University of Alberta, Department of Civil and Environmental Engineering

Higher masonry compressive strength values could be reached if the unit-to-mortar modular ratio is reduced by using higher elastic modulus mortars. Nano-size materials have demonstrated potential for enhancing compressive strength and modulus of elasticity of concretes and mortars. This paper reports the findings of a pilot investigation to utilize nano-silica as a partial replacement of the binder (cement + lime) to produce high modulus masonry mortars. Four different mortar mixes were prepared in addition to a type S mortar control mix. In two mixes, nano-silica was used to replace 1% and 2% of the binder by weight. Silica fume was used in another mix to replace 10% of the binder. The fourth mix contained a combination of 10% silica fume and 1% nano-silica replacements. Fifty millimetre mortar cubes were cast and tested for compressive strength. To determine the modulus of elasticity, 75×150 mm mortar cylinders were instrumented and tested under axial compression. All specimens were air-cured to simulate actual masonry construction conditions. Scanning electron microscopy examination was conducted to study the effect of nano-silica on the mortar’s morphology and microstructure. Significant increases in the modulus of elasticity were found for mixes containing nano-silica. Scanning electron microscopy micrographs revealed that mixes with nano-silica have denser microstructures.

Key words
Nano-silica, high modulus mortar, microstructure, masonry compressive strength