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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]

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]