mens, to 55% for the WL specimens. Correspond-
goal is to redirect errant vehicles to allow the
ingly, the material became stiffer in cold. The com-
occupants to survive the impact, and to ensure
pressive moduli for the cold and dry CDL, CDT,
that the redirected vehicle presents a minimum
and CDTT specimens show about a 239%, 136%,
hazard to following and adjacent traffic. Experi-
and 152% increase, respectively. The compressive
ence and knowledge are the key factors in design-
moduli increase of cold and frozen WCL, WCT,
ing the system; therefore, highway engineers rely
and WCTT specimens are equally dramatic, at
on trial and error of candidate systems, and they
148%, 119%, and 134%, respectively. At 30C the
evaluate such systems by crash testing. Therefore,
flexural strength of the dry DCD specimens
following the above laboratory tests, further
increased 63%, and their modulus 101% (see Table
investigations on the applicability of the RPC
12). For the wet flexural specimens, WCD, the
using crash testing was conducted by the FHWA
strength and modulus increase were 52% and
at the Federal Outdoor Impact Laboratory (FOIL)
104%, respectively. A significant increase in both
at TFHRC in McLean, Virginia. The results of this
strength and modulus at low temperature were
test have been summarized by McDevitt and
also observed for the Douglas fir specimens. Dou-
Dutta (1993) and are reproduced in part in Appen-
glas fir DCD specimens showed a 24% increase in
dix B.
strength, and about a 19% increase in modulus.
After the FOIL test, the FHWA continued the
Relating mechanical properties, such as those
field crash tests. Guardrail blockouts made of RPC
determined for the RPC, to the design of guard-
are considered as separate products that could re-
rail posts or blockouts is not straightforward. The
place the wood blockouts. The RPC blockouts per-
analytical design is too complex, as it depends not
formed satisfactorily in the FOIL test and several
only on the material properties and structural
other crash tests, and were subsequently approved
response of the rails and the posts, but also on the
by the FHWA for use by state highway authori-
soil bearing capacity as the primary source of gen-
ties. Figure 55 shows an example of its use.
erating restraining forces (USDOT 1988). Such an
The general mechanical properties of RPC in-
analysis includes dynamic effects, large displace-
dicate that it has a potential for use as supports
ments, stiffness, yield strength, and the inelastic
for small signs. One of the evaluation criteria for
behavior of the materials in the system. The final
crash tests of small signs is that after the full-scale
test, the height of the stub section will be not higher
than 102 mm (4 in.) above ground (AASHTO 1985).
At the FOIL test, the RPC posts broke off cleanly
at the ground line, indicating that this type of
material may have potential for such applications.
However, since the RPC materials were found to
be stronger and stiffer at lower temperatures than
at room temperature (before their application),
some crash tests at a low temperature may be nec-
essary.
Because some state legislatures have mandated
recycling, interest in RPC is expected to grow in
the future. Its potential applications will probably
include noise barriers, blockouts, guardrail posts,
fence posts, sign supports, delineator posts, etc.
These applications will necessitate further assess-
ment of the RPC's performance under prolonged
stress, wider ranges of temperature, toxicity (if
any), damage by insects, and cyclic periods of heat,
cold, and dampness. The applications themselves
should have some baseline specifications, subject
to local conditions. Also, the RPC material must
be available in consistent composition and prop-
erties, with an assured quality. Finally, the RPC
materials will have to be economically competi-
Figure 55. Use of RPC as a blockout material
tive with the products they are intended to replace.
in a highway.
40
Previous Page
