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Alternative low-carbon cements could contribute significantly to CO 2 reduction in the cement industry. However, the existing methods require the input of the actual production data, and thus cannot be used to calculate CO 2 emissions of alternative low-carbon cements that are not yet produced in cement plants. This study aims to develop a model to analyze the theoretical CO 2 emissions of alternative low-carbon cements. The novelty of this model is that it can be used to calculate the fuel consumed in the production of new low-carbon cements based on the theory of heat balance, and then predict their CO 2 emissions. The model is used to calculate CO 2 emissions of several low-carbon binders and ordinary Portland cement (OPC). The results show that the direct CO 2 emissions of OPC clinker calculated by this model approach the value derived from the cement plants and the Cement Sustainability and Initiative (CSI). Calcium sulfoaluminate (CSA) clinker has the direct CO 2 emissions of 0.540 kg/kg, 34% lower than OPC clinker, while its cost of raw materials is over four times that of OPC clinker. High-belite calcium sulfoaluminate (HB-CSA) clinker, with the direct CO 2 emissions comparable to CSA clinker, lowers its cost of raw materials by half as it requires less expensive bauxite. Moreover, CO 2 emissions from HB-CSA cement production can be further reduced by the use of high volume of supplementary cementitious materials (SCMs). The knowledge gained provides a valuable reference for the design of new low-carbon binders. [ABSTRACT FROM AUTHOR]

Innovations in the cement industry strive towards achieving an eco-friendly alternative to traditional cement. A low-carbon cement, calcium sulfoaluminate-activated supersulfated cement (CSA-SSC), has been recently developed. This cement consists of 80% granulated blastfurnace slag (GBFS), 15% anhydrite, and 5% high-belite calcium sulfoaluminate cement (HB-CSA) clinker. The hydration mechanism of CSA-SSC was experimentally investigated using isothermal calorimetry, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy, and was numerically studied using thermodynamic modeling. CSA-SSC shows a moderate compressive strength at the early stage, which is mainly attributed to the rapid formation of ettringite from the hydration of C 4 A 3 S ¯ with CaSO 4 in HB-CSA clinker. Meanwhile, the hydration of f-CaO in HB-CSA clinker supplies an alkaline environment for the dissolution of GBFS and the formation of more ettringite. In the late stage, apart from ettringite, the hydration of GBFS forms C–S–H, leading to the continuous increase in late strength. A statistical analysis reveals that the high volume of GBFS in CSA-SSC results in a very low direct CO 2 emission, which is only 8.7% of that of Portland cement. [Display omitted] • CSA-SSC is comprised of 80% GBFS, 15% anhydrite and 5% HB-CSA clinker. • The carbon dioxide emission of CSA-SSC is 72.0 kg/t, 8.7% of that of PC. • CSA-SSC shows relatively higher compressive strength than PC and other types of SSCs. • The hydration of CSA-SSC produces ettringite from beginning and C–S–H at later stage. • CSA-SSC has a high ratio of compressive strength to amount of non-evaporable water. [ABSTRACT FROM AUTHOR]

• PCE-type GA was synthesized by grafting acylamino groups and hydroxyl groups. • PCE-type GA led to shorter grinding duration with homogenized particle morphology. • Cement ground by PCE-type GA showed higher fluidity and mechanical strength. Modified polycarboxylate-type (PCE-type) grinding aid (GA) by grafting acylamino group and hydroxyl group into the backbone of PCE polymer was synthesized, and its possibility to be adopted as cement GA was estimated in this research. The grindability of PCE-type GA was measured in terms of grinding duration as well as particle size distribution, and the grindability of PCE-type GA was systematically compared with that of triethanolamine (TEA) and ordinary PCE-type superplasticizer. The cement hydration kinetics, the microstructure, and the physical–mechanical properties of ground cement samples in the function of PCE-based GA were analyzed. The results indicated that PCE-type GA was more effective in cement grinding process than TEA as well as PCE-type superplasticizer, exhibiting shortened grinding duration, optimized particle size distribution, and homogenized particle morphology. And cement ground by PCE-type GA was characterized with lower water demand, higher fluidity property, and increased mechanical strength, ascribed to the dispersion capability of PCE polymer as well as the unified cement particle size distribution. The application of PCE-type GA could slightly prolong the induction period of the ground cement, but gently enhance the hydration degree. Lower porosity and denser microstructure with higher density of cement hydration products uniformly distributing in the hardened matrix could be achieved with PCE-type GA adopted in the ground cement. [ABSTRACT FROM AUTHOR]