Effects of micro and nanoparticles of SiO2 on the permeability of alkali activated slag concrete

The reliability and durability of concrete are issues which often draw marginal attention and are partially overshadowed by other performance factors, in particular the compressive strength of concrete. However, properties such as permeability and microstructural features of concrete matrix and the arrangement of its pores are known to have significant effects on concrete durability. Considering the adverse environmental impacts of cement production, the use of alkali activated slag concrete can be considered as a more environmentally friendly approach to concreting. This study investigated the effect of partial replacement of the slag used in alkali activated slag concrete with nanosilica and microsilica on its permeability. The effect of nanosilica and microsilica, both individually and in combination, on permeability of alkali activated slag concrete was examined through water impermeability test, rapid chloride permeability test, carbonation test, short-term and total water absorption tests, and compressive strength test. In addition, changes in paste microstructure were examined by Scanning Electron Microscopy (SEM) and X-ray Diffraction analysis. The results showed that partial replacement of slag with nanosilica has some effect on microstructure of the paste, leading to undesirable results in regard with permeability; however the use of microsilica improved permeability.