Abstract
According to the practice of temperature control in dam concrete, within a few days after a concrete block is poured, the temperature at the core of the concrete rises rapidly. The maximum temperature may still exceed the standard even under a relatively perfect post-cooling system, which is mostly caused by failure to quickly and correctly judge the development of the early-age temperature. This study investigates concrete temperature at an early age via in situ monitoring data collected from Baihetan arch dam and Wudongde arch dam. A simplified algorithm of temperature prediction is formed, which only considers the heat released by cement hydration and the cooling effect of cooling pipes. The influence of a cooling pipe on the measuring point of the thermometer is investigated, and a simple empirical formula to calculate the cooling effect is obtained. An equation for the rate of hydration temperature rise is achieved by combining measured data and the formula used to calculate the cooling effect. Furthermore, through the explorations of the related data, it is determined that the cement hydration ratio of the two dams is quite low during concreting. On the basis of the data collected from the field, the method to predict temperature proposed in this study is tested and proven.
Highlights
With the rapid development of damming technology, the construction scale of concrete dams is increasing, resulting in higher dam heights, faster construction speeds, and larger volumes of concrete.Owing to the vast quantity of heat released by cement hydration and the poor thermal conductivity of concrete, heat in the core of dam concrete in unlikely to dissipate in time without effective cooling measures, resulting in high thermal stress and even cracks
The application of low-heat cement fundamentally reduces the heat of cement hydration; its successful utilization in Hoover dam further promoted the development of low-heat cement concrete [2]
The adiabatic temperature rise measured by adiabatic calorimetry is a common way of reflecting the heat-release process of cement hydration; on this basis, many methods for temperature prediction were developed
Summary
With the rapid development of damming technology, the construction scale of concrete dams is increasing, resulting in higher dam heights, faster construction speeds, and larger volumes of concrete. Owing to the vast quantity of heat released by cement hydration and the poor thermal conductivity of concrete, heat in the core of dam concrete in unlikely to dissipate in time without effective cooling measures, resulting in high thermal stress and even cracks. The adiabatic temperature rise measured by adiabatic calorimetry is a common way of reflecting the heat-release process of cement hydration; on this basis, many methods for temperature prediction were developed. With the aim to develop rapid and real-time predictions and to facilitate the verification of the method, this paper directly targets the temperatures at the measuring points of thermometers without considering the temperature distribution of the entire concrete block. A simplified method for predicting the early-age temperature of concrete is formed, only considering the effects of cooling pipes and cement hydration, and the feasibility of this technique is proven. The main impact of the concrete temperature during concreting is determined to be the environment rather than cement hydration, and a real-time forecasting and warning system is established based on the real-time monitoring system of the two dams, thereby successfully providing reference and convenience for the maximum temperature control of dam concrete at an early age
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