Analysis of two processing techniques applied on powders from recycling of clay bricks and concrete, in terms of efficiency, energy consumption, and cost

Abstract

Two processing techniques, i.e., grinding and calcination taken on fine powders from recycling of concrete and clay bricks (RCP/RBP) as construction and demolition wastes (CDW) were evaluated in terms of their efficiency, energy consumption, and cost. It was found that replacing OPC with 20 % non-processed RCP/RBP led to up to 22 % loss of compressive strength of mortar, though the fluidity and flexural strength were similar to that of the OPC mortar. By conducting the grinding treatment, the RCP/RBP particles were refined; cement hydration was found to be more complete in the blended mortar meanwhile the pore structure was improved. Calcination led to the formation of new active phases in RCP/RBP which facilitated the early-age cement hydration and contributed to more complete hydration at later ages. Test results on mortar strength showed that the compressive/flexural strengths can be enhanced by both treatments though the 28-day compressive strength of RCP mortar was still 11 % lower than that of OPC. The optimal grinding duration and calcination temperature in terms of enhancing mortar strength was 20 min and 600 ℃/800 ℃ (for RCP and RBP respectively), under which the 28-day compressive strength of the blended mortars can be enlarged by up to 10.11 % and 14.33 %, respectively. Basically, calcination can enhance the mortar strength (28 or 90 days) better than grinding and the enhancement was more significant for the RCP mortar than for the RBP. Further analysis on extra power consumption and cost performance suggests that the calcination treatment was more energy-efficient and cost-effective than grinding to improve the mortar strength so it should be a better option to process CDW powder for preparing lower-carbon cementitious materials with satisfactory fluidity and strength.