Recycled Aggregate Equipment Introduction

This fact sheet is an overview of recycled aggregate, which is produced by crushing concrete, and sometimes asphalt, to reclaim the aggregate. Recycled aggregate can be used for many purposes. The primary market is road base.

Benefits of Recycled Aggregate

The use of recycled aggregate can save money for local governments and other purchasers, create additional business opportunities, save energy when recycling is done on site, conserve diminishing resources of urban aggregates, and help local governments meet the goal of reducing disposal by 50 percent by the year 2000.

Materials/Definitions

Aggregate consists of hard, graduated fragments of inert mineral materials, including sand, gravel, crushed stone, slag, rock dust, or powder. Inert solid waste is concrete, asphalt, dirt, brick, and other rubble.

Portland cement concrete (PCC) and asphalt concrete (AC) consist primarily of aggregate. The cement and asphalt serve as binders. Some PCC contains steel reinforcement bars, or “rebar,” such as a bridge deck or tilt-up slabs. When a road or structure is demolished, the rebar can often be seen protruding from the broken chunks of PCC.

Recycled aggregate comes primarily from PCC and AC from road rehabilitation and maintenance, demolition, and leftover batches of AC and PCC. After processing, the rocks retain bits of cement or asphalt.

A roadway is built in several layers: pavement, base, and sometimes subbase. The pavement is the surface layer, and is made of PCC or AC. The base layer supports the pavement, and is made of aggregate base (AB). The subbase layer supports the base and is made of aggregate subbase (ASB). The subbase layer allows more sand, silt and clay than the AB layer; the subbase layer has less strength, but is used because it is more economical when bringing the road up to grade.

Equipment

The AC and PCC generally arrive at the processor in chunks. Heavy crushing equipment is required to break up the chunks into aggregate. Some equipment is portable and can be set up on site for immediate use of product. A crushing plant may include a hopper to receive the material, a jaw to break it into more manageable pieces, a cone or impact crusher to further reduce its size, a vibrating screen to sort to the required specification, and a conveyor belt with a rotating magnet to remove metal contamination such as rebar.