Dépouillements

Hydration kinetics modeling of Portland cement considering the effects of curing temperature and applied pressure / Lin, Feng in Cement and concrete research, Vol. 39 N° 4 (Avril 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 255–265 Titre : Hydration kinetics modeling of Portland cement considering the effects of curing temperature and applied pressure Type de document : texte imprimé Auteurs : Lin, Feng, Auteur ; Christian Meyer, Auteur Année de publication : 2009 Article en page(s) : pp. 255–265 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Hydration;  Kinetics;  Portland  cement;  Modeling;Thermodynamics Résumé : A hydration kinetics model for Portland cement is formulated based on thermodynamics of multiphase porous media. The mechanism of cement hydration is discussed based on literature review. The model is then developed considering the effects of chemical composition and fineness of cement, water–cement ratio, curing temperature and applied pressure. The ultimate degree of hydration of Portland cement is also analyzed and a corresponding formula is established. The model is calibrated against the experimental data for eight different Portland cements. Simple relations between the model parameters and cement composition are obtained and used to predict hydration kinetics. The model is used to reproduce experimental results on hydration kinetics, adiabatic temperature rise, and chemical shrinkage of different cement pastes. The comparisons between the model reproductions and the different experimental results demonstrate the applicability of the proposed model, especially for cement hydration at elevated temperature and high pressure. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000258 [article] Hydration kinetics modeling of Portland cement considering the effects of curing temperature and applied pressure [texte imprimé] / Lin, Feng, Auteur ; Christian Meyer, Auteur . - 2009 . - pp. 255–265. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 255–265 Mots-clés : Hydration;  Kinetics;  Portland  cement;  Modeling;Thermodynamics Résumé : A hydration kinetics model for Portland cement is formulated based on thermodynamics of multiphase porous media. The mechanism of cement hydration is discussed based on literature review. The model is then developed considering the effects of chemical composition and fineness of cement, water–cement ratio, curing temperature and applied pressure. The ultimate degree of hydration of Portland cement is also analyzed and a corresponding formula is established. The model is calibrated against the experimental data for eight different Portland cements. Simple relations between the model parameters and cement composition are obtained and used to predict hydration kinetics. The model is used to reproduce experimental results on hydration kinetics, adiabatic temperature rise, and chemical shrinkage of different cement pastes. The comparisons between the model reproductions and the different experimental results demonstrate the applicability of the proposed model, especially for cement hydration at elevated temperature and high pressure. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000258

µic: A new platform for modelling the hydration of cements / Shashank Bishnoi in Cement and concrete research, Vol. 39 N° 4 (Avril 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 266–274 Titre : µic: A new platform for modelling the hydration of cements Type de document : texte imprimé Auteurs : Shashank Bishnoi, Auteur ; Scrivener, Karen, Auteur Année de publication : 2009 Article en page(s) : pp. 266–274 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Microstructure;  Modelling;  Platform;  Cement;  Hydration Résumé : A new modelling platform, called µic has been developed to model the microstructural evolution of hydrating cement paste. The platform uses the vector approach and can be used for modelling particulate reactions including the hydration of many different cementitious systems involving millions of particles. In this paper, the ideas behind the development of µic and its main features are presented. The complexity of cement hydration and the gaps in our current understanding of cement played an important role in its design, so the platform has the primary objective of aiding, rather than replacing experiments. The platform is highly customisable as users can define materials, particles and reactions and choose or create external plugins to define models of microstructural development. The platform can be used to test the validity of hypotheses by easily formulating them as input and comparing simulations with experimental results. This paper presents the design of µic and examples that demonstrate the important features of its performance and design. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608002214 [article] µic: A new platform for modelling the hydration of cements [texte imprimé] / Shashank Bishnoi, Auteur ; Scrivener, Karen, Auteur . - 2009 . - pp. 266–274. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 266–274 Mots-clés : Microstructure;  Modelling;  Platform;  Cement;  Hydration Résumé : A new modelling platform, called µic has been developed to model the microstructural evolution of hydrating cement paste. The platform uses the vector approach and can be used for modelling particulate reactions including the hydration of many different cementitious systems involving millions of particles. In this paper, the ideas behind the development of µic and its main features are presented. The complexity of cement hydration and the gaps in our current understanding of cement played an important role in its design, so the platform has the primary objective of aiding, rather than replacing experiments. The platform is highly customisable as users can define materials, particles and reactions and choose or create external plugins to define models of microstructural development. The platform can be used to test the validity of hypotheses by easily formulating them as input and comparing simulations with experimental results. This paper presents the design of µic and examples that demonstrate the important features of its performance and design. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608002214

Influence of citric acid on the hydration of Portland cement / Göril Möschner in Cement and concrete research, Vol. 39 N° 4 (Avril 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) Titre : Influence of citric acid on the hydration of Portland cement Type de document : texte imprimé Auteurs : Göril Möschner, Auteur ; Barbara Lothenbach, Auteur ; Renato Figi, Auteur Année de publication : 2009 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Retardation;  Hydration  products;  Thermodynamic  calculations;  Admixture;  Modeling Résumé : Citric acid can be used to retard the hydration of cement. Experiments were carried out to investigate the influence of citric acid on the composition of solid and liquid phases during cement hydration. Analyses of the solid phases showed that dissolution of alite and aluminate slowed down while analyses of the pore solution showed that citric acid was removed almost completely from the pore solution within the first hours of hydration. The complexation of the ions by citrate was weak, which could also be confirmed by thermodynamic calculations. Only 2% of the dissolved Ca and 0.001% of the dissolved K formed complexes with citrate during the first hours. Thus, citric acid retards cement hydration not by complex formation, but by slowing down the dissolution of the clinker grains. Thermodynamic calculations did not indicate precipitation of a crystalline citrate species. Thus, it is suggested that citrate sorbed onto the clinker surface and formed a protective layer around the clinker grains retarding their dissolution. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000179 [article] Influence of citric acid on the hydration of Portland cement [texte imprimé] / Göril Möschner, Auteur ; Barbara Lothenbach, Auteur ; Renato Figi, Auteur . - 2009. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) Mots-clés : Retardation;  Hydration  products;  Thermodynamic  calculations;  Admixture;  Modeling Résumé : Citric acid can be used to retard the hydration of cement. Experiments were carried out to investigate the influence of citric acid on the composition of solid and liquid phases during cement hydration. Analyses of the solid phases showed that dissolution of alite and aluminate slowed down while analyses of the pore solution showed that citric acid was removed almost completely from the pore solution within the first hours of hydration. The complexation of the ions by citrate was weak, which could also be confirmed by thermodynamic calculations. Only 2% of the dissolved Ca and 0.001% of the dissolved K formed complexes with citrate during the first hours. Thus, citric acid retards cement hydration not by complex formation, but by slowing down the dissolution of the clinker grains. Thermodynamic calculations did not indicate precipitation of a crystalline citrate species. Thus, it is suggested that citrate sorbed onto the clinker surface and formed a protective layer around the clinker grains retarding their dissolution. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000179

Effect of molecular weight of sulfanilic acid-phenol-formaldehyde condensate on the properties of cementitious system / Xinping Ouyang in Cement and concrete research, Vol. 39 N° 4 (Avril 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 283–288 Titre : Effect of molecular weight of sulfanilic acid-phenol-formaldehyde condensate on the properties of cementitious system Type de document : texte imprimé Auteurs : Xinping Ouyang, Auteur ; Xinyuan Jiang, Auteur ; Xueqing Qiu, Auteur Année de publication : 2009 Article en page(s) : pp. 283–288 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Bleeding;  Dispersion;  Retardation;  Workability;  Admixture Résumé : The effect of the molecular weight of sulfanilic acid-phenol-formaldehyde condensate (SPF) on the properties of cementitious system was investigated. It is found that SPF with the molecular weight of 35,000 Dalton (Da) gives a good adsorption capacity on the surface of the cement particles, hence a larger zeta potential to cement particles and a good fluidity to the cement paste. In addition, this fraction has a high chelating capacity to calcium in the cement slurry, causing a long retardation of the cementitious system. However, the fractions of a high molecular weight (42,000 Da, and 45,000 Da) exhibit lower bleed water as a percentage of total mix water (BWP). It can be deduced that there is an ideal molecular weight for the best performances of the superplasticizer investigated, which can be used for optimizing the technical parameters in the preparation. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000064 [article] Effect of molecular weight of sulfanilic acid-phenol-formaldehyde condensate on the properties of cementitious system [texte imprimé] / Xinping Ouyang, Auteur ; Xinyuan Jiang, Auteur ; Xueqing Qiu, Auteur . - 2009 . - pp. 283–288. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 283–288 Mots-clés : Bleeding;  Dispersion;  Retardation;  Workability;  Admixture Résumé : The effect of the molecular weight of sulfanilic acid-phenol-formaldehyde condensate (SPF) on the properties of cementitious system was investigated. It is found that SPF with the molecular weight of 35,000 Dalton (Da) gives a good adsorption capacity on the surface of the cement particles, hence a larger zeta potential to cement particles and a good fluidity to the cement paste. In addition, this fraction has a high chelating capacity to calcium in the cement slurry, causing a long retardation of the cementitious system. However, the fractions of a high molecular weight (42,000 Da, and 45,000 Da) exhibit lower bleed water as a percentage of total mix water (BWP). It can be deduced that there is an ideal molecular weight for the best performances of the superplasticizer investigated, which can be used for optimizing the technical parameters in the preparation. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000064

Cohesion and expansion in polycrystalline solids formed by hydration reactions — The case of gypsum plasters / Ellis M. Gartner in Cement and concrete research, Vol. 39 N° 4 (Avril 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 289–295 Titre : Cohesion and expansion in polycrystalline solids formed by hydration reactions — The case of gypsum plasters Type de document : texte imprimé Auteurs : Ellis M. Gartner, Auteur Année de publication : 2009 Article en page(s) : pp. 289–295 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Hydration;  Microstructure;  Expansion;  Mechanical  properties Résumé : 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. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000234 [article] Cohesion and expansion in polycrystalline solids formed by hydration reactions — The case of gypsum plasters [texte imprimé] / Ellis M. Gartner, Auteur . - 2009 . - pp. 289–295. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 289–295 Mots-clés : Hydration;  Microstructure;  Expansion;  Mechanical  properties Résumé : 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. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000234

Monitoring of cracking and healing in an ultra high performance cementitious material using the time reversal technique / S. Granger in Cement and concrete research, Vol. 39 N° 4 (Avril 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) Titre : Monitoring of cracking and healing in an ultra high performance cementitious material using the time reversal technique Type de document : texte imprimé Auteurs : S. Granger, Auteur Année de publication : 2009 Langues : Anglais (eng) Mots-clés : Acoustics;  Time  reversal;  Cracking;  Healing;  Non-destructive  technique Résumé : A non-destructive testing technique based on the time reversal principle is applied to cementitious materials. Preliminary results are presented showing the reversibility of wave propagation and that focusing by time reversal is feasible in cementitious materials. Then, the technique is implemented on a mechanical test in order to monitor the cracking process of a concrete specimen loaded under three point bending. The acoustic mirror permits qualitative monitoring of the propagation of a crack by analyzing the focusing of a reference signal on a sensor placed near the expected crack path. A decrease of energy and of amplitude of the focused signal is observed upon cracking. Then, the specimen made of a material with high capabilities of self healing, is immersed in water, and healing processes are monitored. The results show a recovery of signal focusing upon healing. Comparisons with mechanical test data indicate that the method is sensitive to the variation of stiffness of the structure due to crack propagation and crack healing. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000076 [article] Monitoring of cracking and healing in an ultra high performance cementitious material using the time reversal technique [texte imprimé] / S. Granger, Auteur . - 2009. Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) Mots-clés : Acoustics;  Time  reversal;  Cracking;  Healing;  Non-destructive  technique Résumé : A non-destructive testing technique based on the time reversal principle is applied to cementitious materials. Preliminary results are presented showing the reversibility of wave propagation and that focusing by time reversal is feasible in cementitious materials. Then, the technique is implemented on a mechanical test in order to monitor the cracking process of a concrete specimen loaded under three point bending. The acoustic mirror permits qualitative monitoring of the propagation of a crack by analyzing the focusing of a reference signal on a sensor placed near the expected crack path. A decrease of energy and of amplitude of the focused signal is observed upon cracking. Then, the specimen made of a material with high capabilities of self healing, is immersed in water, and healing processes are monitored. The results show a recovery of signal focusing upon healing. Comparisons with mechanical test data indicate that the method is sensitive to the variation of stiffness of the structure due to crack propagation and crack healing. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000076

Engineered cementitious composite with characteristic of low drying shrinkage / Zhang, Jun in Cement and concrete research, Vol. 39 N° 4 (Avril 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 303–312 Titre : Engineered cementitious composite with characteristic of low drying shrinkage Type de document : texte imprimé Auteurs : Zhang, Jun, Auteur ; Chengxu Gong, Auteur ; Zili Guo, Auteur Année de publication : 2009 Article en page(s) : pp. 303–312 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Tensile  properties;  Shrinkage;  Composite;  Fiber  reinforcement Résumé : This paper reports a new class of engineered cementitious composite (ECC) with characteristics of low drying shrinkage, tight crack opening and high tensile strain capacity. Research emphasis is placed on the influence of different cementitious matrix on drying shrinkage, tensile property and early age cracking behavior of the composites. Experimental results show that drying shrinkage of the composite is greatly reduced as using the low shrinkage cementitious material in matrix, while the composite remains strain-hardening and multiple cracking characteristics. The measured drying shrinkage strain at 28 days is only 109 × 10− 6 to 242 × 10− 6 for low shrinkage ECCs. For traditional ECC, the shrinkage strain at 28 days is nearly 1200 × 10− 6. The average tensile strain capacity after 28 days curing is 2.5% of the low shrinkage ECC with tensile strength of 4–5 MPa. Further, in the strain-hardening and multiple cracking stage, cracks with much smaller width compared to the traditional ECC are formed in the low shrinkage ECC. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000398 [article] Engineered cementitious composite with characteristic of low drying shrinkage [texte imprimé] / Zhang, Jun, Auteur ; Chengxu Gong, Auteur ; Zili Guo, Auteur . - 2009 . - pp. 303–312. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 303–312 Mots-clés : Tensile  properties;  Shrinkage;  Composite;  Fiber  reinforcement Résumé : This paper reports a new class of engineered cementitious composite (ECC) with characteristics of low drying shrinkage, tight crack opening and high tensile strain capacity. Research emphasis is placed on the influence of different cementitious matrix on drying shrinkage, tensile property and early age cracking behavior of the composites. Experimental results show that drying shrinkage of the composite is greatly reduced as using the low shrinkage cementitious material in matrix, while the composite remains strain-hardening and multiple cracking characteristics. The measured drying shrinkage strain at 28 days is only 109 × 10− 6 to 242 × 10− 6 for low shrinkage ECCs. For traditional ECC, the shrinkage strain at 28 days is nearly 1200 × 10− 6. The average tensile strain capacity after 28 days curing is 2.5% of the low shrinkage ECC with tensile strength of 4–5 MPa. Further, in the strain-hardening and multiple cracking stage, cracks with much smaller width compared to the traditional ECC are formed in the low shrinkage ECC. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000398

Quantitative distribution patterns of additives in self-leveling flooring compounds (underlayments) as function of application, formulation and climatic conditions / A. De Gasparo in Cement and concrete research, Vol. 39 N° 4 (Avril 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. Titre : Quantitative distribution patterns of additives in self-leveling flooring compounds (underlayments) as function of application, formulation and climatic conditions Type de document : texte imprimé Auteurs : A. De Gasparo, Auteur ; M. Herwegh, Auteur ; R. Zurbriggen, Auteur Année de publication : 2009 Article en page(s) : pp. Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Mortar;  Additives;  Polymers;  Microstructure  gradients Résumé : The distributions of organic additives in self-leveling flooring compounds (SLCs) were investigated using laser-scanning microscopy for the selective visualization of the additives, which had been previously stained by a fluorescent dye. The distributions of latex (VC), polycarboxylate ether (PCE), cellulose ether (CE), casein (Cas) and polyvinyl alcohol (PVA, a component of redispersible powders) were analyzed in Portland (PC) and Calcium aluminate cement (CAC) dominated SLC formulations as a function of application thickness and different climatic conditions. It is shown that evaporation induced water flux through the communicating pore system causes considerable enrichments of these additives in the uppermost millimeter of the mortar layer. The resulting fractionation factors can be correlated with the different hydration kinetics of PC or CAC dominated mixed binders as well as with the drying conditions. Investigations on the additive distribution indicate that CAC dominated formulations develop more homogeneous enrichments than PC dominated systems. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S000888460800238X [article] Quantitative distribution patterns of additives in self-leveling flooring compounds (underlayments) as function of application, formulation and climatic conditions [texte imprimé] / A. De Gasparo, Auteur ; M. Herwegh, Auteur ; R. Zurbriggen, Auteur . - 2009 . - pp. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. Mots-clés : Mortar;  Additives;  Polymers;  Microstructure  gradients Résumé : The distributions of organic additives in self-leveling flooring compounds (SLCs) were investigated using laser-scanning microscopy for the selective visualization of the additives, which had been previously stained by a fluorescent dye. The distributions of latex (VC), polycarboxylate ether (PCE), cellulose ether (CE), casein (Cas) and polyvinyl alcohol (PVA, a component of redispersible powders) were analyzed in Portland (PC) and Calcium aluminate cement (CAC) dominated SLC formulations as a function of application thickness and different climatic conditions. It is shown that evaporation induced water flux through the communicating pore system causes considerable enrichments of these additives in the uppermost millimeter of the mortar layer. The resulting fractionation factors can be correlated with the different hydration kinetics of PC or CAC dominated mixed binders as well as with the drying conditions. Investigations on the additive distribution indicate that CAC dominated formulations develop more homogeneous enrichments than PC dominated systems. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S000888460800238X

Embedded NMR sensors to monitor evaporable water loss caused by hydration and drying in Portland cement mortar / P.F. de J. Cano-Barrita in Cement and concrete research, Vol. 39 N° 4 (Avril 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 324–328 Titre : Embedded NMR sensors to monitor evaporable water loss caused by hydration and drying in Portland cement mortar Type de document : texte imprimé Auteurs : P.F. de J. Cano-Barrita, Auteur Année de publication : 2009 Article en page(s) : pp. 324–328 Langues : Anglais (eng) Mots-clés : A:  Drying;  Hydration;  Pore  size  distribution;  Mortar;  Embedded  NMR  sensor Résumé : Providing adequate moisture content in cement-based materials is important during hydration of the cement paste to ensure proper development of their mechanical and durability properties. Subsequently, water is involved in the deterioration of concrete either as a pure liquid or by carrying aggressive species. This paper explores the use of small embedded NMR sensors to monitor evaporable water loss in Portland cement mortars. Results indicate that these sensors are effective in detecting loss of evaporable water due to hydration and drying. During drying, the mass loss is linearly proportional to the NMR signal loss. In addition, the amount of evaporable water detected with the sensor has a good correlation with the amount of evaporable water in a companion specimen tested in a traditional low field magnet by NMR and by gravimetric measurements. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000210 [article] Embedded NMR sensors to monitor evaporable water loss caused by hydration and drying in Portland cement mortar [texte imprimé] / P.F. de J. Cano-Barrita, Auteur . - 2009 . - pp. 324–328. Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 324–328 Mots-clés : A:  Drying;  Hydration;  Pore  size  distribution;  Mortar;  Embedded  NMR  sensor Résumé : Providing adequate moisture content in cement-based materials is important during hydration of the cement paste to ensure proper development of their mechanical and durability properties. Subsequently, water is involved in the deterioration of concrete either as a pure liquid or by carrying aggressive species. This paper explores the use of small embedded NMR sensors to monitor evaporable water loss in Portland cement mortars. Results indicate that these sensors are effective in detecting loss of evaporable water due to hydration and drying. During drying, the mass loss is linearly proportional to the NMR signal loss. In addition, the amount of evaporable water detected with the sensor has a good correlation with the amount of evaporable water in a companion specimen tested in a traditional low field magnet by NMR and by gravimetric measurements. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000210

Modeling of chloride transport coupled with enhanced moisture conductivity in concrete exposed to marine environment / Prince O'Neill Iqbal in Cement and concrete research, Vol. 39 N° 4 (Avril 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp.329–339 Titre : Modeling of chloride transport coupled with enhanced moisture conductivity in concrete exposed to marine environment Type de document : texte imprimé Auteurs : Prince O'Neill Iqbal, Auteur ; Tetsuya Ishida, Auteur Année de publication : 2009 Article en page(s) : pp.329–339 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Chloride  convection;  Diffusivity;  Marine  environment;  Sorption;Moisture  conductivity Résumé : In this research, the chloride penetration in concrete is modeled under marine environment loadings. Moisture migration model is enhanced to simulate the sorption flux under submerged wetting after long exposure to drying. The non-ideal viscosity of flow in the porous media is modified according to the nature of micro-pore structure by modeling the sensitivity of different porous networks (dense and coarse) to react towards the external environment. The strong sorption flux generated as a result of wetting and drying cyclic exposure is modeled by applying hydraulic pressure at the exposed surface. Chloride profiles are then simulated by coupling the enhanced moisture conductivity model with chloride transport model. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000027 [article] Modeling of chloride transport coupled with enhanced moisture conductivity in concrete exposed to marine environment [texte imprimé] / Prince O'Neill Iqbal, Auteur ; Tetsuya Ishida, Auteur . - 2009 . - pp.329–339. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp.329–339 Mots-clés : Chloride  convection;  Diffusivity;  Marine  environment;  Sorption;Moisture  conductivity Résumé : In this research, the chloride penetration in concrete is modeled under marine environment loadings. Moisture migration model is enhanced to simulate the sorption flux under submerged wetting after long exposure to drying. The non-ideal viscosity of flow in the porous media is modified according to the nature of micro-pore structure by modeling the sensitivity of different porous networks (dense and coarse) to react towards the external environment. The strong sorption flux generated as a result of wetting and drying cyclic exposure is modeled by applying hydraulic pressure at the exposed surface. Chloride profiles are then simulated by coupling the enhanced moisture conductivity model with chloride transport model. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000027

Electrokinetic potential of hydrated cement in relation to adsorption of chlorides / Y. Elakneswaran in Cement and concrete research, Vol. 39 N° 4 (Avril 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 340–344 Titre : Electrokinetic potential of hydrated cement in relation to adsorption of chlorides Type de document : texte imprimé Auteurs : Y. Elakneswaran, Auteur ; T. Nawa, Auteur ; K. Kurumisawa, Auteur Année de publication : 2009 Article en page(s) : pp. 340–344 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Chloride  adsorption;  Surface  charge;  Zeta  potential;  Cement;  C–S–H;  Surface  complexation Résumé : In this study, surface charge mechanism of cement hydrates and its relations to adsorption of chloride ions are investigated. Hydrated cement paste (HCP) shows net positive surface charge by dissociation and adsorption. In HCP, chlorides bind as Friedel's salt (chemical binding) as well as adsorb on the surface of hydrates (physical binding). A surface complexation model is used to predict the adsorption of chlorides on calcium silicate hydrates (C–S–H). A good agreement between experimental and predicted chloride adsorption isotherm clearly demonstrate that the chlorides adsorb on the surface of C–S–H and bringing additional negative surface charge (SiOHCl−). However, chloride ions neutralize the positively charged surfaces of portlandite and Friedel's salt by physical adsorption. From the results, it can be concluded that C–S–H is the dominant phase in terms of chloride adsorption in HCP. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000180 [article] Electrokinetic potential of hydrated cement in relation to adsorption of chlorides [texte imprimé] / Y. Elakneswaran, Auteur ; T. Nawa, Auteur ; K. Kurumisawa, Auteur . - 2009 . - pp. 340–344. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 340–344 Mots-clés : Chloride  adsorption;  Surface  charge;  Zeta  potential;  Cement;  C–S–H;  Surface  complexation Résumé : In this study, surface charge mechanism of cement hydrates and its relations to adsorption of chloride ions are investigated. Hydrated cement paste (HCP) shows net positive surface charge by dissociation and adsorption. In HCP, chlorides bind as Friedel's salt (chemical binding) as well as adsorb on the surface of hydrates (physical binding). A surface complexation model is used to predict the adsorption of chlorides on calcium silicate hydrates (C–S–H). A good agreement between experimental and predicted chloride adsorption isotherm clearly demonstrate that the chlorides adsorb on the surface of C–S–H and bringing additional negative surface charge (SiOHCl−). However, chloride ions neutralize the positively charged surfaces of portlandite and Friedel's salt by physical adsorption. From the results, it can be concluded that C–S–H is the dominant phase in terms of chloride adsorption in HCP. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000180

Correlation of hollow and solid cylinder dynamic pressurization tests for measuring permeability / Christopher A. Jones in Cement and concrete research, Vol. 39 N° 4 (Avril 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 345–352 Titre : Correlation of hollow and solid cylinder dynamic pressurization tests for measuring permeability Type de document : texte imprimé Auteurs : Christopher A. Jones, Auteur ; Zachary C. Grasley, Auteur Année de publication : 2009 Article en page(s) : pp. 345–352 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Degradation;  Durability;  Permeability;  Transport  properties;Poromechanics Résumé : An experimental apparatus and analytical derivation are developed for quantifying the permeability of cementitious materials using dynamic pressurization of a hollow cylinder. Experimental results from the newly developed hollow dynamic pressurization technique for measuring permeability are then compared to results obtained using the solid dynamic pressurization test. The measured permeabilities obtained from testing Vycor® glass and hardened cement paste indicate close agreement between the two test methods, which supports the validation of the hollow dynamic pressurization test as an accurate and repeatable method for measuring the permeability of cementitious materials. Three different pore fluids with widely varying viscosities were tested, each yielding equivalent intrinsic permeabilities. Additionally, the permeability values from this study agree reasonably well with relevant values presented in the recent literature. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000040 [article] Correlation of hollow and solid cylinder dynamic pressurization tests for measuring permeability [texte imprimé] / Christopher A. Jones, Auteur ; Zachary C. Grasley, Auteur . - 2009 . - pp. 345–352. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 345–352 Mots-clés : Degradation;  Durability;  Permeability;  Transport  properties;Poromechanics Résumé : An experimental apparatus and analytical derivation are developed for quantifying the permeability of cementitious materials using dynamic pressurization of a hollow cylinder. Experimental results from the newly developed hollow dynamic pressurization technique for measuring permeability are then compared to results obtained using the solid dynamic pressurization test. The measured permeabilities obtained from testing Vycor® glass and hardened cement paste indicate close agreement between the two test methods, which supports the validation of the hollow dynamic pressurization test as an accurate and repeatable method for measuring the permeability of cementitious materials. Three different pore fluids with widely varying viscosities were tested, each yielding equivalent intrinsic permeabilities. Additionally, the permeability values from this study agree reasonably well with relevant values presented in the recent literature. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000040

Rheology of foamed cement / R. M. Ahmed in Cement and concrete research, Vol. 39 N° 4 (Avril 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 353–361 Titre : Rheology of foamed cement Type de document : texte imprimé Auteurs : R. M. Ahmed, Auteur Année de publication : 2009 Article en page(s) : pp. 353–361 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Rheology  ;  Characterization  ;  Transport  properties  ;  Foam  cement  ;  Oil  well  cement Résumé : Foams are being used in a number of petroleum industry applications that exploit their high viscosity and low density. Foamed cement slurries can have superior displacement properties relative to non-foamed cement slurries. This article presents results of an experimental study of foamed cement rheology. Viscosity curves of foamed cements were obtained using a flow-through rotational viscometer. Foamed cements with different foam qualities were generated under different pressures using a foam generator/viscometer apparatus. The foam qualities during the tests ranged from 0% to 30%, and the shear rate varied between 5 s− 1 and 600 s− 1. Experimental results indicate that: i) unlike conventional aqueous foams, low-quality cement foams have a lower viscosity than the base fluid; ii) as the cement foam quality (gas volumetric fraction) increases from 10% to 30%, the viscosity also increases; and iii) the viscosity of low-quality cement foam slightly increases after depressurization or expansion. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608002226 [article] Rheology of foamed cement [texte imprimé] / R. M. Ahmed, Auteur . - 2009 . - pp. 353–361. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 353–361 Mots-clés : Rheology  ;  Characterization  ;  Transport  properties  ;  Foam  cement  ;  Oil  well  cement Résumé : Foams are being used in a number of petroleum industry applications that exploit their high viscosity and low density. Foamed cement slurries can have superior displacement properties relative to non-foamed cement slurries. This article presents results of an experimental study of foamed cement rheology. Viscosity curves of foamed cements were obtained using a flow-through rotational viscometer. Foamed cements with different foam qualities were generated under different pressures using a foam generator/viscometer apparatus. The foam qualities during the tests ranged from 0% to 30%, and the shear rate varied between 5 s− 1 and 600 s− 1. Experimental results indicate that: i) unlike conventional aqueous foams, low-quality cement foams have a lower viscosity than the base fluid; ii) as the cement foam quality (gas volumetric fraction) increases from 10% to 30%, the viscosity also increases; and iii) the viscosity of low-quality cement foam slightly increases after depressurization or expansion. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884608002226

Automated foam index test: Quantifying air entraining agent addition and interactions with fly ash–cement admixtures / John M. Stencel in Cement and concrete research, Vol. 39 N° 4 (Avril 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 362–370 Titre : Automated foam index test: Quantifying air entraining agent addition and interactions with fly ash–cement admixtures Type de document : texte imprimé Auteurs : John M. Stencel, Auteur ; Haiping Song, Auteur ; Federico Cangialosi, Auteur Année de publication : 2009 Article en page(s) : pp. 362–370 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Foam  index;  Surface  tension;  Fly  ash;  Cement Résumé : The use of a new automated foam index test (AFIT) instrument is discussed as a quantitative approach to observe air entraining agent (AEA) interactions with and to measure proper AEA dosage into cement–fly ash mixtures. Based on measuring acoustic emission from bubbles bursting on top of and in water–cement–ash mixtures after AEA addition, AFIT uses computer control to automate steps taken and quantities used during foam index testing, including: water addition; AEA titration; admixture agitation; and acoustic emission data acquisition. Variation of these steps is investigated relative to determining the dynamics of AEA adsorption onto the solid surfaces within water–cement–ash mixtures. Working within time durations needed for AEA equilibration, different water dilution and titration levels of AEA helped elucidate influences of equilibration on the AFIT-determined foam index values. A mathematical discussion about AFIT foam index curves is offered that relates changes in foam stability to surface tension and interactions with free calcia as AEA's are titrated into ash and cement–ash mixtures. Correlations between experimental surface tension data and the foam index curves are also presented. The potential of applying the AFIT to control air content in concrete with and without fly ash is also examined relative to using the C231 ASTM testing procedure on concrete mixes. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000192 [article] Automated foam index test: Quantifying air entraining agent addition and interactions with fly ash–cement admixtures [texte imprimé] / John M. Stencel, Auteur ; Haiping Song, Auteur ; Federico Cangialosi, Auteur . - 2009 . - pp. 362–370. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 4 (Avril 2009) . - pp. 362–370 Mots-clés : Foam  index;  Surface  tension;  Fly  ash;  Cement Résumé : The use of a new automated foam index test (AFIT) instrument is discussed as a quantitative approach to observe air entraining agent (AEA) interactions with and to measure proper AEA dosage into cement–fly ash mixtures. Based on measuring acoustic emission from bubbles bursting on top of and in water–cement–ash mixtures after AEA addition, AFIT uses computer control to automate steps taken and quantities used during foam index testing, including: water addition; AEA titration; admixture agitation; and acoustic emission data acquisition. Variation of these steps is investigated relative to determining the dynamics of AEA adsorption onto the solid surfaces within water–cement–ash mixtures. Working within time durations needed for AEA equilibration, different water dilution and titration levels of AEA helped elucidate influences of equilibration on the AFIT-determined foam index values. A mathematical discussion about AFIT foam index curves is offered that relates changes in foam stability to surface tension and interactions with free calcia as AEA's are titrated into ash and cement–ash mixtures. Correlations between experimental surface tension data and the foam index curves are also presented. The potential of applying the AFIT to control air content in concrete with and without fly ash is also examined relative to using the C231 ASTM testing procedure on concrete mixes. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000192

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