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The increasing volume of waste and the requirements of sustainable development are the reasons for the research on new waste management concepts. The research results presented in this paper show the effect of recycled aggregate on the selected properties of cement concrete. The aggregates obtained from three types of wastes are tested: recycled concrete paving, crushed ceramic bricks, and burnt sewage sludges. The recycled aggregates replaced 25% and 50% of the volume of the fine aggregate. The tested aggregates worsen the concrete mixes' consistency and decrease, to some extent, the compressive strength of the concrete. However, the tensile splitting strength of the concrete with recycled aggregates is similar to that of the reference concrete. Using recycled aggregates worsens the tightness of the concrete, which manifests itself by increasing water penetration depth. The thermal properties of concrete are slightly affected by the type and content of the recycled aggregate. Considering the expected improvement in recycled aggregate processing, they can be an alternative to natural aggregates. Using recycled aggregates in cement concrete requires extensive studies to search for ways to increase their possible content without worsening concrete performance. [ABSTRACT FROM AUTHOR]

The influence of the silica fume (SF) addition on the basic mechanical and thermal parameters of cement concrete was presented in this paper. Numerous studies show that the specific properties of silica fume allow producing concretes with increased strength and durability properties. However, the results of the authors’ own studies demonstrated that under specific circumstances, the SF addition can negatively affect the strength of cement concrete. In this paper, the concretes made from two types of coarse aggregate, 4–8 mm fraction: reference ordinary gravel aggregate (Ref) and broken basalt aggregate (Bas) were tested. Comprehensive tests (microstructural, strength and thermal) were carried out on three formulas: the first one (Ref-0) did not contain any additives or admixtures. Silica fume and superplasticizer were used in the second formula (Ref-8), introduced in the amount of 8% and 0.75% of the cement’s weight, respectively. The third formula, based on basalt aggregate (Bas-8), also contained silica fume and a superplasticizer, dosed in the same amount as in the second formula. Porosimetric studies showed that the use of silica fume in the Ref-8 formula resulted in a decrease in the number of pores smaller than 0.15 μm in comparison to the Ref-0 reference concrete without the silica fume. On the other hand, numerous additional pores with diameters ranging from 0.05 to 300 μm were found in the Bas-8 concrete. In turn, optical porosimetry proved that the basalt-based concrete had numerous pores in the range above 70 μm, which were not observed in the case of the concretes with ordinary pebble aggregate. In the case of the normal concrete, the addition of silica fume resulted in an increase in the compressive strength. However, the basalt-based concrete, due to its much higher porosity, achieved significantly lower strength values. The results showed that the observed changes in porosity, caused by the presence of silica fume, resulted in lower values of thermal conductivity and specific heat of mature composites that it had been added to. This was particularly evident for the basalt-based concrete. [ABSTRACT FROM AUTHOR]

This study characterizes the hygrothermal and microstructural properties of cement composites containing aluminosilicate cenospheres. It involved the preparation of six mortar mixtures based on CEM I 42.5R cement, in which cenospheres accounted for 0 to 100 % of the aggregate content. The research included measurements of thermal properties, compressive and bending strength tests, density tests on the cured mortars, determination of pore distribution and total porosity, and qualitative assessment of the cenosphere-cement matrix contact zone. However, the main emphasis was on moisture-related parameters. The publication discusses the effect of using cenospheres as a substitute for natural sand on water absorption, capillary absorption, and the sorption and desorption of water by the tested composites, along with the influence of individual microstructural properties on moisture properties. The results showed that increasing the amount of cenospheres added as a sand substitute contributed to an increase in the water absorption of the composite and in parallel reduction in the capillary rise coefficient. The increase in the content of cenospheres caused also a clear increase in the sorption capacity of mortars. Moreover as the statistically average distances between the pores decreased, the thermal conductivity of the composites also decreased. Both when considering the porosity and the spacing factor, the conductivity decrease with wet composites was faster than with dry ones. With decreasing distances between the pores, the compressive strength also decreased significantly. Higher content of cenospheres also reduced the density of the composite and at the same time, increased the specific surface area, which contributed to the reduction in the capillary absorption coefficient and the increase in the durability of the entire composite. In addition, relatively good insulating properties of these composites (λ as low as 0.25 W/mK) in comparison to ordinary cement-based mortars make them interesting alternative to traditional solutions, while the appropriate mechanical strength (compressive strength in the range of 37.68 to 17.74 MPa) makes them suitable even for use as structural elements. • Increase in the content of cenospheres caused an increase in the sorption capacity. • Desorption of cement composites with the addition of cenospheres was irreversible. • The addition of cenospheres reduced the spacing factor and thus reduced the capillary rise. • With decreasing distances between pores, the compressive strength decreased. • Higher content of cenospheres translated into an increase in the total water absorption. [ABSTRACT FROM AUTHOR]

• Very good heat wave damping properties of aerogel-incorporated concretes. • Relatively high values of the volumetric specific heat for composites with aerogels. • High internal thermal admittance of aerogel-incorporated concretes. • Good low periodic thermal transmittance of aerogel-incorporated concretes. • High relations between the thermal transmittance to concrete density and heat flux. This study characterizes the dynamic thermal properties of aerogel-incorporated cement composites and other lightweight concretes. The tested specimens were prepared based on three types of aggregates: expanded clay, sintered fly ash aggregate and natural stone aggregate as a reference. The primary method of increasing the overall composite porosity was to prepare specimens by adding aerogel particles. A second method of increasing the cement matrix porosity was obtained using an air-entraining agent. The microstructure of the tested concretes was examined by mercury porosimetry. The novelty of the manuscript is that it presents the comparison of dynamic properties of concretes with the addition of aerogel and other types of lightweight concretes. Thermal properties tests were performed utilizing a non-stationary method. Based on experimentally obtained thermal properties, the values of dynamic thermal characteristics of the tested composites were calculated. The essential part of the experimental research were the tests carried out in non-stationary heat flow conditions in the analyzed composites. The aim of this research was to assess the influence of the thermal properties of a given composite on its behavior in changing temperature conditions. Having the data of the temperature change in specimens and the thermal properties of the tested composites, the total temperature increase, change of the accumulated thermal energy, heat flux, and densities were determined. Based on the experimental data, relationships between physical properties and dynamic thermal characteristics were evaluated. [ABSTRACT FROM AUTHOR]

The paper examines the impact of aggregate shape on the compressive strength and thermal properties of concretes with silica fume based on two different aggregates: natural round gravel aggregate and crushed basalt aggregate. Compressive strength and thermal properties of individual concretes were determined during the first year of specimens curing. Additionally, porosity tests were conducted using mercury intrusion porosimetry and optical porosimetry. Mercury porosimetry tests showed that the use of silica fume led to a decrease in the content of pores of size smaller than 0.15 µm compared to the reference concretes without the addition of silica fume. However, tests carried out on crushed basalt-based concrete showed the presence of numerous additional pores with diameters ranging from 0.05 to 300 μm. In case of natural round gravel aggregate-based concrete, the addition of silica fume brought about an increase in its compressive strength. In turn, basalt-based concrete exhibited notably lower compressive strength values due to significantly higher porosity within the range of more than 70 μm. In basalt concrete, the obtained λ values are much lower than in concretes with normal gravel aggregate. In addition, the specific porosity structure had its impact on the process of drying of specimens of each group which occurred at a significantly faster rate in the basalt-based concrete. In conclusion, it can be stated that the use of crushed basalt aggregate causes a significant aeration of concrete, even despite the use of silica fume. As a result, the concrete based on crushed aggregate is characterized by a definitely lower compressive strength, but also better thermal insulation properties compared to analogous concrete made on natural round gravel aggregate. [ABSTRACT FROM AUTHOR]