مهندسی عمران شریف (Feb 2021)
EVALUATION OF HEAT TRANSFER AND RATE OF STRENGTH GAIN OF CONCRETE
Abstract
Stress gain of concrete is a heated procedure. The amount of heat significantly depends on cement type, cement content, and cement-water ratio. While the rate of generated heat is far more than that of heat transfer to the exterior part of concrete mass, temperature of the interior part of concrete element during that procedure increases. Furthermore, the strength gain of concrete is a function of temperature history of every part of element which is influenced by heat caused by hydration. If the stress generated by heat in fresh concrete is greater than acquired strength of concrete, then early cracks will form in the concrete mass. As a result, thermal analysis and checking the strength gain in massive concrete structures like concrete dams, foundations, and bridge decks would be especially important. The terms heat transfer and thermal analysis are composed of some mechanisms. This models the mechanism and simulates the strength gain of concrete by finite element method. After verifying the finite element model, we will study the strength gain of a concrete slab and a reinforced concrete beam. All the experiments are in accordance with ASTM standard to determine the parameters of cement heating procedure. Controlled environment with a constant temperature is used for curing concrete specimens. Six different ages (first age for about 4 MPa compressive strength and next ages are twice the previous age. The specimens are studied at three different temperatures, $15^{\circ}C$,$25^{\circ}C$ and $35^{\circ}C$, 54 specimens are considered. The results show that this numerical method can estimate heat transfer in the concrete body with acceptable accuracy. In addition, the results exhibit that the proposed time for removal of forms in the ninth part of national building regulation of Iran ``design and construction of concrete structures'' should be considered in greater detail.
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