Generation Of Ettringite Research Articles

Effect of Recycled Asphalt Mixture and Solid Waste-Based Solidification Materials on Performance of Cold-Regenerated Asphalt Mixture

In this study, an aging asphalt mixture was regenerated by a waste-based rejuvenator and cemented by solid waste-based solidification materials (SSMs). A splitting test, wheel tracking test, and three-point bending test were conducted to evaluate the properties of the regenerated asphalt mixture (RAM). The results reveal that the properties of the asphalt mixture were not diminished or were moderately enhanced by the 30% substitution of RAP. With the substitution of RAP to 100%, the splitting tensile strength, dynamic stability, and splitting strength ratio were decreased by 13%, 15%, and 5%, respectively. With the 100% substitution of SSMs for cement, the compressive strength, dynamic stability, flexural strain, and splitting strength ratios of the RAM were increased by 40%, 32%%, 14%, and 8%, respectively. The lightweight components can be supplemented, and low-temperature deformation and interlayer flowability can be improved by the incorporation of the rejuvenator. The generation of hydrated calcium silicate and ettringite for SSMs is greater than those of cement. The massive generation of ettringite has been observed to increase the solid phase volume by 120%, which may facilitate a more complete filling of the remaining pores in the RAM due to water evaporation. The regeneration and cement on green and the high performance of the rejuvenator and the SSM markedly enhanced RAM performance.

Utilization of industrial wastes in non-sintered bricks: microstructure and environmental impacts.

Recycling industrial solid wastes as building materials in the construction field exhibits great environmental benefits. This study designed an eco-friendly non-sintered brick by combining multiple industrial solid wastes, including sewage sludge, fly ash, and phosphorus gypsum. The mechanical properties, microstructure, and environmental impacts of waste-based non-sintered bricks (WNBs) were investigated comprehensively. The results revealed that WNB exhibited excellent mechanical properties. In addition, steam curing could further promote the strength development of WNB. The compressive strength of WNB with 10 wt% of sewage sludge reached 13.5MPa. Phase assemblage results indicated that the incorporation of sewage sludge promoted the generation of ettringite. Mercury intrusion porosimetry results demonstrated that the pore structure of WNB varies with the dosage of sewage sludge. Life-cycle assessment results revealed that the energy consumption and CO2 emission of WNB were 45% and 17% lower than those of traditional clay bricks. Overall, the development of WNB in this study provided insights into the co-disposal of industrial solid wastes.

Mechanical properties, micro-mechanisms, and constitutive models of seawater sea-sand engineered cementitious composites

Three mixing proportions of engineered cementitious composites (ECCs) were prepared using seawater, sea-sand, and PVA fibers, corresponding to three strength grades of C30, C40, and C50, respectively. The mechanical properties of these three kinds of seawater sea-sand engineered cementitious composites (SS-ECCs), including compressive strength, tensile strength, flexural strength, elastic modulus, ultimate elongation, uniaxial compressive and tensile stress-strain relationship, and so on, were analyzed by compressive, tensile, and flexural tests. The tensile and flexural strength of SS-ECCs are influenced by their ductility. The SS-ECC with C40 strength grade exhibited the best ductility, with an average ultimate tensile strain reaching 3.42 %, and possessed the highest tensile and flexural strength. The C50 specimen had the worst ductility, but its tensile strength and flexural strength came in second place. As the strength grade increased, the elastic modulus gradually increased, while the Poisson's ratio decreased. Uniaxial compressive and tensile constitutive models for SS-ECCs were established. The uniaxial compressive constitutive model was divided into a nonlinear ascending stage and a bilinear descending stage. XRD and TGA results revealed that the improvement in the strength of SS-ECCs was mainly attributed to the increased content of Ca(OH)2 in the reaction products. Additionally, the gypsum content in the raw materials decreased with the increasing strength grade, resulting in a reduction in the generation of ettringite (AFt).

Dynamic Mechanical Performance of Sulfate-Bearing Soils Stabilized by Magnesia-Ground Granulated Blast Furnace Slag

Sulfate soils often caused foundation settlement, uneven deformation, and ground cracking. The distribution of sulfate-bearing soil is extensive, and effective stabilization of sulfate-bearing soil could potentially exert a profound influence on environmental protection. Ground granulated blast furnace slag (GGBS)–magnesia (MgO) can be an effective solution to stabilize sulfate soils. Dynamic cyclic loading can be used to simulate moving vehicles applied on subgrade soils, but studies on the dynamic mechanical properties of sulfate-bearing soil under cyclic loading are limited. In this study, GGBS-MgO was used to treat Ca-sulfate soil and Mg-sulfate soil. The swelling of the specimens was analyzed by a three-dimensional swelling test, and the change in compressive strength of the specimens after immersion was analyzed by an unconfined test. The dynamic elastic properties and energy dissipation of GGBS-MgO-stabilized sulfate soils were evaluated using a fatigue test, and the mineralogy and microstructure of the stabilized soils were investigated by X-ray diffraction and scanning electron microscopy. The results showed that the maximum swelling percentage of stabilized Ca-sulfate soil was achieved when the GGBS:MgO ratio was 6:4, resulting in an expansion rate of 14.211%. In contrast, stabilized Mg-sulfate soil exhibited maximum swelling at GGBS:MgO = 9:1, with a swelling percentage of 5.127%. As the GGBS:MgO ratio decreased, the dynamic elastic modulus of stabilized Ca-sulfate soil diminished from 2.8 MPa to 2.69 MPa, and energy dissipation reduced from 0.02 MJ/m3 to 0.019 MJ/m3. Conversely, the dynamic elastic modulus of stabilized Mg-sulfate soil escalated from 2.16 MPa to 6.12 MPa, while energy dissipation decreased from 0.023 MJ/m3 to 0.004 MJ/m3. After soaking, the dynamic elastic modulus of Ca-sulfate soil peaked (4.01 MPa) and energy dissipation was at its lowest (0.012 MJ/m3) at GGBS:MgO = 9:1. However, stabilized Mg-sulfate soil exhibited superior performance at GGBS:MgO = 6:4, with a dynamic elastic modulus of 0.74 MPa and energy dissipation of 0.05 MJ/m3. CSH increased significantly in the Ca-sulfate soil treated with GGBS-MgO. The generation of ettringite increased with the decrease in the GGBS-MgO ratio after immersion. MSH and less CSH were formed in GGBS-MgO-stabilized Mg-sulfate soil compared to Ca-sulfate soils. In summary, the results of this study provide some references for the improvement and application of sulfate soil in the field of road subgrade.

Polydopamine: A novel high-efficiency accelerator for Portland cement

This study develops a novel accelerator with dopamine for rapid setting of shotcrete. Based on the oxidative self-polymerization, the dopamine reacts with O2 to produce polydopamine (PDA) in the agitation process of cement paste. The as-prepared PDA facilitates the generation of ettringite. Additionally, it controls ettringite to nucleate and grow on the surfaces of various clinkers, which decreases the negative effect of surface-bound hydrate on the dissolution of C3A. As a result, with 0.10% dosage of dopamine, the initial setting time of cement paste is shortened from 118 min 45 s to 3 min 38 s, and the final setting time is shortened from 212 min 45 s to 11 min 8 s. This dosage is much lower than those achieved by any hitherto-reported materials. Besides, the compressive strength of cement mortar reaches 33.6 Mpa in 28 days, which can meet the requirements of building engineering.

Al2O3/SO3 molar ratio of PG-CAC-based binders on the macro-micro properties of cement-treated waste dredged clay

The binders promoting the generation of ettringite (AFt) are very suitable for stabilizing waste dredged clay (DC) with high water content, while the variability of components may lead to uncertain workability. In this study, a series of unconfined compression tests were conducted on the DC stabilized by the ternary hydration system consisting of ordinary Portland cement, recycled phosphogypsum and calcium aluminate cement, the effects of the Al2O3/SO3 molar ratio (m) on the mechanical properties were evaluated accordingly. Subsequently, a series of microstructure tests and mineralogical tests were performed to further reveal the influence of m on the mechanism of stabilized DC. The results demonstrate that at the same binder content, the unconfined compression strength (UCS, qu) shows a linear increase with m. The compactness of cement-treated DC was improved by the main generation of ettringite, while excessive ettringite may cause expansion and destroy the existing cementation. As m increases, the excessive Al2O3 promotes the generation of C-(A)-S-H and C-A-H after generating enough AFt, which not only cements the soil particles with the cementation effect, but also repairs cracks induced by the AFt expansion. The collaborative effects of the filling and cementation result in an improvement of qu from 11.2% to 129.5% when m increases from 0.133 to 1.414. It can be anticipated from the study that controlling m around 0.55 will play an important role in stabilizing the DC, thus further promoting the co-utilization of recycled DC and phosphogypsum.

Mutual Activation Mechanism of Cement–GGBS–Steel Slag Ternary System Excited by Sodium Sulfate

To promote the large-scale recycling of solid waste, the hydration characteristics of blended cement with different amounts of GGBS (ground granulated blast-furnace slag) and SS (steel slag) were investigated. The optimum blending amounts of GGBS and SS in cement were 40% and 10% by mass, and the optimum dosage of Na2SO4 in the C50-S40-SS10 (50 wt.% cement–40 wt.% slag–10 wt.% steel slag) system was 2 wt.%. The flexural and compressive strengths of the C50-S40-SS10 system after adding 2 wt.% Na2SO4 are 57.95% and 9.28% higher than that of pure cement at 28 d. XRD, FT-IR and Ca(OH)2 content analysis were chosen to investigate the hydration products of pure cement and blended cement. The results show that GGBS enhanced the hydration of both cement and SS. And GGBS contributed to the generation of calcium silicoaluminate hydrate (C–A–S–H) in the blended cement system. The addition of Na2SO4 promoted the hydration reaction and contributed to the generation of ettringite (AFt) in the ternary system. The hydration heat evolution results showed that GGBS and SS can reduce the hydration heat of cement. Na2SO4 had similar effects and delayed the time of AFt conversion to monosulfide calcium sulphoaluminate (AFm). A mutual activation mechanism of cement–GGBS–SS ternary system mixed with Na2SO4 was proposed in this study.

Interaction of Superplasticizers with C3A: Understanding the Superplasticizer Compatibility with Cement

The incompatibility between the superplasticizer (SP) and cement can cause problems with the cementitious materials’ fresh and hardened qualities, such as unstable workability, uncontrollable setting times, excessive air entrainment, and so on. In this paper, five various types of SPs were prepared. Their interaction with pure tricalcium aluminate (C3A) and its hydration products were investigated and their effect on the generation of Ettringite (AFt) and single-sulfur calcium sulphoaluminate hydrate (AFm) in paste and their compatibility with cement were also studied. The results demonstrate that after 15 min of cement hydration, the AFt and AFm content of mixture with polycarboxylate SP and sulfonated acetone-formaldehyde superplasticizer (PCA-SAF) is 124.6% and 24.8% higher than that of SAF, respectively, which decreases the consumption of SPs molecules and improves the compatibility of SAF with cement. Compared with polynaphthalene sulfonate superplasticizer (PNS), PCA-PNS dramatically enhanced the SP’s compatibility with cement. Accelerating the production of AFt and AFm during the early stages of cement hydration may be one method to increase SP–cement compatibility.

Effects of titanium gypsum on high calcium fly ash system: Physical and microscopic properties, hydration, and Fe transformation

Titanium gypsum (TG) is a solid waste generated in the sulfate method of TiO2 production. The stockpiling of TG causes harmful environmental issues, but TG could be reused for manufacturing green cementitious materials with fly ash (FA) and calcium carbide residue (CCR). However, the effects of TG on the high-calcium FA–CCR system and the transformation rule of Fe compound in TG remain unclear. Therefore, FA–CCR and FA–natural gypsum–CCR were used as the control group. The effects of TG on the physical properties, phase composition, and microstructure of the FA–CCR system were studied. Furthermore, the transformation role of Fe in TG was revealed by calculating the thermodynamic properties and performing X-ray photoelectron spectroscopy. Results demonstrated that the appropriate addition of TG was found to shorten the setting time and increase the compressive strength of the FA–CCR system, whereas the excessive addition will cause a negative effect. The small crystal size of TG has a greater contribution to the physical properties compared with the negative effect of iron impurities. The addition of TG can optimize the pore structure of the FA–CCR composites. TG reduced the hydration rate of C-(A)-S-H gels at an early age but promoted ettringite generation and polymerization of C-(A)-S-H at the late stage. Fe(OH)3 in TG plays an insert-filling role at an early age, but this compound could transform into Fe(OH)63− and form ettringite in the late hydration stage, thereby promoting the growth of ettringite crystals. The relative conversion rate of Fe(OH)3 to Fe(OH)63− at 60 days is 11.8%.

Experimental study of delayed ettringite formation under geothermal high-temperature environment

The geothermal high-temperature environment will potentially damage engineering, which is mainly reflected in the expansion cracking caused by delayed ettringite formation (DEF). The solution method was used to simulate the temperature and humidity coupled liquid-phase environment of ettringite formation, investigate the temperature limit of ettringite generation in concrete pore solution, and analyze the effect of gypsum admixture on DEF under a geothermal environment. The results show that the high temperature has a promoting effect on ettringite generation from the early hydration of cement, and the high temperature causes the AFt generated early to be gradually converted into AFm as the curing age increases. 70–75 °C is the key temperature interval for the transformation of the AFt crystalline phase into the AFm crystalline phase, and it is recommended that the core temperature of concrete during hardening be controlled below 60 °C to avoid the potential risk of AFt decomposing into AFm in large quantities and DEF. The sulfate content of the Portland cement used in the high-temperature region should be strictly controlled, and the amount of gypsum used should not exceed 4%.

Evolution in macro-micro properties of cement-treated clay with changing ratio of red mud to phosphogypsum

To investigate the effect of combined red mud (RM) and phosphogypsum (PG) in cement-treated clay, unconfined compressive strength (UCS) tests and isotropically consolidated undrained triaxial (ICUT) tests were performed to explore the effects of RM/PG ratio on mechanical behavior of stabilized clay. Moreover, x-ray diffractometer (XRD) tests, thermogravimetric analysis/differential scanning calorimetry (TG/DSC) tests and scanning electron microscopy (SEM) tests were employed to observe the evolution in microstructure with changing RM/PG ratios. The results indicate that the combined RM and PG play a significant role in cement-based hydration reactions. The UCS at early curing stages nearly doubles with an optimal proportion of 7.5 %RM and 2.5 %PG. The stabilized clay with high contents of RM exhibits a higher maximum deviator stress and a brittle behavior in undrained shearing process. As the PG content increases, the peak strength decreases but the ductility of the specimen increases remarkably. It is believed that the RM acts as an alkali activator on clay minerals whereas the PG mainly contributes to the generation of ettringite. The combined RM and PG not only promotes sufficient pozzolanic reactions and stronger cementation bonds, but also brings out a principally denser microstructure, though a few large pores can be observed due to expansion potential of ettringite. However, the microstructure of stabilized clay becomes much looser with a high content of PG. Partial amounts of PG are found non-reactive with inadequate active aluminium ions. The mechanical behavior of stabilized clay also gets worse concerning negative effects of impurities in PG.

Long-term performance of ferrite-rich calcium sulfoaluminate cement-based paste under seawater corrosion

Ferrite-rich calcium sulfoaluminate cement (FCSA) is widely used due to its characteristics of short setting time, high early strength, slight expansion and low CO2 emissions. In order to further study the long-term performance of FCSA under seawater environment, this study prepared a quaternary blend based on FCSA clinker, Ordinary Portland cement (OPC), anhydrite and limestone. Meanwhile, artificial seawater solutions were prepared by dissolving granular NaCl, MgSO4 and MgCl2 in deionized water. The long-term performance evolution of physical and mechanical characteristics such as mechanical properties, chloride content, hydration products and micro-structure property were investigated through uniaxial compression test, X-ray diffraction (XRD), thermogravimetric analysis (TG), mercury intrusion porosimeter (MIP) and other test methods by considering different salt concentrations of seawater and corrosion age. The results showed that the mass and expansion rate of corroded specimens increased logarithmically with the corrosion age. The quaternary blend could resist sulfate corrosion by absorbing it in seawater solution and promote the generation of ettringite. In addition, Friedel's salt was mainly generated by ion exchange between chloride and sulfate of monosulfoaluminate. The uniaxial compressive strength of all specimens showed a consistency of increasing first and then decreasing with corrosion age. Meanwhile, the corrosion resistance coefficient K of the specimens varied between 0.95 and 1.30 with the salt concentrations of seawater increasing. According to the mechanical behavior and micro-structure characteristics of the new quaternary blend, it’s indicated that the new cement-based material has adequate ability to resist seawater salt corrosion and has an excellent long-term stable performance.

Synergistic Effect and Mechanism of Nano-C-S-H Seed and Calcium Sulfoaluminate Cement on the Early Mechanical Properties of Portland Cement.

The combined utilization of mineral accelerators and nano-seeding materials is a novel method to promote the early strength of cement-based materials. In this paper, the effects of nano-C-S-H seed (NCS) on the early compressive strength of the Portland cement (PC)- calcium sulfoaluminate cement (CSA) binder were investigated. The results showed that NCS and CSA synergistically contributed to the early strength of PC. In detail, a 326.3% increase in the 10 h compressive strength of PC paste was obtained through the addition of NCS (2 wt%) and CSA (5%) in common. This was higher than the sum of the increases observed with the single additions of CSA (157.9%) or NCS (87.6%), with the same above dosage, in PC. Meanwhile, the early strength enhancement effects of NCS and CSA, when used together in PC, lasted longer than the effects of either used alone. Moreover, the synergetic effect mechanism was analyzed by isothermal calorimeter, QXRD, TGA, MIP, and SEM techniques. The calorimetry, XRD, and TGA results demonstrated that the synergistic mechanism was associated with the synergistic promotion effects of CSA and NCS on the hydrates. The fast hydration of CSA produced large amounts of ettringite and also consumed partial free water to promote the performance of the seeding effect of NCS which, simultaneously, further accelerated the precipitation of C-S-H gel and CH. The high alkie environment was also beneficial for the continuous generation of ettringite. In addition, the results of MIP and SEM measurements showed that the micro-filling effect of NCS significantly optimized the pore structure of a PC-CSA blend-hardened paste. Thus, the synergistic strength enhancement effects of CSA and NCS on PC were attributed to the matching of the promotion of hydration generation and the optimization of pore structures in hardening cement paste. The results of this article provide a new approach to achieving the rapid development of the early strength of cementitious materials, with potential applications in precast concrete and low-temperature construction.

Mechanical Properties of Ultra-High Performance Concrete with Coal Gasification Coarse Slag as River Sand Replacement.

Coal gasification coarse slag (CGCS) is a by-product of coal gasification. Despite its abundance, CGCS is mostly used in boiler blending, stacking, and landfill. Large-scale industrial applications of CGCS can be environment-friendly and cost saving. In this study, the application of CGCS as a substitute for river sand (RS) with different replacement ratios in ultra-high performance concrete (UHPC) was investigated. The effects of CGCS replacement ratios on the fluidity and mechanical properties of specimens were examined, and the effect mechanisms were explored on the basis of hydration products and the multi-scale (millimetre-scale and micrometre-scale) microstructure analysis obtained through X-ray diffraction (XRD), scanning electron microscopy, and X-ray energy-dispersive spectroscopy. With an increase in the CGCS replacement ratio, the water-binder ratio (w/b), flexural strength, and compressive strength decreased. Specimens containing CGCS of ≤25% can satisfy the strength requirement of non-structural UHPC, with flexure strength of 29 MPa and compressive strength of 111 MPa at day 28. According to the XRD results and multi-scale microstructure analysis, amorphous glass beads in CGCS positively influenced ettringite generation due to the pozzolanic activity. Porous carbon particles in CGCS showed strong interfacial bonding with cement slurry due to internal hydration; this bonding was conducive to improving the mechanical strength. However, CGCS hindered hydration in the later curing stage, leading to an increase in the unreacted cement and agglomeration of fly ash; in addition, at a CGCS replacement ratio of up to 50%, an apparent interfacial transition zone structure was observed, which was the main contributor to mechanical strength deterioration.

Investigating mechanical properties and microstructure of reactive powder concrete blended with sulfoaluminate cement

Super absorbent polymers, expansion agents, and shrinkage reduction agents have been used to improve the self-shrinkage of ultra-high-performance concrete (UHPC), but they may degrade the mechanical properties of concrete. Sulfoaluminate cement (SAC) has been proven to improve the compressive strength and self-shrinkage of UHPC. However, few studies have focused on the role of SAC in the tensile strength and pore structure of reactive powder concrete (RPC), a type of UHPC. In our study, we used compressive strength and splitting tensile strength tests, isothermal calorimetry, X-ray diffraction (XRD), thermogravimetric analysis (TG-DTA), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) to determine the mechanical properties and microstructure of RPC modified by SAC. The results showed that the addition of SAC effectively enhanced the strength of RPC, especially the early strength. Specifically, using an 8 wt% SAC caused an 871.4 % increase in compressive strength and 600% improvement in tensile strength after 8 h of curing. The tensile strength exhibited a strong positive linear correlation with the compressive strength. The rapid hydration of SAC promoted the generation of ettringite in RPC, which significantly increased the cumulative heat release and improved the strength of RPC at an early age; however, its effect was not significant on the later strength. The key reasons for the improvement in the mechanical properties of RPC by SAC modification were pore refinement and aggregate-paste interface improvement. Thus, incorporating SAC into RPC significantly enhance its early-age compressive and tensile strengths, which contributes to accelerate the formwork turnover of RPC components and operational efficiency of the stacking area.

Preparation of superfine and semi-hydrated flue gas desulfurization gypsum powder by a superheated steam powdered jet mill and its application to produce cement pastes

The low reactivity, high moisture content, and gap-graded particle size distribution of flue gas desulfurization (FGD) gypsum clearly restrict its large-scale application, particularly for cement production. In this paper, we utilize a superheated steam powdered jet mill with different classifier frequencies (20, 35, and 45 Hz) to modify FGD gypsum. Then, the resulting 5% superfine flue gas desulfurization (SFGD) gypsum powder was applied with cement clinker to produce cement pastes. A series of characteristics (water content, particle size distribution, crystalline phase and morphology) of FGD gypsum before and after jet mill grinding were analysed. The setting time, porosity, mechanical strength and hydration heat, were determined, followed by XRD, SEM and TG/DSC analyses, to explore the performances of cement pastes with FGD gypsum and SFGD gypsum addition. Jet mill grinding with superheated steam significantly reduced the water content and particle size (D50 decreases from 33.810 to 2.667 µm) and produced semihydrated gypsum powders. Superfine and semihydrated FGD gypsum dissolution adequately provided SO42- ions, leading to much more hydration heat release and ettringite generation in the clinker-SFGD gypsum system. Moreover, the addition of superfine FGD gypsum powders helped to achieve even more hydration products, a denser inner structure and better mechanical performance of the cement pastes. Therefore, jet mill grinding with superheated steam could be a novel and effective approach to modify FGD gypsum, which possesses great potential for use in the cement industry.

Activation mechanisms of three types of industrial by-product gypsums on steel slag–granulated blast furnace slag-based binders

Desulphurisation gypsum (DG), desulphurisation ash (DA) and fluor gypsum (FG) are three types of industrial by-product gypsum. The production and stockpiling of these types of gypsum may cause waste of resources and environmental problems. In this study, we focus on the activation mechanisms of these materials on steel slag (SS)–granulated blast furnace slag (GBFS)-based binders and their hydration mechanisms. Results showed that the binder with DA had a lower early strength and higher long-term strength than the other two binders. DG and FG provided Ca2+ and SO42− to generate C–S–H gels with SiO44− and ettringite with AlO45−. The attached spherical C–S–H gel particles and aciculate ettringite formed a reticular structure to achieve improvements in strength. The portlandite in DA promoted the dissolution of AlO45− and SiO44− in GBFS during the production C–S–H gels. However, the generation of ettringite was resisted by the less gypsum content in DA, thereby providing space for C–S–H gels to generate the network structure. The C–S–H gels in the binders containing DA exhibit a low Ca/Si atom ratio and enhanced mechanical properties. Further, the SO2− could be observed after 28 days, and hannebachite was consumed and gypsum was observed to increase. The conversion of SO32− to SO42− in binder with DA may occur at 20 ℃. DA and FG have a similar activation effect to that of DG on SS–GBFS-based binders, offering an alternative utilisation for solid wastes.

Effect of Naphthalene-Based Superplasticizer and Polycarboxylic Acid Superplasticizer on the Properties of Sulfoaluminate Cement.

In order to study what the effect of superplasticizers on the setting time, fluidity and compressive strength of calcium sulfoaluminate cement (CSA) a naphthalene-based superplasticizer (BNS) and a polycarboxylic acid superplasticizer (PC) were selected to interact with CSA pastes and ye’elimite, respectively. X-ray diffraction (XRD), thermogravimetric (TG) analysis and scanning electron microscopy (SEM) analytical methods were used to investigate the class, amount and microstructure of the CSA pastes and ye’elimite pastes hydration products under the effect of the superplasticizers. The results showed that the addition of BNS can promote ettringite generation and thus improve the early compressive strength. As the addition of BNS increased from 0.8 wt% to 2.0 wt%, the initial setting time was prolonged 10 min, the final setting time was prolonged 7 min, the 5 min fluidity was improved from no fluidity to 220 mm. However, as the addition of PC increased from 0.08 wt% to 0.20 wt%, the setting time of the PC just changed within 3 min; the 5 min fluidity increased from 110 mm to 195 mm and no 15 min fluidity at all was observed. AS seen by SEM, it can be stated that generated ettringite under the addition of PC was layered and lacking bonding, and its morphology changed from rod-like to flake-like, leading to a decrease in early compressive strength.

The hydration of nearly pure ye'elimite with a sulfate carrier in a stoichiometric ettringite binder system. Implications for the hydration process based on in-situ XRD, 1H-TD-NMR, pore solution analysis, and thermodynamic modeling

The hydration of synthetic ye'elimite was studied with sulfate carriers in a stoichiometric ettringite binder system. Heat flow calorimetry, in-situ XRD, 1H-TD-NMR and pore solution analysis were applied in order to gain a deeper understanding of the hydration kinetics of the system. Additionally, thermodynamic modeling was used in order to show the evolution of the pore solution in the system Ca-Al-S-H2O. The experiments showed that a first ettringite generation might be formed in a regime where CAH10, monosulfate, ettringite and AHamorphous are stable while at later points in time the ettringite is formed in a regime where AHmicrocrystalline and ettringite is stable. The different shoulders in the heat flow curve seem to arise from the recrystallization of AHmicrocrystalline and the final adjustment of the water content of the aluminum hydroxide towards AH3.

The effect of polymer dispersions on the early hydration of calcium sulfoaluminate cement

The influence of three polymer dispersions [styrene–butadiene copolymer (SB), styrene–acrylic ester copolymer (SA) and polyacrylic ester (PA)] on the hydration of calcium sulfoaluminate (CSA) cement within 72 h was investigated by using isothermal conduction calorimetry, X-ray diffraction analysis and thermal gravimetric analysis. The results indicate that these three polymer dispersions perform different influences on the hydration heat flow of CSA cement during different periods, they all postpone the occurrence time of the maxima peaks, and its extent is mainly dependent on the addition amount. Polymer dispersions manifest great retardation on the initial hydration of CSA cement, and the effect is much more significant within 1 h. In this stage, the generation of ettringite is strongly delayed; however, the formation of ettringite is accelerated by these polymer dispersions at and after 2 h. Among these three polymer dispersions, PA demonstrates the highest acceleration effect on the hydration degree.