Sensitivity analysis of the hygrothermal behaviour of homogeneous masonry constructions: Interior insulation, rainwater infiltration and hydrophobic treatment

Abstract

Historical masonry constructions are difficult to mimic in hygrothermal models. The material properties of the walls are often highly uncertain due to the natural origin of the aggregates and the various, manual production processes used through time. Therefore, sensitivity analyses based on probabilistic simulations are powerful tools to indicate the risks on damage in masonry constructions. Damage criteria for relevant pathologies such as frost damage, potential decay of wooden beam heads and mould growth at the interior surface are used. The assessment methods (Scatter plots, Classification trees and Sobol indices) are based on 1D Heat, Air and Moisture simulations, including realistic variations on climate parameters and wall properties. These methodologies are applied to probabilistic simulations in which a potential damage risk is expected in historic masonries. The application of interior insulation, the use of hydrophobic treatments, and the impact of potential water infiltrations through cracks are discussed. In most of these situations a high dependency of each of the damage criteria on the rain intensity, the trend of the moisture retention/liquid conductivity curve and the absorption coefficient is evident, but also additional insights are found. For example, the thermal impact of interior insulation is negligible compared to its reduction of the first phase drying potential towards the interior. For hydrophobic treatments, the risk for damage typically decreases, but in combination with a rain water infiltration rate above approximately 5% of the wind driven rain the risk on mould growth at the interior surface significantly increases.

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

“…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.…”

“…An aspect not dealt with in detail in this study is imperfections of masonry – while the influence of contact resistances is explored, the additional water infiltration due to cracking is not. 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.…”

“…As exemplified by Calle and Van Den Bossche (2021), decision trees can also be used to assess the parameters and the combinations of them that potentially contribute to failures or, on the contrary, help avoid them. They are class discriminators that reclusively partition the dataset until each partition consists entirely or dominantly of examples from one class (Shafer et al, 1996) – in the current case, ‘pass’ or ‘fail’.…”

Combined Use of Wind-Driven Rain Load and Potential Evaporation to Evaluate Moisture Damage Risk: Case Study on the Parliament Buildings in Ottawa, Canada

“…Additionally, the material should be at a critical degree of saturation of moisture content at the time of freezing, and the internal freezing stresses should be higher than the material strength [54,55]. The accurate representation of these mechanisms and direct conclusions on freeze-thaw damage would require a hygrothermal simulation, eventually coupled to a mechanical simulation, which could resolve the occurrence of freezing and thawing locally, considering the pore-size distribution of the material [12,56,57] and the resulting mechanical stresses.…”

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

“…Therefore, in a second part the scope was extended and the relation between the response behavior and physical properties was assessed based on various sensitivity analyses. This included scatterplots, binary Poison distribution-based classification trees as well as Spearman rank correlations (Calle, 2020; Calle and Van Den Bossche, 2021; Hagentoft, 2017; Hamby, 1994). Three empirical degradation models were adopted and because of their inherent differences in nature, the results were first analyzed separately.…”