doi:10.1038/nindia.2012.170 Published online 22 November 2012
Researchers have designed a new kind of sealing material adding carbon nanotubes and fly ash to bacteria-derived calcium carbonate. This new sealing material could be used to repair cracks and holes in buildings and monuments.
Building materials are usually porous, facilitating the entry of moisture and other harmful chemicals such as acids, chlorides, and sulfates and so reducing their strength and life. Although sealing agents such as latex emulsions and epoxy resins are used to enhance the strength of building materials, such sealing agents are susceptible to ultraviolet radiation and emit toxic gases.
In the search for better sealing agents, the researchers have produced the new sealing agent using Bacillus pasteurii, a bacterium, fly ash, and fine Norris sand. They synthesized the sealing material using beads of cultured bacteria and a mixture of fine Norris sand and fly ash in a flow of nutrient broth containing sodium bicarbonate, ammonium chloride, urea, and calcium chloride. The sealing material mainly consisted of calcium carbonate and fly ash.
They tested the efficacy of the sealing agent in repairing artificially cracked cubes of cement. The bacteria-derived sealing agent formed a complex with the cement materials in the cubes, decreasing permeability and increasing compressive strength. The study also found that adding varying concentrations of carbon nanotubes to the sealing agent increased strength still further.
The researchers say that the use of bacterial cells to improve the strength and durability of fly ash-blended concrete provides greener and more economical options. They add that the presence of bacteria in alkaline pH could increase the resistance of concrete to alkali attack, sulfates, freeze-thaw damage, and drying shrinkage.
The authors of this work are from: Center for Environmental Nuclear Research, Directorate of Research, and School of Civil Engineering, SRM University, Chennai, Tamil Nadu, India.