Assessment of pore structure of foam concrete containing slag for improved durability performance in reinforced concrete applications

The traditionally produced foam concretes (FCs) for light-weight applications have a high air void content of about 10%-60%, are characterized by significant void connectivity, and hence are unsuitable for reinforced concrete applications. Since void connectivity in FCs can pave the way for the entry of external solutions inside their matrices and reach the steel reinforcement, designing such mixtures for durability requires significant attention. The approach is to develop FCs with appropriate GGBS dosages and foam additions that can provide optimum density and strength levels, discontinuous pore structure, and durability characteristics that are sufficient to replace conventional concrete. The main goal is to understand the effect of GGBS addition on the pore structure of FCs. Five different FC mixtures were prepared with 0%, 15%, 30%, 45%, and 60% GGBS dosages as a replacement of cement, and their pore structure aspects were studied using image analysis, scanning electron microscopy (SEM), and mercury intrusion porosity (MIP). Based on the durability test results, the water absorption, porosity, chloride ion permeation, resistivity, and drying shrinkage values decreased with increasing GGBS dosage up to 60%, whereas sorptivity decreased with increasing GGBS dosage up to 30%. Images from image analysis and SEM indicate that the macrovoids created are isolated and discontinuous in nature. Further, SEM images reveal that the addition of up to 60% GGBS improved the microstructure and void structure of FCs. The MIP results indicate that the decrease in porosity of FC was noticeable up to 30% GGBS dosage, with lowered threshold and critical pore diameter values and higher amounts of gel pores. However, 60% of GGBS dosages showed reverse trends. The MIP and SEM results supported the trends obtained with most durability tests up to 30% and 60%, respectively. Overall, the dependence of FC durability on the pore size and pore structure of cementitious matrices is evident, and the potential for developing FC mixtures with enhanced durability seems promising.