Kinetics of hydration of tricalcium aluminate in the presence of gypsum

Pommersheim, James M.; Chang, Jemei

doi:10.1016/0008-8846(88)90027-0

Cited by 42 publications

(16 citation statements)

References 17 publications

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“…Brown and LaCroix [26] determined that the nucleation in ettringite formation was diffusion controlled. It has also been suggested that the C 3 A surface may serve as a vehicle for ettringite nucleation [27]. Silva and Monteiro [16] also observed the ettringite growth on or near the C 3 A surface.…”

Section: C) Initial Solution/aluminate Ratio = 50 Ml/gmentioning

confidence: 97%

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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Section: C) Initial Solution/aluminate Ratio = 50 Ml/gmentioning

confidence: 97%

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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“…Similar kinetics also have been observed during C 3 A hydration in the presence of sulfate, where the presence of such a layer has been confirmed. [5][6][7][8] Thus, the induction periods that are shown in Fig. 7 decrease as the temperature increases, because of the greater extent to which the hydration products become more crystalline, rather than amorphous.…”

Section: July 1999mentioning

confidence: 99%

“…To better understand the mechanism by which the presence of sulfate inhibits 3CaO⅐Al 2 O 3 hydration, numerous studies have been conducted on the CaO-Al 2 O 3 -CaSO 4 -H 2 O quaternary system at 25°C. [5][6][7][8] Based on these studies, a variety of retardation mechanisms have been suggested. Despite their differences, the general consensus is that attenuation of 3CaO⅐Al 2 O 3 hydration is accompanied by the formation of ettringite (6CaO⅐Al 2 O 3 ⅐SO 3 ⅐32H 2 O), which crystallizes as fine needles on and around the 3CaO⅐Al 2 O 3 grains.…”

mentioning

confidence: 99%

Kinetics of Tricalcium Aluminate Hydration in the Presence of Boric Acid and Calcium Hydroxide

Bothe

Brown

1999

Journal of the American Ceramic Society

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Isothermal calorimetry has been used to study the hydration behavior of tricalcium aluminate (3CaO⅐Al 2 O 3 ) in the presence of calcium hydroxide (Ca(OH) 2 ) and boric acid (H 3 BO 3 ). Hydration has been initiated with water and boric acid solutions of 0.18M-0.89M and at constant temperatures of 25°-55°C. The resulting hydration products have been characterized via X-ray diffractometry. Hydration of a 1:1 molar mixture of 3CaO⅐Al 2 O 3 and Ca(OH) 2 in water forms 3CaO⅐Al 2 O 3 ⅐6H 2 O and produces ∼241 kJ/mol of heat. In boric acid solutions with concentrations of >0.27M, well-crystallized 4CaO⅐Al 2 O 3 ⅐ 1 ⁄2B 2 O 3 ⅐12H 2 O forms. The amount of heat that is generated increases as the H 3 BO 3 concentration increases. At H 3 BO 3 concentrations of >0.70M, the total amount of heat that is generated remains constant at ∼330 kJ/mol. The rate curves that are associated with hydration in boric acid solutions of >0.27M are characterized by two reaction peaks, which are separated by an induction period. The first peak indicates initial and rapid hydration, which occurs during the first hour. The second thermal event reflects the remainder of the 3CaO⅐ Al 2 O 3 that is being consumed. The length of the induction period increases as the H 3 BO 3 concentration increases and decreases as the temperature increases. Such behavior is indicative of diffusion-controlled processes. An amorphous calcium borate layer is believed to precipitate around the active 3CaO⅐Al 2 O 3 particles, which retards hydration. Higher temperatures and/or solutions of lower H 3 BO 3 content favor the formation of highly crystalline reaction products. These conditions are associated with a short induction period. The rapid precipitation of 4CaO⅐Al 2 O 3 ⅐ 1 ⁄2B 2 O 3 ⅐ 12H 2 O under such conditions may cause "flash set."

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“…Concentrations of intruding chloride ions in concrete also depend on the affinity of the chloride for cement paste. A quantitative measure of this effect is provided by the Thiele modulus m as defined by equation (29) . .…”

Section: Corrosion Of Reinforcing Steel Embedded In Concretementioning

confidence: 99%

Models of transport processes in concrete

Pommersheim¹

1990

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An approach being considered by the U.S. Nuclear Regulatory Commission for disposal of low-level radioactive waste is to place the waste forms in concrete vaults buried underground. The vaults would need a service life of 500 years. Approaches for predicting the service life of concrete of such vaults include the use of mathematical models. Mathematical models are presented in this report for the major degradation processes anticipated for the concrete vaults, which are corrosion of steel reinforcement, sulfate attack, acid attack, and leaching. The models mathematically represent rate controlling processes including diffusion, convection, and reaction and sorption of chemical species. These models can form the basis for predicting the life of concrete under in-service conditions.

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Kinetics of hydration of tricalcium aluminate in the presence of gypsum

Cited by 42 publications

References 17 publications

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

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

Kinetics of Tricalcium Aluminate Hydration in the Presence of Boric Acid and Calcium Hydroxide

Models of transport processes in concrete

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Kinetics of hydration of tricalcium aluminate in the presence of gypsum

Cited by 42 publications

References 17 publications

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

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

Kinetics of Tricalcium Aluminate Hydration in the Presence of Boric Acid and Calcium Hydroxide

Models of transport processes in concrete

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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

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