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| SCIENCE TRIBUNE | Thursday, May 11, 2000, Chandigarh, India |
CLAY FLYASH BRICKS Shaping theory into practice EFFECTIVE utilisation of flyash generated by coal-based thermal power stations has been a major area of concentration for the scientists and engineers, especially for the last 15 years or so. Large quantities of flyash produced as a by product of coal-based power have been viewed as a serious environmental problem. Its constituents being the oxides of silicon aluminium, iron, calcium and magnesium along with traces of some highly toxic elements, its simple disposal has not been considered safe from environment-protection point of view. Thus its consumption in production of useful building materials has been suggested as the best solution to reduce its bulky presence on the earth. Science Quiz |
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CLAY FLYASH BRICKS EFFECTIVE utilisation of flyash generated by coal-based thermal power stations has been a major area of concentration for the scientists and engineers, especially for the last 15 years or so. Large quantities of flyash produced as a by product of coal-based power have been viewed as a serious environmental problem. Its constituents being the oxides of silicon aluminium, iron, calcium and magnesium along with traces of some highly toxic elements, its simple disposal has not been considered safe from environment-protection point of view. Thus its consumption in production of useful building materials has been suggested as the best solution to reduce its bulky presence on the earth. By now, it has been well understood by India’s power policy makers that it is not possible to meet with the ever rising power-demand unless thermal power stations are brought up at regular intervals. These projects have become extremely viable because of their short time-periods and fully developed technology. Hydel projects, though they provide cheap and pollution free power, never get finished on or around the target dates — slippage extending to years, rather decades. Thermal projects are thus here to stay for many years to come. Therefore the necessity of effective utilisation of flyash gains further importance. A lot of research on the subject of flyash utilisation has been made by scientific organisations such as CBRI, I.I.Sc., Bangalore and various pollution control research institutes. Many suggestions have been put forth CBRI has brought out many data-sheets. I.I.Sc. has held a number of seminars. Individuals BIS has evolved various IS codes issuing guidelines for use of flyash in cement and bricks. On the whole, three major uses suggested have been the use of flyash in production of cement, bricks and in embankments. The utilisation made in actual however is yet to be listed. Gazette notification: On September 14,1999, the Ministry of Environment and Forests, Govt of India had issued the final notification (no. 563) on flyash to conserve top soil, prevent dumping of flyash and to make its effective and time-bound utilisation. The notification lays down that no person, within a radius of 50 km from a coal or lignite based thermal plant, shall manufacture clay bricks or tiles or blocks for use in construction activities without using at least 25 per cent of ash (flyash, bottom ash or pond ash) with soil on weight-to-weight basis. This notification is yet to see its full implementation. However, a brick kiln set up at Lehra Mohabat to produce clay-flyash bricks is fast chasing a target of producing two crore such bricks of first-class quality. This is apart from the second-class and third-class bricks that get produced along with. The kiln has already produced more than 1.6 crore of first class clay-flyash bricks of which about 1.5 crore stand consumed by now. The 2.0 crore target is likely to be achieved by June/July, 2000. Thereafter, further target shall be fixed keeping in view the future requirements. It is a common occurrence that while shaping theory into practical, a number of variations are noted on the ground because of change in properties of local materials, atmospheric conditions, prevailing working conditions and the type of machinery being used. A countdown of whatever is happening in actual rather than standard theory therefore proves quite useful to those connected to the profession. As far as clay-flyash bricks are concerned, such a detail may boost many others to shed unfounded fears and adopt use of flyash in bricks thus contributing towards environmental protection. The kiln setup at Lehra Mohabat is a normal, continuous type Bull’s kiln that bakes the bricks at 1020°±20°C. It has a capacity of producing eight lakh bricks per month. The quantity of flyash mixed with clay is 30% by volume. It has been noted that a further increase in quantity to flyash tends to make the bricks brittle which though having high crushing strength get broken at the edges during transportation. It is important to note here that the quantity of unburnt coal in flyash falls in the range of 6% — 12%. The saturation moisture content of local flyash is about 47% on an average basis while density of dry flyash is about 0.8t/cu.m. All of these observations are tabulated here (Table 1) for easy reference. The figure explains various activities involved in the manufacture of clay-flyash bricks. A normal time cycle of 48 days has been observed. However, the activities of weathering of clay, preparing the mix, moulding and drying of bricks run parallel to the activity of baking of bricks. Thus a kiln having a capacity of 9-10 lakh bricks will produce about 8 lakh first class bricks per month. The bricks are made by extrusion process. Under this process, the bricks are machine moulded by installing brick-moulding-machines at the kiln site. Clay is weathered in open bins before sending it along with flyash to primary mixers where the two ingredients are well mixed before transportation to a pug-mill by means of a conveyer belt. In the pug-mill, required quantity of water is added to the mix. The pug-mill well kneads the mix and sends it to the extruder which pushes it into the mould to get the shape of a running column. The column further runs across the cutting table where wire-cutters are used manually to cut it into bricks of required size. The moulded bricks are then shifted to trays made for the purpose and transported to the sheds for drying. Further process is similar as followed in a conventional brick-kiln. Test results Clay-flyash bricks, when tested for various requirements laid under IS 13757 for these bricks, give satisfactory results. These bricks need to be tested for compressive strength, water absorption and efflorescence. Actual results received on testing of these bricks are exhibited in Table 2. It can be observed that compressive strength of these bricks is very high in comparison to the minimum strength requirement of 105 kg/sq. cm prescribed by PWD specifications. The water absorption and efflorescence are also significantly lower than those noted in the conventional clay bricks normally used in the building. Overall, the test results strongly advocate addition of flyash to clay for the manufacture of bricks. Not only that, a saving in fuel consumption has also been noted while manufacturing these bricks. A fuel consumption of 11 to 12 tonnes of coal for production of one lakh its clay-flyash bricks has been noted. This is three to four tonnes lesser than the normal corresponding consumption of coal. The variety of coal also determines it consumption. If good Assam coal is used, the consumption may be further reduced. The rates of coal vary from Rs 3000 to Rs 5200 per metric tonne. If coal of medium variety, costing around Rs 4000 per MT is used, its consumption per lakh of bricks can be restricted to 12 tonnes. This saving occurs due to presence of unburnt coal in the flyash used. The brick manufacturer therefore gets benefited in many ways — he saves fuel; he saves clay and better test results of bricks help in easy sale of bricks. Then he is serving a cause also — by putting flyash to use and helping in saving the environment. More than 12000 cubic metres of flyash stand consumed in manufacture of bricks at Lehra Mohabat. Though it makes little percentage of the flyash generated by the thermal plant yet it is a significant quantity. Setting up of more such kilns may not only help in saving earth’s crust but solve the flyash problem also. Though issuing of notification by the Government of India binds the brick-kiln-owners to use flyash in the manufacture of bricks, tax incentives such as excise duty exemption and sales tax relief should be given to those complying with the notification. The brick kiln owners will then use flyash by free will and not by force. More facilities such as grant of low-interest-loans and power connections on priority should also be thought of. The kiln-owners on their
part should sell these bricks at competitive rates. This
will help the consumers to switch over to clay-flyash
bricks as they will get machine moulded and stronger
bricks at a cost comparable to that of conventional
bricks. |
Science Quiz 1. A girl asked her boyfriend of the same age to bring stars for her from space if he really loved her. The boy departed with a speed comparable to that of light and, according to his own clock, returned to earth after 10 years. But, to his surprise, he found that the girl had drown older than him. Which main topic of physics will you read for finding an explanation of this interesting and puzzling situation, which has a definite theoretical basis? 2. US scientists have recently discovered a master gene which has been found to bring about changes in at least 90 genes which accelerate ageing and are responsible for many age-related diseases like arthritis, cancer, heart attack, Alzheimer’s disease, etc. Which is this master gene? 3. In this electricity generator, electrically charged hot gases produced by burning of fossil or nuclear fuel pass between the poles of a magnet and produce electricity directly. Which is this generator that has no moving parts? who built the first successful generator of this type and in which year? 4. When nitrogen is passed over calcium carbide at a suitable high temperature, we get a mixture called nitrolim which is a nitrogenous fertiliser. Which are the chemical components of this mixture? 5. SIM card, used with each mobile phone, has a microchip which stores the mobile phone number, personal identification number, the kind of service subscribed to, etc., and thus makes each mobile phone unique in itself. What does SIM stand for? 6. Vegetables like spinach, peas, sweetcorn, pepper and celery contain two pigments which are also found in our eyes. So the use of these vegetables can increase the amount of these pigments and help preserve our eyesight. Can you name these two pigments? 7. Taste buds are located at the tip, base, sides and root of the tongue, and in the roof of the mouth. These buds transfer the taste signals to the brain through the nerves. Do you know about how many taste buds does man have? About how many does a cow have? 8. Which gland of human body is popularly called “Adam’s apple”? 9. In this instrument, a wave, especially a light wave, is split into two component waves which are made to travel unequal distances. It is generally used to measure the wavelength of a light or a sound wave. Which instrument are we talking about? 10. A team of scientists
from the NCCS has recently developed a wonder gel that
can heal certain wounds quickly and has the potential for
use in post-surgical proceedings, cosmetics surgery and
treatment of burns. What is the complete name of NCCS? |
New products & discoveries — IT Digest ICICI payment
gateway The payment gateway will be owned by a subsidiary of ICICI and implemented by Compaq India, QSI payment Technologies, Australia, and Financial Software and systems (FSS). ICICI will be the first financial intermediary to implement an e-commerce payment gateway within India and will be providing services to corporates, consumers, merchants and banks that plan to share the ICICI payment gateway. ICICI’s B2C payment gateway will interface between the Internet shopper, the web merchant and banking systems in a secured environment to facilitate online payments. The gateway offers the flexibility of multiple payment modes including credit, debit and smart cards, direct bank debits and e-cheques. The B2B payment gateway will facilitate e-commerce transactions between corporates in a virtual market place. The gateway would also provide e-procurement services by linking corporates with their network of buyers and suppliers. The gateway will use strong encryption technologies and digital signatures to protect these transactions from potential attacks by hackers. HCL at a higher
level This was following an assessment conducted by the QAI (Quality Assurance Institute of India Ltd). The company’s software development processes are already ISO 9001 certified. HCL Infosys has now entered the prestigious league to 60 global companies who have achieved SEI CMM Levels 4 or 5. The PSO provides single-window enterprise solutions in key vertical segments of telecommunications, manufacturing, finance and banking, government, utilities and transportation. Monalisa
Infotech Propertyrealestate.com is a comprehensive B2B portal on the construction sector giving details about property available, works of architects/civil engineers, completed and proposed projects of builders, details about materials required for the construction industry, details about the laws governing the real estate and property markets. The site offers free listing of properties for sale/lease/rent as also offers free empanelment to suppliers and buyers of materials required for the construction industry and also for all types of interior designing materials. There is a special free section on auction of second hand goods for which sellers can invite bids and offload a used piece of machinery or equipment or any other used item to the highest bidder. — R.
Satyamurthy and Gaurav Chaudhury |
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