|
Frequently Asked Questions
Cement & Concrete
Technology Home > FAQs > Recycled Aggregate
 Q:
What differences can I expect in the behavior and properties of recycled-aggregate
concrete compared to concrete made with natural aggregates?
A:Recycled aggregate
will typically have higher absorption (see Figure) and lower specific
gravity than natural aggregate and will produce concrete with higher
drying shrinkage and creep. These differences become greater with
increasing amounts of recycled fine aggregates. Too many recycled
fines can also produce a harsh and unworkable mix.
Figure: Comparison of water absorption of three different recycled
aggregate particle sizes and one size of natural and lightweight
coarse aggregate.
Many transportation departments have found that using
100% coarse recycled aggregate but only about 10% to 20% recycled
fines works well. The remaining percentage of fines is natural sand.
The chloride content of recycled aggregates is of concern if the
material will be used in reinforced concrete. However, the quantity
of chloride typically found in old concrete pavement is usually
below critical threshold values.
For more information on recycled aggregate, click
here.
More references:
Recycling Concrete Pavement, American Concrete Pavement
Association (www.pavement.com),
and
Recycling Concrete
and Masonry,
Environmental Council of Concrete Organizations |