The Use of Self-Healing Technology to Mitigate the Alkali–Silica Reaction Distress in Concrete

Alkali–Silica Reaction (ASR) is one of the most harmful distress mechanisms affecting the durability and serviceability of concrete infrastructure worldwide. ASR-induced deterioration leads to micro-cracking, loss of material integrity and functionality, significantly impacting the stiffness, tensile, shear, and compressive strength of affected concrete. Over the past decades, studies have demonstrated that the partial replacement of Portland cement by supplementary cementing materials or the addition of lithium-based admixtures (e.g., lithium nitrate, etc.) is effective preventive measures against ASR. Yet, new studies are now finding that the deterioration is only delayed and not entirely prevented. In this context, it has been verified that some products, such as crystalline admixtures, could enhance concrete's healing properties, thus presenting an interesting solution to reduce water ingress and recover damaged concrete elements. However, the potential of these materials to suppress durability-related distress due to ASR has not been assessed. This paper aims to evaluate different concrete mixes presenting two different types/nature of highly reactive aggregates (i.e., coarse vs. fine aggregates), incorporating a GU-type cement, lithium nitrate, a hydrophilic crystalline waterproofing material (CW), and two modified versions (CW-mod). The samples were fabricated, exposed to ASR development, and monitored over two years. Mechanical (i.e., compressive and shear strength, modulus of elasticity, and stiffness damage test) and microscopic (i.e., Damage Rating Index) techniques were selected to further analyze the distinct mixtures’ appraised performance. The results show that the addition of CWs’ agents in concrete minimized ASR development. In general, the mixtures not only delayed the development of inner damage but significantly lowered the compressive strength loss and slowed the crack propagation in the cement paste at equivalent expansion amplitudes than control specimens. Finally, comparisons among the results found are made, and further discussions and recommendations on the reliability of adopting self-healing products to suppress ASR are conducted.