Combined effect of isobutyltriethoxysilane and silica fume on the performance of natural hydraulic lime-based mortars

Natural hydraulic lime (NHL)-based mortars were prepared by introducing isobutyltriethoxysilane (SO) and silica fume (SF) as partial replacement of NHL by percentage of 20%. Main physical, mechanical and durability properties of mortars were evaluated. Compared with control mortars, apparent density, water absorption and shrinkage of modified mortars decreased, mechanical and durability properties were improved. Generally, SF was more effective than SO in improving main physical and mechanical properties of mortars. The reason was attributed to pozzolanic reaction between SF and Ca(OH)2, which generated more hydrate product and refined pore structure. SF modified mortars showed the highest compressive strength (CS). The combined use of SF and SO showed the largest improvement in mortars' flexural strength (FS) and bond strength (BS), for that SO played a bridge coupling role between components in mortars. Durability properties of mortars were greatly improved by the presence of SO and it was related to water repellency of SO. Mortars prepared with SF and SO had the highest durability.