Alkali-reactive aggregates: corrosion and protection of concrete

Introduction. One type of concrete corrosion is caused by the chemical interaction of amorphous silica in aggregates with alkalis in the cement paste. This process develops slowly, and damage to the concrete is often detected only several years after construction is completed. Initially, damage caused by alkali-silica reaction was observed in large structures such as dams, bridges, and road pavements. Repairing and protecting damaged concrete structures is considered a complex process. The present paper addresses issues related to the prevention and protection of structures affected by this type of corrosion. Aim. To evaluate methods for protecting concrete from internal alkali corrosion. Materials and methods. The paper presents the results of determining the reactivity of aggregates from crushed stone and sand of various deposits. A method for protecting against alkali corrosion using lithium nitrate solution for impregnating concrete was tested in the process. To accelerate the impregnation process, concrete was treated with a direct current. Results. The study demonstrates the inconsistency of results obtained through standard testing methods. The most reliable results are achieved through long-term testing (at least one year) of concrete made with the studied aggregates and cements. The study involved assessing feasibility of repairing concrete with signs of alkali corrosion through impregnation with lithium compound solutions while applying electric current. Conclusions. The expansion of concrete due to alkali corrosion from aggregates sourced from various deposits has been investigated. The study confirmed the necessity for long-term testing of concretes using aggregates of specific suppliers, considering the characteristics of the applied cements and mineral additives. The authors examined the potential for protecting concrete from alkali corrosion through the introduction of lithium compound additives, including the use of current. The application of current accelerates the impregnation of concrete with lithium salt solutions; however, it poses certain challenges. Impregnation of the outer layer creates conditions for cracking due to differences in deformation between the outer layer and the inner layers that have not undergone impregnation. If the reactivity of the aggregate with cement alkalis is suspected, it is recommended to introduce finely ground silica-containing additives into the concrete to bind alkalis and prevent the development of concrete damage.