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1

Evolutionary identification method for determining thermophysical parameters of hardening concrete

Długosz Adam, Pokorska Iwona, Jaskulski Roman, Glinicki Michał A.

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 1

585--598

EN

The kinetics of heat transfer in hardening concrete is a key issue in engineering practice for erecting massive concrete structures. Prediction of the temperature fields in early age concrete should allow for proper control of the construction process to minimize temperature gradients and the peak temperatures, which is of particular importance for concrete durability. The paper presents a method of identification of the thermophysical parameters of early age concrete such as the thermal conductivity, the specific heat, and the heat generated by cement hydration in time. Proper numerical models of transient heat conduction problems were formulated by means of finite-element method, including two types of heat losses. The developed experimental–numerical approach included the transient temperature measurements in an isolated tube device and an in-house implementation of an evolutionary algorithm to solve the parameter identification task. Parametric Bezier curves were proposed to model heat source function, which allowed for identifying such function as a smooth curve utilizing a small number of parameters. Numerical identification tasks were solved for experimental data acquired on hardening concrete mixes differing in the type of cement and type of mineral aggregate, demonstrating the effectiveness of the proposed method (the mean-squared error less than 1 °C). The proposed approach allows for the identification of thermophysical parameters of early age concrete even for mixtures containing non-standard components while omitting drawbacks typical for classical optimization methods.

2

The properties of mass concrete with CFBC fly ash-slag binder

Machowska Agnieszka

Archives of Civil Engineering

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2020

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Vol. 66, nr 4

471--484

EN

The manuscript presents the research results concerning the properties of concrete with non-clinker, low-emission binder composed of by-products from metallurgy and power industry: ground granulated blast furnace slag and fly ash from circular fluidized-bed combustion of brown coal. The binder was added in five proportions. The consistency and air content of the concrete mix were measured, as well as the temperature of the concrete mix during hardening. The compressive strength of the hardened concrete was investigated in three periods of samples’ curing: after 28, 90 and 360 days. Also the penetration depth of water under pressure and freeze and thaw resistance of concrete samples were investigated. The results confirm the possibility of application of slag-CFBC fly ash binder for mass concrete due to low temperature during hardening. The obtained results of the compressive strength and penetration depth of water under pressure reveal the influence of changing the proportion of the binder ingredients, as well as the sample damage during testing the freeze/thaw resistance. The CFBC fly ash-slag binder can be used for mass concrete, hydrotechnical concretes in particular, but excluding the zones exposed to frost.

PL

W artykule przedstawiono wyniki badań betonu wykonanego z udziałem niskoemisyjnego, bezklinkierowego spoiwa, powstałego przez zmieszanie mielonego granulowanego żużla wielkopiecowego i popiołu lotnego z fluidalnego spalania węgla brunatnego (w pięciu proporcjach dozowania składników spoiwa, przy stałym w/s=0,5). W celu ustalenia wpływu spoiwa żużlowo-popiołowego na właściwości mieszanki betonowej wykonano badania konsystencji mieszanki metodami stożka opadowego wg PN-EN 12350-2 [12] i stolika rozpływowego wg PN-EN 12350-5 [13], badania zawartości powietrza i zmian temperatury mieszanki podczas twardnienia. Wykonanie mieszanki betonowej bez dodatku domieszki upłynniającej jest niezwykle trudne ze względu na wysoką wodożądności i rozwiniętą powierzchnię właściwą ziaren zastosowanego popiołu lotnego. Dodatek domieszki umożliwił uzyskanie konsystencji S4 wg [12] i F3÷F5 wg [13]. Zawartość powietrza w mieszance wyniosła 0,9÷1,2%. Zmierzona temperatura twardnienia betonu wykonanego według pięciu receptur wskazuje na możliwość wykorzystania do wykonania betonu masywnego (maksymalna temperatura twardnienia 26°C).

3

Formation of temperature cracks of concrete in high-rise buildings and the corresponding measures

Guo L.

Archives of Civil Engineering

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2019

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Vol. 65, nr 4

177--188

EN

A lot of heat will generate in mass concrete after pouring to form temperature cracks, which will reduce structural stiffness. This paper briefly introduces the principle of solid heat conduction and the cause of temperature crack formation and then used COMSOL software to simulate and analyze the mass concrete. The results showed that the simulation model had enough reliability to analyze the temperature change; the internal and external temperature of concrete rose first and then decreased; the formation of temperature crack was related to the internal and external temperature difference; the internal and external temperature difference was inversely proportional to the heat conductivity coefficient of concrete and directly proportional to the pouring temperature. Then, according to the analysis results, two measures were put forward to prevent temperature cracks in mass concrete: selecting concrete materials with high thermal conductivity, i.e., selecting coarse aggregate and fine aggregate with larger heat conductivity coefficient and reducing concrete pouring temperature, i.e., selecting cement with lower hydration heat, paying attention to temperature reduction in the process of concrete stirring, and reducing the amount of cement.

4

The influence of thermodiffusion cross effect on the temperature and moisture distribution in early age mass concrete

Klemczak B.

Architecture Civil Engineering Environment

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2010

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Vol. 3, no. 3

55-62

EN

The issues related to the determination of the thermal and moisture fields in the early age massive concrete are discussed in the paper. The coupled equations, which govern the heat and mass transfer in early age mass concrete as well as the initial and boundary conditions are presented. Next, the discretization in the space was made with the use of the finite element method and the finite difference method was introduced for the discretization in time. As the result the matrix form of the heat and moisture transfer equations was obtained. To recognize the real influence of the thermodiffusion cross effect on the distribution of the temperature and moisture over the curing process, a few comparative analyses were done. The object of the conducted analyses was the massive foundation slabs.

PL

Zagadnienia prezentowane w artykule są związane z wyznaczaniem pól termiczno-wilgotnościowych w początkowym okresie twardnienia betonowych elementów masywnych. Przedstawiono sformułowanie wariacyjne zagadnienia początkowo-brzegowego, które opisuje zjawiska termiczno-wilgotnościowe w konstrukcji masywnej. Wykorzystując metodę elementów skończonych, dokonano dyskretyzacji zagadnienia w przestrzeni, natomiast dyskretyzacji w czasie dokonano za pomocą metody różnic skończonych. W rezultacie otrzymano macierzową postać równań termodyfuzji w twardniejącym betonie. Celem zaprezentowanych analiz numerycznych masywnych płyt fundamentowych było zbadanie wpływu krzyżowego efektu termodyfuzji na rozkład pól termicznych i wilgotnościowych w czasie procesu twardnienia betonu.

5

Modelowanie efektów termiczno-wilgotnościowo-mechanicznych w masywach betonowych

Majewski S., Klemczak B.

Zeszyty Naukowe. Budownictwo / Politechnika Śląska

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2007

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z. 111

293-304

PL

W artykule krótko omówiono możliwości modelowania efektów termiczno-wilgotnościowo-mechanicznych występujących w betonowych konstrukcjach masywnych. Przedstawiono autorski model fenomenologiczny, który może być wykorzystywany w ocenie ilościowej efektów zachodzących w konstrukcjach masywnych. Omówiono również możliwości rozbudowy modelu w ramach teorii lepkoplastyczności.

EN

The different approaches to modeling the thermo-moisture-mechanical effects specific for the massive concrete structures have been briefly presented in the paper. The original phenomenological model developed to estimate these effects in the massive concrete was presented. The possibilities of further development of the authors' model have been also discussed with respect to the viscoplasticity.