Effects of Calcium Sulfate Whiskers and Basalt Fibers on Concrete Properties after High Temperature

Abstract Concrete structures serving in complex environments, represented by subsea tunnels, are deeply affected by high temperature and corrosive environments, and calcium sulfate whisker-basalt fiber reinforced concrete (CSW-BFRC) has the potential to match these environmental requirements. Through cubic compressive tests, splitting tensile tests, and chloride ion penetration tests on specimens after high-temperature exposure, the effects of calcium sulfate whiskers (CSW) and basalt fibers (BF) with single and combined additions on the mechanical properties of concrete after high temperature were studied, and the chloride ion penetration resistance of CSW-BFRC was compared with ordinary concrete (PC). The results show that single addition of CSW and single addition of BF could improve the compressive strength and splitting tensile strength of concrete after high-temperature exposure, with better comprehensive effect when both were combined. The optimal dosages for single addition of CSW and BF were 2% (by mass) and 0.2% (by volume), respectively. The optimal dosages for combined addition are 0.2% BF and 2% CSW, under which the compressive strength of concrete increased by 10.5%–17.4% after exposure to temperatures from 25°C to 800°C, the splitting tensile strength increased by 10.2%–46.2%, and the chloride ion diffusion coefficient decreased by 6.2%–27.1%. X-ray diffraction analysis, thermogravimetric analysis, scanning electron microscopy analysis, and mercury intrusion porosimetry showed that BF and CSW had high temperature stability and could limit the development of high-temperature cracks and failure phase cracks at macro- and microlevels; CSW reduced porosity through filling and the formation of ettringite from cement hydration, improving concrete pore size distribution.