Effect of SCM on porosity

Pores are an inherent part of cement-based materials. The pores range from nm to cm varying in shape and distribution. The amount, size and distribution of pores affect the engineering properties. As a first approximation, the total porosity affects the mechanical behavior, whereas the size and connectivity of pores affect durability. Supplementary cementitious materials (SCMs) are being increasingly used as a substitute for Portland cement in the interests of sustainability and to improve the engineering properties of concrete as strength and durability. SCMs are by-products such as slag from iron blast furnaces, fly ash from coal fired power stations, and silica fume from ferrosilicon production. Studies suggest that the improvement of the strength and durability using SCMs are governed by refinement of the pores in the cement paste. Both the chemical and physical properties of the SCMs and the curing conditions (moisture and temperature) affect the microstructure. To provide improved understanding on the effect of SCMs on the pore structure and state of water of hydrated cement paste varying techniques are applied such as mercury intrusion porosimetry (MIP), low temperature calorimetry (LTC), scanning electron microscopy (SEM), water desorption and nuclear magnetic resonance (1H-NMR). LTC, NMR and water desorption are applied in non dried samples while dried samples are required for the others. These techniques provide information on varying pore characteristics (total porosity, pore threshold, pore size distribution etc.) and in different size ranges and do therefore to a large extent supplement each other. In addition, the experimental results are used to demonstrate the applicability of modeling the development solid phases for prediction of porosity.