Journal of the South African Institution of Civil Engineering
On-line version ISSN 2309-8775
GRAHAM, P C; BALLIM, Y and KAZIRUKANYO, J B. Effectiveness of the fineness of two South African Portland cements for controlling early-age temperature development in concrete. J. S. Afr. Inst. Civ. Eng. [online]. 2011, vol.53, n.1, pp. 39-45. ISSN 2309-8775.
Temperature gradients due to heat of hydration of cement can cause cracking and present serious structural and serviceability concerns in concrete structures. Engineers use a wide range of strategies to limit the potential for such cracking, mainly by minimising the maximum temperature in the concrete. This paper considers the possibility of using more coarsely ground cement as one of the strategies for reducing the maximum concrete temperature. Two cement clinkers were used to produce cements with five different levels of fineness. These ten cements were then used to make concretes which were tested in an adiabatic calorimeter to determine the heat evolution characteristics. The measured results were then used in a computational model to calculate the temperature profiles likely to occur in two types of concrete elements. The results indicate that the effect of increasing fineness on the total amount of heat released during hydration is dependent on the mineralogy and crystal composition of the cement clinker. Also, the use of coarse-ground cement as a means of reducing the maximum temperature in concrete is more effective in the case of concrete elements with high cement content but of moderate dimensions. In sections of larger dimension, coarse-ground cements show lower levels of temperature reduction but also lower thermal gradients.
Keywords : cement; fineness; calorimetry; concrete temperature; modelling.