Traditional building materials like cement, clay, burnt bricks and timber alone can no longer meet the existing demand in construction activities in the country. This necessitates the development and adoption of alternate building materials which can substitute costly and scarce materials like cement and steel. This article presents an overview of the status of alternate building materials in the country, and their development and adoption for low cost housing.
Building materials account for 70 to 75 percent of the total cost of construction. Due to large scale construction programmes including housing, the demand for building materials has far outstripped their production. According to very rough estimates presently there is a shortage of about 53 million dwelling units in the country. In this context, the enormous population growth and the existing housing this backlog make the situation even more alarming. The re is a general shortage of traditional building materials like cement, steel, brick and timber in different parts of the country. As such, in recent years, there has been an emphasis on the production of new and alternate building materials and utilization of industrial and agricultural wastes in a big way. Various research organizations working frantically to develop alternate building materials/components.
Substitutes For Scarce Materials
The findings of various institutions like have led to the introduction of a number of new building materials like hydrated lime, asphaltic corrugated sheets, cellular concrete, flyash bricks, plastic pipes, secondary species of timber, possolana cement and overhead tanks. The applications of these materials have helped to save scarce materials like cement and steel, specially in low cost housing and housing in the rural segment
It is normally assumed that 70 percent of the cement produced is consumed in building construction out of which 40 percent is used for masonry mortars and plasters. Out of this, quite a large percentage of cement can be profitable replaced by lime alone or its conjunction with pozzalana.
In recent times, the use of lime in building construction has decreased due to the varying quantity of material available in the market and its inherent defects such as the slow setting and laborious preparation of mortars.
A new process of hydration of lime has been developed which maker available hydrated lime in the dry form with standard quality and ready to use condition as in the case of cement. It can be stored in bags for six months without any deterioration. It is estimated that millions of tonnes of cement in building construction could be substituted by the materials produced in the aforesaid units with an anticipated saving of over Rs. 2000 crores per year.
Lime Pozzolana Mix
Clay pozzolana available in the market is known as `surkhi’ which is produced by grinding brickbats and is of variable quality. A new process of production of clay pozzolana has been developed in which clays of suitable specifications are caloried to the optimum temperature and then ground to a fine powder. The pozzolana, reactive surkhi has lime reactivity 5 to 10 times that of ordinary surkhi made by powdering burnt bricks.
The lime pozzolana mix is made by grinding the mixture of hydrated lime and clay pozzolana with a small percentage of gypsum/sodium metasilicate, etc. to improve their early characteristics. The investment required for the production of hydrated lime/lime pozzolana mix is about Rs. 2000 to Rs. 2500 per tonnes as compared to a heavy investment of Rs. 1,4000 per tonne required for cement production.
Secondary Species Of Timber
There is presently an acute scarcity of good quality timber, besides which the its price has been sky rocketing in recent times. This is mainly because usually only half dozen conventional or primary species of timber, such as teak, deodar, sal, shishum and rosewood are preferred in building construction due to their durability characteristics, decorative appearance and high strength properties. However, this availability is limited as the pressure on land remains unabated due to excessive population growth. However, the primary species take a comparatively longer time to reach maturity. In view of these facts, there is a need to explore the use of the lesser known varieties of timber, known as the secondary species of timber, in construction. Considerable research has been undertaken in this direction. The FRI has identified 117 secondary species of timber which could be gainfully used after proper seasoning the chemical treatment. By the use of seasoned secondary species of timbers, the primary species can be preserved and a saving of upto 30 percent can be achieved in joinery work. It is estimated that 20 percent of the total timber used (2.5 million cu.m.) in building construction is now secondary timber.
Asphaltic Corrugated Sheets
Asphaltic corrugated sheet is a low cost roofing material manufactured by using waste paper, rags and other road pickings and bitumen. This material is lightweight, water proof, flexible and vermin proof, and is available at less than half the cost of cement asbestos roofing sheets. These roofing sheets have become quite popular for temporary and semi permanent construction, rural housing and slum clearance programmes. Seven units with a total capacity 7 million sq. m. per year have been set up at various places in the country. Asphaltic corrugated sheets are recommended for use in regions where the temperature in shade does not exceed 44C. These roofing sheets are better substitutes for thatch roofing. Their life expectancy is about 8 10 years.
Cellular concrete or aerated concrete is a lightweight material used for walling in place of bricks and for roofing as a composite construction with concrete. It weight is one third that of ordinary brick and it has thermal insulation value, dimensional stability and the requisite structural properties necessary for use as a building component. Cellular concrete blocks can be sawn, cut, drilled and nailed. Because of its light weight, it is particularly suited to the construction of multi storied buildings as it reduces the dead load of the building. Moreover, due to the light weight and high strength to weight ratio of cellular concrete products, their use leads to appreciable savings in the consumption of scarce materials like cement and steel.
Cellular concrete is produced by autoclaving a set slurry consisting of a fine siliceous material and a binder, with the addition to foaming/ air-entraining agent. Based on the type of binder, it is divided into two groups. Cement based and lime based. Gas producing agents commonly used are either organic forming agents based on resin soap, glue or gas generating agents like fine aluminium powder, zinc dust etc.
The lightweight cellular concrete manufactured by many, is produced with lime and sand as raw materials. Blocks of dimension 600 x 200 x 125 by mm. to 200 mm. are utilized for load bearing as well as non load bearing blocks. The general experience is that through the use of cellular concrete for roofing the flooring, there is a saving of 40 to 50 percent in steel, 20 percent in steel, 75 percent in shuttering and 80 percent in water requirement at the construction site with an overall economy of about 10 percent compared to RCC roofslab. This product has been widely used by several construction agencies, both in public and private sectors.
In recent times, plastics have proved to be a versatile building material. Plastics have outdoor as well as indoor applications in the building industry, e.g., door and window profiles, water distribution pipes, interior panellings, toilet fittings and fixtures, drain-ways, water storage tanks, waterproofing treatment, plumbing and sanitary fittings.
Plastics in the building industry were first introduced in the early fifties in West Germany in the form of door and window profiles. Since then, there has been a steep rise in the production of plastics. From a mere 3 million tonnes in 1955, it has touched 1000 million tonnes today. There are more than 10,000 different kinds of plastics marketed today and their performance abilities span those of every other known material from soft rubber to steel.
It is estimated that on an average 35 percent of the total plastic production in the world is used by the building industry. The current per capita consumption of plastics in the developed countries ranges from 50 to 100 kg., while in India, it is a mere 0.2 kg. There is, however, now and increasing awareness regarding the utilization of plastic as a useful building material in the country. Between 20 to 50 percent of plastic used in the domestic building industry is for piping systems and related products required for water supply storage and sanitary applications. A range of plastic sanitary fittings like taps, showers, flushing, gratings, basins, waste traps, float balls and valves, flushing cisterns and overhead water storage tanks, are now available. The se products are resistant to corrosion, light in weight easy in handling and installation and economical. They help in conserving cement, steel and non ferrous metals.
PVC and high density polyethylene are the two major thermoplastic materials used in the manufacture of piping systems for water supply and related applications. In India, rigid PVC (unplasticised) pipes upto 315 mm dia. and high density polyethylene pipes upto 400 mm dia. are produced alongwith matching fittings conforming to relevant Indian Standard specifications. Low density polyethylene overhead storage tanks of upto a capacity of 10,000 litres have been successfully produced and marketed in India. Plastic tanks are corrosion resistant and since these are light weight (a 10,000 litre polyethylene water tank would weights only 50 Kg.), their transportation and installation are much easier. There is certain lobby working against plastics and unfortunately, most of the governments, under their petroleum producing nations influence are trying to reduce the use of plastics.
A suitable replacement of timber could be found in sandwich type composite panels, using plastics foam as core and surfacing of conventional materials like aluminium, plywood, GRP, concrete and gypsum. These materials are lightweight and dimensionally stable, possess high strength to weight, ratio and excellent sound and thermal insulation, and incur low transportation and maintenance costs.
By mixing PVC with sawdust, a composite which can be easily extruded as doors and window frames and other profiles, has been developed. This has excellent dimensional stability and can be painted drilled and nailed like timber. Useful work has been carried out in the preparation of wood/plastic composites by high energy radiation induced polymerization. The se developments could go a long way towards finding appropriate substitutes of scarce primary species of timber.
Sand Lime Bricks
Autoclaved calcium silicate bricks popularly known as sand lime bricks were invented by Van Derburgh in England as far back as 1866. However, such bricks were first produced on a commercial scale only in 1898. Many buildings constructed with sand lime bricks in England, Germany, USA, USSR and Holland about 80 years ago are standing even today, indicating their excellent performance under natural weathering conditions.
The sand lime brick industry is well established in European and other countries. In our country, these bricks have yet to gain popularity due to their limited availability in the market. Sand lime brick is an alternate walling material which may overcome the shortage of ordinary clay bricks in the country. Particularly in the areas where good quality bricks are not being manufactured and sand or siliceous wastes like flyash or one tailings are available, calcium silicate brick can solve the problem of scarcity of good quality bricks as well as the disposal of wastes.
A calcium silicate brick consists of a uniform mixture of sand or a siliceous waste with a small proportion of mechanically pressed and autoclaved line, so that the materials are chemically bound by the action of steam under pressure. Such bricks are quite strong (compressive strength of kg/sq. cm. and can generally compare well in cost with conventional bricks in the aforesaid areas.
Flyash : Flyash is a fine residue obtained from thermal power stations using ground or powdered coal as boiler fuel. The thermal power stations in the country throw large quantities of flyash which goes as waste and causes environmental pollution. About 30 million tonnes of flyash is produced annually from 65 thermal power stations in the country. Flyash can be used in various ways in building construction. It could be utilized in the production of pozzolana cement, lightweight cellular concrete blocks, lime flyash bricks, clay bonded flyash bricks and sintered flyash lightweight aggregate. The level of utilization of flyash as a building material in the developed countries like USA and West Germany is about 70 percent of the total amount produced. In India, however, the level of utilization is a meagre 3.5 percent. Flyash has been utilized as partial replacement (upto 20 percent) of cement in concrete, mortar and plaster in a number of buildings.
CBRI has developed a technology for the production of clay bonded flyash bricks which have been found to be cheaper compared to burnt clay bricks. About 40 to 50 percent flyash is mixed uniformly under the process and the bricks are moulded and fired by the traditional method. The se bricks can be efficiently used for construction purposes.
Blast Furnace Slag : Blast furnace slag is the only industrial waste which has so far found the most accepted application. It is a waste product from steel plants. Presently, India produces more than 7.4 million tonnes of blast furnace slag out of which 3.5 million tonnes are being granulated for the manufacture of portland blast furnace slag cement the present production of which stands at around 3.15 million tonnes. Small quantities of blast furnace slag wool. It can also used for road construction and road repairs.
In addition to the manufacture of blast furnace slag cement, granulated slag can be utilized in the manufacture of super sulphated cement which possesses high sulphate resistance. Air cooled slag is suitable as an aggregate in concrete. Slag fines may be used as a substitute for sand without any deletrious effects. One of the important uses of foamed slag which is produced by rapid discharge and treated water jets, finds application in the manufacture of lightweight concrete with a bulk density of 800 to 950 kg/cu.m. The se foamed slag concrete blocks are used in load and non load bearing walls. While the potential for utilizing blast furnace slag for making foamed slag exists, field trials have yet to be undertaken. Moreover, the commercial production of blast furnace slag cement can be increased by increasing the granulation capacity of the slag at the steel plant itself.
Rice Husk : Rice Husk is obtained as a waste material from rice mills. Investigations have been undertaken with a view to utilizing this as a pozzolanic material. Technical know how has been developed and pilot plant trials carried out at various research institutions. In addition, it can also be used for making building blocks and boards with suitable binders. Plants with capacities of two five tonnes per day have been set up in the small scale sector in the rice producing States in the country for the production of rice husk pozzolana lime binder.
Coir Waste : The production of coconut waste in India is estimated to be 2.0 million tonnes. About 50 percent of the coconut is used for making coir mats/cushions, etc. The remaining raw material is mostly used a fuel. CBRI has developed a process for making corrugated roofing sheets utilizing coir waste or wood-wool waste and cement. These sheets are light and tough, and possess good bonding strength and thermal insulation properties. They are about 50 percent cheaper in comparison to asbestos cement sheets. So far, two entrepreneurs have been given licenses for the production of such sheets in India.
Strategy For Development Of New Building Materials
In order to step up the production of building materials considerably and to encourage the establishment of units for the production of a variety of building materials, the following suggestions may be considered:
1 As the building materials industry is largely in the private sector, financial support for setting up new production units as well as for expansion of the existing units should be provided by the Government and other financial institutions on more liberal terms.
2 Public sector construction agencies should provide encouragement for the establishment of new units for production of new alternate building materials, particularly those that utilize industrial and agricultural wastes by offering assured long range demands.
3 Facilities for test evaluation of raw materials and finished products should be provided in different parts of the country so that the suitability of the raw materials as well as quality of finished products could be easily ascertained.
4 For the promotion of new materials and products in the construction of buildings and housing projects emphasis is to be laid over undertaking experimental demonstration projects in different climatic regions in the country under the Experimental Housing Scheme of NBO to evaluate application advantages under fold trails for creating greater confidence in their use.
5 Research in production of different types of building materials from local raw material resources, particularly by utilization of industrial and agricultural wastes, needs to be considerably augmented. Funds for sponsoring research in specific projects should be made available. The setting up of a research institute by the Manufacturers Associations should be financially supported.
6 Specific attention should be given to the developed of the building materials industry for catering to the requirements of rural development.
Present R&D In Building Materials In India
One basic differences between the pattern of research in building materials in India and advanced countries such as USA Germany and the U.K. has been that, whereas in India only the Government research institutions have been responsible for all the work, right from science to technology transfer, the most remarkable breakthroughs in the area of building materials in other countries have been achieved by and industries and their R&D laboratories themselves. Today, in India also, research and development in cement paints, polymers, plastics and admixtures have now been taken up by the industry to a great extent, but there is almost none to even appreciate research needs in bricks, lime and timber products industries.
A major thrust in building materials research undertaken has been the on process development leading to new building materials. The impact of R&D work undertaken by the institute, however, does not appear to be very impressive in the context of the expected breakthrough in technology development. But, without taking a purely defensive position, it should be said that some of the main limitations in the work done are due to the following facts:
1 The chemistry and design development of plant and machinery leading to building materials manufacturing technology standards had taken a back seat, mainly due to lack of collaboration and engineering oriented laboratories.
2 The practice of very cautions and rather slow approach towards use of new materials and techniques in housing and building by the construction industry, which is often very much a contributing factor towards disappointment in utilization research, is seen.
Since the construction industry in not concerned with the production of building materials, adoption of any new technology has been hindered by the question of who should who take the initiative first the chemical industry, or the construction industry. Moreover, the industries producing burnt clay brick, lime and pozzolana, have never been categorized industries and have, therefore, been totally neglected in planned development programmes of the nation.
1 Alternate building materials such as flyash and sand lime bricks hold great promise as future building materials for satisfying the construction needs of the country.
2 Considering that as much as 50 percent of the total expenditure on national plan accounts goes into construction and two thirds of it is the cost of building materials, it is imperative that advanced planning for augmenting the production of building materials be undertaken.
3 The scarcity of building materials and their high costs have hampered many construction projects, necessitating heavy investment of capital in construction consequently adversely affecting development programmes. To remedy this situation, the development of the building material industry should be undertaken on a priority basis, perhaps one plan ahead of the construction programmes envisaged in the successive plan. Greater emphasis needs to be given to the growth of such industries which utilize local raw material resources for producing
by AK LALL
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