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Effective utilisation of flyash generated by coal based thermal power stations has been a major area of concentration for the scientists and engineers. Large quantities of flyash produced as a by-product of coal-based power have been viewed as a serious environmental problem. JAGVIR GOYAL says that in order to meet with the ever-rising power-demand, and setting up of thermal power stations to meet it, it becomes essential to convert their residue i.e. flyash into a resource. Then the effective utilisation of flyash would gain importance. A lot of research on the subject of flyash utilisation has been made by various scientific organizations. Three major uses suggested have been, the use of flyash in production of cement, bricks and in the rising of embankments. The actual utilisation, however, is yet to be listed. It is a common experience that while shaping a theory into practice, a number of variations are noted on the ground due to changes in properties of local materials, atmospheric conditions, prevailing working conditions and the type of machinery used. A countdown of that happening in actual and its comparison with the theory brings out many such factors that need reconsideration for better achievement of purpose in the future. Use of Flyash in Bricks: Bricks are the most common building material used by man since ancient times.The ever-rising demand for dwelling units is directly resulting into an increase in demand of bricks. Use of flyash in bricks can therefore dilute the problem of disposal of this hazardous material to a large extent. In addition, the depletion of fertile crest of earth, now underway to fulfill the demand of clay for manufacture of bricks, can also be slowed down. Flyash can be used in combination with clay or with lime and sand to produce clay-flyash bricks and flyash-sand-lime bricks respectively. Clay-flyash bricks: IS13757-1993 lays down the specification for burnt clay-flyash building bricks. This standard has been prepared on similar lines to IS1077-1992, the standard for common burnt clay building bricks, keeping in view the same end use. The standard prescribes the dimensions and tolerances in them; classification based on average compressive strength of bricks, physical requirements and certain guidelines on general quality of bricks. The quantum of clay and that of flyash has been suggested to be in optimum proportions to produce uniformly burnt and crack-free bricks. Both hand moulding and machine moulding have been allowed in IS 13757. Gazette Notification: The final notification (no. 563) on flyash, bottom ash and pond ash has been issued by the Ministry of Environment and Forests, Govt. of India on September 14, 1999 with the objective to conserve topsoil, prevent dumping of flyash and to make an 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% of ash (flyash, bottom ash or pond ash) with soil on weight-to-weight basis. With about 60 thermal power stations producing more than 80 million tones of flyash every year, the notification may result in substantial utilisation of flyash. Its full implementation however is yet to be seen. Actual Production of Clay flyash bricks: Production of clay-flyash bricks has been taken up by setting up a brick kiln at Lira Cohabit, district Bastinado of Punjab state with an objective to produce 2 cr. such bricks of first-class quality. The kiln has produced more than 1.8 cr. such bricks of which 1.7 cr. stand consumed by now. Actual production and use of clay flyash bricks has brought forth many such points, which, if considered, dwelt upon and solved, may help in considerable use of flyash in the manufacture of bricks in future. Using the kiln set up at Lira Cohabit as an example, we can catch a glimpse of the manufacturing process of clay flyash bricks. a)Manufacturing process: The kiln set up at Lira Cohabit, is a normal, continuous type bull’s kiln that bakes the bricks at 1020 degree Centigrade. It has a capacity of producing 8 lakh bricks per month. The quantity of flyash mixed with soil is 30% by volume. A further increase in quantity of flyash tends to make the bricks brittle which gets broken at the edges during transportation. Thus, it is not desirable to increase the percentage of flyash.On weight-to-weight basis, this works out as 18% only. The bricks are manufactured by extrusion process. Under this process, the bricks are machine moulded by installing brick-machines at the kiln site. The clay is weathered in open bins before sending it along with flyash to primary mixers where the two ingredients are well mixed before transporting them 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 kneads the mix well, 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 the 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.A normal time cycle of 48 days has been observed.The figure shows various activities involved. However, the activities of weathering of clay, preparation of mix, machines and drying of bricks run parallel to the activity of baking of bricks.On the whole, a net period of 30 days is required to avail full capacity of the kiln. Thus a kiln having a capacity of 9—10 lakh bricks will produce about 8 lakh first-class bricks per month. b)Soil and flyash characteristics: The soil used at Lira Cohabit kiln has a clay content varying from 15-20 %. In conventional bricks, clay content of 20—35 % is recommended. Thus the clay content of soil used is quite low, especially when flyash is to be mixed with it. Site experiments reveal that it is not possible to have more than 30 % of flyash by volume in the soil—clay mix if proper strength and bond are to be achieved. A proportion of 70:30 of soil and flyash by volume gives a cohesive mix that can be machine moulded into bricks of required shape and size. c)Other features: Some of the other features of this clay and fly-ash brick kiln are - 1. Cost of setting up of the kiln having a capacity of 8 lakh bricks per month, which includes the cost of machinery, but excludes the cost of the land, which is Rs. 52 lakh. 2. Total power requirements of the kiln work out to be 82 KW. 3. The cost of conventional bricks varies from place to place, the variation ranging from Rs. 1,200 to Rs. 2,200 per 1000 bricks. In backward regions, conventional clay bricks of first-class quality cost Rs. 1,300 per 1000 bricks.In comparison, the cost of clay and flyash bricks works out at Rs. 1,475 per 1000 bricks. After taking into account the extra labour cost, power consumption, depreciation of machinery and interest charges on capital, the investment is higher by Rs. 175 per 1000 bricks only. This difference will however vary from place to place. d)Provision of frog: Conventional clay bricks carry a frog of size 100 mm X 40 mm with the depth varying from 10 mm to 20 mm. Bricks produced by extrusion process do not carry a frog. The manufacturing process is such that, it is not possible to provide frog in the bricks.IS 13757-1993 also exempts the bricks produced by extrusion process of having a frog? As the clay and flyash bricks are being manufactured at Lira Cohabit by the extrusion process, these do not carry a frog. e)Mixing of clay and flyash: It has been noted that hand mixing, hand-machines of clay-flyash bricks is not possible. However, machine mixing, hand-machines is possible in these bricks.Trial testing of machine-mixed, hand moulded bricks done at kiln site shows that the compressive strength test results of machine-mixed, hand -moulded bricks are quite low as compared to those of machine-moulded bricks. Table 1 shows a comparison of test results of these bricks. f)Test results of clay-flyash bricks: Clay-flyash bricks, when tested for various physical requirements laid in IS 13757-1993, 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 compared to the minimum strength requirement of 105 kg/sq.cm prescribed for conventional bricks. The water absorption and efflorescence results are also better. It has been observed that buildings built with clay-flyash bricks show lesser signs of dampness in comparison to those built using conventional bricks, because of low porosity of these bricks. A comparison of machine-mixed, machine-moulded bricks with and without the use of flyash shows that average compressive strength of clay and flyash bricks is 300-kg/ sqcm while that of bricks without flyash was 190 kg/sqcm. This shows that the addition of flyash to soil has a positive effect on the strength of the bricks. g)Fuel saving: A saving in fuel consumption has been noted while manufacturing clay-flyash bricks. 11 to 12 tons of coals are required for the production of one lakh clay-flyash bricks, being 3 to 4 tons lesser than the normal corresponding consumption of coal.This saving occurs due to presence of unborn carbon in flyash. The quality and calorific value of coal also affect its consumption. h)Flyash utilisation:More than 12,000 cubic meter of flyash has been consumed in the manufacture of bricks at Lehra Mohabat kiln site.A significant percentage can be achieved if the gazette notification is followed, and all the kilns within a 50 km radius of every thermal plant begins to use flyash in the manufacture of bricks. i)Overall performance of clay flyash bricks: Keeping in view the above observations, made on the basis of the example used, the following conclusions on the performance of clay-flyash bricks can be made: 1.Clay-flyash bricks have high compressive strength, low water absorption and no efflorescence, and fulfill all the physical requirements prescribed in IS 13757-1993. 2. The cost of manufacture of clay-flyash bricks is higher by about Rs. 175/- per 1000 bricks than that of conventional bricks. 3. The soil-flyash proportion depends upon the clay content of the soil. The bricks turn brittle and break at corners if high percentage of flyash is mixed with soil having low clay content. 4. Initial investment on machinery and setting up of a kiln for clay-flyash bricks is higher than that for a kiln for conventional clay bricks. 5. For clay-flyash brick-kiln, a power connection of about 82 KW is required, while no such connection is required for conventional brick kiln. 6. Hand mixing is not feasible in the case of clay-flyash bricks, as proper blending of the soil and flyash does not take place. 7. Machine mixed, and machine-moulded bricks have better strength than machine-mixed, and hand-moulded bricks. 8. Machine-mixed, machine-moulded clay-flyash bricks have better strength than machine-mixed, machine-moulded clay bricks, showing that flyash contributes to the strength of the bricks. 9. Clay-flyash brick buildings show lesser signs of dampness as compared to conventional brick buildings, because of low porosity of clay flyash bricks. 10. A saving in fuel is observed when flyash is used in bricks. 11.A saving in soil equivalent to the quantity of flyash consumed is there in case of clay- flyash bricks. In view of these observations, the steps required to promote the production and use of clay flyash bricks can be outlined. Steps to promote clay-flyash bricks: i)Incentives to be given to brick kiln owners: A few benefits are already available to the brick kiln owners choosing to produce clay flyash bricks. These include- sales tax exemption, excise duty exemption on ash-based products, and category incentives by the industry department such as 30 % subsidy on building and fixed machinery. In addition, there are savings in fuel and clay. Yet, the brick manufacturers are reluctant to switch over to clay-flyash bricks. The following incentives need to be given further to the brick kiln owners to promote clay flyash bricks: 1.Lower interest loans to meet with the higher initial investments. The machinery purchased by the manufacturer can be hypothecated to the government against the loan. 2. Easy availability of flyash to the kiln owners from the thermal plants. In the initial years, the thermal plants at all kiln sites falling within a 50 km radius should provide cost-free flyash. 3.Power connection to brick manufacturers should be based on priority basis.4.Kilns producing clay-flyash bricks should be declared as seasonal industry. On average basis, kilns remain closed for 4 months in a year due to the rains or extreme weather. During these months, they have to deposit the minimum electricity charges to the SEBs. If declared as seasonal industry, they will be exempted from depositing these charges. 5.Industry department should maintain a separate list of these kilns for A-category incentives. Now, coupled with other industries, it takes a long time to pay the subsidy to brick manufacturers. ii) Steps to be taken by Pads and SEBs: 1. Items of brickwork in clay-flyash bricks should be added to the common schedule of rates. A higher rate in comparison to that for brickwork with conventional bricks should be allowed to accommodate higher cost of clay- flyash bricks after making a fresh analysis. 2. The work-specifications and tender documents should be revised to include the items with clay-flyash bricks. Government should declare the use of clay- flyash bricks compulsory in all public works. 3. State Electricity Boards should pass a regulation to give power connection to clay-flyash brick manufacturers on priority basis. 4.Thermal plant authorities should supply flyash free of cost to kiln sites within a 50 km radius. This will help them to dispose flyash as well as in meeting with the environment-protection regulations. iii) Amend Gazette Notification no.563: The Gazette notification of September 14, 1999 needs to be amended to the effect that, the percentage of ash to be used in bricks can be reduced, if the local soil does not contain sufficient percentage of clay in it. The authority under Para 1(2) of the notification should be empowered to decide the percentage of ash to be used in the local soil for production of best quality bricks. Conclusion: Based on actual experience in production of clay flyash bricks, it is concluded that steps elaborated above, if taken, will help brick manufacturers in shedding unfounded fears and adopt the use of flyash in bricks, thus contributing towards the utilisation of flyash and thus help reduce an environmental impact. These steps would also help in reduction in cost of production of clay-flyash bricks, further helping the consumer to switch over to clay-flyash bricks, as he will get machine-moulded and stronger bricks at a cost comparable to that of the conventional bricks.
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