Instytut Podstawowych Problemów Techniki

Streszczenie:

The procedure of numerical identification of thermophysical properties of concrete during its hardening is presented. Heat of cement hydration, thermal conductivity and specific heat are determined for purpose of modelling temperature evolution in massive concrete elements. The developed method is based on point temperature measurements in a cylindrical mould and the numerical solution of the inverse heat transfer problem by means of direct search optimization algorithm. The determined thermal characteristics of concrete are not constant and depend on the maturity of concrete. The procedure was verified on set of concrete mixes designed with Portland cement CEM I 42.5R and Portland-slag cement CEM II/B-S 32.5 N. Calcareous fly ash was also used for partial replacement of cement in the mixtures. The obtained results have been compared with experimentally measured temperature in concrete and a fair agreement has been found.

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The paper presents an application of modeling acoustic waves propagation in a carbon fiber reinforced plastic (CFRP) plates for damage detection. This task is a part of non-destructive testing (NDT) methods which are very important in many industry branches. Propagation of Lamb waves is modeled using three-dimensional finite element method by means of commercial software. In the paper three different cases of plate structures with and without flaws are considered to present review of selected methods for the detection of defects in time and frequency domain. These are comparisons of: A-scans, B-scans, dispersion curves, spectrograms, scalograms and energy plots. Developed numerical model first has been validated by means of analytical solution for isotropic plate.

Słowa kluczowe:

Lamb waves, non-destructive testing, finite element method, damage detection

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As a measure to avoid thermally induced cracking in massive concrete, mineral admixtures are often added as a substitute for a certain portion of cement. This paper presents the results of testing in course of which the temperature was measured during hardening of concrete mixtures produced with addition of calcareous fly ash obtained from the Power Station in Bełchatów, Poland. The investigation covered 76 concrete mixtures produced with three different aggregates and diverse binder content. In the experimental part of the research, the thermal parameters of hardening concrete were determined with a specially developed method in which the mixture was placed in a one-dimensional mould which allowed for unrestrained flow of heat in one direction. The results of testing were used to assess the influence of the respective ingredients, in particular calcareous fly ash, on the rate of rise of the fresh concrete temperature, on the time of occurrence of the maximum temperature and on the temperature gradients. Finally, a formula for calculating the specific heat of hydration depending on the mixture composition was proposed.

Słowa kluczowe:

high calcium fly ash, fresh concrete temperature, heat of hydration, massive concrete, multicomponent cement, temperature gradient

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This paper describes the concept of monitoring the massive concrete structures based on the inverse problem solution. Properties of young concrete are changing very intensively in the early stage of hydration process, and therefore it is very important to know material constants as a function of age of concrete in order to accurately modeling the phenomena occurring in it. The main idea is to determine the time-dependent thermal properties of concrete on the basis of point temperature measurements in a small laboratory molds. Then, based on these parameters, the coupled thermo-mechanical equations are solved to describe the maturation and aging of concrete. This allows to specify (at the design stage) the potential risk of structural damage (e.g. thermal cracking) and thus prevent them e.g. through the use of intelligent cooling systems. Own, based on finite element method, software TMC (Thermal & Mechanical modeling of Concrete) gives also the possibility of predicting the formation of cracks during the aging of structure, which will be verified by means of electric sensor networks (so called ELGRID). This integration will enable to provide a complete system for monitoring and prediction of the structural stress state and damage development.

Słowa kluczowe:

Early Age Concrete, Inverse Heat Transfer Problem, Thermal Cracking of Concrete, Thermal Stress

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Streszczenie:

The paper presents the procedure of determining the thermophysical properties of concrete: heat of hardening, thermal conductivity and specific heat, which is based on point temperature measurements in a cylindrical mold and the numerical solution of the inverse heat transfer problem. The procedure was tested on concrete materials made with high-calcium fly ashes. The obtained results show good agreement with the real values of individual parameters and can be used to determine the temperature field in the object of any complex shape.

Słowa kluczowe:

calcerous fly ash, heat equation, inverse problem, massive concrete, thermal gradient

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A numerical and experimental investigation on thermal behavior of young concrete is presented. It haseen performed to establish the range of possible applications of concrete containing non-standard addition of reactive high calcium fly ash. The proposed model of temperature distribution in hardening concrete is based on the non-linear IH TP (inverse heat transfer problem ) solution. Changes in properties of concrete during setting and hardening are included in the model. The proposed approach consists of several stages. First the temperature measurements in a one-dimensional form are performed using real size concrete materials. Then the method of lines is used to solve the one dimensional heat equation. The results are treated as an input to IHTP for determination of thermal properties of concrete: specific heat capacity, thermal conductivity and heat of hardening. To solve IHTP the pattern search method is used, which does not require the calculation of the gradient of the objective function. In the third step the direct heat conduction problem is solved. Own, based on finite element method, software TMC (Thermal & Mechanical modeling of Concrete) is used to predict temperature field. The obtained numerical results have been compared with experimentally measured temperature in concrete and a fair agreement has been found

Słowa kluczowe:

early age concrete, inverse problem, heat transfer, high calcium fly ash

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