External Sulphate Attack (ESA) is one of the main degradation processes affecting concrete structures. It takes place when the concrete is in an environment rich in sulphate ions and with a high humidity index. Once it has penetrated the concrete, sulphate undergoes chemical reactions that lead to the precipitation of expansive ettringite crystals that cause volumetric expansions of the cement paste/mortar, eventually leading to cracking and damage. The FE analysis is undertaken by representing concrete as composed by aggregate pieces inserted in a cement/mortar matrix. Zero-thickness interface elements are pre-inserted to represent potential fractures along all aggregate-matrix as well as along some selected matrix-matrix element contacts. An existing fracture-based non-linear constitutive law is used for the interface elements. Concerning the reactive transport problem, the model follows previous work in the same research group, which combined an older approach from the literature for the continuum medium, with interface elements in the context of meso-mechanical analysis of concrete specimens in 2D, as well as initial work in 3D (but no coupling). In the present paper, the effects of the coupling between mechanical and diffusion/reaction in 3D are introduced and demonstrated. The new results obtained confirm that, also in 3D, penetration of ions, expansive reactions as well as subsequent cracking and degradation, all take place much faster when the coupling effect due to the open interfaces is introduced.This research is supported by grants BIA2016-76543-R from MEC (Madrid), which includes FEDER funds, and 2017SGR-1153 from AGAUR (Generalitat de Catalunya, Barcelona).Postprint (published version
