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Electromagnetic properties of cement paste after microwave pretreatment

Li Yue, Liu Yunze, Jin Caiyun

Archives of Civil and Mechanical Engineering

2023

Vol. 23, no. 3

art. no. e185, 2023

In this paper, the effect of microwave pretreatment on the electromagnetic properties of cement paste was investigated. Four different durations of microwave pretreatment were carried out after the standard conditioning of cement paste specimens for 3 days. Subsequently, the electromagnetic properties of the cement paste were tested, the electromagnetic losses of the specimens were calculated and the changes in the dielectric constants were analyzed. Finally, the mechanism by which microwave pretreatment affects the electromagnetic properties was analyzed based on the pore characteristics and hydration results. The results show that microwave pretreatment can improve the electromagnetic loss as well as the dielectric constant of cement paste specimens, but has no significant effect on the magnetic permeability. With the increase of microwave pretreatment time, the reflection loss, absorption loss, and total loss of electromagnetic waves increase significantly, and the multiple reflection loss decreases. The real part of the dielectric constant, imaginary part, and loss angle tangent all increased. There are two main reasons for the increase in electromagnetic loss and dielectric properties of the specimens after microwave pretreatment. One is the significant increase in the percentage of micropores less than 50 nm in the specimen, which increases the reflection loss and absorption loss of electromagnetic waves. On the other hand, microwave pretreatment significantly increased the degree of hydration of the specimen, making the specimen intermediate electrical properties of the larger proportion of the material phase (such as gel), which in turn increased the electromagnetic loss.In this paper, the effect of microwave pretreatment on the electromagnetic properties of cement paste was investigated. Four different durations of microwave pretreatment were carried out after the standard conditioning of cement paste specimens for 3 days. Subsequently, the electromagnetic properties of the cement paste were tested, the electromagnetic losses of the specimens were calculated and the changes in the dielectric constants were analyzed. Finally, the mechanism by which microwave pretreatment affects the electromagnetic properties was analyzed based on the pore characteristics and hydration results. The results show that microwave pretreatment can improve the electromagnetic loss as well as the dielectric constant of cement paste specimens, but has no significant effect on the magnetic permeability. With the increase of microwave pretreatment time, the reflection loss, absorption loss, and total loss of electromagnetic waves increase significantly, and the multiple reflection loss decreases. The real part of the dielectric constant, imaginary part, and loss angle tangent all increased. There are two main reasons for the increase in electromagnetic loss and dielectric properties of the specimens after microwave pretreatment. One is the significant increase in the percentage of micropores less than 50 nm in the specimen, which increases the reflection loss and absorption loss of electromagnetic waves. On the other hand, microwave pretreatment significantly increased the degree of hydration of the specimen, making the specimen intermediate electrical properties of the larger proportion of the material phase (such as gel), which in turn increased the electromagnetic loss.

Studium przypadku wzrostu właściwości mechanicznych betonu w oparciu o pomiary temperatury

Zych M.

Cement Wapno Beton

2015

R. 20/82, nr 6

383--392

W pracy przeprowadzono pomiary temperatury betonu i jej wpływu na zwiększanie właściwości mechanicznych dwóch różnych betonów, w procesie dojrzewania. Przygotowano stanowisko badawcze pozwalające na mierzenie zmian temperatury występujących w rdzeniu betonowych elementów masywnych. Na tej podstawie określono ilość wydzielonego ciepła przez cementy, zarówno w warunkach semi-adiabatycznych jak i adiabatycznych. Dane te pozwolą na dokładniejsze analizy konstrukcji masywnych, narażonych na zarysowanie termiczne, w okresie dojrzewania betonu. Wyniki zweryfikowano za pomocą metody elementów skończonych, uzyskując dobrą zgodność z wynikami badań. Właściwości mechaniczne betonu, w zależności od zmian temperatury, opisano wzorem Byforsa, stwierdzając równocześnie, że współczynniki w tym wzorze różnią się bardzo znacznie w przypadku betonu klas C20/25 i C30/37. Stosowanie tego wzoru wymaga więc uwzględnienia składu betonu, a przede wszystkim rodzaju stosowanego cementu.

In the work the change of concrete temperature and its influence on the increase of mechanical properties of two types of concrete was examined. The special stand was constructed which gives the possibility of temperature measurement, in core of concrete massive elements and on their surface. On this basis the heat of cements hydration, in semi-adiabatic and adiabatic conditions was determined. These results will give the possibility of more precise analysis of massive concrete construction, particularly the evaluation of cracks formation due to temperature gradient, in the period of cement hydration. The results were verified applying the method of finished elements, which are showing the good correlation with the experimental data. The concrete mechanical properties were defined, as a function of temperature, with Byfors formula and it was simultaneously found that the formula coefficients have different values in the case of concrete classes 20/25 and 30/37. Thus this formula applying needs to take into account the concrete composition, chiefly the type of cement used.