Investigation of the effects of pH, aging and scrap tire content on the dissolution behaviors of new scrap tire-concrete mixture structures

Abstract

Scrap tires represent increasing environmental-pollution problems because they are not biodegradable and require a significantly long time for natural degradation, which is caused by the cross-linked structure of polymeric material and the presence of stabilizers and other additives. Potential use of scrap tires in construction is one of its important application areas and an alternative recovery method. In this study, a series of experiments was conducted to investigate the dissolution behaviors of new concrete-scrap tire mixture structures (brick) under different experimental conditions, such as scrap tire content, aging, and in acidic, basic and natural environments. The obtained results revealed different effects of adding scrap tires, aging and the existence of H+ and OH− on the dissolution of the brick structures. The added sulfuric acid dissolved calcium silicate hydrate, calcium aluminosilicate hydrate and calcium hydroxide of the brick via a naturalization reaction and released more soluble metal ions, particularly calcium, in the solution. Additionally, during acidic corrosion, the porosity significantly increased because calcium was removed from the structure; thus, the transport of other ions was enhanced in the corroded layer by diffusion. However, the addition of sodium hydroxide significantly decreased the solubility of calcium because the calcium silicate hydrate, calcium aluminosilicate hydrate and alkali-silica reaction products precipitated in the presence of calcium. The aging test showed that calcium was substantially dissolved from the brick structure in the first days and slightly slowed down in an acidic medium because the corrosion surface was gradually consumed, which caused the dissolution to occur in the lower part of the corroded region. The increase in scrap tire content increased the surface area and porosity, which resulted in more released calcium and silicon. The study affirmed that the use of granular scrap tires in concrete structures was feasible.