Biomediated Conservation of Unwelded Ignimbrites in Kandovan, Iran

Bacterially induced calcium carbonate precipitation is a newly developed technic in geotechnics and is suggested for soil liquefaction problems in an environmentally friendly process. The utilization of bacterially induced calcium carbonate precipitation in degraded stone conservation, and monument reinforcement is newly proposed. In this study, calcium carbonate biologically produced by Bacillus licheniformis was used as a consolidator cement. The results showed that the biological treatment could increase the uniaxial compressive strength (UCS) of stone to more than 500 kPa in dry samples. The permeability of the samples reduced from 8×10-4 cm/s in untreated samples to around 5.5×10-6 cm/s in biologically cemented samples. The bacterium was also able to reduce water vapor permeability and water absorption by capillary tubes and by the bulk of the stone. SEM analysis showed a wide range of calcium carbonate polymorph genesis effective in pore alteration processes. Elemental analysis coupled with SEM was also indicative of primarily the role of the calcium carbonate precipitation in plugging and the distribution pattern of calcium carbonate within the pores. Data from UCS showed that biological cementation could be considered a convenient alternative to consolidate historical monuments and improve durability.