Growing bricks: Assessing biocement for lower embodied carbon structures

Abstract

Biologically-hardened concrete masonry units (CMUs) utilizing the microbiologically induced calcite precipitation (MICP) process have recently been promoted as a method to increase environmental sustainability in the construction industry. These biological CMUs (BioCMUs) do not require thermal hardening and thus could yield a significant reduction in embodied carbon in structures given that concrete production makes up 5% of overall global CO2 emissions. The objective of this paper is to compare the environmental and economic aspects of BioCMUs and conventional CMUs to determine under what conditions BioCMUs may be sustainable. Several LCAs of conventional CMUs were reviewed and an impact assessment was conducted using the TRACI 2.0 impact methodology. Conservatively, it was determined that conventional CMUs have more than three times the global warming potential (GWP) in kg CO2-eq and more than twice the respiratory effects in kg PM2.5 eq of BioCMUs. Conversely, BioCMUs have more than twice the eutrophication potential of conventional CMUs. On the economic front, estimates show the BioCMU must cost within $0.03 to $0.07 of the conventional CMU to save CO2-eq at a lower cost than contemporary carbon offset programs. Other uses for biocementation, such as for erosion control, are discussed in addition to the sensitivity of the BioCMU's sustainability to critical resources such as water. Given the trade-off between air pollution and water pollution, not to mention cost and performance, the choice between BioCMUs and conventional CMUs must be context specific – particularly until further breakthroughs in biocementation occur.