Effect of pozzolanic additives on structure and chemical durability of concrete

Abstract

This study investigates relationships between concrete containing pozzolanic additive and mineralogical composition, porosity and chemical durability to sulphate ion containing solution. As pozzolanic admixtures micro and nano size silica and biomass ashes were used. The investigation was carried out by X-ray diffraction, Hg absorption porosimetry and optical microscopy. The pozzolanic additives activate the process of mineralization and are acting both as the cementitious admixture as well as the fine filler. The crystalline phases in all depths of the specimen, mass change, porosity were investigated after the exposure of concrete in sulphate ions containing solution for 1-6 months under static conditions. The way of sulphate attack depends on a pozzolanic additives and kind of sulphate solution. X-ray phase analysis of concrete in different depth after exposure in solution identified gypsum for concrete with additives only up to10 mm. The addition of fine dispersed additives decreases the number of pores in all range, especially in 1…103 μm. Cementitious properties of pozzolanic materials and crystallization of sulphate salt in pores decrease number of pores in range 0.5…10–3 μm. Studies have shown that the pozzolanic additives reduce porosity, increase density and as a consequence increase the chemical durability of concrete to sulphate ion containing solution.