Reinforcement corrosion in cementitious capillary crystalline waterproofing concrete under the coupled effect of chloride salt and cyclic wet–dry conditions

Abstract

Steel reinforcement corrosion severely compromises concrete durability, particularly in environments with coexisting chloride and sulphate ions. This study quantifies reinforcement corrosion in concrete treated with cementitious capillary crystalline waterproofing (CCCW) materials under coupled chloride exposure and cyclic wet–dry conditions. We investigated chloride-induced rust pit heterogeneity and CCCW's inhibition efficacy (1% and 2% by mass) across C30, C40 and C50 concrete grades. Specimens underwent accelerated wet–dry cycles, and pit morphology was examined by optical microscopy and scanning electron microscopy (SEM) for microstructural characterisation. SEM revealing crystalline growth within the concrete's dominant 5–10 µm capillary pores and some larger macropores, indicative of CCCW's pore-blocking action. Our novel approach combined experimental quantification of highly irregular corrosion (characterised by a high coefficient of variation) with 3D image analysis and a probabilistic pit growth model, successfully reproducing the observed non-uniformity. CCCW consistently and significantly reduced corrosion across all concrete grades, with reductions ranging from approximately 21% to 62%, depending on the concrete strength and dosage. Baseline corrosion decreased with increasing concrete compressive strength (e.g., C30 < C40 < C50). These statistically validated findings demonstrate CCCW as an effective, economical inhibitor for chloride-induced steel corrosion with optimal dosages identified for different concrete strengths. The pronounced irregularity of rust pits underscores the necessity of incorporating stochastic pit-growth models in service-life predictions of reinforced-concrete structures.