SportsTurf provides current, practical and technical content on issues relevant to sports turf managers, including facilities managers. Most readers are athletic field managers from the professional level through parks and recreation, universities.
Issue link: http://read.dmtmag.com/i/82015
FieldScience | ByTom Serensits and Dr. Andy McNitt Maintaining synthetic surface safety W with athlete safety are under higher levels of scrutiny. The hardness of the playing surface is one of them. While both natural and syn- thetic turf fields can reach unsafe hardness levels, synthetic turf fields seem to receive the most attention. Assuming a proper installation, syn- thetic fields start off well below hard- ness thresholds in the months after install. Over time, these fields may get harder and in some cases, if not properly cared for, can reach unsafe levels. So, why do synthetic turf fields get hard? Is it compaction? Or is there something else going on? It is a common belief that com- paction of the infill is the reason fields get hard. For many of us, that seems to makes sense. We know that heavy use on a natural turf fields leads to soil compaction and, in turn, increased surface hardness. But, to what degree does crumb rubber and sand compact? Certainly there is a "settling-in" period in the weeks after installation, but based on our obser- vations, compaction is minimal after the settling-in period in most cases. In fact, most infill is sized such that only limited compaction is even pos- sible due to the relatively uniform size of the infill particles. ITH THE INCREASING FOCUS on concussions in sports, many aspects associated RESEARCH RESULTS Our research plots at Penn State provide the published threshold of 200 G's set by the American Society for Testing and Materials (ASTM) and the US Consumer Products Safety Commission. Even wheel ruts caused by the tractor repeatedly pulling the traffic simulator over the same area for 8 years the infill resiliency and thus increase surface hardness. For example, excessive and re- peated painting of lines and logos without the occasional cleaning of the painted areas, including removal or wash-through of old paint, can lead to a hard surface. Excessive deposits of debris and particulate matter may compromise the infill if the surface is not cleaned over time. The build-up of this type of debris takes many years in most cases and typically is not a major concern for fields with even moderate maintenance. So why do some fields become Other factors, however, can compromise hard over time? We believe that "walk-off" crumb rubber and the associated loss of infill depth is the main cause for increases in surface hardness of synthetic turf fields. "Walk-off" crumb rubber refers crumb rubber that leaves the field in the shoes, clothing, equipment bags, etc. of field users. While it seems like an in- significant amount on an individ- ual basis, when looked at collectively for all field users, it begins to add up. Add in the infill material that is removed from necessary regular maintenance ac- tivities such as grooming, brush- ing, sweeping, and blowing, and the amount of infill removed from the field can be substantial. >> Top: A FIREPROOFING DEPTH GAUGE is a good tool to measure infill depth and can be purchased for less than $15. >> Bottom: THE SMALL AMOUNTS OF INFILL collected in shoes, clothing, equipment bags, etc., may seem insignificant individually, but those small amounts add up. an interesting example. In 2002, various syn- thetic turf companies installed their products which were then used in a research trial that concluded in 2010. Over the course of 8 years, a section of each of these plots was ex- posed to 96 simulated games per year using our traffic simulator. By the end of the trial, those trafficked sections were exposed to more than 1,500 passes with our traffic sim- ulator. However, by the end of the study, surface hardness values were still well below 10 SportsTurf | September 2012 tested to be well below the 200 G level. This example helps illustrate that compaction alone is most likely not the main cause of ex- cessive surface hardness. We have also observed specialized ma- OBSERVING "WALK-OFF" CRUMB RUBBER chines remove infill from an existing field, "clean" it, and reinstall it back into the carpet in an effort to reduce surface hardness. The Gmax values before and after this process were essentially the same. It was only after new rubber was added that the Gmax was reduced. ated with a low level of infill. The infill cre- ates the padding and shock-absorption for the synthetic turf system. As the thickness of that "padding" is reduced, there is less of a cushion between the surface and the hard base under the turf, thus resulting in elevated surface hardness. This is often most evident in the high-use areas of the fields, where the major- ity of play occurs and, in turn, the majority of the rubber "walks off." Thinking back to our research plots here at Penn State, infill depth remained at or very close to installation levels rubber is supported by our obser- vations as we have tested many fields in the United States. Almost every time our tests show a high surface hardness value, it is associ- This idea of "walk-off" crumb www.sportsturfonline.com