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Basalt fibers based reinforcing elements for concrete structures (Basalt Fiber Reinforced Polymer bars (BFRP), chopped basalt fibers) are supposed to be more corrosion resistant than the common steel rebars and wires, especially in the marine environment. Mild steel, used for production of conventional concrete reinforcing elements, is well-known for its corrosion resistance in the basic environment provided by cementitious concrete matrix. As the pH of concrete goes down in time due to carbonation and other processes, the steel corrosion is activated. The chloride anion (marine environment) is also acting as mild steel corrosion activator. On the other hand, the basalt fibers are supposed to be resistant to the chloride activation. Concerning the pH effect, basalt is sensitive to the both acid and alkaline environment where its dissolution may take place. It means that it should not be vulnerable to the pH decrease as the mild steel does. The present paper aims to test how the lower pH influences the performance of basalt fibers in cementitious matrix. [ABSTRACT FROM AUTHOR]

This paper is focused on the applicability of natural fibres in combination with lime-based plasters. Two plant-based fibres have been selected, namely wood and colza fibres and are investigated as reinforcing materials for air lime, pozzolanic lime and hydraulic lime plasters. As a pozzolanic material biomass fly ash is employed. The dosage of the fibres is up to 2% by volume with an increment of 0.5%. The mechanical strengths belong among investigated properties. The results show that the natural fibres are promising for air lime and hydraulic lime-based plasters, but they are not applicable in the case of lime plasters with pozzolanic additives. Regarding the two fibre kinds, wood fibres show better performance compared to colza fibres. [ABSTRACT FROM AUTHOR]

Calcium aluminate cement (CAC) provides many advantageous properties, such as rapid strength development, great chemical resistance, and higher thermal resistance than Portland cement (PC). From the point of view of CO2 emission sources, CAC production is slightly less demanding in comparison with ordinary PC, but the need for specific pure raw materials makes CAC more expensive. In order to reduce the Portland clinker consumption in composites, PC is commonly used in blended cement containing many different supplementary cementitious materials (SCMs). In the case of CAC, the choice of appropriate SCMs is more difficult as they can affect not only hydraulic processes and physical properties but also the thermal resistance of the matrix. In this paper, the effect of various SCMs on the physical and chemical processes in low-cement heat-resistant composites based on CAC is analysed. Ceramic powder and calcined clay are found to be the most prospective SCMs, while the application of sintered mullite provides a somewhat worse but still acceptable performance of the studied composites. [ABSTRACT FROM AUTHOR]

This paper deals with the thermal activation of brick clays. The main aim was to assess the possibility of their activation and afterwards also the applicability of such clays as supplementary cementitious materials. Three different brick clays were examined, varied in origin localities, and mainly in chemical and mineralogical composition. Their thermal activation was done at two different temperatures, namely exposure to 550 °C and 600 °C were investigated. The impact of temperatures was found to be of great importance. Clays exposed to 600 °C showed extremely higher specific surface area, and somewhat lower bulk density compared to those treated at 500 °C. Afterwards, blended cement pastes containing 10% of particular thermal activated clays were produced, and at the age of 28 days bulk density, bending strength and compressive strength were measured. The impact of temperature was indisputable. The exposure to 600 °C led to the blended cement pastes which showed better performance than the one treated at the lower temperature. However, the studied properties showed suitable values, and thus this study confirmed, that the thermal activation of brick clays is possible. [ABSTRACT FROM AUTHOR]

Two renovation plasters with blended binder based are presented in this paper. The porosity of plaster was increased by the application of expanded perlite. This lightweight aggregate was used alone as well as in combination with ordinary silica sand. Binder of plaster composed also of two kinds, pure lime were supplied by ceramic powder. This pozzolanic material led to improvement of mechanical properties and therefore should compensate for their lowering caused by plaster lightening. Physical properties such as basic physical, mechanical and durability characteristics were determined, and the results are discussed in this paper. The plaster with lightweight aggregate reached desired high porosity and appropriate water transport characteristics to be applicable in the field of building renovation, while the combination of silica sand with lightweight aggregate showed the water absorption coefficient slightly lower than the requirements of the standard. [ABSTRACT FROM AUTHOR]

The main purpose of the research was to evaluate the abrasion resistance of a composite material made from a combination of flax fiber and bio-based epoxy resin. In the second group of samples, bio-epoxy was enriched with corundum additive. Composite material samples were produced using vacuum infusion technology. A Taber Abraser rotary abrasion machine was used to compare the abrasion resistance of the samples. It was found that the added filler has a significant effect on the abrasion properties. The addition of white corundum microcrystals in the amount of 2% by weight to the adhesive mixture led to a significant increase in abrasion resistance. Furthermore, it was found that despite the thorough control of the manufacturing process, the composite samples contain pores in the epoxy layer, which can affect the mechanical and physical properties. [ABSTRACT FROM AUTHOR]

Silica fume (SF, amorphous polymorph of SiO2) is well known mineral admixture for concrete, especially for High Performance Concrete (HPC) structures like bridges, skyscrapers, tunnels etc. The benefits of SF, compared to other (easily available, lower cost) Supplementary Cementing Materials (SCM), is its high fineness and high content of reactive silica, i.e. high reactivity in hydration process. SF is thus not only substituting the Portland clinker, but also improving the durability measures of concrete, thanks to the better space filling by fine SF particles. Unfortunately, the high reactivity of SF results also to a drawback – intensive pozzolanic reaction of SF obviously means also intensive consumption of Ca(OH)2 and thus a risk of its depletion and of consequent decrease of pH to level where a steel reinforcing elements may corrode. In the contrary, the lower pH is beneficial for durability of basalt-based reinforcing elements. Nevertheless the knowledge of pH development in time is crucial. The present contribution deals with kinetics of individual processes controlling the pH of pore solution: Ca(OH)2 generation by Ordinary Portland cement (OPC) hydration; Ca(OH)2 consumption by carbonation; Ca(OH)2 consumption by pozzolanic reaction. The rate of individual processes was monitored by help of thermogravimetry and XRD. It was found that presence of Silica Fume is promoting the rate of Alite hydration since the SF is consuming the Ca(OH)2, and thus the Alite hydration equilibrium is shifted to the right. [ABSTRACT FROM AUTHOR]

Calcium aluminate cement (CAC) is one of the most often utilized binders for high-temperature applications. However, its production is expensive, and also from an ecological point of view, it is quite demanding. In this study, the new type of binders was designed by replacing a substantial amount of CAC with fine alumina-based materials. Specifically, super reactive alumina and boehmite powder was used to produce low-cement heat resistant binders. Five different ratios of mentioned admixtures were examined. Studied blended cement pastes were characterized through the view of DSC, XRD, and SEM analyses. Moreover, also basic physical properties were measured. Their performance was studied in four temperature states: at ambient temperature and after exposure to 400 °C, 1000 °C, and 1400 °C. Designed binders showed promising composition and sufficiently compact structure to be applicable in high-temperature applications. [ABSTRACT FROM AUTHOR]

This study deals with a utilization of super reactive alumina (RA) and boehmite powder (BP) as a partial replacement of calcium aluminate cement (CAC) in refractory composites. The reason for using these substitutes is their positive effect on the environmental performance of heat-resistant composites, specifically on reducing non-renewable resources consumption, CO2 emissions, and on the overall performance of the resulting composites. The basic physical and mechanical properties of five composite mixtures containing RA and BP were determined at room temperature and after exposure to 400 °C, 1000 °C, and 1400 °C. Both admixtures helped to reach better bending and compressive strength than the reference mixture without a replacement of CAC. It was proved that the replacement of CAC with 11.3% RA and 3.8% BP is a suitable combination which significantly improves the properties of the composite and can be recommended for further applications. [ABSTRACT FROM AUTHOR]

The global production of fired ceramic bricks represents a large environmental burden in form of energy consumption and greenhouse gasses emission. The production process has therefore become an object of interests of several studies aiming at its optimization to reduce the negative environmental impacts. Within these optimizations, the precise knowledge of thermal properties of clays undergoing the firing process is one of the key information that conditions the successful solution of the problem. This paper therefore aims at determination of temperature-dependent thermal conductivity of clays. Using a set of thermocouples, the temperature distribution in the sample is monitored, being exposed to one-sided heating. The temperature field deformation due to presence of metal wires is then overcame using computational modelling that is able to distinguish the particular contributions of clay/thermocouples to the ongoing heat transfer. Based on this assumption, such a thermal conductivity of clay is then sought, that provides the same temperature distribution as the experiment. The thermal conductivity values of clays were found to range between 0.58 W·m−1·K−1 and 1.97 W·m−1·K−1, depending on the temperature. [ABSTRACT FROM AUTHOR]

Cement composites exposed to high temperatures change their microstructure, composition and properties. In different temperature ranges, various physical and chemical processes take place in both their matrix and aggregates, which significantly affect the heat and mass transfer parameters, as well as the strength characteristics. In this paper, the effect of plasticizers on thermal properties of heat resistant composites based on calcium aluminate cement is studied. Thermal conductivity, specific heat capacity, and thermal strain are determined as a function of thermal load and compared with a reference material. The experimental results show that for the analyzed composites modified carboxylate is the most convenient choice while melamine-formaldehyde resin is found unsuitable. [ABSTRACT FROM AUTHOR]

Geopolymer-based alternatives to concrete have been mentioned very frequently in the last decade as they conform the topical environmental saving efforts. Utilization of byproducts or waste material make them even more attractive from this point of view. However, the process of a design is not the same like in case of well known concretes which means. it might be difficult to reach the properties desired. This paper therefore aims at the optimization of a geopolymer composition to reach sufficient 7-day compressive strength. Being composed of metashale, water glass, siliceous sand and water, the mixture proposed is supposed to be used in floorings applications. As the optimization technique, the modified downhill simplex method was applied, being tailored to specifics of the mixture design. Proving its effectiveness, the demanded 7-day compressive strength (25.0 MPa) was achieved after the first optimization step (27.8 MPa, due to an combination with an empirical design that exploited authors' experience to set the initial simplex closer to the optimum zone. In the end of the research presented, analytical formulas of the composition were proposed that are supposed to guarantee that the required 7-day compressive strength will be achieved. [ABSTRACT FROM AUTHOR]

The article is focused on the application of ceramic waste powder as a part of blended binder in the production of low-cement heat resistant composites. The idea of cement replacement is commonly employed for Portland cement based concrete. This time the idea of supplementary cementitious materials was taken over to be used in the case of calcium aluminate cement (CAC). The main aim was to design composites suitable for high temperature application, and the CAC is more convenient for such conditions. As a part of the blended binder, also reactive alumina and boehmite powder was utilized. In total six mixtures with varying ratio of mentioned binders were designed and examined. A reference mixture with pure CAC was prepared as well. The experimental program consisted of determination of basic physical and mechanical properties at ambient temperature as well as after exposure to 1400 °C. All designed composites showed better performance compared to the reference mixture. Therefore, it can be concluded that ceramic powder can be used effectively as a part of blended binders for high temperature applications. Taking into account compressive strength, residual compressive strength and ceramic powder dosage, the best result showed the composite with 4.6% of ceramic. [ABSTRACT FROM AUTHOR]

Cement-based composites have a very broad field of applications but their composition has to be designed with care to meet the desired functional properties. High-temperature resistant mixtures can be stated as a characteristic example in that respect. The standard calcium silicate binder should be replaced usually by high alumina cements which can be supplemented by waste materials or byproducts within the global environmental protection efforts. To reach the optimal properties and composition, advanced optimization techniques are supposed to be used rather than empirical approaches. This paper presents an application of downhill simplex method to optimize the composition of a binder based on calcium alumina cement and supplemented by ceramic powder, super reactive alumina and boehmite powder. The optimization procedure results in a 7% improvement of compressive strength, which reaches ∼117 MPa. Due to the high temperature resistant nature of all substances used (chamotte and corundum as fillers), the proposed mixture is supposed to resist increased temperatures up to 1400 °C. [ABSTRACT FROM AUTHOR]

Current tendencies in the field of waste management are influenced by environmental issues, putting among others an emphasis on waste reuse rather than landfilling. By-products of brick industry represent a typical example of a material with a great potential to be further processed to contribute to the environmental protection efforts. Due to its proper phase composition, ceramic powder can be effectively used as a precursor in alkali-activated materials. Focusing on the particle size distribution, this paper therefore deals with a quantification of precursor's parameters on the properties of the alkali-activation final products. Four different particle sizes of the precursors were assumed, being activated by the potassium water glass mixed with the potassium hydroxide to control the silicate modulus (1.0). All the materials studied exhibited consistent basic physical and mechanical properties except the mixture containing the precursor with particles smaller than 0.5 mm which could be caused by a suitable reaction kinetics. Having the smallest pore volume, this material exhibited the highest bulk density as well as the 7-day flexural and compressive strength. After 28 days, the materials exhibited an inverse proportion between the precursor's particle size and 28-day mechanical properties. [ABSTRACT FROM AUTHOR]

In order to follow the progress of cement hydration by analytical methods, the ongoing hydration reaction needs to be stopped by removing free water from the samples. There are several water removal techniques, affecting in varying degrees the chemical composition of cement-based materials. Oven drying is one of the most widely used drying techniques because of its high effectiveness and easy availability. Nevertheless, elevated temperatures may speed up hydration processes and support carbonation. This paper aims to investigate the impact of oven drying and sample dimensions on the amount of calcite generated in the cement pastes. The cement pastes are prepared with a water-to-cement ratio of 0.4 and are stored in water for 28 days. The hydration stoppage methods applied thereafter include oven drying at 50 °C, 80 °C, and 110 °C. Their impact on the chemical composition and microstructure development, with emphasis on the calcite content in the studied cement pastes, is analyzed by means of thermal analysis (DSC/TG), X-ray diffraction analysis, and these results were complemented by mercury intrusion porosimetry. [ABSTRACT FROM AUTHOR]

The influence of metakaolin (MK) additive in ordinary Portland cement (OPC) paste to its pH was studied by direct pore solution pH measurement and by XRD and thermal analysis. This research program was motivated by importance of pH for reinforcement corrosion; while the steel demands the high pH for its corrosion protection, the basalt-based reinforcement elements are damaged in the high pH. The initial hypothesis thus was to reduce the concrete pH by adding of MK. The mixtures containing 0–20% of MK were prepared and characterized after 28 days. MK presence reduced the pH due to proceeding pozzolanic reaction from 12.57 to 12.39, i.e. in terms of OH− molarity from 0.0372 mol/L to 0.0245 mol/L. The pH decrease was obviously caused by pozzolanic reaction between MK and Ca(OH)2 generated in OPC hydration; it means that blended cements are more suitable for basalt elements reinforcement than OPC. There was certain difference between TGA and XRD results indicating, that part of the present Ca(OH)2 is not crystallized in form of portlandite. [ABSTRACT FROM AUTHOR]

In the case of Portland cement (PC) and ordinary concrete, supplementary cementitious materials (SCM) have been successfully employed for decades. Despite that calcium aluminate cement (CAC) shows somehow different performance (composition, properties, stability, durability, etc.) the idea of SCM could be useful also in the case of this primarily refractory binder. In this study high alumina materials were selected as protentional SCM. Specifically, four different admixtures were chosen and the impact of their 15% replacement in CAC based pastes was examined. Through the view of physical properties of cement pastes their possible applicability was evaluated. As it was mentioned CAC is primarily binder for high temperature application, and therefore measured properties were determined also after temperature loading (up to 1400 °C). It was proved that despite that all chosen SCM compose almost entirely form the aluminate, the mineralogy and granulometry of SCM represents the really important factor affecting the performance of CAC paste. [ABSTRACT FROM AUTHOR]

Cement composites are often employed in severe conditions. They might be exposed for instance to high temperatures and/or high mechanical loads. However, their properties are mostly measured in laboratory conditions only, so that designers cannot take into account the changes in their material parameters after loading. In this paper, basic physical and chemical characteristics of heat resistant materials based on calcium aluminate cement are analyzed in the temperature range up to 1400 °C and the results are compared to those obtained for reference materials. The basic physical c haracteristics, namely bulk density, matrix density, and open porosity, are measured using helium pycnometry and gravimetric method. Material characterization experiments using thermal analysis and X-ray diffraction measurements are performed as well to assess the effect of high temperature exposure on the composition of studied materials. The experimental results show a very substantial effect of heat resistant admixtures on both physical and chemical characteristics. [ABSTRACT FROM AUTHOR]