Effect of steel and polypropylene fiber reinforcement on mitigating conversion effects in calcium aluminate cement at varying curing temperatures

Abstract

Calcium aluminate cement (CAC) is widely used in high-performance applications due to its rapid setting and resistance to aggressive environments. However, its long-term durability is often compromised by hydration phase conversion, particularly under varying temperature conditions. At elevated curing temperatures, the conversion from metastable CAH₁₀ and C₂AH₈ phases to the more stable, but porous, C₃AH₆ phase can lead to strength reduction. This study investigates how fiber reinforcement, specifically steel fibers (SF) and polypropylene fibers (PF), can mitigate these adverse effects in CAC composites cured at high temperatures (40 °C and 60 °C). A comprehensive evaluation of fiber-reinforced CAC composites was conducted, focusing on fresh and mechanical properties, chemical composition, and microstructural evolution. Experimental techniques included flowability, bulk density, void vol5me, water absorption, compressive strength, direct tensile strength, and flexural strength tests, complemented by X-ray diffraction (XRD), thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FESEM) to assess phase composition and pore structure. The incorporation of fibers significantly enhanced the mechanical properties of CAC composites, with 1 % fiber addition improving compressive, direct tensile, and flexural strengths. At 40 °C, SF improved these strengths by approximately 26.5 %, 67 %, and 27.6 %, respectively, while PF enhanced them by 4.4 %, 24 %, and 16 %. However, at 60 °C, strength gains were less pronounced due to accelerated phase conversion and changes in porosity. Microstructural analysis reveals both SF and PF yield to reduced pore size, enhancing the strength and durability of the composites, attributed from the stable C3AH6 phase transition in CAC at higher curing temperatures up to 60 °C. This study provides new insights into the potential of fiber reinforcement in mitigating conversion-related strength loss in CAC at elevated temperatures. By enhancing mechanical performance and durability, SF and PF offer a sustainable approach to optimizing CAC composites for high-temperature applications, contributing to the development of eco-friendly, rapid-setting, and high-performance construction materials.