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.

visual monitoring of bridge

Bridge is a construction purposed to connect roads through a lower hindrance. This hindrance commonly formed of water route or common land traffic. Usually, economical period of a bridge needs maintenance; this is because more old some bridge, then its structure will be degraded, whether caused by material durability of bridge’s components, environmental condition surrounds the bridge, or natural disasters which ultimately degrade the capacity of bridge both its safety and comfort for the user. Besides that, it is also for anticipation due to development or change on type and capacity of vehicles, which increases both its volume and weight out of the prediction. Thus, a bridge needs evaluation and maintenance in order to function well.

Indonesia has many bridges, hundreds of thousand; some of these are bridges located in Wonolelo Wonoseto village, Donoharjo, Ngaglik, Sleman, Yogyakarta. This bridge also must be maintained and evaluated. However, it is seen that the bridges are lack in maintenance which actually is a must.

Lack of maintenance is can be observed in each bridge’s component :
1. Grasses sprout up in the surface border of the bridge,
2. Corrosions are found almost in all surfaces of steel’s frame,
3. There is some parts of steel’s part that corrugated,
4. There is porous found in several joints,
5. Corrosions in vertical and parallel thunders,
6. There are crack, voids, and spalling in the deck,
7. Bearing is dirty and grasses sprout up surround it,
8. There is crack on concrete abutment and many wild plants sprout up surround it and in its body.
9.There is little sliding in the slope of bridge.

Accorded to the writer, damages found in this bridge are possibly caused by:
1. Corrosion of steel’s frame :
There are no maintenances for the bridge, such as painting in the frame, causing bridge more susceptible towards atmosphere corrosions.
Waste dumping in the abutment area which cause atmosphere more acidic around this place.
Rain water or non-evaporated dew, especially in the hidden parts (joints), causing more corrosion.
2. Damages on the deck of bridge, i.e. crack and spalling which probably caused by improper pouring, besides volume of vehicles. When the crack occurs, water permeates into the concrete and reaches the frame, causing corrosion. Due to this condition, the plane surface becomes wider because there is electrolyte added from other frame parts; the wider frame then presses the concrete then ultimately causes the concrete’s surface detached. If it is not immediately repaired, then there will be spalling in other parts of the deck and it is harm the stability of structure.
3. Damages on the sloping of oprit are maybe because there is no proper sticking between new river stone and the old one. Thus, the new match declines. If it is continue to happened, probably the old match will be scraped too and water reaches the ground, causing heap ground water rises thus decreases soil heap in the oprit.

Recommendations suggested by the writer for better development of the bridge are:
1. Clearing on the pavement of the bridge thus water can be flowed from it which makes the pavement stay longer. And making drainase thus the water can't flow to truss.
2. Clearing of abutment from trashes and plants because it causes pollution and damages the structure.
3. Clearing of corrosion through wiping and smoothing with sandpaper then painting, thus the steel stay longer in its life. For bent shaft, better it is replaced because it is clearly lack its capability.
4. The making of abutment structure from concrete in east side to replace the structure from stone match is much recommended.
5. The slope on the bridge’s oprit is also more supports. Make sure that the implementation is proper with the technical standard, especially the sticking power between new match with the old one in order to avoid declining on the match of river stone.
6. Damages on the deck part such as crack are can be repaired through injection using epoction material), voids and spalling are can be repaired through shotcrete system (by spraying mortar or concrete on the surface of repaired deck using pressed equipment, mortar or concrete are sprayed with high pressure, thus results strong stickiness on the old surface of concrete).

Fire Dangerous in Densely Populated Area

We always know, hear or read in media or directly witnessed a fire damages buildings or houses. Accorded to information taken from media (newspaper, television, internet, or radio), fire is commonly occurs in densely pupulated residence of urban area. For example, a wildfire that burns Manggarai Utara residence, Jakarta Selatan (2006), Pasar Rebo settlement (2007), residence located behind Salemba penitentiary (2007), settlement located below Jembatan Tiga flyover, Pluit, Jakarta Utara (2007), Karet Tengsin residence, Tanah Abang (2008).
Fire incidents happened in residence or densely populated areas are commonly caused by electrical failure, explosions from stove, outboard lamp, or triggered by cigarette butt which of course started bby human error’s factor. One of several causes of this error, from others, is lack of knowledge on fire dangerous and its prevention, less carefull in using tools or materials can trigger fire, personal unwareness besides indiscipline.
Residence or densely populated area is in the highest position for location that commonly stuck by fire compared to other locations. This is caused by the high fire load and building density. Besides that, slum houses in urban area are commonly identical with material from bamboo and wood. It is very easy to burn and there is no active protection system, therefore this slum area is very susceptible towards fire.
Vehicle unavailability of fire departement that can reach the fire location in densely populated settlement (especially settlement with unregularly layout of houses, with alleys as the only access of approximately 1 to 1.2 meters width) is one obstacle that hamper the alacrity of firemen, moreover with the fast spread of fire and less water availability to channel, it will need more time for firemen to arrive in the location adjacent to the fire location (time for installing additional hose if one can not reach the fire and/or portable pump to improve water pressure), there are many bends thus create more extra time. As the result, fire is difficult to quench and it will cause more losses due to fire. Material loss and life victims will be increased if there is no preventing action or anticipation towards possibility of fire in densely populated area. Preventing action can be taken through the installation of active protecting system (alarm, smoke/heat detector, sprinkler, hydrant or portable fire solver) on house building. However, of course these alternative are not cheap, although it will be more cheaper if compared to the loss suffered after fire.
By installing hydrant on critical spots in the location chosen with water capacity that was designed to supply two or three houses of certain volume, it will become more economical than if every house install their own active protection system.
If there no network of water company (PDAM) installed yet, then water source can be taken from well water or rivers that probably flow across this settlement area. Thus, there must be a special tank designed to accommodate water, pump, and simple pipe network.
In order to allocate water supply into pipe networks for hydrants system, we can use siamese connection installed in the road’s edge. From this siamese connection, firemen can supply water into the system of hydrant pipe network.
Within Keputusan Menteri Negara Pekerjaan Umum No. 11/KPTS/2000, amount of water needed for fire solving in certain building’s volume is stated in a formula :

Total water supply = (V/ARK) x AKK x FB
where,
V = volume total bangunan (total of building’s volume) (m3)
ARK = angka kasifikasi resiko bahaya kebakaran (number of risk classification for fire dangerous)
AKK = angka klasifikasi konstruksi resiko kebakaran (number of construction classification for fire risk)
FB = faktor bahaya dari bangunan yang berdekatan (dangerous factor from the adjacent buildings)

Residence has V of 7, where as the maximum AKK for residence is 1.0. if the distance of adjacent building if less than 15 meters, then it must be multiplied by 1.5.
The operation of this hydrant system must be properly controlled by local people, thus if there a fire happened, local people can responsively anticipate or at least can lessen the damage caused by the fire before firemen arrive. Therefore, counseling and training about fire dangerous besides its prevention are a must to be given to public because it can happens anytime. In the future, people are expected to form a kind of organization to anticipate fire dangerous, they must share responsibilities and duty if there is a fire happened in their houses.

Sumber : Keputusan Menteri Negara Pekerjaan Umum No. 11/KPTS/2000, Keputusan Menteri Negara Pekerjaan Umum No. 10/KPTS/2000, www.detik.com, Koran Tempo, yayasanpalapavc.com