ETL 1110-3-503
15 Sept 99
02749). Further information concerning RAP material is available in the Technical
Instructions Manual (TI 822-08/AFMAN 32-1131V8(I)) Standard Practice Manual for
Flexible Pavements. In 1994, it was estimated that about 50 million tons of RAP were
being milled annually (Collins and Ciesielski 1994). RAP can be used to make hot
mixes, cold mixes, or in-place mixes. The percentage of RAP in a hot mix normally
varies from 10 to 50 percent. Heat ing of the RAP without burning or damaging the
asphalt cement is the limiting factor, although methods that allow 100 percent RAP,
using microwaves for high temperature heating, have been used (Shoenberger et al. 1993
and FHWA 1993).
One state DOT has used RAP as an aggregate in PCC mixtures. Others have used it as
either a stabilized or unstabilized base or subbase course material. The most predominant
use is in hot-mix asphalt paving mixtures. The use of RAP in hot-mix asphalt is
generally an excepted process, with an overall positive impact on the environment
(Ahmed 1991). At least seven states mandate the use of some RAP material in all hot-
mix asphalt placed by the state DOTs (Ciesielski 1995). As a general rule, RAP is not
considered to be hazardous material. The only exception might be when the pavement
was constructed with a hazardous material as one of the components (Thompson and
Haas 1992).
k. Reclaimed concrete pavement . Reclaimed concrete pavement (RCP) has many
uses including: aggregate for new PCC mixtures, unbound base course aggregate,
cement-treated base, embankment base material, and as an asphalt paving aggregate.
RCP has been used successfully for all of these types of applications and in some
instances, it is a viable alternative to concrete pavement rehabilitation (CPR) or an
overlay. It is not recommended for structural concrete (e.g., abutments, bridge decks)
because of concerns with reduced compressive strength and possible deleterious materials
(Shelburne and Degroot 1998). RCP from distressed pavements, caused either by
D-cracking or alkali-silica reaction, can produce strong, durable concrete for pavements
(Collins and Ciesielski 1994).
Most recycling, utilizing RCP, has involved replacement of coarse aggregates. RCP,
when used as a fine aggregate, generally is less workable and requires more cement,
because of the increased water requirements (Yrjanson 1989). With currently available
equipment, all types of PCC can be recycled including: reinforced concrete and even
continuously reinforced pavements. At least one third of state DOT's have used or
actively use RCP material (Yrjanson 1989). RCP would not be considered a hazardous
material unless the pavement had been constructed with a hazardous material as one of
the components (Thompson and Haas 1992). The CE has used RCP in many instances to
produce stabilized base course and new PCC. Further information on RCP is available in
TM 5-822-7/AFM 88-6, Chap.8, Standard Practice for Concrete Pavements. The CE
recommends that when recycling D-cracked concrete, the concrete should be crushed to a
maximum particle size of 19 mm (3/4 in.). There is little long-term experience in
recycling with alkali-silica reaction cracked concrete; therefore, prior to its use the
concrete mixture should be evaluated with the same methods used on a new aggregate
concrete mixture.
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