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The goal of this study was to elucidate the influence of the intrinsic properties of roughness, porosity, and surface pH on the susceptibility of mortars to biodegradation by phototrophic microorganisms. An accelerated fouling test was performed allowing a periodic sprinkling of an algae suspension on sample surfaces. The green alga Klebsormidium flaccidum was chosen due to its representativeness and facility in culturing. The biofouling of sample surfaces was evaluated by means of image analysis and color measurement. Two porosities, three roughnesses, and two surface pHs were examined. The colonization by algae of sample surfaces was not influenced by porosity because of the specific conditions of testing that led to a constant high level of moistening of mortar samples. The roughness, in contrast, played an important role in biological colonization. A rougher surface facilitates the attachment of algal cells and so favors the extension of algae. The surface pH was the most important parameter. A lower surface pH accelerated considerably the development of algae on the samples surface.

Electric arc furnace slag (EAF) has the potential to be re-utilized as an alternative to stone material, however, only if it remains chemically stable on contact with water. The presence of hydraulic phases such as larnite (2CaO SiO2) could cause dangerous elements to be released into the environment, i.e. Ba, V, Cr. Chemical treatment appears to be the only way to guarantee a completely stable structure, especially for long-term applications. This study presents the efficiency of silica addition during the deslagging period. Microstructural characterization of modified slag was performed by SEM and XRD analysis. Elution tests were performed according to the EN 12457-2 standard, with the addition of silica and without, and the obtained results were compared. These results demonstrate the efficiency of the inertization process: the added silica induces the formation of gehlenite, which, even in caustic environments, does not exhibit hydraulic behaviour.