SHRP Asphalt Test Parameters and Structural Mixtures
Development of Relationships Between SHRP Asphalt Test Parameters and Structural Mixtures for Mechanistic Analysis and Rehabilitation Design of Flexible Pavement
By Mang Tia, Byron Ruth, and
Reynaldo Roque
The University of Florida
Problem Statement
The recent Strategic Highway Research Program (SHRP) in the asphalt
area has resulted in the development of performance based asphalt
binder and asphalt-aggregate mixture specifications. The Florida
Department of Transportation (FDOT) is committed to implementing
these new tests and specifications. While these new tests and
specifications offer potential for improved pavement performance
and management, there has been very little experience with them.
There was a need to evaluate these new test methods with regard
to their applicability for use as direct input for developed for
mechanistic pavement analysis and design program previously developed
for FDOT. SHRP test methods and specifications did not address
pavement rehabilitation nor mechanistic analysis. Consequently,
there is a need to relate asphalt properties obtained from these
tests to mix behavior at the critical thermal load conditions
where pavement failures are most likely to occur.
A laboratory study was conducted to evaluate the relationship
between the results of the SHRP binder tests and those of the
conventional binder tests, and the applicability of these tests
for prediction of asphalt mixture properties. The scope of the
study covers six different base asphalts from five different refinery
sources and three types of modifiers, namely a ground tire rubber
(GTR), styrene-butadiene rubber (SBR) and styrene block copolymer.
Objectives
The objectives of this research study were to develop and evaluate
the relationships between the results of SHRP binder tests and
the results of other conventional asphalt tests that have been
commonly used by the FDOT, and to develop and evaluate the relationships
between the results of the SHRP binder tests and the cracking
resistance of the asphalt mixtures under Florida conditions.
The study also evaluated the aging characteristics of selected
modified asphalts and mixtures which are likely to be used in
Florida, and evaluated the SHRP Performance-related tests for
asphalt binders and modified asphalt binders. Modifications were
made to the computer program Rehabilitation Evaluation and Design
of Asphalt Pavement Systems (REDAPS), used for mechanistic analysis
and design of flexible pavements by FDOT using nondestructive
testing techniques.
Findings
The standard rolling thin film oven test (RTFOT) was used to simulate
the short term aging of the binders during the hot-mixing process,
and the SHRP pressure aging vessel (PAV) process at 100C was used
to simulate the additional aging of the asphalt binders in the
field. The original and the aged binders are evaluated by both
the conventional and SHRP binder tests, which include (1) penetration,
(2) absolute viscosity, (3) Brookfield rheometer, (4) Schweyer
rheometer, (5) Frass breaking point, (6) bending beam rheometer,
(7) dynamic shear rheometer, and (8) direct tension tests.
Asphalt mixtures were compacted by the gyratory testing machine
(GTM) and aged according to the SHRP proposed short term oven
aging (STAO) procedure and long term oven aging 9LTOA) procedure.
These aged and unaged asphalt mixtures were evaluated by resilient
modulus, indirect tensile strength, and indirect tensile creep
test at 0, -10, and -20°C. Asphalt residues were recovered from
the broken samples and evaluated by the binder tests.
The results show that the G*sin and G*values as measured by the
SHRP dynamic shear rheometer correlate well with the results of
the penetration and viscosity tests on the same binders at similar
temperatures. The creep stiffness as measured by the bending
beam rheometer at low temperatures correlates well with the Frass
breaking point temperature. However, the failure strain as measured
by the direct tension tester at low temperatures correlates poorly
to the Frass breaking point temperature.
The mixture stiffness as determined by the SHRP indirect tensile
creep test at -10°C was found to be linearly related to the creep
stiffness of the binder at the same temperature. The tensile
strength, failure strain and fracture energy of the mixtures as
measured by the indirect tensile strength test at -10°C were found
to be not related to the binder creep stiffness at the same temperature.
The resilient modulus was found to be close to the stiffness
of the mixture at 1 second as determined by the indirect tensile
creep test.
Conclusion
The test results indicate that asphalt modifications with SBR
or GTR could improve both the high temperature and low temperature
characteristic of the asphalt binders. The findings support the
use of GTR and SBR as asphalt additives for improved resistance
to rutting and low temperature cracking.
This research project was conducted by Mang Tia, Byron Ruth, and
Reynaldo Roque, at the University of Florida. For more information
on the project, contact Gale Page, Project Manager, at (352) 642-3208.
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