Search Results (44)

Additive manufacturing enables the fabrication of complex geometries and structures that are difficult to attain by conventional methods. However, many printable materials exhibit inherent trade-offs among their performance properties. Traditional material design, often relying on intuition-driven and inefficient trial-and-error approaches, frequently fails to identify optimal formulations. In this study, we propose a machine learning-assisted framework to efficiently refine the composition of 3D-printable calcium sulphoaluminate (CSA) cement composites with a balanced trade-off among thixotropy, mechanical strength, and shape stability. Our approach integrates a multi-objective optimization algorithm with a data-driven surrogate model to intelligently propose new mix proportions, thereby reducing the number of required experiments. Starting from seven primary formulations and 28 initial experimental samples, the method identified 23 improved mix proportions after only 20 algorithm iterations. The workflow demonstrates how optimization-assisted formulation refinement can accelerate the search for better-performing materials and is potentially adaptable to other material design challenges. Full article

Infrastructure maintenance and emergency repairs require rapidly setting cementitious materials, yet conventional cement presents issues of high energy consumption and substantial CO₂ emissions. Addressing this challenge, this research has developed a ternary alkali-activated cementitious material (CGFM) composed of calcium carbide residue (CCR), granulated blast furnace slag and fly ash. This study separately investigates the effects of CCR content (0–10%), alkali content (6–12%) and activator modulus (1.0–1.5) on workability and early mechanical strength. The hydration mechanism was examined through X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR), Thermogravimetry-Derivative Thermogravimetry (TG-DTG) and Scanning Electron Microscopy-Energy Dispersive Spectroscopy (SEM-EDS) analysis, whilst life cycle assessment was employed to quantify the ecological impacts. Results indicated that a 3% CCR dosage significantly improved the gel structure, achieving a 7-day compressive strength of 69.8 MPa and a 37% increase in flexural strength. At a CCR dosage of 3%, alkali content of 8%, and modulus of 1.4, CGFM achieved a peak compressive strength of 80.2 MPa by the seventh day. This performance is attributable to its substantial gel content and high degree of polymerisation, which results in a dense structure. Life cycle assessment confirmed that compared to sulphoaluminate cement mortar, CGFM mortar reduced CO₂ emissions by 64.6% and energy consumption by 48.6%. Full article

This study investigated the effects of calcium carbide slag (CCS) (0–12 wt%) incorporation on the workability, electrochemical properties, durability, and microstructure evolution of sulfoaluminate cement (SAC) mortar. Results showed that increasing CCS content reduced mortar fluidity and shortened setting time, indicating that CCS accelerates early hydration. A 9% CCS content was determined to be the optimal dosage; at 28 days, compared to the control group, this dosage group exhibited a 6.53% increase in compressive strength, a 22.47% decrease in drying shrinkage, and a 0.279% decrease in mass loss. These performance improvements stemmed from CCS’s ability to inhibit pore connectivity and limit moisture migration. Electrochemical analysis further revealed that the 9% CCS dosage group had the highest charge transfer resistance and resistivity (30.00% higher than the control group), reflecting a denser matrix and greater ion transport resistance. Consequently, chloride ion permeability was significantly reduced, with electrical flux and diffusion coefficient decreasing by 39.98% and 28.89%, respectively. Microstructural observations confirmed that CCS promotes the formation and densification of hydration products, effectively improving the internal pore structure. While 9% CCS can serve as an effective functional supplementary material, its long-term durability and sustainability still face practical application challenges. Future research should focus on establishing predictive models for chloride ion permeation lifetime and conducting quantitative sustainability assessments of CCS-SAC composites, particularly evaluating material cost, energy consumption, and carbon dioxide emissions. Full article

This study explored the chloride binding characteristics and mechanisms of sulphoaluminate cement (SAC) by isolating its principal mineral component, anhydrous calcium sulphoaluminate (${\mathrm{C}}_4{\mathrm{A}}_3\stackrel{\mathrm{-}}{\mathrm{S}}$), as the research object. Chloride ingress was investigated under external penetration and internal incorporation conditions, with gypsum dosage varied at molar ratios of 1:0, 1:1, and 1:2 relative to ${ \mathrm{C}}_4{\mathrm{A}}_3\stackrel{\mathrm{-}}{\mathrm{S}}$. Through chloride binding experiments and hydration product analysis performed by XRD and TG, the following findings were obtained: under external chloride exposure, the binding capacity increased with rising solution concentration and immersion time. External chloride binding was attributed to SO₄²⁻/Cl⁻ ion exchange in AFm to generate Friedel’s salt and was complemented by physical adsorption of chloride in AH₃ gel. Under internal chloride incorporation, binding capacity increased progressively with curing age. Internal chloride binding involved the direct participation of Cl⁻ in hydration reactions to form Friedel’s salt in addition to the chemical reaction of AFm and the physical adsorption of AH₃. Gypsum dosage critically regulates the AFm/AFt ratio, which in turn governs chloride binding efficiency under both external and internal chloride scenarios (e.g., after immersion in 1 mol/L NaCl solution, the bound chloride content for ${\mathrm{C}}_4{\mathrm{A}}_3\stackrel{\mathrm{-}}{\mathrm{S}}$/gypsum ratios of 1:0, 1:1, and 1:2 was 50.94, 27.28, and 13.47 mg/g, respectively). Full article

This study aims to explore the potential of aerogel to optimise the thermal conductivity of mineralised foam materials. Experiments were conducted with (i) addition methods of aerogel, (ii) proportion of aerogels in cement slurry, and (iii) water/cement ratio as influencing parameters for mineralised foam. Additionally, mixed Ordinary Portland Cement (OPC)/Calcium Sulphoaluminate Cement (CSA) slurries were used to test whether a synergy could be achieved. In this study, the defoaming effect of the aerogel and its mitigation to a certain extent by pre-mixing the aerogel with cement slurry were confirmed. The thermal conductivity of the mineralised foams was reduced from 0.049 to 0.036 W/(m·K) when the aerogel was up to 10 wt.% of the cement. In the specimens prepared from the mixed OPC/CSA slurry, a homogeneous circular pore structure was observed under the microscope along with a reduction in the thermal conductivity. The use of aerogels and CSA cements can effectively reduce the thermal conductivity of ultra-low-density mineralised foams to levels comparable with certain plastic foams that dominate the building insulation market. Full article

In order to shorten the curing time of the cement-treated aggregate base, provide a stable paving base for an asphalt mixture, and finally, achieve rapid traffic reopening during the maintenance of the pavement (milling and resurfacing of the base layer), sulphoaluminate cement (SAC) was used to prepare cement-treated aggregate with high early strength. As a result, the SAC was first optimized by adding several cement admixtures (i.e., polycarboxylic water reducer, borax, lithium carbonate, and calcium formate) based on hydration kinetics, setting time, compressive strength, and morphology tests. Then, the optimized SAC was used to prepare the sulphoaluminate cement-treated aggregate (SACTA). The test results show that the addition of compound retarder and compound early strength agent in SAC could delay the hydration, reduce microcracks, and ensure required setting time and high early strength. Compared with ordinary Portland cement-treated aggregates (OPCTAs) with the same cement content, the 1 d unconfined compressive strength and indirect tension strength of SACTAs increased by 87.7–184.6% and 133.8–263.6% respectively. The SACTA had smaller total drying shrinkage strain and better anti-scouring performance than OPCTA when using the same cement content. Besides, the 1 d interfacial bonding strength between SACTA and OPCTA was 0.18 MPa, which was higher than the indirect tension strength of OPCTA. The findings in this study indicate that the prepared SACTA could be used for rapid traffic opening during road maintenance. Full article

The preparation of low-cost and high-durability cement-based material systems using seawater mixing has become an urgent task in marine engineering construction. The requirements have addressed key challenges, including high transportation costs for fresh water and raw materials, poor structural durability, and difficulty in meeting actual construction schedules. Sulfatealuminate cement (CSA) has become an ideal material for marine engineering due to its high corrosion resistance, rapid early strength, which is 35–40 MPa of 3-day compressive strength and is 1.5–2 times compared ordinary Portland cement (OPC), and low-carbon characteristics, reduced production energy consumption by 35–50%, and CO₂ emissions of 0.35–0.45 tons/ton. The Cl⁻ and SO₄²⁻ in seawater can accelerate the hydration of CSA, promote the formation of ettringite (AFt), and generate Friedel’s salt fixed chloride ions, significantly enhancing its resistance to chloride corrosion. Its low alkalinity (pH ≈ 10.6) and dense structure further optimize its resistance to sulfate corrosion. In terms of environmental benefits, CSA-mixed seawater can save 15–20% fresh water. And the use of solid waste preparation can reduce environmental burden by 38.62%. In the future, it is necessary to combine multi-scale simulation to predict long-term performance, develop self-healing materials and intelligent control technologies, and promote their large-scale application in sustainable marine infrastructure. Full article

To address the high carbon emissions and resource dependency associated with conventional ordinary Portland cement (OPC) production, this study systematically investigated the preparation processes, hydration mechanisms, and chemical properties of high-belite calcium sulfoaluminate (HBCSA) and calcium sulfoaluminate (CSA) cements based from industrial solid wastes. The results demonstrate that substituting natural raw materials (e.g., limestone and gypsum) with industrial solid wastes—including fly ash, phosphogypsum, steel slag, and red mud—not only reduces raw material costs but also mitigates land occupation and pollution caused by waste accumulation. Under optimized calcination regimes, clinkers containing key mineral phases (C₄A₃S⁻ and C₂S) were successfully synthesized. Hydration products, such as ettringite (AFt), aluminum hydroxide (AH₃), and C-S-H gel, were identified, where AFt crystals form a three-dimensional framework through disordered growth, whereas AH₃ and C-S-H fill the matrix to create a dense interfacial transition zone (ITZ), thereby increasing the mechanical strength. The incorporation of steel slag and granulated blast furnace slag was found to increase the setting time, with low reactivity contributing to reduced strength development in the hardened paste. In contrast, Solid-waste gypsum did not significantly differ from natural gypsum in stabilizing ettringite (AFt). Furthermore, this study clarified key roles of components in HBCSA/CSA systems; Fe₂O₃ serves as a flux but substitutes some Al₂O₃, reducing C₄A₃S⁻ content. CaSO₄ retards hydration while stabilizing strength via sustained AFt formation. CaCO₃ provides nucleation sites and CaO but risks AFt expansion, degrading strength. These insights enable optimized clinker designs balancing reactivity, stability, and strength. Full article

Because of their excellent properties, calcium aluminate cement (CAC) and sulphoaluminate cement (SAC), as building materials, have been used in infrastructure construction. However, due to the defects in microstructure, their application and development have been limited. In this study, we explored the negative Poisson’s ratio modification design of cement-based composites by changing the ratio of composite cement’s raw materials and adjusting the stacking method of crystals. On this basis, three types of crystal modifiers were added into cement-based composites. Then, compression and tensile tests were performed to explore the effect of crystal modifiers on the structure of negative Poisson’s ratio. The deformation behavior of the specimens under static load was performed by the digital speckle correlation method (DSCM). The results show that Formula 4 (the mass ratio of CAC is 30% and SAC is 70%) was the most effective in optimizing mechanical properties. In addition, the morphology of crystallization products confirmed that the addition of the crystal modifiers would affect the formation of negative Poisson’s ratio structure. According to the mechanical properties and microstructure, adipic acid is the best crystal modifier. With the mechanism of the negative Poisson’s ratio effect of cement-based composites being analyzed, two crystal stacking modes were predicted, and an ideal calculation model was obtained. Full article

This paper discusses the performance of calcium sulpho-aluminate (CSA) cement and a Sulphate-Resisting Portland Cement (SRPC) with a fly ash (FA) additive (i.e., a SRPC + FA binder system) in a ‘live’ sewer environment; it deepens the understanding of their deterioration mechanisms by using a laboratory test for simulated sewer conditions. It also studies the role of an iron-based additive (‘Hard-Cem^®’, HC) in improving the performance of SRPC + FA concrete under a biogenic acid attack. The performance of 0.4 w/b concrete specimens of the three binders (CSA, SRPC + FA, and SRPC + FA + HC) with calcite aggregates in sewer exposure was assessed by visual observation, measurements of mass and thickness changes, and microstructural analysis for approximately 25 months. The laboratory test, i.e., the Biogenic Acid Concrete (BAC) test, was used to study the deterioration mechanisms of these binders in terms of leaching solution pH and standardised cumulative leached calcium and aluminium. The results indicate that CSA concrete had improved performance in the sewer environment, showing no mass loss and only about one-third of thickness lost in the SRPC + FA concrete over a 25-month exposure period in the sewer environment. The BAC test results complemented the field observations. The iron-based additive in sewer concrete slightly reduced mass loss, likely due to its better resistance to abrasion and erosion, but not due to any chemical influence, since it does not participate in hydration or dissolution reactions. The findings imply that CSA cement may represent a suitable alternative binder for concrete sewer construction. They also suggest that a surface hardener has limited benefits, except when it is under abrasive conditions. Further investigation is required, especially since CSA contains high amounts of sulphate, the effect of which is not well understood. Full article

There are long periods of winter construction in China’s eastern and western Alpine regions. The decreased construction temperature adversely affects the workability, mechanical properties, and durability of cement-based materials and alkali-activated materials. Under low-temperature curing conditions, the hydration reaction of these materials slows down, resulting in limited strength development and reduced durability. In response to this problem, researchers have summarized three measures to improve performance: the use of anti-freezing components, nanoparticles, and pre-curing. The effects of anti-freezing components on the mechanical properties and micro-mechanism changes of Portland cement, sulphoaluminate cement, magnesium phosphate cement-based materials, and alkali-activated cementitious materials are organized. Additionally, the improvement of macro-micro properties in cement-based materials through mineral admixtures, nanoparticles, and hydrated calcium silicate seeds is summarized. The influence of pre-curing on the mechanical properties of cement-based materials is analyzed, focusing on the relationship between pre-curing time and the critical strength of frost resistance. Finally, existing research challenges are summarized, and future research directions are proposed, providing valuable references for the further development of materials and engineering applications. Full article

The acid co-production of cement is a prominent research focus for the large-scale, high-value utilization of phosphogypsum in the context of dual-carbon strategies. This paper builds on extensive research conducted by its authors on the co-production of sulphoaluminate cement clinker through acid production from gaseous-sulphur-reduced phosphogypsum. The solid mineral phase transformations occurring in the kiln during this process are systematically studied, and the effects of various calcination regimes (temperature, time, and atmosphere) on the evolution of clinker mineral phases are elucidated. This paper provides basic data support for the gas-sulfur-reduced phosphogypsum-acid cogeneration of sulfoaluminate cement clinker processes, and promotes the realization of the large-scale high-value utilization of phosphogypsum resources. The generation of the clinker mineral phase anhydrous calcium sulphoaluminate (C₄A₃S̅) begins at 1100 °C. Increasing the calcination temperature and extending the calcination time promote C₄A₃S̅ formation. However, when the calcination temperature exceeds 1350 °C, C₄A₃S̅ decomposes, leading to the formation of low-activity C₂AS. In a CO atmosphere, the main mineral phases in the clinker transform into C₂AS and 12CaO·7Al₂O₃, owing to the decomposition of CaSO₄, which inhibits C₄A₃S̅ formation. At calcination temperatures exceeding 1300 °C, a significant amount of C₂AS appears in the calcined material, and 12CaO·7Al₂O₃ begins to form. Full article

In response to rising CO₂ emissions in the cement industry and the growing demand for durable offshore engineering materials, calcium sulphoaluminate (CSA) cement concrete, known for its lower carbon footprint and enhanced corrosion resistance compared to Ordinary Portland Cement (OPC), is increasingly important. However, the chloride transport behavior of CSA concrete in both laboratory and marine environments remains underexplored and controversial. Accordingly, the chloride ion transport behaviors and mechanisms of CSA concrete in laboratory-accelerated drying-wetting cyclic environments using NaCl solution and seawater, as well as in marine tidal environments, were characterized using the rapid chloride test (RCT), X-ray diffraction (XRD), mercury infiltration porosimetry (MIP), and thermogravimetric analysis (TGA). The results reveal that CSA concrete accumulates more chloride ions in NaCl solution than in seawater, with concentrations 2–3.5 times higher at the same water–cement ratio. Microscopic analysis indicates that calcium and sulfate ions present in seawater facilitate the regeneration of ettringite, thereby increasing the density of the surface pore structure. The hydration and repair mechanisms of CSA concrete under laboratory conditions closely resemble those in marine tidal conditions when exposed to seawater. Additionally, this study found that lower chloride ion concentrations and pH levels inhibit the formation of Friedel’s salt. Therefore, laboratory experiments with seawater can effectively simulate CSA concrete’s chloride transport properties in marine tidal environments, whereas NaCl solution does not accurately reflect actual marine conditions. Full article

CSMSFC (Calcium Sulphoaluminate Cement-based Micro Steel Fiber Concrete) possesses the advantages of early strength, high strength, exceptional toughness, minimal shrinkage, and excellent bond performance with bars. When applied to NLSB (Non-contact Lap Splice of Bars) in prefabricated structures, CSMSFC enhances mechanical performance while preventing shrinkage cracking and reducing seismic damage. Additionally, it shortens construction periods for prefabricated structures and achieves a comprehensive improvement in seismic performance and construction efficiency. However, there is a lack of systematic testing of factors influencing the bond strength between CSMSFC and NLSB and the effect of CSMSFC on the force transfer performance between NLSB. Therefore, the axial tensile tests of NLSB were conducted on 51 non-contact lapping specimens to investigate the bond properties and force transfer mechanism between lapping bars and CSMSFC. The effects of lapping length, volume fraction of steel fibers, spacing of bars, and concrete cover thickness on the lapping characteristics were examined, and the comparison with OPMSFC (Ordinary Portland Cement-based Micro Steel Fiber Concrete) was also considered. The experimental results demonstrate that the bond strength between bars and CSMSFC increased by 36.8%, 42.3%, and 43.3% respectively, with volume fractions of steel fiber at 1.5%, 3%, and 4.5% compared to the absence of steel fiber. The bonding effect between CSMSFC and bars is similar to that of OPMSFC and bars. The bond strength between CSMSFC and the bars improved by 4.3% and 6.6% with the increases of the spacing of bars from 0 to 20 mm and the concrete cover thickness from 10 to 30 mm. Conversely, with the increases of the lapping length from 50 mm to 100 mm, 200 mm, and 300 mm, the bond strength decreased by 46.8%, 72.2%, and 82.0%, respectively. Finally, based on the force transmission mechanism of the non-contact lapping bars, a calculation model is proposed for determining the lapping length while considering the reinforcing effect of steel fiber “stirrups.” A formula is derived from the model to calculate the minimum lapping length of HRB400 bars in CSMSFC, considering the volume fraction of steel fibers, which can assist in designing the minimum lap length of NLSB in practical applications. Full article

The construction industry is a significant contributor to global CO₂ emissions, primarily due to the extensive use of ordinary portland cement (OPC). In response to the urgent need for sustainable construction materials, calcium sulphoaluminate (CSA) cement has emerged as a promising alternative. CSA cement is renowned for its low carbon footprint, high early-age strength, and superior durability, making it an attractive option for reducing the environmental impact of construction activities. While CSA cement offers benefits in carbon emissions reduction, its susceptibility to carbonation presents challenges. Although the body of literature on CSA cement is rapidly expanding, its adoption rate remains low. This disparity may be attributed to several factors including the level of scientific contribution in terms of research focus and lack of comprehensive standards for various applications. As a result, the present study sets out to track the research trajectory within the CSA cement research landscape through a systematic literature review. The study employed the Prefer Reporting Item for Systematic Review and Meta-Analysis (PRISMA) framework to conduct a literature search on three prominent databases, and a thematic analysis was conducted to identify the knowledge gap for future exploration. The study revealed that while CSA concrete demonstrates superior early-age strength and environmental resistance, its susceptibility to carbonation can compromise structural integrity over time. Key mitigation strategies identified include the incorporation of supplementary cementitious materials (SCMs), use of corrosion inhibitors, and optimization of mix designs. The review also highlights the global distribution of research, with notable contributions from the USA, China, and Europe, emphasizing the collaborative effort in advancing CSA concrete technology. The findings are crucial for enhancing sustainability and durability in the construction sector and advancing CSA binders as a sustainable alternative to traditional cement. Full article