Akademik Veri Yönetim Sistemi
73rd International Conference on Innovative Materials for Sustainable Civil Engineering, Nanjing, Çin, 26 - 30 Ağustos 2019, ss.94
Cracks in concrete will act as preferential location for ingress of aggressive agents towards the reinforcement. Especially intrusion of chlorides or carbon dioxide will result in corrosion of the reinforcing steel. Self-healing concrete is engineered to heal cracks at the moment they appear. One self-healing methodology consists of the addition of protected bacteria, which will become active when cracks form and precipitate calcium carbonate. The bacteria can use various metabolic pathways to induce carbonate precipitation, the most important ones being ureolysis, conversion of organic compounds and denitrification. The pathway, the specific bacterial strain, and several external factors affect the precipitation efficiency and the carbonate yield. Anyhow, complete crack healing takes time, generally a number of weeks depending on the initial crack width. This means that during the process of crack healing corrosion may already be initiated.
In this study, the effect of ureolytic and
denitrifying bacterial consortia on corrosion of steel in chloride containing
environments was studied. Initially, the crack healing efficiency was
evaluated. Further, a proof-of-concept experiment was carried out on steel
plates in chloride containing solution, either or not with addition of the
inhibitor sodium nitrite or granules containing consortia of denitrifying
bacteria. Denitrifiers reduce nitrate to nitrite and in alkaline conditions
further microbial reduction of nitrite is suppressed, causing nitrite to
accumulate and inhibit steel corrosion (partial denitrification). Finally,
self-protected bacterial granules were integrated in mortar specimens
containing a steel rebar. Artificially cracked samples were then exposed to
chloride solution. It was shown granules with ureolytic bacteria did provide
crack healing in the mortar specimens, but could not completely avoid
corrosion. On the other hand, denitrifying granules produced nitrite and
provided corrosion inhibition at the same level as the chemical inhibitor
sodium nitrite. In conclusion, it was shown that biological nitrate reduction
has significant potential to heal cracks and inhibit corrosion in cracked
concrete