Study On The Fracture Performance Of Basalt Fiber Reinforced Concrete Under Different Loading Rates

Concrete is the most widely used building material in water conservancy and civil engineering construction,but its inherent defects such as poor toughness and easy cracking restrict its application and development in engineering.For this reason,the internal structure of concrete is improved by adding high-performance basalt fiber and nano-CaCO₃,and its anti-deformation performance and crack resistance are improved.In addition,due to the complex service environment of the concrete structure,the size and rate of the load it bears changes at any time,and its mechanical properties vary greatly under different working conditions.Therefore,the research on the fracture performance of composite concrete materials under different loading rates has important guiding significance for the engineering application in the Qinghai-Tibet Plateau region.The research results of this paper are as follows:1.The effect of nano-CaCO₃ at different dosages on the mechanical properties of mortars of different ages was carried out,and the microscopic analysis was carried out through XRD and SEM techniques.The results showed that nano-CaCO₃ could improve the mechanical properties of mortars,and the optimal dosage was 2.0%;The basic mechanical test of basalt fiber mortar with different lengths and different dosages shows that the optimal fiber length,dosage is 6mm,0.20%.The SEM analysis shows that the basalt fiber can increase the toughness and crack resistance of mortar,but the"adhesive"phenomenon caused by excessive fiber will increase the initial defect.2.Set different loading rates to perform basic mechanical tests on basalt fiber concrete,and obtain fitting curves of compressive strength,splitting tensile strength,and flexural strength growth factor.The results show that the growth rate of compressive strength,splitting tensile strength and flexural strength of basalt fiber concrete is higher than that of concrete without basalt fiber.3.The fracture test of basalt fiber concrete was carried out,and the P-CMOD curve was drawn based on the double-K fracture model.The results show that under the force loading and displacement loading modes,with the increase of the loading rate,the initial fracture toughness and the unstable fracture toughness of the three-point bending beam both increase.The reason is that a load with a higher rate will instantly transmit higher energy,and the cracks will develop longitudinally in the shortest time to destroy the specimen.The coarse aggregate and basalt fiber located on the crack propagation path inhibit the development of the cracks,thereby prolonging the stage I and stage.4.Through the fracture test of basalt fiber concrete,the fitting curve of the growth factor of initial fracture toughness and unstable fracture toughness under the action of force loading and displacement loading is obtained.The results show that the initial fracture toughness and unstable fracture toughness growth rate of basalt fiber concrete are higher than those of concrete without basalt fiber.The reason is that basalt fibers are scattered in the matrix.When the cracks propagate,the basalt fibers will be directly pulled out or broken.Especially under the action of high-rate loads,they exert a toughening and crack-resisting effect through bridging.The fracture properties of concrete are improved.5.Based on the random aggregate model combined with the cohesive force constitutive relationship,a numerical model of basalt fiber concrete is established on a meso scale.The test and simulation results are compared,and the applicability of the numerical model in simulating the fracture performance of concrete is analyzed.