A methodology for hygrothermal modelling of imperfect masonry interfaces

Abstract

Hygrothermal models are important tools for assessing the risk of moisture-related decay mechanisms which can compromise structural integrity, loss of architectural features and material. There are several sources of uncertainty when modelling masonry, related to material properties, boundary conditions, quality of construction and two-dimensional interactions between mortar and unit. This paper examines the uncertainty at the mortar-unit interface with imperfections such as hairline cracks or imperfect contact conditions. These imperfections will alter the rate of liquid transport into and out of the wall and impede the liquid transport between mortar and masonry unit. This means that the effective liquid transport of the wall system will be different then if only properties of the bulk material were modelled. A detailed methodology for modelling this interface as a fracture is presented including definition of material properties for the fracture. The modelling methodology considers the combined effect of both the interface resistance across the mortar-unit interface and increase liquid transport in parallel to the interface, and is generalisable to various combinations of materials, geometries and fracture apertures. Two-dimensional DELPHIN models of a clay brick/cement-mortar masonry wall were created to simulate this interaction. The models were exposed to different boundary conditions to simulate wetting, drying and natural cyclic weather conditions. The results of these simulations were compared to a baseline model where the fracture model was not included. The presence of fractures increased the rate of absorption in the wetting phase and an increased rate of desorption in the drying phase. Under cyclic conditions, the result was higher peak moisture contents after rain events compared to baseline and lower moisture contents after long periods of drying. This demonstrated that detailed modelling of imperfections at the mortar-unit interface can have a definitive influence on results and conclusions from hygrothermal simulations.

Hygrothermal performance of a brick wall with interior insulation in cold climate: Vapour open versus vapour tight approach

“…Based on experiments, Calle et al (2020) and Calle & Van Den Bossche (2021) suggested leakage rates to be applied as sources inside the wall. Gutland et al (2021) proposed a methodology to model the cracks as separate material thus accounting for both accelerated wetting and drying through the imperfections. In Calle et al (2020Calle et al ( , 2021 the wall with imperfections resulted in being wetter, while in Gutland et al (2021) drier in long-term than regular baseline model.…”

“…Gutland et al (2021) proposed a methodology to model the cracks as separate material thus accounting for both accelerated wetting and drying through the imperfections. In Calle et al (2020Calle et al ( , 2021 the wall with imperfections resulted in being wetter, while in Gutland et al (2021) drier in long-term than regular baseline model. However, the latter method would benefit from experimental validation and requires simplification to make it applicable to large modelling campaigns.…”

On the potential of clustering approaches for hygrothermal material properties based on three degradation risks in solid masonry constructions

“…In addition, for wood rot assessment, the one-dimensional abstracting of the wooden beam head and the constant load bearing support should be studied in more detail for a precise risk assessment. In this study, the interface resistance between the wooden beam and the brickwork was neglected but the study acknowledges that the interface as well as the load bearing length could have a significant impact on the distribution of moisture in the brickwork (Gutland et al, 2021;Zhou et al, 2020aZhou et al, , 2020b. A more precise assessment of the impact of various levels of moisture sources on the growth and initiation of wood decaying organisms could benefit the building research in a great way, especially when different wood types are to be tested.…”

“…can be represented quite accurate by an individual volume of continuous 1-D historic brickwork for real climate conditions (Vereecken and Roels, 2013). There may be discrepancies on this assumption where the impact of the interface resistance becomes significant (Gutland et al, 2021;Zhou et al, 2020aZhou et al, , 2020b but is not the intention of this paper to make absolute statements about individual cases. The studied historical wall assemblies comprised a single leaf masonry with a plaster finish on the inner surface.…”