Multiscale poromechanics of wet cement paste

Abstract

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.

Time resolved alkali silicate decondensation by sodium hydroxide solution

“…To investigate all these effects, multi-scale approaches will require large simulations that go beyond the scope of this study. Nonetheless, our work paves the way towards the investigation of atomic scale effects on nanoscale arrangements that can be simulated with, for instance, coarse grained model [10,49]. At different scales, alkali type (Na, K) could affect the setting time of gels and their mechanical properties (shear, strength,K) as well as salt concentration [50,51].…”

“…Recently, the continuous growth of the concrete's demand has been driven by the demographic change [6,7]. This has motivated recent studies to assess the structure of cement at the nano-scale [8,9] to maximize the durability of concrete [10,11] and, thus, reduce its environmental impacts.…”

Formation of stable aggregates by fluid-assembled solid bridges

“…In a polydisperse mixture, small particles may bind larger cohesionless grains together by bridging the interparticle space, forming aggregates. This mechanism is manifested in various industrial processes such as the flocculation of polymers (6,7), cement binding of frictional grains (8,9), contact fusion of metal particles during sintering (10,11), and agglomeration of various industrial products, including commercial fertilizers and pharmaceutical products (12,13). Various interfacial interactions-such as electrostatic and electromagnetic attractions (14), chemical bonding (15), capillary adhesion (16), solute (re)crystallization (17,18), and nanoparticle-polymer interactions (19)-can confer strength to the particle assembly and give rise to an effective cohesion.…”

A Poromechanical Model for Sorption Hysteresis in Nanoporous Polymers

“…[33][34][35][36][37][38] Several extensions have been made in poromechanics to model the coupling of sorption and deformation for nanoporous solids. 36,[39][40][41][42][43] For nanoporous materials with small sorption-induced deformation, the sorptioninduced stress can be calculated from the undeformed configurations assuming negligible deformation impact on the sorption process. For instance, Zhou et al 42,44 estimated the structural relaxation of wet granular materials using molecular dynamics (MD) including the precalculated sorption-induced stress from density functional theory (DFT).…”

“…36,[39][40][41][42][43] For nanoporous materials with small sorption-induced deformation, the sorptioninduced stress can be calculated from the undeformed configurations assuming negligible deformation impact on the sorption process. For instance, Zhou et al 42,44 estimated the structural relaxation of wet granular materials using molecular dynamics (MD) including the precalculated sorption-induced stress from density functional theory (DFT). In this approach, by looking at capillary forces at the nanograin level, sorption-induced deformation at the nanoscale such as nonaffine local deformation was discussed in detail.…”