Effect of age and specimen size on the transient thermal strain of concrete

The transient thermal strains of a given concrete heated for the first time under load to 6000C can be regarded, for practical purposes to be independent of the age at heating for ages in excess of 2 months (1 year for temperatures up to about 2000C. The data published previously can, therefore, be employed in computer programs for the thermal stress analysis of concretes heated to 6000C at all ages in excess of about 2 months. The transient thermal strains obtained from the 'large' and 'small' specimens, everything else being equal, were identical although the ratios of volumes and surface areas were 8.8 and 4.3 respectively. This confirms that the data reported earlier for the larger specimens represented true material properties undistorted by 'structural' effects. It can also be concluded that cylindrical specimens, 62 mm in diameter and 186 mm long, can be used to measure the transient thermal strains of concrete for heating rates up to about 10C/min or possibly higher. (orig./HP)