Impact of water content and salts on the mechanical properties of masonry materials used in historic structures

The protection of built cultural heritage is increasingly important due to climate change. Given that flooding is one of the most serious threats to the conservation of heritage objects, the goal of this study was to evaluate the effect of water and soluble salts on the mechanical strength of materials commonly used in old structures. An experimental analysis was conducted by wetting several types of conventional building materials (such as stone, lime mortar, and fired-clay brick), each characterised by distinct mechanical properties and porous structure. The impact of contamination with three types of soluble salts commonly found in historic buildings was also assessed. The results showed that the level of water saturation can have a significant effect on the mechanical properties of all the tested materials. In some cases, the sample heterogeneity surpassed the effect of water content on the mechanical behaviour. Brick and stone samples showed a similar trend in the strength behaviour. Brick had a flexural strength decrease of around 15% after 7 days of submersion in water and also after storage in an environment with high relative humidity. Mortar mixtures were more sensitive to the effect of water and salt solutions compared to stone and bricks. One-cycle of salt contamination followed by drying increased the mechanical strength of the tested materials.