Cement replacement and recycled aggregates for a more sustainable concrete: experimental investigation and conceptual modelling

Cement Concrete & Aggregates Australia (CCAA) is the mean national body in Australia representing the interests of six billion dollar a year heavy construction materials industry. In May 2008 this organization published an interesting document, a sort of Guidelines, fixing the current knowledge about the utilization of recycled aggregate in new concrete production. The most important references were CSIRO (Commonwealth Scientific and Industrial Research Organisation) Standards, and Concrete Institute of Australia. Five types of recycled aggregates are identified and classified: Recycled Concrete Aggregate (RCA), Recycled Concrete and Masonry (RCM), Reclaimed Aggregate (RA), Reclaimed Asphalt Pavement (RAP) and Reclaimed Asphalt Aggregate (RAA). In this chapter only the first one will be taken into account, considering the present work’s purpose and also because, in Australia, RCA is the most common construction and demolition waste used in concrete production.
Recycled Concrete Aggregate (RCA) is defined as crushed sound and clean waste concrete of at least 95% by weight of concrete with typical total contamination lower than 1% of the bulk mass. Other materials that may be present in RCA are gravel, crushed stone, hydraulic-cement concrete or a combination thereof deemed suitable for premix concrete production. As CSIRO reported, Class 1A RCA, which is a good quality RCA with no greater than 0.5% brick content, had the potential for use in a wide range of applications, subject to appropriate test or performance requirements. Applications include partial replacement for virgin material in concrete production for non-structural work, such as kerbs and gutters. It is emphasized that current field experience with the use of recycled concrete aggregates for structural applications is scarce, but on the other hand HB 155 "Guide to the use of recycled concrete and masonry materials" (2002), clarifies the matter. In fact, it is possible to distinguish two different grades of recycled concrete aggregate, both belonging to Class 1A RCA:

. Grade 1 recycled aggregate concrete (RAC) is defined as concrete with up to 30% substitution level of Class 1A RCA recycled coarse concrete aggregate; it has a maximum specified strength limit of 40 MPa.

. Grade 2 recycled aggregate concrete (RAC) is allowed up to 100% substitution level of Class 1A RCA recycled coarse concrete aggregate and the maximum specified strength limit is 25 MPa.

Thus, for structural concrete, it is possible to fix that the maximum allowed percentage of replacement of recycled coarse concrete aggregate (RCCA) is 30%, while there was not any limitation about the use of RCCA for minor concrete.