Determining the water holding capacity of synthetic track materials for thoroughbred horse racing

Wax-coated sand, fiber, and rubber surfaces have been in use for more than a decade at a number of North American Thoroughbred racetracks. These synthetic, all-weather racing surfaces were designed to allow races on wet surfaces without impacting performance. As these tracks have aged, some have areas that no longer drain properly. A number of approaches have been taken to refresh the surfaces including re-waxing, adding fiber, and even turning over the surfaces. The results have shown mixed success, with water pooling on top of some tracks and more water retained in the depth profile on other tracks. A gravity-based water holding capacity (WHC) test has been developed to determine the amount of water retained in these surfaces. Traditional permeability measurements are also used in this study. Samples of new and six-year-old synthetic surfaces are taken from four North American Thoroughbred racetracks to examine both the drainage and water holding of the material. These surfaces were identified as having both adequate and inadequate track performances during wet weather. Control samples were also prepared with and without the wax binder. Measuring the WHC at different surface locations may help racetrack superintendents identify problem areas and quantify material changes over time. Test results generally showed that a certain amount of wax binder is necessary to minimize water holding in synthetic surfaces, but too much wax is detrimental. The amount and size of the polymer fiber and rubber constituents, as well as organic material and particulates present, also affects the WHC. Developing threshold values for an "acceptable" WHC for specific synthetic racetracks, as well as understanding primary factors that affect water holding, will allow researchers to set a performance standard to determine the timing and type of renovations that are needed to maintain safe and consistent synthetic track surfaces.