Recycling fine powder collected from construction and demolition wastes as partial alternatives to cement: A comprehensive analysis on effects, mechanism, cost and CO2 emission

Abstract

Two fine powders collected from construction and demolition wastes (CDW), i.e., recycled concrete powder (RCP) and recycled clay brick powder (RBP), were used as partial alternatives to cement for mortar preparation. The effects of RCP/RBP on fluidity/strength of mortar at varying replacement rates were experimentally investigated meanwhile the mechanism was discussed according to hydration process characterized by hydration heat flow, compositions of hydration products, hydration degree, as well as the pore structure of blended mortars. Extended analysis was also conducted on cost performance and CO2 emission of the blended mortar by considering the mortar strength simultaneously. Test results showed that RCP/RBP at a dosage no larger than 30% had marginal influence on water demand of paste; the mortar fluidity was even improved at replacement rates lower than 20%. The strength, especially compressive strength of mortar was reduced but the reduction was not obvious given the RCP and RBP dosages were below 10% and 20%, respectively. Both RCP and RBP can facilitate early cement hydration and improve the 28-day hydration degree likely due to the nucleation effects. The finer RBP also refined large pores in mortar while RCP increased the total porosity and made pore coarser. This work also confirmed that both RCP/RBP can improve the cost performance of mortar and help achieve extra environmental profits by reducing CO2 emission given their dosage did not exceed 20%. RBP should be a more favorable alternative than RCP to OPC for preparing more cost-effective and lower-carbon cementitious materials with ensured fluidity and strength.