Simulation Of Chloride Ions Erosion In Concrete Under Loadings And Environmental Factors

The durability of reinforced concrete structures under chloride environment is a prominent problem for offshore structures.It is significant for the life prediction of marine structures to study the transport of chloride ions in concrete.In the service process,concrete structures bear inevitably various loadings and environmental factors.The damage and crack will initiate and propagate under loadings,which will increase dramatically the transport channels of chloride ions;consequently,the erosion process of chloride ions will be accelerated seriously.The environmental factors,including drywet cycle and freeze-thaw cycle,also aggravate chloride ions erosion,which cannot be ignored.In present study,Peridynamics was adopted to investigate the transport process of chloride ions under various loadings and typical environmental factors.The main innovative work and results were as follows.(1)Development of the peridynamic model for chloride ions transport in saturated concrete at macro-and meso-scaleEstablish the macroscopic peridynamic model for the transport of chloride ions,and verify the validity of the proposed model by benchmark examples;meanwhile,discuss the effects of parameters on the accuracy and efficiency of the model.Considering the diffusion properties of each material phase,the peridynamic model was generalized into the meso-scale.In what follows,the effects of aggregate distribution,aggregate gradation,aggregate volume fraction,the thickness of the interfacial transition zone(ITZ)and the diffusivity of ITZ on the transport process of chloride ions were evaluated.(2)Establishment of the peridynamic models for the transport of water and chloride ions in unsaturated concrete at macro-and meso-scaleThe macroscopic peridynamic model for the transport of water in unsaturated concrete was proposed.Considering the influence of water convection on the transport of chloride ions,the transport model of water was incorporated into the transport model of chloride ions;as a result,the peridynamic model for the transport of chloride ions in unsaturated concrete was developed.Comparing with the analytical solution and experimental results,the model was verified.Furthermore,in order to take into account the impact of heterogeneity of meso-structures,the peridynamic model for the transport of water and chloride ions in unsaturated concrete at meso-scale were proposed and validated.(3)Construction of the peridynamic model of concrete with three phases for simulating the cracking processA mesoscopic peridynamic model of concrete for simulating the cracking process was proposed,which could be used to conduct quasi-static analysis by solving the equilibrium equation.Numerical simulations including uniaxial tension,uniaxial compression,Mode I fracture,and three-point bending(TPB)tests were implemented to validate the proposed model in concrete specimens.These simulated results were consistent with the experimental data and observations.Especially,the salient features of crack initiation and propagation including the formation of micro-cracks and bond cracks,crack coalescence,crack bridging and crack branching could be observed.(4)Investigation into the effect of various loadings on chloride diffusion in saturated concreteConsidering the impact of the crack width on the transport of chloride ions,the peridynamic transport model of chloride ions in cracked concrete was developed and validated.The effects of the width and depth of artificial cracks on chloride diffusion were studied with above model.On the basis,the coupling mechanical-diffusive model was proposed and the effect of tortuous cracks caused by loadings on chloride diffusion was investigated.Finally,the coupling model was adopted to study the effects of compressive,tensile and flexural loadings on the transport of chloride ions.The results showed that the predicted results were consistent with the experimental results under high stress levels,and the penetration rate of chloride ions increased with the increasing stress level.(5)Study of the influences of typical environmental factors on the transport process of chloride ionsEnvironmental factors could influence the chloride diffusivity,the water diffusivity and the boundary conditions,consequently,the transport process of chloride ions could be affected by environmental factors.The effects of typical environmental factors including temperature,freeze-thaw cycle,erosion direction of chloride ions,distance from coastline and dry-wet cycle,were investigated,especially for freeze-thaw cycle and dry-wet cycle.The results showed that the erosion process of chloride ions could be aggregated by freeze-thaw cycle and dry-wet cycle.(6)Analysis of the transport process of chloride ions under loading and drywet cycleThe peridynamic water transport model in concrete with cracks was proposed,and the effects of cracks on water transport under immersion and dry-wet cycle were studied.Then,combining with the peridynamic model for simulating the cracking process,the coupling model of cracking process and water transport was developed.With the coupling model,the influences of compressive and tensile loadings on water transport were investigated.Finally,the coupling model of cracking process,water transport and chloride transport was established and verified.The results showed that the penetration depth of chloride ions increased with the increase of stress level and number of cycles.