Alkali-activated protective coatings for reinforced concrete exposed to chlorides

Abstract

The interaction of the reinforced concrete with chloride-rich environments is a predominant cause of the corrosion of reinforcing steel, which may result in the appearance of damage affecting the structural performance. One way of protecting the concrete and extending its useful life is by applying surface coatings, to limit the penetration of aggressive agents. This study evaluated the effectiveness of inorganic coatings based on alkali-activated materials (AAM) applied to concretes of Portland cement (substrate) exposed to chlorides. Two types of AAM were used, one based on volcanic natural pozzolan (70%)/granulated blast furnace slag (30%) and the other on fly ash (90%)/Portland cement (10%) added with polymeric acrylic emulsion. A mixture of NaOH and sodium silicate was used as the alkaline activator. Uncoated concrete (UCC) and commercial epoxy coating (CEC) were used as reference materials. Properties such as capillary water absorption, resistance to chloride ion penetration, adhesion strength, setting time and porosity were evaluated. The corrosion resistance of the reinforcing steel was evaluated using impressed voltage technique and immersion in NaCl 3.5%. According to the results, the AAM coatings based on volcanic natural pozzolan with 5% acrylic emulsion (by precursor weight) mortar type AMCP5 and paste type APCP5, showed the best performance. Compared to the uncoated concrete, AMCP5 and APCP5 reduce the corrosion rate following the exposure period by 86% and 96%, respectively.