A BIO-BASED RHEOLOGY MODIFYING AGENT INSPIRED FROM NATURE

Abstract

Interaction of microorganisms and building materials, particularly with concrete and stone, were a main topic of interest for many researchers. Initially, studies focused on degradation of concrete by organic acids, produced by microbial acidification such as microbial induced corrosion. This was followed by prevention of microorganisms fouling on building materials. However, the interaction of microorganisms with materials is not necessarily negative. Recent research in the field shows that microorganisms can have positive effects on concrete and stone, such as in biological cleaning and biocalcification, which resulted with stronger and more durable materials. Further, studies revealed that it was possible to develop smart-cement based materials that could self-heal microorganisms by leveraging metabolic activity of microorganisms. Through the development of this so-called smart bio-based mortar, it became possible to improve the fresh state performance of the mix. This study focusses on design of a cement-based mortar with improved rheological properties with use of Bacillus megaterium (B. megaterium) and Bacillus subtilis (B. subtilis) cells. The bacterial cells were directly incorporated to the mix water and influence of cells on viscosity and yield strength was evaluated by rheological tests. In addition, the influence of bacteria dosage, water to cement ratio (w/c), use of superplasticizers and fly ash on performance of biological VMA were investigated. Our results showed that the apparent viscosity and yield stress of the cement-paste mix were increased with the addition of the microorganisms. Moreover, B. megaterium cells were found to be compatible with both fly ash and superplasticizers however B. subtilis were only be able to increase the viscosity when they were incorporated with superplasticizers.