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Concrete Aggregate
Recycled Concrete Aggregate in New Pavements
 The
cost of virgin aggregates is typically between 10 and 15 percent
of the total construction cost of a new roadway section. A century
of modern growth and urbanization in America has depleted once plentiful
aggregate supplies. Frequently, aggregates come from either distant
quarries at great expense or from local sources offering only marginal
quality. Recycled concrete aggregates (RCA) have proven to be a
sustainable substitute for virgin aggregates in almost any application
that uses conventional virgin aggregates, in some cases proving
to be an even better choice than the typically more costly virgin
aggregate. This situation has led many state agencies to recognize
the engineering, economic, and environmental benefits that can be
achieved using RCA. According to a 2004 Federal Highway Administration
study, 41 states recycle concrete for use as aggregates.
Concrete pavements are 100 percent recyclable!
When used in pavement infrastructure applications as a substitute
for virgin aggregates, experiences and research studies have shown
that RCA can produce strong, durable materials. Actually, the recycling
of concrete is a relatively simple process. It involves breaking
and crushing existing concrete. Any reinforcing steel in the existing
concrete is removed prior to crushing. The crushed material is then
processed according to aggregate size and quality. Once processed,
RCA can be used in the following pavement applications:
- Conventional concrete
- Roller-compacted concrete
- Cement-treated base
- Unstabilized graded aggregate base/subbase
- Granular fill
- Rip-rap
- Mechanical stabilizer for marginal soils
 When
RCA is used to produce new concrete mixtures, its effects on the
mixture’s properties can range from minimal to signifcant,
depending upon the nature, composition and gradation of the RCA.
For example, when little reclaimed mortar is present in coarse RCA,
and when virgin fine aggregate is used, the handling characteristics
and engineering properties of the resulting concrete will be practically
the same as if all virgin aggregate had been used. Minor adjustments
in mixture design and admixture usage may be required to reduce
any differences in the properties of RCA concrete mixtures. As far
as production is concerned, recycled concrete can be batched, mixed,
transported, placed, and consolidated in the same manner as conventional
concrete.
For more information on the applications, benefits, design, construction,
testing, performance, and sustainability of RCA in pavement applications,
please refer to the American Concrete Pavement Association publication
Recycling
Concrete Pavements.
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