Dépouillements

Aluminum-rich belite sulfoaluminate cements: Clinkering and early age hydration / M. Carmen Martín-Sedeño in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 359–369 Titre : Aluminum-rich belite sulfoaluminate cements: Clinkering and early age hydration Type de document : texte imprimé Auteurs : M. Carmen Martín-Sedeño, Auteur Année de publication : 2012 Article en page(s) : pp. 359–369 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : 3CaO·3Al2O3·CaSO4  ;  Clinkerization  ;  Belite  ulfoaluminate  cement  ;  Hydration  ;  Quantitative  mineralogical  phase  analysis Résumé : Belite sulfoaluminate (BSA) cements have been proposed as environmentally friendly building materials, as their production may release up to 35% less CO2 into the atmosphere when compared to ordinary Portland cements. Here, we discuss the laboratory production of three aluminum-rich BSA clinkers with nominal mineralogical compositions in the range C2S (50–60%), C4A3$ (20–30%), CA (10%) and C12A7 (10%). Using thermogravimetry, differential thermal analysis, high temperature microscopy, and X-ray powder diffraction with Rietveld quantitative phase analysis, we found that burning for 15 min at 1350 ºC was the optimal procedure, in these experimental conditions, for obtaining the highest amount of C4A3$, i.e. a value as close as possible to the nominal composition. Under these experimental conditions, three different BSA clinkers, nominally with 20, 30 and 30 wt.% of C4A3$, had 19.6, 27.1 and 27.7 wt.%, C4A3$ respectively, as determined by Rietveld analysis. We also studied the complex hydration process of BSA cements prepared by mixing BSA clinkers and gypsum. We present a methodology to establish the phase assemblage evolution of BSA cement pastes with time, including amorphous phases and free water. The methodology is based on Rietveld quantitative phase analysis of synchrotron and laboratory X-ray powder diffraction data coupled with chemical constraints. A parallel calorimetric study is also reported. It is shown that the β-C2S phase is more reactive in aluminum-rich BSA cements than in standard belite cements. On the other hand, C4A3$ reacts faster than the belite phases. The gypsum ratio in the cement is also shown to be an important factor in the phase evolution. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003342 [article] Aluminum-rich belite sulfoaluminate cements: Clinkering and early age hydration [texte imprimé] / M. Carmen Martín-Sedeño, Auteur . - 2012 . - pp. 359–369. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 359–369 Mots-clés : 3CaO·3Al2O3·CaSO4  ;  Clinkerization  ;  Belite  ulfoaluminate  cement  ;  Hydration  ;  Quantitative  mineralogical  phase  analysis Résumé : Belite sulfoaluminate (BSA) cements have been proposed as environmentally friendly building materials, as their production may release up to 35% less CO2 into the atmosphere when compared to ordinary Portland cements. Here, we discuss the laboratory production of three aluminum-rich BSA clinkers with nominal mineralogical compositions in the range C2S (50–60%), C4A3$ (20–30%), CA (10%) and C12A7 (10%). Using thermogravimetry, differential thermal analysis, high temperature microscopy, and X-ray powder diffraction with Rietveld quantitative phase analysis, we found that burning for 15 min at 1350 ºC was the optimal procedure, in these experimental conditions, for obtaining the highest amount of C4A3$, i.e. a value as close as possible to the nominal composition. Under these experimental conditions, three different BSA clinkers, nominally with 20, 30 and 30 wt.% of C4A3$, had 19.6, 27.1 and 27.7 wt.%, C4A3$ respectively, as determined by Rietveld analysis. We also studied the complex hydration process of BSA cements prepared by mixing BSA clinkers and gypsum. We present a methodology to establish the phase assemblage evolution of BSA cement pastes with time, including amorphous phases and free water. The methodology is based on Rietveld quantitative phase analysis of synchrotron and laboratory X-ray powder diffraction data coupled with chemical constraints. A parallel calorimetric study is also reported. It is shown that the β-C2S phase is more reactive in aluminum-rich BSA cements than in standard belite cements. On the other hand, C4A3$ reacts faster than the belite phases. The gypsum ratio in the cement is also shown to be an important factor in the phase evolution. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003342

A comparative structural study of wet and dried ettringite / G. Renaudin in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 370–375 Titre : A comparative structural study of wet and dried ettringite Type de document : texte imprimé Auteurs : G. Renaudin, Auteur ; Y. Filinchuk, Auteur Année de publication : 2012 Article en page(s) : pp. 370–375 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Ettringite  ;  Crystal  structure  ;  X-ray  diffraction  ;  Raman  spectroscopy  ;  Hydration Résumé : Two different techniques were used to compare structural characteristics of “wet” ettringite (stored in the synthesis mother liquid) and “dried” ettringite (dried to 35% relative humidity over saturated CaCl2 solution). Lattice parameters and the water content in the channel region of the structure (site occupancy factor of the water molecule not bonded to cations) as well as microstructure parameters (size and strain) were determined from a Rietveld refinement on synchrotron powder diffraction data. Local environment of sulphate anions and of the hydrogen bonding network was characterized by Raman spectroscopy. Both techniques led to the same conclusion: the “wet” ettringite sample immersed in the mother solution from the synthesis presents similar structural features as ettringite dried to 35% relative humidity. An increase of the a lattice parameter combined with a decrease of the c lattice parameter occurs on drying. The amount of structural water, the point symmetry of sulphate and the hydrogen bond network are unchanged when passing from the wet to the dried ettringite powder. Ettringite does not form a high-hydrate polymorph in equilibrium with alkaline solution, in contrast to the AFm phases that lose water molecules on drying. According to these results we conclude that ettringite precipitated in aqueous solution at the early hydration stages is of the same chemical composition as ettringite present in the hardening concrete. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003172 [article] A comparative structural study of wet and dried ettringite [texte imprimé] / G. Renaudin, Auteur ; Y. Filinchuk, Auteur . - 2012 . - pp. 370–375. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 370–375 Mots-clés : Ettringite  ;  Crystal  structure  ;  X-ray  diffraction  ;  Raman  spectroscopy  ;  Hydration Résumé : Two different techniques were used to compare structural characteristics of “wet” ettringite (stored in the synthesis mother liquid) and “dried” ettringite (dried to 35% relative humidity over saturated CaCl2 solution). Lattice parameters and the water content in the channel region of the structure (site occupancy factor of the water molecule not bonded to cations) as well as microstructure parameters (size and strain) were determined from a Rietveld refinement on synchrotron powder diffraction data. Local environment of sulphate anions and of the hydrogen bonding network was characterized by Raman spectroscopy. Both techniques led to the same conclusion: the “wet” ettringite sample immersed in the mother solution from the synthesis presents similar structural features as ettringite dried to 35% relative humidity. An increase of the a lattice parameter combined with a decrease of the c lattice parameter occurs on drying. The amount of structural water, the point symmetry of sulphate and the hydrogen bond network are unchanged when passing from the wet to the dried ettringite powder. Ettringite does not form a high-hydrate polymorph in equilibrium with alkaline solution, in contrast to the AFm phases that lose water molecules on drying. According to these results we conclude that ettringite precipitated in aqueous solution at the early hydration stages is of the same chemical composition as ettringite present in the hardening concrete. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003172

Influence of gypsum additive on the gyrolite formation process / K. Baltakys in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 376–383 Titre : Influence of gypsum additive on the gyrolite formation process Type de document : texte imprimé Auteurs : K. Baltakys, Auteur ; R. Siauciunas, Auteur Année de publication : 2012 Article en page(s) : pp. 376–383 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Gyrolite  ;  Calcium  sulphate  ;  Calcium–Silicate–Hydrate  ;  X-Ray  Diffraction  (B) Résumé : The influence of gypsum additive on the gyrolite formation process and a sequence of intermediary compounds formation in the CaO–SiO2·nH2O–H2O system was examined and explained. The synthesis has been carried out in unstirred suspensions. The molar ratios of primary mixtures were CaO/SiO2 = 0.66. The amount of sulphate ions to be added to a raw mixture was 1–10%. The duration of isothermal curing at 200 °C was 4, 8, 16 and 72 h. It was determined that the quantity of sulphur which penetrates into the crystalline structure of gyrolite depends not only on the synthesis conditions but also on the composition of initial mixture. A larger amount of sulphate ions stimulate the formation not only of gyrolite, but also of CaSO4. Gypsum additive has no influence on the re-crystallization temperature of C–S–H(I), Z-phase and gyrolite into wollastonite. The composition of initial mixtures is recommended to calculate according to molar ratios. In other cases, upon increasing the amount of sulphate ions, the basicity of the mixture decreases and gyrolite forms more difficult. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003354 [article] Influence of gypsum additive on the gyrolite formation process [texte imprimé] / K. Baltakys, Auteur ; R. Siauciunas, Auteur . - 2012 . - pp. 376–383. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 376–383 Mots-clés : Gyrolite  ;  Calcium  sulphate  ;  Calcium–Silicate–Hydrate  ;  X-Ray  Diffraction  (B) Résumé : The influence of gypsum additive on the gyrolite formation process and a sequence of intermediary compounds formation in the CaO–SiO2·nH2O–H2O system was examined and explained. The synthesis has been carried out in unstirred suspensions. The molar ratios of primary mixtures were CaO/SiO2 = 0.66. The amount of sulphate ions to be added to a raw mixture was 1–10%. The duration of isothermal curing at 200 °C was 4, 8, 16 and 72 h. It was determined that the quantity of sulphur which penetrates into the crystalline structure of gyrolite depends not only on the synthesis conditions but also on the composition of initial mixture. A larger amount of sulphate ions stimulate the formation not only of gyrolite, but also of CaSO4. Gypsum additive has no influence on the re-crystallization temperature of C–S–H(I), Z-phase and gyrolite into wollastonite. The composition of initial mixtures is recommended to calculate according to molar ratios. In other cases, upon increasing the amount of sulphate ions, the basicity of the mixture decreases and gyrolite forms more difficult. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003354

Influence of clays on the rheology of cement pastes / Nathan A. Tregge in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 384–391 Titre : Influence of clays on the rheology of cement pastes Type de document : texte imprimé Auteurs : Nathan A. Tregge, Auteur ; Margaret E. Pakula, Auteur Année de publication : 2012 Article en page(s) : pp. 384–391 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Clay;  Fresh  concrete;  Rheology;  Cement  paste;  Flocculation Résumé : The fresh state of concrete is becoming increasingly important in furthering the types of applications of today's construction world. Processing techniques have resulted in technologies such as self-consolidating concrete and depend on the microstructural changes that take place during and immediately after mixing and placing. These changes to the microstructure reflect the flocculation behavior between the particles in suspension. The ability to modify this behavior allows control over the balance among flowability and shape-stability of concrete. This study investigates how clay admixtures affect the microstructure of cement pastes from a rheological stand point. Shear and compressive rheology techniques are used to measure how the solids volume fraction of suspensions with different admixtures evolves with stress. Based on these relationships, the effectiveness of clays on the balance between flowability and shape-stability is measured. Results are consistent with green strength tests performed on concrete mixes derived from the cement paste mixes. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003160 [article] Influence of clays on the rheology of cement pastes [texte imprimé] / Nathan A. Tregge, Auteur ; Margaret E. Pakula, Auteur . - 2012 . - pp. 384–391. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 384–391 Mots-clés : Clay;  Fresh  concrete;  Rheology;  Cement  paste;  Flocculation Résumé : The fresh state of concrete is becoming increasingly important in furthering the types of applications of today's construction world. Processing techniques have resulted in technologies such as self-consolidating concrete and depend on the microstructural changes that take place during and immediately after mixing and placing. These changes to the microstructure reflect the flocculation behavior between the particles in suspension. The ability to modify this behavior allows control over the balance among flowability and shape-stability of concrete. This study investigates how clay admixtures affect the microstructure of cement pastes from a rheological stand point. Shear and compressive rheology techniques are used to measure how the solids volume fraction of suspensions with different admixtures evolves with stress. Based on these relationships, the effectiveness of clays on the balance between flowability and shape-stability is measured. Results are consistent with green strength tests performed on concrete mixes derived from the cement paste mixes. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003160

Effect of TEA on fly ash solubility and early age strength of mortar / D. Heinza M. Göbel in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 392–397 Titre : Effect of TEA on fly ash solubility and early age strength of mortar Type de document : texte imprimé Auteurs : D. Heinza M. Göbel, Auteur ; H. Hilbig, Auteur Année de publication : 2012 Article en page(s) : pp. 392–397 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Acceleration  ;  Glass  ;  Pore  solution  ;  Fly  ash  ;  KOH Résumé : The investigations focused on the dissolution behaviour of fly ash in alkaline solution and the effect of triethanolamine (TEA) addition. TEA is known as a grinding aid in cement production and is an Al and Fe chelating agent. To determine the effect of TEA on the dissolution behaviour of fly ash constituents, fly ash was mixed with a KOH solution at pH 13 and different dosages of TEA. Samples were taken after different times and analysed by ICP-OES. The effect of TEA on the heat evolution rates of fly ash cement pastes was investigated using isothermal calorimetry. Strength tests were also conducted to investigate the effect of TEA on plain Portland cement and fly ash/cement mortars. TEA was found to increase the dissolution rate of Al, Ca and Fe from fly ash. A slight, but reproducible, effect on heat evolution rates and an increase in early age strength was observed for fly ash cements. En ligne : http://www.sciencedirect.com/science/article/pii/S000888460900283X [article] Effect of TEA on fly ash solubility and early age strength of mortar [texte imprimé] / D. Heinza M. Göbel, Auteur ; H. Hilbig, Auteur . - 2012 . - pp. 392–397. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 392–397 Mots-clés : Acceleration  ;  Glass  ;  Pore  solution  ;  Fly  ash  ;  KOH Résumé : The investigations focused on the dissolution behaviour of fly ash in alkaline solution and the effect of triethanolamine (TEA) addition. TEA is known as a grinding aid in cement production and is an Al and Fe chelating agent. To determine the effect of TEA on the dissolution behaviour of fly ash constituents, fly ash was mixed with a KOH solution at pH 13 and different dosages of TEA. Samples were taken after different times and analysed by ICP-OES. The effect of TEA on the heat evolution rates of fly ash cement pastes was investigated using isothermal calorimetry. Strength tests were also conducted to investigate the effect of TEA on plain Portland cement and fly ash/cement mortars. TEA was found to increase the dissolution rate of Al, Ca and Fe from fly ash. A slight, but reproducible, effect on heat evolution rates and an increase in early age strength was observed for fly ash cements. En ligne : http://www.sciencedirect.com/science/article/pii/S000888460900283X

Pozzolanic activity of clinoptilolite: A comparative study with silica fume, fly ash and a non-zeolitic natural pozzolan / B. Uzal in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 398–404 Titre : Pozzolanic activity of clinoptilolite: A comparative study with silica fume, fly ash and a non-zeolitic natural pozzolan Type de document : texte imprimé Auteurs : B. Uzal, Auteur ; L. Turanlı, Auteur Année de publication : 2012 Article en page(s) : pp. 398–404 Langues : Anglais (eng) Mots-clés : Fly  ash  ;  Ca(OH)2  ;  Pozzolan  ;  Silica  fume  ;  Zeolite Résumé : Pozzolanic activity of clinoptilolite, the most common natural zeolite mineral, was studied in comparison to silica fume, fly ash and a non-zeolitic natural pozzolan. Chemical, mineralogical and physical characterizations of the materials were considered in comparative evaluations. Pozzolanic activity of the natural zeolite was evaluated with various test methods including electrical conductivity of lime–pozzolan suspensions; and free lime content, compressive strength and pore size distribution of hardened lime–pozzolan pastes. The results showed that the clinoptilolite possessed a high lime–pozzolan reactivity that was comparable to silica fume and was higher than fly ash and a non-zeolitic natural pozzolan. The high reactivity of the clinoptilolite is attributable to its specific surface area and reactive SiO2 content. Relatively poor strength contribution of clinoptilolite in spite of high pozzolanic activity can be attributable to larger pore size distribution of the hardened zeolite–lime product compared to the lime–fly ash system. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002993 [article] Pozzolanic activity of clinoptilolite: A comparative study with silica fume, fly ash and a non-zeolitic natural pozzolan [texte imprimé] / B. Uzal, Auteur ; L. Turanlı, Auteur . - 2012 . - pp. 398–404. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 398–404 Mots-clés : Fly  ash  ;  Ca(OH)2  ;  Pozzolan  ;  Silica  fume  ;  Zeolite Résumé : Pozzolanic activity of clinoptilolite, the most common natural zeolite mineral, was studied in comparison to silica fume, fly ash and a non-zeolitic natural pozzolan. Chemical, mineralogical and physical characterizations of the materials were considered in comparative evaluations. Pozzolanic activity of the natural zeolite was evaluated with various test methods including electrical conductivity of lime–pozzolan suspensions; and free lime content, compressive strength and pore size distribution of hardened lime–pozzolan pastes. The results showed that the clinoptilolite possessed a high lime–pozzolan reactivity that was comparable to silica fume and was higher than fly ash and a non-zeolitic natural pozzolan. The high reactivity of the clinoptilolite is attributable to its specific surface area and reactive SiO2 content. Relatively poor strength contribution of clinoptilolite in spite of high pozzolanic activity can be attributable to larger pore size distribution of the hardened zeolite–lime product compared to the lime–fly ash system. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002993

Modelling the rapid chloride permeability test / Peter A. Claisse in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 405–409 Titre : Modelling the rapid chloride permeability test Type de document : texte imprimé Auteurs : Peter A. Claisse, Auteur ; Hanaa I. Elsayad, Auteur ; Esmaiel Ganjiana, Auteur Année de publication : 2012 Article en page(s) : pp. 405–409 Langues : Anglais (eng) Mots-clés : Diffusion  ;  Electrical  properties  ;  Transport  properties Résumé : A computer model has been written to simulate the Rapid Chloride Permeability Test (RCPT) described in ASTM C1202. The model represents the key processes of diffusion and electromigration using standard equations but then maintains charge neutrality by modelling changes to the voltage distribution. This method enables the model to predict current–time transients similar to those recorded in experiments and it can then be used to obtain basic parameters such as diffusion coefficients for tested samples by optimising to the observed data. Experimental data showing a non-linear voltage distribution is presented together with model results which show that non-linearity has a significant effect on the current. Other predictions from the model are compared with published data and shown to give good agreement. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002877 [article] Modelling the rapid chloride permeability test [texte imprimé] / Peter A. Claisse, Auteur ; Hanaa I. Elsayad, Auteur ; Esmaiel Ganjiana, Auteur . - 2012 . - pp. 405–409. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 405–409 Mots-clés : Diffusion  ;  Electrical  properties  ;  Transport  properties Résumé : A computer model has been written to simulate the Rapid Chloride Permeability Test (RCPT) described in ASTM C1202. The model represents the key processes of diffusion and electromigration using standard equations but then maintains charge neutrality by modelling changes to the voltage distribution. This method enables the model to predict current–time transients similar to those recorded in experiments and it can then be used to obtain basic parameters such as diffusion coefficients for tested samples by optimising to the observed data. Experimental data showing a non-linear voltage distribution is presented together with model results which show that non-linearity has a significant effect on the current. Other predictions from the model are compared with published data and shown to give good agreement. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002877

Surface corrosion of steel fibre reinforced concrete / S. U. Balouch in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 410–414 Titre : Surface corrosion of steel fibre reinforced concrete Type de document : texte imprimé Auteurs : S. U. Balouch, Auteur ; J.P. Forth, Auteur Année de publication : 2012 Article en page(s) : pp. 410–414 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Fibre  reinforcement  ;  Concrete  skin;  Corrosion  ;  Durability Résumé : Corrosion of SFRC (Steel Fibre Reinforced Concrete) in an adverse environment, less harmful as compared to corrosion of steel reinforced concrete, is often considered to be of minor importance, however it exists. It can affect the fibres bridging the cracks and then decrease the strength of the concerned structures. As well, it results in the appearance of corrosion spots at exposed surfaces. Then the damaging effect is no longer expressed in terms of resistance, it is only aesthetic. It is especially undesirable in prefabricated structures. The work developed in this paper focuses on this second point: surface corrosion. Fibre reinforced concrete prisms have been subjected to cycles of salt fog (1 week) and drying (1 week). The results obtained demonstrate that with high W/C ratio (0.78), all the fibres which are embedded in concrete less than 1 mm are susceptible to give corrosion spots at the surface. When W/C is reduced to about 0.5, the minimum necessary cover to prevent surface corrosion drops to 1/10 mm or 2/10 mm and further decrease of W/C does not bring extra significant benefit. This result is in agreement with the analysis, by mercury intrusion, of the skin concrete porosity. It confirms a sharp change in the pore diameters when W/C is decreased from 0.78 to 0.48 and a quasi stability when it is varied from 0.48 to 0.36. Le travail présenté dans cet article est centré sur ce second point : la corrosion de surface. Des prismes de BFM ont été soumis à des cycles d'une semaine de brouillard salin alternant avec une semaine de séchage. Il en ressort que dans un béton de rapport E/C élevé (0,78), toutes les fibres enrobées de moins 1 mm sont susceptibles de donner naissance à des taches de rouille en surface. Lorsque E/C est réduit à environ 0,5, l'enrobage minimum nécessaire pour se prémunir de la corrosion de surface chute à 1/10 ou 2/10 mm et toute diminution supplémentaire de E/C n'apporte pas de bénéfice significatif. Ce résultat est en accord avec l'analyse porosimétrique du béton de peau. En effet, celle-ci confirme une chute importante du diamètre des pores lorsque E/C passe de 0,78 à 0,48 et une stabilités lorsqu'il est ensuite diminué jusqu'à 0,36. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002841 [article] Surface corrosion of steel fibre reinforced concrete [texte imprimé] / S. U. Balouch, Auteur ; J.P. Forth, Auteur . - 2012 . - pp. 410–414. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 410–414 Mots-clés : Fibre  reinforcement  ;  Concrete  skin;  Corrosion  ;  Durability Résumé : Corrosion of SFRC (Steel Fibre Reinforced Concrete) in an adverse environment, less harmful as compared to corrosion of steel reinforced concrete, is often considered to be of minor importance, however it exists. It can affect the fibres bridging the cracks and then decrease the strength of the concerned structures. As well, it results in the appearance of corrosion spots at exposed surfaces. Then the damaging effect is no longer expressed in terms of resistance, it is only aesthetic. It is especially undesirable in prefabricated structures. The work developed in this paper focuses on this second point: surface corrosion. Fibre reinforced concrete prisms have been subjected to cycles of salt fog (1 week) and drying (1 week). The results obtained demonstrate that with high W/C ratio (0.78), all the fibres which are embedded in concrete less than 1 mm are susceptible to give corrosion spots at the surface. When W/C is reduced to about 0.5, the minimum necessary cover to prevent surface corrosion drops to 1/10 mm or 2/10 mm and further decrease of W/C does not bring extra significant benefit. This result is in agreement with the analysis, by mercury intrusion, of the skin concrete porosity. It confirms a sharp change in the pore diameters when W/C is decreased from 0.78 to 0.48 and a quasi stability when it is varied from 0.48 to 0.36. Le travail présenté dans cet article est centré sur ce second point : la corrosion de surface. Des prismes de BFM ont été soumis à des cycles d'une semaine de brouillard salin alternant avec une semaine de séchage. Il en ressort que dans un béton de rapport E/C élevé (0,78), toutes les fibres enrobées de moins 1 mm sont susceptibles de donner naissance à des taches de rouille en surface. Lorsque E/C est réduit à environ 0,5, l'enrobage minimum nécessaire pour se prémunir de la corrosion de surface chute à 1/10 ou 2/10 mm et toute diminution supplémentaire de E/C n'apporte pas de bénéfice significatif. Ce résultat est en accord avec l'analyse porosimétrique du béton de peau. En effet, celle-ci confirme une chute importante du diamètre des pores lorsque E/C passe de 0,78 à 0,48 et une stabilités lorsqu'il est ensuite diminué jusqu'à 0,36. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002841

Concrete cover cracking with reinforcement corrosion of RC beam during chloride-induced corrosion process / Angliang Zhang in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 415–425 Titre : Concrete cover cracking with reinforcement corrosion of RC beam during chloride-induced corrosion process Type de document : texte imprimé Auteurs : Angliang Zhang, Auteur Année de publication : 2012 Article en page(s) : pp. 415–425 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Crack  detection  ;  Corrosion  ;  Reinforcement  ;  Concrete  ;  Modeling Résumé : This paper deals with the evolution of the corrosion pattern based on two beams corroded by 14 years (beam B1CL1) and 23 years (beam B2CL1) of conservation in a chloride environment. The experimental results indicate that, at the cracking initiation stage and the first stage of cracking propagation, localized corrosion due to chloride ingress is the predominant corrosion pattern and pitting corrosion is the main factor that influences the cracking process. As corrosion cracking increases, general corrosion develops rapidly and gradually becomes predominant in the second stage of cracking propagation. A comparison between existing models and experimental results illustrates that, although Vidal et al.'s model can better predict the reinforcement corrosion of beam B1CL1 under localized corrosion, it cannot predict the corrosion of beam B2CL1 under general corrosion. Also, Rodriguez's model, derived from the general corrosion due to electrically accelerated corrosion experiments, cannot match natural chloride corrosion irrespective of whether corrosion is localized or general. Thus, for natural general corrosion in the second stage of cracking propagation, a new model based on the parameter of average steel cross-section loss is put forward to predict steel corrosion from corrosion cracking. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002798 [article] Concrete cover cracking with reinforcement corrosion of RC beam during chloride-induced corrosion process [texte imprimé] / Angliang Zhang, Auteur . - 2012 . - pp. 415–425. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 415–425 Mots-clés : Crack  detection  ;  Corrosion  ;  Reinforcement  ;  Concrete  ;  Modeling Résumé : This paper deals with the evolution of the corrosion pattern based on two beams corroded by 14 years (beam B1CL1) and 23 years (beam B2CL1) of conservation in a chloride environment. The experimental results indicate that, at the cracking initiation stage and the first stage of cracking propagation, localized corrosion due to chloride ingress is the predominant corrosion pattern and pitting corrosion is the main factor that influences the cracking process. As corrosion cracking increases, general corrosion develops rapidly and gradually becomes predominant in the second stage of cracking propagation. A comparison between existing models and experimental results illustrates that, although Vidal et al.'s model can better predict the reinforcement corrosion of beam B1CL1 under localized corrosion, it cannot predict the corrosion of beam B2CL1 under general corrosion. Also, Rodriguez's model, derived from the general corrosion due to electrically accelerated corrosion experiments, cannot match natural chloride corrosion irrespective of whether corrosion is localized or general. Thus, for natural general corrosion in the second stage of cracking propagation, a new model based on the parameter of average steel cross-section loss is put forward to predict steel corrosion from corrosion cracking. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002798

Corrosion of steel bars in OPC mortar exposed to NaCl, MgCl2 and CaCl2: Macro- and micro-cell corrosion perspective / A. Poursaee in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 426–430 Titre : Corrosion of steel bars in OPC mortar exposed to NaCl, MgCl2 and CaCl2: Macro- and micro-cell corrosion perspective Type de document : texte imprimé Auteurs : A. Poursaee, Auteur ; A. Laurent, Auteur ; C.M. Hansson, Auteur Année de publication : 2012 Article en page(s) : pp. 426–430 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : X-ray  diffraction  ;  Corrosion  ;  Chloride Résumé : In North America, corrosion of the steel rebar commonly occurs due to chloride attack from deicing salts. In Canada, based on the severity and temperature of the ambient environment, three different deicing salts, or combination of them, are used: NaCl, MgCl2 and CaCl2. In this paper, the effect of each of these salts on the corrosion of steel rebar and their impact on the durability of the mortar have been investigated. The results show that CaCl2 has the most negative effect on the steel and, in high concentrations, on the integrity of the mortar. MgCl2 also deteriorates the mortar if used in high concentration, while NaCl has no apparent effect on mortar durability even in high concentration. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002828 [article] Corrosion of steel bars in OPC mortar exposed to NaCl, MgCl2 and CaCl2: Macro- and micro-cell corrosion perspective [texte imprimé] / A. Poursaee, Auteur ; A. Laurent, Auteur ; C.M. Hansson, Auteur . - 2012 . - pp. 426–430. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 426–430 Mots-clés : X-ray  diffraction  ;  Corrosion  ;  Chloride Résumé : In North America, corrosion of the steel rebar commonly occurs due to chloride attack from deicing salts. In Canada, based on the severity and temperature of the ambient environment, three different deicing salts, or combination of them, are used: NaCl, MgCl2 and CaCl2. In this paper, the effect of each of these salts on the corrosion of steel rebar and their impact on the durability of the mortar have been investigated. The results show that CaCl2 has the most negative effect on the steel and, in high concentrations, on the integrity of the mortar. MgCl2 also deteriorates the mortar if used in high concentration, while NaCl has no apparent effect on mortar durability even in high concentration. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002828

Threshold chloride concentration for stainless steels activation in concrete pore solutions / Milan Kouřil in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 431–436 Titre : Threshold chloride concentration for stainless steels activation in concrete pore solutions Type de document : texte imprimé Auteurs : Milan Kouřil, Auteur Année de publication : 2012 Article en page(s) : pp. 431–436 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Stainless  steel;  Corrosion;  Reinforcement;  Chloride Résumé : The threshold chloride concentration for stainless steels activation in concrete environments depends not only on chemical composition of the steel and on pH level of concrete pore solution but is also considerably affected by the superficial state of the steel. The presence of scales leads to significant decrease of corrosion resistance. This study evaluates the corrosion resistance of various stainless steels exposed to pore solutions of fresh concrete by means of electrochemical methods. All tested materials with bare surface, except for martensitic chromium steel FeCr12, proved to be completely resistant to fresh concrete pore solution containing chlorides. If the surface is scaled, the identically high resistance cannot be expected even for the most alloyed stainless steels. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003366 [article] Threshold chloride concentration for stainless steels activation in concrete pore solutions [texte imprimé] / Milan Kouřil, Auteur . - 2012 . - pp. 431–436. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 431–436 Mots-clés : Stainless  steel;  Corrosion;  Reinforcement;  Chloride Résumé : The threshold chloride concentration for stainless steels activation in concrete environments depends not only on chemical composition of the steel and on pH level of concrete pore solution but is also considerably affected by the superficial state of the steel. The presence of scales leads to significant decrease of corrosion resistance. This study evaluates the corrosion resistance of various stainless steels exposed to pore solutions of fresh concrete by means of electrochemical methods. All tested materials with bare surface, except for martensitic chromium steel FeCr12, proved to be completely resistant to fresh concrete pore solution containing chlorides. If the surface is scaled, the identically high resistance cannot be expected even for the most alloyed stainless steels. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003366

Effects of calcination condition on expansion property of MgO-type expansive agent used in cement-based materials / Liwu Mo in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 437–446 Titre : Effects of calcination condition on expansion property of MgO-type expansive agent used in cement-based materials Type de document : texte imprimé Auteurs : Liwu Mo, Auteur ; Min Deng, Auteur ; Mingshu Tang, Auteur Année de publication : 2012 Article en page(s) : pp. 437–446 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Hydration;  Microstructure;  Expansion;  MgO Résumé : Previous research indicated that the expansion property of MgO-type expansive agent (MEA) depended strongly on the calcining conditions, i.e. kiln temperature and residence time. However, the intrinsic effect of calcination condition on the expansion property of MEA has not been clearly demonstrated. In the present work, the effects of calcination condition on the microstructure, hydration activity, and expansion property of MEA have been investigated, and their correlations are also studied. Results indicate that the microstructure of MEA is the intrinsic factor that controlling its expansion property, which is influenced by the calcination condition. MEA produced under higher temperature and longer residence time has less interior pores, larger crystal size of MgO, and smaller specific surface area, thus resulting in lower hydration activity and slower expansion at early age, but larger “ultimate” expansion at late age. While, a new expansion model of MEA is proposed to explain these results. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002786 [article] Effects of calcination condition on expansion property of MgO-type expansive agent used in cement-based materials [texte imprimé] / Liwu Mo, Auteur ; Min Deng, Auteur ; Mingshu Tang, Auteur . - 2012 . - pp. 437–446. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 437–446 Mots-clés : Hydration;  Microstructure;  Expansion;  MgO Résumé : Previous research indicated that the expansion property of MgO-type expansive agent (MEA) depended strongly on the calcining conditions, i.e. kiln temperature and residence time. However, the intrinsic effect of calcination condition on the expansion property of MEA has not been clearly demonstrated. In the present work, the effects of calcination condition on the microstructure, hydration activity, and expansion property of MEA have been investigated, and their correlations are also studied. Results indicate that the microstructure of MEA is the intrinsic factor that controlling its expansion property, which is influenced by the calcination condition. MEA produced under higher temperature and longer residence time has less interior pores, larger crystal size of MgO, and smaller specific surface area, thus resulting in lower hydration activity and slower expansion at early age, but larger “ultimate” expansion at late age. While, a new expansion model of MEA is proposed to explain these results. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002786

Effect of maturation time on the fresh and hardened properties of an air lime mortar / H. Paiva in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 447–451 Titre : Effect of maturation time on the fresh and hardened properties of an air lime mortar Type de document : texte imprimé Auteurs : H. Paiva, Auteur ; A. Velosa, Auteur ; R. Veiga, Auteur Année de publication : 2012 Article en page(s) : pp. 447–451 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Lime  ;  Mortar  ;  Rheology  ;  Maturation Résumé : The restoration and maintenance of old renders is one of the key aspects of correct rehabilitation practice. The ideal course of action is to replace the damaged material by a material with compatible characteristics. This work aims to analyze the effect of the maturation process on hardened state characteristics of hydrated powder lime mortars. The rheological characterization shows an air lime mortar thickening behaviour with the length of the test. The different mixes were subjected to a maturation process consisting on keeping them in the fresh state, covered with water, isolated from CO2, during seven days. The specimens and applications were prepared both with the non-matured and the matured mortars. Maturation seems to influence the hardened state characteristics causing a decrease in the capillary values, and an increase on the mechanical strength, which are more evident for mortars with higher binder contents. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002580 [article] Effect of maturation time on the fresh and hardened properties of an air lime mortar [texte imprimé] / H. Paiva, Auteur ; A. Velosa, Auteur ; R. Veiga, Auteur . - 2012 . - pp. 447–451. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 447–451 Mots-clés : Lime  ;  Mortar  ;  Rheology  ;  Maturation Résumé : The restoration and maintenance of old renders is one of the key aspects of correct rehabilitation practice. The ideal course of action is to replace the damaged material by a material with compatible characteristics. This work aims to analyze the effect of the maturation process on hardened state characteristics of hydrated powder lime mortars. The rheological characterization shows an air lime mortar thickening behaviour with the length of the test. The different mixes were subjected to a maturation process consisting on keeping them in the fresh state, covered with water, isolated from CO2, during seven days. The specimens and applications were prepared both with the non-matured and the matured mortars. Maturation seems to influence the hardened state characteristics causing a decrease in the capillary values, and an increase on the mechanical strength, which are more evident for mortars with higher binder contents. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002580

The encapsulation of Mg(OH)2 sludge in composite cement / N.C. Collier in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 452–459 Titre : The encapsulation of Mg(OH)2 sludge in composite cement Type de document : texte imprimé Auteurs : N.C. Collier, Auteur ; N.B. Milestone, Auteur Année de publication : 2012 Article en page(s) : pp. 452–459 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Blended  cement  ;  Fly  ash  ;  Granulated  blast-furnace  slag  ;  Waste  management  ;  Magnesium  hydroxide Résumé : A range of magnesium hydroxide waste sludges arising from the re-processing of nuclear fuel exist in the UK and require safe long-term disposal. Similar wastes undergo a cementation process in order to immobilise radioactive material prior to disposal. Simulant magnesium hydroxide sludges have been prepared and their subsequent interactions with composite cement systems based on the partial replacement of ordinary Portland cement with blastfurnace slag and pulverised fuel ash have been studied. This work has concluded that there was little reaction between the sludge and any of the composite cements during hydration. Apart from a small quantity of a hydrotalcite-type phase containing magnesium from the sludge, the main phases detected were C–S–H and unreacted brucite. This indicates that the magnesium in the sludges is encapsulated by the cement, rather than being immobilised or chemically bound within the hardened matrix. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002907 [article] The encapsulation of Mg(OH)2 sludge in composite cement [texte imprimé] / N.C. Collier, Auteur ; N.B. Milestone, Auteur . - 2012 . - pp. 452–459. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 452–459 Mots-clés : Blended  cement  ;  Fly  ash  ;  Granulated  blast-furnace  slag  ;  Waste  management  ;  Magnesium  hydroxide Résumé : A range of magnesium hydroxide waste sludges arising from the re-processing of nuclear fuel exist in the UK and require safe long-term disposal. Similar wastes undergo a cementation process in order to immobilise radioactive material prior to disposal. Simulant magnesium hydroxide sludges have been prepared and their subsequent interactions with composite cement systems based on the partial replacement of ordinary Portland cement with blastfurnace slag and pulverised fuel ash have been studied. This work has concluded that there was little reaction between the sludge and any of the composite cements during hydration. Apart from a small quantity of a hydrotalcite-type phase containing magnesium from the sludge, the main phases detected were C–S–H and unreacted brucite. This indicates that the magnesium in the sludges is encapsulated by the cement, rather than being immobilised or chemically bound within the hardened matrix. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002907

A micromechanical approach to elastic and viscoelastic properties of fiber reinforced concrete / V.F. Pasa Dutra in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 460–472 Titre : A micromechanical approach to elastic and viscoelastic properties of fiber reinforced concrete Type de document : texte imprimé Auteurs : V.F. Pasa Dutra, Auteur ; S. Maghous, Auteur Année de publication : 2012 Article en page(s) : pp. 460–472 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Short-fiber  composite;  Creep  ;  Micromechanics Résumé : Some aspects of the constitutive behavior of fiber reinforced concrete (FRC) are investigated within a micromechanical framework. Special emphasis is put on the prediction of creep of such materials. The linear elastic behavior is first examined by implementation of a Mori–Tanaka homogenization scheme. The micromechanical predictions for the overall stiffness prove to be very close to finite element solutions obtained from the numerical analysis of a representative elementary volume of FRC modeled as a randomly heterogeneous medium. The validation of the micromechanical concepts based on comparison with a set of experiments, shows remarkable predictive capabilities of the micromechanical representation. The second part of the paper is devoted to non-ageing viscoelasticity of FRC. Adopting a Zener model for the behavior of the concrete matrix and making use of the correspondence principle, the homogenized relaxation moduli are derived analytically. The validity of the model is established by mean of comparison with available experiment measurements of creep strain of steel fiber reinforced concrete under compressive load. Finally, the model predictions are compared to those derived from analytical models formulated within a one-dimensional setting. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003019 [article] A micromechanical approach to elastic and viscoelastic properties of fiber reinforced concrete [texte imprimé] / V.F. Pasa Dutra, Auteur ; S. Maghous, Auteur . - 2012 . - pp. 460–472. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 460–472 Mots-clés : Short-fiber  composite;  Creep  ;  Micromechanics Résumé : Some aspects of the constitutive behavior of fiber reinforced concrete (FRC) are investigated within a micromechanical framework. Special emphasis is put on the prediction of creep of such materials. The linear elastic behavior is first examined by implementation of a Mori–Tanaka homogenization scheme. The micromechanical predictions for the overall stiffness prove to be very close to finite element solutions obtained from the numerical analysis of a representative elementary volume of FRC modeled as a randomly heterogeneous medium. The validation of the micromechanical concepts based on comparison with a set of experiments, shows remarkable predictive capabilities of the micromechanical representation. The second part of the paper is devoted to non-ageing viscoelasticity of FRC. Adopting a Zener model for the behavior of the concrete matrix and making use of the correspondence principle, the homogenized relaxation moduli are derived analytically. The validity of the model is established by mean of comparison with available experiment measurements of creep strain of steel fiber reinforced concrete under compressive load. Finally, the model predictions are compared to those derived from analytical models formulated within a one-dimensional setting. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003019

Effect of water saturation and porosity on the nonlinear elastic response of concrete / Cédric Payan in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 473–476 Titre : Effect of water saturation and porosity on the nonlinear elastic response of concrete Type de document : texte imprimé Auteurs : Cédric Payan, Auteur ; Garnier, Bernard, Auteur ; Joseph Moysan, Auteur Année de publication : 2012 Article en page(s) : pp. 473–476 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Characterization  ;  Spectroscopy  ;  Mechanical  Properties  ;  Nonlinear  acoustics Résumé : Nonlinear interaction of a monochromatic elastic wave with a low frequency should be a good tool for non-destructive evaluation of existing concrete structures. Nonlinear indicators have already proved efficient in detecting global damage by exhibiting a significant sensitivity regarding classical linear ultrasonic methods like wave speed or attenuation. However, it is necessary to understand the influence of some structural parameters such as porosity, stress state, or water saturation on the nonlinear processes. In this way, a recent model containing all of these potential contributors is presented in this paper. It is sustained by nonlinear interaction experiments in impact mode. This method reveals a great potential for in situ measurements with a low frequency propagating into the whole structure. We make use of a calibrated concrete sample's series, conditioned at different water saturation states, to quantify the influence of water content and porosity on the nonlinear response of concrete. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003159 [article] Effect of water saturation and porosity on the nonlinear elastic response of concrete [texte imprimé] / Cédric Payan, Auteur ; Garnier, Bernard, Auteur ; Joseph Moysan, Auteur . - 2012 . - pp. 473–476. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 473–476 Mots-clés : Characterization  ;  Spectroscopy  ;  Mechanical  Properties  ;  Nonlinear  acoustics Résumé : Nonlinear interaction of a monochromatic elastic wave with a low frequency should be a good tool for non-destructive evaluation of existing concrete structures. Nonlinear indicators have already proved efficient in detecting global damage by exhibiting a significant sensitivity regarding classical linear ultrasonic methods like wave speed or attenuation. However, it is necessary to understand the influence of some structural parameters such as porosity, stress state, or water saturation on the nonlinear processes. In this way, a recent model containing all of these potential contributors is presented in this paper. It is sustained by nonlinear interaction experiments in impact mode. This method reveals a great potential for in situ measurements with a low frequency propagating into the whole structure. We make use of a calibrated concrete sample's series, conditioned at different water saturation states, to quantify the influence of water content and porosity on the nonlinear response of concrete. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609003159

Temperature, pore pressure and mass variation of concrete subjected to high temperature — Experimental and numerical discussion on spalling risk / Jean-Christophe Mindeguia in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 477–487 Titre : Temperature, pore pressure and mass variation of concrete subjected to high temperature — Experimental and numerical discussion on spalling risk Type de document : texte imprimé Auteurs : Jean-Christophe Mindeguia, Auteur Année de publication : 2012 Article en page(s) : pp. 477–487 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Temperature  ;  Spalling;  Pore  vapour  pressure;  Mass  loss;Fire  behaviour;  Thermomechanical  behaviour Résumé : Spalling at high temperature is a phenomenon that can be observed in different materials such as ceramics, rocks and bricks. For concrete, this phenomenon, considered as a thermal instability of the material, can seriously jeopardize the integrity of a whole structure during fire and can even constitute a risk for people. Many explanations to the spalling risk exist but still no model can accurately predict it. Among them, models based on thermo-hydral behaviour of concrete have been proposed and developed by several authors. In particular, an important role is given to the pore vapour pressure, considered by many authors as the main mechanism for the trigger of such a thermal instability. However, pore vapour pressure is not easy to measure and numerical works still need more experimental results to validate their assumptions regarding the spalling risk. This paper presents the results of an experimental study carried out on five different concrete mixtures. We used a device intended for measuring temperature, pore vapour pressure and mass loss of concrete specimens. The aim of the study was to better understand the thermo-hydral behaviour of concrete exposed to high temperature and the possible link to spalling risk. In particular, we focused on the influence of matrix compactness on the transfer properties of concrete and we discussed about the importance of pore vapour pressure on spalling risk. Moreover, based on our experimental observations, a numerical analysis of the influence of water content on the thermomechanical behaviour of concrete during heating is done. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002944 [article] Temperature, pore pressure and mass variation of concrete subjected to high temperature — Experimental and numerical discussion on spalling risk [texte imprimé] / Jean-Christophe Mindeguia, Auteur . - 2012 . - pp. 477–487. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 477–487 Mots-clés : Temperature  ;  Spalling;  Pore  vapour  pressure;  Mass  loss;Fire  behaviour;  Thermomechanical  behaviour Résumé : Spalling at high temperature is a phenomenon that can be observed in different materials such as ceramics, rocks and bricks. For concrete, this phenomenon, considered as a thermal instability of the material, can seriously jeopardize the integrity of a whole structure during fire and can even constitute a risk for people. Many explanations to the spalling risk exist but still no model can accurately predict it. Among them, models based on thermo-hydral behaviour of concrete have been proposed and developed by several authors. In particular, an important role is given to the pore vapour pressure, considered by many authors as the main mechanism for the trigger of such a thermal instability. However, pore vapour pressure is not easy to measure and numerical works still need more experimental results to validate their assumptions regarding the spalling risk. This paper presents the results of an experimental study carried out on five different concrete mixtures. We used a device intended for measuring temperature, pore vapour pressure and mass loss of concrete specimens. The aim of the study was to better understand the thermo-hydral behaviour of concrete exposed to high temperature and the possible link to spalling risk. In particular, we focused on the influence of matrix compactness on the transfer properties of concrete and we discussed about the importance of pore vapour pressure on spalling risk. Moreover, based on our experimental observations, a numerical analysis of the influence of water content on the thermomechanical behaviour of concrete during heating is done. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002944

High temperature behaviour of self-consolidating concrete: Microstructure and physicochemical properties / Hanaa Fares in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 488–496 Titre : High temperature behaviour of self-consolidating concrete: Microstructure and physicochemical properties Type de document : texte imprimé Auteurs : Hanaa Fares, Auteur Année de publication : 2012 Article en page(s) : pp. 488–496 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Self-consolidating  concrete;  Temperature  ;  SEM  ;  Image  analysis  ;  Physical  properties Résumé : This paper presents an experimental study on the properties of self-compacting concrete (SCC) subjected to high temperature. Two SCC mixtures and one vibrated concrete mixture were tested. These concrete mixtures come from the French National Project B@P. The specimens of each concrete mixture were heated at a rate of 1 °C/min up to different temperatures (150, 300, 450 and 600 °C). In order to ensure a uniform temperature throughout the specimens, the temperature was held constant at the maximum temperature for 1 h before cooling. Mechanical properties at ambient temperature and residual mechanical properties after heating have already been determined. In this paper, the physicochemical properties and the microstuctural characteristics are presented. Thermogravimetric analysis, thermodifferential analysis, X-ray diffraction and SEM observations were used. The aim of these studies was in particular to explain the observed residual compressive strength increase between 150 and 300 °C. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002890 [article] High temperature behaviour of self-consolidating concrete: Microstructure and physicochemical properties [texte imprimé] / Hanaa Fares, Auteur . - 2012 . - pp. 488–496. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 488–496 Mots-clés : Self-consolidating  concrete;  Temperature  ;  SEM  ;  Image  analysis  ;  Physical  properties Résumé : This paper presents an experimental study on the properties of self-compacting concrete (SCC) subjected to high temperature. Two SCC mixtures and one vibrated concrete mixture were tested. These concrete mixtures come from the French National Project B@P. The specimens of each concrete mixture were heated at a rate of 1 °C/min up to different temperatures (150, 300, 450 and 600 °C). In order to ensure a uniform temperature throughout the specimens, the temperature was held constant at the maximum temperature for 1 h before cooling. Mechanical properties at ambient temperature and residual mechanical properties after heating have already been determined. In this paper, the physicochemical properties and the microstuctural characteristics are presented. Thermogravimetric analysis, thermodifferential analysis, X-ray diffraction and SEM observations were used. The aim of these studies was in particular to explain the observed residual compressive strength increase between 150 and 300 °C. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002890

A new test method for determining the fracture toughness of concrete materials / John Jy-An Wang in Cement and concrete research, Vol. 40 N° 3 (Mars 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 497–499 Titre : A new test method for determining the fracture toughness of concrete materials Type de document : texte imprimé Auteurs : John Jy-An Wang, Auteur ; Ken C. Liu Dan Naus, Auteur Année de publication : 2012 Article en page(s) : pp. 497–499 Note générale : Bibliogr. Langues : Anglais (eng) Mots-clés : Fracture  toughness  ;  Mortar  ;  Concrete Résumé : The Spiral Notch Torsion Test (SNTT) determines the intrinsic fracture toughness (KIC) of structural materials by applying pure torsion to cylindrical specimens having a notch line that spirals around the specimen at a 45° pitch. KIC values are obtained with the aid of a three-dimensional finite-element computer code, TOR3D-KIC. The SNTT method is suitable for testing a wide variety of materials used extensively in pressure vessel and piping structural components and weldments, as well as ceramic and graphite materials. One important characteristic of SNTT is that neither a fatigue precrack nor a deep notch is required for evaluation of brittle materials, significantly reducing the sample size requirement. Results are reported for a Portland cement-based mortar demonstrating applicability of the SNTT method to cementitious materials. The estimated KIC of the tested mortar samples with compressive strength of 34.45 MPa was found to be 0.360 ± 0.017 MPa √m. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002725 [article] A new test method for determining the fracture toughness of concrete materials [texte imprimé] / John Jy-An Wang, Auteur ; Ken C. Liu Dan Naus, Auteur . - 2012 . - pp. 497–499. Bibliogr. Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 3 (Mars 2010) . - pp. 497–499 Mots-clés : Fracture  toughness  ;  Mortar  ;  Concrete Résumé : The Spiral Notch Torsion Test (SNTT) determines the intrinsic fracture toughness (KIC) of structural materials by applying pure torsion to cylindrical specimens having a notch line that spirals around the specimen at a 45° pitch. KIC values are obtained with the aid of a three-dimensional finite-element computer code, TOR3D-KIC. The SNTT method is suitable for testing a wide variety of materials used extensively in pressure vessel and piping structural components and weldments, as well as ceramic and graphite materials. One important characteristic of SNTT is that neither a fatigue precrack nor a deep notch is required for evaluation of brittle materials, significantly reducing the sample size requirement. Results are reported for a Portland cement-based mortar demonstrating applicability of the SNTT method to cementitious materials. The estimated KIC of the tested mortar samples with compressive strength of 34.45 MPa was found to be 0.360 ± 0.017 MPa √m. En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609002725

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