Ageing of portland cement concrete cured under moist conditions

Deterioration of microstructure in cement concrete will cause changes in the transport properties of the concrete. Transport properties at different ages of the concrete provide information about the microstructural changes of the material. A way to measure the transport properties, i.e. the chloride diffusion coefficient, in the laboratory is rapid chloride migration (RCM) Test. With this test, the resistance of concrete to chloride ingress is evaluated. Changing losing resistance represents deterioration and ageing of concrete. In this study, RCM tests were carried out for Portland cement concrete cured in moist conditions at various curing ages up to 3 years. Scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM/EDS) and X-ray diffraction (XRD) analysis were performed to identify the reaction product, like delayed ettringite. The experimental results show that the resistance of Portland cement concrete to chloride ingress decreases when ettringite is formed in concrete. Based on the result it is concluded that delayed ettringite formation contributes to the deterioration of Portland cement concrete, and should thus be considered as a relevant factor in the ageing process of concrete structures at moist curing condition.