be associated with changes in viscosity of the f i l ler-asphalt binder containing different f i l l e r s .

However, direct correlation between f i l ler-asphalt binder viscosity and compacted mixture properties was d i f f i cu l t . The reason fo r this was the variable effects of different f i l l e r s on compaction or densification characteristics of the specimens. This

resulted in different volumetric proportions of mixture components when specimens were compacted by constant compactive e f for t .

This paper considers correlation between f i l ler-asphalt binder viscosity and test properties of specimens that were compacted to nearly constant volume proportions of a l l mixture components, regardless of the f i l l e r used. Such compaction was ac­complished by the use of a mechanical gyratory compactor. The effects of three different asphalt cements on properties of compacted paving mixtures were also ex­amined. The three asphalts varied widely in consistency characteristics. Additionally, densification characteristics as affected by asphalts and f i l l e r s were evaluated. It is believed that the use of a mechanical gyratory compactor fo r these studies contributes substantially to a clearer understanding of the function of different types of mineral f i l l e r s in asphalt paving mixtures.

DESCRIPTION OF MATERIALS

Asphalt

Three asphalts used in this study varied widely in consistency characteristics. Their properties are given in Table 1.

TABLE 1

Asphalt

Property A B C

Penetration at 77 F , 100 g, 5 sec 222 91 42 Softening point, r ing and bal l (°F) 104 118 143 DuctiUty at 77 F (cm) 75 150+ 13 Specific gravity, 77/77 F 1.001 1.022 1.022 Viscosity: (poises)

At 77 F 1.60x10* 19.0x10* 65.75x10* At 140 F 2.54x10* 26.00x10* 110.79x10* At 275 F 1.72 4.14 6.58

Asphalts are identified by the letter designations shown in the table.

Mineral Aggregates Two mineral aggregates (natural sand and trap rock), both f r o m commercial

sources in Maryland, were used in the preparation of test specimens. The natural sand was used fo r sheet asphalt mixtures. It was predominantly quartz,

with particles of medium angularity. The sand was poorly graded and contamed 5 percent of natural dust passing sieve No. 200.

The same sand, combined with trap rock was used for dense-graded asphalt con­crete mixtures. However, fo r that purpose i t was necessary to supplement the poorly graded natural sand with additional sand fractions between the No. 8 and No. 30 sieves. The trap rock had highly angular particles with rough surface texture.

Gradations and specific gravities of sand and trap rock are given in Table 2.

Mineral F i l le rs Five mineral f i l l e r s : limestone dust, kaolin clay, hydrated l ime, short-fibered

asbestos, and fu l l e r ' s earth were studied. These f i l l e r s were used in previous Asphalt Institute studies, and their selection f o r this study was based on their

TABLE 2

Sand

Sieve Size Total % Passing

Trap Rock

Sieve Size Total i Passing

No. 16 100 No. 30 93 No. 50 32 No. 100 10 No. 200 5

ASTMapparentsp.gr. 2.655

%-in. y^-in. %-in. No. 4 No. 8

ASTM apparent sp. gr.

100 83.3 66.6 33.3 0.0 3.103

KAOLIN C L A Y

/ v ^ H Y D R A T E D / / 1 ihjr- /

^ / / F U L L E R ^ E A R T H

T Linnt -T

— L I M E S T O N E [ )UST

100

90

80 z o 70 I U) 111 60 N in z 50 < I t- 40 UJ _i _i 30 < 30

ss 20

10

0 001 005 01

P A R T I C L E S E E IN MM 05

Figure 1. Particle-size distribution of mineral f i l l e r s .

TABLE 3 PROPERTIES OF MINERAL FILLERS

Filler Specific Gravity

Hygroscopic Moisture

Content (̂ ) Ignition Loss (?-) pH

Specific Surface Area

(cm V gm)

Limestone dust 2,746 0.009 42.8 9.3 3.1 Hydrated lime 2.390 0.80 29.0 12.7 Asbestos 2.550 0.60 13.6 9.1 4.8 Kaolin 2.670 0.75 13.3 5.9 60.0 Fuller's earth 2. 760 5.90 10.3 7.7 24.9

^ q u a l f i l l e r to water weight ratio. Glycerol retention method.

widely varying effects on the viscosity of asphalt and on the test properties of asphalt paving mixtures. Particle-size distributions fo r a l l of the f i l l e r s except asbestos are shown in Figure 1. Properties of these f i l l e r s are given in Table 3.

EXPERIMENTAL PROCEDURES

Proportioning of Materials

Proportioning of materials fo r sheet asphalt test specimens was based on a mix meeting Asphalt Institute Mix Type V m (fine sheet) gradation requirements. For asphalt concrete, a mixture meeting Asphalt Institute Mix Type IV (dense-graded) gradation requirements was used. The aggregate gradations, including limestone dust f i l l e r , f o r both sheet asphalt and the asphalt concrete are shown in Figure 2. Weight and volume proportions of total mixture (aggregate, f i l l e r and asphalt) fo r both types of mixtures are given in Table 4.

The optimum asphalt contents as determined by the Marshall design method in previous studies were used for both mixtures. However, when f i l l e r s or asphalts other than limestone dust or asphalt B were used, adjustments were made so that in a l l cases the same volume proportions were maintained.

Volumetric f i l ler- to-asphal t ratios were varied fo r a l l mixtures. This was done while maintaining constant volumes of aggregate and f i l ler-asphalt binder. However, within this constant volume of f i l ler-asphalt binder, volumetric ratios of f i l l e r to asphalt were varied. j

Mixing

Blending of mixture ingredients was accomplished with a Hobart mechanical mixer (Model N-50). Aggregates and mineral f i l l e r s heated to 325 F were placed in a pre­heated mixing bowl, and a required amount of asphalt heated to 275 F was introduced. Mixing time of I 'A min was used fo r a l l mixtures. Each time an amount of mixture sufficient fo r individual test specimens was prepared. After mixing and before com­paction, mixture temperature ranged between 250 and 265 F.

Compaction of Test Specimens

A mechanical gyratory compactor s imi lar to the one described by McRae and McDaniel (2) was used f o r compaction of a l l test specimens. However, certain modi f i ­cations were made on this apparatus. The compaction mold holder was equipped with

TABLE 4

WEIGHT AND VOLUME PROPORTIONS OF BASIC MIXTURES

Basic Mixture W e i ^ t (iH) Volume (i)

Sheet asphalt: Maryland sand 79.3 67.6 Limestone dust 9.7 8.0 Asphalt 11.0 24.4

Asphalt concrete: Aggregate (Md. 88.4 80.4 trap rock and Md. sand) Limestone dust 6.6 6.5 Asphalt 5.0 13.1

10

100

9 0

8 0

7 0

6 0

5 0

4 0

3 0

2 0

10

0

/ /

S H E E T ASPH

SPHALT :oN : R E T

2 0 0 100 5 0 3 0 16 8 4

U & STANDARD S I E V E NO

3/8" 1/2" 3 /4"

Figure 2. Aggregate gradations for sheet asphalt and asphalt concrete.

a thermostatically controlled electric heater. This allowed maintenance of approxi­mately constant specimen temperatures when additional compaction was applied to specimens at a temperature of 140 F. The compactor also was equipped with a ca l i ­brated dial gauge attached to the lower hydraulic ram. This gauge permitted measure­ment of the heights of specimens to the nearest 0.001 in . at any time during compac­tion. For compaction of a l l specimens, the mechanical gyratory compactor settings of 100-psi ram pressure and l " angle of gyration were used.

Immediately after mixing, the mixture, weighed to the nearest gram, was placed in the compaction mold and compactor-gyrated until predetermined height of specimens was obtained. The weight of mixture was such that after compaction constant volume specimens contained nearly the same volumes of a i r voids, aggregate, and f i l l e r -asphalt binder. The weights of mixture were calculated using ASTM apparent specific gravities fo r a l l mixture components as a basis. Adjustments in mixture weights were required when different f i l l e r s , asphalts, or f i l ler- to-asphal t ratios were used. The difference between the volume of compacted specimens and the sum of solid volumes of mixture ingredients represented the theoretical volume of a i r voids in the specimens. These theoretical volumes of a i r voids were 4.9 percent f o r sheet asphalt specimens, and 5.8 percent for asphalt concrete specimens, both based on the volume of compacted specimens calculated f r o m the diameter of the compaction molds and height of specimens.

In studies of the effects of different f i l l e r s and asphalts on compaction or densifica-tion characteristics of mixtures, specimens were ini t ia l ly compacted as described previously. Additional gyratory compaction was then applied to these specimens. However, the additional compaction was applied at 140 F, using the same compactor settings (rampressure 100psi and l " gyration angle). Additional compaction was continued until predetermined height of specimens was obtained. The predetermined height of specimens was calculated to reduce theoretical a i r void volume of sheet asphalt speci­mens f r o m 4.9 to 3.0 percent, and fo r asphalt concrete specimens f r o m 5. 8 to 4.0 percent.

The number of gyrations required to compact the specimens to constant volumes ini t ia l ly , and after the additional compaction at 140 F, were recorded fo r a l l specimens.

11

These gyrations were used as a cr i ter ion f o r the evaluation of densification characteris­tics of mixture's.

Tests on Compacted Specimens

For each individual mixture, three specimens were prepared. One specimen was used to determine Hyeem stability and cohesiometer values. Marshall stability and flow tests were made on the second specimen. The th i rd specimen was subjected to additional gyratory compaction at a 140 F temperature. Before such testing, bulk volumes of each specimen were determined by the water displacement method.

TEST RESULTS

Test data are given in Tables 5 and 6, respectively, f o r sheet asphalt and asphalt con­crete specimens. Mixture components are given in percent by weight and volume. Volumetric proportions are based on volumes of specimens determined by the water displacement method. Also given are Marshall and Hveem test properties, and the number of compactor revolutions required to compact specimens to constant volumes.

Slight differences in specimen volumes resulted, accounting fo r differences in the calculated a i r void contents, depending on the method used to determine specimen volumes. Volumes based on specimen height indicated by the gyratory compactor and the 4- in. diameter of the compaction molds were about 0. 5 to 1.0 percent greater fo r sheet asphalt and about 2 to 4 percent greater fo r asphalt concrete than volumes determined by the water displacement method. The volumes of water-permeable voids

TABLE 5 SHEET ASPHALT

Filter to Speci­Asphalt Mix Composition Specimen Volume men No. d

Filler Asphalt Ratio Percent by Weight Proportli •ns' (%) Unit Compac­ Marshall Hveem Asphalt (F/A) dt Total Mix Air Weight*

(lb/ft*) tion Stab,

(lb) Flow

(1/100 in.) Stab. Cohes.

by Vol. Agg. Filler Asphalt Agg. Filler Asphalt Voids Weight* (lb/ft*) Revs.'

Stab, (lb)

Flow (1/100 in.) Value Value

None A 0 64 5 0 IS. 6 63.8 0 30.6 5.6 124 6 15 230 16 14 40 B 0 84. S 0 16.5 63.6 0 30.4 6.0 125.1 14 400 24 11 41 C 0 84. S 0 16.5 63.7 0 30.3 6.0 124 7 14 576 34 11 82

Lime- A 0.141 61.6 6.0 13.2 64.6 3.8 27.1 4 6 130.5 32 345 12 16 42 stons 0.227 60. S 7.4 12.1 64.6 5.7 26.3 4.4 132.7 43 425 11 19 74 • dust 0.S28 79.3 9.7 11.0 64.8 7.6 23.4 4.2 135.0 68 425 11 21 78

a 446 76.2 11.9 9.9 64 8 9.6 21.2 4.4 137.0 91 625 11 22 92 B a 141 81.8 5.0 13.2 64 5 3.6 27.2 4.5 130 7 18 620 19 16 101

0.22T 80. S 7.4 12.1 64.8 5.8 26.4 4.0 133.3 28 720 16 19 116 0.328 76.3 9.7 11.0 65.0 7.7 23.5 3.6 135.8 40 920 15 21 129 a 446 78.2 11.9 9.9 85.0 9.6 21.5 3.9 137.8 62 1,200 14 22 131

C 0.141 81.8 5.0 13.2 64.6 3.8 27.0 4.7 130.6 26 935 23 18 174 a 227 80.5 7.4 12.1 64.6 5.6 26.2 4.4 133 0 • 36 1,210 18 19 161 a 328 79.3 9.7 11.0 64.9 7.7 23.4 4.0 135.5 45 1,460

1,820 IS 22 174

a 446 78.2 11.9 9.9 64 9 9.6 21.3 4.2 137.3 78 1,460 1,820 15 24 187

Kaolin B 0.141 81 9 4.9 13.2 64.8 3 9 27.2 4.4 131.0 13 590 24 14 101 clay 0.227 ' 80.7 7.2 12.1 66.0 5.8 25.5 3.7 133.6 16 740 22 19 108 clay

0.328 76.5 9.5 11.0 65.1 7.7 23.6 ' 3.7 135.6 20 005 20 18 142 a 446 78.4 11.7 9.9 84.8 9 6 21.4 4.2 137.0 26 1,315 19 18 154

Hydrated B 0.141 82.4 4.3 13.3 64.9 3.9 27.3 3.9 130.4 17 660 20 17 105 lime 0.227 81.5 6.3 12.2 66.1 5.7 25.5 3.7 132 4 22 800 19 19 127

a 328 80.6 8.3 11.2 64.9 7.6 23.5 4.0 133.5 29 1,100 17 18 151 0.446 79.6 10.3 10.1 64.9 9.8 21.4 4.0 136 2 129 1,600 IS 22 307

Asbestos A a 066 83.3 2.4 14.3 65.0 2.0 29.1 3.9 128.8 24 245 12 19 48 0.141 82.1 4.7 13.2 66.0 3.9 27.2 3.9 130.8 46 600 12 20 87 a 227 81.0 6.9 12.1 66.0 5 7 26.2 4.1 132.4 158 796 13 22 133 a 328 79.8 9.1 11.1 64.8 7.7 23.4 4.1 134.2 1,421 1,105 14 22 187

B a 068 83.3 2.4 14.3 64.9 1.9 29.1 ' 4.1 129.1 18 610 19 20 115 a 141 82.1 4.7 13.2 64.9 3.9 27.2 4.0 131.0 37 930 18 21 207 0.227 81.0 6.9 13.1 64.9 5.7 25.5 4.0 132.5 113 1,235 16 24 166 a 328 79.8 9.1 11.1 64.7 7.7 23.4 4.2 134.2 622 1,735 16 28 328

C 0.066 83.3 2.4 14.3 66.2 2.0 28. B 4.3 129.3 20 950 22 21 162 a 141 82.1 4.7 13.2 65.2 3.9 26.7 4.2 131.2 35 1,245 21 24 245 a 227 61.0 6.9 12.1 65.2 5.8 24.6 4.2 132.9 90 1,600

1,985 18 27 309

a 328 79.6 9 1 11.1 65.1 7.7 23.0 4.2 134.7 509 1,600 1,985 18 29 333

FUler's B 0.066 83 1 2.6 14.3 64.7 1.9 29.0' 4.4 128.9 21 730 20 17 105 earth a 141 81. S 5.0 13.2 64.9 3.6 27.3 4.0 131.4 47 1,255 17 22 272

0.227 8a 5 7.4 12.1 64.9 5.7 25.4 4.0 133.4 204 2,180 16 22 264 \Av8rage test values for three speclmeiifl7 ^est values (ur one qieclineiL

12

TABLE 6

ASPHALT CONCRETE

FUler to Speci­Asphalt Mix Composition Specimen Volume men No of

FUler Asphalt Ratio Percent 1̂ Weight Proportions ' (% Unit Compac­ Marshall' Hveera" (F/A) of Total Mix Air Weight' tion Stab. Flow Stab Cohes by Vol Agg. Filler Asphalt Agg. Filler Asphalt Voids (lb/ft») Revs ' (lb) (1/100 in ) Value Value

None A 0 92 2 0 7 8 77.5 0 19 3 3 2 154.4 6 203 9 B 0 92.2 0 7.8 77 5 0 19 0 3 5 154 4 7 697 15 21 103 C 0 92. 2 0 7 8 77 3 0 18 8 3 9 154.0 7 885 15 26 244

Lime­ A 0. 146 90 7 2 6 6.7 77.7 2 4 16 9 3 0 157 2 7 374 10 28 84 stone 0. 298 89.5 4 7 5 8 78 0 4 4 14 9 2 7 160 2 9 744 10 30 140 dust 0.496 88 4 6.6 5 0 78 2 6 3 13 0 2 5 162 5 14 1, 024 9 33 194

0.766 87 2 8 6 4 2 77.4 8 2 11 0 3.4 163 2 22 1, 225 8 45 207 B 0 146 90 7 2 6 6 7 78 5 2.4 16.8 2 4 158 9 9 946 16 25 176

0. 298 89 5 4 7 5.8 78.5 4.4 14 7 2 4 161 0 10 1,435 15 28 315 0 496 88.4 6 6 5.0 78 1 6 3 12.8 2 8 162 3 13 1,674 13 30 329 0 766 87 2 8.6 4 2 77 6 8 2 10 8 3.4 163 5 23 2, 105 13 39 337

C 0. 146 90.7 2 6 6.7 78 0 2.4 16.6 3 0 159 2 11 1,492 15 25 273 0.298 89 5 4 7 5 8 78 1 4.4 14 6 2 9 160 3 12 1, 669 15 31 314 0 496 88 4 6 6 5 0 78 0 6.3 12 7 3 0 162 2 17 2,402 13 36 412 0.766 87 2 8 6 4 2 77.5 8 2 10.8 3.5 163 4 33 2,928 11 45 493

Kaolin B 0. 146 90.8 2.5 6 7 78 3 2 4 16.7 2.6 158 3 8 983 18 22 270 clay 0.298 89 6 4.6 5.8 78 3 4 4 14.7 2 6 160 4 9 1,399 17 25 330

0.496 88 5 6 5 5 0 78 1 6 3 12 7 2 9 162.0 13 1, 955 16 33 450 0 766 87 4 8 4 4 2 77 3 8.2 10 7 3 8 162.4 97 3. 070 16 43 546

Hydrated B 0 146 91 1 2 2 6 7 78 3 2 4 16.6 2.7 157 9 9 905 15 24 273 lime 0 298 90 1 4 0 5 9 78 3 4 4 14.8 2 5 159 6 12 1,451 15 27 374

0.496 89 3 5.7 5 0 77 6 6 3 12.6 3.6 159.6 34 2, 195 14 36 485 0 766 88 4 7 4 4 2 76 7 8 2 10 5 4 6 159 5 595 3, 550 12 57 571

Asbestos A 0 146 90 9 2 4 6.7 77 5 2.4 16 8 3 3 156.7 15 670 14 34 193 0 298 89 8 4 4 5.8 77 0 4 4 14.6 4.0 157.6 46 1,200 13 47 285 0.496 88 8 6 2 5 0 76.5 6.2 12. 7 4.6 158 2 314 1, 725 12 55 277

B 0 146 90 9 2 4 6 7 77 6 2 4 16 5 3 5 156.8 20 1,305 14 35 306 0 298 89 8 4 4 5 8 77 0 4 4 14 4 4 2 157 6 42 1, 760 14 45 394 0 496 88.8 6 2 5 0 76 7 6.2 12 5 4.6 158 7 1, 098 2,715 14 56 472

C 0. 146 90.9 2 4 6 7 77.6 2.4 16 5 3 5 156.8 14 1,565 15 31 386 0. 298 89 8 4.4 5 8 77.2 4.4 14.3 4 1 157 8 42 1,910 13 44 449 0.496 88.8 6.2 5 0 76.8 6 2 12.5 4.5 158.9 217 3, 040 16 65 578

Fuller's B 0 026 91 9 0 5 7 6 78 8 0 5 18.6 3. 1 155 6 10 820 17 22 159 earth 0 146 90 7 2 6 6.7 78 0 2 4 16.7 2.9 158.0 19 1,487 14 31 324

T 0 298 89 5 4 7 5.8 76 7 4.3 14.4 4.6 157 5 122 2, 943 14 52 360

Average test values for three specimens "Test value for one specimen.

on the surfaces of specimens included in one case and excluded in the other undoubtedly are the major cause of these differences.

Small differences between heights of specimens mdicated by the gyratory compac­tor, and heights measured after cooling and removal from compaction molds were also observed. Specimens, after removal from compaction molds, were generally 0.002 to 0.040 in. higher than indicated by the gyratory compactor. Specimen re­bound of this magnitude was therefore indicated. Trends in specimen rebound were consistent and appeared to be influenced by asphalt viscosity and filler-asphalt ratio, ^ecimen rebound increased with higher viscosities of the asphalt. Rebound was also higher for the lowest and the highest f i l ler concentrations. However, the differences in specimen volumes due to specimen rebound, or depending on method of volume determination, were not large. They did not appreciably affect the objective of the compaction procedures; namely, to compact specimens with nearly constant volume proportions of mixture components.

Test results include a number of figures of mixture test properties plotted on the verticalaxisvs f i l ler asphalt ratios on the horizontal axis. Volume proportions of all mixture components are nearly constant at the same filler-asphalt ratio. As the filler-asphalt ratio increases from zero (no added f i l ler) , given volumes of asphalt are replaced by the same volume of f i l ler so that the total volume of filler-asphalt binder is maintained constant. Volume proportions of aggregates and air voids also remain constant.

13

2500

2000

01

i

1500

1000

I 500

ASPHALT B

FULLERS EARTH

ASBESTOS

HYDRATED LIME

LIMESTONE DUST

( ) FLOW l/lOO IN

01 0 2 03 Q4 Q5 FILLER TO ASPHALT (F/A) RATIO BY VOLUME

Figure 3. E f fec t of f i l l e r s on Marshall s tab i l i ty and flow of sheet asphalt.

3 5 0 0

3 0 0 0

I >-

• 2500

S2000

1 1500

1000

5001

„(I2)

HYDRATED

KAOLIN a

LIME

.AY ^ / ^(16)

FULL ER'S EARTl

i

1 /

(14)

1 (14)

/ A S B t STOS

I (13)

( 1 4 ) / ^

(14) (13),

(16)

^ ( I5 ) |

^ v ^ L i r tESTONE DL ST

^ 5 ^ ( 1 6 ) > ^ I 5 )

{ ) FLOW-!/ 0 0 IN

FILLER TO ASPHALT (F/A) RATIO BY VOLUME

Figure U. Ef fec t of f i l l e r s on Marshall s tab i l i ty and flow of asphalt concrete.

14

Effects of FUlers and Asphalts on Marshall Test Properties Marshall stability is plotted vs filler-asphalt ratio for sheet asphalt containing

Asphalt B and the five fi l lers in Figure 3. Marshall stability increases with increasing filler-asphalt ratio for all the f i l lers . The increase in Marshall stability varies with f i l ler type and is greatest for fuller's earth, followed by asbestos, hydrated lime, kaolin clay, and limestone dust. There is little difference between the latter two fi l lers.

Figure 4 is a similar plot of Marshall stability vs filler-asphalt ratio for asphalt concrete containing Asphalt B and the five mineral f i l lers. Marshall stability increases with increasing filler-asphalt ratios for all the f i l lers . The increase in stability varies with the type of f i l ler similar to sheet asphalt, and is greatest for fuller's earth, followed by asbestos, hydrated lime, kaolin clay, and limestone dust. The volume per­cent of filler-asphalt binder in asphalt concrete specimens is about 19 percent compared to approximately 31 percent in sheet asphalt. However, in spite of this difference, trends in the effects of fi l lers on Marshall stability of asphalt concrete are similar to sheet asphalt.

The effects of the three widely varying viscosity asphalts on Marshall stability for sheet asphalt containing Asphalts A, B, and C, limestone dust, and asbestos f i l ler , are shown in Figure 5. Marshall stability is plotted vs filler-asphalt ratio. The increase in Marshall stability with increasing asphalt viscosity is almost constant regardless of fUler-asphalt ratio for both fi l lers. The relative effects of both f i l ler and asphalt type on Marshall stability are indicated by this figure. For example, asbestos fi l ler specimens at a fUler-asphalt ratio of 0. 22 with Asphalt A (lowest viscosity) have the same Marshall stability as Asphalt B (medium viscosity) limestone dust f i l ler speci­mens at the same filler-asphalt ratio.

A general trend of almost constant increase in Marshall stability with increasing asphalt viscosity also results for asphalt concrete. Figure 6 shows Marshall stability vs filler-asphalt ratio for asphalt concrete containing Asphalts A, B, and C, and lime­stone dust, and asbestos f i l le r . The test results shown in Figures 5 and 6 indicate that filler-asphalt ratio or type of f i l ler may have equal or greater effect on Marshall sta­bility as large variations in the viscosity of asphalt used.

2500

2000

OQ _l

I

.5

1500

1000

LIMESTONE DUST

ASBESTOS —

ASPHALT C

ASPHALT B ASPHALT C

ASPHALT B

ASPHALT A

ASPHALT A

500

0 0 01 0.2 Q3 Q4 05 0 6 FILLER TO ASPHALT (F/A) RATIO BY VOLUME

Figure 5. Ef fec t of various asphalts on Marshall s tab i l i ty of sheet asphalt. I

15

3 0 0 0

2500

I

<

2000

1500

lOCO

5 0 0

LIMESTONE DUST ASPHALT C

ASBESTOS —

ASPHALT C ASPHALT B

ASPHALT B

ASPHALT A

ASPHALT A

0 0 01 0 2 0 3 0 4 0 5 0 6 FILLER TO ASPHALT (F/A) RATIO BY VOLUME

0 7 0 8

Figure 6. Effect of various asphalts on Marshall stability of asphalt concrete.

I

The influence of asphalt viscosity on Marshall stability has been recognized for some time. Fink and Lettier (3) found that for a particular aggregate-asphalt system, Marshall stability was almost directly proportional to the logarithm of the viscosity of the recovered asphalt. Because Marshall stability is influenced by the viscosity of asphalt used, and because type and concentration of mineral f i l ler have an appreciable effect on viscosity of asphalt, i t is expected that Marshall stability would be related to the viscosity of the filler-asphalt binder as well as viscosity of asphalt alone. A gener­al trend of increasing Marshall stability with increasing filler-asphalt binder viscosity was indicated for sheet asphalt mixes with different f i l lers in previous Asphalt Institute f i l ler studies (1). Tests on the constant volume proportion specimens in this study permit clearer evaluation of filler-asphalt binder viscosity and Marshall stability re­lationships.

The concentration effects of the five fi l lers on the viscosity of Asphalt B are shown in Figure 7, a plot of viscosity at 77 F of asphalt-filler mixtures vs filler-asphalt ratio by volume. Al l fUlers greatly increase the viscosity of asphalt with increasing con­centration. The increase in viscosity is greatest for fuller's earth and asbestos, followed by hydrated lime, kaolin clay, and limestone dust.

The relationship of filler-asphalt binder viscosity at 77 F and Marshall stability of sheet asphalt for Asphalt B and the five fi l lers is shown in Figure 8. Marshall stability values shown in Figure 3 for the various fi l lers at different filler-asphalt ratios are plotted vs the viscosity of the fUler-asphalt binder in the specimens at the same f i l l e r -asphalt ratios. Despite the difference in temperature at which the viscosity of the

16

1̂

P

o >

1 1

n M l c — 1

FULLER'S EARTH_^ KAO LIN CLAY_

^ H Y D WTED LIM

V ASBE STOS 7

\ LIMESTTDNP DUST

ASPHALT B

00 01 02 03 04 05 FILLER TO ASPHALT (F/A) RATIO BY VOLUME

06 07

Figure 7. E f f ec t of concentration of various f i l l e r s on v i scos i ty of f i l l e r - a s p h a l t mixtures.

filler-asphalt binder was measured (77 F), and Marshall stability test temperature (140 F), the results mdicate that Marshall stability is almost directly proportional to the logarithm of the filler-asphalt binder viscosity for each fi l ler type.

The same general relationship between filler-asphalt binder viscosity and Marshall stability results for asphalt concrete. This is shown in Figure 9, a plot of f i l l e r -asphalt binder viscosity at 77 F at different fUler-asphalt ratios vs Marshall stability of asphalt concrete at the same filler-asphalt ratios for the five fi l lers.

Marshall stability may therefore be related to the viscosity of the filler-asphalt binder as well as the viscosity of the asphalt. Because filler-asphalt binder viscosity is appreciably affected by mineral f i l ler concentration and type, type and concentration of mineral f i l ler may have an equal or greater influence on Marshall stability than large differences in the viscosity of asphalt alone.

The test results m Figures 8 and 9 also indicate that f i l ler properties such as particle shape and particle-size distribution, in addition to f i l ler properties that influ­ence asphalt viscosity, affect Marshall stability. If the fil lers had no effect on Marshall stability other than their effect on aspahlt viscosity, the plotted points would fall on a common line, or within a narrow band, with a width corresponding to the reproducibility of the Marshall stability test.

Marshall flow values are indicated in parentheses beside the plotted stability values in Figure 3 for sheet asphalt and Figure 4 for asphalt concrete. There is no significant effect of f i l ler type on Marshall flow value at the same filler-asphalt ratio, except for kaolin clay. Kaolin clay consistently increases the Marshall flow value. Decreasing flow values for all fi l lers with increasing filler-asphalt ratio reflect decrease in asphalt content in the specimens as f i l ler replaces the same volume of asphalt.

I

17

HYDRATED LIME

FULLER'S EARTH

KAOLIN CLAY

LIMESTONE DUST

NO ADDED FILLER

ASPHALT B

400 600 800 1000 1200 1400 MARSHALL STABILITY AT I40»F ( LBS)

1600 1800

Figure 8. Binder viscosity at 77 F vs Marshall stability at II4D F of sheet asphalt containing f i l l e r s at different concentrations.

I

Effects of Fillers and Asphalts on Hveem Test Properties Hveem stability values increase as progressively larger volumes of asphalt are re­

placed by the same volumes of mineral f i l ler in compacted test specimens. Stability increases with increasing filler-asphalt ratio may vary considerably for some fil lers. Figure 10 shows Hveem stability vs filler-asphalt ratio for sheet asphalt containing Asphalt B and five different f i l lers . Fuller's earth and asbestos produce the greatest and approximately the same increase in Hveem stability as filler-asphalt ratios are in­creased. Lesser and about the same stability increases result for hydrated lime, lime­stone dust, and kaolin clay.

Figure 11 shows Hveem stability vs filler-asphalt ratio for asphalt concrete contain­ing Asphalt B and the different f i l lers. The same general trends of stability increase with increasing filler-asphalt ratios result for asphalt concrete as for sheet asphalt. Hydrated lime, however, produces considerably higher stability than limestone dust or kaolm clay at the higher filler-asphalt ratios for asphalt concrete.

It is generally accepted that the Hveem stability test is more dependent on aggregate and fi l ler characteristics than on asphalt characteristics. Testresults, however, indicate that Hveem stability may be influenced by the viscosity of the filler-asphalt binder. Trends in viscosity of asphalt-filler mixtures for different types and concentrations of fil lers

18

KAOLIN CLAY

FULLER'S EARTH

LIMESTONE OUST

HYDRATED LIME

ADDED FILLER

ASPHALT B

400 800 1200 1600 2000 2400 MARSHALL STABILITY AT I40«F(LBS)

2800 3200

Figure 9. Binder viscosity at 77 F vs Marshall stability at ll;0 F of asphalt concrete containing f i l l e r s at different concentrations.

shown in Figure 7 are quite similar to trends in Hveem stability for the same types and concentrations of f i l ler .

Figure 12 shows Hveem stability vs filler-asphalt ratio for asphalt concrete con­taining Asphalts A, B, and C, limestone dust, and asbestos f i l le r . There is no con­sistent or significant effect of the widely differing viscosity asphalts on Hveem stability. Asphalt concrete specimens with Asphalt A and no added f i l le r disintegrated at 140 F. Stability tests could not be made for these specimens.

Figure 13 shows Hveem stability vs filler-asphalt ratio for sheet asphalt containing Asphalts A, B, and C, limestone dust, and asbestos. There is no significant effect of asphalt type on Hveem stability for the limestone dust f i l le r mixes. However, for sheet asphalt containing asbestos, there is consistent trend of increasing stability with increasing viscosity of asphalt. Thus, with the exception of sheet asphalt containing asbestos, Hveem stability is not appreciably affected by large differences in viscosity of the asphalt.

Cohesion of compacted paving mixtures as measured by the Hveem cohesiometer test is greatly influenced by type of f i l le r , filler-asphalt ratio, and type of asphalt. The effects of these variables on cohesiometer test values are quite similar to their effects on the Marshall stability test.

I

19

50

40

S i i i > X

30

20

10

ASPHALT B

FULLER'S

SBESTOS_

\ _ L I M E S 1

HYDRAT

ONE DUST

ED LIME

X A Y KAOLIN

ONE DUST

ED LIME

X A Y

00 01 02 03 04 05 FILLER TO ASPHALT ( F / A ) RATIO BY VOLUME

06

Figure 10. Effect of f i l l e r s on Hveem stability of asphalt concrete.

60

50

40

>

i 30

i s UJ ^ 20

10

L

ASBESTC s ^ ;

^ 1

^ HYC RATED LIME

a

FUL LER'S EAR1 A

• " H ^ /

LME£

KAOLIN

TONE DUSl

CLAY ^

^ m

c

^_ 0

I I i i

— + » — — -

1 ...11 ^ ^

00 01 02 03 0 4 05 06 FLLER TO ASPHALT ( F/A) RATIO BY VOLUME

07 OB

Figure 11. Effect of f i l l e r s on Hveem stability of asphalt concrete.

20

70

60

u 50

I 30

20

LIMES! rONE DUST

ASBESTOS / • /

/

ASPHAL T A ^ /

A

-V AS

SPHALT C -

'HALT B

/ m

> •

X

_ASPHALT

-V AS

SPHALT C -

/ / .

- X

ASPHALl B

.ASPHALT

10 0 0 01 02 03 0 4 05 06

FILLER TO ASPHALT (F /A) RATIO BY VOLUME 07 0 8

Figure 12. Ef fec t of various asphalts on Hveem s t a b i l i t y of asphalt concrete.

LMESTONE DUST

ASBESTOS . •

ASPHALT C

ASPHALT B ASPHALT A

ASPHALT C

ASPHALT A

ASPHALT B

01 0 2 03 0 4 0 5

FILLER TO ASPHALT (F/A) RATIO BY VOLUME

Figure 13. Ef fec t of various asphalts on Hveem s t a b i l i t y of sheet asphalt.

J

21

Figure 14 shows Hveem cohesiometer values vs filler-asphalt ratio for sheet asphalt containing Asphalt B and five mineral f i l lers . Cohesiometer values increase with increasing filler-asphalt ratio for all of the f i l lers . The Increase is greatest for fuller's earth, followed by asbestos, hydrated lime, kaolin clay, and limestone dust. The relative effects of the fil lers on cohesiometer test values are closely related to the effects of the fi l lers on viscosity of asphalt. Trends in cohesiometer values for the different fi l lers correspond closely to trends in the viscosity of fUler-asphalt mixtures shown previously in Figure 7. Fillers that produce the greatest increase in asphalt viscosity also produce the greatest increase in Hveem cohesiometer values.

4 0 0

300

I 200

^ 100

FULLER^ E ASBESTOS _ A n n 1

1 ASPHALl

0

B

FULLER^ E ARTH

^ • ^ ^ H Y D F ATED LIME

/ •

a 1 ' II

^ — * KAC LIN CLAY

\ UMESl ONE DUST

0 0 0! 02 0 3 0 4 0 5

FILLER TO ASPHALT (F/A) RATIO BY VOLUME

0 6

Figure lU. Effect of f i l l e r s on Hveem cohesiometer values of sheet asphalt.

500

400

300

200

100

I I LIMESTONE DUST

ASBESTOS _ - •

ASPHALT C

ASPHALT B

ASPHALT C

ASPHALT B

ASPHALT A

PHALT A

\ 01 02 0 3 0 4 05

RLLER TO ASPHALT (F/A) RATIO BY VOLUME

Figure 15. Effect of various asphalts on Hveem cohesiometer values of sheet asphalt.

22

Hveem cohesiometer values are influenced by type of asphalt as well as type of f i l ler . Figure 15 shows cohesiometer values vs filler-asphalt ratio for sheet asphalt containing Asphalts A, B, and C, limestone dust, and asbestos fiUer. The increase in cohesiometer values for limestone f i l ler mixes with increasing viscosity of asphalt is fairly uniform regardless of filler-asphalt ratio. Although a considerable scatter of test values results for asbestos f i l ler mixes, there is also a general trend of increasing cohesiometer values with increasing viscosity of asphalt. Effects of Fillers and Asphalts on Compaction Characteristics

Compaction by the gyratory compaction method results from direct vertical pressure on the ends of the specimen while movement of aggregate particles is produced by a continuous gyratory motion of the compaction mold confining the specimen. The vertical pressure and gyration angle were maintained constant for compaction of speci­mens. Therefore, the number of compaction revolutions required to produce constant volume specimens provides an indication of mixture compaction characteristics or required compactive effort. Further, the proportioning procedures used permit evalu­ation of the relative effects of f i l ler type, asphalt type and filler-asphalt ratio on com­paction characteristics of mixtures.

Test data were obtained for compaction at two different temperatures. High Temperature Compaction. —The number of compaction revolutions required to

produce constant volume specimens is given in Table 5 for sheet asphalt and Table 6 for asphalt concrete.

Two factors should be mentioned concerning the high temperature compaction of mixtures, or compaction immediately after mixing. Temperature control, other than maintaining mixtures between 250 and 265 F at the beginning of compaction, was not provided. Also, the initial bulk volume of loose mixtures as placed in the compaction mold varied for the different fiUers, even though the theoretical volume of mixture components was kept constant.

The differences in viscosity of Asphalts A, B, and C did not affect the number of re­quired compaction revolutions for sheet asphalt or asphalt concrete containing no added f i l ler . Required compactor revolutions for sheet asphalt with Asphalts A, B, and C were 15, 14, and 14, respectively. For asphalt concrete the required compaction revolutions with Asphalts A, B, and C were 6, 7, and 7, respectively.

Trends in the number of compaction revolutions for both sheet asphalt and asphalt concrete with limestone dust and asbestos dependent on type of asphalt were not con­sistent. More revolutions, or greater compactive effort were required to compact sheet asphalt with limestone dust with Asphalt A (lowest viscosity) than Asphalt C (highest viscosity). On the other hand, slightly increasing number of required compac­tion revolutions were required for asphalt concrete with limestone dust with increasing viscosity of asphalt. In any case, differences in required compactive effort were not large for high temperature compaction dependent on asphalt type or viscosity of asphalt. Air entrapment related to type and grading of aggregate may have been a factor in high temperature compaction, or the gyratory compaction techniques used may singly not be sensitive to relatively small viscosity differences in asphalt at about 250 F.

Trends in required compactive effort dependent on filler-asphalt ratio were con­sistent for sheet asphalt and asphalt concrete with all f i l lers and Asphalt B. The number of compactor revolutions increases rapidly with Increasing filler-asphalt ratios. The increase varies considerably for some fi l lers . For example, sheet asphalt with asbestos required 622 compactor revolutions at a filler-asphalt ratio of 0.322. The required number of compactor revolutions for a similar mix with limestone dust at the same filler-asphalt ratio was only 40.

Asbestos and fuUer's earth, which cause the greatest increase in viscosity of asphalt, require considerably higher compactive efforts. Hydrated lime, limestone dust, and kaolin clay, which have less effect on asphalt viscosity, require lower com­pactive effort. The test data for high temperature compaction also indicate that con­siderably higher compactive efforts are required for sheet asphalt than asphalt concrete.

In general, the high temperature gyratory compaction test results indicate that type of asphalt or viscosity of asphalt does not greatly influence compaction characteristics.

23

Filler-asphalt ratio and type of f i l ler have by far the greater influence on high tempera­ture compaction characteristics of paving mixtures.

Compaction at 140 F.—The factors of temperature variation and bulking effects pres­ent in the high temperature compaction were largely eliminated when additional compaction was applied to specimens at 140 F. Test data for the 140 F compaction are summarized in Table 7 for sheet asphalt and Table 8 for asphalt concrete. The summary includes mix coiiq)osition in percent by weight of total mixture, volume percent of mixture com­ponents after compaction, and the number of conq)action revolutions required to reduce the theoretical volume of air voids by about 2 percent. Air void contents based on volumes of specimens determined by the water displacement method indicate that air void contents were fairly uniformly reduced approximately 1 percent by the additional coiiq>action at 140 F. Considerable influence of specimen rebound after the additional

TABLE 7 SHEET ASPHALT A F T E R ADDITIONAL COMPACTION AT 140

FlUer Asphalt

Filler to Asphalt

RaUo (F/A)

by Vol.

Mix Composition Percent by Weight

of Total Mix Agg. ^Uer Asphalt Agg

Specimen Volume Proportions (%)

FlUer Asphalt Voids

Speci­men No. of Unit Compac-

Welght tion (lb/ft*) Revs.

None

Lime­stone dust

A B C A

B

Kaolin B clay

Hydrated B lime

Asbestos A

FuUer's B earth

,141 .227 .328 .446 .141 .227 .328 .446

0.141 0.227

.328

.446

.141

.227

.328 0.446 0.141 0.227 0.328 0.446 0.066 0.141 0.227 0.328 0.066

.141

.227

.328

.066

.141

.227

.328

.066

.141

.227

84.5 84.5 84.5 81.8 80.5 79.3 78.2 81.8 80.5 79.3 78.2 81.8 80.5 79.3 78.2 81.9 80.7 79.5 78.4 82.4 81.5 80.5 79.6 83.3 82.1 81.0 79.8 83.3 82.1 81.0 79.8 83.3 82.1 81.0 79.8 83.1 81.8 80.5

0 0 0 5.0 7.4 9.7

11.9 5.0 7.4 9.7

11.9 5.0 7.4 9.7

11.9 4.9 7.2 9.5

11.7 4.3 6.3 8.3

10.3 2.4 4.7 6.9 9.1 2.4 4.7 6.9 9.1 2.4 4.7 6.9 9.1 2.6 5.0 7.4

15.0 15.0 15.0 13.2 12.1 11.0 9.9

13.2 12.1 11.0 9.9

13.2 12.1 11.0 9.9

13.2 12.1 11.0 9.9

13.3 12.2 11.2 10.1 14.3 13.2 12.1 11.1 14.3 13.2 12.1 11.1 14.3 13.2 12.1 11.1 14.3 13.2 12.1

64.6 64.0 64.1 65. 65. 65. 65. 65. 65. 65.9 65.6 65.0 65.1 65.6 65.6 65.7 65.9 65.9 65.6 65.8 66.1 65.9 66.3 66.0 66.1 66.2 65.4 66.2 66.3 66.2 65.6 65.9 66.3 66.2 65.5 66.0 66.1 65.9

9.7 3.8 5.8 7.8 9.7 3.9 5.8 7.8 9.7 3.9

9.8 2.0 3.9 5.9

5.9 7.8 2,0 3.9 5.8

30.9 30.6 30.6 27.4 25.6 23.7 21.4 27.4 25.7 23.8 21.7 27.2 25.4 23.6 21.6 27.6 25.8 23.8 21.6 27.7 25.8 23.9 21.9 29.5 27.5 25.7 23.6 29.6 27.8 25.8 23.8 28.9 27.2 25.2 23.2 29.6 27.8 25.9

4.5 5.4 5.3 3.7 3.3 2.8 3.6 3.6 3.1 2.5 3.0 3.9 3.7 3.0 3.1 2.8 2.5 2.5 3.1 2.6 2.3 2.5 2.0 2.5 2.3 2.2 3.2 2.2 2.0 2.1 2.8 3.2 2.6 2.7 3.5 2.4 2.2 2.4

126. 125. 125. 131. 134. 137. 138. 131.9 134.5 137.6 140.2 131.7 134.0 137.0 139.0 133.0 135.3 137.3 138.6 132.4 134.3 135.6 138.0 130.9 133.0 135.0 135.5 131.6 133.7 135.3 136.2 130.8 133.4 135.2 135.7 131.5 133.8 135.7

5 9

11 12 31 68 87 17 37 80

219 36 48

122 398

16 27 33

120 23 51

131 1,017

32 100

1,126 2,000b

39 159 445

2,000^ 58

328 1,095 2,000b

29 143

2,000b

5Test values for individual specimens. '̂ Coiopaction discontinued at 2,000th revolution.

24

TABLE 8 ASPHALT CONCRETE AFTER ADDITIONAL COMPACTION AT 140 F *

FiUer Asphalt

FUler to Asphalt Ratio (F/A)

by Vol.

Mix Composition Percent by Weight

of Total Mix Agg. Filler Asphalt

Specimen Volume Proportions (%)

A i F Agg. FUler Asphalt Voids

Speci­men No. of Unit Compac-

Weight tion (lb/ft*) Revs.

None

Lime­stone

A B C A

Kaolin clay

Hydrated B lime

Asbestos A

B

C

Fuller's B earth

0 0 0 0.146 0.298 0.496 0.766 0.146 0.298 0.496 0.766 0.146 0.298 0.496

.766

.146

.298

.496 766

0.146 0.298 0.496 0.766 0.146 0.298 0.496 0.146 0.298 0.496 0.146 0.298 0.496 0.026 0.146 0.298

92.2 92.2 92.2 90.7 89.5 88.4 87.2 90.7 89.5 88.4 87.2 90.7 89.5 88.4 87.2 98.8 89.6 88.5 87.4 91.1 90.1 89.3 88.4 90.9 89.8 88.8 90.9 89.8 88.8 90.9 89.8 88.8 91.9 90.7 89.5

0 0 0 2.6 4.7 6.6 8.6 2.6 4.7 6.6 8.6 2.6 4.7 6.6 8.6 2.5 4.6 6.5 8.4 2.2 4.0 5.7 7.4 2.4 4.4 6.2 2.4 4.4 6.2 2.4 4.4 6.2 0.5 2.6 4.7

7.8 7.8 7.8 6.7 5.8 5.0 4.2 6.7 5.8 5.0 4.2 6.7 5.8 5.0 4.2 6.7 5.8 5.0 4.2 6.7 5.9 5.0 4.2 6.7 5.8 5.0 6.7 5.8 5.0 6.7 5.8 5.0 7.6 6.7 5.8

78.8 78.1 78.6 78.7 78.6 78.3 79.2 79.1 78.7 78.6 78.6 78.7 78.7 78.3 79.2 79.0 78.7 78.1 79.3 77.0 78.8 78.3 78.5 78.2 78.0 78.5 78.0 78.1 78.3 78.3 78.2 78.9 78.9 78.1

0 0 2.4 4.4 6.4 8.3 2.4 4.5 6.4 8.3 2.4 4.4 6.4 8.3 2.4 4.5 6.4 8.3 2.5 4.4 6.3 8.3 2.4 4.4 6.3 2.4 4.4 6.3 2.4 4.4 6.3 0.5 2.4 4.4

19 3 19.1 17.0 15.0 13.1 11.1 16.9 14.8 12.9 10.9 16.7 14.7 12.8 10.9 16.9 14.8 12.8 10.9 16.8 15.0 12.7 10.7 17.0 14.9 12.9 16.7 14.6 12.7 16.6 14.6 12.7 18.8 16.9 14.6

1.9 2.8 2.0 1.9 1.9 2.3 1.5 1.6 2.0 2.2 2.3 2.2 2.1 2.5 1.5 1.7 2.1

2.5 2.8 2.4 3.0 2.9 2.7 2.7 2.8 1.8 1.8 2.9

156.9 155.8 159.1 161 5 163.6 164.9 160.2 162.3 163.7 165.4 159.2 161.5 163.6 165.0 160.1 161.9 163.2 164.2 159.7 161.2 161.9 162.6 158.6 160.0 161.3 158.6 159.6 161.4 158.2 160.1 161.7 157.6 159.8 160.2

2 5 3 3 5

22 11 12 17 60 10 8

28 79 6 9

25 185

8 13

103 990

12 60

496 41

107 ,220

30 168 732

3 32

353

*rest values for indlvidiial specimens.

compaction is indicated by the results. Fairly consistent trends of slightly higher air voids at the lowest and highest fnier-asphalt ratio for all of the fil lers are indicated. Slightly increasing air void contents with increasing viscosity of asphalt are also in­dicated.

Type of f i l ler and fUler-asphalt ratio are the dominant factors in compaction charac­teristics of sheet asphalt and asphalt concrete indicated by gyratory compaction at a temperature of 140 F. Figure 16 shows number of compaction revolutions vs fUler-asphalt ratio for sheet asphalt with Asphalt B and the five different f i l lers. The number of compactor revolutions increases for all of the fUlers as fUler-asphalt ratio increases.

Fuller's earth and asbestos require the greatest compactive effort followed by hy­drated lime, limestone dust, and kaolin clay. Relation of required compactive effort for the different fillers to the effect of f iUers on viscosity of asphalt is evident. Fillers requiring the greatest compactive effort also cause greatest increases in viscosity of asphalt.

Figure 17 shows number of compactor revolutions for asphalt concrete with Asphalt B and the five different fUlers. The effect of fUler type and fUler-asphalt ratio on re­quired compactive effort for asphalt concrete is similar to sheet asphalt.

25

\(f\

10-

10'

IT

10

/ O

^ -aiU-ER'S -aiU-ER'S t A K I J y

/ X )RATED E /> V MTl

LIM )RATED E

A o

// • w A o D b b l U b

+ DU! ESTONE 5T

? y - ^ T T ^ ^ •Jd 1 J y JLIN CLAY-/ / JLIN CLAY-

/ , //

/ / +

NOTE SPE :iMENS COMRI CTED TO C0^ STANT VOLUM i

ASPHALT B

0 0 0 1 0 2 0 3 0 4 0 5 FILLER TO ASPHALT (F/A) RATIO BY VOLUME

0 6

Figure 16. Effect of f i l l e r s on compaction characteristics of sheet asphalt.

Type of asphalt has a significant effect on compaction characteristics of sheet asphalt and asphalt concrete at 140 F. Increased compactive effort is required with increasing viscosity of asphalt. The effect of type of asphalt, or wide viscosity dif­ferences in asphalt, is relatively small compared to effect of the entire range of f i l le r -asphalt ratios used or type of f i l ler for such widely differing types as asbestos and limestone dust.

Test results for sheet asphalt and asphalt concrete with limestone dust are used to show the effect of asphalt type on compaction characteristics at 140 F. Figure 18 shows number of compaction revolutions vs filler-asphalt ratio for sheet asphalt with limestone dust and Asphalts A, B, and C. Compactive efforts required for Asphalt C are the highest, followed by Asphalt B and Asphalt A. Required compactive effort in­creases with increasing viscosity of asphalt.

The effect of asphalt type on compaction characteristics of asphalt concrete is simi­lar to sheet asphalt. Figure 19 shows number of compactor revolutions for asphalt concrete with limestone dust f i l ler and Asphalts A, B, and C. Although a considerable scatter of test data results at lower filler-asphalt ratios, a trend of increasing number of compactor revolutions with increasing viscosity of asphalt results.

26

O

S

o o

z

10'

10

)

ASE E S T O 5 Y YDRA"

IME "ED

F U L L E R ' S <

n y r

+

"f

^ w 1 U ESTOf

5T JE

DUI ESTOf 5T

JE

—H- — T ^ H lOLIN n A Y

11 lOLIN

/ / i

/// //^ W NOTE. SPEC MENS ( ;OMRAC FED TC CONS" ANT V( )LUME

1 ASPHAL'

1 ' B

OS

Figure 17.

0 0 01 0 2 0 3 0.4 0 5 0.6 0.7 OB F I L L E R TO ASPHALT (F /A) RATIO BY VOLUME

Effect of f i l l e r s on compaction characteristics of asphalt concrete.

In general, compaction characteristics of mixes at 140 F are similar to compaction characteristics at high temperature, with the exception of effect of type of asphalt. Filler-asphalt ratio, or relative proportions of asphalt and f i l ler , and type of f i l ler are dominant factors. Large increases in compactive effort are required with increasing filler-asphalt ratio. Fillers that increase the viscosity of asphalt most also require greatest compactive efforts. The effect of type of asphalt or viscosity of asphalt on compaction characteristics is more pronounced at 140 F than at high temperatures.

27

io»|

10'

8 10

\ _ A S P H A L T C 1 ASPHALT B

1 ornMi.1 M -

o

NOTE SPECB EISS COMFWCT ED TO CONST m VOLUME

6 0 01 0 2 0 3 0 4 0.5 FILLER TO ASPHALT (F/A) RATIO BY VOLUME

06

Figure l 8 . Compaction characteristics of sheet asphalt containing limestone dust and various asphalts.

Increased compactive effort is required at 140 F with increasing viscosity of asphalt. This was not necessarily true for high temperature compaction.

SUMMARY AND CONCLUSIONS The purpose of tests described in this p ^ e r was to evaluate the effects of different

fi l lers on properties of asphalt paving mixtures. In this respect, this study can be re­garded as a continuation and extension of the Asphalt Institute work on this subject which has been described in previous p^ers . In earlier work, a constant compactive effort, such as Marshall, was used to compact test specimens. Because different f i l lers affect compaction characteristics of mixtures differently, such compaction resulted in speci­mens which varied in density and, therefore, in the relative proportions of mixture components.

In this phase of work, however, a different approach was used. Mixtures, regard­less of type and concentration of f i l ler , were compacted to nearly the same air voids content by using variable compaction efforts. A mechanical g3rratory compactor was used for this compaction. Because volumetric proportions of mineral aggregate and filler-asphalt binder were kept constant and only type of fiUer or volumetric f i l le r con­centrations were varied, such compaction permitted a clearer and more direct evalua­tion between the effects of different f i l lers or f i l le r concentrations. Stability by Marshall and Hveem methods and compaction or densification characteristics were two main mixture properties determined under these rigidly controlled compaction condi­tions. Two mixtures (sheet asphalt and asphalt concrete) containing three asphalt cements varying in viscosity and five different f i l lers , were evaluated.

Test results obtained in this study indicate the following: 1. Al l mineral f i l lers regardless of type or concentration increase stability or

28

II.

I < CO 2 IC^ g I -3 - I

UJ q:

i tc UJ

10

NOTE SPECI HEHS ( OMPAC' 'ED TO CONST XNT V( LUME

•

ASPh ALT C

• o

X

AQD HALT A

HALT

MOr HALT M

_ASR HALT B

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 OS 0.9 FILLER TO ASPHALT (F/A) RATIO BY VOLUME

Figure 19. Compaction characteristics of asphalt concrete containing limestone dust and various asphalts.

strength properties of compacted asphalt paving mixtures. However, fillers also in­crease compactive efforts required to coiiq)act specimens to the same volume or air voids content. Such effects become more pronounced with increasing concentration of fillers.

2. Properties of paving mixtures are strongly dependent on type of mineral filler. For example, at the same volumetric concentration highly absorptive fuller's earth or fibrous asbestos increase stability or compactive efforts considerably more than hy-drated lime, kaolin, or limestone dust.

3. Use of higher viscosity asphalts results in higher stability and the need for higher compactive effort. However, it spears (particularly at higher concentrations of filler) that the effects of asphalt viscosi^ are less pronounced than the effects of type or con­centration of filler. This may indicate that at certain concentrations filler, besides changing viscosity of the binder, also contributes contact points between coarser mineral particles.

4. In general, viscosity of the filler-asphalt binder correlates with physical proper­ties of paving mixtures. Factors such as type and concentration of filler and viscosity of asphalt contribute to the viscosity of the filler-asphalt binder. Because of these

29

combined effects, it is difficlut to evaluate which factor is more important in influencing the properties of paving mixtures.

5. Marshall stability values are more sensitive and reflect better the effects of different fillers and asphalts than Hveem stability values. Trends in Hveem cohesi-ometer values are similar to those indicated by Marshall stabilities. However, the accuracy of the cohesiometer test is quite poor for some mixes. It spears that Marshall stability values reflect both viscosity of asphalt and influence of fillers. On the other hand, Hveem stability values are primarily influenced by the type and con­centration of fiUer.

6. Initial compaction and subsequent densifications of asphalt paving mixtures are strongly dependent on the type and concentration of mineral filler. The effects of asphalt viscosity on these mixture properties are relatively small, particularly at higher temperatures. Higher compaction temperatures are indicated for mixtures con­taining high viscosity filler-asphalt binders. However, high compaction efforts re­quired to densify further mixtures containing high viscosity flQer-asphalt binders at or near 140 F may indicate improved resistance to densification by traffic and therefore better performance of the pavement.

REFERENCES 1. Kallas, B. F . , and Puzinauskas, V. P . , "A Study of Mineral Fillers in Asphalt

Paving Mixtures. " Proc., Assoc. of Asphalt Paving Technologists, Vol. 30 (1961).

2. McRae, J . L . , and McDaniel, A .R. , "Progress Report on the Corps of Engineers' Kneading Compactor for Bituminous Mixtures. " Proc., Assoc. of Asphalt Paving Technologists, Vol. 27 (1958).

3. Fink, D. F . , and Lettier, J . A. , "Viscosity Effects in the Marshall Stability Test. " Proc , Assoc. of Asphalt Paving Technologists, Vol. 20 (1951).