Study On Durability Of Basalt Fiber Reinforced Concrete After High Temperature

Basalt fiber reinforced concrete is a kind of high-performance concrete suitable for lining structures of subsea tunnels.The mechanical properties,carbonation resistance and chloride corrosion resistance of basalt fiber reinforced concrete after high temperature are important indexes to determine the durability of structure after fire.In this paper,through the mechanical properties and durability tests of basalt fiber reinforced concrete at room and high temperature,the improvement effect of basalt fiber on the mechanical properties,carbonation resistance and chloride corrosion resistance of concrete was analyzed from macro and micro perspectives,and the development model of carbonation and chloride diffusion coefficient model after high temperature were derived.The compressive strength and splitting tensile strength of basalt fiber reinforced concrete with different content(0,0.05% ~ 0.3%)were tested.It was found that the mechanical properties of basalt fiber reinforced concrete increased first and then decreased with the increase of fiber content.Micro scanning showed that a proper amount of basalt fiber can form a three-dimensional network structure to bear part of the load and improve the strength and toughness of the concrete,while too much basalt fiber would gather and overlap,resulting in inadequate bonding between the concrete matrix and the fiber,leading to initial defects.The mechanical properties of basalt fiber reinforced concrete and ordinary concrete after different high temperature(room temperature,100?~600?)were tested.The results showed that the addition of basalt fiber significantly improved the compressive and tensile strength of concrete after high temperature.Through micro analysis,the difference of synergistic mechanism between basalt fiber and concrete matrix at different temperatures was revealed.Based on the carbonization test of basalt fiber reinforced concrete after different high temperature(room temperature,100?~ 600?),it was found that the depth of the burned layer of concrete increased significantly with the rise of heating temperature.The carbonation depth of concrete after high temperature increased linearly with the rise of heating temperature,and the accelerated effect of high temperature on the development of concrete carbonation should be paid attention to.The burn-out layer and carbonization depth of basalt fiber concrete were always smaller than ordinary concrete,which means that its carbonization resistance was superior.A depth prediction model for the carbonization of concrete after high temperature was proposed.The carbonization depth of the fired subsea tunnel lining structure was predicted within 100 years and the service life of the structure was also predicted.Based on the chloride erosion test of basalt fiber reinforced concrete under different high temperature(room temperature,200?,400?,600?)and different compressive stress levels(0,0.1,0.2,0.3),it was found that the chloride ion content in concrete increased linearly with the rise of heating temperature.Basalt fiber reinforced concrete has better impermeability than ordinary concrete.After normal temperature and 200?,the compressive stress can prevent chloride ion from entering the concrete.After 400?,the chloride ion content in the concrete decreased first and then increased with the rise of compressive stress,which means the compressive stress threshold stress was between 0.1 and 0.2.The compressive stress after 600? had a negative impact on the impermeability of concrete.Considering the influence of heating temperature,pressure stress ratio and erosion time,the calculation model of chloride diffusion coefficient under environment-load coupling erosion after high temperature was put forward.