Investigation of the effects of colemanite and colemanite concentrator wastes on the rheological and hardened properties of self-compacting concrete

Abstract

In this study, the use of colemanite (C) and colemanite concentrator wastes (CW) in self-compacting concrete (SCC) mixtures was investigated. It is known that additives containing boron minerals have a retarding effect on cement hydration. From this viewpoint, boron minerals containing various concentrations of C and CW were used and their effects on fresh concrete properties were investigated. In this context, single point tests and rheometer tests were applied. In addition, the setting times and unit weights of the samples were measured, and the compressive strengths at 7, 28 and 90 days were determined. The hydration developments of the samples were investigated by TGA and SEM investigations. The use of C and CW generally negatively affected the compressive strength, while the use of 1% C provided a slightly higher strength than the reference at the end of 90 days. The degree of hydration data obtained using TGA and the microstructural investigations via SEM supported these results. As a result of fresh state tests, it has been observed that the use of C improves and maintains the fresh properties and rheological parameters of self-compacting concrete, while the use of CW generally had the opposite effect. It is thought that this is due to the negative effect of the clay minerals in CW's composition and the fact that the B2O3 amount in its content is less when compared to the C.