The performance of self-healing concrete in different exposure conditions

Abstract

The presence of microcracks, which emerge during the service life of all reinforced concrete structures, has a significant impact on concrete durability. Wide cracks compromise the structural integrity of reinforced concrete as the rate of penetration of deleterious substances accelerates upon reaching the cementitious matrix and eventually the steel reinforcement. The durability is significantly affected when the structure is exposed to an aggressive chloride environment, as chemicals in coastal salts enter the pore structure, accelerating the rate of steel corrosion. Concrete inherently possesses certain natural autogenous healing features as the dissolution and carbonation of Calcium hydroxide precipitates Calcium carbonate, sealing the microcrack. To increase the healing efficiency and rate of healing, various approaches have lately been adopted to facilitate the hydration process, decrease the rate of shrinkage, and enhance watertightness by introducing an additive to the concrete mixture. In recent years, researchers have looked into natural solutions as alternative options to environmentally unsustainable components including bacterial spores in the concrete mixture, healing the cracks through microbially-induced calcium carbonate precipitation which reduces the rate of absorption to the cementitious matrix. Another approach is to introduce a crystalline admixture which substantially improves the healing performance. Prismatic and cylindrical test specimens were cast, pre-cracked and cured in an aqueous solution of Sodium chloride or tap water. The healing rate and sealing efficiency were recorded using different methodologies as described in in the COST Action SARCOS (“Self-healing As preventive Repair of COncrete Structures”) RRT programme, an EU funded interlaboratory testing protocol to search for smart self-healing materials and preventative repair methods. Crack width closure was monitored using digital microscopic techniques whereas crack healing throughout the depth of the crack was measured using the colorimetric technique of silver nitrate application on the faces of split specimens. Water permeability tests were performed to assess the crack sealing of concrete specimens whereas sorptivity testing assessed the infiltration of water through concrete samples. Mechanical properties were also assessed in relation to the durability performance. The testing was performed at different stages of curing. The study shows an improved recovery of durability properties, with noticeable enhanced healing in the additive-containing specimens whose intensity was dependent on the additive type, initial crack width and exposure condition.