Early age thermal cracking tendency assessment on mass concrete (Controlling temperature by pre cooling method)
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Date
2019-04
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Addis Ababa University
Abstract
Thermal dilation and autogenous shrinkage are produced by the continued
hydration of cement, this volume changes are partly or wholly restrained, and
therefore they induce stress. This is issue for massive concrete especially at
early age when concrete is immature. This thesis presents assessment on the
tendency of cylindrical axisymmetric strictures and massive wall at early age with
multiple thickness and placement temperatures. This master thesis focuses on
assessment of cracking tendency of massive concrete structures which are
subjected to realistic field temperature boundary conditions at early age. The
assessment is based on the analysis results of analytical models. This work also
shows the efficiency of precooling method in controlling of temperature
differential and cracking tendency structures by comparing with reference
placement temperature (placement temperature without introducing pre cooling).
At early age, the core of thin sections of mass concrete structures have high
tendency of cracking. The reason is that the high temperature drops of the core
during cooling phase. Cracking tendency at cores of thin sections is high at high
placement temperature. This susceptibility of cracking of thin section structures
are controlled by precooling method. Similarly surface of mass concrete
structures are susceptible for cracking at early age in moderately hot weather.
The tendency of surface cracks can be significantly minimized by reducing the
placement temperature but for thick sections precooling method should
combined with other temperature differential controlling methods (e.g. surface
insulation) to minimize surface early age cracking tendency.
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Keywords
Massive Concrete Structures, Hydration Heat, Shrinkage, Thermal Dilation, Young Concrete, Pre-Cooling, Placement Temperature, Temperature Reduction, Crack Risk