Abstract
Sand-cement hollow blocks are widely applied in building construction in most countries. Attempt to lower the high costs of the material constituents, as well as the desire to enhance properties, has led to the substitution of the constituents with different admixtures. Thermophysical properties of most cementitious materials are found to change with the quantity of admixtures. One of the commonly used admixtures is metakaolin. This study investigates the thermal characteristics of hollow sandcrete blocks produced with metakaolin-blended cement. The replacement of cement with metakaolin is varied in steps of 5% to a maximum of 30% by volume. The results show increasing heat transfer rate, heat energy storing capacity and thermal mass with the mekaolin content. Time-response properties such as thermal admittance and thermal effusivity rise while most of the insulating properties reduce with increasing metakaolin substitution. The results show the potential use of metakaolin-based blocks for building applications should be with caution

Key words: Metakaolin, cement, admixtures, sandcrete blocks, thermal properties