Abstract
The thermal model and the relevant parameters of concrete are the most important issues to study the space‐time characteristics of temperature field, which are also the theoretical foundation of temperature control and crack prevention for the mass concrete structures. In this research, the improved adiabatic temperature rise test is carried out, and the temperature variation of fly ash concrete is analyzed. Furthermore, a thermal model of concrete considering the hydration degree is established based on the existing achievements. Meanwhile, the thermal conductivity and specific heat of concrete are measured via three approaches: by treating the parameters as constant values, by computing the parameters as variables of the degree of hydration, and by back‐analyzing the parameters through BP neural network. Finally, the thermal parameters determined by different methodologies are substituted into the thermal model, respectively, and the finite element analysis of the concrete specimen is performed. By comparing simulated temperatures with various measured results, it can be found that the numerical analysis results of parameters calculated by BP neural network are closest to the measured values in the whole curing ages. Therefore, BP neural network method is an effective way to calculate the thermal parameters, and BP inversion algorithm provides a new way for accurately study the temperature profile of mass concrete structures.
Highlights
Cracking is a common phenomenon in the concrete structures
The temperatures of concrete change quickly with the rapid hydration of cement, and the temperature distributions in concrete structures are uneven because of the varied heat boundary conditions. e changes of both the temperature and the boundary conditions can lead to the obvious temperature gradients of the concrete structures, and the temperature gradients will lead to the temperature stress. e larger the temperature gradients are, the greater the temperature stress will become
It is well known that the thermal model and the relevant parameters of concrete are the basic conditions for studying the space-time character of the temperature field and are the prerequisite for accurate calculation of the temperature stress. e determinations of the thermal model and the relevant parameters are the key issues of studying the temperature. erefore, it is necessary to carry out a thorough research
Summary
Cracking is a common phenomenon in the concrete structures. Even some buildings which were carefully designed and constructed appear with cracks. There were common shortcomings in the experimental method and in the numerical inversion method; thermal conductivity, specific heat, and other thermal parameters of concrete were regarded as constant values, and the changes of the concrete thermodynamic parameters in the hydration exothermic process were not taken into account. Cui et al [11] carried out some experiments to study the temperature change rules of the early-age concrete, introduced the thermal conductivity and specific heat considering the hydration degree, and simulated the temperature field by the finite element method. Erefore, it is urgent to research the thermal parameters considering the hydration degree during the entire curing ages, in order to provide suitable parameters for the thermal model and simulate the temperature field of concrete structure accurately. The results from three different algorithms were compared and analyzed thoroughly, showing that the temperatures obtained from the approach proposed in this paper are closer to the experimental data than others
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