Impact of the drying rate on the moisture retention curve of porous building materials

Effect of dynamic contact angle variation on spontaneous imbibition in porous materials

“…The main innovation refers to the upscaling approach employed to describe the dynamic effect and the link established between dynamic contact angle at the capillary level and such macroscopic dynamic effect. While previous studies (1) P c,d S, Ṡ = P c,e (S) − 𝜏 Ṡ (Hassanizadeh and Gray 1993;Carroll et al 2010;Janssen et al 2016;Bianchi Janetti and Janssen 2020;Hassanizadeh et al 2002;Joekar-Niasar and Hassanizadeh 2011) express the local dynamic capillary pressure P c,d S, Ṡ in a purely empirical manner, we suggest here an alternative closed-form equation expressing the dynamic local capillary pressure as a function of local saturation and saturation rate. This equation is obtained by upscaling the contact-angle-meniscus-velocity relationship defined at the capillary level.…”

“…Often these material functions are assumed to be independent of the (de)saturation rate (speed of local saturation changes over time), by describing the moisture transfer via the well-known diffusion equation. Experimental findings reveal that this assumption may not always be valid though, having shown that the (de)saturation rate may significantly influence the moisture retention curve (Hassanizadeh and Gray 1993;Carroll et al 2010;Janssen et al 2016;Bianchi Janetti and Janssen 2020;Hassanizadeh et al 2002;Joekar-Niasar and Hassanizadeh 2011). The occurrence of this phenomenon, which is still not fully explained, is addressed in the literature as "dynamic effects" on the moisture retention curve.…”

“…Such dynamic effects can be taken into account by defining a local dynamic capillary pressure, being a function of both local saturation and saturation rate. Generally, this empirical relation is used (Hassanizadeh and Gray 1993;Carroll et al 2010;Janssen et al 2016;Bianchi Janetti and Janssen 2020;Hassanizadeh et al 2002;Joekar-Niasar and Hassanizadeh 2011):…”

“…Equation (1) reflects the experimental evidence that dynamic effects vanish for sufficiently slow processes ( Ṡ → 0 ), reducing the moisture retention curve to a function of local saturation only: P c,d (S, 0) = P c,e (S) . The equation presumes that the deviations between dynamic and static local capillary pressure are proportional to the saturation rate via the dynamic storage coefficient, which is empirically determined by inverse fitting of experimental data (Carroll et al 2010;Janssen et al 2016;Bianchi Janetti and Janssen 2020) or with pore-scale simulations (Hassanizadeh et al 2002;Joekar-Niasar and Hassanizadeh 2011). Various studies suggest this coefficient being related to the fluid properties (viscosity, density, interfacial tension) (Hassanizadeh and Gray 1993;Joekar-Niasar and Hassanizadeh 2011), the material properties (porosity and pore size distribution) (Hassanizadeh and Gray 1993) as well as the pore surface wettability (contact angle of fluid and solid) (Hassanizadeh and Gray 1993;Carroll et al 2010).…”

Reliability Study of Equilibrium Moisture Content Methods for Sorption/Desorption Isotherms Determination of Autoclaved Aerated Concrete

“…The measurement of building material moisture, using well-established methods as well as the inclusion of new approaches [10,11], are one of the current relevant research challenges to establish more detailed studies of the basic physical processes fundamental to moisture transport. The results of measurements by standard stead-state procedures for moisture transfer in AAC building materials may show slightly underestimated data compared to the methodologies using dynamic effects [12]. In case of highly hygroscopic materials, such as AAC, the samples going through different preconditioning methods (especially in wet cup tests) may have a statistically different moisture content and permeability [13].…”