Sulfoaluminate Phase Research Articles

Early-age hydration of ye'elimite (calcium sulfoaluminate phase) in presence of alkalis: role of calcium sulfate

Early-age hydration of ye'elimite (calcium sulfoaluminate phase) in presence of alkalis: role of calcium sulfate

EVALUATION OF THE EFFECTIVENESS OF INFLUENCE CAUSED BY ULTRA AND NANO-DISPERSE ADDITIVES FOR MODIFICATION OF SULFATE PHASES AND SULFOALUMINATE PHASES

Problem statement. We offer stabilization of ettringite with the help of nanocomponents introduced. When conducting these studies, the problem of developing compositions of new construction materials based on gypsum and cement binder was solved by means of introducing nano-additives. Nanotechnology is a tool that allows you to reliably understand the processes that occur during hydration of composite materials, interaction of chemical and mineral additives with newly formed hydrated structures, formation and development of macro- and microstructure. The next stage in the effective application of nanotechnologies and techniques used in nanotechnologies for studying hydration processes and structure formation of gypsum- and cement-containing binding materials consists in the development of molecular models of hydration of Portland cement products. Creation of a high-strength cement frame is possible by adjusting the size of the solid phase and crystallization centers, as well as by modifying the gypsum- and cement-containing binder with ultra and nanodisperse additives. Purpose is to investigate effectiveness of ultra- and nanodisperse additives for modification of sulfate phases and sulfoaluminate phases. Conclusions. Modification of the compositions of radiation protection solutions of sulfate phases and sulfoaluminate phases with nanodisperse additives led to a decrease in the coefficient of linear expansion to 0.8 %. Herewith, an increase in solid indicators occurred by 8−12 %, which was caused by a change in the structure of neoplasms and the mineralogical composition. Thus, modification of the solution of sulfate and sulfoaluminate phases with carbon nanotubes (CNTs) leads to a decrease in the coefficient of linear expansion and an increase in the scattering coefficient of gamma rays by 30−40 % due to a high specific surface area of CNTs (80−120 m2/g). An optimal solution with the following composition has been experimentally developed: alumina cement, gypsum, BaSO4, nanotubes. It has been established that this solution has a 10−15 % higher water content, which is associated with the formation of ettringite during the process of setting and hardening. As a result, the arithmetic average amount of chemically bound moisture increased, which affected the change in the linear attenuation coefficient of ionizing radiation of the coating by 0.0088−0.009 cm-1. The total coefficient can reach 0,354 cm-1. Such results lead to reduced equivalent thickness (14,6 mm) of the radiation protective layer by 1−1,5 mm.

The effect of boron oxide on the microstructure and hydration of calcium sulfoaluminate phase

Boron-rich waste causes numerous environmental problems when discharged directly into the environment. Here, various quantities of boron oxide (B2O3) were added to calcium sulfoaluminate (C4A3$) during the sintering process to demonstrate a potential use of boron-rich waste. The microstructure and hydration performance of C4A3$ with various B2O3 contents were investigated with scanning electron microscopy, x-ray diffraction, isothermal conduction calorimetry, thermogravimetric studies and compressive strength tests. B2O3-doped C4A3$ had a larger grain size than the pure phase; and were surrounded by amorphous phases. The presence of B2O3 was shown to promote the phase transition process through which C4A3$ changes from the orthorhombic to the cubic structure; and the substitution of Al3+ for B3+ in AlO4 tetrahedra was surveyed by structural refinements. As the B2O3 content increased, the induction period of C4A3$ increased while the hydration rate decreased because of the amorphous phases around the C4A3$. However, the hydration degree of doped C4A3$ increased due to the slower reaction rate. Thus, when an appropriate amount of B2O3 was added to the C4A3$ during sintering, a significant improvement in the compressive strength of pastes was observed.

Fingerprinting the Hydration Products of Hydraulic Binders Using Snapshots from Time-Resolved In Situ Multinuclear MAS NMR Spectroscopy

The very early hydration behavior of a hydraulic binder phase, ye’elimite, Ca4Al6O12SO4, in the absence and in the presence of calcium sulfate, has been investigated. A time-resolved in situ multinuclear magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopic suite involving 1H and 27Al MAS as well as two-dimensional 27Al multiple quantum MAS (MQMAS) experiments has been employed to detect the transient species and to govern the sequence of hydration reactions and the subsequent formation of the hydration products. The results of the study show that the rates of formation of ye’elimite hydration products vary substantially according to the absence or the presence of calcium sulfate. Hydrated calcium sulfoaluminate phases such as ettringite and monosulfate as well as aluminum hydroxide gel have been detected during the various stages of hydration. The direct observation of various transient species during the hydration stages of calcium aluminates and calcium sulfoaluminates illustrates the potential of a newly designed time-resolved in situ 1H MAS NMR experimental approach for fingerprinting phases and offers significant advantages over other established techniques in detecting transient species.

The Incorporation of Steel Slag into Belite-Sulfoaluminate Cement Clinkers

The potential use of steel slag from treated steel slag in belite-sulfoaluminate cements was investigated in this study. Cement clinkers with two phase compositions were synthesized, allowing the incorporation of different amounts of steel slag. The phase composition and microstructure of cement clinkers at three different sintering temperatures were studied by X-ray powder diffraction and the Rietveld method, as well as scanning electron microscopy with energy dispersive spectrometry. The results showed that the targeted phase composition of clinkers was achieved at a sintering temperature of 1250 °C. However, a higher amount of perovskite instead of ferrite was detected in the clinker with a higher content of Ti-bearing bauxite. Apart from the main phases, such as belite, calcium sulfoaluminate, and ferrite, several minor phases were identified, including mayenite, perovskite, periclase, and alkali sulfates. In both clinker mixtures, a higher content of MgO in the steel slags resulted in the formation of periclase. Furthermore, the hydration kinetics and compressive strength at 7 and 28 days were studied in two cements prepared from clinkers sintered at 1250 °C. As evidenced by the results of isothermal calorimetry, the hydration kinetics were also influenced by the minor clinker phases. Cement with a higher content of calcium sulfoaluminate phase developed a higher compressive strength.

On the interaction of Class C fly ash with Portland cement–calcium sulfoaluminate cement binder

Shrinkage cracking in concrete is a widespread problem, especially in concrete structures with high surface-to-volume ratio such as bridge decks. Expansive cements based on calcium sulfoaluminate phase were developed to mitigate the shrinkage cracking of concrete. The compressive stress induced due to restrained expansion of concrete has been shown to counteract the tensile stress generated during drying shrinkage. This research attempts to address the differential behavior of fly ash type (i.e., Class C vs. Class F) on early-age expansion and hydration characteristics of ordinary Portland cement (OPC)–calcium sulfoaluminate (CSA) cement blend. It was observed earlier that the presence of Class C fly ash (CFA), unlike Class F fly ash, shortened the expansion duration of OPC–CSA cement blend, which was hypothesized to be correlated to early depletion of gypsum. This paper presents a detailed verification of the hypothesis. Addition of external gypsum to OPC–CSA–CFA blend led to simultaneous increase in expansion and disappearance of a shoulder peak in the calorimetric curve. Thermodynamic calculations using a geochemical modeling program (GEMS-PSI) revealed higher saturation levels of ettringite in presence of external gypsum, which led to higher crystallization stress, and thereby increased expansion.

Cementitious materials exposed to high concentration of sodium chloride solution: Formation of a deleterious chemical phase change

This paper investigates deleterious chemical interactions between cementitious materials and high concentrations of sodium chloride (NaCl) solution (i.e., salt concentration >12% by mass). The behavior of mortar specimens made using Type I and Type V ordinary portland cements was investigated as the temperature varied in the presence of NaCl solution with concentrations of 15% and 20% (by mass). A low-temperature longitudinal guarded comparative calorimeter (LGCC) in conjunction with an acousto-ultrasonic technique were used to monitor the damage development in mortar samples. Cooling-heating cycles were applied with a minimum temperature above the freezing temperature of the solution to avoid ice formation. Nevertheless, damage was observed in specimens. Calcium aluminate phases, mainly tricalcium aluminate (C3A), seem to be the source of damage as the magnitude of damage was relatively minor when Type V cement (C3A < 5% by mass) was used. To further investigate the source of the damage, a low-temperature differential scanning calorimeter (LT-DSC) was used to study chemical phase transitions during temperature change in three types of powder specimens exposed to different concetrations of NaCl solution: (1) hydrated cement pastes, made using Type I and Type V cements, (2) cement pure phases, consisting of C3A and gypsum, and (3) cement hydration products, consisting of calcium hydroxide (CH) and calcium sulfoaluminate phases (monosulfate (AFm) and ettringite (AFt)). A formation of a chemical phase at a temperature range between 0 °C and 10 °C was observed that may be the source of damage in cementitious materials exposed to high concentration of NaCl solutions. It was found that the interaction of high concentrations of NaCl solution with C3A and calcium sulfoaluminate phases in the cementitious system are the origin of the chemical phase formation.

Hydration and Physico-mechanical Properties of Blended Calcium Sulfoaluminate-belite Cement Made of Industrial By-products

Portland cement blended Calcium Sulfoaluminate-belite (CŜAB) cements were studied in order to improve its binding properties and workability for specific applications. The binders consisted of calcium sulfoaluminatebelite, Flue Gas Desulfurization-gypsum and Ordinary Portland Cement (OPC). In this research, effects of OPC contents (25, 50, 75 wt%) as a CŜAB replacement on hydration behaviors and physico-mechanical properties of the binders were observed. Used CŜAB cement was synthesized using industrial by-products viz., fly ash, Flue Gas Desulfurization-gypsum, Al-rich sludge as starting materials via hydrothermal-calcination method. The results revealed that the replacement of CŜAB cement with OPC extended the setting times of pastes. The reduction of hydration rate with higher OPC content was due to dilution of fast setting phases such calcium sulfoaluminate and mayenite. Hydration products of calcium sulfoaluminate cement were ettringite responsible for high early strength together with Al(OH)3. From 6 h onwards, hydration of tricalcium silicate phase from the OPC generated calcium silicate hydrate. Stratlingite was also found in low OPC content mix resulting from the reaction between the Al(OH)3 and either alite phase in OPC or belite phase in CŜAB cement. Ettringite could also react with Al(OH)3 to generate monosulfate at later ages. The calcium sulfoaluminate phase was mainly responsible for the early mechanical properties, while OPC played an important role to improve strength at later ages.

Performance of carbonated calcium silicate based cement pastes and mortars exposed to NaCl and MgCl2 deicing salt

This paper investigates the performance of two cementitious systems exposed to freezing or deicing salts. The first cementitious system is made using an ordinary portland cement (OPC) that reacts through hydration. The second cementitious system is made using a calcium silicate cement (CSC) that reacts and gains strength through carbonation (i.e., carbonated calcium silicate based cement (CCSC)). Two experimental techniques were used to evaluate the performance of these materials. The first technique measures the potential reactivity between the concrete paste and the deicing salt (NaCl and MgCl2) using a low temperature differential scanning calorimeter. The second technique uses a longitudinal guarded comparative calorimeter equipped with acoustic emission to assess the freeze–thaw performance of mortar samples saturated with water or deicing solutions. No chemical reaction is observed between CCSC paste and NaCl while a damaging reaction is observed between the OPC paste and NaCl due to the presence of calcium sulfoaluminate phases. A chemical reaction occurs for both the CCSC and OPC paste exposed to MgCl2: for the CCSC paste, this appears non-deleterious since relatively no reduction in dynamic elastic modulus is observed; for OPC paste, however, this is a damaging reaction due to formations of magnesium silicate hydrate and calcium/magnesium oxychloride. CCSC mortar sample saturated with water shows freezing in the large pores at approximately −5°C and smaller pores at approximately −28°C. Both the OPC and CCSC mortars show similar freeze–thaw performance when the system is water saturated. When the water in the pores of the mortar is replaced with a salt solution (NaCl and MgCl2), the CCSC mortar shows less freeze–thaw damage (mainly due to possessing a different pore structure) and more resistance to salt degradation (mainly due to possessing a different chemistry) than the OPC mortar does.

The Impact of Aluminum-Containing Set Accelerators on Sulfate Resistance of Portland Cement Compositions

This study contains comparative research of sulfate resistance of ordinary Portland cement pastes with addition of basic aluminum sulfate (hydroxosulfate, Al(OH)1.78(SO4)0.61) and amorphous Al(OH)3. Over 3 months of storing in sodium sulfate solution, the most significant expansion and deterioration occur in case of samples with aluminum hydroxide. During sulfate resistance test, the ratio between aluminum nuclei in AFt (ettringite) and AFm phases was studied by 27Al-MAS NMR, and the impact of aluminum-containing admixtures on this ratio was specified. In accordance with NMR data, in samples with Al(OH)3, the rate of secondary ettringite formation becomes noticeable after one month of storing in sulfate solution. For samples with Al(OH)1.78(SO4)0.61, the rate of elongation and temper of changes in molar ratio between sulfoaluminate phases were comparable with reference samples without admixtures.

Volume Stability of Calcium Sulfoaluminate Phases

The volume stability of calcium sulfoaluminate phases exposed to water, lime, and gypsum environments was investigated. The length changes of compacted specimens of synthetic monosulfate and ettringite were monitored in distilled water, lime‐saturated water, gypsum‐saturated water, and saturated water vapor. The X‐ray diffraction analysis was also performed on the samples to assess the changes in the crystalline structure of each phase. Evidence was provided in support of the significant role of dissolution of monosulfate and ettringite, and the leaching of their constituent ions, on the expansion of these phases.

Preparation of β-dicalcium silicate (β-C2S) and calcium sulfoaluminate ([formula omitted]) phases using non-traditional nano-materials

This paper describes the synthesis of some nano-compounds such as SiO2, Al(OH)3 and Ca(NO3)2 which can be used in the preparation of nano β-C2S as well as nano C4A3S¯. The preparation of β-C2S from nano-SiO2 and Ca (NO3)2 in comparison with traditional materials such as Ca(CH3COO)2, CaCO3 and silica quartz fired at different temperature has been studied. Also, C4A3S¯, can be prepared from nano-materials such as Ca(NO3)2 and Al(OH)3 with pure gypsum in comparison with Ca(CH3COO)2, CaCO3 and calcined Al2O3. The rate of formation of β-C2S and C4A3S¯, can be also studied after firing with chemical and XRD methods. These phases were obtained by crystallization processing at different temperatures. The formation of these phases was monitored by measuring the free lime and insoluble residue contents. The results showed that the extent of formation was found to be much higher with nano-materials as compared to those prepared in a conventional manner. The prepared belite phase from nano-silica and calcium nitrate reduces the temperature synthesis to 1150°C. Also the preparation of C4A3S¯ from nano Al(OH)3 and Ca(NO3)2 and pure gypsum fired at 1290°C, was the perfect composition to produced a well formed calcium sulfoaluminate phase in comparison with traditional materials.

Preparation of β-dicalcium silicate (β-C2S) and calcium sulfoaluminate [formula omitted] phases using non-traditional nano-materials

This paper describes the synthesis of some nano-compounds such as SiO2, Al(OH)3, Ca(NO3)2 and gypsum which can be used in the preparation of nano-β-C2S as well as nano-C3A3CS¯. The preparation of β-C2S from nano-SiO2 and Ca(NO3)2 in comparison with traditional materials such as Ca(CH3COO)2, CaCO3 and silica quartz fired at different temperatures has been studied. Also, C3A3CS¯, can be prepared from nano-materials such as Ca(NO3)2 and Al(OH)3 with pure gypsum in comparison with Ca(CH3COO)2, CaCO3 and calcined Al2O3. The rate of formation of β-C2S and C3A3CS¯, can be also studied after firing with chemical and XRD methods. These phases were obtained by crystallization processing at different temperatures. The formation of these phases were monitored by measuring the free lime and insoluble residue contents as well as with the aid of XRD technique. The results showed that the extent of formation was found to be much higher with nano-materials as compared to those prepared in a conventional manner. The prepared belite phase with nano-silica and calcium nitrate reduces the temperature synthesis to 1150°C. Also the preparation of C3A3CS¯ from nano-Al(OH)3 and Ca(NO3)2 and pure gypsum fired at 1290°C, was the perfect composition to produce a well formed calcium sulfoaluminate phase in comparison with traditional materials.

Hydration behavior of iron doped calcium sulfoaluminate phase at room temperature

Different samples of calcium sulfoaluminate phase doped with iron, (Ca 4Al(6-2x)Fe2xSO16) with x = 0, 0.2 and 0.5, were synthesized at 1350°C. The hydration kinetics of the resulted phases was investigated by calorimetric and conductimetric techniques. The hydrated samples were analyzed by X-ray diffraction and scanning electron microscopy. The hydration of calcium sulfoaluminate was slightly modified by inclusion of iron in its structure. Dissolution rate of calcium sulfoaluminate phase doped with iron appeared to be slowed down such as the nucleation rate during the induction period while the percentage of reaction after 1 day was slightly increased. The analysis of hydrates indicated the formation of the same hydrates, ettringite and calcium monosulfoaluminate and the gibbsite, with or without iron replacement. Gibbsite played a major role in the kinetics of the induction period and thus the presence of iron may decrease its nucleation rate forming (A, F)H3 instead of AH3.

Performance simulation and quantitative analysis of cement-based materials subjected to leaching

A 3D numerical modelling platform (MuMoCC) developed in a previous work by the authors is applied in this paper to investigate the effect of leaching of some solid phases of cement paste (portlandite and hydrated aluminates or sulfoaluminate phases) on the mechanical and diffusivity performances of cement paste and mortar. The platform is based on a multi-scale approach and uses two numerical tools. First, NIST’s CEMHYD3D code is used to simulate 3D Representative Volume Elements of cement paste and mortar. Then mechanical and diffusivity behaviour of the numerical materials are simulated using ABAQUS software. The proposed three-dimensional heterogonous model presents at least two advantages. Firstly, it is able to capture the complexity of the random microstructure of cement-based materials. Secondly, only a few parameters have to be fitted compared to the other existing models, which indicates the relevance of the model. The numerical simulations of leached cement paste and mortar performance highlight and quantify the significant effect of portlandite and hydrated aluminate and sulfoaluminate phases’ dissolution on the decrease of elastic modulus and compressive strength and on the increase of ductility and diffusivity. The numerical results show that the leaching of portlandite decreases the compressive strength of a w/ c = 0.4 cement paste by a factor of 1.33. The dissolution of portlandite and hydrated aluminates or sulfoaluminate phases involves a decrease by a more important factor (1.86). The leaching of portlandite phase involves an important increase, by a factor of 31, of the effective diffusion coefficient. Using the developed multi-scale modelling and knowing the leaching kinetics values, the mechanical and diffusion performances of cement-based materials can be estimated correctly according to leaching duration.

Blended systems with calcium aluminate and calcium sulphate expansive additives

The high alumina cements were ground together with special sulphate–lime sinter to produce an expansive additive to Portland cement. This expansive additive in the environment of hydrating cement transforms into the hydrated calcium sulfoaluminate phase known as ettringite at “right time” to give the expansion before the early hardening process is completed. The studies were focused at first on the synthesis of the sulphate–lime sinter and subsequently on the mixture proportions between the basic Portland cement, calcium aluminate cement and sulphate–lime component giving the compensation of shrinkage or expansion effect during the hydration process. The measurements of volume changes of cementitious materials thus produced, followed by the compressive strength tests, rate of hydration determination, phase composition studies and microstructure of hydration products observations have been carried out to find the optimum proportions of blended cementitious material, as the controlled expansion and hardening are concerned.

Characterisation of iron inclusion during the formation of calcium sulfoaluminate phase

The iron distribution among the sulfoaluminate clinker phases and its ability to enter the calcium sulfoaluminate lattice in solid solution can have a significant influence on manufacturing process and reactivity of calcium sulfoaluminate (CSA) cements. X-ray diffraction (XRD) analysis, Mössbauer spectroscopy, scanning electron microscopy (SEM) equipped with an energy dispersive X-ray analysis system (EDAX) and infrared spectroscopy were used to identify the mineralogical conditions of iron inclusion during the formation of calcium sulfoaluminate (C 4A 3S) phase from different mixtures in the CaO–Al 2O 3–Fe 2O 3–SO 3 system. The mixtures, heated in a laboratory electric oven, contained stoichiometric amounts of reagent grade CaCO 3, Al 2O 3, Fe 2O 3 and CaSO 4·2H 2O for the synthesis of Ca 4Al (6 − 2 x) Fe 2 x SO 16, where x, comprised between 0 and 3, is the mole number of Al 2O 3 substituted by Fe 2O 3. With x increasing from 0 to 1.5, both the iron content of C 4A 3S phase and the amounts of side components such as C 2F and CS increased. For x values included in the range of 1.5–3.0, at temperatures higher than 1200 °C, melting phenomena were observed and, instead of the C 4A 3S solid solution, ferritic phases and anhydrite were formed.

Computer modelling of tritiated water diffusion test for cement based materials

In durability-based design, diffusivity of ions through cement based materials is one of the most important factors that determine the service life of concrete structures. This paper gives a method and numerical tool to estimate and predict in a short time the effective diffusion coefficient of cement paste, mortar or concrete starting from the microstructure scale and taking into account important factors like calcium silicate hydrate (C–S–H) and interfacial transition zone (ITZ) phases. The numerical model works in two main steps. First, the CEMHYD3D model is used to generate a realistic 3D Representative Volume Element of the cement based material at different scales. Second, the finite element method is used to simulate diffusion of tritiated water (HTO) through a saturated material. The method is then applied to simulate the well-known HTO diffusion test and to derive the effective diffusion coefficient of the heterogeneous material based on Fick’s law. In order to validate the proposed tool, the effective diffusion coefficient of two cement pastes and two mortars with water-to-cement ratio (w/c) of 0.25 and 0.45 are computed and successfully compared to experimental data. The model results provide an approximation for diffusivity through the C–S–H and ITZ phases. Finally, the model is applied to investigate the effect of changes in the microstructure due to the leaching of portlandite, hydrated aluminates and sulfoaluminate phases on the increase of the effective diffusion coefficient.

Examination of the jarosite–alunite precipitate addition in the raw meal for the production of sulfoaluminate cement clinker

The aim of the present research work was to investigate the possibility of adding a jarosite–alunite chemical precipitate, a waste product of a new hydrometallurgical process developed to treat economically low-grade nickel oxides ores, in the raw meal for the production of sulfoaluminate cement clinker. For that reason, two samples of raw meals were prepared, one contained 20% gypsum, as a reference sample ((SAC) Ref) and another with 11.31% jarosite–alunite precipitate ((SAC) J/A). Both raw meals were sintered at 1300 °C. The results of chemical and mineralogical analyses as well as the microscopic examination showed that the use of the jarosite–alunite precipitate did not affect the mineralogical characteristics of the so produced sulfoaluminate cement clinker and there was confirmed the formation of the sulfoaluminate phase (C 4A 3 S ¯ ), the most typical phase of this cement type. Furthermore, both clinkers were tested by determining the grindability, setting time, compressive strength and expansibility. The hydration products were examined by XRD analysis at 2, 7, 28 and 90 days. The results of the physico-mechanical tests showed that the addition of jarosite–alunite precipitate did not negatively affect the quality of the produced cement.

Formation and hydraulic behavior of chromium–phosphorus doped calcium sulfoaluminate cement

The formation and the hydration processes of solid solutions based on calcium sulfoaluminate with chromium and phosphorus additions are studied. The synthesized solid solutions are analyzed with X-ray diffraction and infrared spectroscopy. The high concentrations of additives slow the formation of the calcium sulfoaluminate phase. The early hydration behavior is followed by Tian–Calvet calorimetry. The results show that incorporation of chromium and phosphorus in the crystal lattice of calcium sulfoaluminate induces a long induction period. The setting period in the doped sample has a higher heat output than the pure phase. Identification of the hydration products is done by differential thermal analysis (DTA). The degree of transformation of ettringite into the monosulfate is lower in the modified calcium sulfoaluminate than in the additives-free cement.