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Assessing the influence of ITZ on the steady-state chloride diffusivity of concrete using a numerical model / Jian-jun Zheng in Cement and concrete research, Vol. 39 N° 9 (Septembre 2009) 

Public ISBD [article]  in Cement and concrete research > Vol. 39 N° 9 (Septembre 2009) . - pp.805–813 Titre : Assessing the influence of ITZ on the steady-state chloride diffusivity of concrete using a numerical model Type de document : texte imprimé Auteurs : Jian-jun Zheng, Auteur ; Hong S. Wong, Auteur ; Nick R. Buenfeld, Auteur Année de publication : 2009 Article en page(s) : pp.805–813 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Interfacial  transition  zone;  Transport  properties;  Microstructure;  Modeling;  Transfer  matrix  method Résumé : In this study, the influence of the aggregate-cement paste interfacial transition zone (ITZ) on the steady-state chloride diffusivity of mortars and concretes was examined using a semi-empirical, three-phase composite sphere model. Mortars and concretes were modelled as three-phase composites consisting of the aggregate, bulk cement paste and an inhomogeneous ITZ. The latter was divided into a series of homogenous concentric shell elements of equal thickness. The initial porosity and cement gradients at the ITZ were first estimated from the overall water/cement ratio (w0/c). The evolution of the porosity, solid hydration products and remnants of unreacted cement were then calculated from the hydration degree and local water/cement ratio (w/c) using Powers' empirical model. Based on the Laplacian equation, an element transfer matrix was derived analytically to predict the steady-state chloride diffusivity. The model was calibrated using the available experimental data and then applied to perform a sensitivity analysis to evaluate the effects of aggregate content, water/cement ratio, curing period, ITZ width, maximum aggregate size and aggregate gradation on diffusivity. Some of these variables are impractical to quantify by laboratory experimentation. Implications of the findings with regard to the role of ITZ on mass transport properties are discussed. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001306 [article] Assessing the influence of ITZ on the steady-state chloride diffusivity of concrete using a numerical model [texte imprimé] / Jian-jun Zheng, Auteur ; Hong S. Wong, Auteur ; Nick R. Buenfeld, Auteur . - 2009 . - pp.805–813. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 39 N° 9 (Septembre 2009) . - pp.805–813 Mots-clés : Interfacial  transition  zone;  Transport  properties;  Microstructure;  Modeling;  Transfer  matrix  method Résumé : In this study, the influence of the aggregate-cement paste interfacial transition zone (ITZ) on the steady-state chloride diffusivity of mortars and concretes was examined using a semi-empirical, three-phase composite sphere model. Mortars and concretes were modelled as three-phase composites consisting of the aggregate, bulk cement paste and an inhomogeneous ITZ. The latter was divided into a series of homogenous concentric shell elements of equal thickness. The initial porosity and cement gradients at the ITZ were first estimated from the overall water/cement ratio (w0/c). The evolution of the porosity, solid hydration products and remnants of unreacted cement were then calculated from the hydration degree and local water/cement ratio (w/c) using Powers' empirical model. Based on the Laplacian equation, an element transfer matrix was derived analytically to predict the steady-state chloride diffusivity. The model was calibrated using the available experimental data and then applied to perform a sensitivity analysis to evaluate the effects of aggregate content, water/cement ratio, curing period, ITZ width, maximum aggregate size and aggregate gradation on diffusivity. Some of these variables are impractical to quantify by laboratory experimentation. Implications of the findings with regard to the role of ITZ on mass transport properties are discussed. ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science/article/pii/S0008884609001306

Influence of aggregate size and volume fraction on shrinkage induced micro-cracking of concrete and mortar / Peter Grassl in Cement and concrete research, Vol. 40 N° 1 (Janvier 2010) 

Public ISBD [article]  in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 85-93 Titre : Influence of aggregate size and volume fraction on shrinkage induced micro-cracking of concrete and mortar Type de document : texte imprimé Auteurs : Peter Grassl, Auteur ; Hong S. Wong, Auteur ; Nick R. Buenfeld, Auteur Article en page(s) : pp. 85-93 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Microcracking  Interfacial  transition  zone  Transport  properties  Shrinkage  Aggregate  Lattice  modelling Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : In this paper, the influence of aggregate size and volume fraction on shrinkage induced micro-cracking and permeability of concrete and mortar was investigated. Nonlinear finite element analyses of model concrete and mortar specimens with regular and random aggregate arrangements were performed. The aggregate diameter was varied between 2 and 16 mm. Furthermore, a range of volume fractions between 0.1 and 0.5 was studied. The nonlinear analyses were based on a 2D lattice approach in which aggregates were simplified as monosized cylindrical inclusions. The analysis results were interpreted by means of crack length, crack width and change of permeability. The results show that increasing aggregate diameter (at equal volume fraction) and decreasing volume fraction (at equal aggregate diameter) increase crack width and consequently greatly increases permeability. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...] [article] Influence of aggregate size and volume fraction on shrinkage induced micro-cracking of concrete and mortar [texte imprimé] / Peter Grassl, Auteur ; Hong S. Wong, Auteur ; Nick R. Buenfeld, Auteur . - pp. 85-93. Génie Civil Langues : Anglais (eng) in Cement and concrete research > Vol. 40 N° 1 (Janvier 2010) . - pp. 85-93 Mots-clés : Microcracking  Interfacial  transition  zone  Transport  properties  Shrinkage  Aggregate  Lattice  modelling Index. décimale : 691 Matériaux de construction. Pièces et parties composantes Résumé : In this paper, the influence of aggregate size and volume fraction on shrinkage induced micro-cracking and permeability of concrete and mortar was investigated. Nonlinear finite element analyses of model concrete and mortar specimens with regular and random aggregate arrangements were performed. The aggregate diameter was varied between 2 and 16 mm. Furthermore, a range of volume fractions between 0.1 and 0.5 was studied. The nonlinear analyses were based on a 2D lattice approach in which aggregates were simplified as monosized cylindrical inclusions. The analysis results were interpreted by means of crack length, crack width and change of permeability. The results show that increasing aggregate diameter (at equal volume fraction) and decreasing volume fraction (at equal aggregate diameter) increase crack width and consequently greatly increases permeability. DEWEY : 620.13 ISSN : 0008-8846 En ligne : http://www.sciencedirect.com/science?_ob=PublicationURL&_tockey=%23TOC%235562%23 [...]