To address the growing volumes of waste generated by society (coupled with hurdles in the approval process for citing landfills and the resulting escalation of waste handling and disposal costs) many manufacturers are attempting to recycle plastics and other materials in various roadside and work-zone traffic control devices. The number and cost of these devices installed and replaced annually within Texas and the rest of the nation are significant, and so there is a potential for having a measurable, positive, and cost-effective impact on environmental problems.
This summary reviews the first phase of a three-phase research project. In Phase I, researchers compiled information on existing products manufactured in part or in whole from recycled materials, which have been evaluated and recommended for experimental implementation. Roadside safety devices evaluated in this study included, but were not limited to: guardrail support posts and offset blocks; sign blanks and their supports; energy absorbing elements in crash cushions, end terminals, and truck mounted attenuators; delineator posts; mailbox supports; and work zone traffic control devices such as drums, cones, and barricades.
For some products, there is insufficient data to make a conclusive decision about that products' suitability for use. Phase II of this study will focus on further assessment and evaluation of products through laboratory and dynamic testing. Phase III of the study will then perform full-scale crash testing of selected products (from Phase II) to validate laboratory results and verify their crashworthiness.
The Texas Transportation Institute (TTI) conducted Study 0-1458, "Applications of Recycled Materials in Roadside Safety Devices," for the Texas Department of Transportation (TxDOT), the Texas Commission on Environmental Quality (TCEQ), and the Federal Highway Administration (FHWA) to evaluate the use of recycled materials in roadside safety devices. The goal of the study is the implementation of recycled-content roadside safety devices that meet established safety criteria.
The materials that appear most suitable for use in roadside safety applications include: recycled plastics, fiberglass, rubber, and wood fibers, either alone or in various combinations. For strength, it appears practical to design roadside safety devices to match the properties of wood. Consequently, recycled material can conceivably be applied where wood is currently used, such as: guardrail posts and offset blocks, sign supports, sign blanks, and barricades. Other potential applications include: flexible delineator posts, channelizing drums, and traffic cones.
To meet the requirements of various end uses, most plastics generally contain some amount of an additive. The main classes of additive in plastic are: lubricants, stabilizers, plasticizers, fillers, impact modifiers, reinforcing agents, fire retardants, and colorants. Occasionally, virgin material is required as a binder for the recycled material. Plastics are often blended or reinforced with other materials to obtain desired physical or mechanical properties. Wood, glass fibers, and rubber/polyolefin blends are employed to enhance the strength of plastic products. Generally speaking, the addition of rubber degrades the mechanical properties of recycled plastic. However, if rubber is used as an impact modifier, the properties of the product may be improved.
The relative density of commercially available plastic lumber products typically varies from about .7 to .96, making them 1.5 to 2 times heavier than wood. Susceptibility to moisture for 100 percent recycled plastics and plastic-rubber blends tends to be slight. Blends containing wood and paper products tend to have higher rates of water absorption. Studies have shown that the strength of wood and paper products decreases with increasing moisture content. In addition, since wood fibers expand with moisture content, the entire product will tend to expand. Various additives can be used to reduce moisture uptake.
Because the coefficient of thermal expansion of plastic products can be up to 12 times greater than wood or steel, they will expand and contract to a much greater extent for a given change in temperature. This fact should be considered in the design of connections and construction details. Where plastics are bonded to steel or wood in a composite fashion, the difference in expansion between the two materials could lead to cracking of the plastic or delamination at the interface. Generally speaking, a decrease in temperature will result in a gain in strength of recycled plastics. Conversely, an increase in temperature generally decreases mechanical properties such as compressive strength, bending strength, and modulus of elasticity in plastics.
Information collected and evaluated by the research team was summarized and categorized in two groups: (1) commercially available roadside safety products and traffic control devices having the potential for immediate implementation, and (2) other products and materials not specifically designed for use in roadside safety devices but having the potential for use in such applications.
Researchers developed a prioritization scheme for evaluating roadside safety products currently on the market. The fulfillment of specified safety requirements was of primary importance. Relevant field experience reported by state agencies, and the availability of physical and mechanical properties from laboratory testing were also weighed heavily in evaluation. Based on this evaluation scheme, products suitable for immediate implementation were identified and categorized by application type. Researchers performed no independent testing or field evaluation of the identified products. Recommendations in this study are based solely on information found in the literature and provided to the researchers by manufacturers and state agencies.
The contents of this summary are reported in detail in The Texas A&M University System - Texas Transportation Institute Research Report 1458-1, "Applications of Recycled Materials in Roadside Safety Devices," Roger P. Bligh, Dean C. Alberson, and Barbara G. Butler, June 1995. This summary does not necessarily reflect the official views of the TCEQ, FHWA, or TxDOT.
Additional research reports on this project: