Evaluation of the thermo-physical, mechanical, and fire resistance performances of limestone calcined clay cement (LC3)-based lightweight rendering mortars

Limestone-calcined clay cement (LC3) is one of the potential green or low-carbon binders for replacing ordinary Portland cement (OPC), leading to sustainable infrastructure development. Improving the thermal properties of the building's rendering mortar is an effective solution to reduce the building's energy consumption. In this study, LC3 has been prepared by replacing 60 wt% of OPC with a blend of limestone (LS) powder and metakaolin (MK) with LS: MK of 1:2 (wt %). Three mixtures of LC3-based lightweight mortars were prepared in which the binder was combined with three types of expanded/exfoliated insulant lightweight aggregates (LWAs), including expanded perlite (EP), expanded clay (EC), and exfoliated vermiculite (EVM), with aggregate volume contents of 75%. Compressive strength, in-direct tensile strength, bulk density, thermal conductivity, thermal diffusivity, specific heat, volume of permeable voids, and capillary water absorption, have been assessed. The effect of fire on the compressive strength and micro-structure has been studied to explore the thermal stability of the prepared mortars. The newly developed LC3-mortars possessed densities below the specified limit for lightweight rendering mortars (i.e., <= 1300 kg/m3) accompanied with good thermal insulation performance. The mortar incorporating EP showed the lowest thermal conductivity (R-.10.2 W/m.K), the highest thermal mass (R-.12.3 MJ/m3. K) and the lowest compressive strength (R-.16.76 MPa). The EVM mortar showed the highest strength retention efficiency; a residual strength of about 79.4% was obtained after standard fire exposure for an hour. The integration of LWAs into the LC3 binder matrix is helpful in improving the structural integrity upon fire exposure. The simultaneous improvement of thermal and mechanical properties in addition to fire resistance with the potential to reduce carbon footprint summarize the major innovation presented in this study.