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    Effects of Colemanite and Fiber Types on Strength and Water Absorption of Mortar Mixtures Containing Air-Entraining Admixture
    (Mdpi, 2025) Ozansoy, Ayse Irem; Ozen, Suleyman
    The global construction industry heavily relies on cementitious systems, which are a major contributor to carbon dioxide emissions due to the energy-intensive nature of cement production. These emissions account for approximately 8% of global CO2 output, exacerbating climate change and environmental degradation. The global reliance on cementitious systems has led to substantial carbon dioxide emissions during cement production, intensifying the need for environmentally sustainable alternatives. Turkey, which holds 73% of the world's boron reserves, offers a unique opportunity to explore boron-based minerals like colemanite as potential replacements for cement. In this study, the effects of colemanite (a boron mineral) and four fiber types-steel, basalt, carbon, and polypropylene-on the compressive strength, flexural strength, and water absorption of mortar mixtures incorporating air-entraining admixtures were investigated. All mixtures contained 0.1% air-entraining admixture (by cement weight), with fixed parameters: a water/binder ratio of 0.485, a sand/binder ratio of 2.75, and slump-flow values of 190 +/- 20 mm. Cement was partially replaced with colemanite at 3% and 5%, while fibers were added at 0.5% by volume. Fresh-state properties (slump-flow and admixture requirements) and hardened-state properties (28-day compressive/flexural strength and water absorption) were evaluated. Selected samples underwent SEM analysis for microstructural assessment. Key findings revealed that both colemanite and fibers increased admixture demand to achieve target slump flow. While colemanite and fibers collectively enhanced compressive strength, their interactions varied: basalt and carbon fibers exhibited superior performance in mixtures without colemanite, whereas steel fibers showed greater efficacy in colemanite-containing mixtures. The strength increase was less pronounced when colemanite was introduced to mixtures containing carbon, polypropylene fibers, and basalt. The trend of flexural strengths was comparable to that of compressive strengths. SEM images revealed that the void distribution in the samples, influenced by the effects of colemanite and fibers, had a more dominant effect on compressive and flexural strengths. Water absorption inversely correlated with mechanical performance. This study not only contributes to reducing the carbon footprint of cementitious systems by partially replacing cement with colemanite but also provides practical insights to optimize the use of fibers to increase strength performance and reduce water absorption properties from durability parameters. These findings support the development of more sustainable and durable materials.
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    High-temperature and drying shrinkage behavior of mortars containing colemanite and different fiber types with air-entraining admixture
    (Taylor & Francis Ltd, 2025) Benlioglu, Arif; Ozansoy, Ayse Irem; Ozen, Suleyman
    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.