Physical characteristics of sintered fly ash aggregate containing clay binders

A comprehensive research has been conducted to explore the influence of sintering on the properties of fly ash aggregate containing clay binders (bentonite and kaolinite). Fly ash aggregate containing clay binders, have been subjected to various sintering temperatures at different durations of 700–1400 °C and 15–120 min, respectively. The variation in aggregate properties, viz strength, water absorption, density and shrinkage during sintering, have been determined and discussed. In addition to these, the uniformity of sintering and rate of water absorption of sintered aggregate were also determined. No significant changes in aggregate properties were observed for aggregate sintered up to 900 °C, due to the insufficient sintering temperature range. However, the aggregate properties substantially enhanced for temperature above 1000 °C, which is attributed to the activation of liquid phase sintering. For temperatures between 1000 and 1300 °C, the aggregate with bentonite shows significant increase in shrinkage (30 %), density (density ratio 0.70), higher ten percent fines value (TPFV) (6.13 tonne), reduction in porosity (35 %), and water absorption of 4 %. However, at 1400 °C, the aggregate properties degraded due to the decomposition of mineral phases in bentonite. For aggregates with kaolinite, highest TPFV of 8.5 tonne with lowest water absorption of 2 % have been observed at 1400 °C. The presence of a higher amount of interconnected pores for aggregates sintered between 700 and 1000 °C leads to a higher rate of water absorption and then reduces to 30 % for temperatures between 1200 and 1300 and 1200 to 1400 °C for bentonite and kaolinite aggregates, respectively. This reduction is due to the reduced interconnected pores. Duration of sintering has no impact on the aggregate properties for temperatures up to 800 and 1000 °C for aggregates with bentonite and kaolinite, respectively. However, between 1000 and 1400 °C, there has been considerable improvement in the aggregate properties for increasing duration up to 60 min. In comparison, during sintering, aggregates with bentonite possessed better properties for temperature less than 1000 °C, whereas aggregates with kaolinite exhibited superior properties between 1100 and 1400 °C.