Finite Element Analysis Of The Cracking Tendency Of Repair Mortar On Concrete Substrate

The repairing of old concrete has caused great concerns from 1950s in the world, and many kinds of repair methods were adopted. However, the poor compatibility between the old and new concrete often requires a repeated repair in 2-3 years. The buildings and structures of concrete requiring repair or reinforcement is increasing in these years, and there is an urgent demand to determinate the cracking mechanisms and the factors that influence the cracking tendency of the repair system.In this paper, the cracking of repair mortar on the concrete substrate was modeled using the universal finite element analysis software (ANSYS). In the temperature field calculation, in consideration of the effects of temperature and age on the rate of cement hydration, the theory of hydration degree was used to offset the deficiency of conventional cement hydration heat formula. In the thermal stress field calculation, the theory of mature degree was used in consideration of the effects of temperature and age on the strength and modulus of elasticity development of repair mortar. Finally, the methods of relaxation coefficient and equivalent difference in temperature were used in consideration of the effects of creep and shrinkage in integrative stress field calculation.This paper simulates the cracking of repair mortar on the concrete substrate through a restrained shrinkage test. The strains were measured in each direction on the repair mortar surface using micrometer gauges and the test results were analyzed. Based on the theory of temperature and stress field, a three-dimensional finite element analysis model of repair system was established. The results from the model calculation were compared with the measured values to verify the validity of the theoretical arithmetic.The factors that influence the cracking of repair mortar on the concrete substrate, such as cement hydration heat, content of cement, thickness and length of repair layer, casting temperature, ambient temperature, diurnal amplitude of temperature, ultimate shrinkage, creep, modulus of elasticity and coefficient of thermal expansion were simulated using finite element calculation model. The influence of each factor was discussed by analyzing the greatest principal tensile stress and cracking risk. Finally, the existing shortages in this paper were indicated and the research direction in the future was put forward. The content and conclusions of this paper may provide a reference for concrete repairing research.