Analysis of the impact of calcitic aggregates on the properties of air-lime mortar

This paper reports on research conducted on air lime mortars made using calcitic aggregates. Three different calcitic aggregates were compared with a mortar made from a standard silicate sand (BS EN196-1:2016, with an additional 2mm fraction). The results show that calcitic aggregate/air lime mortars can be designed to have compressive strengths of a similar order to weak NHL2 mortars (2-2.5MPa) without running the risk of the strength increasing excessively over time, as is seen in many NHL mortars. Early compressive strengths of the order of 1.5MPa mean that these mortars also contribute to ‘buildability’. The analysis suggests that the reasons for this higher strength are partly due to more rapid and complete carbonation, and partly due to better interfacial bond between binder and aggregate.