United States Department of Transportation
i
Ground tire rubber (GTR) as a component material in concrete mixtures for paving concrete.
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2015-02-01
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Abstract:This research was done to investigate if the problems associated with flexibility and temperature sensitivity (expansion and
contraction) in roadway concrete pavements can be addressed by replacing some of the fine or coarse aggregate component
with crumb rubber, specifically, Ground Tire Rubber (GTR). The research also intended to find out the general effects of
adding the GTR to the conventional pavement concrete, in terms of the mechanical properties and workability, requiring
several laboratory tests to be conducted as part of the study. Finally, the research was required to evaluate the practical
implementation at a ready mix plant, of the proposed use of GTR as a component in the concrete. It was found from the
study that the modulus of elasticity of concrete is reduced when GTR is used in concrete, thus the pavement concrete
becomes more flexible. Based on the results of the tests for the coefficient of thermal expansion (CTE), it was not
conclusive from this study, that adding GTR will significantly affect the expansion and contraction in the concrete
pavement.
Many valuable findings from this study include the following: the optimal content for GTR for use as a component in the
paving concrete mixture is 15% by weight of the fine aggregate; at a water/cementitious ratio of 0.44, concrete with GTR of
15% by weight of the fine aggregate, using water-reducing admixtures, can achieve a 28-Day compressive strength of about
3000 psi as well as reasonable values of the flexural strength and split tensile strength; slump was observed to typically
decrease with addition of GTR but use of the water-reducer will eliminate this problem; the unit weight of the GTR
concrete is less than that of the conventional concrete; air content will always increase with addition of GTR to the concrete
but the use of a defoaming agent will reduce the foam and air content; GTR concrete has a non-brittle mode of failure in
compression and flexure; examining GTR concrete under the Scanning Electron Microscope (SEM) indicated that there is
good bonding between the rubber particles and the cement matrix in the concrete; pretreatment of GTR by simple washing
and drying may improve the compressive strength of the GTR concrete; GTR concrete has very good plastic and dry
shrinkage attributes, with the ability to resist shrinkage cracking; the ready mix plant operations will require dry-safe
storage of the GTR, customized packaging (bag sizes or bag material) of the GTR for convenient batching, and a less
duration for mixing before placement (when compared to the 90 minutes mixing duration allowed for conventional
concrete); the GTR concrete can be used in the following applications: Class I pavement; sidewalks; curbs and inlets; or
applications where the compressive strength of 3000 psi or less is adequate and also where shrinkage may be a problem.
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