Frost Damage of Internally Insulated Retrofitted Solid Brick Walls: Experimental Work and Hygrothermal Modeling

Frost damage is one of the most common deteriorations in porous clay bricks. Furthermore, adding internal thermal insulation (ITI) to a building envelope increases its thermal resistance and decreases conductive heat loss; however, it may cause durability performance issues of the wall in cold areas. Although numerous previous studies have examined the addition of ITI, there is still a need for additional research on this subject that considers other factors, including brick properties (BP), wind-driven rain (WDR) exposure levels, and insulation thicknesses and types. Considering exposure level, this study investigates frost durability (FD) and BP of five brick types and their effect on the retrofitting process. This study is divided into two sections: the first is to predict the FD of five brick types using three different methods: Canadian standard CSA A82.1, critical degree of saturation (Scrit), and durability factor (Df); the second is coupling Scrit measurements and BP with predictive modelling hygrothermal performance to assess the risk of freeze damage using hygrothermal simulation program WUFI Pro 6.5. The results revealed that the five brick types presented interesting variations between their properties, probably due to the effects of the service life for old brick types, where it has been manufactured and built for hundreds of years, the manufacturing process for new bricks, and heterogeneity between samples in terms of pore size distribution. Therefore, comprehending the influence of BP on the frost resistance (FR) of clay bricks plays a fundamental role in controlling the FD phenomena and avoiding the deterioration of the clay bricks, particularly after adding ITI. A good correlation was found between 5-h BWA, C/B, A-value, and 24-h CWA. The Scrit is around 55%, 50%, 50, 65%, and 35% of ERP, ERU, ENB, ENO, and IRM, respectively, ±5%. An empirical formula was developed to determine Scrit based on 24-h CWA, 5-h BWA, and compressive strength. The modelling showed that depending on the BP and moisture exposure level, adding ITI increases frost damage (FD) mainly in the second layer (i.e., 15 mm inwards from the outer side) and the middle layer and adding ITI did not impact walls made with samples having a Scrit of 0.60 or higher, even when subjected to higher WDR. In contrast, clay bricks with a Scrit of 0.55 or less require additional attention, particularly when exposed to higher WDR. Furthermore, depending on the 24-h CWA standard limit may provide a good result for preventing FD after adding ITI; however, the 24-h CWA of a brick is not an absolute indicator to predict FR. In addition, the insulation types and level do not impact FD for the wall made with brick samples with a Scrit of 50% and higher. Although correlations in the BP were found in the experimental and the modelling phases, a certain percentage of bricks are likely to fail, given the wide variation in properties.

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