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  • 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    Early unpublished work is presented on the measurement for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,

    121

  • 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

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