Dépouillements

Use of porous ceramic waste aggregates for internal curing of high-performance concrete / Masahiro Suzuki in Cement and concrete research, Vol. 39 N° 5 (Mai 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 373–381 Titre : Use of porous ceramic waste aggregates for internal curing of high-performance concrete Type de document : texte imprimé Auteurs : Masahiro Suzuki, Auteur ; Mohammed Seddik Meddah, Auteur ; Ryoichi Sato, Auteur Année de publication : 2009 Article en page(s) : pp. 373–381 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Autogenous  strains;  Induced  stress;  Internal  curing;  Porous  ceramic  waste  aggregates;  Silica  fume  concrete Résumé : Internal curing has become extensively used to reduce autogenous shrinkage and consequently mitigate the high risk of early age cracking of high-performance concrete (HPC). This paper investigates the efficiency of internal wet curing provided by a new type of aggregate, "recycled waste porous ceramic coarse aggregates" (PCCA). Six different silica fume HPCs with and without the PCCA are examined with respect to measured physical and mechanical property development. Four different replacement proportions of normal weight coarse aggregate (NCA) by the PCCA have been evaluated. The results have shown a high effectiveness of the PCCA for internal curing purposes, to drastically reduce and even to completely eliminate autogenous shrinkage of HPC prepared with a very low water/binder ratio (w/b) of 0.15. It has been found that the incorporation of 40% of the PCCA leads to a non-shrinking HPC that results in an insignificant internal stress accompanied by a significant increase of the compressive strength. It should be noted that for the different proportions of the PCCA incorporated no decrease of the compressive strength has been observed at either early or later ages, as is the case with some conventional lightweight aggregates. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000209 [article] Use of porous ceramic waste aggregates for internal curing of high-performance concrete [texte imprimé] / Masahiro Suzuki, Auteur ; Mohammed Seddik Meddah, Auteur ; Ryoichi Sato, Auteur . - 2009 . - pp. 373–381. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 373–381 Mots-clés : Autogenous  strains;  Induced  stress;  Internal  curing;  Porous  ceramic  waste  aggregates;  Silica  fume  concrete Résumé : Internal curing has become extensively used to reduce autogenous shrinkage and consequently mitigate the high risk of early age cracking of high-performance concrete (HPC). This paper investigates the efficiency of internal wet curing provided by a new type of aggregate, "recycled waste porous ceramic coarse aggregates" (PCCA). Six different silica fume HPCs with and without the PCCA are examined with respect to measured physical and mechanical property development. Four different replacement proportions of normal weight coarse aggregate (NCA) by the PCCA have been evaluated. The results have shown a high effectiveness of the PCCA for internal curing purposes, to drastically reduce and even to completely eliminate autogenous shrinkage of HPC prepared with a very low water/binder ratio (w/b) of 0.15. It has been found that the incorporation of 40% of the PCCA leads to a non-shrinking HPC that results in an insignificant internal stress accompanied by a significant increase of the compressive strength. It should be noted that for the different proportions of the PCCA incorporated no decrease of the compressive strength has been observed at either early or later ages, as is the case with some conventional lightweight aggregates. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000209

Autogenous healing of engineered cementitious composites under wet–dry cycles / Yingzi Yang in Cement and concrete research, Vol. 39 N° 5 (Mai 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 382–390 Titre : Autogenous healing of engineered cementitious composites under wet–dry cycles Type de document : texte imprimé Auteurs : Yingzi Yang, Auteur Année de publication : 2009 Article en page(s) : pp. 382–390 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Self-healing;  Mechanical  properties;  Transport  properties;  Tensile  properties;  Permeability;  Cracks Résumé : Self-healing of Engineered Cementitious Composites (ECC) subjected to two different cyclic wetting and drying regimes was investigated in this paper. To quantify self-healing, resonant frequency measurements were conducted throughout wetting–drying cycles followed by uniaxial tensile testing of self-healing ECC specimens. Through self-healing, crack-damaged ECC recovered 76% to 100% of its initial resonant frequency value and attained a distinct rebound in stiffness. Even for specimens deliberately pre-damaged with microcracks by loading up to 3% tensile strain, the tensile strain capacity after self-healing recovered close to 100% that of virgin specimens without any preloading. Also, the effects of temperature during wetting–drying cycles led to an increase in the ultimate strength but a slight decrease in the tensile strain capacity of rehealed pre-damaged specimens. This paper describes the experimental investigations and presents the data that confirm reasonably robust autogenous healing of ECC in commonly encountered environments for many types of infrastructure. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000222 [article] Autogenous healing of engineered cementitious composites under wet–dry cycles [texte imprimé] / Yingzi Yang, Auteur . - 2009 . - pp. 382–390. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 382–390 Mots-clés : Self-healing;  Mechanical  properties;  Transport  properties;  Tensile  properties;  Permeability;  Cracks Résumé : Self-healing of Engineered Cementitious Composites (ECC) subjected to two different cyclic wetting and drying regimes was investigated in this paper. To quantify self-healing, resonant frequency measurements were conducted throughout wetting–drying cycles followed by uniaxial tensile testing of self-healing ECC specimens. Through self-healing, crack-damaged ECC recovered 76% to 100% of its initial resonant frequency value and attained a distinct rebound in stiffness. Even for specimens deliberately pre-damaged with microcracks by loading up to 3% tensile strain, the tensile strain capacity after self-healing recovered close to 100% that of virgin specimens without any preloading. Also, the effects of temperature during wetting–drying cycles led to an increase in the ultimate strength but a slight decrease in the tensile strain capacity of rehealed pre-damaged specimens. This paper describes the experimental investigations and presents the data that confirm reasonably robust autogenous healing of ECC in commonly encountered environments for many types of infrastructure. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000222

Potential pitfalls in assessing chloride-induced corrosion of steel in concrete / A. Poursaee in Cement and concrete research, Vol. 39 N° 5 (Mai 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 391–400 Titre : Potential pitfalls in assessing chloride-induced corrosion of steel in concrete Type de document : texte imprimé Auteurs : A. Poursaee, Auteur ; C.M. Hansson, Auteur Année de publication : 2009 Article en page(s) : pp. 391–400 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Corrosion;  Electrochemical  properties;  Pore  solution;  Acceleration;  Potentiostatic  polarisation Résumé : Electrochemical assessment of the condition of embedded reinforcing bar (rebar) in concrete is being carried out increasingly routinely, both in the laboratory and in the field. However, because of the perceived need to produce results very rapidly, the results may not, in fact, be representative of the actual behaviour of the rebar. This paper describes some of the pitfalls the authors have encountered in their own work and have, therefore, analysed and quantified, together with others which have appeared in the literature. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S000888460900026X [article] Potential pitfalls in assessing chloride-induced corrosion of steel in concrete [texte imprimé] / A. Poursaee, Auteur ; C.M. Hansson, Auteur . - 2009 . - pp. 391–400. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 391–400 Mots-clés : Corrosion;  Electrochemical  properties;  Pore  solution;  Acceleration;  Potentiostatic  polarisation Résumé : Electrochemical assessment of the condition of embedded reinforcing bar (rebar) in concrete is being carried out increasingly routinely, both in the laboratory and in the field. However, because of the perceived need to produce results very rapidly, the results may not, in fact, be representative of the actual behaviour of the rebar. This paper describes some of the pitfalls the authors have encountered in their own work and have, therefore, analysed and quantified, together with others which have appeared in the literature. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S000888460900026X

Yield stress during setting of cement pastes from penetration tests / D. Lootens in Cement and concrete research, Vol. 39 N° 5 (Mai 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 401–408 Titre : Yield stress during setting of cement pastes from penetration tests Type de document : texte imprimé Auteurs : D. Lootens, Auteur ; P. Jousset, Auteur ; Laetitia Martinie, Auteur Année de publication : 2009 Article en page(s) : pp. 401–408 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Rheology;  Yield  stress;  Penetration  tests Résumé : Measurements of highly visco-elastic media such as cementitious materials during hardening and setting are difficult with standard rheometers. That is why the transition between liquid and solid state of cement based materials is currently measured with standardized penetration tools such as Vicat needles, ball indentation, penetrometers and Hilti nail guns. The obtained results however depend on the measuring device and only give information in arbitrary units. Moreover, no existing theory correlates these tests together although empirical correlations between the Vicat, the Proctor or the Hilti nail gun measurements and more classical rheology can be found in literature. In the present paper, an overview of this type of test is presented. By examining in detail experimental results, elasto-plastic finite elements simulations and visco-plastic fluid dynamic simulations in the specific case of penetrometer test, it is demonstrated that there exists a systematic correlation between these test results and the yield stress of the tested material. Finally more general analytical relations for several penetration tests between yield stress of the tested material and experimental data are proposed. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000271 [article] Yield stress during setting of cement pastes from penetration tests [texte imprimé] / D. Lootens, Auteur ; P. Jousset, Auteur ; Laetitia Martinie, Auteur . - 2009 . - pp. 401–408. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 401–408 Mots-clés : Rheology;  Yield  stress;  Penetration  tests Résumé : Measurements of highly visco-elastic media such as cementitious materials during hardening and setting are difficult with standard rheometers. That is why the transition between liquid and solid state of cement based materials is currently measured with standardized penetration tools such as Vicat needles, ball indentation, penetrometers and Hilti nail guns. The obtained results however depend on the measuring device and only give information in arbitrary units. Moreover, no existing theory correlates these tests together although empirical correlations between the Vicat, the Proctor or the Hilti nail gun measurements and more classical rheology can be found in literature. In the present paper, an overview of this type of test is presented. By examining in detail experimental results, elasto-plastic finite elements simulations and visco-plastic fluid dynamic simulations in the specific case of penetrometer test, it is demonstrated that there exists a systematic correlation between these test results and the yield stress of the tested material. Finally more general analytical relations for several penetration tests between yield stress of the tested material and experimental data are proposed. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000271

Observations of air-bubbles escaped from fresh cement paste / M. Tyler Ley in Cement and concrete research, Vol. 39 N° 5 (Mai 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 409–416 Titre : Observations of air-bubbles escaped from fresh cement paste Type de document : texte imprimé Auteurs : M. Tyler Ley, Auteur ; Kevin J. Folliard, Auteur ; Kenneth C. Hover, Auteur Année de publication : 2009 Article en page(s) : pp. 409–416 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Freezing  and  thawing  ;  Admixture  ;  Fresh  concrete  ;  Air  entrainment Résumé : Recent experimental work is presented using a new technique to observe bubbles that have escaped from cement pastes and suspended in the bleed water. These experiments suggest that the stability of an air-entrained bubble may be related to the integrity of the hydration shell. This paper also reviews literature dealing with changes to air bubbles with time in fresh air entrained cement paste and concrete and to the existence of a shell surrounding these bubbles. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000428 [article] Observations of air-bubbles escaped from fresh cement paste [texte imprimé] / M. Tyler Ley, Auteur ; Kevin J. Folliard, Auteur ; Kenneth C. Hover, Auteur . - 2009 . - pp. 409–416. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 409–416 Mots-clés : Freezing  and  thawing  ;  Admixture  ;  Fresh  concrete  ;  Air  entrainment Résumé : Recent experimental work is presented using a new technique to observe bubbles that have escaped from cement pastes and suspended in the bleed water. These experiments suggest that the stability of an air-entrained bubble may be related to the integrity of the hydration shell. This paper also reviews literature dealing with changes to air bubbles with time in fresh air entrained cement paste and concrete and to the existence of a shell surrounding these bubbles. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000428

The physical and chemical characteristics of the shell of air-entrained bubbles in cement paste / M. Tyler Ley in Cement and concrete research, Vol. 39 N° 5 (Mai 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 417–425 Titre : The physical and chemical characteristics of the shell of air-entrained bubbles in cement paste Type de document : texte imprimé Auteurs : M. Tyler Ley, Auteur ; Ryan T. Chancey, Auteur ; Maria C.G. Juenger, Auteur Année de publication : 2009 Article en page(s) : pp. 417–425 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Freezing  and  thawing  ;  Admixture  ;  Fresh  concrete  ;  Air  entrainment Résumé : Recent research has suggested that the shell of an air-entrained void is important for resisting coalescence between air-voids and diffusion of gas from the surrounding fluid. The current paper describes the physical and chemical properties of an air-void shell during the first 2 h of hydration and chemical characteristics at 60 days. Results from this research suggest that the air-void shells found in air-entrained paste have varied physical properties and the crystalline material of these shells is largely made up of fine cement particles during the first 2 h of hydration. Observations of paste at 60 days of hydration suggest that the shell is made up of calcium silicate hydrate (C–S–H) with a morphology different from that in the bulk paste. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000441 [article] The physical and chemical characteristics of the shell of air-entrained bubbles in cement paste [texte imprimé] / M. Tyler Ley, Auteur ; Ryan T. Chancey, Auteur ; Maria C.G. Juenger, Auteur . - 2009 . - pp. 417–425. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 417–425 Mots-clés : Freezing  and  thawing  ;  Admixture  ;  Fresh  concrete  ;  Air  entrainment Résumé : Recent research has suggested that the shell of an air-entrained void is important for resisting coalescence between air-voids and diffusion of gas from the surrounding fluid. The current paper describes the physical and chemical properties of an air-void shell during the first 2 h of hydration and chemical characteristics at 60 days. Results from this research suggest that the air-void shells found in air-entrained paste have varied physical properties and the crystalline material of these shells is largely made up of fine cement particles during the first 2 h of hydration. Observations of paste at 60 days of hydration suggest that the shell is made up of calcium silicate hydrate (C–S–H) with a morphology different from that in the bulk paste. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000441

Active and passive monitoring of the early hydration process in concrete using linear and nonlinear acoustics / K. Van Den Abeele in Cement and concrete research, Vol. 39 N° 5 (Mai 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 426–432 Titre : Active and passive monitoring of the early hydration process in concrete using linear and nonlinear acoustics Type de document : texte imprimé Auteurs : K. Van Den Abeele, Auteur ; W. Desadeleer, Auteur ; G. De Schutter, Auteur Année de publication : 2009 Article en page(s) : pp. 426–432 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Curing;  Hydration;  Fresh  concrete;  Elastic  moduli;  Physical  properties;  Nonlinearity Résumé : Microstructural changes occurring in freshly poured concrete during curing have been monitored on a laboratory scale using a combination of the Acoustic Emission (AE) Technique with linear and nonlinear ultrasonic/elastic wave spectroscopy. The AE technique is a passive ultrasonic signal recording technique capable of online monitoring the internal microstructural activity of young concrete during the hydration process. Ultrasonic wave spectroscopy is traditionally used to evaluate the material's longitudinal and shear wavespeed and attenuation properties (providing properties such as Young's Modulus of Elasticity, Poisson's Ratio and Quality factor) by means of an active excitation of a medium with pulsed sound waves. In addition to these traditional techniques, we have implemented a nonlinear version of ultrasonic wave spectroscopy which probes the nonlinear elastic properties of the microstructure (offering information about the micromechanical behaviour) through the analyses of the harmonic generation from a continuous wave transmission through the concrete sample. The evolution in the AE events, and in the linear and nonlinear ultrasonic behaviour of young concrete is analyzed as a function of the degree of hydration for various initial compositions during the first three days of the curing process. The results show a good correlation between the linear and nonlinear acoustic properties and the phase changes in the concrete due to chemical reactions and mechanical setting seen in the temperature profile. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000453 [article] Active and passive monitoring of the early hydration process in concrete using linear and nonlinear acoustics [texte imprimé] / K. Van Den Abeele, Auteur ; W. Desadeleer, Auteur ; G. De Schutter, Auteur . - 2009 . - pp. 426–432. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 426–432 Mots-clés : Curing;  Hydration;  Fresh  concrete;  Elastic  moduli;  Physical  properties;  Nonlinearity Résumé : Microstructural changes occurring in freshly poured concrete during curing have been monitored on a laboratory scale using a combination of the Acoustic Emission (AE) Technique with linear and nonlinear ultrasonic/elastic wave spectroscopy. The AE technique is a passive ultrasonic signal recording technique capable of online monitoring the internal microstructural activity of young concrete during the hydration process. Ultrasonic wave spectroscopy is traditionally used to evaluate the material's longitudinal and shear wavespeed and attenuation properties (providing properties such as Young's Modulus of Elasticity, Poisson's Ratio and Quality factor) by means of an active excitation of a medium with pulsed sound waves. In addition to these traditional techniques, we have implemented a nonlinear version of ultrasonic wave spectroscopy which probes the nonlinear elastic properties of the microstructure (offering information about the micromechanical behaviour) through the analyses of the harmonic generation from a continuous wave transmission through the concrete sample. The evolution in the AE events, and in the linear and nonlinear ultrasonic behaviour of young concrete is analyzed as a function of the degree of hydration for various initial compositions during the first three days of the curing process. The results show a good correlation between the linear and nonlinear acoustic properties and the phase changes in the concrete due to chemical reactions and mechanical setting seen in the temperature profile. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000453

Early hydration and setting of Portland cement monitored by IR, SEM and Vicat techniques / Rikard Ylmén in Cement and concrete research, Vol. 39 N° 5 (Mai 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 433–439 Titre : Early hydration and setting of Portland cement monitored by IR, SEM and Vicat techniques Type de document : texte imprimé Auteurs : Rikard Ylmén, Auteur ; Ulf Jäglid, Auteur ; Britt-Marie Steenari, Auteur Année de publication : 2009 Article en page(s) : pp. 433–439 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Hydration;  Calcium-silicate-hydrate  (C-S-H);Spectroscopy;  Cement  paste;  Portland  cement Résumé : Diffuse Reflectance Infrared DR-FTIR spectroscopy is employed to monitor chemical transformations in pastes of Portland limestone cement. To obtain a sufficient time resolution a freeze-dry procedure is used to instantaneously ceasing the hydration process. Rapid re-crystallization of sulphates is observed during the first 15 s, and appears to be complete after ~ 30 min. After ~ 60 min, spectroscopic signatures of polymerizing silica start to emerge. A hump at 970–1100 cm− 1 in conjunction with increasing intensity in the water bending mode region at 1500–1700 cm− 1 is indicative of the formation of Calcium Silicate Hydrate, C-S-H. Simultaneously with the development of the C-S-H signatures, a dip feature develops at 800–970 cm− 1, reflecting the dissolution of Alite, C3S. Setting times, 180 (initial) and 240 (final) minutes, are determined by the Vicat technique. Combining DR-FTIR, SEM and Vicat measurements it is concluded that the setting is caused by inter-particle coalescence of C-S-H. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000465 [article] Early hydration and setting of Portland cement monitored by IR, SEM and Vicat techniques [texte imprimé] / Rikard Ylmén, Auteur ; Ulf Jäglid, Auteur ; Britt-Marie Steenari, Auteur . - 2009 . - pp. 433–439. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 433–439 Mots-clés : Hydration;  Calcium-silicate-hydrate  (C-S-H);Spectroscopy;  Cement  paste;  Portland  cement Résumé : Diffuse Reflectance Infrared DR-FTIR spectroscopy is employed to monitor chemical transformations in pastes of Portland limestone cement. To obtain a sufficient time resolution a freeze-dry procedure is used to instantaneously ceasing the hydration process. Rapid re-crystallization of sulphates is observed during the first 15 s, and appears to be complete after ~ 30 min. After ~ 60 min, spectroscopic signatures of polymerizing silica start to emerge. A hump at 970–1100 cm− 1 in conjunction with increasing intensity in the water bending mode region at 1500–1700 cm− 1 is indicative of the formation of Calcium Silicate Hydrate, C-S-H. Simultaneously with the development of the C-S-H signatures, a dip feature develops at 800–970 cm− 1, reflecting the dissolution of Alite, C3S. Setting times, 180 (initial) and 240 (final) minutes, are determined by the Vicat technique. Combining DR-FTIR, SEM and Vicat measurements it is concluded that the setting is caused by inter-particle coalescence of C-S-H. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000465

Effect of HMEC on the consolidation of cement pastes: Isothermal calorimetry versus oscillatory rheometry / A. M. Betioli in Cement and concrete research, Vol. 39 N° 5 (Mai 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 440–445 Titre : Effect of HMEC on the consolidation of cement pastes: Isothermal calorimetry versus oscillatory rheometry Type de document : texte imprimé Auteurs : A. M. Betioli, Auteur ; P.J.P. Gleize, Auteur ; D.A. Silva, Auteur Année de publication : 2009 Article en page(s) : pp. 440–445 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Oscillatory  rheometry;  Calorimetry;  Cement  paste;  Cellulose  ether Résumé : Chemical admixtures increase the rheological complexity of cement pastes owing to their chemical and physical interactions with particles, which affects cement hydration and agglomeration kinetics. Using oscillatory rheometry and isothermal calorimetry, this article shows that the cellulose ether HMEC (hydroxymethyl ethylcellulose), widely used as a viscosity modifying agent in self-compacting concretes and dry-set mortars, displayed a steric dispersant barrier effect during the first 2 h of hydration associated to a cement retarding nature, consequently reducing the setting speed. However, despite this stabilization effect, the polymer increased the cohesion strength when comparing cement particles with the same hydration degree. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S000888460900043X [article] Effect of HMEC on the consolidation of cement pastes: Isothermal calorimetry versus oscillatory rheometry [texte imprimé] / A. M. Betioli, Auteur ; P.J.P. Gleize, Auteur ; D.A. Silva, Auteur . - 2009 . - pp. 440–445. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 440–445 Mots-clés : Oscillatory  rheometry;  Calorimetry;  Cement  paste;  Cellulose  ether Résumé : Chemical admixtures increase the rheological complexity of cement pastes owing to their chemical and physical interactions with particles, which affects cement hydration and agglomeration kinetics. Using oscillatory rheometry and isothermal calorimetry, this article shows that the cellulose ether HMEC (hydroxymethyl ethylcellulose), widely used as a viscosity modifying agent in self-compacting concretes and dry-set mortars, displayed a steric dispersant barrier effect during the first 2 h of hydration associated to a cement retarding nature, consequently reducing the setting speed. However, despite this stabilization effect, the polymer increased the cohesion strength when comparing cement particles with the same hydration degree. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S000888460900043X

Release of major elements from recycled concrete aggregates and geochemical modelling / Gerdes, Christian J. in Cement and concrete research, Vol. 39 N° 5 (Mai 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 446–459 Titre : Release of major elements from recycled concrete aggregates and geochemical modelling Type de document : texte imprimé Auteurs : Gerdes, Christian J., Auteur ; Hans A. van der Sloot, Auteur Année de publication : 2009 Article en page(s) : pp. 446–459 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : pH;  Hydrate  phases;  Leaching;  Equilibrium;  Geochemical  modelling Résumé : The pH dependent leaching characteristics were assessed for different types of recycled concrete aggregates, including real construction debris and crushed fresh concrete samples prepared in laboratory. Carbonation effects were identified from the characteristic pH dependent leaching patterns for the major constituents Al, Ca, Fe, Mg, Si and SO42–. The original particle size ranges were different for the samples investigated and this factor influenced the cement paste content in the samples which in turn controlled the leachable contents. Cement paste contents for concrete samples with fine particle size fractions (0–4 mm) were found to be higher than the originally present amount in the hardened concrete. Geochemical speciation modelling was applied over the entire pH range using the speciation and transport modelling framework ORCHESTRA, for which mineral saturation, solution speciation and sorption processes can be calculated based on equilibrium models and thermodynamic data. The simulated equilibrium concentrations by this model agreed well with the respective measured concentrations. The main differences between the fresh and aged materials were quantified, described and predicted by the ORCHESTRA. Solubility controlling mineral phase assemblages were calculated by the model as function of pH. Cement hydrate phases such as calcium silicate hydrate, calcium aluminate hydrate (AFm and AFt) and hydrogarnet were predominating at the material pH. The concentration of carboaluminates was found to be strongly dependent on the available carbonates in the samples. As the pH was decreased these phases decomposed to more soluble species or precipitates were formed including iron- and aluminium hydroxides, wairakite and amorphous silica. In the most acid region most phases dissolved, and the major elements were approaching maximum leachability, which was determined by the amount of cement paste. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000477 [article] Release of major elements from recycled concrete aggregates and geochemical modelling [texte imprimé] / Gerdes, Christian J., Auteur ; Hans A. van der Sloot, Auteur . - 2009 . - pp. 446–459. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 446–459 Mots-clés : pH;  Hydrate  phases;  Leaching;  Equilibrium;  Geochemical  modelling Résumé : The pH dependent leaching characteristics were assessed for different types of recycled concrete aggregates, including real construction debris and crushed fresh concrete samples prepared in laboratory. Carbonation effects were identified from the characteristic pH dependent leaching patterns for the major constituents Al, Ca, Fe, Mg, Si and SO42–. The original particle size ranges were different for the samples investigated and this factor influenced the cement paste content in the samples which in turn controlled the leachable contents. Cement paste contents for concrete samples with fine particle size fractions (0–4 mm) were found to be higher than the originally present amount in the hardened concrete. Geochemical speciation modelling was applied over the entire pH range using the speciation and transport modelling framework ORCHESTRA, for which mineral saturation, solution speciation and sorption processes can be calculated based on equilibrium models and thermodynamic data. The simulated equilibrium concentrations by this model agreed well with the respective measured concentrations. The main differences between the fresh and aged materials were quantified, described and predicted by the ORCHESTRA. Solubility controlling mineral phase assemblages were calculated by the model as function of pH. Cement hydrate phases such as calcium silicate hydrate, calcium aluminate hydrate (AFm and AFt) and hydrogarnet were predominating at the material pH. The concentration of carboaluminates was found to be strongly dependent on the available carbonates in the samples. As the pH was decreased these phases decomposed to more soluble species or precipitates were formed including iron- and aluminium hydroxides, wairakite and amorphous silica. In the most acid region most phases dissolved, and the major elements were approaching maximum leachability, which was determined by the amount of cement paste. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000477

Chemical, microstructural and strength development of calcium and magnesium carbonate binders ☆ / P. De Silva in Cement and concrete research, Vol. 39 N° 5 (Mai 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 460–465 Titre : Chemical, microstructural and strength development of calcium and magnesium carbonate binders ☆ Type de document : texte imprimé Auteurs : P. De Silva, Auteur ; L. Bucea, Auteur ; V. Sirivivatnanon, Auteur Année de publication : 2009 Article en page(s) : pp. 460–465 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Carbonation;  Microstructure;  Magnesium  hydroxide;  Cement;  Composite Résumé : The influence of magnesium on the chemistry of calcium carbonate formation has been studied. It was found that the type of carbonate formed by subjecting compacts of Ca(OH)2 and Mg(OH)2 to carbon dioxide (up to 20 atm CO2 pressure) for variable periods of time is largely controlled by the molar proportion of calcium to magnesium in the initial mixture. Increasing magnesium content in the initial mixture favours the formation of nesquehonite and other carbonates containing both calcium and magnesium. The compressive strength of the carbonate is improved with the presence of nesquehonite and/or other magnesium-containing phases. Curing time and CO2 exposure influence the strength differently, depending on the initial Ca/Mg ratio of the initial mixture. The formation of magnesium-containing carbonate phases is particularly favoured at higher CO2 pressures combined with prolonged exposure times. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000489 [article] Chemical, microstructural and strength development of calcium and magnesium carbonate binders ☆ [texte imprimé] / P. De Silva, Auteur ; L. Bucea, Auteur ; V. Sirivivatnanon, Auteur . - 2009 . - pp. 460–465. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 460–465 Mots-clés : Carbonation;  Microstructure;  Magnesium  hydroxide;  Cement;  Composite Résumé : The influence of magnesium on the chemistry of calcium carbonate formation has been studied. It was found that the type of carbonate formed by subjecting compacts of Ca(OH)2 and Mg(OH)2 to carbon dioxide (up to 20 atm CO2 pressure) for variable periods of time is largely controlled by the molar proportion of calcium to magnesium in the initial mixture. Increasing magnesium content in the initial mixture favours the formation of nesquehonite and other carbonates containing both calcium and magnesium. The compressive strength of the carbonate is improved with the presence of nesquehonite and/or other magnesium-containing phases. Curing time and CO2 exposure influence the strength differently, depending on the initial Ca/Mg ratio of the initial mixture. The formation of magnesium-containing carbonate phases is particularly favoured at higher CO2 pressures combined with prolonged exposure times. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000489

Probabilistic approach for durability design of reinforced concrete in marine environment / F. Deby in Cement and concrete research, Vol. 39 N° 5 (Mai 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 466–471 Titre : Probabilistic approach for durability design of reinforced concrete in marine environment Type de document : texte imprimé Auteurs : F. Deby, Auteur ; M. Carcassès, Auteur ; A. Sellier, Auteur Année de publication : 2009 Article en page(s) : pp. 466–471 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Concrete;  Corrosion;  Chloride  diffusion;  Probabilistic  approach;Reliability  index Résumé : A probabilistic approach to durability is proposed for the design of reinforced cover of a concrete immersed in sea water. It uses a non-linear chloride diffusion model for a saturated medium, which is first exposed with its physical parameters. Parameter variability is estimated and used through the probabilistic approach to assess the probability of reaching a critical chloride concentration near the reinforcement for a given service life. Based on the concrete formulation and the cement chemical composition, the model parameters are evaluated with their associated random distribution. The corrosion risk is then estimated through the Hasofer–Lind reliability index. Currently, the methodology is available for Ordinary Portland Cement (OPC) and for saturated media. A practical application is proposed to underline the applicability of the methodology. The decrease in the reliability index with time is computed for a cover depth coming from actual design rules. The probabilistic sensitivity factors are also assessed and show the importance of some model parameters called “durability indicators”. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000507 [article] Probabilistic approach for durability design of reinforced concrete in marine environment [texte imprimé] / F. Deby, Auteur ; M. Carcassès, Auteur ; A. Sellier, Auteur . - 2009 . - pp. 466–471. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 5 (Mai 2009) . - pp. 466–471 Mots-clés : Concrete;  Corrosion;  Chloride  diffusion;  Probabilistic  approach;Reliability  index Résumé : A probabilistic approach to durability is proposed for the design of reinforced cover of a concrete immersed in sea water. It uses a non-linear chloride diffusion model for a saturated medium, which is first exposed with its physical parameters. Parameter variability is estimated and used through the probabilistic approach to assess the probability of reaching a critical chloride concentration near the reinforcement for a given service life. Based on the concrete formulation and the cement chemical composition, the model parameters are evaluated with their associated random distribution. The corrosion risk is then estimated through the Hasofer–Lind reliability index. Currently, the methodology is available for Ordinary Portland Cement (OPC) and for saturated media. A practical application is proposed to underline the applicability of the methodology. The decrease in the reliability index with time is computed for a cover depth coming from actual design rules. The probabilistic sensitivity factors are also assessed and show the importance of some model parameters called “durability indicators”. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000507

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