Concrete is a common material and mostly used in constructing building's structure. Concrete has many advantages as a material for building's structure, such as able to hold high pressure (depend on its design), hold when exposed to high temperature (above 200oC the holding for pressure decreases). However, as other materials for structure (steel, wood, etc), concrete is susceptible towards damages which can decrease its durability.
These damages can be caused for example by misplanning, misimplementation, misfunction or because of external / environmental factor where the concrete structure exists.
Damages typically happened on concrete such as crack, voids (honey combing, sand streaking, bugholes and form scabbing), spalling, scaling, erosion, drummines, chemical factors (sulphide acid, alkali reaction, chlor), physical factors (over loading, temperature, shake, cyclic load, etc).
To avoid damages on concrete, engineers developed many improvement methods such as coating, routing and sealing, drypacking, injection / grouting, shotcrete, repacked concrete, jacketing.
Beside above methods, since early 1990s, many scientists also developed method for concrete that can 'manage' itself. The main principle of the method is imitating organism, when there is injury then it will systematically produce substance that can cover or heal the injury.
Delft University of Technology (TU Delft) in Holland decided to research application of bacteria as an agent for 'self-healing' within concrete. Dr. Henk Jonkers, a researcher from Delft Centre for Materials TU Delft, with several co-workers actively observed bacterized concrete.
Not only imitate the mechanism within organisms, Henk used micro-organisms such as bacteria to design a concrete that able to repair itself. Accorded to him, bacteria not only alter food become 'rubbish product', but it also alter food become construction material. There are bacteria which constantly form calcite sedimentation (calcium carbonate) that helps repair cracks thus the deepening not become more serious.
Henk and his team selected bacteria with several criteria as follow: the bacteria should not give negative effects towards concrete, it resist to alkali, hold to stress, and can survive until 50-100 years. It also must sturdy during constructing or mixing of the concrete.
Many researchers try to find bacteria with above criteria to the whole world. Accorded to Henk, such bacteria live in lakes with high pH such as alcalihilic bacteria in alkaline lake and bacteria live in concrete-like stones such in Chiprana, Spain (dessert crust); Playa, Spain (carbonate/gypsum rock); Wadi Natrun, Egypt (alkaline lake); and Kulanda Lake, Siberia (alkaline lake).
Bacteria, 'supplier' material for bacteria, and materials composing concrete then mixed together. When there is damage on concrete due to corrosion and water, bacteria incubated within water permeating into the cracks. Then, bacteria forms biomineral calcite (calcium carbonate—such a crystal) which fills the crack and covers its surface, thus the concrete lasts longer. Base don Henk, this method is appropriate especially for area where water becomes the irritant.
Gram positive spore-forming bacteria are suitable for concrete. Experiment in the laboratory with B. Pseudofirmus within concrete and 'food' composed of yeast extract or peptone—such an enzyme—shows a relative good result that is 'healing' within ten days. Experiment using B. Cohnii plus Ca-organic incubated in water within concrete can result in 'healing' in eight days.
This research is a laboratory scale research. Accorded to Henk, there is still further research needed whether this technology can be implemented in the real condition, at least within twenty years. There is still continuous research taking on what kind of 'food' or bacteria catalysts which used within concrete to stay survive.
Henk optimistic that his 'micro friends' within concrete will breaks the industrial world in the future and give great benefits.
(sources: Kompas/IP and lecture materials of MPSP/ATW).
