Archetypes in Thoroughbred dirt racetracks regarding track design, clay mineralogy, and climate

In Thoroughbred dirt racetracks, clay content plays a critical role in moisture management and influences mechanical properties. We hypothesized that different dirt track designs developed in response to the track materials used, particularly the clay content of the material. These designs are in turn a function of the local climate, in particular the amount of rainfall and the evaporation rate. X-ray diffraction makes it possible to determine whole rock and clay mineralogy for 26 tracks that were assigned to one of three track designs: shallow sand (SS), false base (FB), or false base with a pad (FBP). Results demonstrate that SS tracks occur in areas with the highest annual precipitation and have the lowest average clay content, whereas FBP tracks have the lowest annual precipitation and the highest average clay content. FB tracks have intermediate levels of precipitation and clay relative to other track styles. Understanding the effects of clay minerals in dirt and how different racetrack designs have evolved to handle differing levels of clay and moisture can aid in quantifying track maintenance decisions.