Numerical Simulation Research On The Frost Damage Of Early-age Concrete

For construction in cold regions,it is of great importance to determine the frost damage of early-age concrete scientifically.This could guide winter construction to effectively prevent the occurrence of the frost damage,ensure the quality of concrete projects and promote the winter construction technology.To this end,this paper adopts numerical simulation to achieve damage prediction analysis of early-age frost concrete.The main research contents including:Establishing a model for predicting the time-dependent physical properties of concrete.A one-way bridge is built between the initial input information of the cement hydration system(water to cement ratio,ambient temperature,mineral composition of the clinker,specific surface area of the cement particles,etc.)and the time-dependent information of the components contained,by coupling the cement hydration kinetic model and thermodynamic calculation methods.Based on a multiscale model spanning the hydrated calcium silicate gel to concrete,the time-dependent physical properties of concrete are predicted by applying the self-consistent and general self-consistent methods.The predicting physical properties include modulus of elasticity,thermal conductivity and chloride diffusive coefficient.Experimental measurements from the literature are cited to verify the accuracy of the prediction results.Proposing a numerical calculation method for the deformation of frost concrete.A method for calculating the pore size distribution of concrete at different ages is proposed based on the BSB adsorption model and two semi-empirical formulas.The equilibrium conditions to be met when the porous material is subjected to freezing are summarised,and the information on the pore size distribution is combined to achieve the prediction of the pressure of each phase of water within the pore structure and the overall deformation of the frost cement paste.A parallel paste-aggregate model is proposed to extend the calculating cement paste deformation results to the mortar and concrete levels.Experimentally measured strains of frost mortar at different pre-curing times are introduced to analyse the reliability of the model.Developing a frost damage prediction model for concrete.A microscale elasticplastic model for cement paste is suggested and a method for calculating the frost damage of frost damage is developed.A hypothetical structure model of mortar and concrete was introduced to determine the frost damage of frost mortar and concrete.The test data of dynamic modulus of elasticity of early-age frost mortar is selected and compared with the prediction results to analyse the reliability of the model.Some important factors in winter construction,such as water to cement ratio,curing temperature,antifreeze,ambient temperature and air-entraining agents,were selected to analyse their effects on the early frost damage and minimum pre-curing time of cementitious materials.It was found that antifreeze and ambient temperature had little effect on the early frost damage of cementitious materials,while the incorporation of air-entraining agents significantly improved the early frost resistance of cementitious materials.