Materials and Structures

, Volume 37, Issue 1, pp 43–58 | Cite as

Is concrete a poromechanics materials?—A multiscale investigation of poroelastic properties

  • F. -J. Ulm
  • G. Constantinides
  • F. H. Heukamp
Article

Abstract

There is an ongoing debate, in Concrete Science and Engineering, whether cementitious materials can be viewed as poromechanics materials in the sense of the porous media theory. The reason for this debate is that a main part of the porosity of these materials manifests itself at a scale where the water phase cannot be considered as a bulk water phase, but as structural water; in constrast to water in the gel porosity and the capillary porosity. The focus of this paper is two-fold: (1) to review the microstructure of cementitious materials in the light of microporomechanics theory by starting at the scale where physical chemistry meets mechanics, and which became recently accessible to mechanical testing (nanoindentation):(2) to provide estimates of the poroelastic properties (drained and undrained stiffness, Biot coefficient, Biot modulus, Skempton coefficient) of cementitious materials (cement paste, mortar and concrete) by means of advanced homogenization techniques of microporomechanics. This combined experimental-theoretical microporomechanics approach allows us to deliver a blueprint of the elementary poroelastic properties of all cementitious materials, which do not change from one cementitious material to another, but which are intrinsic properties. These properties result from the intrinsic gel porosity of low density and high density C-S-H, which yield a base Biot coefficient of 0.61<b⪯0.71 and a Skempton coefficient ofB=0.20–0.25. While the base Biot coefficient decreases gradually at larger scales, because of the addition of non-porous solid phases (Portlandite,..., aggregates), it is shown that the Skempton coefficient is almost constant over 3–5 orders of magnitude.

Keywords

Cementitious Material Porous Matrix Concrete Research Interfacial Transition Zone Ultrasonic Pulse Velocity 

Résumé

Une question divise encore la communauté scientifique du sujet de la nature des bétons: les bétons peuvent-ils être considérés comme des milieux poreux au sens de la théorie des milieux poreux? Ce débat provient de la nature d'une partie de la porosité des bétons. Cette dernière se manifeste à une échelle où la phase aqueuse ne peut plus être considérée comme un simple fluide newtonien, mais comme une phase structurale, contrairement à la porosité capillaire ou celle du gel. L'objectif de cet article est double: (1) Décrire la microstructure des ciments sous l'angle de la théorie de la micro-poromécanique, en partant d'une échelle décrite à la fois par la physico-chimie et la mécanique, et qui est récemment devenue accessible aux tests mécaniques (nanoindentation); (2) Estimer les propriétés poroélastiques (élasticité drainée ou non drainée, coefficient de Biot, module de Biot, coefficient de Skempton) des matériaux dérivés du ciment (ciment, mortier et béton) à l'aide des techniques d'homogénéisation de la micro-poromécanique. Cette approche micro-poromécanique à la fois expérimentale et théorique nou permet de reconnaître une marque de fabrique de tous les ciments, qui ne change pas d'un matériau à l'autre, mais qui donne accès à leurs propriété inrinsèques. Ces propriétés résultent de la porosité intrinsèque au gel des C-S-H à faible et forte densités, qui donnent un coefficient de Biot entre b=[0,61–0,71], et un coefficient de Skempton B=[0,20–0.25]. Tandis que le coefficient de Biot diminue progressivement aux grandes échelles, en raison de la contribution des phases solides non poreuses (Portlandite,... granulats), le coefficient de Skempton est presque constant sur une plage de 3 a 5 ordres de grandeur.

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Copyright information

© RILEM 2000

Authors and Affiliations

  • F. -J. Ulm
    • 1
  • G. Constantinides
    • 1
  • F. H. Heukamp
    • 1
  1. 1.Massachusetts Institute of TechnologyCambridgeUSA

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