Thermal treatment of recycled concrete aggegate for general use in concrete. A preliminary study

In this paper, the results of a preliminary laboratory study to assess the effectiveness of thermally treating recycled concrete aggregate for genera) use in concrete are presented. 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 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 concrete specimens, prepared with one of the treated samples was slower than that of conventional Dutch 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 propertjes which are reasonably comparable to conventionally used Dutch river-dredged aggregate