Investigation On Mechanical Behavior And Failure Mechanism Of Basalt Fabric Reinforced Concrete

Concrete has become the most widely used civil engineering material in today’s construction field with its excellent characteristics of high compressive strength,low cost,easy access,and strong plasticity.However,due to its shortcomings such as low tensile strength,large brittleness,poor ductility,and easy cracking,its buildings often crack during service and exist potential safety hazards.At present,the reinforcement of concrete materials is mainly in the form of incorporating short fiber,and its reinforcement mechanism is principally that chopped fiber can play the role of a bridge to transfer stress when the structure bears the load.However,the dispersion technology of chopped fiber in concrete matrix is difficult and has not been well solved.The continuous fiber,such as the fabric with textile structure,can be arranged according to the stress direction of the structure,not only the construction technology is simple,but also can maximize the utilization rate of the fiber.In recent years,the basalt fiber has been widely favored in the construction field due to a series of advantages such as high tensile strength,high elastic modulus,low cost,high temperature resistance,and environmental protection.Basalt textile reinforced concrete(BTRC)is made by using textile technology to weave basalt fiber bundles into fabrics with different structures and then compounding with concrete.Compared with traditional concrete,it has the advantages of "light weight,high strength,durability,and crack control",which meets the application requirements of today’s construction engineering field.This paper focused on the the requirements of geotechnical and construction engineering,focusing on the bridge structure composed of the bridge span and the bridge column as the application environment,taking basalt fabric reinforced concrete composite material as the research object,the mechanical behavior and failure mechanism of basalt fabric reinforced concrete composite material were studied by the combined method of experimental characterization,theoretical analysis,and numerical simulation,so as to make it more scientifically,safely,and reliably to serve the bridge construction engineering and application.The main contents of this paper are as follows:(1)In view of the weak point of basalt fabric,which is susceptible to the alkaline environment of concrete,starting from the design of preventing hydroxyl ions to corroding the silica/alumina tetrahedron structure of basalt fabric,zirconia was prepared by the sol-gel method and then loaded on the surface of basalt fabric through polydopamine adhesive to improve its alkali resistance.The chemical structure,morphology,composition,surface hydrophilicity,and tensile property of the basalt fabric before and after modification were characterized and analyzed.The alkaline environment of concrete was simulated by the standard method of accelerated aging with alkali solution.The surface morphology and mechanical property of basalt fabric before and after modification were tested.The interfacial property between concrete and basalt fabric before and after modification was investigated using acoustic emission in-situ characterization technology,and the interfacial bond slip mechanism and stress transfer mechanism were discussed.The results showed that the modifier was successfully loaded on the surface of basalt fabric,and the alkali resistance of basalt fabric was significantly improved.The ultimate pull-out load of the interface between the modified basalt fabric and concrete was increased by 129.65% compared with the pristine basalt fabric.The five stages of the whole process of interfacial extraction corresponded to five regions respectively: the elastic region,the elastic-plastic region,the elastic-plastic-debond region,the plastic-debond region,and the debond region.The acoustic emission characteristics were highly correlated with the load-displacement curves.(2)In order to study the effect of different reinforcement modes of basalt fabric on the property of concrete,based on the research on basalt fabric modified above and bond slip mechanism,the basalt fabric was compounded with concrete in different reinforcement modes.The influences of different curing periods on ultimate tensile strength and crack pattern of basalt fabric reinforced concrete were discussed.The influences of different reinforcement structures on tensile properties and crack evolution of basalt fabric reinforced concrete under the same fiber volume content were compared.The tensile failure mechanism and crack morphology characteristics of basalt fabric reinforced concrete with different mesh sizes,different ply angles,different warp densities,and different weft densities were systematically analyzed.The damage mechanism of basalt fabric reinforced concrete composites under continuous tensile load was investigated by acoustic emission correlation analysis and cluster analysis,and the strain hardening characteristics and multiple cracking patterns of basalt fabric reinforced concrete composites were revealed.The results illustrated that different reinforcement modes appeared a greater effect on the property of basalt fabric reinforced concrete.Under the same fiber volume content,the tensile strength of concrete with three layers of woven fabrics was improved by 104.61% compared with chopped fiber.The number and parallelism of yarns arranged along the principal stress direction of the composite determined the effect of basalt fabric in the strengthening stage.The acoustic emission energy ratio of fiber/matrix debonding and fiber breakage was increased from 0% to 34.6% with the increase of layers of basalt fabrics,which could contribute to absorbing more energy for the composite materials.(3)Based on the influence law of reinforcement modes of basalt fabric on concrete property,starting from the "material-structure" property design,focusing on the application environment of bridge span,the mechanical behavior,internal damage mechanism,and external failure pattern of basalt fabric reinforced concrete under continuous flexural load were studied quantitatively and visually by using acoustic emission in-situ monitoring technology and highspeed photographic transient imaging technology.The inner relation between reinforcement modes and the property of basalt fabric reinforced concrete composite was further revealed.The influences law of the reinforcement structure,the fabric structure parameters,and the fabric stacking method on the flexural property of the composites were emphatically analyzed.The structural effect,stress concentration effect,load transfer mechanism,damage initiation,fabric reinforcement effect,and structural crack evolution law of basalt fabric reinforced concrete under flexural load were clarified.Based on the compressive constitutive model of concrete beam and the equivalent stress transformation theory of beam section,a prediction model of the ultimate flexural bearing capacity of basalt fabric reinforced concrete based on different stacking methods was proposed,and the prediction results were compared with the experimental results.The results indicated that there exhibited a significant relationship between the flexural properties of the composite and the structural parameters of the basalt fabric,and the structural cracks turned due to the stress transfer,load bearing,and energy absorption of the basalt fabric during the evolution process.With the increase of layers of basalt fabric,the damage failure modes of the composite material changed from matrix cracking to fiber pulling out,fiber debonding,and fiber breakage.The ultimate flexural strength of the composite could be increased by 50.23% by the designed stacking method.The model prediction results were in good agreement with the experimental results.The established theoretical prediction model had certain accuracy and reliability.(4)The finite element numerical simulation was carried out on the basis of the flexural experiment and theory of basalt fabric reinforced concrete composites with different structural parameters.A concrete plastic damage model and a fabric constitutive model were selected as the material properties of concrete matrix and basalt fabric reinforcement,respectively.The cohesive crack model was used to simulate the generation,propagation,and evolution of composite cracks.The constitutive relation was defined by fully considering the tractionseparation criterion,damage initiation criterion,and damage evolution criterion.The numerical simulation results were verified by the comparison of load-displacement curves,the comparison of concrete structure crack morphology and evolution path,the analysis of fabric equivalent stress distribution and deformation,and the damage evolution and failure of composite materials.The results demonstrated that the established finite element model of basalt fabric reinforced concrete composite was feasible and accurate.The results of the numerical simulation appeared in good agreement with the experimental results.(5)The bridge column was vulnerable to impact damage and failure,resulting in the devastating collapse of the whole bridge structure.Based on the previous research on the static mechanical behavior and the failure mechanism of basalt fabric reinforced concrete composites,focusing on the application environment of bridge column,the low-speed impact and highspeed impact mechanical behavior and the failure mechanism of reinforced concrete with different reinforcement structures,different pre-impact energies,and hybrid effects of chopped basalt fiber and basalt fabric were studied by using the drop hammer and Hopkinson bar test systems.The structural crack evolution behavior of different composite materials was captured and recorded by high speed photography.The propagation mechanism of disturbance wave and elastic stress wave in basalt fabric reinforced concrete composites was discussed.The strengthening and toughening mechanism and energy absorption characteristics of basalt fabric on concrete under impact load were also revealed.The research results manifested that the ultimate load of chopped basalt fiber reinforced concrete and basalt fabric reinforced concrete were 24.13% and 88.62% higher than that of plain concrete respectively under the low speed impact energy of 65 J.Basalt fabric reinforced concrete composite had a variety of damage mechanisms under low speed impact load,and each damage form affected,coexisted,correlated,and competed with each other.The ultimate high speed impact strength of 1 layer,2layers,and 3 layers of basalt fabrics in concrete was increased by 48.14%,88.12%,and 93.60%,respectively.The crack morphology of plain concrete,chopped basalt fiber reinforced concrete,and basalt fabric reinforced concrete under a high speed impact load corresponded to slag state,gravel state,and unbroken state respectively.The basalt fabric could absorb a great deal of energy timely and effectively.In summary,based on the integrated design concept of material-structure-property,from the modification and preparation of reinforcement to the discussion of interfacial property,then from the shallower to the deeper,the experiment,characterization,theory,and numerical simulation of basalt fabric reinforced concrete composite materials were carried out.The mechanical behavior,damage process,and failure mechanism of composite materials were analyzed.The strengthening and toughening mechanism of basalt fabric was revealed.The research results of this paper lay a theoretical foundation for the further scientific research and the application of basalt fabric reinforced concrete composites in the field of bridge construction engineering.