Study On The Early-age Crack Of Massive Concrete With Multi-field Coupling Based On Phase-field Theory

Early cracking of concrete is an important technical problem plaguing the civil engineering field.Although early cracking does not always affect the safety of the entire engineering structure in a relatively short period of time,the presence of cracks seriously affects the long-term safety,durability,and service life of the structure.The problem of early cracking in concrete is extremely complex and is influenced by numerous factors such as the hydration process,ambient temperature,humidity and the construction process.How to quantitatively analyse these effects on the structural scale and accurately predicting the crack resistance of early-age concrete is a pressing technical challenge in engineering.In this paper,numerical simulations combined with field measurements are used to study the multi-field coupling,as well as the whole process of crack evolution and the crack resistance performance of concrete.The main works are as follows:(1)The unified phase field theory is introduced to analyze the problem in the modeling of damage and quasi-brittle failure in solids,which simultaneously considers the strengthbased nucleation,energy-based propagation criteria and the energy minimization-oriented path following criterion,providing a new method to quantify the crack evolution and laying the theoretical foundation for the simulation of early-age cracks in this paper.(2)Based on the understanding of the phase field theory and the hydration process of early-age concrete,the hydration model based on the unified phase field theory is established,which takes into account the interaction between hydration reaction,heat transfer and crack evolution,and can accurately simulate the hydration reaction and crack evolution of early-age concrete,and has certain reference and guiding significance for the prediction and control of early-age cracks.(3)Combined with engineering examples,the early-age concrete hydration model based on the unified phase field theory is applied to a cut-and-cover under-lake tunnel,through the analysis of field measured data and finite element simulation results,it provides help for the prediction of early-age cracks in the project,and based on the analysis results,effective crack resistance control measures are proposed.