Experimental study on the relationship between shrinkage and interior humidity of concrete at early age

Abstract

The calculation of shrinkage-induced stresses and evaluation of cracking risk in concrete structures require information on shrinkage strain that always relates to the moisture decrease caused by drying or cement hydration. In the present paper, the development of internal relative humidity (RH) and global deformation in early-age normal and high-strength concrete were experimentally measured simultaneously by monitoring humidity and deformation sensors, respectively, starting from the time of concrete casting. The experimental results show that the development of the internal RH of concrete first follows a vapour-saturated stage (RH = 100%, stage I), followed by a gradually reducing stage (RH ≤ssthan 100%, stage II). Meanwhile, the global deformation behaves first as a plastic swelling for the initial several hours after casting and then shrinking occurs with a gradually reduced rate. The end of swelling normally corresponds to the point of concrete setting, at which point the transformation of fresh concrete from a liquid-like plastic state to a solid state is finished. Shrinkage has been measured even in the vapour-saturated stage with RH = 100%. In the humidity reduction stage, a linear relationship between free shrinkage strain and humidity reduction exists. In practice, the relationship of free shrinkage strain and local RH may be used to calculate the free shrinkage strain field and further to calculate the shrinkage-induced stresses in structures as well.

Evaluation of Shrinkage Induced Cracking in Concrete with Impact of Internal Curing and Water to Cement Ratio

“…First, let we look at the progress of internal humidity of all kinds of concrete. From the results shown in the figures, we can observe that the general developing manner of the internal relative humidity of concrete since casting can be described by a water-vapor saturated stage with 100% relative humidity (stage I) followed by a stage in which the relative humidity is gradually decreasing (stage II) (Zhang et al 2010;Zhang et al 2012). The reduction of internal relative humidity in early-age concrete is significantly influenced by surface drying, water to cement ratio and addition of PSLWA.…”

“…Cracks allow water and chemical agents, such as deicing salt, to go through the cover layer to make contact with the reinforcement, leading to reinforcement corrosion and rupture in steel reinforced concrete. The magnitude of the shrinkage strain is normally proportional to the amount of moisture loss (Bissonnette et al 1999;Baroghel-Bouny et al 1999;Ayano and Wittmann 2002;Zhang et al 2010). In general, environmental drying and cement hydration are the two major processes causing moisture loss inside the concrete.…”

Combination Effects of Internal Curing and Permanent Formwork on Shrinkage of High Strength Concrete

“…( Kamen et al 2008;Sule et al 2000;Bentur 2001;Zhang et al 2010). After achieving the first peak of swelling (P 1 in Figs.…”

“…Therefore, shrinkage of concrete may be one of the major sources of the formation of cracks in concrete structures. The magnitude of the shrinkage strain is normally proportional to the amount of moisture loss (Bissonnette, et al 1999;Baroghel-Bouny et al 1999;Ayano et al 2002;Zhang et al 2006). In general, environmental drying and cement hydration are the two main processes causing moisture loss of concrete.…”

“…These methods were specially developed for cement paste. Recently, Zhang et al developed a testing method to measure both deformation and interior humidity inside concrete simultaneously starting from concrete setting, meanwhile a drying environment for surface drying of the tested specimen was created as well in the experiments (Zhang et al 2010). Thus the total shrinkage resulted from both self-desiccation and environmental drying can be measured at the same time by the above testing method through using two parallel specimens.…”