Thermal Gradient Control of Roller Compacted Concrete Dams

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Title: Thermal Gradient Control of Roller Compacted Concrete Dams

Author(s): A.A. Ramezanianpour, A. Hassankhani, and A.M. Ramezanianpour

Publication: Special Publication

Volume: 235

Issue:

Appears on pages(s): 137-146

Keywords: construction method; heat generation; pozzolanic cement; roller compacted concrete; thermal gradient

Date: 3/22/2006

Abstract:
Heat of hydration of cement and resulting thermal gradient has a great influence on the quality of concrete and concrete structures particularly in the mass concrete for dams. In roller compacted concrete (RCC) method for dam construction, surface of concrete layers are very large in comparison with thickness of the layers. Therefore the thermal condition in the center of layers is almost adiabatic in horizontal direction. t means that, the generated heat of hydration mostly flows in the vertical direction and a great proportion of heat dissipates through the upper face of the layer before the next layer is placed. Low thermal conductivity of concrete layers has a great influence on the dissipation of generated heat. Thermal gradient induced by generated and remaining heat in the layers can cause thermal cracking in RCC dams which have no post-cooling system. In this investigation a laboratory model is set up to optimize the layer thickness and required time for dissipating of generated heat and controlling thermal cracking. The laboratory model consists of a 90x90 cm cylinder filled with 3 layers of concrete with 30cm thickness each layer. In this simulation the variables were the thickness of layers and the exposure time for each before placing the subsequent layer. Temperature variations were recorded at the center of each layer and at different distances from the center of the laboratory model. From the results of this research, the thickness of the layers and their related exposure time were determined for various concrete mixtures in order to minimize the heat problem and thermal crack prevention. The proposed guide for placing concrete in RCC dams seems to be beneficial for the construction of such dams under various conditions.