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In winter construction, it is of crucial importance to predict the temperature field of concrete, to avoid frost damage, control the temperature gradient, and ensure the construction quality of concrete. In this study, a modified finite element model (FEM) considering the characteristics of winter construction was proposed to predict the temperature field of concrete. The freezing process of free water and the heat release of hydration varied with concrete temperature was involved in this model. Then, the temperature histories of two types of concrete placed at different subzero temperatures were monitored experimentally and simulated by using the modified FEM. Good agreement of these results confirms the validity and reliability of this model. Finally, some numerical experiments were performed to explore the effects of engineering parameters on the temperature field of early age concrete by using the validated finite element model. The results show the law of influence of concrete placing temperature and geometry, ambient temperature, and the thickness and thermal conductivity of insulation material on the concrete temperature field.
Keywords: Finite Element Analysis; winter construction; temperature field; thermal insulation curing
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1.Introduction
When the temperature drops to or is expected to be lower than 4 °C, concrete will enter the winter construction period. The curing time for concrete called protection period needs to be carefully calculated to prevent it from being affected by subzero temperatures, such as frost damage and thermal cracking [1]. Newly placed concrete usually has a high degree of moisture saturation since there is a small amount of mixing water participates in the cement hydration reaction. If early age concrete subjects to cold weather before hardening, the frost heave of free water in the concrete will cause early frost damage to the structure. Moreover, the rapid cooling of concrete surfaces and temperature rise of its interior from cement hydration heat is associated with high-temperature gradient and thermal stresses inside the concrete. Whether the concrete produces a thermal cracking depends on the tensile strength of the concrete at this time. Thus, the combination of frost damage and thermal cracking will reduce the strength, durability and inevitably shorten the service life of the concrete structure [2-4].
To prevent concrete from freezing and cracking damage at an early age, many...