The aim of this work was to examine the influence of the addition of aerogel particles on the properties of cement composites manufactured using fly ash aggregate. The composites were tested at three different concentrations of water saturation of the coarse aggregate. Moreover, two methods of aerogel particle application were used – plasticising the mix with superplasticiser and aerating with an air-entraining admixture. An assessment of the thermal properties was made during the first 28 d of curing of the composites and compressive strength tests were conducted after 7 and 28 d. For pore structure characterisation, mercury pore structure analysis was carried out on the pure aerogel, the cement composites and the composites with the addition of granulate. The data obtained indicate that adding aerogel particles to concrete composites is an appropriate method of improving thermal parameters: thermal conductivity coefficients were two times smaller compared with control samples without aerogel and, simultaneously, the volumetric specific heat was comparable to that of the control samples. However, the addition of aerogel resulted in a reduction in compressive strength to approximately only 30% of that of the control samples.

This study examines the thermal parameters of mortars based on different cement type and water-cement W/C ratios. The presented relationships are important from the point of view of thermal insulation of the entire building component, of which the mortar is a part. The thermal properties of the mortar, and in particular its dependence on the degree of moisture, is important information from the point of view of hygrothermal simulations of building components. The moisture effect on the thermal properties was tested using nine mortar types. The study consisted of producing nine types of mortar on the basis of three cements (CEM I 42.5R, CEM II A-S 52.5N, CEM III A 42.5N). For each cement type, three variants of specimens were prepared which differed according to their water/cement ratio (0.50, 0.55 and 0.60). The main research of thermal parameters was carried out using a non-stationary method based on the analysis of changing heat flux readings. The thermal conductivity, volume-specific heat and thermal diffusivity values were analyzed. The tests performed allowed for determination of the density of specimens, water absorbability and thermal parameters in three water saturation states: dry, natural and wet. Additional microstructural tests were performed using mercury intrusion porosimetry. The obtained parameters were used to determine the relationship between the measured properties. An adverse effect of dampness on the thermal insulation of the studied materials was confirmed. In extreme cases, the increase in thermal conductivity due to material high moisture was 93%. The cement used affects the relationship between the total specific surface area and the W/C ratio. As expected, the total porosity of specimens was higher for mortars with higher W/C ratios. A strong correlation has been demonstrated between the total surface area and thermal conductivity. The opposite results were obtained when assessing the relationship between the total specific surface area and water absorbability. In case of specimens CEM II A-S 52.5N, the relation was the proportional, and in specimens CEM III A 42.5N, the relationship was inversely proportional to the W/C ratio.

The aim of the research was to determine how the admixture of nanosilica affects the structure and mechanical performance of cement concrete exposed to high temperatures (200, 400, 600, and 800 °C). The structural tests were carried out on the cement paste and concrete using the methods of thermogravimetric analysis, mercury porosimetry, and scanning electron microscopy. The results show that despite the growth of the cement matrix’s total porosity with an increasing amount of nanosilica, the resistance to high temperature improves. Such behavior is the result of not only the thermal characteristics of nanosilica itself but also of the porosity structure in the cement matrix and using the effective method of dispersing the nanostructures in concrete. The nanosilica densifies the structure of the concrete, limiting the number of the pores with diameters from 0.3 to 300 μm, which leads to limitation of the microcracks, particularly in the coarse aggregate-cement matrix contact zone. This phenomenon, in turn, diminishes the cracking of the specimens containing nanosilica at high temperatures and improves the mechanical strength.

The thermal and strength properties and microstructural characteristics of lightweight composites composed of cement matrices aerated by various methods are evaluated. The influence of methods that increase the overall porosity of the cement composites and their overall effect on the thermal and strength properties of the composites are discussed. The porosity of the composites was increased using either an air-entraining admixture, reactive aluminum powder, or aerogel particles. The porosity distribution graphs determined by using mercury and optical porosimetry are presented. A discussion on the technical difficulties that arise during porosity evaluation of the composites with aerogel additive is reviewed. The increased porosity of individual composites results in a significant reduction of the thermal conductivity coefficients, $\lambda$ . Relatively low values of $\lambda$ were observed in concretes aerated with the air-entraining admixture and with aerogel particles. Simultaneously, none of the composites showed any significant decrease of the volumetric specific heat, $c_v$ . However, aeration of the composites brought about a strong reduction of the compressive strength. The biggest drops were observed for the concretes with air-entraining admixture.

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.