Development of synthetic aggregate using off-ASTM specification ashes

This paper presents a comprehensive laboratory evaluation for developing synthetic aggregate using off-ASTM specification ash produced through a fluidized bed combustion (FBC) process. To determine optimum mix design which produces strong and durable synthetic aggregate, different combinations of water to fly ash ratio, various combination of fly ash (FA_f) to stockpiled material (FA_sp) ratio, curing temperature, and calcium chloride content were applied. Then, to evaluate the performance of synthetic aggregate for construction application, basic characteristics of synthetic aggregate such as density, specific gravity, absorption, gradation, strength, abrasion resistance, and soundness were carried out. The results indicate that 100% RH and 40 °C was determined to be the optimum curing conditions for both fly ash paste and FA_f/FA_sp mortar mixtures in terms of strength and minimal potential sulfate attack. The aggregate characterization results indicate that the produced synthetic aggregates met ASTM C 33/330 criteria for a concrete aggregate without inducing any soundness problems despite their relatively high water absorption. Therefore, the FBC ash and stockpiled ash can be used as primary resource materials for manufacturing synthetic light weight aggregate.