Waste brick’s potential for use as a pozzolan in blended Portland cement

Abstract

This study investigated the pozzolanic reactions and engineering properties of waste brick-blended cements in relation to various replacement ratios (0—50%). The waste brick consisted of SiO2 (63.21%), Al2O3 (16.41%), Fe2O3 (6.05%), Na2O (1.19%), K2O (2.83%) and MgO (1.11%), and had a pozzolanic activity index of 107%. The toxic characteristic leaching procedure (TCLP) results demonstrate that the heavy-metal content in waste bricks met the Environmental Protection Agency regulatory limits. Experimental results indicate that 10, 20, 30, 40 and 50% of cement can be replaced by waste brick, which causes the initial and final setting times to increase. Compressive strength development was slower in waste brick-blended cement (WBBC) pastes in the early ages; however, strength at the later ages increased significantly. Species analyses demonstrate that the hydrates in WBBC pastes primarily consisted of Ca(OH)2 and calcium silicate hydrate (C—S—H) gel, like those found in ordinary Portland cement (OPC) paste. Pozzolanic reaction products formed in the WBBC pastes, in particular, various reaction products, including hydrates of calcium silicates (CSH), aluminates (CAH) and aluminosilicates (CASH), formed as expected, resulting in consumption of Ca(OH)2 during the late ages of curing. The changes in the properties of WBBC pastes were significant as blend ratio increased, due to the pores of C—S—H gels and CAH filling via pozzolanic reactions. This filling of gel pores resulted in densification and subsequently enhanced the gel/space ratio and degree of hydration. Experimental results demonstrate waste brick can be supplementary cementitious material.