Interest in recycled concrete is growing for a number of reasons: supplies of high-grade concrete aggregates are being depleted in some regions; better methods are in demand for solid waste disposal; and there is increasing need for energy conservation. Recycling should be considered wherever good aggregates are not available locally, where aggregate costs are excessive or where disposal of existing pavement or structures would be a problem.
Recycled concrete is old concrete that has been removed from pavement, foundations, or buildings and crushed to produce aggregate. This aggregate can then be used as aggregate in new concrete, in soil cement or simply as stone for aggregate bases or pavement subbases. Recycled concrete can be used in econocrete (lean concrete) bases built with concrete mixers and slipform pavers. Before use as aggregate in new concrete pavement, tests must be made to show whether the new concrete made with crushed concrete aggregate will have acceptable strength and durability. In recycling concrete, reinforcing steel or other embedded items must be removed. Care also must be taken to prevent contamination of the concrete by dirt or other undesirable materials, such as gypsum plaster products from buildings. Sizes of crushed concrete can be specified for the intended use.
The largest concrete pavement recycling project to date is the Edens Expressway reconstruction job in Illinois, at $113 million. On this project, the contractor decided to recycle the pavement and use it in the new, improved subgrade. The savings were obvious. If the contractor had chosen to waste the old pavement after removal he would have had to haul it approximately 20 miles, pay a dumping fee for each truckload, and then buy and haul in approximately 10 to 18 inches of new, granular material.