The influence of specimen geometry upon weight change and shrinkage of air-dried mortar specimens

Synopsis Results are given of an investigation into the influence oj specimen size and ‘shape’ upon the weight change and shrinkage of mortar specimens dried at 20°C and 65% R.H. The specimens tested had a water/cement ratio of 0·71 and were moist-cured for 7 days. It is shown that the falling-rate curve may be divided into three periods in which it is suggested that a single mechanism predominates, namely, capillary moisture loss, diffusion moisture loss or carbonation weight gain, and also two intermediate periods in which a combination of two of these three mechanisms gives rise to significant weight changes. The shrinkage measurements are shown to support the division oj the falling-rate curve into a number of periods, and it is shown that the ultimate shrinkage due to moisture loss increases with specimen size. Two methods are suggested for obtaining the ultimate shrinkage of a practical concrete section for which carbonation shrinkage can be assumed to be negligible.