High-temperature and drying shrinkage behavior of mortars containing colemanite and different fiber types with air-entraining admixture

Abstract

In recent years, the construction industry has become a major source of global greenhouse gas emissions, primarily because of the energy-intensive process of cement production. Turkey holds about 73% of the world's boron reserves, providing a significant opportunity to use boron-containing minerals such as colemanite as alternative binders. In this study, mortar mixtures were developed incorporating colemanite, air-entraining admixtures (AEAs), and various fiber types (steel, basalt, carbon and polypropylene). The AEA was used at 0.1% of cement weight, while colemanite replaced 3% and 5% of the cement, and each fiber type was added at 0.5%. The results indicated that mixtures containing 3% and 5% colemanite with steel fibers exhibited the highest performance after thermal exposure, showing up to 130% higher residual compressive strength and 60% higher flexural strength compared to the reference mixture. Moreover, the inclusion of colemanite and fibers generally reduced drying shrinkage, while their combined use significantly enhanced the high-temperature and shrinkage resistance of cement-based mortars. In contrast to previous studies, this work emphasizes the eco-friendly use of colemanite as a partial cement replacement and its synergy with fibers and an AEA, offering practical potential for sustainable and heat-resistant construction materials.