Calcium Sulphoaluminate Cement Research Articles

Investigation on the Impacts of Three Sea Salt Ions on the Performance of CSA-OPC Binary System

This study aimed to explore the impact of three corrosive ions—SO42−, Cl−, and Mg2+—on the hydration property of calcium sulphoaluminate (CSA) cement. Cement paste was prepared using three types of sea salt ion solutions with varying concentrations as mixing water. The experimental program encompassed assessments of porosity, compressive/flexural strength, heat of hydration, pH of pore solution, XRD, and SEM analysis. To modulate the hydration environment, Ordinary Portland cement (10%) was incorporated to elevate the pH and enhance the stability of ettringite, thereby facilitating the formation of additional C-S-H gel for the observation of M-S-H and other compounds. Findings revealed that the Cl− accelerated the hydration of CSA, resulting in heightened heat release. However, it also decreased the length-to-diameter ratio of ettringite, leading to cracking in CSA test blocks. The addition of SO42− resulted in elevated internal alkalinity, prompting alterations in hydration product types and subsequent reduction in CSA strength. Conversely, Mg2+ was observed to ameliorate the microstructure of CSA test blocks, diminishing porosity and augmenting strength.

Hydration, strength, and microstructure evolution of Portland cement-calcium sulphoaluminate cement-CSH seeds ultra-early strength cementitious system

Improving the very early age strength of precast concrete components at ambient temperature and ensuring the development of later strength is of significant engineering importance. This objective was successfully achieved by incorporating a specific percentage of 0–3% CSH seeds (CSHs) and 5%-20% calcium sulphoaluminate cement (CSA) into Portland cement (PC). The hydration, strength and microstructure evolution of Portland cement-calcium sulphoaluminate cement-CSH seeds cementitious system were investigated. Hydration heat tests reveal that CSHs effectively accelerated the early hydration of the slurry within the first 12 h without affecting its later hydration. CSHs and CSA acted synergistically to enhance hydration kinetics. However, it is crucial to control the proportion of CSA within the range of 5%-10%; exceeding this ratio can severely inhibit the hydration of silicates. Strength tests indicate that the addition of CSHs and CSA can increase the compressive and flexural strengths of mortar within the first 12 h by 282% and 208%, respectively, without impacting the development of its later-age strength. Together, they synergistically provide favorable support for the strength and toughness of matrix. Based on linear regression analysis and nitrogen adsorption and desorption tests, it was concluded that CSHs enhance the hydration dependence of matrix strength, while CSA diminishes this characteristic. This is because CSHs refine the pore size distribution of the paste, increasing the proportion of micropores, whereas CSA promotes the formation of more mesopores and macropores, leading to coarser pores; however, 5% CSA is beneficial for further refining the pore structure. The microcosmic phase evolution of the early-strength cementitious system was analyzed through X-ray diffraction and scanning electron microscope-energy dispersive spectrometer experiments. Results demonstrate that low proportions of CSA and CSHs promote the co-growth of ettringite and C-S-H gel, ensuring a more rapid formation of a dense hydration network in the early stages, thereby accelerating strength development. These findings provide a reference for the design and preparation of precast concrete.

Synergistic Effects of Ethylene Glycol Solution and Polycarboxylate Superplasticizer on the Hydration of Calcium Sulphoaluminate Cement at −10°C

Synergistic Effects of Ethylene Glycol Solution and Polycarboxylate Superplasticizer on the Hydration of Calcium Sulphoaluminate Cement at −10°C

Effects of early vibration and resistant strategies on bond performances between high-strength concrete and rebar

The local bond performances between rebar and high-strength concrete (HSC) exposed to early vibration were experimentally investigated in this study. In addition, three vibration-resistant strategies, including additions of special rapid-hardening cement(calcium sulphoaluminate cement, CSA), shrinkage compensation admixture (expansion agent, EA), and toughening metallic fibers (steel fiber), were verified through penetration resistance, compressive, and central pull-out tests, respectively. Finally, two-way ANOVA tests were conducted to understand the significance of each strategy from a statistical perspective. The results demonstrated that early disturbances compromise bond performances by weakening chemical adherence and mechanical interlocking effects, which considerably degrade bond strength and stiffness. The presence of EA delayed the setting and hydration of concrete and prolonged vibration-sensitive duration. However, the later expansive hydrate products effectively strengthen the bond performances and compensate for early-stage vibration-induced damage. In comparison, the synergetic effects between CSA and Portland markedly enhance the hydration reactivity of blends at early stages, which can achieve threshold maturity and vibration resistance within hours. However, excessive CSA (10%) severely compromises the construction time of mixtures and amplifies the cracking potentials of HSC under the constraints of steel bars. The synergetic effects of steel fibers and aggregates formed disordered networks to enhance the vibration resistance and rigid skeletons for bridging cracks of HSC. The two-way ANOVA results indicate that EA significantly improves the mechanical performances of HSC, followed by steel fibers. The additions of expansive agents and steel fibers are highly recommended in engineering with vibration scenarios. In contrast, the dosages of CSA (or similar early-strength agents) should be carefully controlled unless with a robust shrinkage compensation strategy.

Strength and capillary water absorption of SB modified CSA cement mortar cured for 360 days under different conditions

AbstractThe effects of curing conditions including temperatures (0°C, 5°C, 10°C, 20°C and 40 °C), relative humidities (30%RH, 60%RH and 90%RH) and outdoor curing on the strength and capillary water absorption of styrene‐butadiene copolymer (SB) modified calcium sulphoaluminate (CSA) cement mortar cured for 360 days were studied. The results showed that when the addition of SB reached 10% and more, the flexural strength increased and the capillary water absorption decreased significantly. Appropriate temperature and relatively high humidity were conducive to the development of flexural and compressive strength. The capillary water absorption increased with increasing temperature and decreasing humidity. Compared with curing under different temperatures and relative humidities controlled by laboratory, the modified mortar cured outdoors with more than 10% SB addition had higher strength and lower capillary water absorption.

Properties of Fine Graded Perlite-Based Lightweight Cement Mortars Subjected to Elevated Temperatures

The present research compared the behaviours of lightweight mortars based on ordinary Portland cement (OPC), calcium sulphoaluminate cement (CSAC), and calcium aluminate cement (CAC) containing expanded perlite and subjected to elevated temperatures. The perlite substituted natural sand in amounts of 25, 50, 75, and 100% by volume. The mortars were subjected to heating at up to 300 °C, 650 °C, and 1000 °C at a rate of 20 °C/min. The consistency and density of fresh mortars, compressive strength and density of hardened mortars after heating and cooling, and absorbability were assessed. Such a holistic testing approach is the main novelty of this research, which is related to the aforementioned mixtures and elevated temperatures. The main contribution of this article is a comparison of various cement types coupled with variations in the level of sand replacement with expanded perlite. In previous studies, comparisons were made in pairs of OPC-CSAC and OPC-CAC for normal-weight concrete. There is a gap in our knowledge of triple comparisons and lightweight cement composites which is filled by the current study. The use of OPC at up to 650 °C is recommended because it is the most common solution, its performance is similar to that of CAC, and it is cheaper than other solutions. Above 650 °C and up to 1000 °C, CAC is the only solution because it performs better than other cements. CSAC is not suitable for use at elevated temperatures because of its poor strength performance, even if it is the best solution from an environmental point of view. Sand replacement with perlite does not increase the strength performance under elevated temperatures, but its efficiency is different for various types of cement.

The Effect of Different Particle Sizes of SiO2 in Sintering on the Formation of Ternesite

Ternesite is synthesized through sintering a mixture of CaCO3, SiO2, and CaSO4 in a molar ratio of 4:2:1. Ternesite has a hydration rate between ye’elimite and belite in an aluminum-containing environment, and is considered to be a new material that can be used to enhance the performance of calcium sulphoaluminate cements. This experiment investigated the influence of different particle sizes of SiO2 on ternesite formation. Controlled partial pressure sintering was employed within the temperature range from 1100 °C to 1200 °C, with a 72 h incubation period. The highest purity of ternesite in the samples reached 99.47% (500 nm SiO2 sample). The analysis results from scanning electron microscopy and an energy dispersive spectrometer indicated that the particle size of SiO2 exerted a significant influence on the formation of ternesite. In the preparation of ternesite from 10 μm particle size SiO2, traces of calcium silicate were found in the product. The results of a thermal analysis further demonstrated significant distinctions in the thermal stability of ternesite prepared with SiO2 of different particle sizes. Additionally, the crystallinity of ternesite was influenced by the particle size of SiO2, consequently impacting the hydration performance of ternesite–calcium sulphoaluminate cement.

Repairing performance and bottleneck analysis of concrete with encapsulated oxygen-dependent microbial Agent: Simulation-Aided characterization

Microbial self-healing concrete has natural advantages because of its environmental harmlessness and compatibility. Appropriate nutrients, microbial composition, and carriers are critical for microbial repairing agents to maximize restoration effectiveness in the harsh environment of concrete. However, little attention has been paid to the evolution of the healing process and the underlying mechanisms of bottlenecks. In this study, the potential of calcium lactate as the main nutrient source for Bacillus alcalophilus (B. alcalophilus), an alkali-resistant spore-producing microorganism, has been demonstrated firstly. The repairing performances and bottlenecks of oxygen-dependent microbial agent were then explored. Considering the harsh environment of concrete, calcium sulphoaluminate (CSA) cement was introduced to form a protective shell through artificial aggregate technology. Simultaneously, to reduce the influence of un-hydrated cement particles and to stabilize the continuous supply of calcium ions, the matrix has a higher maturity through 60 days of hydration. The results show that the encapsulated microbial self-healing agent had good repairing effects on cracks introduced after 60 days of hydration. Moreover, the distribution of repairing products in cracks was observed by X-CT, and the microbial remediation ability based on aerobic decomposing organic compounds was verified by simulation. The bottlenecks, shallow restoration depth and uneven distribution of restoration products, are mainly caused by gas transport and microbial biochemical activity. Finally, increasing the oxygen content in the fracture zone is an effective means to promote carbonate production and fracture filling.

Effects of premixed Cl− on performance of calcium sulphoaluminate cement: mechanism of anti-chloride penetration

Effects of premixed Cl− on performance of calcium sulphoaluminate cement: mechanism of anti-chloride penetration

Recycling thermal modified phosphogypsum in calcium sulfoaluminate cement: Evolution of engineering properties and micro-mechanism

The phosphogypsum (PG) can be used as a substitute for calcium sulphoaluminate cement (CSC) due to its high content of calcium sulfate dehydrate. In this study, the engineering properties including setting time, compressive strength and fluidity index of CSC with addition of thermal modified phosphogysum (MPG) were experimentally investigated. Furthermore, the micro-mechanisms including crystalline phase and microstructure evolutions of CSC incorporating MPG under different thermal treatment temperatures were analyzed via conducting X-ray diffraction (XRD), heat of hydration, thermogravimetry (TG) and scanning electron microscopy (SEM) tests. The results show that the optimum PG content and thermal modification temperature were respectively 10% and 300℃, which achieved the maximum compressive strength of 41.59 MPa. The hydration heat release peak of CSC with 300℃ MPG was advanced, contributing to shorter setting time and poor fluidity of CSC. Whereas after incorporating untreated and 100℃ MPG, the hydration exothermic peak of CSC lagged behind, causing higher retarding effect and better fluidity. The main hydration products of ettringite (AFt) and alumina gel (AH3) in CSC-MPG mixture were respectively produced in the early and later stages, which were similar to that in pure CSC. The amount of AFt was the most under the optimum incorporation of 10% MPG at 300℃, which was mainly responsible for the highest structure density. The key findings in this study can achieve the double benefits of utilizing waste PG and improving the engineering properties of CSC.

Introducing fiber to enhance the mechanical properties and durability of polymer-modified cement-based coating

Polymer-modified cement-based coatings are widely used in the field of concrete protection. However, in harsh environments such as the ocean, the core durability indicators such as anti-UV aging resistance and anti-chloride corrosion of the coating need to be further improved. In this study, the polypropylene (PP) fiber was introduced into the composite coating with silicone-modified polyacrylate (SPA) emulsion and calcium sulphoaluminate (CSA) cement as the main body. And the influences of PP fiber on the mechanical properties, UV aging resistance and chloride penetration were mainly discussed. Results showed that PP fiber not only significantly improved the tensile strength of the coating as expected (increment > 60%), but also showed the obviously positive effect on the bonding strength and wear resistance. For UV aging conditions, PP fiber could reduce the loss rate of elongation at break of the coating. For chloride corrosion, the chloride penetration resistance of the coating was also significantly improved by 48.92%. The enhancement was attributed to PP fiber itself and its effects on the coating, resisting the external stress, promoting the break of bubbles and reducing microporosity. In addition, the application was also attached to this study to verify the performance of the coating.

Synthesis of Ye’elimite from Anthropogenic Waste

Calcium sulphoaluminate cement (CSA) is characterized by a different chemical and mineralogical composition than common cements based mainly on Portland clinker. Its main component is ye’elimite—Ca4(AlO2)6SO4. This cement is characterized by a shorter setting time and a dynamic increase in strength in the early aging process. Currently, CSA cements are gaining more and more popularity due to their favorable ecological aspects, including a reduction in carbon dioxide emissions and negative impacts on the environment. The aim of the study was to determine the possibility of obtaining ye’elimite from waste materials of anthropogenic origin, which in this case were by-products from the aluminum anodizing process and cement–asbestos waste. The results of this preliminary research indicated the possibility of obtaining ye’elimite from secondary raw materials of anthropogenic origin. In each material, the phase of ye’elimite was identified to be the main mineral component, and the obtained materials displayed binding properties after mixing with water.

Calcium sulphoaluminate cement from solid waste with nano-TiO2 addition for high-efficiency CO2 capture

Calcium sulphoaluminate cement from solid waste (WCSA) has a relatively lower sintering temperature and low CO2 emission, meanwhile, the low cost of WCSA and the good CO2 absorption capacity make it one of the current hot topics of research. In this work, based on the optimal water-cement ratio, the effect of titanium oxide (TiO2) on the pore structure and the hydration process of WCSA were explored. The hydration process and microscopic evolution were studied by compressive strength test, carbonization test, Brunauer-Emmet-Teller measurement (BET), X-ray diffraction (XRD), the heat of hydration, thermogravimetric analysis (TG), and scanning electron microscope (SEM). The effect of nano-TiO2 on the carbon sequestration behavior of WCSA was also analyzed. The results show that WCSA with a water-cement ratio of 0.4 is the optimal carbonization substrate and nano-TiO2 will make the pore structure more uniform and dense, simultaneously increasing the adsorption pressure for the CO2. Meanwhile, the nano-TiO2 can effectively promote and regulate the crystallization, nucleation, and growth of ettringite crystals. It can be found that the WCSA containing 1% nano-TiO2 has the highest carbon capture ability among all the contents, and the ettringite crystal is concave hexahedron. The research considered that the concave surface with large specific surface energy can effectively increase the contact area between CO2 and ettringite, which greatly improved the CO2 absorption of ettringite. Overall, WCSA containing nano-TiO2 may provide some new opportunities for efficient carbon capture.

Rapid self-sealing of macro cracks of cementitious composites by in-situ alginate crosslinking

Despite the development of several self-healing concrete techniques, only micro cracks can be effectively self-repaired. To achieve self-healing of macro cracks (>1 mm), a strategy by in-situ calcium alginate crosslinking within cracks was proposed herein. This strategy was accomplished by encapsulating sodium alginate in polyethylene glycol granules coated with epoxy resin and calcium sulphoaluminate cement as protective shells. The capsules can release alginates and leach calcium in water once broken and subsequently the gelation can be conducted, thereby generating hydrogels. By incorporating the capsules in mortar specimens, hydrogels were successfully formed through calcium alginate crosslinking after cracking, which led to closures of 1–4 mm wide cracks and significant reduction of water permeability mainly in 1 day. The crack sealing due to crosslinking generation was further simulated by a modified model in terms of hydrogel volume growth and the predicted crack sealing evolutions were consistent with the experimental results.

The influence of calcium sulphoaluminate cement on the hydration process of cement paste mixed with alkali free liquid accelerator

Sulphoaluminate cement is considered green cement, which has the characteristics of rapid setting and high early strength. The partial substitution of sulphoaluminate cement (CSA) for ordered portland cement (OPC) was investigated in the system mixed with alkali free liquid accelerator. The hydration process and products were analyzed by hydration heat exothermic curve, XRD, TG and SEM. The results showed that CSA could promote the early hydration of pastes mixed with alkali free liquid accelerator and delay the later hydration. In addition, combined with the analysis results, the hydration conceptual model of CSA for paste mixed with alkali free liquid accelerator was proposed. The sulphoaluminate cement OPC composite cement is used in shotcrete for the first time. Combined with hydration heat, XRD, and TG tests, the theoretical hydration model of CSA-OPC composite cement is proposed. The application of environment-friendly sulphoaluminum cement in shotcrete is realized.

Enhanced comprehensive performance of polymer-CSA cement coating with graphene oxide

Graphene oxide (GO) is widely used in cement-based materials due to its high aspect ratio and excellent mechanical properties. In this study, to further enhance the mechanical properties and durability of polymer-modified cement-based coating, GO was introduced into the coating with silicone-modified polyacrylate (SPA) emulsion and calcium sulphoaluminate (CSA) cement as the main body. The results showed that the overall mechanical properties were optimal when the dosage of GO was 0.05%. Meanwhile, the UV aging resistance, anticorrosion and impermeability of the coating were also enhanced by the incorporation of GO. In addition, MIP, SEM, and FTIR test were used to investigate its mechanism. Obtained results demonstrated the coating doping GO could optimize the three-dimensional network structure, effectively prolong the water salt transmission path and reduce the water and ion permeability.

New findings on the contribution of Mg-Al-NO3 layered double hydroxides to the hydration and chloride binding capacity of cement pastes

The impact of the addition of layered double hydroxides (LDHs) on binding of chloride ions was studied by pore expression experiments. A Mg-Al-NO3 type of LDHs was added to paste samples blended with 3 % NaCl in different proportions (4 % and 10 % by mass of the binder). In addition, the influence of LDHs on the hydration process, morphology and porosity of samples containing Portland cement, calcium sulphoaluminate cement and silica fume was investigated. The potential physical and chemical contributions of LDHs to the system (e.g. AFm formation) were discussed comprehensively. According to the results, addition of LDHs by 10 % could reduce the chloride content in the pore solution by over 25 % and increase the carbonate AFm phases. Moreover, formation of reaction products on the LDH grains was observed. Finally, it was clear that a part of the Cl− ions is bound to the surface of LDHs and can be washed out.

Effects of C$H2 and CH on Strength and Hydration of Calcium Sulphoaluminate Cement Prepared from Phosphogypsum

Using phosphogypsum (PG) as a raw material to prepare calcium sulphoaluminate cement (CAS) is an effective way of treating phosphogypsum. In order to meet the different application requirements of CSA cement and promote the application of CAS cement, it is necessary to add mineral admixtures to adjust the performance of cement. This paper incorporated two minerals, gypsum dihydrate (C$H2) and calcium hydroxide (CH), into cement clinker prepared from phosphogypsum. The compressive strength and hydration process of the mixtures with different blending levels were investigated around the C4A3$-C$H2 system (SC) and the C4A3$-C$H2-CH system (SCC). The optimum dosing level was determined on the basis of the strength and hydration properties. In the SC system, adding C$H2 promoted the hydration of C4A3$. The compressive strength of the cement was highest at a C$H2/C4A3$ molar ratio of 1.5, with a 7-day compressive strength of 56.5 MPa. AFt was mostly needle-rod and columnar and was tightly cemented to the gel phase, improving the denseness of the matrix. When the molar ratio was 2, the strength of the cement was inverted, and the shape of the AFt changed from needle and rod to columnar, the size of the grains increased, and it could not be filled with the AH3 phase in an excellent staggered manner. At the same time, C$H2 was not fully reacted, increasing matrix porosity and inversion of strength. In the SCC system, adding CH reduced the cement’s compressive strength, and the compressive strength reduction increased with the increase in admixture. According to the experimental results, CH inhibited the formation of AFt, resulting in the appearance of new hydration products, AFm. As the amount of CH increased, the amount of hydration products, AFm, increased, while the amount of AFt and AH3 decreased. However, adding CH raised the paste’s pH and later facilitated the development of strength. The optimum admixture of CH/C4A3$ was 0.5 mol.

Effects of Limestone Powder on the Early Hydration Behavior of Ye'elimite: Experimental Research and Thermodynamic Modelling.

To investigate the effects of limestone powder and gypsum on the early hydration of ye’elimite, the hydration behavior of C4A3-LP-CaSO4·2H2O-H2O systems are researched. The hydration behavior of systems are researched by employing isothermal calorimetry, XRD technique and chemical shrinkage. The thermodynamic modelling method is employed to predict the equilibrium phase assemblages. The results show that the system with 5 wt.% LP has a comparable hydration heat evolution to limestone powder-free systems. Limestone powder can take part in the reaction to produce monocarboaluminate in the system with M-value (molar ratio of gypsum to ye’elimite) of 1, but monocarboaluminate is not found in the system with M-value of 2. The level off time of chemical shrinkage shortens with the increase of limestone powder dosage. Thermodynamic modelling results show that monocarboaluminate is no longer formed in all systems when M-value exceeds 1.27, which corresponds to the XRD results. This study can provide theoretical guidance for the rational utilization of limestone powder in calcium sulphoaluminate cement.

Passivation behaviour of mild steel embedded in magnesium potassium phosphate cement-calcium sulphoaluminate cement blended paste

• Passivity of mild steel embedded in MKPC-CSA blended paste were investigated. • CSA addition significantly influences the degree of passivity. • Passivity increases with increased CSA addition and 30% CSA addition leads to a much higher passivity. • 30 % CSA addition benefits the precipitation of phosphate ions and formation of Fe 2+ oxide in passive film. This study did a pioneer work focused on the passivation of mild steel embedded in magnesium potassium phosphate cement (MKPC)-calcium sulphoaluminate cement (CSA) blended paste via electrochemical measurements and materials characterization techniques. Results showed that 30 % CSA addition in MKPC leads to a passivity of mild steel much higher than that in Portland cement (PC) paste. The passivity of mild steel increased with an increase in CSA content in MKPC paste due to an increase in pH and phosphate concentration in pore solution. The formation of iron phosphate and Fe 2+ oxide in passive film of MKPC-30 %CSA contributes to its highest passivity.