Date of Award

2010

Level of Access

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Interdisciplinary Program

Advisor

Michael L. Peterson

Second Committee Member

Douglas J. Gardner

Third Committee Member

Paul A. Wlodkowski

Abstract

Wax-coated granular composite materials or "synthetics" are used on the surface of nine Thoroughbred horse racetracks in North America. The composition of these surfaces differs from that of a conventional dirt track as they contain silica sand, polymer fibers, and rubber particles that are bound together with a paraffin-based, high-oil content wax coating. It is hypothesized that the solid-to-liquid thermal response of the wax coating has a major effect on the mechanical properties of the track. The purpose of this dissertation is to understand the thermal-mechanical response of a synthetic racetrack surface under operational conditions. This research investigates; (1) the hydrocarbon composition and thermal characteristics of the wax coating that binds the track constituents, (2) the temperature effects on the quasi-static and dynamic triaxial shear strength (and cohesion) of the track material, and (3) the temperature effects on the tangent modulus (vertical stiffness) of the track material. The testing temperatures used in mechanical testing are based on the thermal transition regions measured in the wax during the first phase of testing. The results of the quasi-static triaxial shear tests showed significant sensitivity to the DSC thermal transition peaks with shear strengths peaking at temperatures near the first thermal transition region (followed by an immediate drop in strength). Strength increased by as much as 29% during this temperature change. This increase is consistent with reduced wax viscosity that allows increased mobility of sand grains to interlock and resist shear. A test sample which was modified with a high-oil, high-melting temperature microcrystalline wax showed significantly less dependence on temperature. These materials are also rate-dependent with up to 38% higher triaxial shear strength as load rates increased when tested below the first DSC transition peak. In contrast, above the first DSC transition peak temperature, no significant load rate effect on strength was exhibited. Finally, tangent modulus values were highest at the highest loads and coolest temperatures tested, and decreased (by as much as 54%) as temperature increased through the first DSC thermal transition region. Understanding the property changes that occur in a synthetic track surface as temperatures change has the potential to determine how maintenance can be used to increase surface consistency which is expected to improve equine safety and performance.

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