Utilising under-burnt waste bricks from kilns as supplementary cementitious material

Abstract

The pozzolanic performance of crushed brick powder (CBP), obtained by grinding under-burnt waste bricks from a continuous brick kiln, is studied. Two size fractions of CBP considered for cement replacement are CBP1 (passes through 150 μm but is retained on 75 μm) and CBP2 (passes through 75 μm). Compressive strength tests on mortar with CBP reveal that strength does not exceed that of the control; however, 10–15% cement replacement by CBP is the optimum. The presence of hydrate phases by X-ray diffraction and quantification of portlandite in the paste samples as studied by thermogravimetric analysis up to 90 days confirms the action of pozzolanicity. Furthermore, to determine the feasibility of CBP1 and CBP2 fractions in concrete, the strength and carbonation of M25 grade concrete were studied by replacing 45% cement with a combined proportion of CBP1 (20%) and CBP2 (25%). This reduced the concrete grade from M25 to M20 and increased the accelerated carbonation depth. Nevertheless, the projected natural carbonation coefficient with accelerated carbonation data is determined as low. The CBP used is cost-effective, requiring little mechanical processing and no chemical activation; thus it can satisfactorily be used for low-cost housing construction and lower-grade structural and non-structural uses.