Algae attachment on carbonated cements in fresh and brackish waters—preliminary results

In order to evaluate the usefulness of different cements as substrates for artificial reefs, we have performed preliminary tests of both conventional and pH-neutral molded cements for attachment of microalgae populations. Neutrality was achieved by molding in the presence of carbon dioxide. It was verified through analysis of carbonate and hydroxide content and measurement of contact pH. Algae attachment tests were conducted at both brackish and freshwater conditions. We have found pH-neutral materials to which microalgae readily attach. These include silica-enriched (pozzolanic) cements, but also blast-furnace slag and fly ash, which are also silica-rich, and mixtures of these with Portland cement. In most cases the pH-neutralized, carbonated cements outperformed the conventional materials in rate of algae attachment, in some cases by wide margins. The high pH, conventional cements preferentially attached barnacles in brackish water. There was no evidence of weight loss in any of the test specimens.