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Abstract:Highway guardrail assemblies play an important role in enhancing the safety of motorists. Guardrail assemblies
contain three main components: (1) galvanized steel guardrail, (2) posts, and (3) blockouts. The purpose of the
blockout is to increase the spacing between the rail and the post and thereby reduce the interaction of the vehicle
with the post. It is essential that the blockouts are durable so that that the guardrail assembly can function
properly. The goal of this study was to explore the feasibility of using recycled chromated copper arsenate
(CCA)-treated wood to produce a composite blockout. This study had three tasks: (1) determine the properties of
the raw materials, (2) production and testing of molded guardrail blockouts, and (3) conduct finite element
analyses and design optimization. Decommissioned blocks were chemically analyzed and found to contain
residual CCA that is consistent with over 10 years of service. The used bocks were shredded to particles,
combined with polypropylene plastic, and used to make composite blockouts with varying amounts of wood,
plastic, block density, and resin. Group 1 yielded superior results: internal bond strength, IB, (108 psi), modulus
of rupture, MOR, (2,536 psi), modulus of elasticity, MOE, (440,250 psi), linear expansion, LE, (0.632 in.), and
thickness swelling, TS, (12.6%). A finite element analysis conducted on this group revealed that a guardrail
assembly comprised with wood/plastic blockouts should perform similar to one with solid wood blockouts. The
development of the composite blockout will provide the motoring public and taxpayers a low-cost, high-performance
blockout and enhance environmental stewardship. The success of the overall project will lead to
the development of a durable, green composite blockout.
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