LAUSR

Significance Capillary effects in cement paste are associated with multiple degradation mechanisms. Using a framework, we investigated the role of capillary forces in cement paste under partial saturation from the nanograins level to the mesoscale. We show that the largest capillary forces concentrate at the boundary between gel pores and larger capillary pores, inducing nonaffine deformations with correlations up to a few tens of nanometers. Our results suggest a homogenization length scale common to liquid and solid stresses correlated with the scale of inherent structural heterogeneities. This opens the route to studying the poromechanics of complex multiscale media with explicit fluid–solid coupling. Capillary effects, such as imbibition drying cycles, impact the mechanics of granular systems over time. A multiscale poromechanics framework was applied to cement paste, which is the most common building material, experiencing broad humidity variations over the lifetime of infrastructure. First, the liquid density distribution at intermediate to high relative humidity is obtained using a lattice gas density functional method together with a realistic nanogranular model of cement hydrates. The calculated adsorption/desorption isotherms and pore size distributions are discussed and compare well with nitrogen and water experiments. The standard method for pore size distribution determination from desorption data is evaluated. Second, the integration of the Korteweg liquid stress field around each cement hydrate particle provided the capillary forces at the nanoscale. The cement mesoscale structure was relaxed under the action of the capillary forces. Local irreversible deformations of the cement nanograins assembly were identified due to liquid–solid interactions. The spatial correlations of the nonaffine displacements extend to a few tens of nanometers. Third, the Love–Weber method provided the homogenized liquid stress at the micrometer scale. The homogenization length coincided with the spatial correlation length of nonaffine displacements. Our results on the solid response to capillary stress field suggest that the micrometer-scale texture is not affected by mild drying, while nanoscale irreversible deformations still occur. These results pave the way for understanding capillary phenomena-induced stresses in heterogeneous porous media ranging from construction materials to hydrogels and living systems.