The Improving Role of Basalt Fiber on the Sulfate-Chloride Multiple Induced Degradation of Cast-In-Situ Concrete

In salt lake areas, the cast-in-situ concrete structure has been corroded by the combination of sulfate and chloride for a long time. The incorporation of basalt fiber materials into concrete helps to improve the durability of concrete. In this paper, experiments were conducted to study the corrosion deterioration mechanisms of basalt fiber-reinforced cast-in-situ concrete under sulfate, chloride, and combined attack. The appearance, size, mass, flexural, and compressive strength of specimens were investigated during the immersion period to determine the changes in the physical and mechanical properties of specimens. Moreover, the microstructure and mineral changes of specimens during the immersion period were observed by Scanning Electron Microscope (SEM), Energy Dispersive Spectrometer (EDS), X-ray diffraction (XRD), and Thermogravimetric (TG)/ Derivative Thermogravimetric (DTG) analyses. Results show that premixed chloride has a significant detrimental influence on the strength development of cast-in-situ concrete, with concrete powder spalling occurring on the surface of the specimen. Severe corrosion degradation of specimens occurs under the external sulfate and internal chloride combined attack, resulting in lower flexural and compressive strength. The compressive strength and flexural strength of the corroded specimens decreased by 15.4% and 24.8%, respectively, compared with the control group at 28 days. Moreover, premixed basalt fiber has a beneficial influence on cast-in-situ concrete. When the basalt fiber content is 0.5%, the flexural strength of the specimen is increased by 16.2%. The filling and bridging effect of basalt fiber alleviates the negative effects caused by corrosion. In addition, increasing fiber content is beneficial for enhancing its effectiveness when the fiber content is less than 0.5%. This paper provides a valuable reference for the application of basalt fiber-reinforced cast-in-situ concrete under the condition of sulfate-chloride compound corrosion.