Influence of pozzolanic materials on the properties of natural hydraulic lime based mortars

•Slag powder and silica fume have positive effect on the mechanical property of NHL based mortar.•Pozzolanic materials can improve the environmental resistance of NHL based mortar effectively.•The hydration reaction of NHL based mortars can be promoted by both slag powder and silica fume.•The hardened products and their existential forms of NHL, S-NHL and F-NHL mortars are different. To evaluate the influence of pozzolanic materials (slag powder and silica fume) on the properties of natural hydraulic lime (NHL) based mortars, the properties of NHL mortar, slag powder-NHL based mortars (S-NHL) and silica fume-NHL based mortars (F-NHL) were studied deeply from the aspect of physical and mechanical properties, environmental resistance properties, hardening reaction process and micro morphology in this paper, among which S-NHL are prepared with 10% and 20% slag powder to substitute NHL and F-NHL are prepared with 10% and 20% silica fume to substitute NHL, respectively. The results indicate that the NHL mortars have preferable fluidity compared to the S-NHL and F-NHL mortars. In terms of mechanical properties, the compressive strength of S-NHL and F-NHL mortars have been significantly improved, among which the compressive strength of S20-NHL and F20-NHL mortars reached 7.73 MPa and 7.99 MPa at 28 days, respectively. The environmental erosion resistance of S-NHL and F-NHL mortars have been improved by a proportion of NHL is replaced by pozzolanic materials; moreover, the addition of slag powder has a more significant improvement on the sulfate resistance of mortars, and the acid resistance of mortars are improved obviously by the addition of silica fume. The pozzolanic materials and Ca(OH)2 occur pozzolanic reaction with water and produce more calcium silicate (aluminate) hydrate (C-S(A)-H), and CaCO3 crystals are formed by carbonizationreaction in mortar and interweave with hydration products to fill in the air pores of mortar, thereby the micro-structure of mortars have ameliorated, the performance of S-NHL and F-NHL mortars are improved finally. The pozzolanic index P show that the pozzolanic effect of silica fume is higher than slag powder at the early stage (before 28 days) of NHL based mortar hardening, and slag powder is higher than silica fume at the later stage (after 28 days), meanwhile slag powder has better effect for improving the compressive strength of mortar compared to silica fume.