A Study on the Shrinkage Mechanism of Concrete

Abstract

Though various studies on the shrinkage of concrete have been made by many researchers, most of them have not dealt with its mechanism. In order to explain the shrinkage mechanism of concrete, the shrinkage test and water loss test were performed in this study on three different concretes (a crushed stone concrete and two lightweight aggregate concretes). From the test results, the relationship between shrinkage strain and water loss as well as the effect of ambient humidity on shrinkage and water loss were discussed.
The results of this study can be summarized as follows :
(1) The water loss of concrete by drying increases with increasing water content in concrete and with decreasing relative humidity in the atmosphere.
(2) When the ambient humidity is low, it is suggested that the mechanism of water loss may be divided into two processes.
(3) The shrinkage strain decreases with increasing ambient humidity.
(4) It is suggested that the shrinkage mechanism of concrete may be divided into two processes. In the first process, the water loss from the aggregate or capillary pore is so dominant that the shrinkage accompanied with the water loss increases slowly. In the second process, the water loss from the gel pore becomes significant and subsequently the shrinkage increases rapidly.
(5) The shrinkage of concrete is roughly proportional to the water loss. However, the proportional constant varies depending upon the kind of concrete.