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

Abstract

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.