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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]

Gypsum composites with different lightweight aggregates were studied. The importance of gypsum as one of the most environmentally friendly building binder increases nowadays and new ways of its utilization are searched. Using of aggregates in the gypsum is generally not necessary, because gypsum does not shrink, but they can be used for economic reasons or to improve the thermal or fire properties of the gypsum material. We studied the structure and properties of the gypsum composites with three types of lightweight fillers (perlite, expanded clay aggregate, recycled PUR) and compared them with the gypsum mortar with siliceous sand. The SEM and porosity analyses were performed together with the mechanical tests. The influence of each type of aggregate on the structure and properties of gypsum composite was studied. It was found, that the type of the aggregate has principal impact on the microstructure of gypsum composites and their mechanical and thermal properties. [ABSTRACT FROM AUTHOR]

The production of red-clay hollow bricks belongs to the sources of industrial waste which gained on importance during the last decades. Although the amount of scrap is similar to the traditional red-clay bricks, the total waste generation is higher. As the current technologies of hollow brick production do not make it possible to provide sufficiently smooth and even surfaces, the brick blocks have to be ground after leaving the production line. This grinding generates a significant amount of waste powder containing both coarser and finer particles. The coarser fractions can be disposed of in the form of aggregate in concrete, as it is common for other types of ceramic waste. Finer fractions, which often possess pozzolanic activity, were reported to have a good potential as a partial replacement of cement in concrete. Using the ceramic waste powder instead of a part of cement is a solution more beneficial from an environmental point of view than its use as aggregate, as it contributes to a decrease of overall energy consumption and CO2 emission which accompanies the Portland cement production. In this paper, several geopolymer mixes are designed, using two different waste brick powders as precursors with a combination of water glass and sodium hydroxide as alkali activator. At first, the raw powders are subject of detailed material characterization experiments, including determination of chemical and mineralogical composition using X-ray fluorescence and X-ray diffraction methods. The development of microstructure of studied ceramic-based geopolymers is studied by means of scanning electron microscopy and mercury intrusion porosimetry. Then, their functional properties are assessed by the measurement of basic physical properties and mechanical parameters. Experimental results show satisfactory performance of all analyzed mixes which makes good prerequisites for their practical application as an environmental friendly alternative to cement-based materials. [ABSTRACT FROM AUTHOR]