asphalt-rubber hot mix research hot mix research findings ... asphalt concret e inc luding aging,...
Post on 06-Feb-2018
Embed Size (px)
ASPHALT-RUBBER HOT MIX
TECHNICAL DIRECTOR ARPG
As phalt-Rubber ( A-R ) has been used in 4 5 s tates and
four contine nts for 20 years in the following types o f
SAM- Stress Absorbing Membra n e (Seal Coats)
SAMI- Stress Absorbing Membrane Interlayer
As phalt-Rubber Hot Mix
Design mixtures of crumb rubbe r from waste tires and
asphalt cement were developed by C.H. McDonald along with
indus try , demonstrations (FHWA), re sear c h by Universities
a nd agencies both here in the United States and abroad.
As more and mo re projects were placed, it become obv i ous
Asphalt-Rubber did n ot fall within kno wn properties of
s tandard asphalt . Observations we re made by Engineers a nd
Scientist indicating property values far better than the
When As phalt-Rubber hot mixes are test.ed using t h e
same procedures as for convent ional asphalt cement ( AC ).
Some engineers have shied a way from the A-R mi x es because
of the difference from conventio nal test values.
In 1987,the Asphalt-Rubber Producer Group (ARPG)
commenced a program to determine criteria of property
values for Asphalt Rubber using kn own standar d test
A r esear c h contract was established with the
University of Nevada-Reno, t he Univer sity of Ari zon a a nd
the U.S. Army Corps o f Engineer, Waterways EXpe rime nt
Station (WES) through its Construction Productivity
Kdvancement Research (CPAR) . Also, ARPG member
engineer ing person al and ,their testing facilities we r e
included along with Sout hwest Testing Labo r atories
Houston, Texas,and Wester n Technology Laboratories,
Phoen i x , Ar izona .
Aggregates and asphalt ceme nts selected for this
r esearch have been o r a r e to be included in the Str a t egic
Hi ghwa y Research Pr oB r am (SHRP)
Goal s and Objec tives
The purpos e of this researc h is to:
1. Develop mix design procedures using
a. Mars hall Method b. Hveem Method c . Gyrotory Compaction Method
2. Develop design properties s uch as air voids, flow s tab ility and water sens itivity. Evaluate paveme nt desgins using dense and open g raded Asphalt - Rubber mixes .
3. Set phys i c al properties us ing a specific des ign. Establis h property parameters for Asphalt - Rubber mixtures using current tes t methods.
4. Establish standards for test methods.
5. Compare physical properties and performance values with s tandard asphalt in dense graded asphalt concret e inc luding aging, fatigue, flexibility, a nd duc tility f o r high and low t e mperatures.
6 . Establish p ractical and theor etical equivalenc y values f o r Aspha l t-Rubber hot mix , both as an overlay a nd for new construction.
Design Approach for the Research
A pre-agreed resea r ch flow chart wi 't h goals and
timing is shown in Figure 1.
1. As goals were met and new information became ava i lable,
strategy changes were made. The total program is
monitored by an advisory committ ee selected from two
states agencies, two uni versit i es and two private
companies, along with t he Asphalt-Rubber P r oducers Group.
Where Are We Now ?
Binder contents have been determined for the dense
graded hot mix, with and without rubber. Selections were
based on Marshall and Hveem test methods by the advisory
A design binder content using the gyrotory compaction
method with Asphalt-Rubber could not be established.
Modifications of the gyrotory test procedure are being
Binders were tested before and after aging. Aging
methods used were Rolling Thin Film Oven, Weatherometer
through 160 cycles , ASTM Method D-1754. Ductility, ASTM
D-11 3, tests were performed, however the rubber particles
in the mix did cause problems.
Job Mix Formul a
It was the decision of the research team to use a
single aggregate and asphalt source. This aggregate and
asphalt sou r ce would be one of the select SHRP materials
i nclude d in the Strategic Highway Research Program.
Aggregate i s a 100% crushed granite from
Watsonville, Cal if o r nia, meeting gradation requirements of
Cal Trans 1/2-inch hot mix, Nevada type 2 hot mix and
ASTH D 3315 1/2-inch dense. The selected g radation is as
follow a nd in Figure 2.
Aggr egate Gradat ion Sieve Size % Passing
3/4 1/2 3/8 .. .8 016
The mix design for rubber content was set by the
research committee at 16-17-percent by weight of the
asphalt cement based upon labor at ory test re sults.
Binder contents for conventional asphalt cement and
Asphal t-Rubber dense graded mixtures selected, were based
on the Marshall and Hveern Tests. Air voids were set
between two-and- five-percent with stabi lity and flow
established using industry and current practices.
The Marshall Method (ASTM D-1559) was modified in the
testing procedure for A- R hot mix as follow:
1. Material placed in a 275-degree oven for one-hour after mixing and before compacting to insure mixture was at the appropriate temperature for compaction.
2. Compacted samples were allowed to remain in the mold overnight before extruding.
The Hveem method (ASTM D- 1560 and 1561) was modified
in the testing procedure for A-R Hot Mix as follow:
1. Samples were mixed and placed in a 300-degree oven for three hours.
2 . Samples were extruded immediately after a leveling load was applied. Samples were not cooled down prior to extrusion.
Binder contents were selected using both test methods
within the criteria established and they produced the same
binder contents. The conclusion was, either Marshall o r
Hveern method can be used for designing A- R Mixes.
The halfway point of this research has revealed
Asphalt -Rubbe r has significantly modified the physical
properties of hot asphalt mixtures when compared, to
conventional mixes. Modifications include inc reased high
temperature modulus. viscosity, elasticity and less age
hardening. Figures 3 through 7 show the general range of
mix properties of Asphalt-Rubber mixes and standard
asphalt. As phalt-Rubber mixes establishes a property
range different from known standar ds .
The graphs show the physical properties of Asphalt-
Rubber mixes compared to standard AC. Standard marshall
stabilities accepted in the industry are in the r anges
shown in Figure 3. Usually, stability ranges from 1,800 to
3,500 pounds. Asphalt-Rubber on the other hand, provides
stability values of 1 , 000 to 1,500.
Unit weights are the same except, Asphalt - Rubber mix
has two-percent higher binder content as shown in Figure
4. Void contents are inc reas ed with higher A-R binder
contents. Standard asphalt mixes range from three-to-
five-percent voids and Asphalt-Rubber can be a s low a~
two-percent with as high as three-percent more binder as
shown in Figure 5.
Marshal l flows are dramatically increased in a
Asphalt-Rubber hot mix as shown in Figure 6. The
relatio nship between stability and flow gives an
indication of flexibility of the mix. Current flow
requirements are 8 to 16, whereas Asphalt-Rubber fl ow
values are 18 to 25, stablilities are l ower .
Flows and stability indicate a very flexible elastic
material to prevent cracking.
Hveem stabilities plotted reveal higher binder
contents give lower stabilities (Figure 7). Acceptable
ranges for standard hot mixes are 35 to 45 whereas the
higher Asphalt-Rubber content offer s lesser stabilities.
However due to the flexibility and elasticity of A- R
mixes, the lower range of stability maybe acceptable.
The next phase of this r esearch is to compare binder
properties and mix properties via fatigue, creep, and
stress-strain analysis. This seement will also include a
mix design procedure for binder contents for open graded
Asphal t-Rubber hot mix. The interesting aspect of this
research is the binder contents . When using standard
asphalt cement the binder content is limited to runoff of
AC. The binder content can not exceed the r unoff factor
for practical placement.
Asphalt-Rubber however has allowed the binder
content to increase by 50% or more. A higher binder
content in open graded mix offer s thicker films and
greater durability. At the same time the r ubber inclusion
offers age hardening resistance.
The purpose of this part of the research i s to
develop a mix design method to determine optimum binder
content needed for an open graded hot mix seal to obtain
Ultimate Goals of this Research
Research will provide the parameters of properties
required for Asphalt-Rubber using accepted test methods.
It will allow any qualified engineer, technician and/or
laboratory to test and develop a hot Asphalt-Rubber mix.
Design procedures and property parameters will be
published and available to the public.
Also, acceptable design procedu