Time-Dependent Prediction And Mitigation Measures For The Transport-Damage Performance Of Structural Concrete Under Sulfate Attack

Sulfate transport through the pores/joints of concrete to the interior of concrete structures in saline soils and coastal areas causes expansion-cracking of concrete materials and is the main cause of structural concrete deterioration.Therefore,it is of great importance to carry out the study on the transmission-reaction-damage damage process and deterioration mechanism of concrete under sulfate erosion,quantify the damage "force" of the environmental load of sulfate on the structure,and the degradation law and inhibiting measures of concrete durability to evaluate the service performance,service life and durability enhancement technology of concrete structures.Supported by the National Natural Science Foundation of China(NSFC)"Damage deterioration mechanism and performance assessment and control of structural concrete under sulfate-chlorine salt coupling(5217083308)".In this paper,the damage mechanism of concrete under sulfate attack is firstly revealed systematically through experimental and theoretical methods,and the pore curvature model with significant effect on ion transport is established.(1)For the transport-reaction-damage problem of sulfate-erosion concrete,sulfate immersion tests were conducted to obtain the property and physical phase change laws of cement net/mortar,and reveal the reaction-damage mechanism of sulfate-erosion concrete generating calcium alumina and other products.(2)Based on the compositional characteristics of cementitious materials and the geometric characteristics of their component materials such as cement particles,sand and stone,a model for the transport curvature of cementitious materials such as cement net,mortar and concrete considering the water-cement ratio,volume fraction and particle shape was established using geometric methods,and the reasonableness of the model was verified by MIP tests.(3)Homogeneous composites consisting of three phases of coarse aggregate,mortar and interfacial transition zone are considered from the fine-scale,and the concrete random aggregate model is established by determining the geometric position of aggregates with the help of Monte Carlo method,and the random generation and placement of polygonal aggregates are realized according to the specific aggregate gradation and aggregate shape,and the interfacial transition zone is generated to get the three-phase fine-scale model.(4)Based on Fick’s second law,crystallization pressure theory and volume expansion theory as well as,establish a transport model considering porosity,curvature and critical damage degree to obtain the crystallization pressure generated by calcium alumina and other expansive products in concrete and the time-varying law of volumetric expansion strain induced in concrete,and to establish the concrete material and structure under sulfate erosion from ion transport to expansion stress strain change law The computational theory and method are established,and the prediction results of sulfate distribution,expansion strain and damage spalling are obtained.