C 3 A polymorphs related to industrial clinker alkalies content

Gobbo, Luciano de Andrade; Sant'Agostino, Lília Mascarenhas; Garcez, L.L.

doi:10.1016/j.cemconres.2003.10.020

Cited by 62 publications

(34 citation statements)

References 9 publications

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“…On the other hand, SEM-EDS studies are carried out to quantify the chemical (elemental) composition of selected phases within OPCs (see for instance: Gobbo et al 2004;Crumbie et al 2006). Both optical and electron microscopies are good complementary techniques to RQPA of clinkers and cements (Campbell and Galehouse 1991;Stutzman and Leigh 2002;Suherman et al 2002;Stutzman 2011 and references therein).…”

Section: Optical and Scanning Electron Microscopiesmentioning

confidence: 99%

Rietveld Quantitative Phase Analysis of OPC Clinkers, Cements and Hydration Products

Aranda

Torre

León‐Reina

2012

Reviews in Mineralogy and Geochemistry

142

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Section: Optical and Scanning Electron Microscopiesmentioning

confidence: 99%

Rietveld Quantitative Phase Analysis of OPC Clinkers, Cements and Hydration Products

Aranda

Torre

León‐Reina

2012

Reviews in Mineralogy and Geochemistry

142

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“…The crystallographic informations fi les (CIF) for C 2 S polymorphs were taken from [9] and for triclinic C 3 S from [19]. Rietveld refi nement strategy was based on [20,21] and Paiva-Santos (personal communication), comprising background fi tting with the shifted Chebyschev function (10 terms), cell parameters, scale factors for individual phases, peak displacement (shift), surface roughness correction, isotropic atomic displacement parameter (Uiso), pseudo-Voigt function of peak profi le (GSAS #4) and spherical harmonic preferential orientation for all phases.…”

Section: Sixmentioning

confidence: 99%

Effect of sulfur on the polymorphism and reactivity of dicalcium silicate of Portland clinker

Andrade¹,

Gomes²,

Pecchio³

et al. 2011

Cerâmica

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The present study regards the effect of sulfur in dicalcium silicate (Ca 2 SiO 4 ), a major crystalline phase (20 to 40 wt.%) of the ordinary Portland cement clinker. Dicalcium silicate is also known as C 2 S (2CaO.SiO 2 ) or belite. The synthesis of the C 2 S samples was made with high purity reactants with addition of sulfur as CaSO 4 .2H 2 O, mixed according to the stoichiometric proportion 2Ca:(1-x)Si:xS, in which x corresponds to the cationic proportion of sulfur, with values ranging from 0 to 20%. Added amounts of SO 3 in the samples were 0.23, 1.39, 2.77, 4.60 and 9.71wt.%. Chemical composition of the samples was determined by X-ray fl uorescence before and after sintering. Large-scale sulfur loss by volatilization leads to an excess in calcium and consequently to formation of increasing amounts of tricalcium silicate with increasing sulfur content in the starting mixture. Mineralogical composition of the samples and cell parameters of C 2 S polymorphs were determined by X-ray diffraction and Rietveld refi nements. Structural analysis of diffraction data indicates that the presence of sulfur stabilizes the intermediate temperature polymorph β C 2 S, with increasing unit cell volume. The reactivity with water (heat of hydration) of the samples was measured by differential scanning calorimetry, which was strongly infl uenced by the highly reactive tricalcium silicate.

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“…In industrial clinkers, a more typical mechanism of formation of this phase is the metastable extension of the solid solution series accompanied by rapid cooling [5]. In cement, higher percentages of Na 2 O in the raw materials lead to formation of orthorhombic C 3 A [7].…”

Section: Introductionmentioning

confidence: 99%

Real-Time High-Resolution X-ray Imaging and Nuclear Magnetic Resonance Study of the Hydration of Pure and Na-Doped C₃A in the Presence of Sulfates

et al. 2011

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This study details the differences in real-time hydration between pure (cubic) and Na-doped (orthorhombic) C 3 A. First, pure phases were synthesized in the laboratory to develop an independent benchmark for the reactions, then the reactions of others phases were isolated. Because the kinetics of this reaction moves extremely quickly, most methods are not adequate to study the reactions in the early phases. Here, a high-resolution full-field soft X-ray imaging technique operating in the X-ray water window was used to capture the mechanism of the C 3 A hydration. The results show that there are differences in the hydration mechanism of each type of C 3 A, dependent on the concentration of sulfates ions in solution. The reactions with cubic C 3 A (pure) seems to be more susceptible to higher concentrations of sulfate ions by forming smaller ettringite needles at a slower pace than the orthorhombic C 3 A (Na-doped) sample.Keywords: tricalcium aluminate, hydration, hydration products, ettringite, image analysis IntroductionThe properties of clinkers are strongly affected by the quantity and composition of the clinker phases [1], which can drive the kinetic process of hydration. The hydration of C 3 A is an important stage in the overall hydration of cement because it has considerable influence on its setting and early hardening. The hydration of C 3 A is far more strongly affected by environment conditions than that of C 3 S and, in particular, by the presence of other substances with which it can react [8]. The reaction of C 3 A with water is a primary consideration. Calcium aluminate hydrates (e.g., C 3 AH 6 , C 4 AH 19, and C 2 AH 8 ) form quickly and liberate large amounts of heat [9]. If the very rapid and exothermic hydration of C 3 A is allowed to proceed unhindered in cement, then the setting occurs too quickly and the cement paste does not develop strength. Therefore, calcium sulfate is added to slow down the C 3 A hydration. In the presence of gypsum, C 3 A forms needle-like ettringite. Thus, for practical purposes, it is not the hydration reaction of C 3 A alone that is important but the hydration reaction of C 3 A in presence of gypsum (sulfates). The reactivity of C 3 A in clinker and the availability of sulfate in solution control the setting characteristics of concrete, making these compounds ideal for addressing probable setting problems.Because of the high contents of C 3 A in some cement, special attention must be paid to the mineralogy and reactivity of this phase. Industrial clinkers and their phases contain minor elements such as Na 2 O, K 2 O, SO 3, and Cl -, which may be attributed to several sources, such as raw materials, fuel and/or the lining of the kilns. Alkalis can be incorporated into a number of phases of the clinker and often Na 2 O is

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C 3 A polymorphs related to industrial clinker alkalies content

Cited by 62 publications

References 9 publications

Rietveld Quantitative Phase Analysis of OPC Clinkers, Cements and Hydration Products

Rietveld Quantitative Phase Analysis of OPC Clinkers, Cements and Hydration Products

Effect of sulfur on the polymorphism and reactivity of dicalcium silicate of Portland clinker

Real-Time High-Resolution X-ray Imaging and Nuclear Magnetic Resonance Study of the Hydration of Pure and Na-Doped C₃A in the Presence of Sulfates

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C 3 A polymorphs related to industrial clinker alkalies content

Cited by 62 publications

References 9 publications

Rietveld Quantitative Phase Analysis of OPC Clinkers, Cements and Hydration Products

Rietveld Quantitative Phase Analysis of OPC Clinkers, Cements and Hydration Products

Effect of sulfur on the polymorphism and reactivity of dicalcium silicate of Portland clinker

Real-Time High-Resolution X-ray Imaging and Nuclear Magnetic Resonance Study of the Hydration of Pure and Na-Doped C3A in the Presence of Sulfates

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Real-Time High-Resolution X-ray Imaging and Nuclear Magnetic Resonance Study of the Hydration of Pure and Na-Doped C₃A in the Presence of Sulfates