modulus for glass fiber composites cause a major
identified by the U.S. Navy as a pilot project to
design problem if deflections are to be limited. At
determine the feasibility of creating a "recycling
higher temperatures, the properties of most com-
loop" for shipboard-generated plastic wastes.
posites degrade. Some degradation of properties
Recycling the shipboard-generated plastic wastes
at lower temperatures has been reported (Dutta
was found to be successful in producing the so-
1992). The fire resistance capacity and the toxic-
called "plastic lumber" without a lot of internal
ity of the smoke of most composites remain prac-
voids, but the sections had a relatively coarse
tically unknown. The test methods to define the
grain due to the size of the sawdust particles
properties of composites are still evolving, and
(Middleton et al. 1991). In the present study, this
material standards as well as design and analysis
RPC was investigated for application in highway
codes are lacking.
structures, and the results are discussed briefly in
Chapter 4.
Recycled plastic composites (RPC)
Because of growing concerns about pollution
Fracture behavior and energy absorption
of the environment and decreasing capacity of the
characteristics of FRP composites
sanitary landfill sites, the recycling of plastics
The energy absorption mechanism of ductile
started gaining momentum in the U.S. in the mid-
metals, steel or aluminum largely results from
1980s. At this time, there is considerable empha-
plastic deformation. In contrast, the fracture of
sis by the FHWA on the use of recycled materials
composites involves a large number of different
for highway construction. Section 1038 of public
microcracking processes, which depend on the
law 102-240, the "Intermodal Surface Transporta-
properties of the fibers and resins and on the geo-
tion Efficiency Act," enacted by Congress on 18
metrical arrangement of the fibers. Experience has
December 1991, directs the U.S. Environmental
shown that although the fiber-reinforced-compos-
Protection Agency and the U.S. Department of
ite tubes or rods can fail in a brittle manner when
Transportation, in cooperation with the states, to
loaded in compression, a progressive crushing
conduct studies on the use of recycled materials
failure can still be produced by appropriately trig-
in highway construction (Bloomquist et al. 1993).
gering microcracking (Hull 1983). The actual frac-
Recycled polyethylene terephthalate (PET) bottles
ture mode is strongly dependent on the fiber
have been considered as a cheap source mate-
arrangements. The microcracking processes can
rial for polymer concrete and polymer mortar.
lead to extensive breakdown of the material and
Recycled PET has also been tested as a secondary
the absorption of large amounts of energy. In-
reinforcement in concrete (Auchey and Dutta
depth studies of polymer composites by Hull
1996). During the last several years, a large num-
showed that when a composite fails, the fracture
ber of recycled plastics, both with reinforcements
energies are absorbed by matrix cracking, fiber
and without, have appeared in the market. Many
breaking, fiber-matrix debonding, frictional work
of them have been fabricated in the shapes of
following debonding, and fiber pullout. He
structural components, such as rods and bars of
observed that in composites, the specific absorp-
various cross sections and diameters. Their
tion energies are significantly larger than those
mechanical and physical properties have been
observed in the collapse of ductile metallic tubes.
investigated (Cao et al. 1991). Some of these mate-
The energy absorption property is a significant
rials contain large voids in the interior because of
consideration in the design of guardrails in high-
the unescaped air during the manufacturing. Cao
way barriers.
et al. observed that for these materials the core
area is the weakest region because of these voids.
General requirements of
The voids appeared to be elliptical with the
roadside safety hardware
major axis oriented in the longitudinal direction.
A discussion of specific roadside safety ele-
Thus, the properties differed across the cross sec-
ments and their requirements are not within the
tion of the materials. Initially, the application of
purview of this report. However, the proper
these structural materials was restricted to non-
design of roadside hardware is important to the
critical load-bearing structures, such as park
safe operation of highways. Although most driv-
benches, picnic tables, fences, fence posts, curbs,
ers operate their vehicles safely within the road-
parking blocks, etc. In 1990 a composite form of
way, statistics show that a certain percentage of
recycled plastics, in which an admixture of saw-
drivers in any stream of traffic is likely to leave
dust or wood-waste fibers were blended, was
the road unintentionally (Tutt and Nixon 1970).
8
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