Every year, it is estimated that 2% to 10% (average of 5%) of the estimated 455 million cubic yards of ready mixed concrete produced in the USA (est. 2006) is returned to the concrete plant. The returned concrete in the truck can be handled in several different ways. A common approach is to discharge the returned concrete at a location in the concrete plant for processing (Figure 1). The hardened discharged concrete can be subsequently crushed by a crusher (Figure 2) and the coarser material can be reused as base for pavements or fill for other construction. However it is not easyto utilize the material finer than 2 inches (Figure 3). A research project was undertaken by the NRMCA Research Laboratory to study the use of crushed returned concrete, referred as Crushed Concrete Aggregate (CCA), as aportion of the aggregate component in new concrete. The project was funded by the Ready Mixed Concrete Research and Education Foundation (RMCREF).Demolishing old concrete structures, crushing the concrete and using the crushed materials as aggregates is not new and has been researched to someextent. This material is generally referred as Recycled Concrete Aggregates (RCA). However, RCA is different from CCA as construction debris tends to have a high level of contamination (rebar, oils, deicing salts, and other building components). CCA on the other hand is prepared from concrete that has never been in service and thus likely to contain much lower levels of contamination. The main objective of the research project was to develop technical data that will support the use of CCA from returned concrete by the industry and to provide guidance on a methodology for appropriate use of the material. Such a step can help the ready mixed concrete industry to save an estimated $300 million/year in operating costs. In addition, it will reduce landfill space by as much as 845 – 10 feet high football fields every year. The use of CCA could also help attain points under systems like the Leadership in Energy and Environmental (LEED) for certifying building projects for sustainable construction. This short article summarizes the key findings from the 20 month study. The complete reports canbe downloaded from either one of the following locations http://www.rmc-foundation.org/newsite/index.htm and http://www.nrmca.org/research/eng_articles.asp.
Abstract