Shrinkage characteristics of repair mortar with organic corrosion inhibitors

Premature deterioration and failure of reinforced concrete (RC) structures due to aggressive environments have become a global issue. Hence, effective and durable repair techniques are needed to enhance the service lifespan of RC structures. The use of repair mortar with other additives, such as corrosion inhibitors, is an innovative approach to retrofit structures and reduce further potential corrosion. However, it is vital to consider the properties of repair mortars before application. Drying shrinkage is regarded as a critical parameter for repair mortars because shrinkage (volume change) can cause a relative movement between the repair and the substrate, leading to an ineffective restoration. This study investigated the effect of organic corrosion inhibitors (OCIs) on the variation of drying shrinkage in four types of repair mortars. Commercial polymer mortar, general cementitious mortar, fine-grained mortar, and alkali-activated geopolymer mortar were considered. Two OCIs based on alkanol amine and sodium gluconate were added in varying contents to the repair mortars to assess the shrinkage behaviours with time. The results indicated that sodium gluconate-based inhibitors lower the drying shrinkage by around 45% and 65% for polymer-modified and geopolymer mortars, respectively. In contrast, alkanol amine-based inhibitors did not significantly affect the drying shrinkage development of geopolymer mortar, whereas it increased the drying shrinkage of fine-grained mortar by 30%.