EVALUATION OF THE PLAYING SURFACE HARDNESS OF AN INFILLED SYNTHETIC TURF SYSTEM

Abstract

New configurations of synthetic turf, infilled systems, have been introduced into the market place. These infilled systems are comprised of vertical fibers that are much longer than traditional synthetic turf and can be filled with sand and crumb rubber (infill media). The objectives of this study were to evaluate the surface hardness of varying configurations of an infilled synthetic turf system called SofSportTM under wet and dry conditions. Specifically, we wanted to determine 1) the effect of underlying pad thickness and type, infill media depth, sand sizes, and sand to crumb rubber ratio, on surface hardness as measured by the F355 method and the CIT and 2) compare the F355 method with the CIT to determine if one method is preferred when testing synthetic infill systems. Surface hardness differences between pad thickness and types were small but all pad treatments had lower surface hardness values compared to the no-pad treatments. Infill media depth did not affect surface hardness under dry conditions. Under wet conditions, the 38-mm infill media depth resulted in lower surface hardness than the 25mm depth. The mixing of sand and crumb rubber infill media resulted in lower surface hardness values than sand or crumb rubber alone. When mixed with crumb rubber, finer sands measured higher in surface hardness than coarser sands. Under the conditions of this study the relationship between the Gmax values generated by the F355 method can be compared to the values generated by the Clegg Impact Tester using the regression equation F355 x 0.66 9.3 = Clegg Impact Tester. The regression coefficient for this equation was 0.95 and indicates that the Clegg Impact Tester would be a suitable device to measure the surface hardness of Sofsport installations. INTRODUCTION Since the introduction of synthetic turf in 1966, numerous studies have been conducted to evaluate the safety and playability of synthetic surfaces. These studies have included material tests on the traction and hardness of these surfaces (Valiant, 1990; Martin, 1990) as well as epidimeological studies that have counted athlete injuries on synthetic versus natural turfgrass (Powell and Schootman, 1992; Powell, and Schootman, 1993). Different methods of measuring playing surface hardness have been developed for synthetic turf versus natural turfgrass surfaces. For synthetic turf surfaces the U.S.A. standard is the F355 method (American Society for Testing and Materials, 2000a). For natural turfgrass the standard method is the Clegg Impact Tester (CIT) (American Society for Testing and