Microbial interactions with mineral building materials

(Willem De Muynck, Sandra Manso, for more information contact )

Due to their porous nature, mineral building materials are susceptible to a variety of degradation processes resulting from the ingress and/or presence of water. In addition to chemical and physical degradation processes, the presence of water contributes to undesirable changes in the material properties resulting from the activities of living organisms, i.e. biodeterioration. Since microorganisms are present in about all habitats and posses an amazingly diversified metabolic versatility, their presence on building materials is quite normal. Although microorganisms have often been associated with degradation processes, their presence on building materials is not always harmful to the material. More recently, the use of microorganisms has been explored for conservation purposes. The work deals with both aspects of the microbial presence on building materials, i.e. biodeterioration and bioconservation. The research interests include the stimulation of microbial activity for the improvement of material properties, i.e. strength and durability (protection against ingress of weathering agents and further decay) and alteration of material properties to prevent microbial activity.

Simplified representation of the events occurring during the ureolytic induced carbonate precipitation

Simplified representation of the events occurring during the ureolytic induced carbonate precipitation.

Modular setup used for the accelerated fouling of building materials by means of algae. The image in the middle gives a schematic presentation of one unit

Modular setup used for the accelerated fouling of building materials by means of algae. The image in the middle gives a schematic presentation of one unit.

 

Another positive application of micro-organisms on concrete is for the creation of living or green walls. The concrete walls are purposefully designed to obtain a specific microstructure and bioreceptivity as substrate for biological growth. These green walls may provide a visually attractive appearance, may form a sink for fine dust and CO2, and may reduce the urban heat island effect. One of the most important properties of the primary bioreceptivity of a substratum is the pH and consequently, the chemical and mineral composition. Secondly, properties such as porosity and roughness will also define the nature of the colonization due to the retention of organic matter, dust and raindrops. In a joint PhD between Universitat Politècnica de Catalunya (UPC-BarcelonaTech) and Ghent University, a low-pH cementitious material is developed and its bioreceptivity is studied. Two types of cement are used, i.e. Ordinary Portland cement (OPC) (with subsequent carbonation of the samples) and Magnesium Phosphate Cement (MPC). OPC and MPC samples with different porosity and roughness were produced by varying the aggregate sizes, w/c ratios and amounts of cement paste. The bioreceptivity is studied in the accelerated fouling test developed in house. For practical applications, the UPC team has envisioned this biological concrete as the middle layer in a multilayer panel. This panel includes furthermore an inner structural layer, with a waterproofing layer on top (protecting the latter from possible damage caused by water seeping through); and an outer coating layer with a reverse waterproofing function (permitting the entry of rainwater and preventing it from escaping).