Bio-derived rheology modifying agents for cement-based materials

Abstract

In recent few years, significant development has been made in concrete technology to accommodate the requirements of high-performance concrete. Rheology Modifying Agents (RMAs) (such as superplasticizers) and Viscosity Modifying Agents (VMAs) have been developed as two alternative admixtures to obtain the required workability. However, these admixtures not only increased the environmental impacts of concrete production but also increased the unit cost of concrete. Following these concerns, several studies have been focusing on exploring more sustainable approaches in concrete production such as the use of bio-based admixtures in concrete production. Throughout the literature, bio-based polysaccharides (cellulose, chitosan, etc.) were found to be highly effective as VMAs. Long chain molecules of these polysaccharides stick to the water molecules, decrease their relative motion and forms a gel, so increase the yield stress and plastic viscosity. This behaviour reduces the bleeding and segregation, which results in robust highly workable concrete. The interest in this study was motivated by the vital demand to introduce a greener and more sustainable VMA to improve the rheological properties of cement paste. To this end, bacterial cells proposed as VMAs for cement-based materials. The bacterial cells were directly incorporated into the mix of water without any additional intervention. The rheological measurements were implemented to evaluate the influence of cells on apparent viscosity and yield strength. In addition, the use of superplasticizers and fly ash on the performance of biological VMA were also 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, bacterial cells were found to be compatible with the use of both fly ash and superplasticizers.