Trees are some of the most steadfast natural structures in the world; owing to their particularly strong and durable cell walls they are able to withstand extraordinary stresses in the natural environment. It’s this characteristic that makes wood a natural choice for so many current applications and for the development of BrockFILL. There aren’t any additives or modifications that make BrockFILL more durable, it’s just wood doing what it does best.
Once Brock determined that wood was a promising candidate for infill development, laboratory testing became the logical next step. Effective product development requires rigorous testing, and for our infill, durability is of chief concern. Largely, infill durability is measured through particle size analysis. Particle breakdown is currently the best measure of particle durability and analyzing particle size distributions is the best way to characterize that change. ASTM has not currently set forth a standard for testing infill durability, so much of the testing results are proprietary. Primarily, this testing is performed with the Lisport Classic machine which is designed to simulate turf wear in the highest traffic zones of an artificial turf field. By evaluating the infill from these test samples, Brock can assess the wear BrockFILL would experience under these same circumstances.
Figure 1. Comparison of BrockFILL and SBR particle size.
In order to simulate turf wear, the Lisport machine uses a pair of large weighted cylinders which roll over and shear the test sample. The cylinders have cleats protruding from their surfaces and are connected using gears and a chain. In the same way a bicycle’s pedals drive its rear wheel, the lead cleated cylinder rolls over the surface of the turf and causes the trailing roller to slip as it moves over the turf surface. This creates a shearing action similar to an athlete’s foot turning or accelerating through the turf fibers. As the rollers traverse the turf sample, the tray containing them translates perpendicular to the rollers, further increasing the shearing of the cleats through the turf.
After performing the requisite number of cycles on the plot sample, the infill is collected and evaluated for size and appearance. Size evaluation is reported as a particle size distribution. The figure below shows the results from independent lab testing of BrockFILL and compares them to crumb rubber without any wear testing.
Figure 2. Freeze-Thaw Particle Size Analysis
Additionally, we have been investigating the effects of freezing temperatures on infill to evaluate the seasonal effects of using a hydrophilic material as infill. BrockFILL readily absorbs water which helps it maintain comfortable playing temperatures even in the hottest environments, but it also means the absorbed water will sometimes be subject to freezing. Freezing water can cause significant damage to infrastructure, as we see every year on our roads; similar damage to BrockFILL would be unacceptable. The data shows no correlation among the number of freeze-thaw cycles; the conclusion from this is that BrockFILL is durable enough to withstand harsh weather conditions without reducing its efficacy. In addition to particle size analysis, visual characterization is a valuable tool for evaluating BrockFILL durability. The photos below show the results of visual analysis.
Figure 4. BrockFILL after 10 freeze-thaw cycles and 20,000 Lisport cycles
A rigorous testing schedule is critical to the effective development of a new product, and BrockFILL has undergone an intensive battery of tests. Durability is the one of the most important factor to a quality, reliable infill product; the properties of wood ensure that BrockFILL will withstand the abuse inherent to playing fields of all levels.