Abstract: In order to prevent the cracking of concrete caused by internal restraint, the internal humidity field and self restraint stress field of concrete were studied in this paper. The shrinkage, internal temperature and humidity of concrete under different strength and curing conditions were tested by displacement sensors, temperature and humidity sensors. Afterwards, through theoretical derivation, a theoretical calculation model for the internal humidity, relationship betweenstrain and internal humidity of concrete were established. Studies indicate that the humidity in concrete decreases with the increase of cement hydration and drying. The moisture diffusion coefficient of concrete is a function of its internal humidity. As the distance from the drying surface increases, the internal moisture diffusion coefficient of concrete increases. There is a significant correlation between the shrinkage deformation and the internal humidity of concrete. The calculation model proposed in this paper is in good agreement with the experimental results. The existence of the humidity field in concrete leads to the existence of a strain gradient, which in turn causes the self restraint stress in concrete. Under the same environmental conditions, the internal self restraint stress of high-strength concrete is higher than that of ordinary-strength concrete.

Key words: concrete, shrinkage stress, internal restraint, internal humidity field, self restraint stress field