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| SCIENCE TRIBUNE | Thursday, September 21, 2000, Chandigarh, India |
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Dampness: Silent killer of buildings Science Quiz |
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Dampness: Silent killer of buildings DAMPNESS in buildings is a serious problem. It is unpleasant for the occupant and undesirable from an aesthetic point of view and causes the serious, slow and unseen deterioration of the building. The rise of the ground water in walls due to capillary action and presence of damp patches is termed as dampness. If proper care is not taken to check the entry of dampness during or after the construction, the building becomes inhabitable and unhygienic with the passage of time. Therefore, the basic requirement of living in a clean and neat environment is not achieved. The building material like bricks, timber and concrete have some moisture contents which is not harmful under normal conditions. The rise in moisture where it becomes visible causes deterioration and leads to real dampness. Dampness badly affects the structure in many ways as reinforcement steel gets rusted, deteriorated electric fittings lead to leakage of current. Inner and outer finish is destroyed by unsightly patches of dampness. Floor coverings and flooring tiles are loosened on entering of dampness through floors. Dampness also leads to breeding of mosquitoes and termites causing decay of wooden doors and windows. Presence of salts in dampness results in weakening, cracking and crumbling of wall plaster and creating unhygienic condition for its occupants. The buildings constructed under the supervision of architects /engineers are provided with
damp-proofing treatments but still the problem of dampness exists in many buildings not having
damp-proof course especially walls of rice shellers, sheds and long boundary walls of factories and schools etc. Generally the bricks used in foundation of walls absorb moisture by capillary action. This is the most serious problem and can be checked fully by laying a layer of 40mm to 75mm thick (1:2:4) cement concrete (with waterproof compound) followed with two coats of bitumen @ 1.65
Kg. per sq. mt. laid hot and sanded at floor level in case of middle walls and 6” or 9” above ground level in case of outer walls as shown in figure 1&2. To prevent the entry of moisture from soil under the floors, the inside of the external walls should be provided with vertical
damp-proof course consisting of 1/2” to 3/4” thick (1:3) cement plaster covered with two coats of hot bitumen 85/25 extending from horizontal damp proof level to floor level. Heavy showers of rains also causes the entry of moisture from outer faces of walls if not protected suitably either by cement pointing, cement plastering (with waterproof compound) or cladding with some type of stone tiles according to availability of funds. Poorly ventilated and badly designed toilets and kitchens are always a source of dampness. By providing sufficient ventilation and proper orientation such dampness can be checked. Stagnation of rain water on rooftops is a major source of dampness and can be prevented by laying the tile terracing on roofs in a slope not less than 1:60 (preferably if should be 1:40). Minimum one 4 inch dia rain water pipe is required to drain off the rain water for an area of 400 to 500 sqft. to avoid stagnation of water. Dampness due to defective joint between slab and parapet wall can be checked by providing 10cm x 10 cm size concrete gola of (1:2:4) cement concrete along the junction of roof slab and parapet wall. DPC can also be provided in existing building to check dampness. It is provided at floor level. Firstly, a slot of about two feet long in the wall is made by removing two layers of bricks then already precast
damp-proof membrance of cement concrete or tarfelt is inserted in it and then bricks are relaid tightly in the slot. The cycle of cutting the slot and inserting the
damp-proof membrance is repeated till the entire length of wall is completed. The wall surface is finished with plastering or skirting matching to floor finish. This treatment must be carried out under the supervision of some skilled mason or supervisors to avoid any cracks/damage to the wall. Another way of concealing ugly appearance of dampness is by lining the wall with wood panelling. The
damp-proofing is must for all types of basements otherwise the basement will become useless after some time as the ground water may enter the basements through its floor and walls, if not provided with horizontal and vertical
damp-proof coating. Entry of dampness and termites through floors can be checked by laying a 100mm thick layer of fine sand/river sand under the sub base of floors in dry location and by providing a
damp-proof membrance where there is a possibility of moisture penetrating the floors. The cost of damp proofing is negligible as compared to its role in protection of building from dampness. Whenever DPC is found to be ineffective, it is only due to bad workmanship or its wrong location. The DPC may be horizontal or vertical. It should be continuous and cover the full thickness of wall and should not be carried across doorways etc. To check the overturning of boundary walls, bitumen coating of DPC should be replaced with floating coat of neat cement. Proper laying of
damp-proof course would help to protect the buildings from dampness, the silent killer of the buildings. |
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Science Quiz 1. The Limca Book of Records has already accepted this model as the world’s smallest working stationary steam engine and is to feature in the 2001 edition of this book. Of the size of a matchbox and weighing just 90 gm, this stationary engine is set into motion a minute after some water is injected into its boiler and fired. Name the Nagpur-based non-matriculate inventor of this miniature working engine named “Micro Victoria”. 2. Black holes are still a mystery and can be studied only by the effects they produce on the nearby gases and stars. Researchers have now planned to use a circular group of spacecraft designed to capture the most detailed images of black holes. This plan, called MAXIM, would study the X-rays emitted from the swirling matter that falls into a black hole. Can you state the full form of MAXIM? 3. “Electrons may be split”, said a news report recently. Which property of an electron, in your opinion, could be the basis for such an idea? 4. It has been found that only three types of birds have similar brain structures enabling them to learn and repeat songs. Can you name these three birds which evolved at quite different times with respect to each other? 5. GRP is a strong composite material and is used in making car bodies, boats, aircraft parts and containers. It has very high resistance to heat, corrosion, rot and most chemicals. What is GRP which can be, weight for weight, stronger than steel? 6. If we take two plano-convex lenses of equal focal length and place them at a distance equal to 2/3 of the focal length of either lens with their convex surfaces facing inwards, what name will you give to such an arrangement which is generally used in optical instruments? 7. Who discovered the cellular nature of nerve cells and in which year? Who discovered the electrical nature of nerve impulses and in which year? 8. These small, wingless, blood-sucking insects are external parasites on warm-blooded animals. Their monthparts can pierce their host and such blood. Which are these insects and to which order do they belong? 9. Which parts of human body are adversely affected by the chemical elements arsenic, barium and cadmium normally present in contaminated water? 10. CEDTI is a premier training organisation of Ministry of Information Technology, Government of India, which conducts both short and long term courses in high-tech computer education. What is the complete name of this institute and where is it located? Answers 1. Iqbal Ahmed. 2. Micro-Arcsecond X-ray Imaging Mission 3. Behaviour of an electron as a wave. 4. Humming bird, parrot and songbird 5. Glass-reinforced plastic 6. Ramsden’s eyepiece, named after the British instruments-maker Jesse Ramsden 7. Swiss anatomist Rudolf von Koillker in 1849; German biologist Emile du Bois-Reymond in 1843 8. Fleas; siphonaptera 9. Skin and nervous system, circulatory system and kidneys respectively 10. Centre for Electronics Design and Technology of India, Mohali, Punjab. |
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New products and discoveries Electronic bugs Ranging between $ 30 and $ 500 depending on the size and sophistication — the bugs are fast becoming every kid’s companion. And the manufacturers are busy putting up exhibitions to show more and more worms which are a marvel of electronic wizardy in that they not just crawl but even talk, throw fire and guzzle up vegetation and iron filings.
VLF antenna for
pre-quake signals
Based on analysis of data collected since February 1998 and correlating them with large tremors that shook India since then, Rajpal Singh and Birbal Singh conclude that VLF monitoring “may prove to be an important tool in the field of earthquake prediction.” Their experimental set up at Bichpuri, 20 kilometres from Agra, essen tially consists of a 120-metre long vertical copper wire inside water-tight plastic pipe driven into ground through a borehole. An electrode placed 3-metre down from the ground surface and in contact with the ground constituted the earth terminal. The natural potential between these two electrodes was found to be 20 milli-volts in a noise-free environment and increased when the antenna received electromagnetic radiation. The project was funded by the Department of Science and Technology. In their report published in Current Science, the scientists said analysis of one year data from the borehole antenna showed large variation in the vertical component of the electric field occurred in the form of noise burst “both prior to and after the occurrence of major earthquakes.” Out of the total number of noise bursts associated with major earthquakes, they said, about 60 per cent occurred prior to the earthquake as “precursors.” The rest were those that appeared after the earthquakes. The precursory signals were detected between one hour and 2 to 3 days prior to the actual occurrence of the earthquakes.
MRI for surgery on babies Doctors in Boston used MRIs to get images of twins joined from chest to belly and see details unavailable by ultrasound, needed to separate them quickly and save the one who had a chance at life. The use of MRI could prove effective not only in preparing and successful twin separations in the future, but also for other operations immediately after birth. Ultrasound had shown doctors that only one of the conjoined twins had a heart, and that their livers were fused together, Errol R.Norwitz of Brigham and Women’s Hospital wrote in the journal. The MRIs showed details needed to separate the pair quickly enough to save the twin with a heart, including precisely where the babies were joined and the exact placement of internal organs.
Radiation therapy A new kind of radiation therapy is now being used which enables physicians to deliver greater amounts of radiation to the precise location of a tumour while minimising the dose to the healthy tissues that surrounds it. Researchers are hopeful that the new techniques called Intensity Modulation Radiotherapy (IMRT) will improve treatment of may cancers. Until recently, radiation therapy has employed beams of nearly uniform intensity with rudimentary devices for modifying the intensity. As a result, there were some instances in which the desired dose of radiation could not be delivered to the entire tumour without harming healthy tissue in the process. IMRT solves this problem by allowing the intensity of each
radiation beam to be varied for “modulated.” Each beam can send out a sophisticated radiation pattern that varies in time and space. Firing non-uniform beams from several angles could deliver the desired doses to the tumour while minimising dose to surrounding organs. |
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