Concretagem de grandes volumes e como controlar os efeitos da alta temperatura.

Abstract

Concrete is currently the most used structural element in civil construction works, taking into account factors such as its good water resistance, the possibility of use in structures of different shapes and sizes and its low cost when compared to other materials with similar function. On the other hand, there are a number of precautions that need to be taken with concrete to ensure its efficiency and durability, including measures to control the heat of hydration of the cement in the concrete mix, especially in large-scale works. The present study aimed to analyze the methods of prevention and monitoring of cracks resulting from the heat of hydration in large-volume concreting. It was an exploratory and bibliographical research, carried out from a bibliographic survey involving books, scientific articles, monographs and dissertations that addressed the topic. To avoid problems arising from the heat of hydration in large structural elements, several preventive methods have been used, ranging from choosing the most suitable cement and aggregates for the manufacture of mass concrete to the use of pre and post- cooling techniques, in addition to layered concreting. Pre cooling has been the most used method to prevent problems of thermal origin due to its low cost and high level of effectiveness. The best method for preventing cracks resulting from the heat of hydration in large-volume concreting is the pre-cooling technique with ice in flakes, although care with the materials used in mixing the concrete is also important. Flake ice reduces the thermal stresses of the concrete, decreasing the heat of hydration in the first hours after casting, which avoids the appearance of cracks and generates a better evolution of the compressive strength. It also prevents the formation of expansive compounds during cement hydration that can reduce the durability of structures. Temperature control, on the other hand, must be carried out as soon as there is authorization to release the concrete. As a rule, this monitoring takes place through electrical sensors, such as thermometers and thermocouples, embedded in the concrete mass itself. In cases where an irregularity in the temperature or slump of the concrete is verified, the correction can be made with the insertion of superplasticizer additives, capable of reducing the consumption of cement in the dosage, or even with the addition of more ice, in cases where that this has been used as a form of pre cooling. Keywords: Concret mass. Large structural elements. Hydration heat. Control and prevention