Research On Durability And Mechanical Properties Of Basalt Fiber Reactive Powder Concrete In Seasonal Frozen Area

Reactive Powder Concrete(RPC)is a kind of ultra-high performance concrete.RPC has the characteristics of ultra-high strength,high durability and high temperature adaptability,which can effectively reduce the self-weight of the structure and increase the spanning ability.Jilin Province is rich in basalt ores.The promotion and application of basalt products is of great significance to the economic transformation and development.Green and environmentally friendly basalt fiber produced by melt drawing of basalt ore is a new high-performance inorganic fiber.In this paper,basalt fiber with high tensile strength and resistance to acid and alkali corrosion was used as a dopant to modify RPC materials.The durability and mechanical properties of basalt fiber RPC composites were investigated.The main research work and results are as follows:(1)The response surface method was used to design experiments to optimize the mix ratio of basalt fiber RPC.This paper puts forward a preparation scheme of basalt fiber RPC,which is suitable for bridge and road engineering in Jilin province and meets the requirements of workability,mechanical properties and durability.The experimental results showed that the best mix ratio of basalt fiber RPC was as follows:sand-binder ratio of 0.9,water-binder ratio of 0.18,basalt fiber content of 8 kg/m~3 and silica cement ratio of 0.25.(2)The influences of crack,freeze-thaw cycle and chlorine salt erosion were considered.Not only the durability of basalt fiber RPC matrix,but also the durability of basalt fiber RPC embedded steel bar was studied.Besides,the durability mechanism of basalt fiber RPC was analyzed from the perspective of microstructure.The results showed that the thickness of interface transition zone between quartz sand and cement matrix could be ignored,and the hydration products of basalt fiber RPC were mainly dense C-S-H matrix.Moreover,the basalt fiber in the RPC material were disorderly distributed without agglomeration,and were closely bonded with the cement matrix.(3)The influences of different crack properties(crack depth,crack number,crack width)and freeze-thaw cycles on basalt fiber RPC durability were studied in detail.Acoustic emission technology and Weibull distribution theory were introduced.The durability of basalt fiber RPC was evaluated by the cumulative energy and amplitude parameters of acoustic emission.The Weibull distribution theory was used to establish the freeze-thaw damage model to characterize the whole process of freeze-thaw damage of cracked basalt fiber RPC.The results showed that basalt fiber RPC has excellent freeze-thaw action resistance.The traditional evaluation method based on mass loss rate is not suitable for the evaluation of basalt fiber RPC freeze-thaw action resistance,but the strength loss after freeze-thaw action should be used as its evaluation index.(4)The influences of cracks,interface damage and chloride erosion on the durability of basalt fiber RPC embedded steel bar were quantitatively analyzed.The steel corrosion degree in basalt fiber RPC was evaluated by electrochemical method based on corrosion potential,self-corrosion current density and polarization resistance,and then the influence of chloride corrosion on basalt fiber RPC was evaluated,which provided a reference for the development of RPC special test method and evaluation standard for chlorine corrosion resistance.The results showed that the electrochemical method was a feasible method to evaluate the resistance durability of basalt fiber RPC against chlorine salt.Basalt fiber was not easy to corrode,which could increase the matrix resistance of RPC and make the connection of each part of RPC more compact,thus inhibiting the steel corrosion and prolonging the service life of steel.(5)Considering the bond length of rebars and concrete cover thickness,the bond performance between rebars and basalt fiber RPC was studied through the beam test method.According to the test results,the bond stress between rebars and basalt fiber RPC was fitted,and the complete bond stress-slip constitutive relationship between rebars and basalt fiber RPC was established.(6)The static response of reinforced basalt fiber RPC beam in the whole process of bending was tested by the four-point bending test,and the formulas of cracking moment,normal section bending bearing capacity and crack width for reinforced basalt fiber RPC beam were derived by fitting the test data.The fracture behavior of reinforced basalt fiber RPC beam was analyzed based on acoustic emission parameter fracture characterization.The results showed that the addition of basalt fiber could effectively reduce the generation of type I cracks,reduce the brittle fracture caused by type I cracks,improve the tensile capacity of the RPC simply supported beam in the bending zone,and increase the bending bearing capacity of the simply supported beam.