Stabilized Engineered Wood Fiber for Accessible Trails

Background

The initial research effort included a variety of resin (e.g., latex, silicone, and polyurethane) binders and various types of EWF. We chose adhesive binders for their inert and non-toxic nature in the environment and the retention of a natural look for the surface. Consideration was given to the need to add material or patch the surfaces after major damage. Use of a trail surface for 3 to 5 years was considered adequate time for the binder to fulfill its function. These adhesive systems have not been previously used in this application with EWF, therefore there is no experience with their functioning for that extended period. The preliminary evaluation included laboratory testing of energy absorption and surface firmness and stability on trial surfaces in 0.5- by 0.5-m (18- by 18-in.) plywood boxes; the surfaces had a uniform depth of 0.3 m (12 in.). Seven systems were identified as having reasonable performance and thence recommended for Phase II outdoor field evaluations.

Phase II research focused on outdoor evaluation of the binder and fiber options identified as minimally acceptable and promising in the Phase I evaluations. The Phase II work studied field durability and looked at changes in performance by quantifying the impact and accessibility of these novel surfaces after field exposure. This series included seven surface treatments, and a control surface, installed in a series of outdoor test beds in Madison, Wisconsin, to gather field experience on long-term performance and durability. The binders evaluated were (a) synthetic latex emulsion, (b) a low molecular weight silicone, and (c) foaming and non-foaming resilient polyurethane. Systems were evaluated over a 6-month period, from April to October 2002.

Tests were performed at regular intervals to provide a quantitative measure of accessibility. The results indicate that latex and polyurethane stabilizers consistently met the requirements for accessibility on playgrounds (Laufenberg and Winandy 2003). The foaming polyurethane formulation produced a hard brittle shell that became even harder with exposure/age and would increase the injury rate for falls on the surface. The silicone system did not maintain its integrity adequately during the rain/dry cycles in this outdoor test.

Monitoring of the Phase II test plot continued for 2 years after the initial 6-month evaluation reported by Laufenberg and Winandy (2003). In those 2 years, the synthetic latex emulsion and the non-foaming polyurethane continued to performed acceptably. As anticipated, the foaming polyurethane system continued to harden with exposure, rendering it unsuitable for meeting the impact absorption requirements for playground surfaces.