Salt frost resistance and micro characteristics of polynary blended concrete using in frost areas

Abstract

To explore the deterioration process and improvement mechanism concrete blended with supplementary cementitious materials (fly ash, slag, and silica fume) in frozen areas, the SCM content, w/b ratio, curing age, freeze-thaw (F-T) cycle, and salt-frost (S-F) cycle were varied to systematically evaluate the chloride permeability resistance and S-F resistance. Pore structures, hydration degree, phase composition and interfacial transition zone (ITZ) between aggregate and matrix of investigated mixtures were characterized by mercury intrusion porosimetry (MIP), thermogravimetric analysis (TGA), X-ray diffraction (XRD) and SEM-EDS, respectively. The S-F resistance of blended concrete is greater than that of control mixture without SCMs. The crystallization pressure is dominated by larger saturation with higher salt concentration at the early stage of S-F cycles, and greatly affected by the actual volume expansion of salt solutions at its later stage. SCMs can compensates the structure deterioration under S-F and F-T conditions, where quaternary blends shows an optimal refinement for the pore structures. It is found that the total pore volume, average pore size, and porosity are highly correlated with the chloride permeability resistance of concrete by grey degree analysis. The SCMs blends can improve cement hydration degree by pozzolanic and hydraulic reactions at the later curing age. With the S-F cycles, the internal stresses could cause pore nucleation and crack propagation, while SCMs can effectively control the ITZ width and mitigate the structural deterioration of concrete.