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The article presents durability results for cement mortars made with the addition of slag from municipal waste incineration plants as a replacement for natural aggregate. The undertaken durability tests included frost resistance tests and evaluation of strength, microstructure, water absorption and abrasiveness before and after 150 freeze–thaw cycles. The work reveals that MSWI slag in amounts up to 50 vol. % caused deterioration in the workability and water absorption of cement mortars, regardless of the type of cement used. This, in turn, resulted in a reduction in the compressive and flexural strengths of the composites compared to mortars made with sand alone. Nevertheless, the use of a higher grade of cement, CEM I 52.5 R, resulted in an increase in compressive strength and thus increased the mortars’ frost and abrasion resistance. In addition, after the induced freeze–thaw cycles, mortars made with MSWI slag showed comparable or higher frost and abrasion resistance than those made using natural aggregate.

This paper presents an analysis of research results for silica aerogel cement composites over the past twenty years. Recently, two trends in the development of these composites have been noted, towards structural applications and towards ultralight composites for coatings and renders. Ongoing research shows that important aspects of cementitious composites with good mechanical performance are the proper selection of aggregates and improved adhesion at the silica aerogel–cement binder interface, which will guarantee high compressive strength with the lowest possible thermal conductivity. The best physicomechanical performance of aerogel cement composites with low thermal conductivity below 0.03 W/(m·K) was obtained when cenospheres and aerogel were used in a weight percentage of 5%. In turn, the prerequisites for using aerogel cement composites as coatings for energy-efficient building façades are the use of large amounts of silica aerogel as a substitute for lightweight aggregates or the selection of an optimal composition of lightweight aggregates and aerogel, ensuring the lowest possible thermal conductivity coefficient. Other important standpoints are water transport and moisture protection of the silica aerogel-based coatings. Therefore, in recent years, more and more elements of the hygrothermal performance, porosity and durability of silica aerogel cement composites have been developed. The article also points out the weaknesses of the application of silica aerogel in the cement matrix, the most important of which are the lack of adhesion at the boundary of the aerogel–cement binder, the increased porosity of the composite, the high water absorption capacity and the significant decrease in compressive strength with large volumes of silica aerogel. Solving these issues will certainly contribute to the wider applicability of these materials in the construction industry.

In recent years, increasing attention has been paid to the durability of building materials, including those based on cementitious binders. Important aspects of durability include the increase of the strength of the cement matrix and enhancement of material resistance to external factors. The use of nanoadditives may be a way to meet these expectations. In the present study, zinc, titanium and copper oxides, used in single and binary systems (to better the effect of their performance), were applied as additives in cement mortars. In the first part of this work, an extensive physicochemical analysis of oxides was carried out, and in the second, their application ranges in cement mortars were determined. The subsequent analyses were employed in determining the physicochemical properties of pristine oxides: Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray fluorescence (EDXRF), scanning electron microscopy (SEM), measurement of the particle size distribution, as well as zeta potential measurement depending on the pH values. Influence on selected physicomechanical parameters of the cement matrix and resistance to the action of selected Gram-positive and Gram-negative bacteria and fungi were also examined. Our work indicated that all nanoadditives worsened the mechanical parameters of mortars during the first 3 days of hardening, while after 28 days, an improvement was achieved for zinc and titanium(IV) oxides. Binary systems and copper(II) oxide deteriorated in strength parameters throughout the test period. In contrast, copper(II) oxide showed the best antibacterial activity among all the tested oxide systems. Based on the inhibitory effect of the studied compounds, the following order of microbial susceptibility to inhibition of growth on cement mortars was established (from the most susceptible, to the most resistant): E. coli < S. aureus < C. albicans < B. cereus = P. aeruginosa < P. putida.

The response of nonreinforced concrete to high-speed flying fragments depends on many factors such as composition, geometry and boundary conditions of the obstacle. In this study, the authors verified experimentally a series of concrete slabs with various aggregate types and amounts of steel reinforcement. The material properties were previously developed and verified during the laboratory experiments with standard cubic specimens. Moreover, the main goal of this research was the verification of high-strength concrete plates using different kinds of aggregate, that is, traditional gravel, granite, basalt and amphibolite subjected to the military bullet impact. It is known that the aggregate filled about 70% of total concrete volume, and therefore, the properties of aggregate, like density, strength and surface will be the main factors influencing the concrete strength and further concrete resistance to projectiles. The research presented shows that the type and shape of aggregate determined the conditions of concrete failure. The outcomes show that the obtained compressive strength varied between 60 and 80 MPa. In the second stage of the test, randomly distributed reinforcement was added to selected concrete mixtures. Hooked steel fibres with an aspect ratio of 50 in the amounts of 50 and 100 kg per cubic metre were applied. The influence of steel fibres on the concrete properties was verified in compressive and splitting strength tests. On the basis of preliminary laboratory tests, the final slab specimens, with the dimensions of 0.5 × 0.5 m and 0.05 m thickness, were produced. The final verification was performed in the real field conditions using the most popular military bullet, whose kinetic energy was more than 2000 J. The measurements of the initial and final velocities of the bullets and concrete fragments were obtained using high-speed camera measurement equipment. The final failure of the slabs was presented as the primary outcome.

The intensive development of construction in recent years and the increasing demands on the durability and service life of buildings have increasingly caused construction scientists to pay attention to new material solutions based on nanotechnology. One of these solutions is the use of titanium dioxide, with its photocatalytic and antibacterial properties, in building materials. Although this solution has been known for decades, there are few articles that review the latest trends in this area. Compared with other literature studies, this article pays particular attention to the possibility of modifying nanotitania to expand its photocatalytic properties, and analyzes the effects of these alterations on the self-cleaning, air-depolluting and antibacterial properties of building materials, mainly cement-based composites. It is complemented by a section dedicated to the mechanical and durability properties of pristine and functionalized TiO2-modified building materials, taking into account dispersion methods, rheological and mechanical parameters, as well as resistance to external factors.

Limitations in natural aggregate resources and the continuous increase in the demand for concrete as a building material, as well as the increase in the production of waste and the problem with its storage were the reasons for attempts to replace the sand fraction in cement matrices with a corresponding slag fraction. Municipal solid waste incineration (MSWI) slag, which is a product of waste incineration, can be used as an aggregate. This extends its service life and reduces landfill waste. Therefore, three types of cement mortars with different aggregate composition were prepared. In addition, to increase the durability of the cement matrix and the degree of immobilization of harmful heavy metals and salts present in the slag, a natural zeolite with pozzolanic properties was used. A set of tests was carried out on fresh mortar and hardened mortar, including strength tests after 7, 28 and 360 days. What is more, chemical tests were undertaken, including the content of chlorides and sulfates, leaching using the TCLP method and oxide composition. The conducted tests revealed that all mortars had similar strength properties and demonstrated the effectiveness of immobilizing harmful substances contained in the municipal solid waste incineration (MSWI) slag by cementing.

Inorganic–organic systems based on ZnO or ZnO–SiO2 and lignin were used for the first time to counteract the biodeterioration of cement composites. The stability of the oxide–lignin and interoxide–lignin combinations was confirmed by Fourier transform infrared spectroscopy, while electrokinetic studies confirmed the stability of the systems in the alkaline environment of the cement matrix. Moreover, lignin-enriched admixtures showed very good water wettability, which enabled their uniform dispersion in the cement matrix. Physical and mechanical tests confirmed the retarding effect of zinc oxide on the hydration of the cement binder in the initial setting period, which was manifested by lower mechanical parameters up to the 7th day of setting. The use of interoxide systems with silica balanced this adverse effect. The designed systems based on ZnO and lignin caused the inactivation of both bacterial and fungal pathogens, the effect being weaker in the case of the systems with silica.

In presented research the silica aerogel nanocomposites with carbon microfibers and nanofibers, as well as carbon microfibers/carbon nanotubes hybrid system were investigated. It was shown, that an important element of tailoring the properties of silica aerogel nanocomposite was the right choice of the type and the length of the carbon material. In case of carbon nanofibers with length of 20 nm, the applied amount of fibers was too low to keep the silica aerogel frame in monolith and resulted in obtaining the nanocomposite in form of granulate. Only longer fibers with length of 700 µm gave the monolith structure of silica aerogel nanocomposite. As a result of hybrid reinforcement, which enables reduction of cracking on micro and nano level, a monolith nanocomposite was received, which had very good structural parameters and low contraction during drying. All the received nanocomposites were characterized by good thermal resistance and all applied carbon materials did not deteriorate the high thermal resistance of silica aerogel.

Silica aerogel-based materials exhibit a great potential for application in many industrial applications due to their unique porous structure. In the framework of this study, carbon fiber and nickel coated carbon fiber&ndash, silica aerogel nanocomposites were proposed as effective electromagnetic shielding material. Herein, the initial oxidation of the surface of carbon fibers allowed the deposition of a durable Ni metallic nanolayer. The fibers prepared in this way were then introduced into a silica aerogel structure, which resulted in obtaining two nanocomposites that differed in terms of fiber volume content (10% and 15%). In addition, analogous systems containing fibers without a metallic nanolayer were studied. The conducted research indicated that carbon fibers with a Ni nanolayer present in the silica aerogel structure negatively affected the structural properties of the composite, but were characterized by two-times higher electrical conductivity of the composite. This was because the nickel nanolayer effectively blocked the binding of the fiber surface to the silica skeleton, which resulted in an increase of the density of the composite and a reduction in the specific surface area. The thermal stability of the material also deteriorated. Nevertheless, a very high electromagnetic radiation absorption capacity between 40 and 56 dB in the frequency range from 8 to 18 GHz was obtained.

The paper describes the results of the influence of three metal oxides’ particles: microparticles of Fe 2 O 3 (d ≤ 5 μm) and Fe 3 O 4 (d ≤ 5 μm) as well as nanoparticles of NiO (d ≤ 50 nm) on the cement matrix properties. Four different contents of each metal oxides’ particles were applied: 0.5, 1, 2 and 3 wt.%. The studies regarding different physical and chemical parameters of cement matrix specimens such as compressive strength, water absorption, microscopic and structural properties have been carried out and the results of these studies are presented and discussed. It was shown that the micro and nanoparticles in the amounts of 2÷3 wt.% can influence the cement hydration process and thereby enhance the compressive strength of mortar. The higher enhancement was obtained during the first seven days of hardening due to so called filling effect. In the following stage of hydration the strengthening effect diminished. This phenomena was convergent with the XRD analysis, which proved that the micro- and nano-particles did not react with the cement paste components.

In the latest period, hundreds of concrete viaducts were built in Poland within a short time range. Their characteristic feature was the use of high class concrete containing the CEM I 52.5 cement. The concreting works often took place during winter time. Despite successful laboratory tests, the concrete prepared on the concreting site often did not achieve the assumed freeze-thaw resistance. The lack of freeze-thaw resistance in concrete had an unusual course. A higher than normative decrease of strength with simultaneous high tightness was observed. There was no surface spalling, typical for the low freeze resistance concrete, no edge curvature, etc. In addition, on the sample surface, a characteristic mesh of white leakage of unknown chemical compounds around big aggregate grains was identified. Those compounds were thoroughly investigated with the use the SEM analysis. It was found that the direct reason of lowering the concrete strength after 150 cycles of freezing and defrosting was the occurrence of numerous micro-cracks formed during the hydration of high amount of clinker cement in concrete block. Moreover, these phenomena were enhanced by the occurrence of white, needle-shaped, hard-soluble salts localised in the boundary between aggregate and cement paste. Based on the EDS analysis, these salts were identified as nickel and calcium phosphates, ettringite ana thaumasite formations and others, which delayed cement hydration [1] , [2] , [7] , [8] , [9] . The variety of occurring white salts forced the commencement of model laboratory tests on a specially built station for reproducing the processes taking place during concreting and developing recommendations for the construction workmanship.

The aim of this work was to compare the influence of the electrocorundum and silicon carbide on the strength and the microstructure of the cement composite with the addition of granulated blast-furnace slag, before and after exposition to higher and high temperature. Research proved that compressive strength of the cement composite with addition of Al2O3 in the amount of at least 2 wt.% increased in comparison to the referential samples, regardless of the high temperature, by about 25%, and the best results in the whole temperature range were obtained in case of cement binder with 6 wt.% addition of electrocorundum. On the other hand, addition of silicon carbide resulted in a relevant increase of the sample resistance (by 20-30%) only when added in the amount of at least 10 wt.%.

In presented article the polymer-modified cement mortars with expanded graphite covered by the oligomer film, being a by-product of phenol electro-oxidation, were investigated. The changes in the morphology of EG and EG/oligomer as well as in the microstructure of cement-polymer composites modified with EG/oligomer were verified using the scanning electron microscopy (SEM). The evaluation of adhesion between EG/oligomer and cement-polymer mortar based on the mechanical tests, especially their flexural behavior. It was shown that the oligomer film formed on EG surface made graphite flakes more durable and resistant to bending. Moreover, the oligomer due to the interaction with polymer network in cement-polymer mortar led to the improvement of flexural toughness of composite.

Experimental results on the physical and chemical properties of silica aerogel and its composites with carbon microfibers are reported. The aerogels and silica aerogel/carbon microfibers nanocomposites were prepared via the sol–gel process of organosilicon compound followed by successive washing and drying in different conditions. Part of nanomaterials was surface modified in TMCS/n-hexane mixture in 50 °C and dried in ambient pressure. Simultaneously, the supercritical drying of aerogels and its nanocomposites in CO2 atmosphere was carried out. The carbon microfibers before usage in silica aerogel composites were chemically treated in nitric acid. The physical properties of silica aerogels were studied by measuring the bulk density, volume shrinkage, porosity, pore volume and thermal conductivity. In the case of pure aerogels dried via supercritical conditions, the structure presented much less contraction during drying and was more resistant to higher temperature. However, the properties of silica aerogels composites with carbon microfibers drying in ambient pressure were better than corresponding composites subjected to supercritical drying. It was shown that simultaneous oxidation of carbon fibres and chemical modification of silica aerogel in TMCS/n-hexane mixture contributed to the stable mesoporous structure of composite with very good physical properties, especially lower shrinkage.

Nanoporous silica aerogel–carbon fiber composites were prepared via a sol–gel process by surface modification at ambient pressure. Oxidizing modification of the carbon microfibers improved the adhesion between hydrophilic silica gel and the carbon material surface. Suggested solution contributed to the blocking of hydroxide bonds of silica gel via reaction with the oxidized carbon material surface, which lowered the contraction of gel volume during its drying in atmospheric pressure and led to the more stable structure.

The presented paper contains a brief review on the synthesis and characterization of silica aerogels and its nanocomposites with nanofibers and fibers based on a literature study over the past twenty years and my own research. Particular attention is focused on carbon fiber-based silica aerogel nanocomposites. Silica aerogel is brittle in nature, therefore, it is necessary to improve this drawback, e.g., by polymer modification or fiber additives. Nevertheless, there are very few articles in the literature devoted to the synthesis of silica aerogel/fiber nanocomposites, especially those focusing on carbon fibers and nanofibers. Carbon fibers are very interesting materials, namely due to their special properties: high conductivity, high mechanical properties in relation to very low bulk densities, high thermal stability, and chemical resistance in the silica aerogel matrix, which can help enhance silica aerogel applications in the future.

The purpose of this paper was to prepare the silica aerogel using the sol-gel and supercritical drying processes. The supercritical drying was chosen as the most effective process, ensuring the best properties of product. For this reason the authors designed and built the supercritical dryer stand that allowed drying samples in high pressure and elevated temperature. The obtained silica aerogels exhibited good transparency, homogeneity, and comparable density. The specific surface measured by means of BET analysis equaled 870.5 g/cm.

Compared to concrete, the compressive strength is not a very important property of cement mortar. It is very important that mortar forms a complete, strong, and durable bond with the building material elements, because it is used as an adhesive and sealant material. The physical and mechanical properties of cement mortar, especially flexural strength, toughness, tensile strength, reduction of plastic as well as drying shrinkage, can be enhanced by the use of randomly dispersed fibres, such as steel, carbon or polymer. In the present research there were investigated cement mortars modified with randomly dispersed polypropylene and steel fibres in different volume fraction used both separately and in a hybrid system. The conducted research proved that the low modulus polypropylene fibres with good flexibility added to cement matrix resulted in good properties of fresh mortar and caused the reduction of early age cracking. The beneficial effects of flexible fibres could be attributed to their high aspect ratio and increased fibre availability at a given volume fraction due to their low density. Because of low stiffness, these fibres are particularly effective in controlling the propagation of micro-cracks. It was found that the hybrid combination of metallic and nonmetallic fibres can offer potential advantages in improving cement matrix properties, such as the ultimate strength and toughness of composites.

In this research, the influence of carbon spheres additive on mechanical properties of cement-carbon composites, such as flexural strength, flexural toughness and compression strength, were investigated. Carbon spheres were added to cement mortars in amount of 0.5 wt.%. Chemical treatment in hot nitric acid was applied in order to improve interfacial bonding between carbon fibres and cement mortar.