The Effect of Fly Ash on the Temperature Rise in Concrete

One of the most serious problems facing the concrete industry in Texas is the effect of high temperatures in concrete on conrete performance. Hot weather and the hydration of cement produce high temperature conditions. One of the major problems associated with high temperatures in concrete is the potential for thermal cracking. The temperature rise can be lowered through the use of mineral admixtures such as fly ash. This report is the first in a comprehensive study which addresses the effect of fly ash on the temperature rise in concrete and the thermal gradient in concrete resulting from the hydration of cement.

This report presents the results from a research program in which the temperature rise in mortar samples and the thermal gradient in concrete are examined. Other tests were conducted to monitor the thermal gradient along the vertical cross section of concrete members having various dimensions, curing conditions, and mix proportions.

The results of this study show that the replacement of cement with Type A fly ash results in a reduction in the temperature rise in concrete, whereas replacement of cement with Type B fly ash has no significant effect on the temperature rise in concrete. The results also show that the thermal gradient is not linear through the depth of a concrete member from mid-depth to the exposed concrete surface. Most of the temperature drop within a concrete member occurs near the exposed concrete surface. The project engineer is provided with guidelines to produce more durable concrete structures by reducing the internal concrete temperature, thus reducing the potential for thermal cracking.