Blended cement-lime mortars for conservation purposes: Microstructure and strength development

Blended lime-cement mortars are commonly used in conservation practices even though they may show lack of adequate strength and durability for certain cement-lime compositions. This paper focuses on understanding the hardening reactions and their influence on the strength development, microstructure and porosity for the cement-lime mortars in various compositions. Mortars composed of 30%, 50% and 70% ce-ment replacement with lime hydrate and lime putty by mass were studied. Cement hydration has been found to contribute to the early stage strength development while carbonation is mostly favoured after 3 days and con-tributes to the strength development until 180 days. The degree of carbonation is much more pronounced with increasing lime content and porosity of the mortars and the reaction is still in progress at 90 days. All the blended mortars revealed lower compressive and flexural strength than that of the reference cement mortar due to their lower cement content and higher porosity. Long-term compressive strength development has been achieved after 180 days while flexural strength for certain mortar compositions does not increase beyond 28 days. Unlike cement mortar, the mortars blended with lime hydrate and lime putty exhibit an elastic-plastic deformation before failure occurs, which is preferred for repair mortars to adapt to differential settlements and to allow more deformation under critical stresses in the masonry.status: publishe