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Masters Theses Student Theses and Dissertations

1965

The prediction of mix design properties for dense graded The prediction of mix design properties for dense graded

bituminous mixtures bituminous mixtures

Robert Ernest Weeks

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THE PREDICTION OF MIX DESIGN PROPERTIES FOR DENSE GRADED BITUMINOUS MIXTURES

BY

ROBERT E 'o WEEKS

A

THESIS

submitted to the faculty of the

UNIVERSITY OF MISSOURI AT ROLLA

in partial fulfillment of the requirements for the

Degree of

MASTER OF SCIENCE IN CIVIL ENGINEERING

Rolla, Missouri

1965

Approved by

,/7 I , 1./

ii

ABSTRACT

The purpose of this investigation was to ascertain the feasibility

of interpolating values of the physical properties of a dense graded

bituminous mix between known values. Also the effects of limestone

mineral filler on the properties of a dense graded mix are evaluated.

The variables in this study were mineral filler and asphalt

cement. Control mixes were established at 2, 6 and 10 percent mineral

filler and experimental mixes were prepared at 4 and 8 percent filler.

The aggregate consisted of limestone and was mixed with an asphalt

cement of 85-100 grade penetration. All mixes were tested by the

Marshall Method.

The physical properties analyzed were stability, flow, unit

weight, air voids and voids in the mineral aggregate. It was deter­

mined that interpolation between known values of the physical

properties of a dense graded mix is valid for a specific range of

asphalt contents and that asphalt content was critical at low (3-4

percent) and high (7-8 percent) ranges. Mineral filler increased

the desirable properties of a bituminous mix up to a certain asphalt

content and then the desirable properties diminished rapidly.

iii

ACKNOWLEDGMENT

The author wishes to extend his sincere appreciation to his ad­

visor, Dr. Thomas s. Fry, for his continuous guidance and his astute ob­

servations during the preparation of this thesis.

Thanks is also offered to Mr. Duane Edge, Area Engineer for The

Asphalt Institute, who suggested the subject for this investigation and

made available important references which helped to clarify many areas

of ambiguity.

The author is also indebted to the staff and faculty members of

the Department of Civil Engineering, University of Missouri at Rolla,

for their generous assistance.

TABLE OF CONTENTS

PAGE

ABSTRACT • ••••.••••••••••••••••••••••••••••••••••••••••••••••••••••• ii

ACKNOWLE~NTS •••••••••••••••••••••••••••••••••••••••••••••••••••• iii

LIST OF Fl GURES • • • • • • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • v

LIST OF TABLES••••••••••·•·•••••••••••·•••••••••••••••••••••••••••• vi

I.

III.

IV.

v.

INTRODUCTION •••• . . . . . . . . . . . . . . . . . . . . . . . . .... . .. A. Constituents of a Bituminous Mix. . . . . .. B. c.

Mineral Aggregates ••••.•• Purpose of Investigation.

. ............ . . ......... . . . . . . . . . . . . REVIEW OF LITERATURE ••••••••••••••••••.••••••••••••••• A. Methods for Obtaining Maximum Density Gradation ••• Bo Factors Affecting a Dense Graded Bituminous Mix. C. Factors to be Analyzed in a Bituminous Mix ••••••

. ...

PROCEDURE AND RESULTS . . . . . . . . . . . . . . . . . . ............... . A. B. c. D. E.

Scope of Tests ••••. Materials •••••• . . . . . Test Procedure •• Preparation and Testing of Specimens Results ......................•.......

. . . . ... . .... . . . ..

. . . . . . ... DISCUSSION •••••...••••••••.•.••••••••••••••••••••••••••••• A. B.

c. D. E.

of Behavior Variables

Dense Gradation in a Bituminous Mix. the Marshall Method for Testing in

Bituminous Samples. . . . . . . . . . . . . . .

Control Mixes •••.•• Experimental Mixes •••

. . . ....... . . . . . ...... .

Validity for Interpolating Between Predetermined

. .

1 1 1 3

4 4 8

11

13 13 13 14 14 21

26 26

27 27 33

Control Values.......................................... 34

CONCLUSIONS ••••••••••••••••••••••••••••••••••••••••••••••••• 39

BI BLI {)(;RAPIIY'. • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 40

VITA. • • . • . . • • . • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • 42

v

LIST OF FIGURES

FIGURE PAGE

1 FULLER-THOMPSON GRADING CURVE............................ 5

2 CAMPEN MAXIMUM DENSITY CURVE. • • . • • • • • • • • . • • • • • • • • • • • • • • • • 7

3 GRADATION CUR.VE.S......................................... 16

4 MARSHALL STABILITY RELATIONSHIPS......................... 29

5 AIR VOIDS RELATIONSHIPS.................................. 30

6 UNIT WEIGHT RELATIONSHIPS................................ 30

7 VOIDS IN THE MINERAL AGGREGATE RELATIONSHIPS............. 31

8 nrn RELATIONSIUPS....................................... 31

9 FILLER CONTENT CURVES FOR ALL MIXES...................... 35

10 RELATIONSHIP BETWEEN MAXIMUM MARSHALL STABILITY AND MINERAL FILLER CONTENT................................... 36

11 PHYSICAL PROPERTIES AT 6 PERCENT ASPHALT CONTENT BY WEIGIIT OF TOTAL MIX. • • • • • • • • • • • • • • • • • • • • • • . • • • • • • • • • . • • • • 37

vi

LIST OF TABLES

TABLE PAGE

I AGGREGATE GRADATION DATA ••••••••••••••••••••••··········· 15

II CALCULATIONS FOR THE ASPHALT ABSORBED BY THE AGGREGATE .•.. 17

III PROPERTIES OF ASPHALT CEMENT 0 AT 77 F ..••.••••..•••.•..•.. 17

IV DESIGNATIONS OF TEST POINTS •••••••••••••.••••••••••••••••• 19

v TEST PROPERTIES OF BITUMINOUS MIXES -CONTROL MIXES ..•.••• 20

VI SAMPLE CALCULATIONS-AIR VOIDS, EFFECTIVE ASPHALT CON'rEN'r, ~. • • • • • • • • • • • • • • • . • • • • • • • • • • • • • • • • • • • • • • • . . • • • • 22

VII PROPERTIES OF BITUMINOUS MIXES TESTED VALUES VSo PREDICTED VALUES........................................... 23

VIII TEST PROPERTIES OF BITUMINOUS MIXES AT OPTIMUM ASPHALT CON'rEN'r • • • • • • • • • • • • • • • • • . • • • • • • • • • . • • . • • • • • • • • • • • . • • • • • • • • 24

I • INTRODUCTION

Asphalt paving technology has advanced more rapidly than any other

phase of road building. Asphalt is a strong cementing agent, readily

adhesive, significantly hydrophobic and durable. Although a solid or

semisolid under ordinary atmospheric conditions it can easily be lique­

fied by the application of heat, or by dissolving it in petroleum sol­

vents, or by emulsification. The refining of petroleum products is the

primary method used to procure asphalt in the United States (1).

A. Constituents of a Bituminous Mix.

1

A bituminous paving mixture consists of three basic components;

mineral aggregate, asphalt cement (AC), and air. Common types of ag­

gregates that may be used are crushed limestone, basalt, gravel, slag,

and sand (1). Asphalt cement is defined by its penetration number which

is usually between 40 and 300. The higher the penetration number the

less viscous the asphalt cement. Air may be entrapped within the ag­

gregate, or within the surface pores of the individual aggregate

particles, or in the form of air bubbles within the bituminous mixture

after compaction.

B. Mineral Aggregates.

Since almost 90% of a bituminous mix consists of mineral aggregate,

it is important to evaluate the suitability of the aggregates used. Ag­

gregates are usually classified according to individual particle size,

such as, coarse aggregate, fine aggregate, and mineral filler. Coarse

aggregate refers to the material retained on the No.8 sieve (2). It

is this particle size that contributes to the stability (high resistance

to deformation) of the mix. The coarse aggregate should be free from

2

coatings of clay, silt or other undesirable matter. It should be highly

angular, possess a rough surface, and be durable to contribute to

maximum stability. Fine aggregate consists of all material passing the

No.8 sieve and retained on the No. 200 sieve (2). The fine aggregate

helps to fill the voids between the coarse particles and to provide

grain to grain contract within the structure of the mix. For the pur­

pose of this investigation mineral filler is the material that has 100

percent passing the No. 200 sieve.

There are several characteristics incorporated in the specifications

of an aggregate that determine its suitability.

1. Resistance to Abrasion. The aggregate must be tough and

durable since the aggregate is primarily responsible for carrying the

load in a compacted mix. Inherent to abrasion is the ability of the

aggregate to resist weathering, such as, heat, cold, oxidation, and

surface moisture.

2. Interparticle Friction. In order to develop maximum stability

there must exist a high degree of interlock between particles. The

frictional resistance developed on the surface of each particle contri­

butes significantly to the stability factor that can be developed for

any given bituminous mix. Other factors that contribute to inter­

particle friction include particle shape, void ratio, particle size and

gradation, and mineralogical composition.

3. Cleanliness. Clay, silt, or other undesirable materials may

interfere with the coating of the aggregate and reduce the stability of

the mix by a significant amount.

4. Surface Properties. The surface properties of aggregates differ

considerably in their affinity for asphalt. Aggregates which have a high

affinity for asphalt are hydrophobic, while those aggregates which do not

coat easily with asphalt are hydrophilic.

5. Grading. The grading of an aggregate delineates the size dis­

tribution. The standard sieve sizes recently adopted by the Asphalt

Institute consist of the No.4, 8, 16, 30, 50, 100 and 200 (3).

C. Purpose of Investigation.

Bituminous mixtures may be dense graded, open graded, or uniform

graded. A dense graded bituminous mixture is one which contains small

void spaces, whereas, an open graded mixture will consist of large

void spaces. One sized materials consist of one particle size and are

used in macadam pavement construction. Considerable research has been

performed to ascertain the properties of high quality dense graded

mixes, and the effect on the properties of high quality dense graded

mixes, and the effect on the properties of the mixes caused by varying

the amounts of the different aggregate fractions placed in the mixes.

However, no information has been found where attempts have been made to

predict the properties of a dense graded mix by interpolating between

known sets of test data. The primary purpose of this investigation is

3

to predict the properties of the dense graded mixtures whose mineral

filler content lies between the mineral filler content of the mixtures

designated control mixtures. In addition there will emanate an evalua­

tion of the basic properties of dense graded mixtures prepared at various

mineral filler contents.

4

IIo REVIEW OF LITERATURE

Percentage of air voids in a dense graded bituminous mix is usually

less than 8. This implies satisfactory resistance to water and air

penetration and, therefore, less susceptibility to weathering action as

compared to open graded mixes. The need for maximum densification in a

mix has long been acknowledged by the bituminous design engineer. How­

ever, evaluation of the methods used to obtain maximum densification has

led to confusion and misunderstanding. Many investigations of dense

gradation have been conducted for the purpose of obtaining gradation

strength relationships for portland cement concrete. Much of these

test data have provided results which are applicable to the grading of

aggregates for bituminous materials.

A. Methods for Obtaining Maximum Density Gradation.

William Bo Fuller conducted tests in 1901 to evaluate factors

affecting the strength and density of portland cement concrete. Fuller

concluded that there is an aggregate gradation that provides a high

strength in the material. His tests results established a gradation

curve with a parabolic shape which is illustrated in Figure la (4).

Fuller and Thompson made additional tests in 1904 using combinations of

crushed stone, screenings, bay gravel, and mixtures of crushed stone and

sand with maximum particle sizes 2.25 inches in diameter. They con­

cluded from these tests that the ideal gradation curve would have an

elliptical shape for the fine portion with a tangent to the elliptical

portion passing through the maximum particle size, as shown in Figure lb.

It should be noted that the Fuller-Thompson curve includes portland

cement as part of the aggregate mixture.

100

90

80

bO 70 c: . .-; (/)

60 (/)

C\1 p...

.w so c: Q)

u 40 H Q)

p...

30

20 I '

10

0 200

100

9 0 •

8 r.

7 r '

:]J 0

6

s

4

cl IJV rl v '

3

2

1 rl/ r.

30 4

I

I

100 so

\

l

I l

I I

i i I

I '

I I I /I

I 1/! I I i I

I i v I

I

!L I I 1/i I I

i I I I I

_j

~

~ -~ ~ -

30 16 8 4

A l I

I

I

I .k" 2

U. S. Standard Sieves

I i I

! i i i I

i i I I

I I I

'

I

\ I 1"

s

'

I

I

(a) Sieve size plotted on logarithmic scale

y / !

/( l l i I I

I ./ VI i

~ l./ I I

v I !I / I I I I v I I v I I I

' I I I I l

I

I I I

I ! 1:" 2 1" l}z" 2" 2U' -2

u. s. Standard Sieves (b) Sieve size plotted on arithmetic scale

FIGURE l. FULLER-THOMPSON GRADING CURVE

6

The work of Fuller and Thompson was analyzed by Campen who noted

that their work could not be easily applied to bituminous aggregate

gradation because of the different effects of the bituminous binder.

Campen prepared eleven sizes of aggregates ranging in size from 2 1/2

inch crushed quartzite to limestone dust passing the No. 200 sieve (5).

Starting with the largest size aggregate succeeding amounts of the next

smaller size were added until maximum density with each size was achieved.

A plot of Campen's maximum density curve is illustrated in Figure 2.

Campen's curve can be applied to a maximum size aggregate less than

2 1/2 inches by setting the new maximum size at 100 percent and

reapportioning the curve accordingly. A comparison of the Fuller-

Thompson curve (Figure lb) with the Campen curve (Figure 2) reveals a

striking similarity with the only noticeable difference occurring at

the No. 200 sieve size.

Ao No Talbot and Fo Eo Richart performed a series of tests in an

attempt to study the effect of density on the strength of portland

cement concrete. Their objective was to determine how to proportion

the ingredients in concrete mixes. During the tests performed they

noted the effect of density on the strength of the concrete and its

effect on the other properties of the mix. From their many observations

a gradation curve was established and is expressed in the following

mathematical equation (6).

where

P = 100 (d)n D

p

d D n

= = = =

Percent finer than particle size d Particle size under consideration Maximum particle size Arbitrary exponent

The maximum aggregate size was varied from No. 4 sieve size to 2

inches in diameter, and the exponent was varied from .24 to 1.20. Peak

9

--

I " J---

100

8 ) -I

I bO 7 ~ ·~ (/) 6 (/)

C'j

~

.w 5 ~ C) (.) !I-H C)

~

3

2

1

0- I 0-!---·

/ /

0 /

L 0 -

/ /

0 ~

~ c . . ---~ ~ c --

v c ...

200 80 40 10 4 1/2" 1" l_lz" 2%"

U.S. Standard Sieves

FIGURE 2. CANPEN HAXH1UH DENSITY CURVE

-....)

8

densities for the portland cement mixes were obtained when "nn had a

value between 1.00 and 1.20 for mixes having maximum particle size less

than 3/8 inch. This equation is generally accepted as the expression by

which an aggregate may be graded for maximum density. No effort was

made to correlate nnrr to particle size other than to show that this ex-

ponent would not necessarily be constant.

L. W. Nijboer of Holland conducted tests to determine a maximum

density grading curve for bituminous paving mixtures. Using both crushed

and uncrushed aggregates maximum density was achieved with the Talbot

Curve When rrnrr q alled 0 45 (7) e u • .

Goode and Lufsey repeated Nijboer's test using~ inch maximum size

aggregate and confirmed Nijboer's conclusions. They went one step

further and developed a technique whereby each individual particle size

was raised to the 0.45 power. This made it possible to draw a straight

line from the maximum particle size to zero percent at zero diameter (8).

The inter-relationship between gradation and the properties in a

bituminous mixture is most significant. Many of the properties in a

bituminous mixture are directly effected by gradation, however, there

are additional factors that contribute to the overall analysis of a

bituminous mixture.

B. Factors Affecting a Dense Graded Bituminous Mix.

Gradation plays a significant role in the final evaluation of a

bituminous mix. A dense graded mix yields higher stability values when

compared to open graded mixes containing the same materials. This is

due primarily to the increased contact surface which is a direct result

of dense gradation. There are many factors that are effected by

gradation, among the more expressive are workability, permeability,

9

stability, and internal friction (9). Plasticity and mobility are

usually grouped under the heading of workability. A mix that possesses

a high percentage of asphalt and/or mineral filler does not exhibit a

high degree of workability. The degree required depends upon the

conditions of use and type of equipment. The degree of permeability is

dependent almost entirely upon the type of gradation (9). When it is

necessary to protect a vulnerable subgrade from surface water an im­

permeable mixture is required. Conversely when a plastic subgrade is

saturated by capillary moisture it will frequently promote failure due

to an overabundant accumulation of moisture. The proper degree of

permeability will help to maintain a state of equilibrium in the sub­

grade. Stability of a mix is defined as the resistance to deformation

under a sustained load (1). This stability is a function of friction

and cohesion. Inferred within this definition is the significance of

interparticle adhesion. The stronger the bond between the particles

the greater the stability. All solid particles offer resistance to

sliding depending upon their surface texture and the applied pressure.

A reduction in fines will provide maximum interparticle contact in the

coarse aggregate, however, cohesion is influenced by the amount of

fines in the mix and any reduction in fines causes a loss in cohesion

(9). It is apparent that a compromise among the various properties

must take place in order to achieve the many requirements in a satis­

factory bituminous mix.

The asphalt cement (AC) content serves a dual role in a bituminous

mix. As a binding agent it increases cohesion between the separate

particles and, when added in sufficient quantities, it occupies a

portion of the voids in the mix. If the asphalt content is too high a

reduction in the quantity of asphalt will increase the voids, but at the

10

same time a decrease in the film thickness causes a reduction in the

durability of the pavement (9). Care must be taken not to reduce the

asphalt content to a value which would produce a low viscosity brittle

mix. The influence of asphalt viscosity on stability has been re­

cognized for some time. Fink and Lettier found that for a particular

aggregate-asphalt mix, stability was directly proportional to the

logarithm of the viscosity of the asphalt used (10).

Portland cement, fly ash, and limestone dust are typical materials

used for mineral filler. Kallas, Puzinauskas, and Krieger sought to

evaluate the effects of different fillers on the properties of asphalt

paving mixtures. The fillers tested were Fuller's earth, Asbestos,

Hydrated Lime, Kaolin clay, and Limestone dust. The test results re­

vealed that Fuller's earth produced the greatest stability while Kaolin

clay and Limestone dust yielded the lowest stability values (11). The

workability and performance of bituminous mixes depends largely on the

quantity and type of filler used (12). Failure to properly evaluate the

effect of a mineral filler on the properties of a paving asphalt mix may

result in an unsatisfactory mix. Other important properties of a filler

that have an effect on its behavior are particle - size distribution,

particle shape, chemical composition, and surface reactivity (13).

The compactive effort applied directly effects all the physical

properties of a specimen. An increase in compactive energy reduces the

amount of asphalt required to fill the voids due to a reduction of the

void spaces between the aggregate particles. It is imperative to

recognize that an asphalt pavement ultimately becomes further consoli­

dated under traffic loads and, therefore, the compactive effort ex­

pended must be proportioned to allow for this additional compaction,

otherwise a plastic condition may result (14).

11

C. Factors To Be Analyzed In A Bituminous Mix.

No single factor can be established as a criteria for the analysis

of a bituminous mixture. Air Voids, Voids in the Mineral Aggregate (VMA),

Density, Stability, and Flow are test properties that have been found to

be rather consistent in the evaluation of a bituminous mix design.

A limited range of air voids is necessary to insure that the mix is

not too permeable to water and air, and at the same time provides

sufficient space to allow further densification and the expansion of

the binder due to climate variations. The Asphalt Institute recommends

a range between 3-8 percent for a dense graded mix (15). Specific

values for a mix are dependent upon its use, such as, surface course or

base course.

Voids in the Mineral Aggregate, hereafter designated VMA, should

have a minimum value established for a given mix design. The VMA con­

sists of the air voids and the volume of bituminous binder necessary to

provide a durable pavement. Any value for VMA less than the minimum

value calculated will cause a deficiency in asphalt binder or air voids.

N. w. McCleod, Engineering Consultant, Department of Transport, Ottawa,

Canada recommends a minimum value of 15 percent for VMA for surface

courses and 14 percent for binder and base courses. He concludes that

selection of these values reduces the use of restrictive gradation

limits and broadens the range of acceptable aggregates, thereby reducing

the cost of the bituminous paving mix (16).

When a constant compactive effort and gradation are maintained,

density is primarily dependent upon the change in asphalt content. High

density values help to protect against water and air penetration.

However, aggregates that provide a high VMA indicate a large amount of

asphalt binder is required to sustain high density values and this

condition may result in an unworkable mix. The proper procedure for

attaining high density mixtures is to reduce the VMA to within the

limits previously discussed by adjusting the aggregate gradation (14).

Stability has been previously defined as the resistance to de­

formation under load. Since interparticle friction is an essential

part of stability it can be concluded that as the VMA is reduced (or

density increased) the stability values will increase. Crushed

aggregates produce higher stability values than uncrushed aggregates.

This results from better frictional interlocking between the

aggregates (17).

12

The flow value is an index of the plasticity and is a measure of

the resistance of the pavement to distortion under applied loads (14).

Other factors remaining constant the amount of asphalt in the voids is

the primary factor which affects flow. As the asphalt binder content

increases the flow values increase, and if the aggregate gradation con­

tains large amounts of mineral filler (10-15 percent) the flow values

rise rapidly.

13

III. PROCEDURE AND RESULTS

The primary objective for the design of asphalt paving mixes is to

determine an economical blend of aggregate and asphalt that yields a

mix having the properties listed below.

1. Sufficient asphalt to insure a durable pavement.

2. Sufficient mix stability to prevent distortion or displacement.

3. Sufficient voids to allow for additional compaction.

4. Sufficient workability to permit efficient construction (15).

A. Scope of Tests.

The variables in this investigation were asphalt content and

mineral filler content. The primary objective of these tests was to

ascertain the reliability of interpolated values of the physical

properties of a mix between known test data. A second objective was to

study the effects of variations in mineral filler content on the

physical properties of a dense graded bituminous mixture.

B. Materials.

The materials used in this investigation were chosen to represent

those in commercial use. The coarse and fine aggregates were a crushed

limestone that met the minimum standards established by the Missouri

State Highway Department. They were provided by the city engineer of

Rolla, Missouri. These aggregates had more than three crushed faces

with rough surfaces that indicated particle interlock would be

effective for certain asphalt contents. The mineral filler was a

commercial limestone dust known commercially as Rode-Rite and was ob­

tained from Bridges Paving Company, St. Louis, Missouri. The gradation

of the aggregates was established in accordance with recommended

14

procedures of the Asphalt Institute. With 100 percent of the aggregate

passing the 3/4 inch sieve, the following sieve sizes were used: 3/8

inch, Nos. 4, 8, 16, 30, 50, 100 and 200. The gradations used are listed

in Table I. The three gradation curves of the control mixes, which

consisted of 2, 6, and 10 percent mineral filler content respectively,

and the two gradation curves for the experimental mixes which contained

4 and 8 percent mineral filler content respectively, are designated in

Figure 3. The bulk specific gravity for the coarse, fine and filler

materials was 2.70. This value was determined by the water displacement

method. The absorption value, using the Rice Method, was 0.272 percent.

Since the amount of asphalt absorbed by the aggregate was small, the

bulk specific gravity was used to calculate the mix properties as shown

in Table II. The asphalt used in the tests was 85-100 penetration grade

asphalt supplied by the American Bitumuls and Asphalt Company of St.

Louis. Some properties of the asphalt are given in Table III.

C. Test Procedure.

In general the testing procedure followed nResistance to Plastic

Flow of Bituminous Mixtures Using Marshall Apparatus", ASTM Designation

Dl559 (14). The Marshall Method was developed by Bruce Co Marshall and

it determines five basic properties of a bituminous mix: (1) stability,

(2) flow, (3) air voids, (4) unit weight and (5) VMA.

D. Preparation and Testing of Specimens.

The specimens are prepared by heating approximately 1200 grams of

0 0 the properly graded aggregate to a temperature of 325 F (+ 5 F) and

mixed with the specified amount of asphalt binder which has been heated

to 300°F (+ 10° F). The constituents are mixed thoroughly for a maximum

duration of two minutes and placed in a compaction mold which has been

15

TABLE I - AGGREGATE GRADATION DATA

GRADATION - % FINER BY WEIGHT PASSING

Control Points Experimental Points Sieve Size A B c E F

3/4 100 100 100 100 100

3/8 71.5 72.5 74 72 73

4 50 52.5 54.5 52 54

8 35 38 40.5 36.5 39

16 24 27 30 25 28

30 16 19 22.5 18 21

50 9.5 13 17 11.5 15

100 5 9 13 7 11

200 2 6 10 4 8

Sieve Sizes Raised To 0.45 Power

100 r-----.----,---.---.-- --,---------r-- -----,.---

90 f----- t----+

80 ----~--·--·--~----4------~--------~ _____ J ___ //

70 ---!----! -1-------f----l--------- ---~- ---------- --

cc c:: 60 ~------l---t---1 ----!--------+-----+---

··-' [!; (/)

l~ p..

.w ~ <l) (.)

l-<

50 i-------1- --~-- ·--·-

CJ 40 J----l-+---1-----+--------+ '/ p..

30 ·----~----

20 1------+---+

10 ( __ ___£:_

-- ~ -- E

0 t-- A ·---· J.._.j_,__.__

0 200 100 30 16 8

B- 6/o Filler

'l----k.l9!o Filler E- 4% Filler F- 8% Filler

4

Sieve Sizes

1" 2

FIGlJRE 3. GRADATION CURVES (DEVELOPED BY LUFSEY & GOODE)

3/4" r-' 0"1

TABLE II - CALCULATING FOR THE ASPHALT ABSORBED BY THE AGGREGATE

VIRTUAL SPECIFIC

G = Wag v v - w

nrrn tac G ac

G = 863.8 v 343

G = 2.72 v

- 25.2 1.02

GRAVITY

BULK SPECIFIC GRAVITY (AGGREGATE)

G = Virtual Specific Gravity v Wag = Weight of Aggregate

v = Volume of Voidless Mix mm

w = Total Weight of Asphalt tac =

G Apparent Specific Gravity = ac Asphalt

G = ag Weight in Air = 671 = 2. 70 671 - 423 Weight in Air - Weight in Water

ASPHALT ABSORBED BY AGGREGATE

A = G G ac v ag X 100 G - G r ag

A = 2.72 - 2.70 .272 ac (2.7)

X 100 = 2.72

A ac

= Amount Asphalt Absorbed by Aggregate- Lb./100 lbs.

TABLE III - PROPERTIES OF ASPHALT CEMENT AT 77° F

Penetration Softening Point Ductility Specific Gravity

96 150 em. (Plus) 1.02

17

of

18

h 0 0 pre eated to a temperature of 225 F (+ 5 F). The loose mix is compacted

by applying 50 blows to each face of the specimen with a 10 pound hammer

dropped from a height of 18 inches. Heating the compaction hammer on a

hot plate located near the compaction blockminimizesthe heat lost by

the specimen during compaction. The specimen is then placed in a cold

water bath to cool for a period of not less than two minutes. After

the specimen has cooled it is extracted from the mold by means of a

hydraulic jack. Upon removal the specimen is appropriately marked and

allowed to dry and cool to room temperature. The unit weight of the

specimen is determined by weighing it first in air and then in water.

The specimen is then placed in a hot water bath at a temperature of

140°F (~ 1.8°F) for 30 - 40 minutes and then compressed in the Marshall

Apparatus until failure occurs. As the specimen is compressed at a

uniform rate the stability dial reading and flow value measured in 1/100

inch increments are observed simultaneously and recorded. Due to rapid

heat loss it is imperative that the specimen be tested within 30

seconds from the time it is removed from the water bath, otherwise the

observed values for stability and flow must be discarded. The stability

dial readings are converted to pounds based on conversion factors that

take into account the volume of the specimen.

Points were labelled for the control mixes (2, 6, 10 percent

filler) and for the experimental mixes (4, 8 percent filler). They are

shown in Table IV. Increments of 1.0 percent asphalt cement, except as

noted in Table IV, were added to aggregate batches with six briquettes

compacted at each point. This allowed for more accurate results to be

obtained. The properties for the control mixes were determined first

and they are listed in Table V. Calculations to determine some of the

19

TABLE IV - *DESIGNATION OF TEST POINTS X ·~ ::E: r-1 8.0 C-10 ell .!.J 0

E-l 7.0 E-IIIA B-6 F-VII C-9 4-l 0

.!.J 6.0 A-3 E-III B-5 F-VI C-8 !=! (J) u 5.0 A-2 E-ll B-4 F-V C-7 $-I (J) 4.5 F-IV C-7A p..;

... .!.J 4.0 A-1 E-1 B-4a !=! (J) 3.5 A-lA .!.J !=! 0 u 3.0 .!.J r-1 ell

..!:: 0.. 2.0 4.0 6.0 8.0 10.0 rJl

<C

Mineral Filler Content, Percent of Total Mix

*ARABIC NUMBERS = Control Points

ROMAN NUMBERS = Experimental Points

20

TABLE V - TEST PROPERTIES OF BITUMINOUS MIXES - CONTROL MIXES

AIR AC DENSITY STABILITY VMA VOIDS FLOW SPECIFIC

MIX % pcf pounds % % 1/100 in. GRAVITY

A 3.5 146.6 2300 16.1 8.4 5.7 2 .34

4.0 149.3 2860 16.2 7.6 6.3 2.39

5.0 149.0 2639 15.9 4.6 6.3 2.39

6.0 148.5 2550 17 .o 3.6 8.0 2.38

B 4.0 150.3 2685 14.4 5.2 11.5 2.41

5.0 151.0 3926 14.9 3.7 12.6 2.42

6.0 151.0 3291 15.7 2.1 13.2 2.42

7.0 151.2 2710 16.5 .3 17.0 2.42

c 4.5 151.7 3330 13.7 3.5 10.0 2.44

5.0 152.6 3633 13.6 2.9 10.7 2.45

6.0 153.8 2913 14.5 .6 13.3 2.46

7.0 150.4 2135 16.5 .6 23.0 2.41

8.0 148.9 1860 18.5 0.0 25.0 2.39

21

physical properties of a test point within a given mix are illustrated

in Table VI. Data obviously in error required the point in question to

have six new specimens made. Whenever data at a given asphalt content

was widely separated, the specimens were remade. It is believed that

this procedure provided the most accurate and realistic values for the

analysis. From the data tabulated a table was made with space beneath

each property for the actual tested value and a predicted value that

was estimated from the existing control data and inserted prior to the

testing of the specimens E-I through E-IIIA and F-IV through F-VII.

The predicted values were determined by interpolation between the con-

trol mix values for each mix property. The results are tabulated in

Table VII.

The optimum asphalt content for a particular mix design is deter-

mined by selecting the asphalt content that produces maximum density,

maximum stability, and 4 percent air voids and obtaining the average

value from these three properties. The optimum asphalt content for each

mix and associated physical properties are tabulated in Table VIII.

E. Results.

The test results are presented in a manner similar to that re-

commended by the Asphalt Institute. The effect of asphalt content on

the five basic mix properties is included in the results. Definite

trends have been noted and are outlined as follows:

1. Interpolation between asphalt contents 4.5 - 6.5% and mineral filler contents 2 - 10% is valid.

2. Filler content is not always critical.

3. Asphalt content is critical at low filler content (2%) and at high filler contents (8- 10%).

4. Air voids are critical at high filler contents.

TABLE VI - SAMPLE CALCULATIONS - AIR VOIDS, EFFECTIVE ASPHALT CONTENT, VMA

Calculations are based on 100.0 Gram Sample.

Specific Gravity of Sample= 2.41

Weight Aggregate= 241 (.96) = 231.0 gms. (To nearest gram)

Weight total AC = 241 (.04) = 10.0 gms. (To nearest gram)

Weight absorbed AC = .00272 (231) = .63 gms.

22

*(Where .00272 is the amount of asphalt absorbed/100 lbs. of aggregate)

Weight effective asphalt in sample= 10 - .63 = 9.37 gm.

Volume Aggregate = 231 85.6 cc 2.7 =

Volume effective asphalt content

Effective AC content in mix

VMA = 100 - 85.6 = 14.4%

= 9 · 37 9.19 cc 1.02 =

9. 37 100 231+9.37x

Air Voids = 100 - (85.6 + 9.19) = 5.21%

3.9%

A = Asphalt lost by absorbtion ~·:A = G - Gag 100 where,

ac into the aggregate ac v X as

G - Gag lbs./100 lbs. aggregate. v

G = Virtual specific gravity of v aggregate.

G = Bulk specific gravity of ag aggregate.

TABLE VII - PROPERTIES OF BITUMINOUS MIXES TESTED VALUES VS. PREDICTED VALUES

POINT DENSITY STABILITY FLCM VMA - % NUMBER -,\-p ~'rl<A p A p A p A

E-I 149 149.0 2800 2740 8.7 8.3 15.2 15

E-ll 150 149.7 3300 3257 9.7 10 15.6 15.5

E-III 150 150.0 3000 2997 11 11.4 16.3 16.5

E-IIIA 148.5 149.0 2500 2405 13.3 13.5 17.5 17 .6

F-IV 150.5 150.7 3400 3230 11.2 12 14.3 14.6

F-V 151.5 151.5 3750 3643 11.7 12 14.4 14.5

F-VI 152.1 152.0 3100 3000 14.2 14 15.3 15.1

F-VII 150.7 150.7 2400 2220 17.5 19.5 16.5 16.8

*P = Predicted Values

**A = Actual Tested Values

23

AIR VOIDS - % p A

6.2 6.7

4.3 4.4

2.7 3.0

2.0 1.8

4.5 4.6

3.3 3.4

1.5 1.3

.4 .8

MIX AC

A

B

c

E

F

TABLE VIII - TEST PROPERTIES OF BITUMINOUS MIXES AT OPTIMUM ASPHALT CONTENT

OPTIMUM CONTENT - % DENSITY STABILITY VMA

4.90 148.8 2750 16.2

5.19 151.2 3850 15.3

5.03 152.5 3630 13.6

5.23 150.0 3150 15.8

5.1 151.8 3620 14.6

24

AIR VOIDS FLOW

5.0 6.5

3.0 13.0

2.5 10.7

3.7 10.2

3.0 12.0

5. VMA are little affected until an asphalt content of 5 or 6'/.', is reached, then VMA values increase rapidly.

6. Density increases with increasing mineral filler content.

7. Stability is maximum at 6% mineral filler content.

8. Flow values are not significantly effected until a filler content of 8 - 10% is reached and then they rise rapidly.

The properties for the various mixes are listed in Table V (Con-

2')

trol Mixes) and Table VII (Experimental Mixes). An increase in mineral

filler yielded an increase in the desirable properties, notably

stability, for a dense graded mix up to a certain filler percent, then

the stability and the associated properties decreased and resulted ~n

undesirable mixes.

26

IV. DISCUSSION

The development of the dense gradation chart based on the Talbot

formula with an exponent of 0.45 by Goode and Lufsey greatly facili­

tates the ability to obtain values of an aggregate gradation for any de­

sired dense graded mix design. Ease and accuracy are the salient trade­

marks of this chart. The curve is a straight line and the values on the

ordinate scale can be determined readily.

As mentioned previously the variables in this investigation are

asphalt cement and mineral filler. Prior to discussing the effects of

the variables on the ability to predict the physical properties of a

mix and how the variables effect a dense graded mix it is imperative

to evaluate the role of each of these two variables in a dense graded

bituminous mix. The asphalt cement performs a dual role by acting as

a cementing agent, thereby increasing the cohesive properties of the

mix and partially filling the voids in the mineral aggregate. The

mineral filler frequently performs a dual role, but it is somewhat less

obvious. Intergranular contact between the particles is increased and

some of the finer particles of mineral filler are in suspension in the

asphalt cement and they either coat the larger particles or have an

appreciable effect on the apparent viscosity of the asphalt (11).

A. Behavior of Dense Gradation in a Bituminous Mix.

By definition a dense graded mix has a low percentage of voids.

This implies that good interparticle interlock exists and that there is

some internal friction, although it must be remembered that internal

friction is primarily dependent upon the surface characteristics of

the aggregate. Of the three factors that effect stability, namely,

friction, cohesion, and inertia, the effects of friction and inter­

granular interlock are most significant. The quantities of each size

27

of aggregate must be closely controlled. An excessive amount of mineral

filler, for example, can actually increase the volume of voids present

in the mix and consequently decrease stability.

B. Variables in the Marshall Method for Testing Bituminous Samples.

The Marshall Method is a comparatively simple laboratory procedure

to perform. The test results are quite useful because the test results

have been correlated to field behavior over an extended period of time.

From the many sources of error considered in the test procedure the most

important variable is the individual who performs the test. It is

essential that good laboratory technique be developed before any test

data is recorded for analysis. Time, temperature fluctuation, and rate

of compaction are other factors that have an important role in the out­

come of the test results for each specimen. These factors are all

interrelated. Too much time consumed in preparation of a specimen

causes an excessive heat loss which effects the ultimate properties of

the specimen. A uniform rate of compaction is essential to insure a

reasonable range of values for the bulk specific gravity and the unit

weight. The physical properties determined by the Marshall Method are

directly dependent upon these weight-volume relationships.

C. Control Mixes.

Mix A consisted of a high density gradation with two percent

mineral filler. While mixing the AC and aggregate on the hot plate the

bitumen was readily adsorbed by the fine aggregate and the mineral.

28

filler and any remaining asphalt was then available to coat the coarse

fractions. This indicates a difference in surface energy or wetability

exhibited by the various sized aggregates. Specimens with two percent

filler and with asphalt contents less than 3.5 percent did not produce

consistent results. This is attributed to the fact that an in­

sufficient quantity of asphalt was present to coat all of the particles

properly. The basic physical properties for all mixes are represented

graphically in Figures 4 through 8. At two percent filler it is noted

that Marshall stability, flow, and unit weight values are low. (See

Figures 4, 6 and 8). The low stability and unit weight values are due

to the inability of a small amount of filler to fill enough of the

voids and add to the intergranular contact between particles. In addi­

tion there is more aggregate retained on the larger sieve sizes in

this particular mix and as a result less AC is required than in the

more dense mixes. Conversely adding bitumen beyond the optimum asphalt

content of the mix will have a tendency to form a layer of asphalt be­

tween the particles which reduces intergranular contact. The high per­

centage of air voids in Mix A (Figure 5) renders it an unsatisfactory

mix because the allowable limits (3-5 percent) for air voids in the

mix are exceeded. A high air void content in a mix tends to open the

mix, reducing interparticle contact, and subjects the bituminous mix

to oxidation and weathering action.

Mix B contained six percent mineral filler and exhibited the

most desirable properties of all the mixes tested. Stability was a

maximum at this filler content and a significant increase was noted

in unit weight. (See Figures 4 and 6). High internal friction caused

by good intergranular contact and excellent cohesive qualities of the

asphalt provided the high values for stability. The fact that the

r:tJ '"0 !:! ;j 0

p.,

.. ;>-, .u •.4 ....-l -H ..n

Clj .u Cf.l

....-l

..-4 t\l

..r:: r:tJ H Clj

:a:

4000 l- (I 2% Filler

A 4% Filler [] 6"/o Filler 0 8% Filler

I I // "' \ [] 10% Filler

3000

,,

2000 I. \c '\ .c~·-L·--~ .. ~- .. 1 1 I 1"' < ·---~ --· .... ~--- ... - --··· ..... --·-··~ • - -·---~··'· ... 3 4 5 6 7 8

AsphA.lt Content, Percent by \·!ci~._;ht of Total Hix

FIGL.(E !.f. HAI~SIL-\LL STABJLl'lY PEIXJ.'TO:\'SlllPS

N \0

30

:L 0 2/o Filler

t:. 4% Filler

7~ 0 6% Filler

.w 0 8% Filler c

6~ t.i 10% <l) Filler u H ; <l) ' p..

sf-I

(/)

41-'"0 •.-I 0 > 3r H •.-I <!! 2

- ..... -

1

3 4 5 6 7 8

Asphalt Content, Percent by Weight of Total Mix

FIGURE 5. AIR VOIDS RELATIONSHIPS

15t 0 2% Filler A 4/o Filler

154 0 6% Filler .....

153 ~ 0 8% Filler g 10% Filler

4-1 ' u 1s2 r-Q... t .w 151 ~ ..c: b()

•.-I

150 ~ <l)

:3: .w •.-I 149 ;- ~ c

I :::>

1481

147 r ! , I

146 i I l I

3 5 6 7 8

A:,phalt Content, Percent by Weight of Total Mix

FIGURE 6. UNIT WEIGHT RELATIONSi.:IPS

31

19 0 2% Filler .w ~ c 4% Filler ,:; u [J 6% Filler l-< 18 <lJ 0 8% Filler p...

rw 10% Filler C)

17 r .w M bD <lJ l-< bD 16 bD

-< .---1

M 15 l-< <l)

c: •M ;:E::

(fj 14 -'"Cl ' •M I 0 >

13b I

I 1 I I l 3 4 5 6 7 8

Asphalt Content, Percent by Weight of Total Mix

FIGURE 7. VOIDS IN THE MINERAL AGGREGATE RELATIONSHIPS

26f ,.- ;

24r 0 2% Filler -i

2t ~ 4% Filler I I

[J 6% Filler I

201 0 8% Filler I

18~-- II 10% Filler ...c l u

161-c: ·M

...--~j§ 11,~ 12

;3 10-• 0

8i-.---1 ~

! 0 6'--

4L

~t I I I I I , I . ....l

3 4 5 6 7 0

Asphalt Content, Percent by Weight of Total Mix

FIGURE 8. FLOW RELATIONSHIPS

32

unit weight curve was not the maximum unit weight curve suggests that

there are unfilled voids present which is a desirable characteristic.

Asphalt contents from 4.5-6 percent provide sufficient air voids to

meet the recommended limits for air voids (Figure 5). The allowable

range of 3-5 percent air voids insures sufficient space for the AC,

for additional compaction of the mix due to the applied loads, and for

the expansion of the asphalt in warm weather. The Asphalt Institute

recommends a VMA value of not less than 15 percent for the gradation

used in this investigation (15). Figure 7 reveals that AC contents

above approximately five percent will satisfy this requirement. The

VMA value is that value that insures sufficient space for the AC and the

air voids in the compacted bituminous mix. Flow values measure the

amount of compression of the specimen at the time maximum stability

is being recorded. Figure 8 indicates that the flow readings for six

percent filler vary between 12 and 16. The recommended limits for

flow are 8-18. Thus, at six percent filler all specimens tested yield

flow values within the acceptable limits.

Mix C contained ten percent mineral filler. As the percent of

mineral filler was increased the unit weight continually increased.

It is apparent that the unit weight increased to produce maximum values at

ten percent filler (Figure 6). Unit weight and stability values in­

creased simultaneously and then a continued increase in unit weight

resulted in a reduction in the stability values (Figures 4 and 6). A

reduction in the amount of air voids present indicates insufficient

space for the bitumen. This will cause a loss in cohesion which, in

turn, has a negative effect on the stability of the mix. For speci-

mens tested with ten percent filler it was almost impossible to ob-

tain a value for air voids within the allowable limits as shown in

33

Figure 5 because the filler material occupied most of the air voids

space. The additional filler also causes a reduction in the VMA. This

can be associated with the high values for unit weight. However, at

7 and 8 percent asphalt content the VMA begins to increase rapidly.

This is caused by an increase in bitumen content which tends to move

the particles apart. A noticeable amount of bulking was observed at

the higher bitumen contents. High unit weight values are noted in

spite of the increased volume because the added asphalt has a higher

specific gravity than the air it displaces. An insignificant amount

of deformation is observed at the low asphalt contents (4.5 and 5

percent), but as the asphalt content increases the asphalt forces the

particles apart, thus reducing interparticle contact, and rendering

the specimens more compressible, as illustrated in Figure 8.

D. Experimental Mixes.

Mix E consisted of a dense graded mix containing four percent

mineral filler. As previously discussed the predicted values for the

physical properties of the specimens prepared with 4 and 8 percent

mineral filler are entered in Table VII. A comparison of these data

illustrates the close relationship between the predicted values and

the actual test values. The curves representing the physical properties

selected for analysis plotted from the actual test data recorded and

they are illustrated in Figures 4 through 8. It was anticipated that

the various plotted curves representing the physical properties of the

mix would lie within the limits of the control mixes. Therefore, the

properties of Mix E should fall between the curves which represent the

properties of Mix A and Mix B. The data obtained support this con­

cept. Since Mix E is approaching the optimum mix (Mix B) fairly

accurate interpolation can be made for the asphalt contents between

4.5 and 6.5 percent (Figures 4-8).

Mix F contained eight percent mineral filler. The observations

for Mix F would generally be a compromise between the discussions of

Mixes Band C. The curves depicted in Figures 4 through 8 corroborate

this conclusion. However, the further away the design mix is from the

ideal mix the range of asphalt contents which is valid for inter­

polation becomes quite restricted. An indication of this phenomenon

is suggested in Figure 9. The steep peaks show the narrow range of

flow values at maximum stability. As stability values decrease the

34

range of flow values increase rapidly and the curve takes a parabolic

shape. Thus at low and high asphalt contents for each increment of

mineral filler tested a straight line relationship between the physical

properties would not be accurate. A thorough analysis of the data re­

veals that the asphalt content is critical in the design of dense graded

bituminous mixes. Small variations in asphalt content causes significant

changes in the physical properties of the mixture.

E. Validity for Interpolating Between Predetermined Control Values.

The validity for interpreting between known test data can be

evaluated from an analysis of the test data for the control mixes and

the experimental mixes and from the curves plotted in Figures 4 through

8 and Figures 10 and 11. Figures 4 through 8 depict curves generally

equidistant for asphalt contents between 4.5 and 6.5 percent. As long

as the curves remain parallel it is reasonable to assume that inter­

polation between the mix design curves is valid. Figure 10 was pro­

duced by selecting an asphalt content within the limits mentioned above

UJ '"0 (:': ::l 0

p...

I

>-. w

·.-1 r-1 ·.-1 ..0 C'j w

Ct:l

r-1 r-1 (1j

...c: UJ )..< C'j

:8

~'+-000 . -r ---~---- 1" -- r -- I r--

0 2% Filler A 4% Filler

3500 r- I \1 {\ \ [J 6% Filler 0 8/o Filler t1 10% Filler

I J I l \,.,

3000

2500 ~' 2000 ·-

1500 :.L ___ L __________ .L ____ j ___ _ 20 2~--~ 30 0 5 10 15

Flow Values - 1 inch 100

FIGURE 9. FILLER CO:JTE~T CURVES FOR ALL MIXES w \J1

4000

Ul '"0 ~ ::l 0 ~

n

;::.., .w ·.-4 ,..., 3000 •.-4 ..D (\j .w C/)

,..., rl (\j

..c Ul )..< (\j

~

2000

. ..I 0

0

·~ ·····-"·-·.-.1- .. r~...,.,.. ~<~ ·•-•L. --···-.. ·-~---~-~- 1.. ··· . -~--L V~>~· -~~--0 2 4 6 8 10

Hineral Filler Conte ~, Percent by l·!cigi,l of Total Hix

FIGUI~E 10. RETATIOC::SHlP BEHJL~F:\ HAXINLl-1 :1'1ARSllJ\l.L s·/,\JilLI'T':' .1\!\D NDJEI~;\Jo

FitLER co:rrn:·i·. w 0'1

37

; l 20r i \

I ~ Voids in the Mineral Aggregate!

) I I

I ~

.w 12 I l.--i ~ r 154 (J)

G

C) I (::...

H

I (J) .w p...

153 -I

CD

(f) ·ri

'"0 (J ~ ... .....

8L Unit Weight -

0 :.> 152 .w

i

- .,.., ~

::;J

! l51

4L -

_,i 149 i

f _( 148 ' I I I ol I

' I : __ ._.._... 0 2 4 6 8 lG

Mineral Filler Content, Percent by Weight OI Total Nix

FIGURE 11. PHYSICAL PROPERTIES AT 6 PERCE~T ASPHALT CO-:\TENT BY WEIGE':;' OF 'i'OTAL NIX

38

and measuring maximum stability values for each filler content. In

essence this figure verifies the conclusion that interpolation is valid

for the conditions noted previously. The curve accurately represents

what should occur for a dense graded bituminous mixture when asphalt

content and mineral filler content increase simultaneously. The

flatness of the stability curve indicates that a relatively wide

range of asphalt contents may be employed without an unreasonable loss

in stability. This is a desirable characteristic in any bituminous

mix design. In Figure 11 the shape of the unit weight, the air voids,

and the VMA curves indicates that as the mineral filler is increased

it occupies the voids between the larger sized aggregates. In other

words the filler has not been added in sufficient quantity to force

the larger particles apart. The straight line depicting air voids

also indicates the validity of the interpolation within specified

limits. The volume of voids are related to the filler content and

the volume of free bitumen (bitumen remaining after adsorbtion and

coating the aggregate). Since these materials are combined pro­

portionately throughout the range of asphalt contents selected for

valid interpolation, the air voids curve should decrease linearly as

asphalt content and filler content increase. Therefore, since the VMA

consist of air voids plus the effective volume of bitumen, it is

reasonable to expect the VMA curve at 6 percent asphalt content to

be a linear function of the mineral filler content.

V o CONCLUSIONS

From the data accumulated and analyzed there are several con­

clusions that can be. expressed.

39

Interpolation between known values of the physical properties of

the dense graded bituminous mixes tested are valid for asphalt con­

tents in the range of 4.5 to 6.5 percent. Relatively accurate results

are obtained provided interpolation occurs between parallel sets of

data.

The asphalt content for the dense graded mixes used in this in­

vestigation is more critical than mineral filler content. This ob­

servation is most apparent from the test results obtained from Mixes

A and C.

The addition of mineral filler results in a decrease in percentage

of voids (or increase in unit weight) in Marshall compacted specimens.

It is possible to attain high values for unit weight and have an

appreciable loss in stability as illustrated in Figure 4.

40

BIBLIOGRAPHY

1. MARTIN AND WALLACE (1958) Design & Construction of Asphalt Pave­ments, p. 36, 54.

2. THE ASPHALT INSTITUTE The Asphalt Handbook (1962), p. 62, 64.

3. THE ASPHALT INSTITUTE Introduction to Asphalt (1962), p. 34.

4. EDGE, D. (1957} Review and Development of General Equations for Dense-Graded Aggregate Mixtures, Thesis, University of Kansas.

5. CAMPEN, W. H. (1940} Proceedings, Association of American Paving Technologists, Vol. 11, p. 302.

6. TALBOT, A. N. & RICHART, F. E. (1923) Bulletin 137, University of Illinois Engineering Experiment Station.

7. GOODE, J. F. & LUFSEY, L.A. (1962) A New Graphical Evaluating Aggregate Gradations. of American Paving Technologists, p. 178.

Chart for Association Vol. 31,

8. BUREAU OF PUBLIC ROADS (1962) Aggregate Gradation for Highways.

9. HVEEM, F. N. (1949} Gradation of Mineral Aggregates in Dense Graded Bituminous Mixtures, The Crushed Stone Journal, p. 13.

10. HUDSON, S. B. & VOKAC, R. (1962) The Effect of Fillers on the Marshall Stability of Bituminous Mixtures, Highway Research Board Bulletin 329.

11. KALLAS, B. F., PUZINAUSKAS, V. P., & KRIEGER, H. C. (1962) Mineral Fillers in Asphalt Paving Mixtures, Highway Research Board Bulletin 329, p. 15.

12. HEUKELOM, W. (1965} The Role of Filler in Bituminous Mixes, Proceedings, Association of American Paving Technologists.

13. CSANYI, L. H. (1962) Functions of Fillers in Bituminous Mixes, Highway Research Board Bulletin 329.

14. MARSHALL CONSULTING & TESTING LABORATORY ( 1949) The Marshall Method for the Design & Control of Bituminous Paving Mixtures, p. 8.

15. THE ASPHALT INSTITUTE Mix Design Methods for Asphalt Concrete, Manual Series No.2 (1962), p. 34.

16. McLEOD, N. W. (1956) Relationships Between Density, Bitumen Content and Voids Properties of Compacted Bituminous Paving Mixtures, Highway Research Board, Vol. 35.

41

17. WEDDING, P. A. & GAYNOR, R. Eo (1961) The Effects of Using Crushed Gravel as the Coarse and Fine Aggregate in Dense Graded Bituminous Mixtures, Pro­ceedings, Association of American Paving Technologists, Vol. 30.

42

VITA

Robert Ernest Weeks was born on February 4, 1932 at Detroit,

Michigan. He attended primary and secondary schools in Detroit,

graduating from Mackenzie High School in June, 1949. After attending

a preparatory school in Minneapolis, Minnesota for one year he entered

the United States Military Academy from which he graduated in 1954 and

was commissioned a Second Lieutenant, United States Army.

Duty assignments include tours at Fort Benning, Georgia, Fort

Belvoir, Virginia, Korea, and the University of Missouri at Rolla

where he served as Assistant Professor of Military Science, 1961-1964.

Upon completion of this last tour of duty he was selected to remain

at this institution in order to pursue a course of instruction leading

to a Master of Science Degree in Civil Engineering. Recently he was

promoted to the rank of Major.

Major Weeks is married to the former Janet K. Ford, also of

Detroit. They have three children, Kathleen Sue, Robert Edward, and

Thomas Selleck.