Mechanical Properties Of Basalt Fiber Reinforced Concrete Under Chloride Salt-sulfate Attack

Concrete structures located in the eastern coastal and western saline soil areas in China will inevitably suffer from the erosion and damage of salts such as chloride and sulfate during service.If the building structure in the above-mentioned areas encounters fire damage in the service cycle,it is a complex engineering problem of initial durability damage coupled with fire damage to the bearing capacity and safety of reinforced concrete structures.Basalt fiber reinforced concrete(BFRC)is a green and economical high-performance concrete,and it is significant to clarify its mechanical property changes after erosion by chloride salt-sulfate,ion penetration resistance,and mechanical properties after high temperature of fire,in order to evaluate the disaster resistance of reinforced concrete structures with erosion damage and structural safety after fire after a period of service.In this thesis,with reference to the results of the existing basalt fiber concrete admixture tests,a better fiber admixture(0.15%)was selected,and the accelerated erosion tests were carried out with the consideration of the erosion age(60-270 days),chloride concentration(3%,5%,10%),sulfate concentration(1%,10%)and other factors in the dry and wet cycles.The main research contents and results are:The compressive strength and relative dynamic elastic modulus of BFRC were tested after different erosion ages,and it was found that the presence of chloride salt reduced or retarded the strength change caused by sulfate in the solution at the early stage of erosion;when the sulfate concentration was the same,the influence of chloride salt concentration change on the compressive strength and relative dynamic elastic modulus of the specimens was smaller,and the trend of strength change and relative dynamic elastic modulus change was basically the same;when the chloride salt concentration was the same,there was a significant difference in the trend of compressive strength change between low sulfate concentration and high sulfate concentration,and the influence of sulfate concentration change on strength and relative dynamic elastic modulus was greater than that of chloride salt.The contents of chloride ions and sulfate ions in BFRC specimens undergoing different erosion ages were measured,and it was found that the contents of chloride ions and sulfate ions decreased non-linearly and rapidly from the surface to the interior of the specimens,and the decrease of sulfate ions from the surface to the interior of the specimens was greater than that of chloride ions;the presence of sulfate played a certain degree of inhibition on the transport of chloride ions,and chloride salts retarded the transport and accumulation of sulfate ions in basaltic fiber concrete.The compressive strength of BFRC with chloride salt-sulfate erosion damage after different high temperatures was tested,and it was found that chloride salt-sulfate coerosion would aggravate the deterioration of the specimen’s high temperature resistance;and the longer the specimen eroded,the greater the chance of bursting during the high temperature heating at 500℃.A diffusion model of chloride ions and sulfate ions in basalt fiber concrete under chloride salt-sulfate attack conditions was proposed,and the effects of chloride salt concentration and attack time on the ion concentration and diffusion coefficient of the surface of the specimen were considered.The evolution equation of the relative compressive strength of BFRC under the action of dry and wet cycles of chloride saltsulfate solution is given;the relationship between the relative compressive strength coefficient of basalt fiber concrete and the sulfate ion content of the surface layer(0～5mm)is characterized.A parametric analysis based on the relative residual compressive strength of BFRC after the coupled action of erosion and high temperature was carried out,and a residual compressive strength prediction model considering two parameters of erosion time and temperature was established;the influence factors of erosion damage and the degree of influence of high temperature action on the strength of specimens were analyzed.