Bacterized Concrete

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).

Sightseeing

At 23rd July 2008, the author and other participants of international seminar (The 5th International Workshop on Coastal Disaster Prevention) visited Samas beach to see green belt, after the seminar was held in Hyatt Yogyakarta Hotel one day before. The seminar was talked about disaster prevention in coastal area.
Back to Samas beach, the green belt which has function to detain tsunami and wind was formed of cemara udang (Casuarinas equisetifolia) trees that spread from Samas beach to Pandansimo in limited population.
This plant is firstly planted by Prof. Suhardi from Forestry Faculty of UGM, which then continued by local people. Cemara udang originated from Madura. This plant was chosen as green belt because from many types of vegetation planted before in south beach area, cemara udang was the only tree that can survives. This plant is cultivated through cutting or shoot. Cemara udang has a strong stem and many branches; this was the reason why cemara udang can sturdily detain wave and wind. Within age of 5-6 years, this plant was strong enough to detain tsunami wave. This plant’s height can achieve 15 meters. Survivability of this plant is categorized into good because although it is supplied with minim water, but it can survive well. Spacing of this plant was also possible to bunch up, as long still under water. Beside that, this plant also contributed to decrease the impacts of global warming. Cemara udang also capable to keep salt in order to not reach the land, thus soil and sand located behind this plant are suitable to cultivate for agriculture in sandy area. Before planted with cemara udang, plants planted in sandy area such as red onion, peanut, and soybean were unevenly spreads stacked by strong wind from the beach.

Cemara udang also can improve beauty of the beach; its dense is very beautiful. When the author came into its dense, the author feels amazed; unfortunately its population is minim. As we know that this vegetation has many benefits, then the government must pay more attention to its population, maintenance, and of course its survival.

After sight seeing cemara udang, we also saw agriculture area behind the green belt. Then, we went to Depok beach for lunch.

The journey then continued to Nglepen village to see anti-earthquake houses that very unique. Its form is similar to igloo, Eskimo’s house. These houses were built by NGOs from America named Domes for the World in order to help people in Nglepen village due to earthquake attacked Jogja in 27th May 2006. Because of this earthquake, land in Nglepen village, Sumberharjo, Prambanan, Sleman was shifted to form an indent like a canyon with depth approximately of 6 meters. This caused severe damage on houses in Nglepen village, even there were many houses mired in soil.

The ‘teletubbies’ houses (many people said like this because form of the house is similar to teletubbies’ house, a kid serial on television) were made from concrete. From sites read by the author on the web, the benefit of this house is more stabile thus more strong, more easy and faster to build, more economical, thus this house if cheaper than the cost to build a house in common.