Sustainable Concrete through Reuse of Crushed Returned Concrete

Every year an estimated 2% to 10% (average of 5%) of the estimated 455 million yd³ of ready-mixed concrete produced in the United States (2006 estimate) is returned to the concrete plant. The returned concrete can be handled in several different ways. A common approach is to discharge the returned concrete in the concrete plant and crush the hardened concrete. The coarser material can be reused as base for pavements or fill for other construction. However, it is not easy to utilize the material finer than 2 in. A research project was undertaken by the National Ready Mixed Concrete Association Research Laboratory to study the use of crushed returned concrete, referred to as crushed concrete aggregate (CCA), as a portion of the aggregate component in new concrete. Demolishing old concrete structures, crushing the concrete, and using the crushed materials as aggregates, referred to as recycled concrete aggregate (RCA), have been researched to some extent. RCA is different from CCA because construction debris tends to have a high level of contamination (rebar, deicing salts, etc.). CCA, however, is prepared from concrete that has never been in service and thus is likely to contain much lower levels of contamination. The main objective of the research project was to develop technical data and provide guidance on a methodology for appropriate use of the material. Such a step can help the ready-mixed concrete industry achieve lower operating costs, reduce substantial landfill space, and support sustainable development.