Shrinkage and Interior Humidity of Concrete under Dry–Wet Cycles

Abstract

The dry–wet cycle is one of the aggressive environmental conditions suffered by concrete. This article focuses on the experimental study and theoretical simulation of shrinkage of concrete during dry–wet cycles. The experimental results show that the interior relative humidity of concrete is periodically changed during dry–wet cycles. As concrete undergoes wetting, a fast increase in interior humidity takes place in a short time and then the relative humidity reaches a stable level, which depends on the strength of concrete or on the water-to-cement ratio of concrete. In contrast, as concrete undergoes drying, the interior relative humidity does not drop immediately but decreases in a gradual manner. Accordingly, the shrinkage of concrete during dry–wet cycles is also periodically changed, exhibiting shrinkage as drying and expansion as wetting. Based on the experimental findings, a model for shrinkage predictions of concrete during dry–wet cycles is developed. The model is based on the capillary tension created in capillary pores in concrete and uses the interior relative humidity (RH) as the driving parameter for shrinkage predictions. The model predictions on the development of shrinkage strain under plastic sealed and dry–wet conditions are compared with experimental results and a reasonable agreement was found.

Keywords:

• Concrete
• Dry–wet cycles
• Humidity
• Model
• Shrinkage

ACKNOWLEDGMENT

This work was supported by a Specialized Research Fund for the Doctoral Program of Higher Education (20100002110016), a grant from the National Science Foundation of China (No. 51178248), and a grant from the National Basic Research Program of China (No. 2009CB623200) to Tsinghua University.