Stabilized Engineered Wood Fiber for Accessible Playground Surfaces

Background

Some engineered wood fiber (EWF) and chipped wood surfaces on playgrounds are difficult for those who use mobility aids, such as wheelchairs and walkers, because the surfaces are soft and uneven. This study is the third phase of a research project in pursuit of a stable, smooth, and impact-attenuating surface, based on wood materials, for playgrounds. In Phase I, processing techniques and material properties were evaluated in small bench-top and full-depth laboratory tests (Laufenberg and others 2003). Phase II involved 6 months of outdoor field testing (Laufenberg and Winandy 2003). In Phase III, reported here, we continued to develop the concept for stabilizing EWF to improve wheelchair and walker accessibility.

Phases I and II demonstrated that our new binder-EWF system can (a) enhance mobility, as related to the provisions of the Americans With Disabilities Act (ADA 1990), (b) meet test requirements for playground surface cushioning to reduce head impact injuries, and (c) perform in an outdoor environment. In Phase III, the two most promising EWF stabilizing binders were installed on a working playground. The concept was to mix a binder throughout the upper surface of EWF to create a stiff (firm) and scuff-resistant (stable) composite. The combination of a top layer of bonded EWF and a thick underlying layer of unbonded EWF creates a soft, impact absorbing playground surfacing system. In this report, the term SEWF refers to ìstabilizedî EWF and indicates the system with the bonded top layer of EWF.

Phase I

In previous work (Laufenberg and others 2003), numerous processing techniques and binders were evaluated for the development of woodñbinder composite playground surfaces. Our goal was to improve accessibility for users of wheelchairs and walkers. Although traditional EWF performs well for nearly all expectations of a play surface, a pertinent shortcoming is the amount of energy required by a wheelchair user to maneuver over the surface, primarily because it is soft and uneven. Thus, the EWFñbinder composite system needed to achieve two seemingly conflicting performance requirements: to promote accessibility and to retain adequate impact-energy absorption to preclude injuries. The composite systems developed consisted of the combination of a binder and EWF in a thin top surface layer over a layer of unmodified EWF.

The effort identified designs using compatible resin (e.g., latex, silicone, and polyurethane) binders and various species and textures of EWF. Adhesive binders were chosen for their inert and non-toxic nature in the playground environment and the retention of a natural look for the surface. Consideration was given to the need to add materials and to the possibility of patching the surfaces after damage from major impact. Use of a play surface for 3 to 5 years was considered adequate time for the binder to fulfill its function. The surface could then be renewed by adding EWF. Composite systems with EWF have not been used before in this application. Therefore, there is no guarantee or warranty that they will function for that extended period.

The preliminary evaluation included laboratory testing of energy absorption and surface stability (firmness) 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 were recommended for Phase II outdoor field evaluations.

Phase II

Phase II research focused on outdoor evaluation of binder and fiber combinations identified as minimally acceptable and promising in the Phase I evaluations. Seven surface treatments and a control surface were 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) a synthetic latex emulsion, (b) a low molecular weight silicone, and (c) foaming and nonfoaming 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 and impact attenuation. An impact test was performed after the 6-month exposure period. The results indicated that all the surfaces passed the existing specifications for impact attenuation of playground surfaces (Laufenberg and Winandy 2003). The results further indicated that 6 months of aging had changed the impact performance of all systems except the unsurfaced (no additive) EWF. The latex binder and both polyurethane binders consistently met the accessibility requirements for playgrounds. However, the foaming 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 adequate integrity during rain/dry cycles in this outdoor test. Moisture measurements indicated that the bonded surface retarded the drying of the underlying EWF. That finding might have long-term implications for the rate of decay for the systems, and alternative treatments might be used to retard decay.

Phase III

In Phase III, a few of the most promising SEWF systems were tested in a working playground. The desired binder-EWF system needed to provide impact safety and appropriate accessibility over a number of seasons. It needed to retain the performance characteristics of impact-energy absorption and surface resiliency. To accomplish this, the first order of business was to objectively assess the field-use requirements of any successful SEWF.