Utilisation of electrolytic manganese residue and phosphogypsum in calcium sulfoaluminate cement

Influence of phosphorus impurities on the performances of calcium sulfoaluminate cement

The purpose of this research was to probe beyond the scope of the “National Strategy Project on Carbon Mineralization” to develop a “United Nations Framework Convention on Climate Change, Clean Development Mechanism” (UNFCCC CDM) methodology that enables reduction of greenhouse gas (GHG) by “green cement” under the calcium sulfoaluminate (CSA) cement technologies. The findings will be utilized as the foundations and developed into the UNFCCC CDM project. There were two existing methodologies related to cement, but neither was applicable for CSA cement. The existing methodologies are applicable only when there is one clinker, but CSA cement utilizes more than one clinker. Through this research, we developed methodologies to use waste-based material for avoiding emission leakage and utilized more than one clinker to calculate GHG emissions and reduction. For this purpose, we utilized the CSA cement methodology for calculating GHG reduction compared to Portland cement and found that CSA cement allowed for a reduction of 0.281 tCO2-eq/ton above the reduction enabled by Portland cement. We are presently preparing to register the CSA cement methodology for UNFCCC CDM methodology approval. With the technology transfer and support for this CSA cement technology and methodology, developing countries will be able to achieve their national GHG reduction targets and gain carbon credits. Thus, CSA cement technology could serve as an important tool to deal with GHG emissions and climate change.

Investigation of the mechanical and durability properties of sustainable high performance concrete based on calcium sulfoaluminate cement

Early age hydration, rheology and pumping characteristics of CSA cement-based 3D printable concrete

Concrete industry produces a great environmental impact. The total, or partial, substitution of ordinary Portland cement (OPC) with Calcium sulfoaluminate (CSA) cement could be a possible solution, due to its lower production temperature and thus lower CO2 emission. Therefore, there is an essential need to assess the durability properties of concrete produced with CSA cement. In this work a preliminary study on durability of high performance fiber reinforced concretes produced with CSA cement in total or partial substitution of OPC, also with ground granulated blast-furnace slag (GGBS), was performed. Compressive strength and electrical resistivity of the different concrete mixes and electrochemical tests to evaluate corrosion condition of the embedded steel fibers, were assessed. The results show that substitution of OPC with CSA cement improves the mechanical properties of concrete but promotes corrosion of the steel fibers, affecting the durability of this material.

Potential application of Portland cement-calcium sulfoaluminate cement blends to avoid early age frost damage

Investigation on the preparation of low carbon cement materials from industrial solid waste phosphogypsum: Clinker preparation, cement properties, and hydration mechanism

The effective stabilization of arsenic-containing bioleaching waste (BW) remains a key barrier in metallurgical waste valorization. This study introduces a self-stabilizing approach in which BW serves both as a sulfate donor and an arsenic source within a calcium sulfoaluminate (CSA) cement system, enabling internal immobilization through its own reactive constituents. Experimental results showed that increasing BW content reduced ettringite formation and compressive strength, with the 1-day strength decreasing from 27.3 MPa (10 wt% BW) to 10.5 MPa (50 wt% BW). Incorporating 5 wt% carbide slag (CS) markedly enhanced hydration, increasing 1-day strength by 38.3 % and refining the pore structure by 21.6 % in total pore volume. With respect to arsenic stabilization, sequential extraction and toxicity characteristic leaching procedure (TCLP) tests indicated that over 95 % of arsenic was immobilized in the residual fraction, with leaching concentrations well below regulatory limits, and this stability was maintained even under freeze–thaw conditions. The immobilization mechanism was found to involve both physical encapsulation within a densified microstructure and chemical stabilization through arsenic incorporation into ettringite and adsorption onto C-S-H gels. Furthermore, density functional theory (DFT) calculations confirmed that AsO 4 3- and AsO 3 3- exhibit strong chemisorption onto C-S-H surfaces via Ca–O coordination, with adsorption energies reaching up to –4.98 eV. Overall, the co-utilization of BW and CS in CSA cement presents an effective and low-carbon strategy for the stabilization of arsenic-bearing wastes, offering both structural integrity and long-term environmental safety. • A self-stabilizing CSA system was developed where arsenic-containing waste acts as both contaminant and sulfate source. • Carbide slag addition enhanced arsenic immobilization by promoting ettringite and C–S–H formation. • Arsenic stabilization was confirmed by sequential extraction and TCLP under highly acidic conditions. • DFT simulations revealed strong chemisorption of arsenate/arsenite on C-S-H surfaces.

High autogenous shrinkage property is one of the disadvantages of ultra‐high‐performance concrete (UHPC), which may induce early age cracking and threaten the safety of concrete structure. In the present study, different dosages of calcium sulfoaluminate (CSA) cement were added in UHPC as an effective expansive binder. Hydration mechanism, autogenous shrinkage property, and compressive strength of UHPC were carried out to investigate the effect of CSA addition on the mechanical properties of UHPC. Scanning electron microscopy was also employed to characterize the intrinsic microstructural reasons relating to the changes in macroproperties. Based on the XRD diagram, increasing formation of ettringite and Ca(OH)2 can be found with increasing CSA content up to 15%. In the heat flow results of UHPC with 10% CSA addition, the maximum heat release increases to 2.6 mW/g, which is 8.3% higher than the reference UHPC, suggesting a higher degree of hydration with CSA addition. The results in autogenous shrinkage show that CSA expansion agent plays a significantly beneficial role in improving the autogenous shrinkage of UHPC. The corresponding autogenous shrinkage of UHPC is −59.66με, −131.11με, and −182.31με, respectively, at 7 d with 5%, 10%, and 15% addition, which is 108%, 117%, and 123% reduction compared to the reference specimen without CSA. In terms of compressive strength, UHPC with 5%, 10%, 15%, and 20% CSA addition has 10.5%, 17.4%, 30.2%, and 22.1% higher compressive strength than that for the reference UHPC at 28 d. Microstructural study shows that there is an extremely dense microstructure in both the bulk matrix and interfacial transition zone of UHPC with 10% CSA addition, which can be attributed to the higher autogenous shrinkage property and can therefore result in higher mechanical performance.

This study presents a comprehensive experimental evaluation of high-performance concretes incorporating calcium sulfoaluminate (CSA) cement as a partial replacement for ordinary Portland cement (OPC). Five CSA replacement levels (0, 15, 30, 45, and 60%) and two water-to-cement ratios (0.40 and 0.45) were examined to assess their effects on mechanical performance and key durability parameters. The experimental program simultaneously investigated compressive strength, tensile splitting strength, water absorption, sorptivity, gas permeability, and freeze–thaw resistance, offering an integrated assessment rarely addressed in previous studies, which typically focus on selected parameters or narrower replacement ranges. The results show that CSA addition enhances microstructural densification, substantially reducing sorptivity and gas permeability and markedly improving freeze–thaw performance even without air entrainment. High CSA contents (45–60%) yielded superior transport-related durability while maintaining competitive 28-day strengths, especially for w/c = 0.40. These findings clarify the interplay between CSA content, transport properties, and frost resistance, highlighting CSA–OPC hybrid binders as a durable and sustainable solution for high-performance concrete applications.

Effect of steel slag on the hydration and strength development of calcium sulfoaluminate cement

This paper focuses on rapidly stabilizing very high moisture soils via calcium sulfoaluminate (CSA) cements. Producing a short-term construction material and/or handling contaminated sediments are the two primary anticipated applications. Literature review showed CSA cements have promise for an application of this nature, but that this subject has largely been unexplored. Behaviors of CSA cements were compared with ordinary portland cements (OPCs) where multiple soil types at a range of cement dosages and moisture contents were tested. There were distinct conditions where OPC outperformed CSA and vice versa. With the exception of very rare and isolated instances, there appears to be no advantage to using CSA cement below 10 % dosage. Moisture contents of 133 % or higher and high cement dosages (e.g., 15 to 20 %) in conjunction with a relatively low organic soil with a moderate liquid limit (e.g., 45 to 65) appears to be a good application for CSA cements.

To better understand the influence of the impurities in phosphogypsum (PG) on the early-age hydration of calcium sulfoaluminate (CSA) cement manufactured with PG, the study prepared synthetic ye’elimite doped with fluorine (F) and phosphorus (P) and also synthesized ye’elimite with natural gypsum (NG) and PG. The acquired ye’elimite was characterized, and its early-age hydration within 24 h was investigated. Results demonstrate that F contributes to the crystallization and leads to the formation of large crystal synthetic ye’elimite. P and the simultaneous presence of F and P could stabilize C4A3$-c. Without the presence of gypsum, pure ye’elimite is much more active than synthetic ye’elimite doped with F and P, and synthetic ye’elimite prepared with NG is much more active than that prepared with PG. Although the presence of gypsum significantly boosts the hydration activity of synthetic ye’elimite doped with F and P and pared with PG, their hydration activity is still slightly lower. It is suggested that manufacture of alite-calcium sulfoaluminate cement and binary blends of CSA cement and Portland cement is an available way to boost the early-age hydration CSA cement manufactured with PG.

Phosphogypsum as a component of calcium sulfoaluminate cement: Hazardous elements immobilization, radioactivity and performances

Hydration characteristics of calcium sulfoaluminate cements synthesized using an industrial symbiosis framework