Abstract
The problems of cracking condition when concrete was subjected to rapid temperature change and cracked in a short time after heating were discussed in Part 1. In this paper, Part 2, cracking conditions of concrete subjected to slow temperature change and cracked in a long time after heating, were reported. In this case, the effect of time-dependent deformation due to flow of concrete had to be taken into consideration. The same procedure as in Part 1 was used also in Part 2. But in Part 2. the rate of temperature change was varied in the region of 0.46〜28.5℃/hr measured by a scale of F_0/t, F_0 being the temperature distribution coefficient specified in Part 1. The age of concrete when tested was selected from 6 hours to 7 days, centering the young age range in which mass concrete comes into question concerning thermal cracking. The test results show that, when concrete was subjected to slow temperature change, cracking condition was greatly affected by the time-dependent deformation due to flow of concrete, and the influence of flow became quite significant as the age of concrete became younger. In order to compensate the influence of flow, correcting factor R was introduced applying the thermal stress theory and was determined quantitatively based upon the test results. It became clear that cracking condition of any mass concrete could be evaluated with accuracy by utilizing the temperature distribution coefficient F_0 and the correcting factor R, irrespective of rate of temperature change and other factors.
