Long-term drying shrinkage characteristics of repair mortars with organic corrosion inhibitors in aggressive environments

Corrosion of reinforced concrete (RC) structures is a global challenge, requiring durable repair strategies. Repair mortars with organic corrosion inhibitors (OCIs) offer a promising solution to mitigate reinforcement corrosion and improve durability. However, their effectiveness depends on both corrosion resistance and dimensional stability, with drying shrinkage being particularly critical. This study examined the long-term effects of two OCIs (amino alcohol and sodium gluconate) on the drying shrinkage of four repair mortars (polymer-modified, cementitious, fine-grained, and alkali-activated geopolymer). Drying shrinkage was monitored over 556 days, with an initial drying phase of 360 days followed by cyclic water and chloride exposure conditions. The results indicated that shrinkage increased during early drying and stabilised after 90 days in all mortar groups. Water-immersion cycles caused temporary reductions in shrinkage, with values returning to stabilised levels after drying, indicating a reversible effect governed by moisture exchange. In contrast, chloride cycles produced permanent shrinkage reductions, with magnitudes dependent on mortar type, inhibitor, and dosage. Reductions reached 135.18 µε in polymer-modified and 69.64 µε in geopolymer mortars with sodium gluconate, while amino alcohol led to shrinkage reductions of 166.79 µε and 102.01 µε in cementitious and fine-grained mortars, respectively. This permanent effect is associated with Friedel’s salt formation, which was consistent with void content, bound chloride, and XRD/TGA results. A strong correlation between bound chloride and shrinkage reduction suggested that chloride binding played an important role in the observed shrinkage behaviour. Overall, the findings demonstrate that OCIs mitigate long-term shrinkage and enhance the durability of repairs in chloride-rich environments.