Evaluation of strategies to prevent algal fouling on white architectural and cellular concrete

In this study, different strategies have been examined for the prevention of algal fouling on two types of concrete with different bioreceptivity, i.e. white architectural and autoclaved aerated concrete (AAC). These strategies are aimed towards the decrease of the bioreceptivity and comprised the application of water repellents and/or biocides. Both traditional (stearates, silanes, silane siloxane mixtures and a pyridine biocide) and innovative compounds (quaternary ammonium silane-based biocides, silver copper zeolites and silver nanoparticles) have been assessed for their performance by means of an accelerated water run-off test. A modular setup was designed which allowed the simultaneous evaluation of 12 different product formulations. Algal fouling was evaluated by means of colorimetric and image analysis, for which two new evaluation criteria have been proposed. For white concrete, contrary to untreated specimens which had 40% of the surface covered with algae, no fouling was observed for surface treated specimens after 12 weeks of exposure to algae under the test conditions. For AAC, the different strategies examined were unable to completely prevent the algal fouling. The use of water repellents resulted in green algal streaks along the surface. Biocide treated specimens showed a delay of onset of fouling of two to four weeks under the test conditions. The best performance was obtained with a combination of a silane-based water repellent and a chlorinated pyridine-based biocide, for which only limited fouling was observed after eight weeks of intensive fouling exposure. (C) 2009 Elsevier Ltd. All rights reserved.