Dépouillements

Experimental study of Si–Al substitution in calcium-silicate-hydrate (C-S-H) prepared under equilibrium conditions / Xiaolin Pardal in Cement and concrete research, Vol. 39 N° 8 (Août 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 637–643 Titre : Experimental study of Si–Al substitution in calcium-silicate-hydrate (C-S-H) prepared under equilibrium conditions Type de document : texte imprimé Auteurs : Xiaolin Pardal, Auteur ; Isabelle Pochard, Auteur Année de publication : 2009 Article en page(s) : pp. 637–643 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Calcium-silicate-hydrate  (C-S-H);  Aluminium;  Thermodynamic  equilibria;  Chemistry Résumé : C-A-S-H of varying Al/Si and Ca/(Al + Si) ratios have been prepared introducing C-S-H (Ca/Si = 0.66 and 0.95) at different weight concentrations in a solution coming from the hydration of tricalcium aluminate (Ca3Al2O6) in water. XRD and EDX (TEM) analyses show that using this typical synthesise procedure, pure C-A-S-H is obtained only for calcium hydroxide concentrations below 4.5 mmol L− 1. Otherwise, calcium carboaluminate or strätlingite is also present beside C-A-S-H. The tobermorite-like structure is maintained for C-A-S-H. A kinetic study has shown that the formation of C-A-S-H is a fast reaction, typically less than a few hours. The Ca/(Al + Si) ratio of C-A-S-H matches the Ca/Si ratio of the initial C-S-H, in the ionic concentration range studied i.e., less than 4.5 and 3 mmol L− 1 of calcium hydroxide and aluminium hydroxide respectively. The Al/Si ratio increases with the aluminium concentration in the solution and reaches a maximum value of 0.19. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S000888460900091X [article] Experimental study of Si–Al substitution in calcium-silicate-hydrate (C-S-H) prepared under equilibrium conditions [texte imprimé] / Xiaolin Pardal, Auteur ; Isabelle Pochard, Auteur . - 2009 . - pp. 637–643. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 637–643 Mots-clés : Calcium-silicate-hydrate  (C-S-H);  Aluminium;  Thermodynamic  equilibria;  Chemistry Résumé : C-A-S-H of varying Al/Si and Ca/(Al + Si) ratios have been prepared introducing C-S-H (Ca/Si = 0.66 and 0.95) at different weight concentrations in a solution coming from the hydration of tricalcium aluminate (Ca3Al2O6) in water. XRD and EDX (TEM) analyses show that using this typical synthesise procedure, pure C-A-S-H is obtained only for calcium hydroxide concentrations below 4.5 mmol L− 1. Otherwise, calcium carboaluminate or strätlingite is also present beside C-A-S-H. The tobermorite-like structure is maintained for C-A-S-H. A kinetic study has shown that the formation of C-A-S-H is a fast reaction, typically less than a few hours. The Ca/(Al + Si) ratio of C-A-S-H matches the Ca/Si ratio of the initial C-S-H, in the ionic concentration range studied i.e., less than 4.5 and 3 mmol L− 1 of calcium hydroxide and aluminium hydroxide respectively. The Al/Si ratio increases with the aluminium concentration in the solution and reaches a maximum value of 0.19. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S000888460900091X

Activation of blast furnace slag by a new method / F. Bellmann in Cement and concrete research, Vol. 39 N° 8 (Août 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 644–650 Titre : Activation of blast furnace slag by a new method Type de document : texte imprimé Auteurs : F. Bellmann, Auteur ; J. Stark, Auteur Année de publication : 2009 Article en page(s) : pp. 644–650 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Acceleration;  Hydration;  Granulated  blast  furnace  slag;  Blended  cement Résumé : Blast furnace slag is used as supplementary cementing material for the production of blended cement and slag cement. Its latently hydraulic properties can be activated by several methods. Most applications employ the use of high pH values in the pore solution (> 13.0) to accelerate the corrosion of the glass network of the slag. It is shown in this work that activation is also possible by lowering the pH to a range between 11.8 and 12.2 by the addition of calcium hydroxide and soluble calcium salts. Among the salts investigated in this study are calcium chloride, calcium bromide, calcium nitrate, calcium formate, and calcium acetate. Other salts can be used alternatively as long as they are able to increase the calcium ion concentration and thus reduce the pH in the pore solution via the calcium hydroxide equilibrium. Complex formation of organic anions with calcium ions in the pore solution is a serious handicap when using organic calcium salts. This concept was tested on a particular slag improving its early compressive strength. It was possible to increase the strength of mortar bars produced from the pure slag from 3 MPa to 25 MPa after seven days by adding calcium hydroxide, calcium carbonate and calcium acetate. The early strength of slag cement containing 80% slag was increased from 6 to 16 MPa after two days by adding calcium chloride. The final strength was increased from 36 to 53 MPa after 28 days (water/cement-ratio = 0.40, 20 °C). Analytical data is included to demonstrate that application of the aforementioned concept is able to increase heat liberation and degree of slag consumption. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001276 [article] Activation of blast furnace slag by a new method [texte imprimé] / F. Bellmann, Auteur ; J. Stark, Auteur . - 2009 . - pp. 644–650. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 644–650 Mots-clés : Acceleration;  Hydration;  Granulated  blast  furnace  slag;  Blended  cement Résumé : Blast furnace slag is used as supplementary cementing material for the production of blended cement and slag cement. Its latently hydraulic properties can be activated by several methods. Most applications employ the use of high pH values in the pore solution (> 13.0) to accelerate the corrosion of the glass network of the slag. It is shown in this work that activation is also possible by lowering the pH to a range between 11.8 and 12.2 by the addition of calcium hydroxide and soluble calcium salts. Among the salts investigated in this study are calcium chloride, calcium bromide, calcium nitrate, calcium formate, and calcium acetate. Other salts can be used alternatively as long as they are able to increase the calcium ion concentration and thus reduce the pH in the pore solution via the calcium hydroxide equilibrium. Complex formation of organic anions with calcium ions in the pore solution is a serious handicap when using organic calcium salts. This concept was tested on a particular slag improving its early compressive strength. It was possible to increase the strength of mortar bars produced from the pure slag from 3 MPa to 25 MPa after seven days by adding calcium hydroxide, calcium carbonate and calcium acetate. The early strength of slag cement containing 80% slag was increased from 6 to 16 MPa after two days by adding calcium chloride. The final strength was increased from 36 to 53 MPa after 28 days (water/cement-ratio = 0.40, 20 °C). Analytical data is included to demonstrate that application of the aforementioned concept is able to increase heat liberation and degree of slag consumption. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001276

Enhancement in early strengths of slag-cement mortars by adjusting basicity of the slag prepared from fly-ash of MSWI / Tzen-Chin Lee in Cement and concrete research, Vol. 39 N° 8 (Août 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 651–658 Titre : Enhancement in early strengths of slag-cement mortars by adjusting basicity of the slag prepared from fly-ash of MSWI Type de document : texte imprimé Auteurs : Tzen-Chin Lee, Auteur ; Wei-Jer Wang, Auteur ; Ping-Yu Shih, Auteur Année de publication : 2009 Article en page(s) : pp. 651–658 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : MSWI  fly-ash;  Cement  mortar;  Pozzolanic  reaction;  Slag;  Basicity;  Early  strength Résumé : The insufficient early strengths of cement mortars in which partial cement had been replaced by pulverized slag melted from municipal solid waste incinerator (MSWI) fly-ash were tackled in this study by adjusting the basicity of the slag through the addition of various amounts of CaCO3 into MSWI fly-ash, melted into a ‘modified slag’, pulverized to partially replace cement. Increased basicity in the modified slag manifestly improves the early compressive strengths of cement mortar with 20% Portland cement replaced by the modified slag powder (20 wt.% CaCO3 added). The 14-day and 28-day compressive strengths of the mortars evidently increased to nearly that of the reference specimen made of only Portland cement mortar. The 90-day compressive strength is even higher than that of the reference specimen. Porosity and Fourier transform infrared spectra (FTIR) analyses evidenced the improvement in early strengths by hydration while the enhancement in long-term strength by pozzolanic reaction in the CaCO3 added slag-cement mortar. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000908 [article] Enhancement in early strengths of slag-cement mortars by adjusting basicity of the slag prepared from fly-ash of MSWI [texte imprimé] / Tzen-Chin Lee, Auteur ; Wei-Jer Wang, Auteur ; Ping-Yu Shih, Auteur . - 2009 . - pp. 651–658. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 651–658 Mots-clés : MSWI  fly-ash;  Cement  mortar;  Pozzolanic  reaction;  Slag;  Basicity;  Early  strength Résumé : The insufficient early strengths of cement mortars in which partial cement had been replaced by pulverized slag melted from municipal solid waste incinerator (MSWI) fly-ash were tackled in this study by adjusting the basicity of the slag through the addition of various amounts of CaCO3 into MSWI fly-ash, melted into a ‘modified slag’, pulverized to partially replace cement. Increased basicity in the modified slag manifestly improves the early compressive strengths of cement mortar with 20% Portland cement replaced by the modified slag powder (20 wt.% CaCO3 added). The 14-day and 28-day compressive strengths of the mortars evidently increased to nearly that of the reference specimen made of only Portland cement mortar. The 90-day compressive strength is even higher than that of the reference specimen. Porosity and Fourier transform infrared spectra (FTIR) analyses evidenced the improvement in early strengths by hydration while the enhancement in long-term strength by pozzolanic reaction in the CaCO3 added slag-cement mortar. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609000908

Sulfur speciation in granulated blast furnace slag: An X-ray absorption spectroscopic investigation / Amitava Roy in Cement and concrete research, Vol. 39 N° 8 (Août 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 659–663 Titre : Sulfur speciation in granulated blast furnace slag: An X-ray absorption spectroscopic investigation Type de document : texte imprimé Auteurs : Amitava Roy, Auteur Année de publication : 2009 Article en page(s) : pp. 659–663 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Glass;  Spectroscopy;  Granulated  blast  furnace  slag;  Sulfate Résumé : Sulfur speciation in a granulated blast furnace slag (GGBFS) was analyzed by X-ray absorption near edge structure spectroscopy (XANES) before and after activation by saturated calcium hydroxide and five normal sodium hydroxide solutions. The solution to GGBFS ratio was 0.4. XANES showed that sulfur in GGBFS existed mostly as sulfides (frozen in calcium polyhedra) with a minor amount as sulfate. A slowly-cooled blast furnace slag, in contrast, had most of the sulfide transformed to sulfate. After activation of GGBFS, more sulfate formed and crystalline sulfide phases became more apparent. More slag reacted at lower pH than at higher pH. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001215 [article] Sulfur speciation in granulated blast furnace slag: An X-ray absorption spectroscopic investigation [texte imprimé] / Amitava Roy, Auteur . - 2009 . - pp. 659–663. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 659–663 Mots-clés : Glass;  Spectroscopy;  Granulated  blast  furnace  slag;  Sulfate Résumé : Sulfur speciation in a granulated blast furnace slag (GGBFS) was analyzed by X-ray absorption near edge structure spectroscopy (XANES) before and after activation by saturated calcium hydroxide and five normal sodium hydroxide solutions. The solution to GGBFS ratio was 0.4. XANES showed that sulfur in GGBFS existed mostly as sulfides (frozen in calcium polyhedra) with a minor amount as sulfate. A slowly-cooled blast furnace slag, in contrast, had most of the sulfide transformed to sulfate. After activation of GGBFS, more sulfate formed and crystalline sulfide phases became more apparent. More slag reacted at lower pH than at higher pH. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001215

Current understanding of cellulose ethers impact on the hydration of C3A and C3A-sulphate systems / J. Pourchez in Cement and concrete research, Vol. 39 N° 8 (Août 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 664–669 Titre : Current understanding of cellulose ethers impact on the hydration of C3A and C3A-sulphate systems Type de document : texte imprimé Auteurs : J. Pourchez, Auteur ; P. Grosseau, Auteur ; B. Ruot, Auteur Année de publication : 2009 Article en page(s) : pp. 664–669 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Cellulose  ethers;  Hydration;  Adsorption;  C3A;  Calcium  sulphate Résumé : The impact of cellulose ethers (CE) on C3A hydration was examined to support the understanding of the retarding effect of CE on cement hydration. In this sense, we successively studied the CE adsorption on ettringite and calcium hydroaluminates, and then the CE influence during C3A hydration in presence or absence of calcium sulphate. We emphasized a phase-specific adsorption of CE depending on CE chemistry. Besides, in addition of CE, we highlighted a gradual slowing down of C3A dissolution as well as ettringite and calcium hydroaluminates precipitation. Again, a great impact of CE chemistry and CE adsorption behaviour were noticed. Thus, HECs induce always a stronger adsorption on calcium hydroaluminates and a longer C3A hydration delays than HPMCs. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001239 [article] Current understanding of cellulose ethers impact on the hydration of C3A and C3A-sulphate systems [texte imprimé] / J. Pourchez, Auteur ; P. Grosseau, Auteur ; B. Ruot, Auteur . - 2009 . - pp. 664–669. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 664–669 Mots-clés : Cellulose  ethers;  Hydration;  Adsorption;  C3A;  Calcium  sulphate Résumé : The impact of cellulose ethers (CE) on C3A hydration was examined to support the understanding of the retarding effect of CE on cement hydration. In this sense, we successively studied the CE adsorption on ettringite and calcium hydroaluminates, and then the CE influence during C3A hydration in presence or absence of calcium sulphate. We emphasized a phase-specific adsorption of CE depending on CE chemistry. Besides, in addition of CE, we highlighted a gradual slowing down of C3A dissolution as well as ettringite and calcium hydroaluminates precipitation. Again, a great impact of CE chemistry and CE adsorption behaviour were noticed. Thus, HECs induce always a stronger adsorption on calcium hydroaluminates and a longer C3A hydration delays than HPMCs. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001239

Adsorption of superplasticizer admixtures on alkali-activated slag pastes / M. Palacios in Cement and concrete research, Vol. 39 N° 8 (Août 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 670–677 Titre : Adsorption of superplasticizer admixtures on alkali-activated slag pastes Type de document : texte imprimé Auteurs : M. Palacios, Auteur ; Y.F. Houst, Auteur ; P. Bowen, Auteur Année de publication : 2009 Article en page(s) : pp. 670–677 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Alkali-activated  slag  cement;  Admixtures;  Portland  cement;  Adsorption;  Rheology Résumé : Alkali-activated slag (AAS) binders are obtained by a manufacturing process less energy-intensive than ordinary Portland cement (OPC) and involves lower greenhouse gasses emission. These alkaline cements allow the production of high mechanical strength and durable concretes. In the present work, the adsorption of different superplasticizer admixtures (naphthalene-based, melamine-based and a vinyl copolymer) on the slag particles in AAS pastes using alkaline solutions with different pH values have been studied in detail. The effect of the superplasticizers on the yield stress and plastic viscosity of the AAS and OPC pastes have been also evaluated. The results obtained allowed us to conclude that the adsorption of the superplasticizers on AAS pastes is independent of the pH of the alkaline solutions used and lower than on OPC pastes. However, the effect of the admixtures on the rheological parameters depends directly on the type and dosage of the superplasticizer as well as of the binder used and, in the case of the AAS, on the pH of the alkaline activator solution. In 11.7-pH NaOH-AAS pastes the dosages of the superplasticizers required to attain similar reduction in the yield stress are ten-fold lower than for Portland cement. In this case the superplasticizers studied show a fluidizing effect considerably higher in 11.7-pH NaOH-AAS pastes than in OPC pastes. In 13.6-pH NaOH-AAS pastes, the only admixture observed to affect the rheological parameters is the naphthalene-based admixture due to its higher chemical stability in such extremely alkaline media. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001082 [article] Adsorption of superplasticizer admixtures on alkali-activated slag pastes [texte imprimé] / M. Palacios, Auteur ; Y.F. Houst, Auteur ; P. Bowen, Auteur . - 2009 . - pp. 670–677. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 670–677 Mots-clés : Alkali-activated  slag  cement;  Admixtures;  Portland  cement;  Adsorption;  Rheology Résumé : Alkali-activated slag (AAS) binders are obtained by a manufacturing process less energy-intensive than ordinary Portland cement (OPC) and involves lower greenhouse gasses emission. These alkaline cements allow the production of high mechanical strength and durable concretes. In the present work, the adsorption of different superplasticizer admixtures (naphthalene-based, melamine-based and a vinyl copolymer) on the slag particles in AAS pastes using alkaline solutions with different pH values have been studied in detail. The effect of the superplasticizers on the yield stress and plastic viscosity of the AAS and OPC pastes have been also evaluated. The results obtained allowed us to conclude that the adsorption of the superplasticizers on AAS pastes is independent of the pH of the alkaline solutions used and lower than on OPC pastes. However, the effect of the admixtures on the rheological parameters depends directly on the type and dosage of the superplasticizer as well as of the binder used and, in the case of the AAS, on the pH of the alkaline activator solution. In 11.7-pH NaOH-AAS pastes the dosages of the superplasticizers required to attain similar reduction in the yield stress are ten-fold lower than for Portland cement. In this case the superplasticizers studied show a fluidizing effect considerably higher in 11.7-pH NaOH-AAS pastes than in OPC pastes. In 13.6-pH NaOH-AAS pastes, the only admixture observed to affect the rheological parameters is the naphthalene-based admixture due to its higher chemical stability in such extremely alkaline media. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001082

Mixing of concrete or mortars: Distributive aspects / Véronique Collin in Cement and concrete research, Vol. 39 N° 8 (Août 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 678–686 Titre : Mixing of concrete or mortars: Distributive aspects Type de document : texte imprimé Auteurs : Véronique Collin, Auteur ; Pierre-Henri Jézéquel, Auteur Année de publication : 2009 Article en page(s) : pp. 678–686 Langues : Anglais (eng) Mots-clés : Dispersion;  Fresh  concrete;  Mixing Résumé : This article describes an experimental methodology offering efficiency criteria for granular materials in terms of their mixing distributive capability. The methodology is based on analyzing the distribution kinetics of colored tracer particles which were demonstrated to respond similar to cement particles during mixing. The effect of certain critical parameters such as the mixer type, the volume and the mixer speed are investigated. The influence of mix design characteristics on distribution is also presented for several mixer types. Finally, a comparison of the dispersive versus the distributive capability is achieved for several (mixer, mix design) systems, which opens opportunities for defining rules for transfer and extrapolation. Note de contenu : Génie Civil ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001252 [article] Mixing of concrete or mortars: Distributive aspects [texte imprimé] / Véronique Collin, Auteur ; Pierre-Henri Jézéquel, Auteur . - 2009 . - pp. 678–686. Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 678–686 Mots-clés : Dispersion;  Fresh  concrete;  Mixing Résumé : This article describes an experimental methodology offering efficiency criteria for granular materials in terms of their mixing distributive capability. The methodology is based on analyzing the distribution kinetics of colored tracer particles which were demonstrated to respond similar to cement particles during mixing. The effect of certain critical parameters such as the mixer type, the volume and the mixer speed are investigated. The influence of mix design characteristics on distribution is also presented for several mixer types. Finally, a comparison of the dispersive versus the distributive capability is achieved for several (mixer, mix design) systems, which opens opportunities for defining rules for transfer and extrapolation. Note de contenu : Génie Civil ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001252

Characterization of concrete properties from dielectric properties using ground penetrating radar / W.L. Lai in Cement and concrete research, Vol. 39 N° 8 (Août 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 687–695 Titre : Characterization of concrete properties from dielectric properties using ground penetrating radar Type de document : texte imprimé Auteurs : W.L. Lai, Auteur ; S.C. Kou, Auteur ; W.F. Tsang, Auteur Année de publication : 2009 Article en page(s) : pp. 687–695 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Lightweight  and  normal  aggregate  concrete;  Ground  penetrating  radar;  real  permittivity;  Wave  energy  level;  Free  water;  Absorbed/bound  water Résumé : This paper presents the experimental results of a study of the relationships between light-weight (LWAC) and normal aggregate concrete (NAC) properties, as well as radar wave properties that are derived by using ground penetrating radar (GPR). The former (LWAC) refers to compressive strength, apparent porosity and saturated density, while the latter (NAC) refers to real part of dielectric permittivity (ε' or real permittivity) and wave energy level (E). Throughout the test period of the newly cast concrete cured for 90 days, the above mentioned material properties gradually changed which can be attributed to the effects of cement hydration, different types of aggregates and initial water to binder ratios. A number of plots describing various properties of concrete such as dielectric, strength and porosity perspectives were established. From these plots, we compare the characteristics of how much and how fast free water was turned to absorbed water in LWAC and NAC. The underlying mechanisms and a mechanistic model are then developed. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001070 [article] Characterization of concrete properties from dielectric properties using ground penetrating radar [texte imprimé] / W.L. Lai, Auteur ; S.C. Kou, Auteur ; W.F. Tsang, Auteur . - 2009 . - pp. 687–695. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 687–695 Mots-clés : Lightweight  and  normal  aggregate  concrete;  Ground  penetrating  radar;  real  permittivity;  Wave  energy  level;  Free  water;  Absorbed/bound  water Résumé : This paper presents the experimental results of a study of the relationships between light-weight (LWAC) and normal aggregate concrete (NAC) properties, as well as radar wave properties that are derived by using ground penetrating radar (GPR). The former (LWAC) refers to compressive strength, apparent porosity and saturated density, while the latter (NAC) refers to real part of dielectric permittivity (ε' or real permittivity) and wave energy level (E). Throughout the test period of the newly cast concrete cured for 90 days, the above mentioned material properties gradually changed which can be attributed to the effects of cement hydration, different types of aggregates and initial water to binder ratios. A number of plots describing various properties of concrete such as dielectric, strength and porosity perspectives were established. From these plots, we compare the characteristics of how much and how fast free water was turned to absorbed water in LWAC and NAC. The underlying mechanisms and a mechanistic model are then developed. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001070

Hilbert transformation of waveforms to determine shear wave velocity in concrete / Recep Birgül in Cement and concrete research, Vol. 39 N° 8 (Août 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 696–700 Titre : Hilbert transformation of waveforms to determine shear wave velocity in concrete Type de document : texte imprimé Auteurs : Recep Birgül, Auteur Année de publication : 2009 Article en page(s) : pp. 696–700 Langues : Anglais (eng) Mots-clés : Nondestructive  (new);  Elastic  moduli  ;  Physical  properties  ;  Concrete Résumé : Given the density value, elastic properties of a homogeneous and isotropic material can be determined provided that primary and shear wave (P- and S-wave) velocities are known. P-waves are easier to monitor and detect compared to the S-waves. In concrete, along with P-wave velocity, shear wave velocity measurement is important in determining the elastic properties. These elastic properties could be implemented in assessing the quality of in-situ concrete. After an extensive literature survey, this study focused on the applicability of Hilbert transformation of waveforms to determine shear wave velocity in concrete material. The experimental work consisted of a set of ultrasonic measurements on the surface of a reinforced concrete deck. The recorded waveforms were then analyzed to obtain the arrival times of P- and S-waves. Hilbert transformation of the waveforms proved to yield reliable and repeatable results. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001069 [article] Hilbert transformation of waveforms to determine shear wave velocity in concrete [texte imprimé] / Recep Birgül, Auteur . - 2009 . - pp. 696–700. Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 696–700 Mots-clés : Nondestructive  (new);  Elastic  moduli  ;  Physical  properties  ;  Concrete Résumé : Given the density value, elastic properties of a homogeneous and isotropic material can be determined provided that primary and shear wave (P- and S-wave) velocities are known. P-waves are easier to monitor and detect compared to the S-waves. In concrete, along with P-wave velocity, shear wave velocity measurement is important in determining the elastic properties. These elastic properties could be implemented in assessing the quality of in-situ concrete. After an extensive literature survey, this study focused on the applicability of Hilbert transformation of waveforms to determine shear wave velocity in concrete material. The experimental work consisted of a set of ultrasonic measurements on the surface of a reinforced concrete deck. The recorded waveforms were then analyzed to obtain the arrival times of P- and S-waves. Hilbert transformation of the waveforms proved to yield reliable and repeatable results. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001069

Application of nanoindentation testing to study of the interfacial transition zone in steel fiber reinforced mortar / Xiao Hui Wang in Cement and concrete research, Vol. 39 N° 8 (Août 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 701–715 Titre : Application of nanoindentation testing to study of the interfacial transition zone in steel fiber reinforced mortar Type de document : texte imprimé Auteurs : Xiao Hui Wang, Auteur ; Stefan Jacobsen, Auteur ; Jian Ying He, Auteur Année de publication : 2009 Article en page(s) : pp. 701–715 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Nanoindentation;  Scanning  Electron  Microscopy  (SEM);Interfacial  transition  zone  (ITZ);  Elastic  modulus  and  hardness;  Steel  fiber  reinforced  mortar Résumé : The characteristics of the profiles of elastic modulus and hardness of the steel fiber–matrix and fiber–matrix–aggregate interfacial zones in steel fiber reinforced mortars have been investigated by using nanoindentation and Scanning Electron Microscopy (SEM), where two sets of parameters, i.e. water/binder ratio and content of silica fume were considered. Different interfacial bond conditions in the interfacial transition zones (ITZ) are discussed. For sample without silica fume, efficient interfacial bonds across the steel fiber–matrix and fiber–matrix–aggregate interfaces are shown in low water/binder ratio mortar; while in high water/binder ratio mortar, due to the discontinuous bleeding voids underneath the fiber, the fiber–matrix bond is not very good. On the other hand, for sample with silica fume, the addition of 10% silica fume leads to no distinct presence of weak ITZ in the steel fiber–matrix interface; but the effect of the silica fume on the steel fiber–matrix–aggregate interfacial zone is not obvious due to voids in the vicinity of steel fiber. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001057 [article] Application of nanoindentation testing to study of the interfacial transition zone in steel fiber reinforced mortar [texte imprimé] / Xiao Hui Wang, Auteur ; Stefan Jacobsen, Auteur ; Jian Ying He, Auteur . - 2009 . - pp. 701–715. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 701–715 Mots-clés : Nanoindentation;  Scanning  Electron  Microscopy  (SEM);Interfacial  transition  zone  (ITZ);  Elastic  modulus  and  hardness;  Steel  fiber  reinforced  mortar Résumé : The characteristics of the profiles of elastic modulus and hardness of the steel fiber–matrix and fiber–matrix–aggregate interfacial zones in steel fiber reinforced mortars have been investigated by using nanoindentation and Scanning Electron Microscopy (SEM), where two sets of parameters, i.e. water/binder ratio and content of silica fume were considered. Different interfacial bond conditions in the interfacial transition zones (ITZ) are discussed. For sample without silica fume, efficient interfacial bonds across the steel fiber–matrix and fiber–matrix–aggregate interfaces are shown in low water/binder ratio mortar; while in high water/binder ratio mortar, due to the discontinuous bleeding voids underneath the fiber, the fiber–matrix bond is not very good. On the other hand, for sample with silica fume, the addition of 10% silica fume leads to no distinct presence of weak ITZ in the steel fiber–matrix interface; but the effect of the silica fume on the steel fiber–matrix–aggregate interfacial zone is not obvious due to voids in the vicinity of steel fiber. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001057

Alkali–silica reaction, pessimum effects and pozzolanic effect / Tsuneki Ichikawa in Cement and concrete research, Vol. 39 N° 8 (Août 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 716–726 Titre : Alkali–silica reaction, pessimum effects and pozzolanic effect Type de document : texte imprimé Auteurs : Tsuneki Ichikawa, Auteur Année de publication : 2009 Article en page(s) : pp. 716–726 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Concrete;  Aggregate;  Alkali  silica  reaction;  Pessimum  effect;  Pozzolanic  effect Résumé : The pessimum proportion and pessimum size effects for alkali–silica reaction-induced deterioration of concrete (ASR) and the pozzolanic effect of fine siliceous admixtures in concrete have been explained based on the proposed ASR model [T. Ichikawa, M. Miura, Modified model of alkali–silica reaction, Cem. Concr. Res. 37 (2007) 1291–1297.]. The attack of alkali hydroxide to aggregate particles composed of ASR-reactive minerals generates the layer of hydrated mature alkali silicate and the layer of less hydrated immature alkali silicate under the mature layer. The mature alkali silicate preferentially reacts with Ca2+ ions to convert to fragmental calcium alkali silicate, because the reaction accompanies a significant volume contraction. The immature alkali silicate gradually reacts with Ca2+ ions to cover the surface of the reactive minerals with tight layers of calcium alkali silicate called reaction rims. The reaction rims allow the penetration of alkaline solution but prevents the leakage of viscous alkali silicate generated afterward, so that the alkali silicate is accumulated inside the rims to give an expansive pressure enough for cracking the aggregate and the surrounding concrete. Due to the absorption of Ca2+ ions by mature alkali silicate, too much increase of the proportion of reactive aggregate causes the deficiency of Ca2+ ions for the formation of reaction rims, so that the ASR expansion decreases after passing the pessimum proportion. Very fine reactive aggregate and admixtures with the grain size less than ~ 50 µm preferentially react with alkali hydroxide to convert to mature alkali silicate without leaving any reactive minerals. Homogeneous mixing of the sufficient amount of very fine siliceous admixtures in concrete therefore inhibits the ASR by absorbing Ca2+ ions for the rim formation. The resultant fragmental calcium silicate fills the pores in concrete to increase the strength and the durability of the concrete. The admixtures thus act as pozzolanic materials. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001331 [article] Alkali–silica reaction, pessimum effects and pozzolanic effect [texte imprimé] / Tsuneki Ichikawa, Auteur . - 2009 . - pp. 716–726. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 716–726 Mots-clés : Concrete;  Aggregate;  Alkali  silica  reaction;  Pessimum  effect;  Pozzolanic  effect Résumé : The pessimum proportion and pessimum size effects for alkali–silica reaction-induced deterioration of concrete (ASR) and the pozzolanic effect of fine siliceous admixtures in concrete have been explained based on the proposed ASR model [T. Ichikawa, M. Miura, Modified model of alkali–silica reaction, Cem. Concr. Res. 37 (2007) 1291–1297.]. The attack of alkali hydroxide to aggregate particles composed of ASR-reactive minerals generates the layer of hydrated mature alkali silicate and the layer of less hydrated immature alkali silicate under the mature layer. The mature alkali silicate preferentially reacts with Ca2+ ions to convert to fragmental calcium alkali silicate, because the reaction accompanies a significant volume contraction. The immature alkali silicate gradually reacts with Ca2+ ions to cover the surface of the reactive minerals with tight layers of calcium alkali silicate called reaction rims. The reaction rims allow the penetration of alkaline solution but prevents the leakage of viscous alkali silicate generated afterward, so that the alkali silicate is accumulated inside the rims to give an expansive pressure enough for cracking the aggregate and the surrounding concrete. Due to the absorption of Ca2+ ions by mature alkali silicate, too much increase of the proportion of reactive aggregate causes the deficiency of Ca2+ ions for the formation of reaction rims, so that the ASR expansion decreases after passing the pessimum proportion. Very fine reactive aggregate and admixtures with the grain size less than ~ 50 µm preferentially react with alkali hydroxide to convert to mature alkali silicate without leaving any reactive minerals. Homogeneous mixing of the sufficient amount of very fine siliceous admixtures in concrete therefore inhibits the ASR by absorbing Ca2+ ions for the rim formation. The resultant fragmental calcium silicate fills the pores in concrete to increase the strength and the durability of the concrete. The admixtures thus act as pozzolanic materials. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001331

Evaluation of the short and long-term efficiencies of electro-chemical chloride extraction / G. E. Abdelaziz in Cement and concrete research, Vol. 39 N° 8 (Août 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 727–732 Titre : Evaluation of the short and long-term efficiencies of electro-chemical chloride extraction Type de document : texte imprimé Auteurs : G. E. Abdelaziz, Auteur ; A.M.K. Abdelalim, Auteur ; Y.A. Fawzy, Auteur Année de publication : 2009 Article en page(s) : pp. 727–732 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Durability;  Corrosion;  Electro-chemical Résumé : The short and long-term effects of electro-chemical chloride extraction (ECE) treatment on corrosion rate of corroded reinforcement have been studied. The factors controlling ECE treatment were identified, and the alterations which occurred in the chloride profile of the cover zone due to ECE process were followed. Contaminated reinforced OPC and SRC mortar specimens made with 1 or 2% NaCl, by mass of cement, were prepared, cured and then subjected to 3 or 5% NaCl for one year. These specimens were finally treated with ECE using various impressed current densities (1 and 2 A/m2) and electrolytes (water and calcium hydroxide) for 2, 4 and 8 weeks. The state of corrosion was monitored regularly every 2 weeks from halting ECE process up to 52 weeks using zero-resistance ammeter device for measuring the corrosion current density of reinforcement. Selected samples from the cover zone of the untreated and treated specimens were finally taken to assess their chloride profiles. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001264 [article] Evaluation of the short and long-term efficiencies of electro-chemical chloride extraction [texte imprimé] / G. E. Abdelaziz, Auteur ; A.M.K. Abdelalim, Auteur ; Y.A. Fawzy, Auteur . - 2009 . - pp. 727–732. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 8 (Août 2009) . - pp. 727–732 Mots-clés : Durability;  Corrosion;  Electro-chemical Résumé : The short and long-term effects of electro-chemical chloride extraction (ECE) treatment on corrosion rate of corroded reinforcement have been studied. The factors controlling ECE treatment were identified, and the alterations which occurred in the chloride profile of the cover zone due to ECE process were followed. Contaminated reinforced OPC and SRC mortar specimens made with 1 or 2% NaCl, by mass of cement, were prepared, cured and then subjected to 3 or 5% NaCl for one year. These specimens were finally treated with ECE using various impressed current densities (1 and 2 A/m2) and electrolytes (water and calcium hydroxide) for 2, 4 and 8 weeks. The state of corrosion was monitored regularly every 2 weeks from halting ECE process up to 52 weeks using zero-resistance ammeter device for measuring the corrosion current density of reinforcement. Selected samples from the cover zone of the untreated and treated specimens were finally taken to assess their chloride profiles. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001264

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