Degradation characteristics of Portland cement mortar incorporating supplementary cementitious materials under multi-ions attacks and drying-wetting cycles

The multiple corrosive ions in seawater cause more severe concrete corrosion in tidal and splash zones. To understand the mechanisms of harmful ions in seawater under the real field conditions, four different synthetic multi-ions solutions (NaCl, NaCl + MgCl2, NaCl + Na2SO4 and NaCl + MgCl2+Na2SO4) were prepared. This study investigated the effects of external multi-ions solutions and repeated drying-wetting cycles on the degradation mechanisms of Portland cement mortar/paste with and without supplementary cementitious materials (SCMs) by using different microstructural techniques. It was found that the multi-ions solutions of Cl− + SO42− and Cl− + Mg2++SO42− aggravated the deterioration of mortar samples compared to the solution with Cl− alone under drying-wetting cycles. The cracks and larger pores were induced due to the formation of secondary ettringite, and the enlarged size of microvoids in mortar obviously affected the damage evolution and resulted in an accelerated deterioration of mortar samples. In addition, the incorporation of ground blast furnace slag (GBFS) significantly improved the corrosion resistance of cement-based materials and showed more efficient than other pozzolanic materials. This may be due to that aluminum incorporation could bridge the defective silicate chains and increase the polymerization degree of silicate tetrahedra in the C–S–H gel. Moreover, the matrix incorporated GBFS could effectively reduce pore defects and volumes of connected pores and large pores, which enhanced the resistance to multi-ions attack. These results can be provided a theoretical basis on the improvement of concrete durability under severe marine environmental attacks.