The paper presents results of investigations of compressive strength and shrinkage of concrete samples made on the basis of the Portland cement CEM I 32.5R, after 2, 7, 14, 28, 90, and 365 days of maturation in four different maturation conditions. It was shown that after 28 days the samples cured according to the standard in the cuvettes with water achieved the highest compressive strength, although the early-age compressive strengths after 7 and 14 days were lower than those for the samples cured in building film and in dry conditions. A determined correlation between the compressive strength and shrinkage of the concrete proves that wet curing also allows a total elimination of the shrinkage in the first 28 days. Along with the growth of the compressive strength, the drying shrinkage reduces. Obtained results confirmed that the best way of concrete curing, among the analyzed methods, from the point of view of both compressive strength and volume changes is the wet curing.
Concrete is a highly alkaline material; therefore, the presence of organic acids (acetic, butyric, lactic) from agricultural sewage constitutes a threat to the concrete and the environment. The investigations were aimed at simulating the influence of highly concentrated organic acids on concrete elements of livestock buildings. Cubic samples 100 × 100 × 100 mm of the ordinary concrete were immersed in 10% acetic acid for 270 days. Then, the compressive strength and mass decrement of the samples were determined as well as using SEM images and a 3D-profilograph to profile the surface roughness and depth of changes evoked in the structure of the samples by penetrating acid. The results were compared with those for a control sample (not subjected to the effects of aggressive agents) as well as for samples placed in a neutral and alkaline environment. The compressive strength of the samples stored in the acidic environment was 22.23% lower than that of the control sample, whereas the compressive strength of those samples stored in an alkaline environment were 44.27% higher. Conclusions from these investigations can be of innovative importance in the preparation of environmental impact reports, which are necessary for obtaining permission for the construction and use of livestock buildings, and afterward in the reduction of the impact of these buildings on the environment and surface and underground water resources.
The object of analysis is a heat conduction problem within the framework of tolerance modelling in laminated media with a functional gradation of effective properties. In contrast to the known asymptotic models (based on the homogenization technique), the characteristic feature of the tolerance model equations is that they make it possible to analyze the effect of the microstructure size on the overall behavior of the laminate. The proposed model equations describe heat conduction in laminates by mean of partial differential equations with smooth and slowly varying functions. This paper describes a certain extension of the unified tolerance modelling procedure, which makes it possible to analyze specific problems of heat conduction in laminates with a transversal gradation of effective properties.
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