Injecting a liquid bacteria-based repair system to make porous network conrete healed

Abstract

Bacteria induced calcite precipitation has been proven to be effective in making concrete structure self-healing. In Microlab TU Delft, the concept has been enhanced by developing a liquid bacteria-based concrete repair system. The solution contains calcite precipitating bacteria, nutrients and buffer compound which may demonstrate high potential as healing agent to be injected into porous network concrete (PNC). This type of concrete has a porous core which can be used as a media to transport healing agents into the fracture zone. The concept was tested in the 55×55×285 mm PNC prisms with 23×23×285 mm porous concrete core in the interior. Ø2 mm threaded steel rebar was installed below the core. A crack was formed by three-point bending loading and the solution was injected through porous network until it reached and flew out through the crack opening. The bacteria then precipitated calcium carbonate blocking the crack. The healing efficiency was measured by water permeability test before and after injection at several time intervals. Second cycle mechanical loading was carried out to assess regain of mechanical properties. Eventually, calcite precipitation in the crack wall was examined by polished section with ESEM. Preliminary results showed more than 90% permeability reduction has been achieved at 11 days which appeared to be temporary since after 19 days permeability reduction drop to 70%.This could be attributed to the flushing of the solution after 11 days as the process could be not yet complete. However, bacteria imprints obtained from ESEM observation of polished section of Ø26-30 mm cylindrical porous core 21 days after injection with the solution provided strong evidence of bacterial activity and confirm the previous observation. The on-going research program has been devised implementing tap water and bacteria-based solution injected specimens with wet and dry curing. The results showed that wet cured bacteria series exhibited 99% permeability reduction while dry cured specimen only shows 60% reduction.