Simplified coupled chemo‐mechanical modeling of cement pastes behavior subjected to combined leaching and external sulfate attack

Abstract

SUMMARYIn the context of radioactive waste storage, underground concrete structures may be subjected to external sulfate attack due to penetration of sulfate combined with leaching. This paper proposes a coupled chemo-mechanical modeling relying on a simplified chemical description of the solid phase composing the cement paste to address this issue. The sulfate and calcium species diffusing through the pore solution are supposed to completely control the chemical system, in particular the precipitation of gypsum and ettringite, which may lead to significant macroscopic expansions and cracking. The crystallization pressure generated by the growing crystals is introduced in the modeling through a poroelasticity analogy. Based on a representation of the cement paste of the matrix-inclusion type, the application of the Mori-Tanaka (MT) scheme provides estimates of the mechanical and diffusive properties and of the interaction coefficient as a function of the degradation state. The obtained coupled system is applied to two-dimensional numerical simulations of laboratory tests; the confrontation between experimental and computational results shows a good agreement in terms of both hydrated product evolutions as a function of time and macroscopic cracking appearance.

Alternative methodology to consider damage and expansions in external sulfate attack modeling

“…(11), represents the updated porosity value, calculated by the Eq. (12). The term is a shape factor, adjusted in 1.5 as proposed by Idiart [16].…”

Modelling of the interaction between chemical and mechanical behaviour of ion exchange resins incorporated into a cement-based matrix

“…(8). Based on previous works by Dvorak & Benveniste [28] and extended latter by among others Bary and Lemarchand et al [14,15], it is shown, for an isotropic behavior, that the interaction coefficient may take the form:…”

“…The composite is composed of swelling spherical IER embedded into a cement paste matrix; and we propose to apply a homogenization method to upscale the microscopic swelling effects of the IER at the level of the REV (Figure 4). To achieve that goal, a solution might be an analogy with the poroelasticity, as Lemarchand et al [15] or Bary [14] did before in another context. In fact by introducing an interaction coefficient similar to the Biot coefficient, for an isotropic behavior the macroscopic stress tensor may be expressed as a function of the microscopic pressure and macroscopic strain in the form:…”

“…To estimate the microscopic swelling of the IER, a formulation based on existing approaches has been developed, which takes into account the cement matrix surrounding the resins. Next, the microscopic pressure effects have been upscaled to the macroscopic level via an analogy with the poroelasticity theory and the introduction of an interaction coefficient [14,15]. Analytical homogenization techniques have been applied for this purpose to estimate the mechanical homogenized properties and the interaction coefficient [16][17][18][19].…”

Contribution to the French program dedicated to cementitious and clayey materials behavior in the context of Intermediate Level Waste management – Hydrogen transfer and materials durability

“…Sulphate attack has been experimentally evidenced [6] and then modeled considering a simplified chemo-mechanical coupling approach including damage initiation and growth [7].…”