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For their advantageous properties and availability, basalt products have become an emerging green high-tech industrial material that is used in various building- and civil engineering applications as an alternative to widely used traditional types of reinforcement. Nevertheless, compared to the glass-, carbon- or steel-based fibers in cement composites, the literature focused on basalt reinforcing elements has been far less numerous. This paper is focused on a comparison of the impact of basalt (BF) and steel fibers (SF) on the mechanical properties of hardened concrete after 16 hours for the verification of early-age strength, which is essential in precast production, and at 28 days of hydration as a standard request. Several mixtures were prepared, containing different dosages of fibers: It was found that when a similar amount of both types of fibers was used, BF provided approximately 9% higher compressive strength of studied samples after 28 days. Moreover, when 0.48 vol.% and 0.90% of BF and SF, respectively, were added to the mixtures, the samples with BF showed more promising compressive strength by 15.3%. Nevertheless, in terms of the residual tensile strength, the same samples with BF exhibited almost five times worse performance than those prepared with SF, which should be addressed in future research. [ABSTRACT FROM AUTHOR]

Green building materials are gaining attention for achieving carbon neutrality in civil engineering. To reduce CO2 emissions from cement, using low-cement or cement-free materials with local supplementary cementitious materials (SCMs) is promising. Blended cements with SCMs enhance long-term strength, but low-clinker blends often have low early strength. To address this, understanding the hydration of ordinary Portland cement is crucial. While C3S has been studied, the role of C3A, the most reactive component of cement, has been explored less. This study aims to produce C3A in laboratory conditions, assessing the effects of calcination temperature and time on its composition and morphology. The C3A samples are prepared using the empirically computed amounts of CaCO3 and Al2O3. The proposed design aims to produce pure cubic C3A, with up to 3 wt.% of unreacted CaO and no mayenite C12A7 as side products. The results obtained demonstrated that the duration for which the maximum temperature is maintained before extracting the samples from the furnace is a crucial factor that exerts the most significant influence on the presence of mayenite in the C3A structure. The synthesized C3A will then be added into blends, and its impact on early strength will be evaluated. The findings from this study have the potential to provide valuable insights for designing and producing more environmentally friendly cements, with a specific focus on achieving superior early strength performance. [ABSTRACT FROM AUTHOR]

Aerial lime-based binders and rendering mortars belong to the most traditional building materials with a long history. These materials play an important role in cultural heritage, providing support for wall paintings, stuccoes, or simply protecting covered structures. Nowadays, lime is associated with a considerable scale of production and thus, is also responsible for high amounts of CO2 emissions. One of the possibilities for decreasing its carbon footprint is to partially replace it with pozzolanic active materials based on local availability. The Czech Republic belongs to the countries with high ceramic production and needs to deal with the considerable amounts of waste from the final bricks cut. This study aims to utilize this ceramic waste to design aerial lime binders with different ceramic powder dosages from 0 mass% to 70 mass% and analyze the influence of selected drying methods on the compositional changes at an early age. The drying methods for water removal include air drying (reference), solvent exchange (isopropanol and acetone), and direct drying in an oven at 40 °C and 105 °C. The microstructural changes of the studied binders are accessed with the help of thermal analysis (simultaneous differential scanning calorimetry and thermogravimetry) and X-ray powder diffraction. The obtained results pointed out the importance of carefully handling (drying) lime-based samples before their analysis. [ABSTRACT FROM AUTHOR]

The construction industry is currently struggling with a shortage of primary raw materials that are needed for buildings, road construction in particular. Taking into account the availability issues, dredging operations in river bands, dams, and lakes associated with a big volume of excavated sediments represent a very interesting precursor source for the alkali-activated materials (AAMs) production. However, despite the good availability and favorable chemical composition, the alkali activation of WS was studied only rarely. This study investigates the potential of dredged freshwater sediments as alkali-activation precursors through elevated temperature exposure. The reactive amorphous phase content is increased by treatment at 800 °C and changes in the mineralogical composition are evaluated. The suitability of freshwater sediments as construction materials is accessed by the determination of the mechanical strength. The obtained results reveal, that the utilization of thermogravimetry can be viewed as an effective tool for the determination of optimal temperature treatment. Achieved values of compressive and flexural strength point to the potential of this material as the construction material, notwithstanding, follow-up research is required to increase the mechanical performance through mixtures optimization. [ABSTRACT FROM AUTHOR]

Effects of different drying methods on structural changes of ternary gypsum-based composites were investigated by mercury intrusion porosimetry. The composites were prepared from gypsum, lime, ceramic waste, and sand. The samples were stored for 28 days in a climate chamber (relative humidity 80%, 20 ± 2 °C), and then, they were crushed into pieces smaller than 5 mm, and these pieces were dried at temperatures of 50 °C and 105 °C. The results obtained by mercury intrusion porosimetry confirmed that even a relatively low drying temperature of 50 °C, which is commonly used for drying cement composites, affects the structure of the gypsum-based composites. It was also found that a composition of ternary mixture with an optimized amount of fine ceramic powder can suppress the negative effect of drying. [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]

Whereas the hydration stoppage of cementitious materials has been widely studied and discussed, there is a lack of knowledge concerning water removal techniques/arresting of hardening processes of non-cementitious materials, such as environmentally friendly calcined gypsum. This article, therefore, aims to apply the commonly used water removal methods, namely direct drying and solvent replacement for arresting processes of gypsum paste, and compare their effects on its composition. The effects of drying methods were studied with the help of thermal analysis consisting of differential scanning calorimetry and thermogravimetry, and these results were complemented with X-ray powder diffraction analysis. [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]

Water removal from hardened samples plays a critical role in the preparation of analyses requiring dry samples. Such a requirement can arise for two reasons: method constraints or hydration stoppage. Indeed, measurements such as mercury intrusion porosimetry (MIP) should not be performed on wet samples, as the free water in the pores might bias their results. Additionally, measurements can be delayed due to laboratories' capacity: timely stopping the hydration process within these samples becomes essential to the accuracy of the results. This paper investigates the effects of two widely used methods of water removal from early-aged cement paste on results of thermogravimetric analysis (TGA) and MIP. [ABSTRACT FROM AUTHOR]

Alkaline activation is a globally expanding, innovative technology that involves the chemical reaction between an aluminosilicate precursor and an alkaline activator which results in a very compact and well-connected structure. The alkali activated aluminosilicates (AAA) are usually prepared with the utilization of industrial waste, and therefore, they present a promising way for design of cement-free environmentally friendly binders. For the AAA preparation, ceramic waste powder (CWP) can be utilized in two different ways, depending on its fineness. The finer fractions usually possess pozzolanic activity and as they contain a significant amount of amorphous phase, they can be alkali activated. The coarser fractions can be utilized as a type of chemically inert filler. In this study, the CWP is used partially as a precursor for the alkaline activation and as fine filler for the design and preparation of AAA composites. The preparation of AAA is usually done at room temperature. However, this article aims to demonstrate that the curing temperature has a significant impact on basic physical properties and mechanical properties of AAA. For this purpose, several composites are prepared and cured at 20 °C, 40 °C, 60 °C and 80 °C. The elevated temperatures along with higher dosages of water glass and NaOH resulted in a formation of a more compact structure with lower total porosity and improved mechanical properties. [ABSTRACT FROM AUTHOR]