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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]

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]

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]