An X-Ray Diffraction,Fourier-Transform Infrared Spectroscopy,and Scanning Electron Microscopy/Energy-Dispersive Spectroscopic Investigation of the Effect of Sodium Lignosulfonate Superplasticizer on the Hydration of Portland Cement Type V

This study investigated the effects of a common superplasticizer, ligno-sulfonate, on the hydration of Portland cement Type V. Samples of plain cement and superplasticizer-treated cement have been examined by x-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy/energy-dispersive spectroscopy. Lignosulfonate has been observed to retard the hydration of cement through specific surface chemical reactions which involve Ca²⁺ ions in pore solution. The admixture has been found to retard the formation of Ca(OH)₂ and stabilize ettringite [Ca₆(Al₂2O₆)(SO₄)₃.32H₂O]. The inhibition of the rate of conversion of ettringite to monosulfate [Ca₄Al₂(OH)₁₂.SO₄.6H₂O] is attributed to charge-controlled reactions caused by large quantities of Ca²⁺ ions from initial hydration reactions. Leaching of the admixture doped cement by water-removed lignosulfonate and caused complete hydration of cement. A charge-controlled-reaction model involving the Ca²⁺ ions is proposed to explain the role of the admixtures during hydration of cement.     

Studies on the Stability of Calcium Sulphoaluminate

High calcium sulpho-aluminate (3CaO. Al₂O₃. 3CaSO₄. 31H₂O—C.S.A.) is a deterioration product of Portland cement found in concrete. It is formed by the attack of sulphate solutions on two of the Portland cement components: hydrated calcium Aluminate and lime. These phenomena fostered a study of the synthesis and stability of calcium sulpho-aluminate. Results of the experiments on stability of calcium sulphoaluminate in different media are discussed. Measures for preventing the formation of C.S.A. in Portland cement are described.     

Understanding the adsorption of calcium sulfate on tetracalcium aluminoferrite and tricalcium aluminate surfaces

Calcium sulfate (CaSO₄), an essential retarder in cement, retards the hydration of tricalcium aluminate (C₃A) and tetracalcium aluminoferrite (C₄AF) phases. However, its retarding mechanism remains unclear. This paper focused on the adsorption of CaSO_4f on C₄AF and C₃A surfaces based on isothermal calorimetry, the measurement of the ionic concentrations in a diluted system, and density functional theory to enhance the understanding of the retardation mechanism. The results showed that the retarding effect of CaSO₄ on C₄AF was stronger than that on C₃A due to the slower CaSO₄ consumption rate, lower driving force for CaSO₄ adsorption, and surface coverage of Fe(OH)₃ gel. The adsorption of CaSO₄ hindered Ca dissolution more markedly on C₄AF than C₃A, which was pronounced on Fe-free C₄AF surfaces. The adsorption of CaSO₄ weakened the affinity of water on C₄AF and C₃A surfaces, lowering the driving force for H₂O adsorption. The adsorption of H₂O and CaSO₄ promoted the dissolution of Al on the [AlO₆] octahedral surface of C₄AF, which may be responsible for the maintenance of a higher Al concentration in the solution. Based on the above results, the adsorption of CaSO₄ on initial C₄AF and C₃A hydration was explained.     

Studies on the Stability of Calcium Chloraluminate

Calcium chloraluminate (3CaO · Al₂O₃ · CaCl₂ · 10H₂O) is a deterioration product of Portland cement found in concrete. It is formed by the attack of chloride solutions on two of the Portland cement components: hydrated calcium aluminate and lime. A study of the synthesis and stability of calcium chloraluminate in different media are described. Calcium chloraluminate enhances the growth of high calcium sulphoaluminate crystals (3CaO · Al₂O₃ · 3CaSO₄ · 31H₂O).     

Mineralogical and engineering characteristics of dry flue gas desulfurization products

Fifty-nine coal combustion products were collected from coal-fired power plants using various dry flue gas desulfurization (FGD) processes to remove SO₂. X-ray diffraction analyses revealed duct injection and spray dryer processes created products that primarily contained Ca(OH)₂ (portlandite) and CaSO₃·0.5H₂O (hannebachite). Most samples from the lime injection multistage burners process contained significant amounts of CaO (lime), CaSO₄ (anhydrite), and CaCO₃ (calcite). Bed ashes from the fluidized bed process were often dominated by CaSO₄ but also contained CaCO₃, CaO (lime), and MgO (periclase). Cyclone ashes were similar in composition to the bed ashes but contained more unspent sorbent and CaSO₄ and less MgO. Fly ash in all samples ranged from 10 to 79 wt%. Samples usually exhibited two distinct swelling episodes. One occurred immediately after water was applied due to hydration reactions, especially the conversion of CaO to Ca(OH)₂ and CaSO₄ to CaSO₄·2H₂O (gypsum). The second began between 10 and 50 d later and involved formation of the mineral ettringite (Ca₆[Al (OH)₆](SO₄)₃·26H₂O). The final pH after 112 d ranged from 10.0 to 12.1. If samples are incubated under ‘closed’ (i.e. incomplete recarbonation with atmospheric CO₂) and alkaline weathering conditions, gypsum and portlandite are initially formed followed by the conversion of the gypsum to ettringite. Closed, alkaline conditions typically can occur when FGD products are placed in confined settings such as a road embankment or buried as a discrete layer as occurs in some surface mine reclamation projects.     

Energy and Cost Estimation for Application of Chemical Heat Pump Dryer to Industrial Ceramics Drying

Abstract

In this article we estimate the potential of a new chemical heat pump dryer (CHPD) application to an industrial ceramics drying process from the viewpoints of energy and cost saving. A CaSO₄/H₂O/CaSO₄·1/2H₂O hydration/dehydration CHPD system and a CaO/H₂O/Ca(OH)₂ hydration/dehydration CHPD system were examined. The CHPD systems store heat and simultaneously release the increased amount of heat at different temperature levels by using two chemical heat pumps (CHP) in their heat-enhancement mode. Furthermore, we propose enhanced systems using chemical heat pipes (CHPipe) for their environmental and cost merits. As a result, the consumed energy and the cost of using the CHPD systems in the industrial ceramics drying process are found to decrease to less than half of the conventional drying process using gas-fired boilers. For example, the energy efficiency and the cost of the present drying process are 28.4% and 604 × 10³ (JPY/month) (JPY: Japanese Yen), respectively. The energy efficiency and the cost of the proposed CHPD system are found to be 79.7% and 216 × 10³ (JPY/month), respectively, based on our experiments.     

Quantitative X-ray diffraction analysis of ettringite,thaumasite and gypsum in concretes and mortars

A method for quantitative Xray diffraction analysis (QXDA) of three sulphate minerals frequently associated with building materials has been devised. Sulphate minerals which form within concretes, mortars and other cementitious-based materials include ettringite, (3CaO.Al₂O₃.3CaSO₄.31H₂O), thaumasite (CaSiO₃.CaCO₃.CaSO₄.15H₂O) and gypsum (CaSO₄.2H₂O). Calibration standards were prepared using pure samples of these minerals and incorporating boehmite as an internal standard. The equations obtained from the standard calibration curves were used to calculate the percentage of ettringite, thaumasite and gypsum in a) samples which contained known percentages of these minerals mixed together and b) laboratory prepared concrete cubes undergoing sulphate attack. The cubes contained 0%, 20% or 40% pulverized fuel ash (pfa) by weigth of cementitious material and had been stored in various sulphate solutions including sea water for one year.Quantitative Xray diffraction analysis of the standard mixtures successfully detected the expected ettringite, thaumasite and gypsum concentrations. The concrete cube results showed that the sulphate mineral concentration within the surface of the cubes decreased when larger amounts of pfa were used in the concrete mixes. This effect was less noticeable in the sea water cubes.     

Selection of threshold agents for calcium sulfate scale control on the basis of chemical structure

The effects of polyvinyl sulfonate (PVS) and polyglutamic acid (PGA) on the precipitation of 2CaSO₄· H₂O and CaSO₄ · 2H₂O were compared. PGA strongly retards CaSO₄ · 2H₂O precipitation from sea water, and also significantly changes its crystal habit. PVS has a similar effect on 2CaSO₄ · H₂O precipitated at ca. l00°C. The selectivity is related to structural compatibility between the additive and the crystal lattice. A possible mechanism of heterogeneous nucleation of the two crystallographic species upon the suitable polymers is proposed. The hardening of scale in the presence of an unsuitable additive is explained within the framework of the proposed mechanism.     

Factors influencing the reaction between phlogopite and CaSo4·2H2O plus CaO mixtures

According to earlier studies phlogopite reacts with CaSO₄.2H₂O and a mixture of CaSO₄.2H₂O and CaO exchanging 40–80% of its potassium with calcium. The same reactions occur only poorly in the case of muscovite. The structural difference between phlogopite and muscovite is small so that some unknown factors must effect the exchange reaction. In the present work the factors influencing the reaction between phlogopite and a CaSO₄.2H₂O/CaO mixture have been studied by means of X-ray diffraction and an electron microscope. A rod mill has been employed in the separation of the solid phases produced during the reaction. The results have been calculated and drawn by computer programs created for the study. The effects of gypsum, calcium oxide, iron, aluminium and magnesium have been treated in the exchange reaction. Also the poor reactivity of muscovite in the reaction conditions used has been discussed.     

Utilization of borogypsum as set retarder in Portland cement production

Boron ores are used in the production of various boron compounds such as boric acid, borax and boron oxide. Boric acid is produced by reacting colemanite(2CaO·3B₂O₃·5H₂O) with sulphuric acid and a large quantity of borogypsum is formed during this production. This waste causes various environmental problems when discharged directly to the environment. Portland cement is the most important material in the building industry. This material is produced by adding about 3-5% gypsum (CaSO₄·2H₂O) to clinker as a set retarder. The aim of this study was to stabilize borogypsum, and to produce cements by adding borogypsum instead of natural gypsum to clinker. Concrete using cement produced with borogypsum was tested to find the mechanical properties and the test values were compared with those of concrete from cement with natural gypsum. Compressive strength of concrete from cement produced with borogypsum was found to be higher than that of natural gypsum. Also, the setting time of cement with borogypsum was longer than that of the Portland cement.     

Utilization of low-cost celestite ore in the production of high-quality calcium-strontium aluminate refractory cement

Calcium-strontium aluminate cement (CSAC) has been successfully prepared for the first time from celestite mineral and corundum (α-Al₂O₃) via solid-state reaction. Various mixing compositions containing 40–70 wt% celestite and 60–30 wt% alumina have been sintered at firing temperatures between 1550 and 1650 °C with an interval of 50 °C. Among these sintered mixes, four cement specimens (CA101-1600, CA101-1650, CA201-1600 and CA201-1650) were selected as the optimal mixes for CSAC preparation based on their physico-chemical and mechanical characteristics. These cement mixes were ground to form a very fine powder with a particle size of less than 4.85 μm and a specific surface area of greater than 3629 cm²/g. Upon mixing these cement mixes with water, they consumed mixing water within a range of 19–27 wt% to form workable cementitious pastes. The initial and final setting times of these four cement mixes were in the range between 80 to 90 min and 290–379 min, respectively. An average compressive strength of approximately ~62 MPa was reached after curing of these cement cubes in a 100% humidity cabinet for 28 days. The main hydration products detected in the cement pastes were strontium aluminate hydrates such as 3SrO·Al₂O₃·H₂O (Sr₃A.H₂O) and 5SrO·Al₂O₃·11H₂O (Sr₅A.11H₂O) along with a minority of calcium aluminate hydrate 4CaO·3H₂O·3H₂O (C₄A₃.3H₂O) and aluminium hydroxide Al(OH)₃. The obtained physico-mechanical results of the four cement samples have met the international standard requirements; demonstrating the high-susceptibility of celestite mineral to be utilized as a potential feedstock in the production of CSAC on an industrial scale.     

Soapfree emulsion polymerization of methyl methacrylate in the presence of CaSO3

In the soapfree emulsion polymerization of a methyl methacrylate-K₂S₂O₈-CaSO₃-H₂O system, the polymerization rate, average molecular weight of polymer, particle size and particle concentration would vary with the concentration of CaSO₃. It was shown that when the concentration of CaSO₃ was well below the saturation concentration (3 × 10^?4mol/litre H₂O), the polymerization rate was higher than that of the system not containing CaSO₃. On the other hand, when the concentration of CaSO₃ was above the saturation concentration, the polymerization rate at the latter stage was lower than that of the system not containing CaSO₃ within our experimental conditions. The molecular weight of polymer was measured by Gel Permeation Chromatography (GPC). It decreased initially and then increased due to the gel effect over the entire course of polymerization. The size of the polymer particles was measured by both photo correlation spectroscopy (PCS) and transmission electron microscopy (TEM), The reaction mechanism was studied according to the above observation. The mechanical property of poly(methyl methacrylate)-CaSO₃ composite obtained from soapfree emulsion polymerization was tested and compared with that obtained from mechanical blending.     

Hydration of cement — role of triethanolamine

Following addition of 0.1, 0.25, 0.35, 0.5 and 1.0 per cent triethanolamine, studies have been made of the hydration and hardening characteristics of (a) tricalcium aluminate, (b) tricalcium aluminate + gypsum, (c) tricalcium silicate, (d) dicalcium silicate, and (e) portland cement. Triethanolamine (TEA) accelerated the hydration of 3CaO.Al₂O₃ and 3CaO.Al₂O₃-CaSO₄.2H₂O systems and extended the induction period of the hydration of 3CaO.SiO₂. In portland cement paste TEA decreased the strength at all ages and setting characteristics were drastically altered, especially at higher TEA contents. Evidence was obtained also of the formation of a complex of TEA with the hydrating silicate phase.     

Tricalcium aluminate hydration in the presence of calcium sulfite hemihydrate

This article reports on the study to evaluate the potential possibility of regulating the tricalcium aluminate (C₃A) hydration process by the addition of calcium sulfite hemihydrate. The kind and the form of hydration products were studied in the system: C₃A-CaSO₃·0.5H₂O-H₂O and C₃A-CaSO₃·0.5H₂O-Ca(OH)₂-H₂O by use of XRD, DTA and SEM/EDS methods as well as the kinetics of hydration along with chemical composition development of the liquid phase. The results thus obtained were compared to the hydration process of C₃A with the addition of natural gypsum. The results show that the reaction rate of C₃A with the addition of calcium sulfite hemihydrate differs from the analogous hydration process of C₃A in the presence of calcium sulfate dihydrate. Also, the kind of hydration products obtained in the presence of CaSO₃·0.5H₂O is different.     

Hydration of tricalcium aluminate in the presence of various amounts of calcium sulphite hemihydrate: Conductivity tests

Hydration of calcium aluminate C₃A (3CaO·Al₂O₃) in the presence of calcium sulphite hemihydrate (CaSO₃·0.5H₂O), with the molar ratio of substrates close to 1, produces the C₃A·CaSO₃·11H₂O calcium monosulphite aluminate phase. Small amounts of calcium sulphite added to calcium aluminate (the ratio of CaSO₃·0.5H₂O / C₃A equalling 0 : 1) change the rate of C₃A hydration and influence the whole reaction. Reaction processes for various ratios of the C₃A-CaSO₃·0.5H₂O mixture were examined in pure distilled water with a considerable amount of liquid W / S = 38-50 (constant W / C₃A). Processes in the liquid phase were monitored with conductivity equipment, and the XRD analysis was used to identify the phases precipitated during the examined reactions.     

Crystal structure refinement and hydration behaviour of doped tricalcium aluminate

In this paper analytical evidence on crystal structure and hydration behaviour of C₃A solid solutions with MgO, SiO₂, Fe₂O₃, Na₂O and K₂O is given. Samples were prepared using an innovative sol-gel process as precursor, examined by X-ray powder diffraction, infra-red spectroscopy and the crystal structure was refined by the Rietveld method. A significant shift of lattice parameters was found for C₃A solid solutions with SiO₂, Fe₂O₃ or Na₂O but only minor changes were detected for K₂O. The hydration of C₃A solid solutions in the absence of CaSO₄ was accelerated for samples doped with SiO₂ or K₂O and it was retarded in the case of MgO, Fe₂O₃ or Na₂O. The hydration in the presence of CaSO₄ was accelerated when C₃A was doped with K₂O or Na₂O, whereas Fe₂O₃ strongly retarded the hydration. The doping with SiO₂ nearly had no influence on the hydration, the effect of MgO was not straight forward.     

Tricalcium aluminate hydration in the presence of lime,gypsum or sodium sulfate

The influence of Ca(OH)₂, CaSO₄·2H₂O and Na₂SO₄ on the C₃A hydration was examined in order to study the retardation mechanism of C₃A hydration caused by lime and/or gypsum additions. When C₃A hydrates in the presence of gypsum, the results do not confirm the retardation mechanism based on sulfate ions adsorption or C₄AH_x impervious coating. They substantially confirm the mechanism based on ettringite crystals coating C₃A grains. In the absence of gypsum C₃A hydration is retarded by C₄AH_x formation coating C₃A grains.     

Cohesion and expansion in polycrystalline solids formed by hydration reactions — The case of gypsum plasters

When powdered plaster (CaSO₄·1/2H₂O) is mixed with sufficient water to give a plastic paste, hydration occurs rapidly, forming a hardened mass of gypsum (CaSO₄·2H₂O), usually with slight bulk expansion. The addition of certain compounds can greatly increase the expansion, which may lead to destructive pressures. Here I show that this effect increases with the size of the alkyl group in an homologous series of simple water-soluble calcium carboxylate salts: Ca(HCOO)₂; Ca(CH₃COO)₂; Ca(CH₃CH₂COO)₂. The latter two, when used at aqueous concentrations of 10% or more, cause large expansions. The results can be explained by a delicate balance between crystal growth pressures and cohesive interactions at the interfaces between crystallites, on the assumption that only two principal classes of interface exist in the hardened structure: “bridging” and “non-bridging.” This hypothesis allows us to make some useful conjectures about the performance of mineral-based hydraulic binders in general, with potential implications for their durability.     

Characteristics and so2 capture capacities of sorbents prepared from products of spray-drying flue gas desulfurization

The characteristics and the SO₂ capture capacities of sorbents prepared from products of spray-drying flue gas desulfurization (FGD) have been studied. Sorbents were prepared by first slurrying Ca(OH)₂ and CaSO₃ and/or CaSO₄ with and without the addition of fly ash and then drying. Compared to the use of pure Ca(OH)₂, the SO₂ capture and Ca(OH)₂ utilization decreased for sorbents prepared without fly ash and increased for sorbents with fly ash. Flakelike ill-crystallized tobermorites were observed for all the sorbents containing fly ash. In addition, significant amounts of needle-shape Ca₄Al₂(OH)₁₂SO₄ . 6H₂O and Ca₆Al₂ (OH)₁₂(SO₄)₃ . 26H₂O (ettringite) were also observed for the sorbents containing CaSO₃ and/or CaSO₄. These newly formed compounds dissociated into CaSO₃ . 0.5 H₂O and inert precursors upon sulfation, and were responsible for the high SO₂ capture capacities and Ca(OH)₂ utilizations of the sorbents prepared with fly ash.     

Effect of early hydration temperature on hydration product and strength development of magnesium phosphate cement (MPC)

This paper investigates the effect of early hydration temperatures on hydration products and strength development of magnesium phosphate cement (MPC). MPC paste specimens with borate contents of 3%, 6%, 9% and 12% are prepared and cured in different air temperatures and in the adiabatic condition. The internal hydration temperatures are measured by pre-embedded temperature probes. MPC samples with different hydration temperatures are also obtained by using thin slice samples. The hydration products in MPC samples with different hydration temperatures are analyzed by X-ray diffractometer (XRD) and scanning electron microscope (SEM) and the strength development is also measured. The results show that NH₄MgPO₄·6H₂O is the major hydration product and beneficial to strength development of MPC at hydration temperature below 70 °C. NH₄MgPO₄·H₂O is another major product, which significantly decreases the strength, when the temperature is higher than a critical temperature between 70 °C and 75 °C. NH₄MgPO₄·H₂O can directly form in the MPC paste, and comes from the decomposition of NH₄MgPO₄·6H₂O when the temperature is above 75 °C. With temperature elevation and duration extension, NH₄MgPO₄·6H₂O decomposes rapidly, and even entirely when the temperature is above 100 °C. The borate content has no effect on the types of major hydration products and the critical temperature.