Ground tire rubber as a stabilizer for subgrade soils.
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2014-05-01
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Abstract:Over 250 million scrap tires are generated annually in the U.S. Historically, a significant portion of these tires
have been processed into finely ground tire rubber (GTR), or crumb rubber, for use as an additive in hot mix asphalt
(HMA) pavements to improve pavement performance. Recently, improved synthetic polymer additives have been
developed that more economically provide the same performance improvements as GTR. This development has
decreased the demand for GTR in HMA, potentially freeing supplies of GTR for other applications.
Over the past two decades, the Florida Department of Transportation (FDOT) has conducted a significant amount
of research on ways to re-use waste materials such as energy generation ash, tires, glass, reclaimed asphalt pavement,
and reclaimed concrete in roadway construction. FDOT initiated this study to investigate whether blending GTR with
subgrade soils would be a beneficial practice.
The objective of this research was to determine the effect of GTR on subgrade soil engineering properties. Three
representative sizes of GTR, 1 inch (25.4 mm), 3/8 inch (9.51 mm), and #40 (0.422 mm) were blended in varying
percentages with three subgrade soils. Subgrade soils were selected with low, medium, and high limerock bearing ratio
(LBR) strength. Blends were evaluated with 4, 8, 16, 24, and 32% GTR by volume. Blends were evaluated for grain
size, moisture-density, LBR, permeability, consolidation, resilient modulus (Mr), and creep.
Ground tire rubber does not make a good stabilizing agent for subgrade soils. Blending GTR with subgrade soils
reduced both LBR and Mr significantly. Blending has minimal impact on consolidation or permeability. Blending
increases creep in the tested soils, however the creep remained within acceptable limits.
Blending GTR with soil did reduce the density of the blend. Additional research should be conducted to evaluate
whether soil/GTR blends would be suitable for low-density fill applications where the benefits from reduction in
vertical and horizontal soil pressures would offset the reduction in strength.
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