VISCOSITY MEASUREMENTS OF ASPHALT-RUBBER BINDERS

R.A. Jimenez University of Arizona

Report ATIT-1

For Presentation at the

National Seminar on Asphalt-Rubber October 30-31, 1989

Kansas City, Missouri

Arizona Traffic and Transportation Institute College of Engineering and Mines

The University of Arizona Tucson, Arizona 85721

July 1989

120

VISCOSITY MEASUREMENTS OF ASPHALT-RUBBER BINDERS

Abstract

Early unpublished work is presented on the measurement for

viscosity of asphalt-rubber blends. The viscometers used were

selected with the thought to minimize "side friction" effects on

the flow of asphalt-rubber. The viscometers were of the falling

coaxial cylinder type and the forced flow Schweyer Rheometer. Most

of the work done was for evaluation of the Schweyer device for

determining effects on rheometer and rubber variables on measured

viscosity. These variables were (a) diameter of flow-tube, (b)

amount of rubber in the blend, (c) gradation of rubber particles,

(d) type of rubber, and (e) test temperature. The shear stress­

shear rate relationship was taken to be a power function ( T =

I i 0) and viscosity ( T / i ) was calculated at a shear rate of 1

sec-1 and therefore equal to I the intercept at 10° on log-log

coordinate axes. The data indicated that:

1. the viscosity be calculated at a shear rate of 1,

2. flow tubes of 9.70 rom and 12.70 rom yielded the same

values of viscosity,

3. the flow tube of 2.43 rom (a standard) was not considered

adequate for asphalt-rubber,

4. the 25C viscosity of one type of rubber blend increased

as the rubber content increased from 20 to 25 to 30

percent,

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5. there was not a direct relationship between viscosity and

range of particle size,

6. the viscosity-temperature susceptibility of one rubber

blend was greater than for the other, and

7. the Schweyer Rheometer was considered a good device for

comparing rheological properties of asphalt-rubber

blends.

122

INTRODUCTION

Asphal t-rubber was developed and patented by C. H. McDonald

during the early 1960s. The use. of asphalt-rubber (A-R) has

increased dramatically since then for highway construction, as a

binder, waterproofing layer, or a strain attenuating layer to

minimize reflection cracking. Public use of A-R requires that

there be specifications of its properties, one of those being the

rheological (flow) characteristics of A-R blends. The material

reported here is concerned with early and unpublished work that was

done for measuring the viscosity of asphalt-rubber blends.

Asphalt-Rubber

The asphalt-rubbers used in the work done were mixtures of

asphalt and fine grindings from rubber tires. The amount of rubber

in the early mixtures varied from 20 to 30 percent by total weight

of the asphalt rubber blends. These mixtures were different from

the old rubberized asphalts in that synthetic rubber (SBR) was used

instead of natural rubber (latex), the amounts of rubber mixed with

asphalt was much greater than the 3 to 5 percent for latex, and the

maximum particle size of the SBR was about 1.2 mm (0.05 in.) and

for the natural rubber about 0.07 rom (0.003 in.).

The rubber and asphalt are mixed at temperatures between 138

to 190 C (280 to 375 F) for some specified period of time. (In our

work, 30 minutes at 191 C (375 F). The dispersion of the rubber

123

particles to produce the desired improvements in the asphalt may

be affected by the following:

1. Mixing temperature--usually detrimental if held too long

above .216 c (420 F) [1].

2. Duration of mixing time, the effect is also dependent on

temperature; however, the effect becomes constant after

a minimum time [2].

3. stirring shear--break down of rubber if too high [1].

4. Particle size and its distribution.

5. Type and quantity of rubber.

6. Amount of aromatic (cyclic) component in the asphalt [1].

There is somewhat general agreement that rubber is not soluble in

asphalt and that under optimum conditions a specific particle size

may increase in volume (swell) by a factor of up to 5 for natural

rubber [2] and by a factor of up to 3 for synthetic rubber [3].

124

VISCOSITY TESTS

Materials

The materials used in this work were furnished by the Arizona

Department of Transportation (ADOT). At that time, ADOT was doing

considerable research and construction with asphalt-rubber. As a

consequence, no specification tests were performed on the materials

other than those used to quantify the variables of the program

being reported.

Asphalt

The two grades of asphalt used were of AR-1000 and AR-4000;

however, different batches of AR-1000 were used for work done at

different periods of time. The asphalts were assumed to contain

a sufficient amount of an aromatic component to react with the

rubber. An oil extender (an aromatic compound) was included to be

mixed with one of the rubber blends.

Rubber

The rubber particles used in the A-R mixtures were identified

with the letters TP for one source and G for the second source.

Gradations of the rubber types are shown in Table 1. In Table 2

are listed the gradation characteristics of coefficient of

uniformity and coefficient of curvature for the rubber sizes and

their combinations. The data in the tables show that the largest

particles were less than 1.2 mm (0.05 in.) and generally larger

125

Table 1 - Gradation of Rubber Particles

sieve size #8 #16 #30 #50 #100

Opening, in. 0.094 0.047 0.023 0.012 0.006

Opening, mm 2.4 1.2 0.58 0.30 0.15

Percent Passing sieve

TP-044 100 98 20 2 0

TP-027 100 95 23 12

TP-0165 100 75 20

G-274 100 72 32 12

Table 2 - Gradation of Parameter Values of Cu and Co for Blends of Various Rubber Particle sizes

Rubber Blends

G-274

TP-044

TP-027

TP-044 + TP-027, (1:1)

TP-044 + TP-027 + TP-0165, (1:1:1)

TP-0165

coefficient of uniformity

---------, coefficient of curvature

126

C * u

3.6

1.8

3.0

2.7

3.2

2.5

C ** o

1.3

1.1

1.6

1.2

0.9

1.2

#200

0.003

0.08

0

1

5

than 0.15 rom (0.006 in.). The G-274 rubber particle sizes had the

largest range while the TP rubber particles were more of a one­

sized distribution.

127

Viscometers

Important characteristics of asphaltic binders are the

rheological properties and how they influence their usage and

performance. These materials are often specified with reference

to viscosity values and durability. During the initial study for

measuring viscosity, attention was given to the usual viscometers

available to us for making such measurements. In consideration of

the swelling of the rubber particles, the Saybolt viscosimeter was

discounted because of the size of orifice and also the Brookfield

because of the possible alignment and separation of particles by

the rotating spindle. Our first determinations were performed with

a home-made falling coaxial cylinder viscometer and later on with

a purchased Schweyer Rheometer.

Falling Coaxial Cylinder

A schematic diagram of the viscometer is shown in Figure 1.

As can be seen, the device was composed of an outer cylinder, an

inner coaxial cylinder, and the cylinders were separated by an

annulus of the sample. The shear stress was obtained at the inner

surface of the annulus and the velocity of the inner cylinder was

determined by following its rate of displacement with a

cathetometer for low viscosity materials on an extensometer dial

gage for high viscosity ones. A derivation of an equation for the

calculation of viscosity is given by Jimenez in Reference 4.

The dimensions of the viscometer were established in

consideration of the swollen maximum particle size of rubber. The

128

I-4--Weight L-..f'\n:-'t-..J

\j~- Coaxial Cylinder (falling)

/]...011-- 0 ute r Cylinder

Figure 1. Schematic of Falling Coaxial Cylinder Viscometer

129

Stand

largest particle was 1..2 nun (0.05 in.) and if it increased in

volume by a factor of 3, its diameter would be 3.6 mm (0.15 in.).

It was assumed that to have free flow through a tube, the tube

diameter should be 3 times the maximum particle size. On that

basis a tube diameter of about 12 .. 7 nun (0.50 in.) would be needed

or an annulus thickness of 6.85 nun (0.25 in.) for the viscometer.

In comparing results obtained with annuli of various

thicknesses and a constant height of 25.4 nun (1.0 in.), it was

established that the 6.85 X 25.4 nun (0.25 X 1.0 in.) annulus was

satisfactory for making the viscosity measurements.

Schweyer Rheometer

The device was obtained through funds from the National

Science Foundation and purchased from the Cannon Instrument

Company. The basics of the device are shown in Figure 2 and the

determination for viscosity is as follows:

The sample (asphalt) is placed in the sample tube and forced

into the test tube which has the desired capillary diameter. A

controlled air pressure is held in the air cylinder and the force

on the piston is transferred to the plunger for applying a constant

stress on the asphalt. Knowing the diameters of the sample tube

and test tube the stress on the sample (asphalt) in the capillary

can be calculated. The velocity of the plunger is obtained with

the LVDT connected to a strip chart recorder. Descriptions and

operations of the rheometer are given in Reference 5 and the manual

furnished by Cannon.

130

AIR CYLINDER

PISTON

PLUNGER

I

SAMPLE TU~E

TEST T UBE (CAPILLA RY)

II I !I H

DS ,I I

~ ~ LS

~ ··l ~ t -'I-

-II- DT

/-( ~ ) PRESSURE GAGE

.

r---{\~ ~

LVDT

I

I TES DENOTES T MATERIAL

Figure 2. Schematic of Schweyer Rheometer

131

Examination of the diagram and conversations with SChweyer

indicated the feasibility of using the sample tube as the measuring

tube and to also increase its diameter to 12.7 rom (0.50 in.).

Measurements for viscosity were made with tubes of 2.43, 9.70, and

12.7 rom in diameter (0.09, 0.38, and 0.50 in.). The 2.43 rom (0.09

in.) tube was the largest size supplied with the device.

Work Programs

The work reported here was done over three different periods

of time; however, the tables shown below are for the investigations

performed with the SChweyer Rheometer. The first viscosity

measurements were obtained with the falling coaxial cylinder

viscometer and the results are presented for comparison with

viscosity values resulting from use of the rheometer.

Table 3 lists the tests that were performed with the

Schweyer Rheometer. Although the two phases are shown under one

table the testing periods and asphalt cements of AR-1000 were

different.

Phase 1 of Table 3 shows the main variables to be

investigated for responses with the rheometer were the test tube

diameter and also the particle sizes of the rubber.

In Phase 2 of the table it is seen that the principal

variables were gradation of the rubber particles, the amount and

type of rubber.

132

..... tH tH

r-~

Rubber Bl end Gradation of Rubber

Test Temperature 15 DC

Test Tube Size 9.70 12.7 Diameter, mm

Type of Rubber

Type of Asphalt

Test Temperature DC

Gradation TP-044 of Rubber

Amount of Rubber, 20 25 % BTW

Table 3. Summary of Tests Performed

Phase I - Rubber Content of 25 Percent BTW

TP-Rubber and AR-I000 Asphalt

TP-044 TP-0165

25 35 25 35

2.43 9.70 12.71 2•43 9.70 12.7 2.431 9.701 12.7 2.43 9.70 12.7

Phase II - Test Tube Diameter of 9.70 mm

TP . ~ Gr274

AR-IOOO AR-4000 AR-4000 AR-1000

25 4 25 4 25 25

TP-044 +

TP-027 TP-044 TP-027 TP-044 TP-027 TP-044 TP-044 + + +

TP-027 TP-0165 TP-027 (I: 1) (1:1:1) (1:1)

30 25 25 25 25 25 25 25 20 10 20 20

RESULTS AND DISCUSSIONS

Results of the viscosity measurements made are presented and

were based assuming that the relationship ~etween shear stress and

shear rate, T vs. i , could be expressed as a power-law fluidity.

This expression was as follows:

; = I l' e ----------------------------- 1

The log-log coordinates of ; and 1'Plot as a straight line; I is

the stress value (intercept) where i' is equal to 1 (100) and c is

the geometric slope of the line.

Falling Coaxial Cylinder

Table 4 shows the viscosity values obtained for both AR-1000

and asphalt-rubber with 25 percent TP-044. The data suggest the

higher viscosity for the A-R blend at higher temperatures (but

< 600 C) and lower viscosity at lower temperatures (~ OOC). The

testing shear rates of the tests were selected at that time to

bracket a selected value of 5 X 10.2 sec· I •

Schweyer Rheometer

As indicated earlier, the work period and the AR-1000 were

not the same for the two phases.

134

Table 4 - Viscosity of AR-1000 Asphalt and Asphalt-Rubber by Falling Coaxial Cylinder Viscometer

Temperature °C. Viscosity, ( ~ = 1.0)104pa-sec

Temperature °C. Viscosity, ('Y = 1.0) 104Pa-sec

135

15 106

14 113

AR-1000

25 3.8

Asphalt-Rubber

25 8.6

35 1.3

40 2.2

Table 5 - Viscosity of Asphalt Rubber by SChweyer Rheometer Affected by Tube Diameter and Temperature

Viscosity (i' =1. 0) 104 Pa-sec

Temperature, ·C

Tube Diam mm

2.43 9.70

12.70

2.43 9.70

12.70

*Test tube diameter of 3.19 rom

136

15

46* 77 80

25

TP-044

4.0 8.0 8.0

TP-0165

2.4 8.2 8.3

35

1.1 5.1 4.8

1.3 4.9 5.1

Phase 1

The results of the tests listed in Table 3 as shown on Table

5 and depicted graphically on Figure 3. In Table 5 it is seen that

there is not much difference on the viscosity values obtained with

the 9.70 and 12.70 mID test tubes for either the TP-044 or TP-0165

rubber particles. The effects of temperature and test tube size

on viscosity are more easily visualized with the curves of Figure

3. The figure shows there was not much overlap of the rheograms

for the two tubes and also that the values for I or viscosity at

a shear rate of 1 sec-1 did not need extrapolation of the curves.

It is apparent that the viscosity obtained with the 2.43 mID

diameter tube were lower than those with the 9.70 mm one. This

result was contrary to first thoughts since one would expect the

swollen rubber particles with sizes of up to 4.5 mID to restrict

flow through the 2.43 diameter tube. The reason for this

difference is given as follows on a conjectural basis.

137

5

0105 a...

5

•

5 . -I "(, sec.

/0. _ 6.:0 - Dlo.-2.43mm

~""-,.c.. .... - I / I::i.

:/ V

/~

Figure 3. Typical Asphalt-Rubber Rheograms

138

It is noted that the viscosity of the asphalt AR-1000 as shown

in Table 4 was 3.8 x 104 Pa-sec and 4.2 x 104 Pa-sec shown in Table

8. These values are very close to the 40 x 104 Pa-sec shown for

the A-R measured with the 2.43 rom tube. This would seem to

indicate that asphalt only was being forced through the test tube.

For this to have occurred, the rubber particles had not formed a

structural skeleton which would have carried part 0 the plunger's

force. If so, then the hydrostatic pressure was not resisted by

the elasticity of the particles and piping of the asphalt was

allowed. It is emphasized that sufficient data are not now

available to support the above statements.

Examination of the data in Table 5 will show that the small

sized particles of TP-0165 in the A-R blend had lower viscosity

than the TP-044 blend when measured with the 2.43 rom tube, but had

essentially the same viscosity when determined with either of those

larger 9.70 or 12.70 mm tube. If the larger particles of the

TP-0165 rubber are assumed to swell to 1.5 mm (3 x 0.50 rom), they

should be able to flow through the 2.43 diameter test tube and the

viscosity should perhaps be slightly higher than that for the

straight asphalt (4.0 x 104 Pa-sec). At the present, the above

response differences of results due to tube size and rubber blends

cannot be explained.

Phase 2

The variables in this portion of those works were principally

amount of rubber and particle gradation. Also two types of rubber

139

and grades of asphalt were used. The test tube size had a diameter

of 9.70 mm which was the sample tube (see Figure 2) that was a

standard part of the rheometer.

For this portion of the report, visc?sity will be given as the

value of I ( 1 = 1. 0 sec-I); however, the T - t relationships

were developed from measured shear rates generally ranging from

0.01 to 0.10 sec-I when testing at 25C. Thus, in order to obtain

a value for I, the T - t curve had to be extrapolated over one

decade of shear rate. As a result of the extrapolation, the

viscosity values obtained in this phase should not be compared with

those obtained for similar mixtures of Phase 1.

In Table 6, an examination of the viscosity values shows that

the TP-044 yielded higher values than did the G-274 rubber. The

difference may be due to the greater amount of TP-044 and also that

the G-274 blend contained an extender oil which would serve to

reduce viscosity of the straight asphalt. The data also shows that

between the temperatures of 4 and 25 C, the increase in viscosity

(temperature susceptibility) of the G-274 was much greater than for

the TP-044 blend.

Table 7 has a listing of viscosity determined at 25 C for the

TP-044 and G-274 blends containing different amounts of rubber.

It can be seen that the viscosity of the TP-044 blend increased as

the amount of rubber increased. However, there was no significant

difference in viscosity for the G-274 blends for rubber content of

10 and 20 percent.

140

Table 6 - Viscosity of Asphalt Rubber Affected by Asphalt Grade and Rubber Type Measured with the Schweyer Rheometer at 4 and 25°C Tube Diameter of 9.70 mm

Asphalt Grade AR-I000 AR-4000

Rubber Type TP-044 G-274 TP-044 G-274

Amount of

Temp. , °c

Viscosity 104 Pa-sec

Rubber % 25 25 20 25 20

4 25 25 25 4

(1 =1. 0) , 480 28.6 18.5 64.9 5830

Table 7 - Viscosity of Asphalt-Rubber Affected by Rubber Content and Type Measured with the Schweyer Rheometer at 25° C

20

25

33.2

Type of A-R TP-044 + AR-I00 G-274 + AR-4000

Amount of Rubber, % BTW

Viscosity ( 1 =1. 0) , 104 Pa-sec

20

18.7

141

25

28.6

30 10 20

41.7 32.1 33.2

The effect of rubber particle gradation on viscosity is shown

in Table 8. The data indicates that with exception to the TP-027,

the viscosity increased as the coefficient of uniformity increased;

that is, the range of particle size increased. The reader is

reminded that the gradation (Cu ) was based on the original non­

swollen particles. There is no assurance that all sizes swell by

the same factor and that the resulting values of Cu would be in the

same numerical order as for the dry rubber.

142

AR-I000 with 25

TP-044

TP-044 +

TP-027

TP-044 +

Table 8 - Viscosity of Asphalt-Rubber Affected by Gradation of Rubber Cu Measured with the Schweyer Rheometer at 25° C

Asphalt Cu of viscosity (1 = 1. 0) percent Dry Rubber 10· Pa-sec

1.8 28.6

027 (1:1) 2.7 47.2

3.0 37.6

027 + 0165 (1:1:1) 3.2 57.5

No Rubber 4.2

143

CONCLUSIONS

An objective of the work reported was to determine a method

for measuring the viscosity of asphalt-rubber at ambient or reduced

temperatures. The problem contemplated was the interference to

flow of rubber particles that were assumed to swell to about 4rom

(0.16 in.) in size. The work reported was not a unified effort;

it was performed during three different periods of time and with

different asphalts.

limited, they are

conclusions.

However, even though the data are somewhat

considered sufficient for the following

1. The viscosity of the asphalt-rubbers used and others of

similar type can be determined through flow of the

material within tubes of effective diameters of at least

9.70 rom (3/8 inch).

2. The viscometers of the falling coaxial cylinder and

Schweyer Rheometer were adequate for determining

viscosity at ambient temperatures.

3. The viscosity of the TP blends increased as the amount

of rubber increased and also as the range (Cu ) of

particle sizes increased.

4. The viscosity of the G-274 blends showed the greater

susceptibility to temperature.

5. Reproducibility of viscosity value is considered to be

affected principally by the preparation of sample and

144

extrapolation of test data rather than by the test

device.

6. It is suggested that the viscosity of asphalt-rubber be

determined at a shear rate of 1 sec-1 for tempe~atures

ranging from 4-35 C (39-95 F).

145

ACKNOWLEDGEMENT

The majority of the tests were performed by students in the civil Engineering Department. The measurements for viscosity were made over a period of time spanning almost two years and so slight variations in techniques for making and testing asphalt-rubber are certain to have existed. We appreciate the help given and thank those students: W. White, S. Wilson, "and K. Stokes.

146

REFERENCES

1. Endres, H.A., "Latest Developments in Rubberized Asphalt," A

paper prese.nted at the Fourth Annual Highway Conference at the

University of the Pacific, Stockton, California, 1961.

2. Bituminous Materials in Road Construction, Roads Research

Laboratory, Her Majesty's Stationery office, London, 1962.

3. Green, E.L. and Tolouen, William J., "The Chemical and

Physical Properties of Asphalt-Rubber Mixtures," Report

ADOT-RS-14(1621, Arizona Department of Transportation, 1977.

4. Jimenez, R.A. and B.M. Gallaway, "Laboratory Measurements of

Service Connected Changes in Asphaltic Cement," Proceedings,

AAPT, Vol. 30, 1961.

5. Schweyer, H.E., L.L. smith and G.W. Fish, "A Constant Stress

Rheometer for Asphalt Cements," Proceedings, AAPT, Vol. 45,

1976.

147

"Viscosity Measurements of Asphalt Rubber Binders" by Dr. Rudy Jimene3, P.E. University of Ari30na, Tucson, AZ

Question: Was the surface area differential between the 044 and the 027 and 0165 taken into account.

Rudy: The one with the greatest amount of -che finer si3es would have -che greatest surface area_ l would be referring to the California factors in this sense but to answer your question they were not taken into account.

Question: Did you actually run or have run natural rubber content, tests on the rubber you were using.

Rudy: No, I just took the samples as they were sent to me.

Question: As SBR and as natural?

Rudy: Right, as they were sent to me.

Gale Page: Florida Dept. of Transportation, I don't have a question but I do have a comment. I am glad too see that you have used the concept of measuring engineering properties of a material at the tempera-cure, environment, and loading of interest. I believe that it is very important -chat the high or low temperature properties of the AC or the AR binder be measured at or near the temperature of interest which you have done rather than extrapolate results. This may not have the precision or result in the discrimination necessary, so that other indicator tests may be necessary until the technology catches up. But the point is that we should not lose sight of the goal of measuring basic engineering properties before accepting indicator test at high and low temperatures.

Rudy: Thank you Gale.

Don White: University of Ari30na-for the benefit of many people here, I might comment that I have done viscosity work on slurrys, and I consider rubber and asphalt as a slurry even though it is a swollen slurry with a lot of the asphalt in -che rubber. I have been measuring the vis­cosity up in the range of one to three million centipoises and we had our best success with a modified Inston-rheometer with larger orifices

148

so the slurry would pass through and would give us the pseudoplastic effects, that is, the shear thinning at high shear rates. These are the shear rates that you would find in extruders, maybe 1,000 to 10,000 reciprocal seconds. Then we also used, a Haake rotary viscometer for a portion of the work. Unfortunately, those will only go up to 100 reciprocal seconds. I pass that information to you, but I am wondering today for asphalt mixtures of rubber, what is the most accepted rheometer for obtaining good viscosity data?

Question/Rudy: Are you asking about the Asphalt-Rubber?

Answer/Don White:·

Answer/Rudy:

Don White:

Rudy:

Yes, and I presume that these viscocities are fairly low. 1000 centi-poises or not, or are they higher than that?

They are much higher than that, about 1,000,000 poises at 77°F., and if you go to a lower temperature, they are going to be higher than even 10,000,000 poises.

OK! 50 what viscometers are people using today for Asphalt-Rubber?

This is ten-year old data and I know that they have been measuring viscosity at the higher temperature of 375 F. Jim, would you like to take a crack at that one?

Question/Jim Chehovits, Crafco, Inc:

I really don't know if anyone is measuring viscosity at o the lower temperatures. By low, I mean about 77 F. or below

today. But I think from what we have seen if we look at the data over the last 15 years, probably one of the most appropriate types of viscometer used for the lower temperature area in a relatively solid type range and your looking at the high viscosities is probably the sliding plate type. They are quite a bit more simple than a 5chweyer and would do the best job. Viscosities today are mostly only measured at high temperatures for applica-tion characteristics using either a Brookfield or a Haake as Rudy mentioned earlier.

Question: Does anybody know if at -the operating temperature

149

Answer/Rudy:

like 3500 F., or whatever. Does anyone know whether the mixtures are shear thinning, are they psuedo plastic in nature. In other words, at the higher shear rate, do you get a lower vis­cosity?

Yes. In figure #3, of the rheogram, note that the slopes of the lines are less than 1:1 (450

).

I do not know personally what they have been doing, as I have stayed away from it for all this time but I know that for control pur­poses, somebody has suggested a large orifice is tabled but that is only for I might say: "rule of thumb" comparison of con"trol in the field. Maybe the producers here can answer that and contractors could answer that question better than I can.

150