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Problem Statement
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.
Objectives
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.
Findings
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.
Implementation
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:
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