Effect of water storage time on frost resistance of concrete

In high performance concrete (HPC) with low water-cement ratio, cement reaction will cause substantial drying expressed in terms of relative humidity (RH) of the pore water. This phenomenon is called self-desiccation. The RH-values as low as 85% have been measured in dense concretes that have been stored for more than 18 months in water. This means that there is almost no freezable water in the concrete until very low temperatures are reached. It also means that freeze-thaw tests made with young concrete might give results on the unsafe side. In this report some results from a bigger study of the effect of longterm water storage on the frost resistance of HPC are presented. The results show that previously self-desiccated concrete absorbs water when it is stored for a long time in water. Dilation tests during freezing indicate that concrete that was frost resistant when tested during the first months might become non-frost resistant after a long period of water storage. This must be considered in the design of freeze-thaw test methods.