Studies on bio based calcareous and silicious construction materials

Abstract

In view of increasing urbanization, a novel interdisciplinary domain of research, Construction Biotechnology is recently being explored to utilize the potential of microorganisms in geo civil engineering applications to develop building materials, which are energy efficient, economical and environmentally friendly at the same time. This emerging bioengineering discipline exploits the potential of microorganisms which induce mineral precipitation, often called biomineralization and contribute to selective cementation in the concrete matrix, termed as biocementation. The present study aimed to explore the alternative pathway of mineralization by bacteria, besides well known ureolytic, feed oxidation pathway and to exploit biomineralization for performance enhancement of building materials in the absence of substrate and chemical feed. The influence of bacterial treatment on the permeability properties of construction and demolition waste was demonstrated and efforts have been made to develop low carbon, unfired building bricks using desert sand and biocementation technique. Detailed investigations of calcareous as well as siliceous system through morphological and mineralogical analysis revealed that bacteria serve as a heterogeneous nucleation site and facilitate the formation of calcite, portlandite and other mineral phases even in the absence of substrate or chemical feed. The biocement creates a filler effect that leads to overall densification of the cementitious matrix restricting the ingress of moisture, aggressive ions and carbon dioxide. Thus, the present study established a direct correlation between bacteria mediated micro scale modifications and improved macro properties viz. engineering and durability properties. Above all, the product of Construction Biotechnology is believed to impart self remediating characteristic to the concrete. Thus, biomineralization seems to be a sustainable approach for the stabilization of sand, development of high performance concrete and other geotechnical applications.