Utilization of carbon dioxide as an alternative to urea in biocementation

• Precipitation of CaCO3 through CO2 influx is comparable with that of urea.
• Compressive strength increased up to 117% compared to control and 47% with urea treated specimens.
• Sorptivity significantly reduced in bacterial carbonated specimens than other treatments.
• Utilization of CO2 serves as an alternative to urea during CaCO3 precipitation.

Ureolytic microbial calcium carbonate precipitation technology has recently emerged as a sustainable, eco-friendly approach for protection and remediation of building materials. However, use of urea has some disadvantages such as production of ammonia, which has raised environmental concerns, as well as risks of damage to concrete materials. In the present investigation, urea is replaced with direct influx of carbon dioxide and studied the precipitation of carbonates by bacteria (Bacillus megaterium SS3). The bacteria is able to grow well and precipitate carbonates well when CO2 influx of 99.5% pure passed (20 ml/min) into the flasks for 60 s. The amount of CaCO3 precipitated through CO2 influx is comparable with that of 2% urea used for precipitation. The percentage improvement in strength with respect to the control specimens by accelerated carbonation curing was 117% while it was 47% in urea treated specimens. Sorptivity was significantly reduced in accelerated carbonation specimens treated with bacteria compared to other treatments. Though carbonation increased compressive strength in control samples, but bacterial treatment significantly reduced the water absorption in concrete specimens. Present study results suggested that utilization of CO2 serves as an alternative to urea during CaCO3 precipitation.