Compressive strength development of binary and ternary lime–pozzolan mortars

This study considers the compressive strength development of broad range of hydraulic lime mortars prepared with a range of commercially available alumino-silicate by-products and modern pozzolanic additions. Specifically this paper considers the effect of mineral addition selection, binary and ternary combinations, pozzolan content and the effect of curing conditions on the compressive strength development of hydraulic lime based mortars. The study was undertaken as the initial phase of a broader investigation considering the feasibility of producing modern, sustainable hydraulic lime–pozzolan concretes with comparable strengths to Portland cement based concretes. The aim of the initial phase was to identify a small number of additions, and combinations thereof, which would result in a structural strength lime–concrete when scaled up from mortars to concretes.

In the absence of a definitive source of information on the mechanical properties of hydraulic-lime mortars prepared with binary and ternary combinations of alumino-silicate by-products, 22 combinations consisting of Natural Hydraulic Lime (NHL5) and a range of possible additions, identified from historical and current practice, were prepared. The results have shown that combining an eminently- hydraulic NHL5 with silica fume and ground granulated blastfurnace slag can produce mortars with a 28-day compressive cube strength of around 28 N/mm2, at a water-to-binder (w/b) ratio of 0.5. This is eight times the strength of an equivalent mortar prepared with NHL5 alone and broadly speaking com- parable with that of low-heat cementitious mortars. The contribution of the pozzolanic reaction to the strength of hydraulic lime mortars is discussed for a range of alumina-silicious materials and combinations thereof.