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This study investigates the early hydration characteristics and kinetics of ordinary Portland cement (OPC) and calcium sulfoaluminate cement (CSA) composite pastes. The hydration mechanisms of OPC-CSA systems with different proportions are analyzed through zonal analysis and the Krstulović–Dabić method. The experimental results show that in OPC-dominated systems, an appropriate amount of CSA promotes the rapid hydration of ye’elimite and optimizes the cumulative hydration heat and pore structure. However, excessive CSA inhibits hydration due to alkalinity imbalance. In CSA-dominated systems, 10% OPC increases the alkalinity, promoting ye’elimite to hydrate into ettringite. Higher OPC content hinders the hydration process due to ion concentration imbalance. The kinetics model indicates that CSA accelerates the interfacial reaction and diffusion in the OPC system, while OPC reduces the overall hydration rate of the CSA system. Microscopic analysis confirms that the composite system improves the pore structure through mineral interaction. In the OPC-dominated area, the pore structure is mainly composed of small and dense pores. In the CSA-dominated area, the characteristics of large pores are affected by the expansion properties of CSA and hydration heat. This study constructs a coupling mechanism of alkalinity regulation and crystal nucleus generation, providing a theoretical basis for the design of high-performance composite cement materials.

Blends of ordinary Portland cement (OPC) and calcium sulfoaluminate (CSA) cement can be used to adjust the properties of cement for specific applications. In this study, CSA cement was used as a shrinkage-compensating admixture to improve the hydration behavior and performance (compressive strength and drying shrinkage) of OPC; the expansion behavior of the blended cement mortar was evaluate based on the saturation index of ettringite. The experimental results showed that incorporating CSA cement resulted in a delayed effect on the hydration of C3S, shortened the induction periods of the blended cement and decreased the setting time. The CSA cement also improved the early compressive strength and drying shrinkage of the OPC due to its compact microstructure. The drying shrinkage of the OPC mortar decreased by 27.8% when 6% CSA cement was used, but the formation of microcracks due to expansion could negatively impact its late compressive strength development and associated pore structures of the blends when the replacement content of CSA cement exceeded 6 wt.%. The results relevant to the expansion behavior of the CSA cements could induce crystallization stress, enhancing its resistance against shrinkage cracking.

This work aims to investigate the effect of additional flue gas desulfurization gypsum (FGDG) on the properties of calcium sulfoaluminate cement (CSAC) blended with ground granulated blast furnace slag (GGBFS). The hydration rate, setting time, mechanical strength, pore structure and hydration products of the CSAC-GGBFS mixture containing FGDG were investigated systematically. The results show that the addition of FGDG promotes the hydration of the CSAC-GGBFS mixture and improves its mechanical strength; however, the FGDG content should not exceed 6%.

Calcium sulfoaluminate (CSA) cements are a promising alternative to Portland clinker, however, a thorough understanding of their properties is needed for their broader use in the industry. One of the topics that requires a good understanding is the effect of the w/c ratio on the properties of CSA cements. To this end, the aim of this paper was to provide research into the effects of a w/c ratio in the range of 0.45–0.6 on the properties of fresh and hardened CSA pastes and mortars. For fresh mortars, consistency and setting time, as well as plastic shrinkage tests, were conducted, and were complemented by hydration heat tests, carried out on pastes. For hardened mortars, tests of compressive and flexural strength and dry shrinkage, as well as SEM photography, were conducted. It was found that, regardless of a higher hydration rate, the increase in w/c ratio decreased flexural and compressive strength, as well as shrinkage, while increasing consistency, setting time, and hydration heat. Also observed was a significant decrease in strength between 3 and 7 days of curing in mortars with a high w/c ratio. It can be concluded that, regardless of the hydration rate, low w/c ratios in CSA mortars provide better properties than high w/c ratios.

Supplementary cementitious materials are considered a viable and affordable way to reduce CO2 emissions from the cement industry’s perspective since they can partially or nearly entirely replace ordinary Portland cement (OPC). This study compared the impact of adding spent coffee grounds (SCGs), fly ash (FA), and volcanic ash (VA) to two types of cement: OPC and calcium sulfoaluminate cement (CSA). Cement samples were characterized using compressive strength measurements (up to 210 days of curing), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), attenuated total reflection infrared spectroscopy, and hydration temperature measurements. In all the studied systems, the presence of SCGs reduced compressive strength and delayed the hydration process. CSA composite cement containing 3.5% SCGs, 30% FA, and 30% VA showed compressive strength values of 20.4 MPa and 20.3 MPa, respectively, meeting the minimum requirement for non-structural applications. Additionally, the results indicate a formation of cementitious gel, calcium silicate hydrate (C-S-H) in the OPC-based composite cements, and calcium alumino-silicate hydrate (C-A-S-H) as well as ettringite in the CSA-based composite cements.

This study investigates the impact of the quicklime and gypsum ratio on grouting material made of sulfoaluminate cement (SAC). Gypsum and quicklime were selected to verify that sulfoaluminate cement retained ettringite (AFt). SAC's efficiency as a grouting material was evaluated using gypsum and quicklime. SAC with varying gypsum-quicklime ratios was subjected to tests for compressive strength, pH, setting time, expansion rate, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The microstructure was investigated with XRD at 1 and 28 days. The result obtained points to two key findings: the retention of AFt was excellent ([greater than or equal to]99%) regardless of the gypsum-quicklime ratio, and the retention of AFt without gypsum and quicklime depended on the SAC; in this case, the setting time was prolonged, leading to expansion strain. Keywords: compressive strength; grouting material; gypsum; hydration product; quicklime; sulfoaluminate cement (SAC).

The enhancement of the durability of sulfoaluminate cement (CSA) in marine environments is of great importance. To this end, an investigation was carried out involving the placement of CSA concrete in the tidal zone of Zhairuoshan Island, Zhoushan, China, and subjected to a 20-month marine tidal exposure test. The comparison was made with ordinary Portland cement (OPC) concrete to evaluate the effectiveness of the former. The test findings indicate that the compressive strength of both types of concrete is reduced by seawater dry-wet cycling, and the porosity of the surface concrete is increased. However, the compressive strength of CSA concrete is observed to be more stable under long-term drying–wetting cycles. When the ettringite in the CSA surface concrete is decomposed due to carbonization and alkalinity reduction, its products will react with Ca2+ and SO42− in seawater to regenerate ettringite to fill in the concrete pores, making the concrete strength more stable and hindering chlorine penetration. Furthermore, CSA concrete exhibits a higher capillary absorption capacity than OPC concrete, which results in chloride accumulation on its surface. However, the diffusion capacity of chloride in CSA concrete is significantly lower than that in OPC concrete.

Calcium sulfoaluminate cement is a promising low-carbon alternative to Portland cement, and the carbonation of its hydration products influences its mechanical performance. However, a comprehensive theoretical model describing its carbonation mechanism remains elusive. This paper established a theoretical reaction range, including different zones and boundaries for ye’elimite (C 4 A 3 S̅)-gypsum (CS̅H 2 )-water (H 2 O)-carbon dioxide (CO 2 ) system via priority-based theoretical calculations of chemical reactions. The reactions and product evolution within each boundary and zone were summarized. A theoretical database was obtained, including the change of Gibbs energy and enthalpy, solid volume and chemical volume, and the theoretical carbon absorption. Calculation results reveal that the reactions of each zone and boundary occur spontaneously and exothermically. The solid volume increases, while the chemical volume decreases conversely. The maximum carbon absorption of 1 mol C 4 A 3 S̅ is 3 mol theoretically regardless of the amount of gypsum. The modeling obtained by Gibbs Energy Minimization software (GEMS-PSI) and experimental verification were carried out to validate the fidelity of the established theoretical reaction range, which demonstrate that the evolution of carbonation products in each zone and boundary was in line with the theoretical calculations. Compared with GEMS modeling, the theoretical reaction range can distinguish the source of ettringite in detail, and provide a more direct and insightful representation of carbonation process.

This study investigated the material properties and hydration characteristics of calcium sulfoaluminate cement (CSA) based mortars cured under 3 different initial curing temperatures. Two CSA cements with different M-values were selected. Obtained experimental results of mechanical properties, dimensional stability, and heat release were explained by hydration characteristics from X-ray diffraction, thermal gravimetric analysis, porosimetry, and thermodynamic modeling. Decomposition of ettringite decreased compressive strength but re-formation of ettringite after additional curing at 30 °C helped to recover the strength in CSA cement with a high amount of calcium sulfate. CSA cement with a low amount of calcium sulfate which was designed to predominantly have monosulfate as the main hydration product, showed increased 1-day strength after higher temperature curing but this occurred was at the expense of decreased 28-day strength.

The effects of ordinary limestone powder (OLP) and ultrafine limestone powder (UFLP) on the fluidity, setting time, compressive strength, hydration heat and microstructure of calcium sulfoaluminate cement (CSA) were investigated. The results show that finer limestone powder reduces the fluidity and setting time of CSA. Increasing fineness of limestone powder improves the growth rates of strength and chemical bound water content, and higher compressive strength and chemical bound water content are obtained. The hydration of CSA is dramatically promoted by adding UFLP, and the promoting effect increases with increasing dosage, but cumulative hydration heat is reduced. The higher content and finer limestone powder result in larger amount of hemicarbonate and minor amount of monosulfate phase (AFm). The microstructure of hardened CSA paste is densified by adding UFLP. Owing to the poor bond between limestone powder and surrounding hydrates, the compressive strength of CSA mortar containing larger amount of limestone powder is low.