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2 2024

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Testing the variability of the chloride ion diffusion coefficient depending on the concrete curing time

Szweda Zofia

Ochrona przed Korozją

2024

nr 7

190--194

This paper presents tests and results on the penetration of chloride ions, accelerated by an electric field, into concrete specimens made of lightweight concrete with foam glass filling. The tests were carried out in four series, depending on the curing time of the concrete, namely after 7, 14, 28 and 56 days of curing at 100% humidity. Based on the chloride ion concentration values obtained, the diffusion coefficients were determined using a thermodynamic migration model. During the first two weeks, the diffusion coefficient value increased by 18% from the value obtained after 7 days of curing. After a longer curing period (28 days), the value of the coefficient decreased by 22% from the initial value. After a further 28 days, there was a further downward trend in the value of the diffusion coefficient of as much as 78% from the initial value.

W pracy przedstawiono przebieg i wyniki badań wnikania jonów chlorkowych, przyspieszonego polem elektrycznym, do próbek betonowych wykonanych z betonu lekkiego z wypełnieniem ze szkła piankowego. Badania wykonano w czterech seriach w różnym czasie dojrzewania betonu: po 7, 14, 28 oraz 56 dniach dojrzewania w warunkach 100-procentowej wilgotności. Na podstawie uzyskanych wartości stężenia jonów chlorkowych wyznaczono wartości współczynników dyfuzji z wykorzystaniem metody termodynamicznego modelu migracji. W ciągu pierwszych dwóch tygodni wartość współczynnika dyfuzji wzrosła o 18% w porównaniu z wartością uzyskaną po 7 dniach dojrzewania betonu. Po dłuższym okresie dojrzewania (28 dniach) wartość współczynnika zmalała o 22% w stosunku do wartości początkowej. Po kolejnych 28 dniach nadal obserwowano tendencję spadkową wartości współczynnika dyfuzji, wynoszącą aż 78% w stosunku do wartości początkowej.

Frost Resistance of Concretes with Low-Clinker Cements Depending on Curing Time

Góra Jacek, Grzegorczyk-Frańczak Małgorzata

Advances in Science and Technology. Research Journal

2024

Vol. 18, no 6

406--421

The article presents the results of tests on the frost resistance, water absorption, and compressive strength of concretes made with three types of cement: CEM I, CEM II/B-M (S-V), and CEM III/A, evaluated after different curing periods (28, 56, and 90 days). Additionally, to assess the effects of the minimum 4% air entrainment recommended by the EN 206 standard, concrete mixes with the same composition but containing an air-entraining admixture in a constant amount of 0.15% by cement mass, were prepared. For a more comprehensive characterization of the concretes, tests were also conducted on the concrete mixes and the physical properties of the concretes, such as density, water absorption, and total porosity, were determined. The paper also presents significant results on the pore distribution in the air-entrained concretes, confirming the achievement of very good basic air-entrainment parameters in all concretes. Based on the test results, it was found that both the type of cement and the introduction of an air-entraining admixture significantly influence not only the frost resistance of the concretes but also their compressive strength depending on the curing time of the samples. This is particularly evident in the low-clinker cements CEM II and CEM III. It was observed that in the case of concretes with these cements, it is possible to achieve an almost zero decrease in compressive strength after 150 cycles of freezing and thawing after 90 days of curing.