Performance of basalt fibre-reinforced cement composites under hydrothermal curing up to 200 °C

This study identifies a temperature-triggered surface activation of basalt fibre (BF) in cement that delivers a 27 % tensile strength gain under hydrothermal curing at 150 °C. BF-cement composites show strong promise for geothermal energy extraction, CO 2 storage, and well plugging, but their long-term durability is limited by fibre degradation in the highly alkaline environment of Portland cement. Through comprehensive microstructural, chemical, and mechanical analyses, we demonstrate that BF remains chemically inert at ambient temperature. However, at elevated temperatures, BF promotes calcium hydroxide (CH) crystal growth and develops a chemically “activated layer” via local CH consumption, significantly enhancing fibre–cement bonding. Prolonged exposure to high temperature accelerates fibre degradation, emphasizing the need to balance interfacial activation and durability. These findings establish a novel temperature-dependent bonding mechanism in BF-cement systems and provide practical design guidelines for optimising composite performance in extreme geothermal and deep-well environments. • BF forms an "activated layer" under hydrothermal alkaline environment, improving matrix bonding via pozzolanic reactions. • Despite progressive fibre degradation, BF maintains positive effect on mechanical properties. • Alkaline environment, curing temperature, and moisture dictate BF performance in cement.