Two types of porous Miocene limestones; a fine-grained, a medium-grained oolitic were studied on monuments that are located in the polluted urban environment of Budapest. The surface alteration is characterized by the presence of very common white (thin and thick) and less abundant black (laminar and framboidal) weathering crusts. Flaking, scaling and blistering are common crust detachment forms. The exposed weaker surface below the crusts often shows granular disintegration. Non-destructive in situ tests such as Schmidt hammer rebound and Duroscope were used to assess the physical properties of the weathered surfaces. These tests clearly document the presence of thin and thick weathering crusts and the degradation of underlying fine- and medium-grained limestones. A textural change is marked by pore occluding calcite and reduction of porosity in the crust zone, which was also recorded by Karsten-tube measurements. The analyses have demonstrated that the air pollution related gypsum crystallization with combination of freeze/thaw weathering lead to crust detachment with rates strongly controlled by the micro-fabric of limestone substrate.
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