Experimental study on shrinkage reduction of calcium sulphoaluminate cement concrete with addition of pre-wetted lightweight aggregate

Abstract

In the present paper, shrinkage reduction with pre-wetted LWA of calcium sulphoaluminate cement (CSA) concrete is experimentally investigated. In the test programs, shrinkage of low, medium and high strength CSA concrete with and without internal curing with pre-wetted LWA is measured. Water movement between a single pre-wetted ceramsite particle and the surrounding cement paste during cement hydration is directly measured through a glass tube connected with the ceramsite. The test results show that the main component of shrinkage of CSA concrete, no matter low or high strength concrete, is autogenous shrinkage other than drying shrinkage. Autogenous shrinkage of high strength CSA concrete is much higher than that of low strength CSA concrete. The addition of pre-wetted LWA can greatly reduce the autogenous shrinkage of CSA concrete even the internal curing water to cement ratio used in the concrete is as low as 0.04. The efficiency of shrinkage reduction is influenced by concrete strength or water to binder ratio. The higher the strength, the greater the shrinkage reduction. Water contained in LWA starts to release at about 15–25 min after mixing depending on water to binder ratio of the cement paste. Water movement between LWA and surrounding cement matrix during cement hydration obeys a two-stage mode, a fast releasing stage followed with a slow releasing stage. Amount of releasing water from LWA is obviously influenced by the initial air content in the LWA and the water to binder ratio of the paste. As air content is varied between 0 and 50% in volume, the more the air content, the more the water moved out of LWA. For given initial air content, the lower the water to binder ratio, the more the water removed from the LWA.