Potential of Cyanobacterial Carbonate Precipitation for Concrete Restoration

Concrete is a widely used construction material with a global production growing by 2.5% annually. However, concrete can easily be cracked and has a limited lifespan. Among strategies for healing cracks and recycling concrete, microbial carbonate precipitation (MCP) by nitrogen-involved heterotrophic bacteria showed great potential. In this study, an alternative technology using autophototrophic cyanobacteria is proposed to overcome the pollution generated by urea-based MCP. This study investigated cyanobacterial carbonate precipitation (CCP) in concrete and mortar, and its impact on their performance. Solution composition and cell viability were monitored, morphology of precipitates and the relation of precipitate-cell-substrate was observed with scanning and transmission electron microscopy as well as atomic force microscopy and epifluorescence microscopy. Chemical components were analyzed by energy dispersive X-ray spectroscopy, X-ray diffraction and Raman spectroscopy. The performance of concrete/mortar were evaluated using water absorption tests, sonication tests, compressive strength tests and mercury intrusion tests. Results show that cyanobacteria were able to survive in cement solution for a certain period, the biotic-formed precipitates were different in morphology and achieved higher amount compared to abiotic-formed precipitates. In addition, the calcite-cell aggregate layer was more cohesive on concrete/mortar than the calcite layer formed in the abiotic condition. The durability of concrete/mortar was greatly enhanced by CCP through decreasing the water absorption and porosity, and increasing the compressive strength. Nevertheless, the capability of cyanobacteria improving concrete/mortar properties is strain-dependent, and varies according to environmental conditions. This study concluded that Synechocystis PCC6803 works better than Synechococcus PCC8806 and Synechococcus LS0519. Generally, UV pretreatment of cyanobacteria contributes to better results by producing higher amount of EPS. Consequently, cyanobacteria, especially UV-killed cells, show a great potential for restoring concrete/mortar.

Department dc:contributor.department

Physical and Environmental Sciences

Year dc:date.issued

2017

Author dc:creator

• Zhu, Tingting

Advisor dc:contributor.advisor

• Dittrich, Maria

• Carbonate Precipitation
• Concrete Restoration
• Cyanobacteria
• Mortar

Handle dc:identifier.uri

http://hdl.handle.net/1807/80738

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/80738