Formation Of Tobermorite Research Articles

Influence of Gypsum Additive on the Formation of Tobermorite in Autoclaved Aerated Concrete

The quality of the aerated concrete strongly depends on the chemical composition of the raw materials, as well as the process of the hydrothermal reaction during autoclaving. Due to the variable chemical composition of fly ashes, it is necessary to identify the effect of each ion on the formation of the microstructure of aerated concrete. This paper examines the process of formation of tobermorite with the addition of sulphates in various percentage representation. The microstructure of aerated concrete is assessed using SEM images and the mineralogical by means of X-ray analysis.

Hydrothermal Synthesis of Tobermorite at 170 and 190 °C from Fly Ash and Quartz Sand

Tobermorite is the main mineral which provides to aerated concrete mechanical properties. It is produces during hydrothermal conditions by reacting silicon and calcium oxides. Within this research was evaluated tobermorite formation using high temperature combustion fly ash and quartz sand, as the siliceous raw materials. As a binder was used lime. Emphasis was also placed on the molar ratio of C/S, which is crucial for the formation of tobermorite and was given 0.73 and 1.00. Hydrothermal synthesis was carried out in a laboratory autoclave at temperatures of 170 and 190 °C.

Synthesis of Tobermorite from the Ash after Treatment of Asbesto-Containing Disaster Waste, and Its Removal Ability of Cs(I) from Aqueous Solution

Tobermorite was synthesized successfully from the ash, which was produced and detoxified from asbesto-containing disaster waste in great east Japan earth quake, by alkali hydrothermal treatment. Tobermorite synthesis was examined as a function of reaction temperature and NaOH concentration. The formation of tobermorite was identified in the product treated with 1-4 M NaOH solution at 130 and 180 o C, while no product phases was identified at 80 o C. With increasing reaction temperature, intensity of tobermorite phase in the product and Cs+ removal ability of the product increase. The product, which was treated with 4 M NaOH at 180 o C for 20 h, revealed the high selective uptake for Cs+ in saline water. The Cs+ uptake of the product was extrapolated using Langmuir and Freundlich isotherm models, experimental data are found to fit Langmuir than Freundlich, and the calculated uptake amount was 0.51 mmol/g. The kinetics for Cs+ uptake was tested for pseudo-second order reactions, and the rate constants of uptake were calculated. With increasing temperature of aqueous solution, the kinetics of uptake is almost same and the uptake amount of Cs+ decreases. The product is expected to be used for Cs+ removal from wastewater.

Formation of tobermorite and xonotlite fiber matrices in well cementing and impact on mechanical properties

Over the last two decades, there has been an increased focus on the stability of the cement sheath under the influence of shear stresses imposed during the lifetime of the well. However, there has been no investigation, on the impact to the cement sheath matrix, on the formation of fibrous crystalline calcium silicate hydrates that occurs under temperature and pressure. In well cements, tobermorite (Ca5Si6O16(OH)2·4H2O) has been reported to form as the predominant phase at temperatures in the range of 120–180 °C and has a platelet, lath, or fibrous habit while xonotlite (Ca6Si6O17(OH)2) forms at temperatures above 150 °C and has a needle-like habit. Tensile strength data were obtained at 150 and 230 °C with phase assemblage of the hydrated cement determined using XRD, crystal habit by SEM analyses, and porosity by mercury intrusion porosimetry. The effect of retarder on crystal formation was also investigated and correlated to thickening time and calorimetry.

Preparation and characterization of high-strength calcium silicate boards from coal-fired industrial solid wastes

To realize the comprehensive utilization of coal-fired industrial solid wastes, a novel high-strength board was prepared from calcium silicate slag, fly ash, and flue gas desulfurization (FGD) gypsum. The changes in mineral phases, chemical structure, and morphology during hydration were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). A traditional board made from quartz and lime was prepared as a reference. The novel board not only consumes a lot of solid wastes, but also meets the strength requirement of the class-five calcium silicate board according to the Chinese Standard JC/T 564.2—2008. Microanalysis showed that hydrated calcium silicate gel (C−S−H(I)), ettringite, tobermorite, and xonotlite were successively generated in the novel board by synergistic hydration of the mixed solid wastes. The board strength was improved by the formation of tobermorite and xonotlite but decreased by unhydrated quartz. It was demonstrated that quartz was not completely hydrated in the traditional board. As a result, the flexural strength of the traditional board was much lower than that of the novel board.

Hydrothermal synthesis of tobermorite from diatomite and its adsorption performance for methylene blue

Disposal of dyes wastewater effluents is one of the most important factors in many industries. Methylene blue is the most commonly used dyes in industries and is very difficult to degrade due to its complex structures. Diatomite is one of the excellent adsorbents owing to its unique properties. However, the small powder form of diatomite, which leads to a large amount sludge produced easily, has limited its wide application in environmental engineering. In our study, diatomite was solidified hydrothermally at low temperature (≤ 200°C) on the basis of sustaining the inherent properties of diatomite. The results showed that tobermorite was found to exert a positive effect on its strength and porosity, and also had higher methylene blue adsorption capability compared with diatomite. The thermodynamic parameters indicated that the adsorption of methylene blue with tobermorite formation was an endothermic and spontaneous process.

THE OCCURRENCE OF HIGH-TEMPERATURE SKARNS FROM ORAVIŢA (BANAT, ROMANIA): A MINERALOGICAL OVERVIEW

A shallow-level dioritic pluton of Upper Cretaceous age caused extensive contact metamorphism of a Mesozoic calcareous sequence at Oraviţa-Ciclova in Romania. The peak metamorphic assemblage (stage I) includes wollastonite, akermanite-rich melilite, Ti-rich calcic garnet, and pyrrhotite. A second, subsequent paragenesis (stage II) is due to local decreases in fluid pressure and includes gehlenite, Ti-poor calcic garnet, monticellite, Al-rich diopside, magnetite, perovskite, and probably a Ca-Si mineral (kilchoanite?). An early hydrothermal stage (stage III) produced retrogression of the first two stages and a paragenesis including vesuvianite, clintonite, fukalite, katoite, and hydroxylellestadite. A second, late hydrothermal event (stage IV) resulted in the formation of clinochlore, talc, epidote, zeolites (scolecite and thomsonite-Ca), thaumasite, and tobermorite. A last, weathering, paragenesis corresponding to stage V includes allophane (C-S-H gels) and probably portlandite, unpreserved because of its transformation to aragonite, then calcite. The peak metamorphic conditions during the prograde evolution are estimated to have been 750–800 °C for a fluid pressure of up to 0.5 kbar. The main constants determined from chemical, optical, and X-ray powder analyses of these mineral species are reported here. This work documents the first occurrence of katoite and the second occurrences of perovskite, fukalite, and hydroxylellestadite in the Romanian skarns.

Formation of Tobermorite at Different Materials Composition of Aerated Concrete

For the production of quality autoclaved aerated concrete product is necessary to know the chemical composition of raw materials and with regard to that optimize the recipe. This paper deals with the verification of the influence raw materials mixture ́s chemical composition, the reactivity of the silica source and the molar ratio C/S on the shape and amount of tobermorite crystals in autoclaved aerated concrete.

Influence of inorganic admixtures on the 11 Å-tobermorite formation prepared from steel slags: XRD and FTIR analysis

Calcium silicate hydrate is synthesized from steel slag by adding lime and quartz by dynamic hydrothermal method at 185°C. The products mainly consist of disordered calcium silicate hydrate, but more crystallized phase such as 11Å-tobermorite forms for the presence of inorganic admixtures. The formation of tobermorite is affected by the types of ions according to XRD and FTIR results. Adding 2% crystallized tobermorite is beneficial to form the ordered structure; alkali cations and SO42− anions are effective accelerators; Al3+ plays a role of stabilization during the reaction. The products also vary with the initial alkalinities of steel slag.

Synthesis, structure and performance of calcium silicate ion exchangers from recycled container glass

Numerous technical, economic and societal factors limit the recycling of waste soda-lime-silica glass back into the primary production process and accordingly alternative applications for this material are sought. This study demonstrates that waste soda-lime-silica container glass is a suitable feedstock material for the production of tobermorite, a calcium silicate cation exchanger. Tobermorites were synthesised at 100 degrees C from stoichiometric mixtures of container glass and lime under alkaline hydrothermal conditions. Increasing concentrations of sodium hydroxide (between 1.0 M and 4.0 M) in the reaction mixture promoted the formation and crystallisation of tobermorite, and also resulted in greater fragmentation of the silicate chains along the b-axis direction. The maximum removal capacities of these tobermorite specimens for Cd2+ (441 mg g(-1)) and Zn2+ (122 mg g(-1)) compared well with those of other waste-derived sorbents. Superior Cd2+- and Zn2+- uptake capacities and kinetics were observed for the least crystalline tobermorite specimen, indicating that stacking defects facilitate the transport and exchange of cations within the lattice.

Hydrothermal synthesis of CSH-phases (tobermorite) under influence of Ca-formate

The influence of Ca-formate (C2H2CaO4) on the crystallization of the CSH-phase 11Å tobermorite was investigated under hydrothermal conditions at 200°C in a wide CaO/SiO2 range of 0.67–1.24. Besides clarifying questions on acceleration or retarding of CSH formation at high Ca-formate contents even a study on the effect of this salt addition on the crystal morphology was a main objective of the present work. All experiments were performed using fine grained SiO2 powder (P) or coarse grained quartz sand (S) as silicate source. The reactions were followed by XRD, SEM/EDX and FTIR. Except the reaction at lowest amount of formate (0.43g), where only a very small effect on the crystallization rate was observed, higher salt concentrations were found to retard the reaction clearly. Here the reduction of the CSH-crystallization velocity and formation of tobermorite with a distinct character of the pre-phase CSH-I could be stated in each case. Its amount and crystal quality was not rigorously dependant on the inserted mass of Ca-formate in the 0.67–1.34g range investigated here.A strong influence on the morphology of the CSH-crystals was further detected already in the whole range of salt concentration, i.e. even at the low value of 0.43g, examined in our experiments. Instead of the typical rod-like morphology of tobermorite formed without Ca-formate, a disturbed bent-needle-like morphology occurred at elevated formate concentrations. In contrast small compact crystals were observed at low amounts of Ca-formate.Syntheses with quartz powder and quartz sand in principle yielded to comparable results concerning the retarding effect and the change of crystal morphology. As expected, the reaction rate of experiments with quartz sand was diminished in general, according to the lower specific surface of the sand grains, compared with the powder.A change of the pH-value with marked influence on the solubility rate of the educts and the further course of reaction can be excluded as cause for the observed behavior. Further reasons, based on crystal growth under influence of adsorption of formate ions at specific crystal faces were discussed.The improvement of knowledge on effects of additives on CSH crystallization will be of importance for future modifications of reaction processes of cement and concrete as well as steam hardened construction materials, where 11Å tobermorite acts as the main binding agent.

Recycling of crushed stone powder as a partial replacement for silica powder in extruded cement panels

The continuously increasing amount of crushed stone powder normally coming from the production of crushed aggregates or sawing stone has led to an increase in the waste disposal costs or instances of improper disposal. In this study, the effective methodology to increase the utilization of crushed stone powder was studied by considering CaO/SiO2 mole ratio in mix design. The hydrothermal reaction to synthesis tobermorite related to strength development was also considered to improve rigidity in hardened cement. The results showed the optimized C/S mole ratio is 0.87 and a valid method for curing conditions relating to hardened cement was desired to be acquired by 2h of pre-curing, 4h of atmosphere steam curing (65°C) and 4h of autoclave curing (180°C, 10atm). The extruded panels satisfied all performance requirements relating to fire resistance as well as sound insulation and can have a possible application to building materials. The main findings of this investigation revealed that the stable crystal formation of tobermorite by the hydrothermal synthesis reaction affects the most important mechanism in hardened cement and mix design by considering C/S mole rate in addition to the analysis of microstructures promotes the recycling of crushed stone powder for building materials.

Investigation of properties of fluorogypsum-slag composite binders – Hydration, strength and microstructure

A composite binder of high strength and low water absorption has been developed using industrial by-products fluorogypsum, granulated blast furnace slag and Portland cement. The development of strength in the binder at an early age is attributed to the conversion of anhydrite into gypsum and at later age is due to the formation of ettringite and tobermorite, as a reaction of slag with lime produced during the hydration of cement. These cementitious phases fill in pores and voids of the hydrating gypsum crystals to form a dense and compact structure of low porosity and low pore volume. The reaction products formed during the hydration period were confirmed by scanning electron microscopy and X-ray diffraction. The reduction in porosity and low pore volume of binders, as studied by mercury intrusion porosimetry, are responsible for attainment of high strength and better stability towards water in composite binders than the conventional gypsum plaster.

Hydrothermal Synthesis of Humidity-Regulating Material from Calcined Loess

To simulate the thermal properties of cave dwellings, which are warm in winter and cool in summer, a mesoporous material with a good humidity-regulating performance was synthesized hydrothermally from loess. Through the calcination of loess, which both provides active calcium through the decomposition of calcite within loess and improves the reactivity by dehydroxylation, a tough mesoporous material could be synthesized without any additives, and tobermorite formation was found to exert a positive effect on its strength and porosity. Mesopores seemed to exert a positive influence on the humidity-regulating performance of the material from loess. Although calcination destroyed the original porosity of the loess, the porosity and thus the humidity-regulating performance could be recovered greatly through hydrothermal treatment. As such, using only calcined loess, a tough mesoporous material exhibiting good humidity-regulating performance was synthesized that could be used as a “cave-dwelling” building mater...

Comprehensive study of fly ash binder developed with fly ash – alpha gypsum plaster – Portland cement

In this study, a new type of fly ash binder has been developed using fly ash, hydrated lime sludge and Portland cement, as well as α-gypsum plaster as stimulator. The hydration process and microstructure of the fly ash binder was investigated with differential thermal analysis, X-ray diffraction and scanning electron microscopy. These studies showed that the strength development of binder takes place through formation of ettringite and tobermorite. The durability of fly ash binder was assessed by its performance in water by immersion and by alternate wetting and drying cycles at 27–50°C. The results reveal absence of leaching of the matrix in fly ash binder as well as reduction in strength and enhancement in weight loss with the increase in temperature and cycles. The fly ash binder is found suitable for use in masonry mortars, concrete and bricks.

Compressive strength, flexural strength and thermal conductivity of autoclaved concrete block made using bottom ash as cement replacement materials

The bottom ash (BA) from Mae Moh power plant, Lampang, Thailand was used as Portland cement replacement to produce lightweight concrete (LWC) by autoclave aerated concrete method. Portland cement type 1, river sand, bottom ash, aluminium powder and calcium hydroxide (Ca(OH)2) were used in this study. BA was used to replace Portland cement at 0%, 10%, 20% and 30% by weight and aluminium powder was added at 0.2% by weight in order to produce the aerated concrete. Compressive strength, flexural and thermal conductivity tests were then carried out after the concrete were autoclaved for 6h and left in air for 7days. The results show that the compressive strength, flexural strength and thermal conductivity increased with increased BA content due to tobermorite formation. However, approximately, 20% increase in both compressive (up to 11.61MPa) and flexural strengths (up to 3.16MPa) was found for mixes with 30% BA content in comparison to just around 6% increase in the thermal conductivity. Thermogravimetry analysis shows C–S–H formation and X-ray diffraction confirm tobermorite formation in bottom ash lightweight concrete. The use of BA as a cement replacement, therefore, can be seen to have the benefit in enhancing strength of the aerated concrete while achieving comparatively low thermal conductivity when compared to the results of the control Portland cement concrete.

Effect of sugarcane biomass waste in cement slurries submitted to high temperature and pressure

Abstract Cementitious materials are subjected to changes in their microstructure and mechanical behavior when submitted to high service temperatures. In the oil industry, Portland-based slurries are used where conditions imply high temperatures and high pressures, e.g., steam injection or recovery of heavy oils. The present study investigated the hydration behavior and mechanical strength of cement slurries containing sugarcane biomass waste or silica flour, submitted to high temperature and pressure cycles using a curing chamber. The slurries were initially cured for 28 days at 22 °C. After that, they were placed in a curing chamber for 3 days at 280 °C and 17.6 MPa. The results showed a decrease in the compressive strength of the slurries submitted to high temperature high pressure. The decrease in strength was less marked in the slurry containing 40% of sugarcane biomass waste, as a consequence of the formation of silica-rich phases, i.e., xonotlite and tobermorite. When the slurries were placed in the curing chamber at 280 °C and 6.9 MPa for 7 days (after initial curing for 14 days at 38 °C), the slurry containing 59% sugarcane biomass waste showed an increase in compressive strength, contrary to what was observed for all the other slurries tested.

Synthesis of Al-Substituted 11Å Tobermorite from Aegirine-Augite Syenite Potash Ores by Hydrothermal Reaction at 300°C

The Al-substituted 11Å tobermorite was synthesized from aegirine-augite syenite potash ores by alkaline hydrothermal reaction at 300°C. The obtained tobermorite was characterized by chemical analysis, X-ray diffraction and scanning electron microscopy. The effect of reaction time on the tobermorite formation and the dissolution ratio of the K2O in the potash ores were investigated. It was revealed that the dislocation ratio of K2O increases with increasing reaction time. The main rock constituents were converted into a well-crystallized Al-substituted 11Å tobermorite after 3 hours hydrothermal reaction at 300°C. The obtained Al-substituted tobermorite forms hollow spherical aggregates with the diameter of 40µm-80µm by the crossing of fibrous tobermorite crystal together. The Al3+ may substitute isomorphously up to 15 at % of Si 4+ in the obtained tobermorite.

Effects of quartz particle size and water-to-solid ratio on hydrothermal synthesis of tobermorite studied by in-situ time-resolved X-ray diffraction

Hydrothermal synthesis process of tobermorite (5CaO·6SiO 2·5H 2O) has been investigated by in-situ X-ray diffraction using high-energy X-rays from a synchrotron radiation source in combination with a purpose-build autoclave cell. Dissolution rates of quartz were largely affected by its particle size distribution in the starting mixtures. However, the composition (Ca/Si) of non-crystalline C–S–H at the start of tobermorite formation was identical regardless of the quartz dissolution rate. An effect of water-to-solid ratio (w/s) was investigated for samples using fine particle quartz. Tobermorite did not occur with w/s of 1.7 but occurred with w/s higher than 3.0. Surprisingly, however, the dissolution curves of quartz were nearly identical for all samples with w/s from 1.7 to 9, indicating that the dissolution rate is predominated by surface area. Possible reaction mechanism for tobermorite formation will be discussed in terms of Ca and/or silicate ion concentration in the liquid phase and distribution of Ca/Si in non-crystalline C–S–H.

In situ time-resolved X-ray diffraction of tobermorite formation process under hydrothermal condition: Influence of reactive al compound

Hydrothermal formation reaction of tobermorite in the autoclaved aerated concrete (AAC) process has been investigated by in situ X-ray diffraction. High-energy X-rays from a synchrotron radiation source in combination with a newly developed autoclave cell and a photon-counting pixel array detector were used. XRD measurements were conducted in a temperature range 100–190°C throughout 12 h of reaction time with a time interval of 4.25 min under a saturated steam pressure. To clarify the tobermorite formation mechanism in the AAC process, the effect of Al addition on the tobermorite formation reaction was studied. As intermediate phases, non-crystalline calcium silicate hydrate (C-S-H), hydroxylellestadite (HE), and katoite (KA) were clearly observed. Consequently, it was confirmed that there were two reaction pathways via C-S-H and KA in the tobermorite formation reaction of Al containing system. In addition, detailed information on the structural changes during the hydrothermal reaction was obtained.