Autogenous shrinkage and stress-strain state of massive foundation slab

Introduction: The reliability of the assessment of the level of tensile stresses in order to predict the risk of early cracking during the construction of massive monolithic reinforced concrete structures increases when taking into account the deformations of autogenous shrinkage, which are often unreasonably ignored. Purpose of the study: to quantify the effect of autogenous shrinkage of concrete on the formation of a stress-strain state in the early period of the construction of massive monolithic reinforced concrete structures. Materials and methods: Modeling the formation of a stress field without taking into account relaxation in a massive block of 20×20×2 m with a layer overlap time («layer birth time») of 4 hours. At the first stage of research, stress calculated as a result of the development of only temperature deformations. At the second stage of research, stress calculated as a result of the development of temperature deformations and autogenous shrinkage. When calculating the temperature field, the layered laying of the concrete mixture is taken into account by assigning an abnormally high coefficient of thermal conductivity to each layer before it is laid (1000 W/ (m·°C)) and zero heat capacity. Results. The effect of a decrease in the heat transfer coefficient from 23 to 3 W/m²·°C on top of the plate is resulted in a decrease in the maximum stress level in the section by 28−32% when taking into account only temperature deformations and by 14−27% when taking into account temperature deformations and autogenous shrinkage. The influence of the kinetics of heat dissipation and hardening during the transition from the rapid group to the slow group is resulted in a decrease in the maximum stress level in the cross section to 6% when taking into account only temperature deformations. Possible increase in the maximum stress level in the cross section up to 20−56% take place if temperature deformations and autogenous shrinkage are taking into account.