Calcium Sulfoaluminate Cement Research Articles

Preparation activated tailings by pH swing process: Towards yielding cemented tailings backfill and in-situ CO2 mineralization

In-situ CO2 mineralization of tailings has shown great potential for large-scale CO2 sequestration, but its development is seriously limited by the low CO2 conversion rate. This study proposed an innovative pH swing process to produce activated tailings through magnesium extraction from raw tailings and subsequent leachate precipitation. By the combination of activated tailings and high-belite calcium sulfoaluminate cement, a new type of cemented activated tailings backfill (CATB) was developed. The results demonstrate that 82.33% of magnesium is extracted from raw tailings and precipitates in the form of Mg(OH)2 serving as the dominating carbonation active phase during the pH swing process. Besides the aragonite forms in the carbonated cemented raw tailings backfill (CRTB), carbonated CATB also contains calcite, nesquehonite, and hydromagnesite. Substituting activated tailings for raw tailings led to the higher CO2 absorption capability (ranging from 8.88% to 14.17% with various binder-to-tailings ratios). These indicate that the activated tailings have a promising application scenario in large scale in-situ CO2 mineralization.

Enhancement in clinker hydration degrees and later stage-ettringite stability of calcium sulfoaluminate cements by the incorporation of dolomite

The hydration degrees of clinkers and ettringite stability in calcium sulfoaluminate (C A) cements in the presence of externally supplied dolomite were investigated in this study. The mineralogical and microstructural characteristics of C A cements containing different dosages of dolomite were characterized using X-ray diffractometry, Rietveld refinement-based quantification analysis, thermogravimetry analysis, mercury intrusion porosimetry, scanning electron microscopy observation, and energy dispersive spectroscopy point analysis. Furthermore, the binder systems were simulated using thermodynamic modeling to observe the phase changes of hydration products and the underlying hydration kinetics. The incorporation of dolomite accelerated clinker consumption and enhanced the stability of ettringite throughout the testing period, due possibly to the nucleation seeding effect and provision of carbonate ions by dolomite. The modeling outcomes showed the stability of ettringite at later stage by the incorporation of dolomite in the simulated timeframe, yet the active dissolution of dolomite assumed in the modeling procedure overestimated the Mg-bearing hydrates in the samples.

Rapid CO2 catalytic activation of binary cementing system of CSA and Portland cement

This study presents a novel approach to activating a binary cementing system composed of calcium sulfoaluminate (CSA) cement and ordinary Portland cement (OPC) using an instant CO2 catalysis. The activation led to significant and rapid strength enhancement, with the binary cement achieving a strength of 15.42 MPa immediately after activation, all within 1 min. The rapid CO2 activation catalyzed a notable heat release, accelerating the hydration of ye'elimite to form ettringite, which is a crucial component capable of bridging gaps and imparting high initial strength. Simultaneously, the CO2 activation catalyzed the increase in sulfur concentration, which in turn, also facilitated the formation of ettringite at an early age. Subsequent strength development was attributed to belite hydration. Apart from the rapid strength gain, employing CO2 activation facilitated control over the pH value of the pore solution, thus enabling the manipulation of ettringite's crystal morphology to strategically enhance the microstructure. Samples with lower pH values exhibited needle-like ettringite formations, whereas samples with higher pH values yielded rod-like and column-like ettringite crystal structures. Comprehensive analytical investigations were analyzed using XRD, FTIR, TGA, 27Al NMR, MIP, SEM, and ICP-OES. The present study provides a new perspective on the potential application of CSA-based cement, such as precast concrete element, instant concrete product delivery, and urgent reconstruction.

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

Calcium sulfoaluminate (CSA) cement offers a sustainable alternative to ordinary portland cement by using less energy and producing fewer CO2 emissions. However, the high cost and limited availability of alumina-rich resources like bauxite pose significant challenges for CSA cement production. This study addresses these issues by synthesizing CSA cement through an industrial symbiosis framework, incorporating natural materials (limestone and gypsum) with industrial wastes and by-products (Serox, ladle furnace slag, ceramic waste, and glass waste). This approach aims to minimize these challenges to CSA production while promoting environmental sustainability in the construction industry. Laboratory studies have resulted in the successful synthesis of three distinct CSA cements with at least 40 % recovered material content. Ye'elimite, anhydrite, merwinite, and fluorellestadite were identified as major compounds of the CSA cements. Hydration studies revealed ettringite as the primary hydration product, contributing to rapid strength gains with compressive strengths over 30 MPa within a day. In addition, a tendency to ettringite carbonation was observed over the long term, the adverse effects of which need to be further investigated. These results demonstrate the feasibility of producing environmentally friendly CSA cements through industrial symbiosis and highlight their potential for scalable and sustainable construction applications.

Early Hydration of Calcium Sulfoaluminate Cement at Elevated Temperatures

Early Hydration of Calcium Sulfoaluminate Cement at Elevated Temperatures

Hydration characteristics and hydration products of calcium sulfoaluminate cement and fly ash blended pastes

This study investigated a binary blend of calcium sulfoaluminate cement and fly ash with a target compressive strength of more than 32.5 MPa based on the EN 197-1 standard, using as much fly ash as possible. In the binder system of calcium sulfoaluminate cement and fly ash, a decrease in the replacement level of fly ash results in an increase in compressive strength. Mortar with a 40% replacement level of fly ash for calcium sulfoaluminate cement and added gypsum shows 49.41 MPa strength at 28 d. Its hydrates are hydroxy-AFm, ettringite, crystalline aluminum hydroxide, amorphous aluminum hydroxide, strätlingite, and monosulfate. They are attributed to the hydration of ye’elimite, C2S, and C3A in calcium sulfoaluminate cement. The reactivity of fly ash is not observed until 28 d of hydration. The formation of ettringite is the main cause of the gains in compressive strength.

Phase quantification of anhydrous CSA cements: a combined X-ray diffraction and Raman imaging approach

Calcium sulfoaluminate (CSA) cements are known for their special properties, such as shrinkage compensation and high early-age strength. These properties are dependent on the hydrated phase assemblage, which in turn is governed by the phases present in the initial anhydrous cement. However, the anhydrous CSA phase quantification by X-ray diffraction (XRD) Rietveld can be challenging due to the presence of overlapping peaks, polymorphs and preferred orientation. To overcome this problem, an approach involving high-resolution large-area Raman imaging (5 mm × 5 mm, 250 000 pixels, with 10 μm/pixel resolution) complemented by XRD analysis is introduced. This integrated approach of combined XRD and Raman imaging is found to be crucial in the initial identification of phases that are present in a CSA system. Most importantly, quantitative analysis shows a strong correlation (R2 > 0.99) and agreement (variation <5 wt%) between the two independent methods, adding confidence and reliability to the phase assemblage obtained by this dual-technique approach.

Evaluating carbonation resistance and microstructural behaviors of calcium sulfoaluminate cement concrete incorporating fly ash and limestone powder

This study investigates the effects of accelerated carbonation on calcium sulfoaluminate (CSA) cement concrete, focusing on mixtures enhanced with 20 % fly ash (FA), 20 % remediated fly ash (RF), 15 % limestone powder (LP), and a combination of 20 % FA with 15 % LP (35 %). The study further evaluates the mechanical properties including compressive strength, splitting tensile strength, elastic modulus, along with drying shrinkage and bulk resistivity. To delve into the microstructural characteristics of moist curing versus carbonation exposure on the CSA cement system, X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were employed, particularly analyzing phase assemblage changes. The results show that the addition of FA reduced the carbonation depth in concrete mixtures over time (105 days). However, LP and the combination of FA and LP presented mixed effects. The microstructural analysis highlighted ettringite as the predominant phase in samples moist cured for 3 days. In contrast, carbonation-cured samples were characterized by different calcium carbonate (CaCO3) polymorphs alongside aluminum hydroxide (Al(OH)3) and residual ye'elimite, with the formation of low-pH carbonic acid facilitating the conversion of ettringite into CaCO3. This study highlights the impact of different SCMs on the durability and microstructural characteristics of CSA cement concrete, underscoring the interplay between curing methods, effects of SCM, and carbonation processes.

Performance of high-strength green strain-hardening cementitious composites incorporating CSA/CAC cements and GGBS

Strain-hardening cementitious composites (SHCCs) possess crack control and durability properties. In the pursuit of reducing CO2 emissions and addressing potential issues of slow strength development for SHCCs with pozzolans, the objective of this study was to develop high-strength green SHCCs (HSG-SHCCs) that exhibit improved early strength, drying shrinkage, and environmental friendliness. A ternary binder system was proposed, comprising of ground granulated blast furnace slag (GGBS), ordinary Portland cement (OPC), and either calcium sulfoaluminate cement (CSA) or calcium aluminate cement (CAC). The fresh, mechanical, and durability properties of the proposed HSG-SHCCs were experimentally investigated. Additionally, the microstructures and chemical phases of the developed CSA/CAC-GGBS-OPC ternary binder system were analyzed using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results revealed that the developed HSG-SHCCs demonstrated 6-hour and 28-day strengths of up to 11 MPa and 110 MPa, respectively. The CSA/CAC-based ternary binder system also exhibited enhanced durability and improved drying shrinkage. However, the inclusion of CSA and CAC in HSG-SHCCs could lead to a reduction in tensile performance, specifically in strain capacity. The main hydration products of the CSA/CAC-GGBS-OPC ternary binder system were C-S-H, ettringite, gibbsite, and calcium hydrate. In addition to the fresh, mechanical, and durability properties, the environmental impact of the developed HSG-SHCCs was also assessed. The results indicated that a 30 % replacement of OPC with CSA cement in the HSG-SHCC mix notably improved the trade-off among CO2 emissions, compressive strength, and tensile cracking resistance.

Synthesis and properties of a belite–calcium sulfoaluminate cement obtained using only waste materials

Synthesis and properties of a belite–calcium sulfoaluminate cement obtained using only waste materials

Feasibility of Sprayable Engineered Cementitious Composites Using Natural Sand and Low Fiber Content: Effect of Hybrid Fiber System, Silica Fume, and Air-Entraining and Shrinkage-Reducing Admixtures

Deterioration of corrugated steel culverts (CSCs) is a significant problem for the Virginia Department of Transportation and other U.S. transportation agencies. Spray-on lining using shotcrete engineered cementitious composites (ECCs) is a promising structural repair strategy for deteriorated CSCs. This study evaluates the feasibility of practical sprayable ECCs using natural silica sand and low fiber content, while forgoing the use of commonly utilized calcium sulfoaluminate cement to allow for delivery of the materials via ready-mixed concrete trucks. Aspects of the compositional space evaluated include the effect of a hybrid polyvinyl alcohol/polyethylene fiber system, silica fume (SF), shrinkage reducing admixture (SRA), and air-entraining admixture (AEA) on the properties of the composites. Experimental results suggested that the development of the proposed materials is feasible, because flow characteristics associated with shotcrete ECCs and ECC-like tensile ductility were achieved in the fresh and hardened state, respectively. Notwithstanding, further mixture optimization may be required for satisfactory field performance, which should be assessed through field testing. Generally, the use of the hybrid fiber system tended to improve the strength and ductility of the composites, especially when coupled with the use of SF. Furthermore, SF was effective at mitigating the strength loss associated with the incorporation of AEA and SRA, and meaningfully improved surface resistivity. SF also tended to reduce the mixture’s flow, whereas the contrary occurred with the use of SRA and AEA. SRA contributed to the reduction in drying shrinkage at early ages. However, the effect of SRA in reducing shrinkage was negligible at later ages.

Study on the composite compatibility and interfacial properties of excess sulfate phosphogypsum cementing system to OPC and C[formula omitted]A

Releasable sulfate contained in the Excess Sulfate Phosphogypsum Cementing System (ESPCS) potentially degrades interfaces when contacted with conventional cements, raising incompatibility concerns. This work evaluated fresh connection, adhesion, and aggregate embedment of ESPCS to ordinary Portland cement (OPC) and Calcium sulfoaluminate cement (CS¯A), with mechanical and interfacial properties studied. Results indicate the discrepancy in hydration properties gives Excess-sulfate Phosphogypsum Slag Cement (EPSC) uncoordinated expansion to OPC, followed by cracks (95 μm) generation. Meanwhile, expansive ettringite forms in the interface due to bleeding sulfate-rich water concentration, thus leaving a porous contact zone (1240 μm, 11.29%) and resultant flexural strength reduction of OPC-EPSC mortar (by > 36%). Conversely, EPSC and CS¯A are close in phase assemblages, resulting in compact interface and higher bond strength. Incorporating the Phosphogypsum-based Cold Bonded Aggregates (PCBAs) into OPC induces the interfacial ettringite formation-sulfate attack by internal curing water, yielding the worst composite performance, i.e., the lowest 360 d compressive strength (38.8 MPa) of concrete OPCC, lower than EPSCC (48.6 MPa) and CS¯AC (50.3 MPa). ESPCS is more compatible to CS¯A than OPC which is advised against exposing directly with ESPCS. This work helps specify composite feasibility and conditions of ESPCS with typical cement composites.

Effects of EVA and SAE Emulsions on Hydration and Drying Shrinkage of Calcium Sulfoaluminate Cement Pastes

Effects of EVA and SAE Emulsions on Hydration and Drying Shrinkage of Calcium Sulfoaluminate Cement Pastes

A coupled chemo-transport-mechanical damage model for the mineral transformation in cementitious materials under a sulfate-rich environment

The present study proposes a coupled chemo-transport-mechanical damage model integrating thermodynamics, fluid-solid transformation, and mechanical damage modeling to predict the physicochemical characteristics of cementitious materials under a sulfate-rich environment. For verifying the proposed model, calcium sulfoaluminate (CSA) cements with various molar ratios of calcium sulfate over ye'elimite (m-values) were adopted for a case study. The thermodynamics model for the phase assemblage of CSA cements with various m-values under a sulfate-rich environment is compared with the experimental outcomes. The model parameters in the fluid-solid transformation and mechanical damage models are fitted through the available experimental data in the literature. Mineral compositions, crystallization pressure, effective elastic modulus, delayed ettringite formation, and microcracks of CSA cement pastes were modeled by a proposed coupled chemo-transport-mechanical damage model, with model parameters fitted to experimental data, thereby assessing the applicability of the proposed model. The predicted results show that an increase in m-value of the samples increases the rate of sulfate ion penetration and crystallization pressures. Moreover, DEF, microcrack evolution, and mechanical degradation can be attributed to the amount of ye'elimite and hydrated monosulfate of the samples.

Improving the performance of iron-rich calcium sulfoaluminate cement from municipal solid waste incineration fly ash through diverse pretreatment approaches

The utilization of municipal solid waste incineration fly ash (MSWI-FA) is environmentally significant. In this study, MSWI-FA was pretreated using organic acid solution and CO2 microbubble carbonation washing. The pretreated MSWI-FAs were then used to produce Iron-rich calcium sulfoaluminate (IR-CSA) cement at different substitution rates (CFA) for various raw materials. The evolution of iron phase distribution, mineral composition, and hydration of IR-CSA cement were investigated, alongside heavy metal migration. The results showed that the MSWI-FA-based IR-CSA clinker had suitable mineralogical phases. However, gehlenite in MSWI-FA reduced CaO availability in the clinker formation reaction, hindering the involvement of Fe2O3 in the ye'elimite formation reaction. The calcination temperature was increased to facilitate clinker and iron phase formation in the case of high CFA levels. CO2 microbubble carbonation washing pretreatment of MSWI-FA, with which the IR-CSA clinker achieved suitable pH values and alkali content, facilitated the early growth and chained evolution of ettringite, resulting in a denser microstructure and lower cumulative hydration heat. Consequently, the compressive strength of MSWI-FA-based IR-CSA cement increased, with a maximum gain of 43.65 MPa. Chromium content in the residual form increased, and heavy metal leaching was well below standard limits. This approach provides a new perspective for the purification treatment of MSWI-FA and its high-value, large-scale recycling in low-carbon cement.

Effect of Water to Cement Ratio on Properties of Calcium Sulfoaluminate Cement Mortars

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.

Corrosion Resistance of Magnesium Ammonium Phosphate Cement-Based Coatings Modified by Calcium Sulfoaluminate Cement on Carbon Steel in a Saline Medium

Corrosion Resistance of Magnesium Ammonium Phosphate Cement-Based Coatings Modified by Calcium Sulfoaluminate Cement on Carbon Steel in a Saline Medium

Chinese raw vermiculite: A potential additive for improving the thermal properties of calcium sulfoaluminate cement-blended mortars for applications in hot regions

Reducing the thermal conductivity (TC) of a cementitious building material can help to slow the rate at which it heats and cools. The present project aims to develop a new construction material with low TC for use in hot regions. The construction material is produced by blending Chinese raw vermiculite (CRV) with calcium sulfoaluminate (CSA) cement in mortar. CSA mortar specimens were cast and tested for a variety of properties, including dry density (σ), void content, ultrasonic pulse velocity (UPV), thermogravimetric variations, microstructure, TC, thermal diffusivity, and specific heat capacity. CSA mortars mixed with CRV had improved workability and σ. However, compared to plain CSA mortar, the compressive strength of the CSA mortars incorporating 60 % and 100 % CRV was reduced by 10 % and 24 %, respectively. This reduction in strength is still acceptable for non-structural applications, and the decrease in strength remains close to that of CSA mortars without CRV. The TC of CSA mortar with 0 % fine aggregate replacement was 1.99 ± 0.17 W/mK, which is 95.07 % higher than when 100 % CRV was used as the fine aggregate replacement. The addition of CRV slows CSA mortar heating by 20 %. The findings confirms CRV's potential as an eco-friendly, energy-efficient construction material.

In situ concrete sewer performance: comparison of Portland cement, calcium sulfoaluminate cement, and calcium aluminate cement

In situ concrete sewer performance: comparison of Portland cement, calcium sulfoaluminate cement, and calcium aluminate cement

Enhancing geomechanical characteristics of calcium sulfoaluminate (CSA) cement-treated soil under low confining pressures

This study examines the efficacy of employing calcium sulfoaluminate (CSA) cement, an environmentally friendly binder, for enhancing the geomechanical characteristics of sand, particularly under low confining pressure conditions. A series of triaxial consolidated drained tests were performed on sand samples treated with varying content (5, 7, and 10%) of CSA cement and 10% ordinary Portland cement (OPC) under various low confining pressures (50, 100, 200, and 400 kPa). The test findings demonstrated the importance of cement content and confining pressure on the mode of failure, stress–strain and volumetric behavior, failure characteristics, and shear strength parameters of the treated quartz sand. After a curing period of 14 days, samples treated with 10% CSA cement exhibited a remarkable 212% increase in peak deviator stress and an 89% reduction in axial strain at failure, indicating higher initial stiffness compared to untreated samples under a 400 kPa confining pressure. Furthermore, the samples treated with 10% CSA exhibited higher peak deviator stress, initial stiffness, and strength development compared to those treated with 10% OPC. The scanning electron microscopy analysis provides insights into particle breakage and bond degradation processes, which increase with confining pressure in CSA-treated samples. Also, the mode of failure analysis reveals a transition from ductile to slightly brittle behavior with increasing cement content. Notably, the geomechanical properties of the treated material emphasized the significant impact of CSA cement on soil improvement. Thus offering a sustainable alternative for soil improvement in construction projects.