Aluminate Hydrate Research Articles

Effects of waterborne epoxy resin on the mechanical properties and microstructure of slag cementing slurries

The enhancement mechanism of epoxy resin on the physical properties of a slag solidified body with poor mechanical properties and susceptibility to cracking was investigated. Furthermore, the mechanical properties of an epoxy resin/slag cured body with varying resin contents and temperatures were studied experimentally. SEM, XRD, FTIR, and TG-DTG were used to test the structure and morphology of the epoxy resin/slag cured body. The results are as follows: (1) When the ratio of epoxy resin to curing agent is 10:3, the cured slag’s 7 days (7d) compressive and tensile strength at 50 °C are 65% and 52% higher, respectively, than the blank sample when the epoxy resin content is 15%. The compressive and tensile strength at 90 °C for seven days increased by 101% and 102%, respectively, compared to the blank sample. When epoxy resin content is 25%, the solidified slag's 7d compressive and tensile strength at 70 °C is 191% and 134% higher, respectively, than the blank sample. (2) Calcium silicate aluminate hydrate (C-A-S-H) is still the main hydration product of the composite, but there is less silica-magnesium hydrotalcite structure, which is different from the slag solidified body; (3) In the composite material, the three-dimensional network structure formed by epoxy resin curing is combined with the hydration products, and the polymer film fills the pores and cracks of the slag, improving the microstructure and mechanical properties of the slag. The results have theoretical significance for enhancing the physical properties of solidified slag and broadening its potential applications.

Development of a calcium aluminate cement from steelmaking slag by altering its mineralogical composition

Strict environmental norms and increasing awareness of the need to recycle solid wastes generated during ironmaking and steelmaking processes are the key driving force for the development of various new materials and manufacturing technologies. In this study, a calcium aluminate clinker was prepared from steel ladle slag by modifying its mineral composition. The slag paste, prepared by mixing slag with water, exhibited flash setting behaviour due to the presence of C12A7 and C3A phases. In contrast, the slag clinker, developed by sintering a mixture of a pre-determined quantity of slag and aluminium oxide at 1400°C for 2 h and 4 h, contained CA, CA2, gehlenite and ‘Q’ phases. Hydrated slag clinker contained stable C3AH6, AH3 and stratlingite with preferential growth of calcium aluminate hydrate prisms along the c-axis, which provided a well-defined raceme-like morphology with an interlinked structure. This improved the setting time and crushing strength of the clinkers after 6 h and 24 h of curing at room temperature. Additionally, the presence of the Q phase, with lamellar prismatic crystals, also helped to enhance strength. The developed clinker also exhibited superior crushing strength as compared with commercially available calcium aluminate cement of medium purity. The slag, used as a source of calcium oxide, could replace calcium carbonate completely and thus contribute to reductions in carbon dioxide emissions during the clinker-making process.

Influence of magnesium-aluminum hydrotalcite on the microstructure and mechanical properties of magnesia castables

The stability of the thermo-mechanical properties of magnesia castables is critical for both the service life of castables and the steel cleanliness. In this study, simultaneous use of magnesium-aluminum hydrotalcite and hydratable alumina was determined to improve the mechanical strength and volume stability of magnesia castables. Hydrotalcite was decomposed to magnesium aluminate spinel and reactive MgO below the medium temperature, which accelerated sintering reactions in magnesia castables and further promoted the formation of spinel and forsterite at high temperature. Suitable volume stability was presented as a consequence of the improved sinterability. The thermo-mechanical properties of magnesia castables were also enhanced. A modified three-dimensional microstructure with the fewer and smaller pores in this optimized magnesia castable at the same time was verified by X-ray micro-computed tomography technology. A correlation analysis identified bending strength and compressive strength of castables having the strongest relationship with the spatial porosity and the number of pores in a diameter range of 0.3–0.5 mm.

A DSC- and X-ray Diffraction Study of Mixtures of Aluminum with 50 wt % of Aluminum Hydrate after Plastic Deformation under High Pressure

A DSC- and X-ray Diffraction Study of Mixtures of Aluminum with 50 wt % of Aluminum Hydrate after Plastic Deformation under High Pressure

Binder effect on ZnAl2O4-containing high-alumina refractory castables

In situ spinel (MgAl2O4, ZnAl2O4, etc.) formation in alumina-based castables has been pointed out as a key issue in the refractory area, as it may enhance the mechanical properties and corrosion resistance of such materials. Nevertheless, the generation of these compounds is usually accompanied by a large volume expansion, which may induce crack formation in the resulting microstructure. Aiming to investigate the influence of zinc and magnesia spinel generation on the properties of alumina-based castables, three vibratable compositions, containing calcium aluminate cement or hydratable alumina as binders, were designed and characterized in this work. Different experimental tests were carried out to analyze the produced samples, such as: cold flexural strength, apparent porosity, hot elastic modulus, assisted sinterability, corrosion cup-tests, etc. According to the results, ZnAl2O4 was mainly formed above 800 °C, favoring an earlier sintering of the samples. The addition of high amounts of ZnO or MgO (3 wt% to 9.4 wt%) to the castables resulted in the expansion of the samples during their first thermal treatment up to 1500 °C, reaching dL/L0 values equivalent to 1.16% up to 2.35%. Thermodynamic simulations indicated that spinel phase presented higher chemical stability when in contact with the evaluated synthetic slag at 1500 °C. Depending on the corrosion cup-test procedure (free or under constraint), different results of the slag infiltrated area were obtained (13.7%–20.5%) and, the combination of two different spinel phases (MgAl2O4 and ZnAl2O4) in a castable composition resulted in a refractory with enhanced corrosion behavior when the tests were carried out under constraint.

An amorphous sodium aluminate hydrate phase mediates aluminum coordination changes in highly alkaline sodium hydroxide solutions

A newly identified intermediate phase containing tetrahedral Al is formed incipient to the crystallization of sodium aluminate hydrates.

Recycling of arsenic-containing biohydrometallurgy waste to produce a binder for cemented paste backfill: Mix proportion optimization

Arsenic-containing biohydrometallurgy waste (BW) is used to prepare a cementitious material, on the one hand, to solve the problem of lack of cheaper and greener binder for cemented paste backfill (CPB), on the other hand, to alleviate the arsenic pollution caused by BW. The binders were prepared by mixing blast furnace slag (BFS), BW, and ordinary Portland cement (OPC). The influence of mix proportions on the binder properties was investigated, including reaction kinetics, strength development, phase assembles of hydration products and arsenic (As) immobilization effects. Isothermal calorimeter analysis suggests that the binder reaction kinetics were highly determined by the mix proportions, and more BW addition decreased the reaction rate according to the Krstulovic-Dabic model. The optimal mix proportion of binder is 65–30-5, i.e., 65 wt% blast furnace slag, 30 wt% BW, and 5 wt% OPC. The compressive strength of this sample after curing for 3 days and 60 days is about 9.25 MPa and 40.88 MPa, respectively, and the hydration products mainly consist of ettringite and calcium silicate aluminate hydrate (C-(A)-S-H). Additionally, arsenic can be effectively immobilized in the binder, resulting from the denser structure (physical encapsulation) and ion exchange between arsenate and sulfate in ettringite.

Formulation of Non-Fired Bricks Made from Secondary Aluminum Ash

The secondary aluminum ash is the black slag left after the primary aluminum ash is extracted from the metal aluminum. To address the environmental pollution and resource waste caused by the accumulation and landfill of aluminum ash, this study fabricated non-fired bricks by using secondary aluminum ash as the principal raw material, which was supplemented by cement, slaked lime, gypsum and engineering sand. The effects of mix proportions of various admixtures on the mechanical properties of non-fired bricks were investigated, and on this basis, the hydration mechanism was analyzed. The results showed that the mix proportions were 68.3% aluminum ash, 11.4% cement, 6.4% slaked lime, 4.2% gypsum and 9.7% engineering sand. The compressive strength of the fabricated bricks reached 22.19 MPa, and their quality indicators were in line with the MU20 requirements for Non-fired Rubbish Gangue Bricks. Evident hydration reaction occurred inside the non-fired bricks, with main products being calcium silicate hydrate (CSH), calcium aluminate hydrate (CAH) and ettringite (AFt). Besides, a dense structure was formed, which enhanced the brick strength.

Use of ladle furnace slag as supplementary cementitious material before and after modification by rapid air cooling: A comparative study of influence on the properties of blended cement paste

Ladle furnace slag (LFS) exhibits excellent early hydration activity due to its special mineral component C12A7. The mineral phase of LFS was optimized and modified by rapid air cooling, which could effectively improve the volume stability and the content of active substances in the amorphous phase of the LFS. To study the performance advantages of LFS after modification by rapid air cooling (CLFS), the hydration processes, physical and mechanical properties, and volume stability of the LFS-OPC (ordinary Portland cement) system before and after modification were compared and analyzed from a macroscopic perspective. The microstructures, compositions, and pore structures of the CLFS-OPC hardened pastes at different ages were studied. The results showed that both CLFS and LFS can accelerate the hydration and setting of cement significantly. With the increase in the LFS content, the second hydration exothermic peak of cement gradually became divided into two main exothermic peaks, which were mainly due to aluminate hydration and silicate hydration. Compared with the LFS-OPC, the CLFS-OPC exhibited a faster hydration rate and shorter setting time. In addition, the mechanical properties and volume stability of the CLFS-OPC were better than those of the original system due to the existence of more active β-C2S crystal forms and smaller f-MgO particles in the CLFS, which provides a good foundation for the use of CLFS to promote the setting of cement-based cementitious materials. CLFS is recommended to be used as mineral component regulator with a dosage of 5% ∼ 10%.

New scientific evidence of the effect of high temperatures and long curing times on MK-blended cement paste mineralogy

This article reports new scientific evidence on the hydrated phases present in blended cement pastes formulated with 10%, 20% or 25% metakaolin (MK) and stored at 60 °C for 15 years. XRD-Rietveld, SEM/EDX, NMR, FT-IR and TG/DTG findings attested to substantial difference in the mineralogy and morphology of the phases present (C2ASH8, C4AH13 and hydrogarnet) between long-term and short-term curing. The predominant crystalline phases in OPC and 10% MK-blended pastes, portlandite, calcite and γ-C2S, were characterised by small, laminar crystals. Stable katoite and hydrogrossular were observed in the pastes with MK content ≥20%, although the cubic phase of the latter (tricalcium aluminate hydrate, Ca3Al2(OH)12) was found only in pastes with an MK content of 25%.

Re-mineralization potential, shear bond strength and hydration characteristics of experimentally prepared tri-calcium aluminate phase-modified glass ionomer cement on sound and caries-affected dentin (An in vitro/in vivo study)

BackgroundThis study aimed to in vivo and in vitro evaluate the remineralization potential and shear bond strength (SBS) of experimentally prepared tri-calcium aluminate (C3A)-modified glass ionomer cements on sound and artificial caries-affected dentin (CAD). A pure tricalcium aluminate (C3A) phase prepared via solid state reaction at elevated temperature from chemically pure calcium carbonate and alumina, to formulate ceramic composite of composition: 75% C3A, 15% CaSO4·2H2O and 10% Bi2O3. The influence of artificial saliva solution on the hydration characteristics and microstructure of the synthesized composite was investigated by X-ray diffraction (XRD) analysis, FTIR spectral analysis, pH determination and scanning electron microscope (SEM) in comparison with distilled water curing medium. Modified cements of C3A glass ionomers (C3A-CGIC) were prepared by addition of the experimentally prepared C3A to the powder component of the conventical glass ionomer cement (CGIC). Five and 10 wt% of C3A- CGICs powder were prepared and compared to CGIC. Cements were applied in prepared class V cavities in rabbits’ teeth either to sound or artificial CAD. All rabbits were killed after 15 days, and then, Ca and P wt% were evaluated at the cement–dentin interface using Energy-Dispersive X-ray Analysis. Specimens for SBS evaluation were prepared for the tested cements bonded either to sound or artificial CAD, then tested using universal testing machine.ResultsThe XRD results indicate that there is an acceleration effect on the hydration reactions and decrease in the rate of conversion process of C3A phase composite due to the presence of free ions in saliva solution which was emphasized by the results of the IR spectral bands of the hydrated paste samples. The SEM micrographs showed a more-dense microstructure with large accumulations of aluminate hydrate crystals of samples cured under saliva solution. Results of the prepared C3A-CGICs showed that 10wt% C3A-GIC group had the highest statistically significant mean Ca, P wt% and SBS values on CAD compared to 5wt% C3A-GIC and CGIC.Conclusions10 wt% C3A-GIC has a remineralizing effect on artificial CAD under in vivo conditions, plus its improved bonding to dentin compared to CGIC. Thus, it might be promising restorative/base with advanced remineralization potential and adequate bond strength to both sound dentin and CAD.

Relationships between reaction products and carbonation performance of alkali-activated slag with similar pore structure

The composition of reaction products is one of the most significant factors affecting the carbonation performance of alkali-activated slag (AAS). However, the relationships between the reaction products and the carbonation performance of AAS have not been established. To address this gap, AAS pastes with different composition and similar pore structure were prepared by adding Al(OH)3 or Mg(OH)2 to evaluate the effect of the composition on the carbonation performance of AAS. Further, in order to gain insight into the influential mechanism of the composition, the principal reaction products in AAS were also synthesized. All produced specimens were tested for carbonation performance, alongside morphological, thermal and chemical characterizations. The results show that among the examined reaction products, the hydrotalcite-like phase (MAH) displayed the strongest carbonation resistance, which was almost immune to the attack of aggressive CO2. By contrast, the calcium aluminate hydrate (CAH) and calcium (alumino) silicate hydrate (C-(A)-S-H) were much more susceptible to the CO2-rich environment. Further, adding Mg(OH)2 to AAS could promote the formation of MAH and in turn, alleviated the carbonation depth of AAS. Whereas, the content of CAH and the A/S (Al2O3/SiO2) ratio of C-(A)-S-H were raised with the increase of Al(OH)3, resulting in a poor carbonation resistance of AAS. Moreover, a multi-factor model with R2 of 0.95 was established to associate the carbonation depth of AAS with the A/S ratio of C-(A)-S-H, the proportion of MAH, and the proportion of CAH. According to the proposed model, the carbonation depth of AAS is believed the most sensitive to the A/S ratio of C-(A)-S-H.

Influence of calcium sulfoaluminate cement on early-age properties and microstructure of Portland cement with hydroxypropyl methyl cellulose and superplasticizer

In order to improve the construction efficiency of thin layer masonry mortar (TLMM) even to realize mechanized construction, it is necessary to maintain suitable workability and at the same time get early-strength. To improve the workability of TLMM cellulose ether and superplasticizer were usually used. Calcium sulfoaluminate cement (CSA) was used as mineral accelerator in the paper to make the mortar get early-strength. Therefore, the effect of CSA on the early-age properties and microstructure of Portland cement (PC) with hydroxypropyl methyl cellulose (HPMC) and polycarboxylic acid superplasticizer (PA) was investigated. The X-ray diffraction (XRD), thermogravimetry (TG), isothermal calorimetry, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM) were used to clarify the impacts. Results showed that the setting time of the PC with HPMC-PA was accelerated with the increase of CSA replacement rate (CRR). CRR also had a significant impact on the development of compressive strength, especially when CRR was over 5.0% by weight, the compressive strength of samples were obtained after curing for 6 h. Moreover, the microstructure of the sample changed with CRR. With the increase of CRR, the content of ettringite (AFt) was increased and its morphology became shorter and thicker, the hydration of aluminate (C3A) and tricalcium silicate (C3S) in PC was delayed and the amount of portlandite was decreased, and the pores with diameter over 20 nm were increased. In addition, a new discovery was that C3A in PC and ye'elimite (C4A3S‾) in CSA were competitive with each other in reaction with gypsum to form AFt, and C4A3S‾ preferentially reacted.

Tritium extraction in aluminum metal by heating method without melting

Tritium was extracted from tritium-contaminated aluminum samples by heating it in a high-temperature furnace at 200, 300, or 400 °C for 15 h. The extracted tritium was analyzed by using a liquid scintillation counter (LSC); the sample thicknesses were 0.4 and 2 mm. The differences in tritium extraction over time were also investigated by cutting aluminum stick samples into several pieces (1, 5, 10, and 15) with the same thickness, and subsequently heating them. The results revealed that there are most of the hydrated material based on tritium on the surface of aluminum. When the temperature was increased from 200 or 300 °C–400 °C, there are no large differences in the heating duration required for the radioactivity concentration to be lower than the MDA value. Additionally, at the same thickness, because the surface of aluminum is only contaminated to tritiated water, cutting the aluminum samples into several pieces (5, 10, and 15) did not have a substantial effect on the tritium extraction fraction at any of the applied heating temperatures (200, 300, or 400 °C). The proportion of each tritium-release materials (aluminum hydrate based on tritium) were investigated via diverse analyses (LSC, XRD, and SEM-EDS).

Effects of Nano-CSH on the hydration process and mechanical property of cementitious materials

Nanomaterials are widely used in cement to improve the various properties of cement-based materials. Nano-CSH is considered as an effective accelerator for the hydration of cement. This paper studied the effects of nano-CSH on the hydration behavior and compressive strength of cementitious materials with various mineral admixtures. Isothermal calorimetry test was used to study the early hydration of cement paste. Thermogravimetric and X-ray diffraction tests were used to study the evolution of hydration product and unhydrated mineral phases in the hydrated cement paste. The presentation of compressive strength can evaluate the influence of nano-CSH on the property of cement-based material at the macro level. The obtained results show that the used nano-CSH can promote the hydration of tricalcium silicate (C3S), and is more active on the hydration of tricalcium aluminate (C3A) in the samples with GGBFS. The presence of nano-CSH can definitely accelerate the secondary hydration reaction of mineral admixtures.

Effect of seawater as mixing water on the hydration behaviour of tricalcium aluminate

This study explored the mechanism of the effect of seawater on tricalcium aluminate (C3A) hydration. The results showed that seawater retarded C3A hydration and reduced the reaction degree of C3A. The co-existence or ion pairing of Ca2+ and SO42− onto the surface of C3A poisoning the reactive sites is the main reason for this retardation. Besides, the precipitation of Mg(OH)2 on the surface of C3A would prolong the induction period for another 30 min and then consequently decrease the dissolution rate of C3A hydration. Trace amounts of MgSO40 and Mg2+ present in the alkaline solution had little retardation effect. It was also found that Cl− would preferentially react with C3A to form Friedel's salt, rather than forming hydroxy-AFm as that in the C3A-deionized water paste. The direct formation of Friedel's salt resulted in an accumulation of Al3+ in solution, which would also hinder the subsequent dissolution of C3A.

Experimental study of the feasibility of using calcium carbide residue as an alkaline activator for clay-plant ash geopolymer

The use of cement is gradually limited due to its enormousthermal energy consumption and carbon dioxide emissions. The plant ash and calcium carbide residue, as waste by-products, are adopted in this research for clay-plant ash geopolymer. The primary purpose of this research is to evaluate the feasibility of calcium carbide residue as an alkaline activator to improve the engineering properties of clay-plant ash geopolymer. Laboratory tests containing the unconfined compressive strength test, atterberg limits, orthogonalexperiment and scanning electron microscope (SEM) tests are carried out and the influence factors include the plant ash contents, calcium carbide residue contents, sodium hydroxide contents and curing time. The experimental results indicate that the calcium carbide residue has a significant effect on unconfined compressive strength of clay-plant ash geopolymer and the strength increases with the increasing calcium carbide residue contents. The strength of clay-plant ash geopolymer also increases with the increase in plant ash content and curing time. The optimalproportionof clay-plant ash geopolymer is obtained from orthogonalexperiment and it demonstrates that the highest strength of sample is achieved from 16% calcium carbide residue, 13% plant ash and 0.8% sodium hydroxide. The brittle strain softening behavior is observed from the stress–strain curves of clay-plant ash geopolymer. With the addition of plant ash and calcium carbide residue, the liquid limit and plastic limit of clay-plant ash geopolymer both increase and the plasticity index decreases. The microstructure of samples is revealed by scanning electron microscope test and it indicates that the main reason of strength improvement is attributed to the formation of gelling substances such as calcium silicate hydrate and calcium aluminate hydrate. Finally, the stabilization mechanism of calcium carbide residue and plant ash is analyzed and discussed in this study.

Parameters Affecting the Precipitation of Al Phases from Aluminate Solutions of the Pedersen Process: The Effect of Carbonate Content

Leaching experiments were performed in calcium aluminate slag with a high-sodium carbonate adaptation of the Pedersen process. A theoretical thermodynamic study of the pregnant leaching solution was conducted to specify the thermodynamically favored species that exist within. Using the HSC 9.0 software, a carbonation process simulation (neutralization of the aluminate solution with CO2 gas) was simulated. Laboratory carbonation experiments were conducted to verify the theoretical predictions. According to the thermodynamic study, at temperatures below 50 °C gibbsite precipitates in the first stages of carbonation and then is transformed to dawsonite. Temperatures over 65 °C favor the direct precipitation of dawsonite. The same route (thermodynamic analysis, carbonation simulation, and experimental verification) was followed by a synthetic solution containing lower amount of sodium carbonate to prove that dawsonite precipitation occurred as a result of the high free carbonate content, to investigate the effect of temperature and to precipitate alumina hydrate phases.Graphical

The sustainable utilization of weathered cement kiln dust in the cleaner production of alkali activated binder incorporating glass sludge

It is recognized that the presence of amorphous aluminosilicates, which have high ability to interact with alkalis, is one requirement for synthesizing conventional alkali-activated cements. This paper presents an innovative method for preparing alkali-activated calcium carbonate (CaCO3)-based cement, in which weathered-cement kiln dust (W-CKD) is the main precursor. Sodium oxide (Na2O) source (sodium hydroxide, sodium silicate, and sodium aluminate), Na2O-content (1.93, 3.87, 5.82, and 7.75 wt%), type of mixing water (tap and sea water), and the content of lead glass sludge (LGS: 10, 30, and 50 wt%) are the main compositional factors, which strongly affect the performance of the prepared cement. Pirssonite double salt CaCO3.Na2CO3·2H2O is alone main binding phase within sodium hydroxide-activated W-CKD with modest 28-day compressive strengths (~2–9 MPa). A significant enhancement in 28-day compressive strength (~15–21 MPa), which associated with the formation of calcium silicate hydrate (C-S-H) and calcium aluminate hydrate (C-A-H) was observed when sodium silicate and sodium aluminate used as alkali activators. On the other hand, mixing sea water with alkali activators results in the formation of nano materials with high effectiveness in the improvement of the mechanical performance of the prepared cement. Incorporating LGS within sodium aluminate-activated W-CKD enhances the formation of C-S-H accompanied by a significant improvement in the compressive strength of the hardened cement (25–52 MPa at 28-day of air curing). Moreover, all hardened W-CKD/LGS mixtures exhibit low Pb-leachability in acidic media. This strongly reflects on the safe application of these mixtures in the construction works.

Sodium chloride impact on cemented clay

When Portland cement (PC) is used for soil stabilisation, exposure to sodium chloride (NaCl) is a major problem in geotechnical engineering. NaCl's effect decreases the soil's structural stability and weakens its mechanical performances. The recycled powder recycled tyre (PRT) can be utilised to improve the mechanical characteristics of soil while reducing the landfills matters. The resistivity to chloride of cement clay after 7 days, 14 days and 28 days of curing were evaluated. Compressive strength tests (UCS) were performed. Half of which were performed on the control sample (unexposed) and half on the sample exposed to NaCl. The addition of 3 % PRT increased the UCS (qu) value under standard conditions and when exposed to NaCl. The same trend was observed for the addition of 5 % and 10 % PRT. The exposure reduced the UCS value, and the higher PRT dosage showed a better outcome. The analysis has shown that, when exposed to NaCl, cement hydration products, such as calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH), are degraded, causing huge voids.