A theory for drying creep of concrete

A theory for drying creep is proposed based on the stress concentrations arising from the presence of a rigid inclusion and a hole in a surrounding medium subjected to an external stress. The analogy is made with cement paste where there are some pores filled with water and other pores empty. When full, the average stress acting on the solid gel is less than the nominal external stress but, when empty, the corresponding stress is greater than the external stress so that there is a stress enlargement as the pores empty of water. By implication, there is an increase in creep of the solid gel as drying or water movement occurs. In contrast to most existing theories, the new theory does not require an interaction with drying shrinkage to account for additional creep. The theory is first developed to account for the water–cement ratio influence on basic creep and then the stress enlargement factor for various pore water contents is calculated to simulate different drying conditions. As well as drying creep, the theory explains the additional creep in tension under drying conditions, transitional thermal creep and transient thermal strain.