Effects of mortars chemical composition on micro-algal biofouling

Prix du meilleur poster du congrès IBBS 2014International audienceIntroduction The main cause of building-facade biodeterioration is the growth of microorganisms. This phenomenon depends on several parameters such as geographical situation and environmental conditions. Among the parameters, the surface state of substrates is often considered as the most crucial parameter favoring the biofouling kinetics. Several researches have been devoted to the study of the effects of porosity and roughness on the biofouling of stones and mortars. However, none of them have addressed the influence of the mortars chemistry on the kinetics of the microorganism growth. Aim The main objective of this study is to highlight the influence of the mortar chemistry in relationship with its physical properties on the algal growth. Materials and methods The biofouling kinetics was followed on samples exposed outdoor and on samples tested in a laboratory bench which consists in spraying an algal culture on mortar specimens. The kinetics of microorganism growth was measured by image analysis which allows calculating the coverage rate. The green algae Klebsormidium flaccidum were chosen because of its representativeness. It is indeed the species the most frequently identified and isolated from samples taken on sites. In order to characterize the influence of the mortar chemistry on biofouling, two Portland cements and two alumina cements were tested. The influence of mortar physical properties was studied by comparing two porosity and two roughnesses for each formulation. The carbonation impact on biofouling was also evaluated. Results The colonization rate increases with the porosity of mortar specimens, whatever the cement used in the mortar formulation. The impact of mortar chemical composition is more easily highlighted for the less porous mortars. In that case the biofouling kinetics is faster for Portland mortars than for aluminate mortars. The accelerated carbonation of the materials increases the biofouling rate, whatever the cement used. The calcium carbonate layer formed by accelerated carbonation produces a more favorable environment and the decrease in surface pH favors the growth of green algae. The roughness also influences the biofouling kinetics since the rough surfaces are colonized quicker than the smoothest one. However, its effect is not major in our case. The results of outdoor tests are similar to the results obtained in laboratory. The influence of mortar chemistry on biofouling kinetics is better highlighted on outdoor test because microalgae are submitted to environmental stresses. It is not the case in the laboratory test since the algal suspension is full of nutrients which make the environment friendlier than outside conditions. Conclusions The chemical composition of mortars strongly influences their biofouling. Calcium aluminate mortars slow down the colonization kinetics compared to Portland based mortars. The porosity increases the biofouling kinetics. The carbonation also influences the biofouling. The outdoor test allows highlighting the chemical influence on biofouling kinetics