Laboratory chamber studies and petrographical analysis as bioreceptivity assessment tools of building materials

Samples of selected building materials (including natural rocks, bricks, mortars and aerated concrete) were exposed over a 9-month period to intermittent sprinkling on steeply inclined runoff surfaces. The sprinkling liquid consisted of nutrient-rich tap water containing a mixture of pioneer colonising plant diaspores. At successive stages of the experiment a quantitative assessment was made of the colonised surfaces. The taxonomic groups identified and roughly quantified were cyanobacteria, green algae, diatoms and mosses. After the laboratory exposure experiment, epoxy-impregnated thin sections were cut perpendicular to the colonised surface of each of the studied building materials. Petrographical analysis revealed the exact mineralogical nature of these building materials, while automated image analysis allowed the quantification of some selected physical parameters (e.g. porosity). A major finding of the petrographical investigation was the observation of conspicuous stratification of the colonising plant associations and a variable penetration depth of the rhizoids and algae. A preliminary evaluation of the biodeterioration potential of the organisms is made. This study demonstrates that the bioreceptivity of building materials is highly variable and that it is controlled primarily by their surface roughness, initial porosity and mineralogical nature.