Low energy pre-blended mortars: Part 1 – Control of the sand drying process using a lime drying technique

•A technique is described for low-energy drying of wet sand to produce pre-blended mortars.•Quicklime is used as the drying medium.•The dominant processes are chemical combination and evaporation of free water.•Four principal process control factors have been identified.•The drying process produces slaked lime to form a component of the binder phase.

Production control methods allow factory produced mortars to be supplied to a more consistent formulation than site produced mortars. However, there is scope to enhance their “sustainability” credentials by addressing the methods of drying the wet sand and the use of lower energy hydraulic components. This paper describes the development of a technique in which quicklime is added in controlled quantities to remove free water by both chemical combination and evaporation. The slaked lime so generated is porous and a third mechanism of absorption is suggested which, however, might have adverse effects during storage of the pre-blended mortar. The principal process-control factors are lime addition based upon a ratio of the stoichiometric requirements for complete slaking of the quicklime, free moisture content of the sand, mixing time of the combined sand and quicklime, and storage of the mixed material.