Monitoring of weathering effect evolution in porous masonry construction materials: NDT and mechanical tests

Weathering agents combined with damp rise from the ground frequently affect masonry structures, causing a visible superficial decay, which usually appears as salt efflorescence, detachments of brick flakes, de-cohesion, crumbling, and powdering of the mortar joints. This phenomenon, leading progressively to a reduction of the resistant section of the porous construction materials, is thought to alter the mechanical behaviour of the material and the resistant capacity of the masonry structure. Thus, from a structural viewpoint, evaluating the effects and spread of this decay process on the masonry’s mechanical properties would be of great importance as there is still a lack of knowledge in this sense. In order to fill this gap, a multi-year experimental campaign was undertaken considering both brick units and mortar specimens stored outdoors in the microclimate of Bologna, Italy, and subjected to low-concentration brine capillary rise from the base. Non-destructive ultrasound as well as mechanical tests (compression and bending tests), were repeated at the end of each ageing season on the different series of materials samples. Thus, the damaging effects on both porous materials were evaluated and their evolution over time monitored. The values of ultrasound velocity, mechanical resistance and modulus of elasticity obtained at the end of different ageing periods were compared, with interesting results in terms of visible deterioration versus mechanical performance.