Preliminary laboratory investigation of thermally treated recycled concrete aggregate for general use in concrete

This paper deals with a preliminary laboratory study to assess the effectiveness of thermal treatment methods to improve the quality of recycled concrete aggregate. The samples used for the study consisted of sieved fractions of crushed concrete that were subjected to various thermal treatments at temperatures of either 650 °C or 800 °C. In each case, the treatment lasted for a period of 0.5 or 1 hour. After the thermal treatments, the samples were first investigated by means of polarising and fluorescence microscopy followed by strength tests on mortar and concrete specimens prepared with one of the treated samples. The thermal treatments caused considerable reduction in the amount of cement paste or mortar adhering to both the fine and the coarse aggregate particles. The reduction was more pronounced in the case of the samples treated at a temperature of 800 °C than those treated at 650 °C. The integrity of the aggregate particles was found to a large extent to be preserved. The strength development of mortar and concrete specimens, prepared with one of the treated samples was slower than that of conventional river-dredged aggregate but reasonably good. Although this is a preliminary study, the results indicate that thermal treatment of recycled concrete aggregate at a temperature of about 800 °C can yield good quality aggregates, with properties which are reasonably comparable to conventionally used river-dredged aggregate