Bacterial calcification for enhancing performance of low embodied energy soil-cement bricks

Soil-cement bricks are vastly more energy efficient than fired clay bricks. Although they have adequate strength, they absorb high levels of moisture and in humid conditions they become soft and non-uniform expansion leads to excessive deformation and cracking. In this research a barrier layer on their surface that impedes moisture ingress is developed by depositing calcite using bacteria. Soil-cement bricks (230 mm x 110 mm x 60-75 mm) were prepared by mixing bacteria (Bacillus megaterium) and cured by spraying a nutrient media for 28 days. The specimens were tested for water absorption, porosity and compressive strength and compared with control specimens. Results showed that the rate of water absorption and porosity were significantly reduced and compressive strength was enhanced in bacteria treated bricks. The results suggest that the barrier layer created by bacterial activity greatly alleviates the weaknesses of energy efficient soil-cement bricks enabling their large scale use.