Supersulfated Cement Research Articles

Exploring the role of calcium sulfate in supersulfated cement: A study of rheological, mechanical, and microstructural properties

In order to investigate the impact of different calcium sulfate (CS) sources and forms on the rheology, hydration, and mechanical properties of supersulfated cement (SSC), SSC pastes were produced with anhydrite from gypsum calcined at 650ºC and raw and calcined phosphogypsum (PG) at 150, 350, and 650ºC. Isothermal calorimetry, rheometry using parallel-plate geometry, compressive strength testing, and microstructural analysis through X-ray diffraction (XRD) and thermogravimetric analysis (TGA/DTG) were performed. Results showed that SSC containing gypsum and PG calcined at 650ºC exhibited similar rheological behavior. Pastes containing PG calcined at 150ºC and raw PG respectively, exhibited the highest and lowest shear stress at a given shear rate. The calcination temperature and CS source did not significantly impact SSC compressive strength. Rietveld XRD analysis revealed that pastes with PG calcined at 350ºC and gypsum calcined at 650ºC had the lowest and highest ettringite development, respectively, from 7 to 28 days of curing.

Performances enhancing of supersulfated cement (SSC) using waste alkaline activators: Red mud and carbide slag

Supersulfated cement (SSC), since its invention, showed lower early-age strength gain, which has limited its practical applications. The urgent issue is how to regulate and enhance its early-age performance. In this context, solid waste materials such as bauxite residue-red mud (RM) and carbide slag residue (CS) from acetylene production by calcium carbide hydrolysis were used to improve the hydration and performance of SSC. By utilizing a range of analytical techniques such as isothermal calorimetry (IC), X-ray diffraction (XRD), backscatter scanning electron images (BSE), and thermogravimetric analysis (TGA), the hydration process, phase assemblages and microstructure of CS/RM-modified SSC were systematically investigated. It’s found that CS, as a calcareous alkaline activator, act as a regulator for adjusting the two main hydration reactions of C-A-S-H deposition and ettringite formation in SSC. The alkaline activator induces the hydration of slag and promotes the formation of hydration products. However, an excessively high dosage of carbide slag delays the primary ettringite formation reaction because it inhibits the dissolution of slag and promotes the formation of outer products. It leads to a looser and more porous paste matrix, resulting in higher expansion strain and poor strength gain at full curing ages. In contrast, red mud improves the hydration rate and enhances the hydration degree of SSC within the studied content (up to 30 wt%). With addition of red mud, SSC hydration is significantly advanced and deepened, resulting in more hydrates, particularly inner products. Red mud facilitates the depolymerization of the slag glass network and promotes the forming of nuclei and growth of hydration products. However, an excessively high red mud content would lead to a looser and more porous paste matrix due to the characteristics of red mud particle itself. An optimal red mud content has been identified as 20 wt%.

Utilization of biochar as a green additive in supersulfated cement: Properties, mechanisms, and environmental impacts

To promote the green development of building materials, this study develops a novel and sustainable method for incorporating coconut-derived biochar (BC) in supersulfated cement (SSC). Moreover, the solid waste desulfurized gypsum is used as a sulfate activator. The macroscopic experimental results show that the addition of 2 % biochar can reduce the fluidity of composites by 12.5 % but increase the 28-day compressive and flexural strength by 10.3 % and 19.1 %, respectively. Hydration heat analysis show that biochar can increase the maximum heat release of SSC. XRD patterns and TGA analysis indicate that 2 % biochar can improve the hydration degree of cement where the bound water content is increased by 8.9 %. SEM observations and 1H NMR spectrum suggest that although biochar can compact the microstructure, it increases the harmful and multiple harmful pores ratio. Furthermore, a comprehensive analysis considering greenhouse gas emissions, energy consumption, cost, fluidity, and mechanical properties is performed to evaluate the BC-SSC composites. The results prove that BC-modified SSC has significantly lower environmental pollution and resource consumption than ordinary Portland cement, but the cost may be increased.

Enhancing self-healing properties of engineered cementitious composites through the application of super-sulfated cement

To date, no prior research has addressed the self-healing performance of engineered cementitious composites (ECC) prepared with super-sulfated cement (SSC), despite its potential to reduce carbon emissions compared to Portland cement (OPC). This paper addresses this significant research gap in the literature by exploring the influence of SSC on the recovery ability of pre-cracked ECC samples. In addition to the mechanical characterization at the sound state, an exhaustive investigation was undertaken to comprehensively assess the self-healing ability of flexural strengths, deflections, ultrasonic pulse velocity (UPV), and rapid chloride permeability (RCPT) of preloaded SSC-based ECCs. Furthermore, scanning electron microscopy (SEM), coupled with energy-dispersive X-ray (EDX) was employed to evaluate the microstructural changes and development of self-healing products within the microcracks of SSC mixtures prepared with various amounts of FA. The findings indicated that SSC-based ECC, while maintaining comparable mechanical and ductility properties, exhibited significant improvements in the recovery rates of ECC, reaching more than 27%, 7%, and 76% for flexural strength, UPV, and RCPT, respectively, compared to the OPC-based control ECC. The microstructural SEM-EDS results confirmed the enhanced precipitation of ettringite as a new self-healing product related to the inclusion of SSC in ECCs, along with the conventional C-S-H/C-A-S-H gels.

Influence of weak acid salts and curing condition on supersulfated cement mortar

This study explores the impact of weak acid salt agents (citrate and tartrate) in the mixture and various curing conditions on the properties of supersulfated cement (SSC) mortar. Compressive strength tests were conducted on prism-shaped samples measuring 4 × 4 × 16 cm. A comprehensive analysis of the phase assemblage of hardened products was carried out using X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS). The results reveal the abundant formation of ettringite (E) and hydrotalcite (Ht) when weak acid salt agents are added, especially in chloride and sulfate-rich curing solutions, leading to a notable increase in compressive strength, up to 200% compared to the control sample. Furthermore, the study demonstrates a substantial improvement in early and overall strength under temperature-stimulated curing conditions, accelerating the hydration reaction of SSC. These findings provide deeper insights into the factors influencing SSC hardening and strength development, offering valuable information for enhancing the efficiency and utilization of SSC in the construction industry, aligning with the goals of sustainable development.

High-efficient stabilization and solidification of municipal solid waste incineration fly ash by synergy of alkali treatment and supersulfated cement

Municipal solid waste incineration fly ash (IFA) designated as hazardous waste poses risks to environment and human health. This study introduces a novel approach for the stabilization and solidification (S/S) of IFA: a combined approach involving alkali treatment and immobilization in low-carbon supersulfated cement (SSC). The impact of varying temperatures of alkali solution on the chemical and mineralogical compositions, as well as the pozzolanic reactivity of IFA, and the removal efficiency of heavy metals and metallic aluminum (Al) were examined. The physical characteristics, hydration kinetics and effectiveness of SSC in immobilizing IFA were also analyzed. Results showed that alkali treatment at 25 °C effectively eliminated heavy metals like manganese (Mn), barium (Ba), nickel (Ni), and chromium (Cr) to safe levels and totally removed the metallic Al, while enhancing the pozzolanic reactivity of IFA. By incorporating the alkali-treated IFA and filtrate, the density, compressive strength and hydration reaction of SSC were improved, resulting in higher hydration degree, finer pore structure, and denser microstructure compared to untreated IFA. The rich presence of calcium-aluminosilicate-hydrate (C-(A)-S-H) and ettringite (AFt) in SSC facilitated the efficient stabilization and solidification of heavy metals, leading to a significant decrease in their leaching potential. The use of SSC for treating Ca(OH)2- and 25°C-treated IFA could achieve high strength and high-efficient immobilization.

Impact of basic oxygen furnace slag on the hydration microstructure, mechanical properties, and carbon emissions of supersulfated cement

Supersulfated cement (SSC) is recognized as a cementitious material with low CO2 emissions, consisting predominantly of ground granulated blast-furnace slag (GGBS) and a minor activator content. The production of GGBS production constitutes the primary source of CO2 emissions in SSC. In contrast, carbon emissions from the production of basic oxygen furnace slag (BOFS) are lower, and BOFS inherently exhibits substantial carbonization potential. Therefore, in this study, BOFS is employed as a replacement for GGBS in formulating an innovative low-emissions binder denoted as BOFS-modified supersulfated cement (BMSC). This study investigates the influence patterns of BOFS substitution for GGBS on the strength properties of BMSC. Furthermore, a series of experiments involving QXRD, TGA, SEM, and MIP were conducted to systematically investigate the mechanistic impact of BOFS on the hydration microstructure of BMSC. The findings reveal that substituting 10 % of GGBS with BOFS contributes to an enhancement in both flexural and compressive strength of specimens at 7 and 28 days. BOFS exerts a positive influence on the formation of ettringite in BMSC. The C2S and C4AF within BOFS also demonstrate distinct hydration activity. Additionally, BOFS can reduce large pores in the early hydration paste and contribute to narrowing the average pore size. Moreover, the evaluation of the Global Warming Potential (GWP) demonstrates that the replacement of slag with BOFS can lead to a further reduction of up to 30 % in the carbon emissions of SSC.

Effect of steel slag as alkaline exciter on the properties of supersulfated cement

In order to investigate the feasibility of steel slag as an alkaline exciter for supersulfated cement, the effects of different steel slag dosages on the properties of supersulfated cement were studied. The results show that when steel slag is used as alkaline exciter, the compressive strength and softening coefficient of supersulfate cement increase and then decrease with the increase of steel slag dosage, and the increase of steel slag dosage accelerates the hydration of slag, forming more hydration products of Ettringite and C-S-H gel. Steel slag dosage in 10% of the best results, excessive steel slag will generate expansion of Ettringite, resulting in expansion of the cement matrix structure cracking, is not conducive to the development of strength.

Engineered Cementitious Composites with Super-Sulfated Cement: Mechanical, Physical, and Durability Performance.

This study aimed to bridge a research gap by exploring the utilization of super-sulphated cement (SSC) in engineered cementitious composites (ECCs) as a sustainable alternative to ordinary Portland cement (OPC)-based mixtures. The SSC was designed with slag, gypsum, and a small amount of OPC. The primary objective was to investigate the effects of incorporating SSC, both with and without fly ash (FA), at various FA/SSC ratios between 0 and 1.5. A comprehensive evaluation was conducted to assess the performance of the ECC-SSC mixtures, including the compressive and flexural strengths, ductility, ultrasonic pulse velocity, rapid chloride permeability, and drying shrinkage. Additionally, advanced microstructural evaluation techniques such as scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis as well as X-ray diffraction (XRD) analysis were employed to analyze the reaction products in selected mixtures. The results showed that the ECC mixture produced with SSC exhibited comparable strength to the ECC-OPC. In general, all the SSC-based ECCs fulfilled the criteria for various engineering applications, especially when the fly ash to SSC ratios were 0 and 0.8. In addition, ECCs with FA/SSC ratios of 1.2 and 1.5 showed ultra-ductile performance higher than the control ECC. Interestingly, all the FA-based ECC-SSC presented lower shrinkage characteristics than the control OPC-based ECC.

Mechanical properties and hydration mechanism of super-sulfated cement prepared with ordinary Portland cement, carbide slag, and sodium silicate

Mechanical properties and hydration mechanism of super-sulfated cement prepared with ordinary Portland cement, carbide slag, and sodium silicate

Study on Sustainable Application of Low-Carbon Supersulfated Cement with Alkanolamines

As an environmentally friendly cement material in green buildings, due to its low contribution to air pollution and its substantial use of solid waste, supersulfated cement (SSC) has been extensively studied. However, the low early strength of sustainably utilized SSC needs to be addressed. In order to use SSC to achieve great reductions in energy consumption during industrial production, the effects of triethanolamine (TEA), diethanolisopropanolamine (DEIPA) and triisopropanolamine (TIPA) (with dosages ranging from 0.02% to 0.08%) on the strength and hydration of SSC were studied, and the underlying mechanism was analyzed by TGA, XRD and SEM. The results show that TEA and DEIPA significantly improve the 3-day and 28-day strength of SSC. The former is better at low dosages, while the latter is more suitable for high dosages. TIPA also enhances the 3-day strength of SSC, but it is not as good as the other two alkanolamines. The chelation of alkanolamine with Al3+ ions plays an important role in the strength development of SSC, which accelerates the decomposition of slag and the formation of ettringite. In summary, adding alkanolamines to low-carbon cement systems with a high proportion of industrial by-products such as SSC is a potential and effective solution. In addition, alkanolamines can be used as a strength promoter for most low-carbon blends, which fully utilize solid waste.

Effect of Calcium Aluminate and Carbide Slag on Mechanical Property and Hydration Mechanism of Supersulfated Cement

Supersulfated cement (SSC), a low-carbon, energy-efficient, eco-friendly cementitious material, is mainly made from industrial byproducts. However, SSC’s slow early strength development leads to inadequate initial hardening and reduced durability, which restricts its practical application. This study investigated the potential enhancement of SSC by incorporating calcium aluminate (CA) and carbide slag (CS) alongside anhydrite as activators to address its slow early strength development. The effects of varying CA and CS proportions on the mechanical property and hydration mechanism of CA-CS-SSC were examined. Results indicate that employing 1% CA and 4% CS as alkaline activators effectively activates slag hydration in the 1CA-4CS-SSC, achieving a compressive strength of 9.7 MPa at 1 day. Despite the limited improvement in early compressive strength of other mixtures with higher CA and lower CS proportions in the CA-CS-SSC system, all mixtures exhibited enhanced compressive strength during long-term hydration. After 90 days, ettringite formation in the CA-CS-SSC system decelerated, whereas anhydrite remained. Concurrently, the formation of C-S-H continued to increase, promoting late compressive strength. The mechanism for enhancing the early compressive strength of the CA-CS-SSC system is attributed to the swift hydration of CA with anhydrite, dissolution of fine slag particles, and reaction with anhydrite under conditions with suitable alkali content to augment the ettringite production. This process also generates a C-S-H and OH-hydrotalcite to fill the void in the skeleton structure formed by ettringite, resulting in a dense microstructure that improves early compressive strength.

Improving the frost-resistance performance of supersulfated cement by reducing the crystalline-to-gel ratio through the addition of nano-SiO2

The poor frost resistance of supersulfated cement (SSC) is of great concerns for its application. This research assessed the frost resistance performance of SSC with 1 wt.% and 3 wt.% cement clinker activator (C1 and C3) and explored the effects of nano-SiO2 (NS) (1 wt.% and 3 wt.%, N1 and N3) on the frost resistance of SSC through macro- and micro-evaluation on loss of the compressive strength/the mass/the relative dynamic elastic modulus and XRD/MIP/SEM. Results showed that the frost resistance of C1 sample was superior than those of C3 sample. The addition of NS enhanced the frost resistance of SSC: the maximum mass loss was reduced by about 92.8% and the maximum relative dynamic elastic modulus loss was decreased by about 34.6%. This could be ascribed to the change of the porous microstructure: the portion of micro-pores smaller than 20 nm increased and the microstructure was densified. Moreover, Moreover, NS changes the long needle-like crystalline phase (AFt) shape to a short rod-like shape, the latter of which was more tightly wrapped by the gel phase, leading to a more compact microstructure, and the detachment of AFt from gel matrix (would be introduced by the difference of their contraction/expansion rate under F-T cycles) could result in the poor performance of SSC, while this could be relieved by the reduction of the AFt-to-gel ratio as seen from the NS-added SSC sample.

Autogenous shrinkage and tensile creep of supersulfated cement concrete at early age

Supersulfated cement (SSC) is an environmentally friendly cementitious material known for its low hydration heat, high flexural strength, as well as resistance to sulfate attack. While existing research on SSC concrete mainly focuses on mechanical properties and hydration mechanisms, there exists a gap concerning the optimization of SSC concrete and the exploration of its early-age behavior. Early-age tensile creep of concrete has the potential to alleviate tensile stresses induced by restrained shrinkage. The current research aimed to fill this research gap by investigating the autogenous shrinkage and tensile creep of SSC concrete under different granulated blast furnace slag (GBFS) substitution rates (0%, 15%, 30%, and 50%) utilizing the Temperature Stress Test Machine. Experimental findings demonstrated that with a higher GBFS substitution rate, the mechanical properties and autogenous shrinkage decreased, while the tensile creep behavior of SSC concrete increased at early age. Additionally, models for predicting the autogenous shrinkage and tensile creep compliance of SSC concrete were proposed considering the GBFS substitution rate at early age.

Hydration mechanism of anhydrite and calcium sulfoaluminate co-activated slag cement: insights into the role of composition

Utilization of Portland cement to initiate the dissolution of blast furnace slag (BFS) in super-sulfated cement is limited by low slag substitution level and poor early strength. In this study, a new activator composed of anhydrite and calcium sulfoaluminate cement clinker was proposed to enhance the utilization of BFS in super-sulfated cement. Tests were conducted on the compressive strength, autogenous shrinkage, hydration heat, pH and conductivity of the composites. XRD, 29Si NMR, BSE and MIP were employed. Results reveal that ettringite, gypsum and C-S-H are the primary hydration products. The composites with 20% activator display the highest compressive strength and shrinkage accompanied by the highest hydration heat and degree, as well as the highest quantity of monomer silica tetrahedrons and the largest volume of fine pores. Thermodynamic modeling confirms the critical value for the activator-substitution level. Additionally, the activator-BFS composite exhibited significantly lower carbon emissions compared to Portland cement.

Utilizations of preheated flue gas desulfurization gypsum and sulfate compositions to modify performances of super-sulfated cement

Utilizations of preheated flue gas desulfurization gypsum and sulfate compositions to modify performances of super-sulfated cement

The evolution characteristics of water absorption, hydration products and microstructure of supersulfated cement containing phosphogypsum by microbial induced carbonate precipitation

In this paper, microbial induced calcite precipitation (MICP) was adopted as a modifying technology for surface property enhancement of supersulfated cement (SSC) containing phosphogypsum (PG). A series of tests including waster absorption test, mercury intrusion porosimetry (MIP), X-ray diffractometry (XRD), thermogravimetric analysis (TGA) and scanning electron microscopy (SEM) were conducted to investigate the modification mechanism of SSC containing PG. The results indicate that the enhancement of surface properties is highly dependent on the modification methods and conditions. The effect of surface treatments on the reduction of water absorption and the refine of pore structure is superior to that of the direct-addition method (DM). After surface treatment, the content of ettringite slightly drops, while the calcite content rises significantly. TM with the volume ratio of bacterial solution to cementation solution of 1:1 leads to the formation of more bio calcite with spherical or square particles, which can fill the inner pores and surface holes of the surface layer. The increase of treatment cycle has a limited effect on the increase of calcite content, while can refine the pore structure and reduce the absorption coefficient when the treatment cycle was 9. DM has a great influence on the alkalinity of SSC mortar, which can significantly reduce the content of ettringite and slightly increase the calcite content and it also changes the morphology of ettringite in matrix.

Mechanisms on the inhibition of alkali-silica reaction in supersulfated cement

The supersulfated cementitious system gains increasing popularity for lowering carbon emissions of the construction industry. However, the alkali-silica reaction (ASR) behavior of this sulfate-rich cement is still unclear. This study first reports the characteristics and suppressing mechanisms of ASR in supersulfated cement (SSC). The results show that nearly no ASR-induced expansion is found in the SSC even if 100% glass aggregates are used, while the expansion ratio of the traditional OPC is twenty times higher than the SSC. In the SSC, the further hydration of unreacted slag during the ASR test refines the pore size and enhances the compressive strength of the matrix. Meanwhile, the consumption of the alkali ions in the pore solution during the formation of N-A-S-H gel reduces the concentration of the alkali ions and the contact possibility with the aggregates. The high bulk electrical resistance of the SSC can mitigate the diffusion of alkali ions from the external solution to the mortar. Moreover, the higher Al/Si ratio of C-A-S-H in the SSC than C–S–H in the OPC system results in a higher adsorption capacity of Na+ due to the more negatively charged surface, reducing the concentration of alkali ions in the pore solution. Furthermore, the high concentration of SO42− in the pore solution of SSC can inhibit the diffusion of OH−. As a result, the low-carbon SSC system would be a promising cementitious material to mitigate the ASR risk.

Durability parameters of three low-carbon concretes (low clinker, alkali-activated slag and supersulfated cement)

The general transfer properties (water porosity, mercury intrusion porosimetry, water permeability, capillary absorption, gas permeability and resistivity) and chloride penetration resistance (natural chloride diffusion test and rapid chloride permeability test) of three low-carbon concretes C25/30 (low clinker (LCK) concrete, alkali-activated slag with sodium carbonate (Na2CO3-AAS) concrete and supersulfated cement (SSC) concrete) were evaluated and compared, in order to identify the strengths and weaknesses of each technology. The results show that the LCK concrete is characterized by “excellent” transfer properties (low water porosity, gas permeability, water permeability and capillary absorption) but high viscosity in the fresh state and very high chloride permeability. AAS and SSC concretes have similar transfer properties, comparable to classical concretes C25/30, and are extremely resistant to chloride penetration. Finally, the use of traditional protocols for durability tests applied to alternative low-carbon binders is questioned and metrology adaptations are proposed.

Experimental study on cracking potential and viscoelastic behaviors of supersulfated cement concrete with different compositions

Supersulfated cement (SSC) is considered as an eco-friendly alternative to ordinary Portland cement. However, the investigations of SSC concrete with fly ash (FA) and granulated blast furnace slag (GBFS) are still limited. This paper presented an investigation on effects of compositions on cracking potential and viscoelastic behaviors of SSC concrete at early age. FA and GBFS were introduced to replace SSC. The replacement ratio was 0%, 30%, and 50% by weight of SSC. Mechanical properties and free shrinkage were determined. Viscoelastic behaviors including stress relaxation and creep were quantified by restrained ring test with different degrees of restraint. Results demonstrated that the mechanical properties of SSC concrete were significantly reduced by replacing SSC with FA and/or GBFS. At a same replacement ratio, combined addition of FA and GBFS enhanced mechanical properties. Shrinkages were mitigated by replacement of FA and/or GBFS and decreased with an increase on FA replacement ratio. A high replacement ratio induced a rapid increase on cracking potential in the first few days. The replacement of FA and/or GBFS decreased the relaxed stress of SSC concrete. The available results of this paper might help to better understand the application potential of SSC concrete in engineering practices.