Performance assessment of limestone calcined clay cement (LC3)-Based lightweight green mortars incorporating recycled waste aggregate

Abstract

Limestone-calcined clay cement (LC3) is one of the green or low-carbon binder options for replacing Portland cement, leading to sustainable construction. Reducing the thermal conductivity of the building's rendering mortar is helpful in reducing energy consumption for heating and cooling in buildings. In this study, LC3 has been prepared by replacing 60 wt% of White Portland Cement (WPC) with a blend of limestone (LS) powder and metakaolin (MK) with LS: MK of 1:2 (wt%). Lightweight LC3-based mortars were prepared in which the binder was combined with recycled fine aggregate (RFA) from autoclaved aerated concrete waste (AACW) with aggregate volume contents of 25, 50, and 75%. Mechanical, thermal, and hygric parameters, including compressive strength, in-direct tensile strength, bulk density, thermal conductivity, volume of permeable voids (VPV), and capillary water absorption, have been investigated after 28 days of curing. In order to explore the thermal stability of the prepared mortars, the residual strength after exposure to standard fire has been examined. The LC3-mortar incorporating 75 vol% of AACW possessed a bulk density of 1230 kg/m3; i.e., below the specified limit for lightweight rendering mortars. In addition, a reduced thermal conductivity (as low as 0.21 W/m K) has been obtained. Even at the highest volume content of AACW in the LC3-binder matrix, the lowest compressive strength was significant (13 MPa). Moreover, the newly developed mortars showed enhanced strength retention efficiency; a residual strength of about 61.5% was achieved after standard fire exposure for an hour (1hr). SEM analysis exhibited adequate bonding and a dense interface between the AACW aggregate and the LC3-binder matrix.