Calcium Sulfoaluminate Research Articles

Effect of gypsum addition on acid resistance of ye'elimite rich calcium sulfoaluminate cement

Calcium sulfoaluminate (CSA) cements exhibit useful properties such as shrinkage compensation and rapid strength development. Acid resistance of CSA cement is majorly governed by its phase composition that varies significantly depending on the desired properties. In this study, acid resistance of CSA cement (i.e., non-expansive) and gypsum blended CSA cement (i.e., expansive) is explored. The current work emphasizes that a small change in phase assemblage can cause large difference in the performance under acidic environment. Conventional acid immersion tests with hydrochloric acid (HCl) of 1 % and 2 % conc., and sulfuric acid (H2SO4) of 2.95 % conc. were considered in the study. Furthermore, a recently developed acid consumption method was used to rank the binders with regard to their acid resistance in HCl and H2SO4 environments. It was found that the gypsum-blended CSA cement showed poorer performance than CSA cement in acidic environment despite having marginally higher compressive strength before the acid exposure.

Biogenic acid resistance of calcium sulfoaluminate cement: Revelations from a field study

Biogenic acid attack of concrete is prevalent in sewers, posing a serious durability concern and financial burden. There are very limited number of field studies on durability of concrete under biogenic acid attack. Field study poses challenges with respect to the variation in climatic conditions and limited accessibility in sewers. Such a biogenic acid attack study in Indian conditions has not been performed. In this study, the biogenic acid resistance of Portland cement (PC) and calcium sulfoaluminate (CSA) cement-based binders under an in-situ sewer exposure is reported. The results show that the CSA-based binder used in this study outperformed PC in the biogenic acid resistance. The superior performance of CSA-based binder could be attributed to its acid neutralisation capacity offered by the aluminum hydroxide phase and bactericidal properties. For the first time, the bacteriostatic effect of CSA cement was demonstrated by analyzing the field exposed specimens.

Cement-based ductile rapid repair material modified with self-emulsifying waterborne epoxy

Ordinary silicate cement repair materials are slow to set and harden, have low early strength, and cannot meet the demands of rapid repair, and the disadvantage of brittleness after repair is obvious. Calcium sulfoaluminate cement (CSA) is more suitable for use as a cementitious material for rapid repair materials due to its fast hardening and early strength characteristics, but this cementitious material still suffers from low bond strength and poor toughness, which cannot be effectively resolved. In recent years, polymer-modified cementitious materials have attracted a great deal of attention in the field of repair and reinforcement. Among the many polymer options, epoxy resins have become the most promising choice due to their excellent compatibility and coupling effect with cement hydration and their excellent overall performance. In this paper, a novel waterborne epoxy resin-CSA cement composite restoration material was prepared by using a self-synthesized waterborne epoxy resin (WEP). The mechanism by which WEP improves the performance of CSA cementitious restorative material was also elucidated. The results show that by adjusting the amount of WEP, the workability of the repair material can be regulated. WEP significantly improved the interfacial bond strength of the repair material, and the toughness of CSA cement repair material with 10% WEP increased by 32.2% and the tensile ductility increased by 93.8% compared to the control group. The fully cured WEP and CSA cement hydration products form a dense cross-linked network-like structure, which refines the pore structure of the repair material and improves the disadvantages of the highly brittle and low ductility of the repair material.

Thermodynamic prediction of complex hydration processes and verification by experiments for the Ca-Al-C (CA, calcite, water) and Ca-Al-S (ye'elimite, gypsum, water) systems

The solubility of relevant phases in the calcium aluminate cements with limestone and in calcium sulfoaluminate cements with gypsum indicate several potential phase assemblages which might be formed during hydration. Thermodynamic calculations and pore solution data indicate that initially the solution is oversaturated with respect to several phases and thermodynamically metastable phase combinations may form. Some initially formed metastable phase assemblages contain more phases than predicted by the Gibbs phase rule and gain less Gibbs free energy than the stable phase assemblage. Solubility curves are used to define potential phase assemblages, the associated potential Gibbs free energy gain, to plot possible kinetic paths and to evaluate their respective probability. If different kinetic paths are conceivable, the reaction occurs along the solubility of the initially formed stable phases, namely monocarbonate in the calcium aluminate and ettringite in calcium sulfoaluminate system.

Effects of AH3 and AFt on the Hydration-Hardening Properties of the C4A3S¯-CS¯-H2O System.

This study aimed to reveal the effects of the hydration products AH3 and AFt phases on the hydration and hardening properties of calcium sulfoaluminate (CSA) cement. In addition, the effects of anhydrite (CS¯) and gypsum (CS¯H2) on the properties of CSA cement were compared. Calcium sulfoaluminate (C4A3S¯) was synthesized with analytical reagents, and the C4A3S¯-CS¯-H2O system with different molar ratios of CS¯ and C4A3S¯ was established. The phase compositions and contents of AFt and AH3 were determined by X-ray diffraction (XRD), Rietveld quantitative phase analysis, and thermogravimetric analysis (TG). The effects of pore structure and hydration product morphology on mechanical properties were analyzed by mercury intrusion porosity (MIP) and scanning electron microscopy (SEM). The results showed that the compressive strength exhibited a correlation with the AH3 content. In the case of relatively sufficient anhydrite or gypsum, C4A3S¯ has a high degree of hydration, and the AH3 content can be considered to contribute more to the strength of the hardened cement paste. When anhydrite was selected, the combined and interlocked AFt crystals were covered or wrapped by a large amount of AH3. The mechanical properties of the hardened cement paste mixed with anhydrite were better than those of that mixed with gypsum.

Effect of Hydroxypropyl methyl cellulose (HPMC) on rheology and printability of the first printed layer of cement activated slag-based 3D printing concrete

Nowadays, Ground Granulated Blast Furnace Slag (GGBFS) is generally used to replace cement for reducing carbon emissions, but due to its low hydration activity and unstable working performance in the early stage, it is difficult to apply in 3D printed concrete (3DPC) as the main binder. In this study, a combination of ordinary Portland cement and calcium sulfoaluminate cement was used to activate GGBFS. In the presence of 0.2 wt% polycarboxylate superplasticizer (PCE), in order to achieve high-precision printing, hydroxypropyl methyl cellulose (HPMC) was used. The rheological properties of mortar were evaluated by the slugs-test and a rotational rheometer. The results show that the yield stress and thixotropy of slag cement-based 3D printing concrete are significantly increased, with addition of HPMC. The slugs-test shows its advantages in measuring rheological properties, such as superior repeatability of rheological data and a better association with 3D printing performance. Pumpability, extrudability, and buildability of the first printed layer of slag cement-based 3DPC were evaluated using pumping pressure, horizontal printing, and vertical printing. The results show that, with a 0.15 wt% HPMC, the 3D printing properties of the first layer are greatly improved, a stable and high-precision slag cement-based 3DPC can be developed, and the relationship between rheological properties and 3D printing performance can be established.

Investigation on the equivalent strength of Portland cement and PC-CSA blends: Experimental findings and thermodynamic modelling

Mixing calcium sulfoaluminate (CSA) cement and Portland cement (PC) can provide several benefits for certain applications, especially reducing the carbon footprint of PC. This study investigated the heat of hydration, hydration products, mechanical properties, autogenous shrinkage and microstructure of blended cement, and phase composition calculations were also made with thermodynamic modelling. The results show that the autogenous shrinkage of the cement paste is effectively mitigated due to the swelling produced by the rapid hydration of ye'elimite before 1 d. However, when the CSA admixture is 15 wt%, many large holes and obvious cracks can be found by three-dimensional rendition of X-ray computed tomography (X-CT), this may be attributed to the adverse effects of phase transformation, specifically the conversion of ettringite into monosulfate. Combined with the thermodynamic modelling results, the hydration of PC and CSA in the blended cement is a competitive relationship, and the presence of AH3 is not found in the PC-rich blended systems. In addition, the compressive strength of the blended mortars with addition of 5 wt% CSA at 28 d reached 61.5 MPa which is equivalent to that of plain PC. However, the strength of 15 wt% CSA addition is about 30 MPa lower than that of 5 wt% CSA. This is significantly correlated with AFt/AFm, and once AFt/AFm exceeds a certain limit, the strength of PC-CSA blends is significantly lower than that of plain PC.

Synthesis, structure, and hydration of stoichiometric ye’elimite and iron-bearing ye’elimite

Ye’elimite is the primary mineral component in calcium sulfoaluminate cements and is responsible for their early hydraulic reactivity. Herein, ye’elimite was synthesized using a novel method with CaSO4 as the sole CaO source to achieve high purity. Stoichiometric ye’elimite and iron-bearing ye’elimite were synthesized, with the highest purity obtained through sintering at 1250°C for 4 h. The crystal structure of iron-bearing ye’elimite was represented through dynamical disordering of the SO4 tetrahedron and Ca atom with the space group I 4 ¯ 3m. Moreover, the early hydration behaviors of stoichiometric ye’elimite and iron-bearing ye’elimite reacting with and without gypsum were studied. In the absence of gypsum, stoichiometric ye’elimite reacts faster than iron-bearing ye’elimite. However, in the presence of gypsum, the hydration of the former is faster than that of the latter and the hydration rates of both these minerals are higher than those observed in the absence of gypsum.

Impact of calcium sulfoaluminate cement on printability and early strength development of a slag-based 3D printing cementitious material

Blast furnace cement (BFC) as a binder for 3D printing cement (3DPC) has potential to lower carbon-footprints, but its unstable workability and strength development hinder its application. In this article, blast furnace cement (BFC), a mixture of ordinary Portland cement (OPC) and ground granulated blast furnace slag (GGBFS) based binder was designed toward low-carbon 3DPC, and the impact of calcium sulfoaluminate cement (CSA) content on printability and early strength of printed materials was discussed. The researched components of the materials, GGBFS, OPC and CSA, were first designed based on the 24 h early strength development. Slugs test was utilized to investigate 3D printability, and adiabatic hydration temperature, compressive strength, X-ray diffraction, thermal gravimetric analysis, and solid Si-nuclear magnetic resonance were used to analyze the early strength development and hydration products. For 1 h of hydration, CSA played a significant role in the hydration, due to generation of rod-shape Aft, which resulted in increase of yield stress as indicated by the slugs test. For 24 h of hydration, when CSA is less than 20%, it is C-S-H gel provided the strength; when CSA content is more than 20%, AFt constructs the skeleton, and unhydrated material and AH3 fill in the voids of the skeleton, resulted in high early strength. Strength response surface results indicated that GGBFS, OPC and CSA mass ratio of 5:4:1 is the best in this research. The 3DP opening time is in the range of 20–40 min, and the compressive strength at 24 h reaches 14.43 MPa.

Effect of particle size distribution on the pre-hydration, hydration kinetics, and mechanical properties of calcium sulfoaluminate cement

Effect of particle size distribution on the pre-hydration, hydration kinetics, and mechanical properties of calcium sulfoaluminate cement

Effects of shrinkage-reducing admixtures and expansive agents on the self-sensing behavior of nanomodified cement-based materials

Shrinkage control is needed to ensure an appropriate installation of cementitious sensors used in the Structural Health Monitoring of concrete elements. However, the effects of shrinkage-reducing admixtures (SRAs) and expansive agents (EAs) on the self-sensing properties of the cementitious sensors is still unknown. Therefore, the present work evaluated the effects of a SRA and EAs based on calcium oxide (CaO) or calcium sulfoaluminate (CSA) on the shrinkage behavior, microstructure, self-sensing response and compressive strength of mortars containing carbon black nanoparticles (CBN). The SRA provided shrinkage reductions up to 47.4%. CaO-based EA and CSA-based EA provided an expansive behavior. The admixtures caused increases in electrical resistivity and gauge factor up to 37.1% and 71.0%, respectively. In contrast, they did not cause statistically significant changes in stress sensibility and compressive strength. A microstructural analysis suggested that portlandite and ettringite crystals provided by the inclusion of EAs caused interruptions in conductive paths inside the mortars, which decreased contact conduction mechanisms and increased the amount of insulating tunneling gaps between CBN, enhancing the gauge factor of the materials. Therefore, shrinking control admixtures were found to be promising alternatives to enable the dimensional compatibility between cement sensors and old concrete elements, and increase the self-sensing properties of smart cementitious composites.

Optimal Design of Micro-expanded ECC and Its Interfacial Bonding Property with Steel Tube

The large shrinkage strain of Engineered Cementitious Composites (ECC) seriously affects its combined application with steel tube in engineering. In order to reduce the shrinkage of ECC and realize the effective bonding between ECC and steel tube, this paper studied the effects of single or multiple doped of expansive and internal curing agent on the shrinkage and mechanical properties of ECC, and tested the interfacial bond strength between ECC and steel tube. CaO and MgO compound expansive agent (CME), calcium sulfoaluminate expansive agent (HCSA), super water-absorbing polymer (SAP) internal curing agent are chosen for test. The results show that ECC mixed with 10% CME expansive agent and 0.2% SAP shows a slight expansion under the condition of sprinkling water curing. Moreover, the push-out test shows that the bond strength between micro-expanded ECC and steel tube reaches 1.27 MPa, which is nearly 2 times higher than that of the ordinary ECC, and higher than the bond strength of C50 filled steel tube. This paper provides the test and theoretical basis for the joint application of ECC with steel tube.

Effects of curing regime, cement type, and water-to-cement ratio on the physicochemical, mechanical, and hydraulic properties of pervious mortar

This study investigated the influence of curing regime, type of cement, and water-to-cement ratio (W/C) on the physicochemical, mechanical, and hydraulic properties of pervious mortar. The carbonation degree of mortar produced using ordinary Portland cement (OPC) and belite-rich cement (BRC) increases with an increase in the W/C ratio. Mortar produced using calcium sulfoaluminate (CSA) cement was completely carbonated within the first three days. A greater degree of carbonation was observed for BRC mortar compared to that of OPC mortar at 28 days. The hydraulic properties of pervious mortar were dominated by the curing regime. Specimens subjected to carbonation curing displayed more open voids and higher permeability. Further, both OPC and BRC mortars displayed higher compressive and flexural strength levels when subjected to carbonation curing. However, mortar produced using CSA displayed significantly lower compressive strength than those of OPC and BRC.

Retarding Effect of Hemp Hurd Lixiviates on the Hydration of Hydraulic and CSA Cements.

Wood wool panels are widely used in the construction industry as sustainable cementitious composites, but there is a growing need to replace traditional Portland cement with a binder that has a lower embodied carbon footprint. In addition, the sustainability of these panels may face serious impediments if the required amount of wood for their production needs a harvest rate higher than the rate at which the tree sources reach maturity. One solution is to use the wooden part of fast-growing plants such as hemp. However, the compounds extracted from the mixture of plants and water are the main cause of the delay observed during the hydration process of hydraulic binders in these cementitious composites. The objective of this study is to evaluate the effect of bio-aggregate lixiviates (hemp hurd) on the hydration kinetics of calcium sulfoaluminate (CSA) cement as a low-embodied-carbon alternative to ordinary Portland cement (OPC). The isothermal calorimeter showed that the hemp hurd lixiviate caused a greater delay in GU's hydration process than CSA's. At a 5% concentration, the main hydration peak for GU cement emerged after 91 h, whereas for CSA cement, it appeared much earlier, at 2.5 h. XRD and TGA analysis showed that after 12 h of hydration, hydration products such as calcium silicate hydrates (C-S-H) and portlandite (CH) were not able to form on GU cement, indicating low hydration of silicate products. Moreover, at 5% concentration, the carbonation of ettringite was observed in CSA cement. The compressive strength values obtained from the mixes containing hemp hurd lixiviate consistently showed lower values compared to the reference samples prepared with distilled water. Furthermore, the CSA samples demonstrated superior compressive strength when compared to the GU samples. After 28 days of hydration, the compressive strength values for CSA cement were 36.7%, 63.5% and 71% higher than GU cement at a concentration of 0.5%, 2% and 5% hemp hurd lixiviate, respectively.

Mechanical and self-healing properties of calcium-sulfoaluminate-cement-based engineered cementitious composites (ECC)

Calcium sulfoaluminate (CSA) cement is uniquely suited for repair work, however, the CSA cement-based material is more vulnerable to cracking, and thus may cause the useless repairing. In this paper, CSA cement-based engineered cementitious composites (CSA-ECC) was developed for ensuring the reliability and durability of repair applications, meanwhile, the crumb rubber (CR) was incorporated to improve its tensile properties, and thus avails the self-healing. The results showed that the compressive strength of the CSA-ECC can achieve 38.1 MPa at 3 days, and can further developed to 60.7 MPa at 28 days. The incorporation of CR resulted in the coarsening of microstructure, and thus decreased compressive strength of CSA-ECC to around 50 MPa. In term of tensile properties, all CSA-ECC mixtures exhibited high ductility with strain capacity of 3.13–5.34%. The CR addings effectively increased strain capacity while negatively affected tensile strength and drying shrinkage of CSA-ECCs. Moreover, the crack width was narrowed within 52 μm as compared with 92 μm that of reference mixture, due to which the self-healing was promoted in rubberized CSA-ECC, as a result, its recover percentage in tensile stiffness, strength, and strain of pre-cracked CSA-ECC was improved upon self-healing.

Electrochemical responses of carbon steel in ordinary Portland cement blended with calcium sulfoaluminate cement

This work investigated the passivation and chloride-induced corrosion of carbon steel exposed to an extract solution (PCSA) of ordinary Portland cement (OPC) blended with calcium sulfoaluminate (CSA) cement. As evaluated by EIS and XPS measurements, carbon steel gained inferior passivity by forming a thinner and less protective passive film in PCSA solution compared with that in the pure OPC solution. However, after chloride attack, comparable corrosion resistance was confirmed for steel exposed to both solutions. Furthermore, enhanced pitting corrosion resistance was identified for steel after 30 d of immersion in PCSA solution, which was mainly attributed to the formation of an Al-rich layer on the steel surface as well as the reduced chloride concentration in solution by the unreacted aluminum phase.

Microstructure of Fe(OH)3 phase in hydration products of calcium sulfoaluminate cement

The Fe(OH)3 phase is one of the important hydration products in Ferric-rich calcium sulfoaluminate (FR-CSA) cement and is an essential contributor to the desirable properties of FR-CSA. However, Fe(OH)3 phase has always been investigated as an auxiliary component of the cement hydration system, and the understanding of the microstructure of Fe(OH)3 phase seems to have not been clarified. Therefore, in order to thoroughly investigate the microstructure of the Fe(OH)3 phase to determine the formation process of this phase. In this study, the Fe(OH)3 phase was synthesized from chemical composition using the sol–gel method, and compared with the hydration product Fe(OH)3 of the ferric phase prepared by solid-phase sintering. The microstructure of the Fe(OH)3 phase was investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier transform infrared spectrometry (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N2 adsorption-Brunauer Emmett Teller (BET) and Mössbauer spectroscopy. The results indicate that Fe(OH)3 phase exists in the form of crystals at different pH, and the crystallinity of Fe(OH)3 phase gradually increases with the increase of pH. At low pH (<10), the Fe(OH)3 phase is microcrystalline (ferrihydrite), while high pH (>10) favours stable Fe(OH)3 (goethite) crystal structures to be obtained. In addition, with the increase of pH, the micro-morphology of Fe(OH)3 phase changes from granular to needle-like, and the particle size (length) gradually increases and the specific surface area decreases. No evidence of amorphous Fe(OH)3 was found during hydration, and XRD, TEM and Mössbauer spectroscopy indicated that Fe(OH)3 has a distinct crystal structure. Compared with the chemically synthesized Fe(OH)3 phase, the hydrated Fe(OH)3 phase exists in a microcrystalline state with a flaky microscopic morphology and smaller particle size.

Durability of GFRP and CFRP Bars in the Pore Solution of Calcium Sulfoaluminate Cement Concrete Made with Fresh or Seawater.

Calcium sulfoaluminate cement concrete (CSAC) reinforced by fiber-reinforced polymer (FRP) bars, termed bars for brevity, is a good alternative to steel-reinforced concrete in marine environments due to the corrosion resistance of FRP and the lower pH of CSAC. For the first time, multi-mechanical tests are conducted to compare the durability of glass FRP (GFRP) to that of carbon FRP (CFRP) after exposure to CSAC pore solution. The bars were immersed in a simulated pore solution of CSAC made with either fresh water and river sand or with seawater and sea sand. Solution temperature was held constant at 30 °C, 45 °C or 60 °C for 30, 60, 90 and 180 days of immersion. Tensile, horizontal and transverse shear tests, as well as detailed microstructural analyses, were conducted to determine the level and mechanisms of degradation for each type of bar. Sea salt increases the degradation of both bars, but it degrades GFRP more than CFRP. The bars' retained tensile strength is a reliable indicator of their durability, while their post-exposure horizontal and transverse shear strengths are found inconsistent and counter intuitive. In the GFRP, the fiber, the epoxy matrix and their interface suffered damage, but in the CFRP, the carbon fiber was not damaged. Under the test conditions in this study, the maximum reduction in the tensile strength of the GFRP was 56.9% while that of CFRP was 15.1%. Based on the relevant ASTM standard, the CFRP bar satisfies the alkaline resistance requirement of the standard in the CSAC pore solution with and without salt, whereas the GFRP bar does not meet the same requirement in the above pore solution with salt.

Comparative study on the electric resistance of mortars made of low carbon binders

Against the background of the high CO2 emissions generated in the production of Portland cement (OPC), research is being carried out worldwide into alternative binders that can be produced with lower energy consumption. These have a lower clinker-cement factor or contain no Portland cement at all. To enable these binders to be used on a large scale, also in reinforced concrete structures, their performance in terms of durability must be ensured. The specific electric resistance is a parameter for characterizing different binders. At a young age, the hydration progress and the formation of the pore structure can be observed based on the specific electric resistance. In connection with the electrical conductivity of the pore solution, statements about the pore structure and the resistance to the penetration of corrosion-promoting substances are possible. Finally, the electric resistance is an influencing factor for estimating possible corrosion rates after depassivation of the steel reinforcement. In this study, a wide range of mortars produced with different alternative binders were characterized in terms of their resistivity as a function of age and water content. From the group of clinker substitutes (SCMs), calcined clays and modified steel slag were investigated. The other binders included in the investigation program are produced entirely without Portland cement: In addition to a calcium sulfoaluminate (CS̅A) cement and the C-S-H binder Celitement®, alkali-activated materials (AAMs) in the form of geopolymers and alkali-activated slags were also investigated. The results show a wide range of specific electric resistances in a naturally water-saturated state of the mortar specimens between 5.5Ωm for an alkali-activated metakaolin and 971Ωm for the Celitement®. Clinker replacements with calcined clays metakaolin, or metaillite result in increased specific electric resistances. In addition, the different binders show a very different influence on the dependence of the resistivity on the water content.

Strength and Microstructure Assessment of Partially Replaced Ordinary Portland Cement and Calcium Sulfoaluminate Cement with Pozzolans and Spent Coffee Grounds.

Supplementary cementitious materials are considered a viable and affordable way to reduce CO2 emissions from the cement industry's perspective since they can partially or nearly entirely replace ordinary Portland cement (OPC). This study compared the impact of adding spent coffee grounds (SCGs), fly ash (FA), and volcanic ash (VA) to two types of cement: OPC and calcium sulfoaluminate cement (CSA). Cement samples were characterized using compressive strength measurements (up to 210 days of curing), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), attenuated total reflection infrared spectroscopy, and hydration temperature measurements. In all the studied systems, the presence of SCGs reduced compressive strength and delayed the hydration process. CSA composite cement containing 3.5% SCGs, 30% FA, and 30% VA showed compressive strength values of 20.4 MPa and 20.3 MPa, respectively, meeting the minimum requirement for non-structural applications. Additionally, the results indicate a formation of cementitious gel, calcium silicate hydrate (C-S-H) in the OPC-based composite cements, and calcium alumino-silicate hydrate (C-A-S-H) as well as ettringite in the CSA-based composite cements.