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Calcium sulfoaluminate (CSA) cements have lower carbon dioxide (CO 2) emissions during production compared with conventional ordinary Portland cement (OPC). However, the high cost of production is a significant limitation of the application of CSA cements. This paper aims to improve the use efficiency of CSA clinker by adding OPC and anhydrite. The low-carbon OPC-CSA clinker-anhydrite system is expected to contain less CSA clinker while showing excellent performance. A design methodology was developed to optimize the component of the OPC-CSA clinker-anhydrite blended system. The hydration mechanism of the ternary system was investigated using isothermal conduction calorimetry, X-ray diffraction (XRD), and thermogravimetric analysis (TGA), and thermodynamic modelling was used to predict the amount of hydration products. The results showed that ettringite is the main hydration products of the OPC-CSA clinker-anhydrite system, and the addition of OPC provides portlandite for the formation of ettringite. The ternary system is characterized by rapid development of strength and low CO 2 emissions. The compressive strength at 4 h and the CO 2 emissions are about 10 MPa and 500 kg/t, respectively. In addition, the ternary system, composed of 27.9 wt% CSA clinker, 32.5 wt% anhydrite, and 39.6 wt% OPC has the highest compressive strength at 28 d and the lowest CO 2 intensity. [ABSTRACT FROM AUTHOR]

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]