Substitutes or Alternatives of Bricks used for Construction in India!
According to one study, our country needs about 60 billion bricks every year and if no suitable substitute is found out, this would exhaust about 1600 x 106 kN of clay fields or other agricultural land annually.
It will thus make barren about 3000 hectares of fertile land. The extent of damage that will be caused can be imagined with the demand for bricks required by the construction industry rising continuously due to tremendous need for housing, growing population, etc. It will also lead to the erosion of fertile soil, degradation of soil and disturbance in ecology.
The Indian construction industry has felt the need to search for an appropriate alternative to the bricks mainly for the following reasons:
(i) High wastage during transportation;
(ii) High water absorption of bricks;
(iii) Inconsistency in size of bricks;
(iv) Increasing cost of kiln fuel;
(v) Unavailability of skilled labour; etc.
It is possible to produce at present a variety of bricks from the materials other than clay and the bricks so produced can be grouped in the following three categories:
(1) Concrete blocks
(2) Fly-ash bricks
(3) Sand-lime or calcium silicate bricks.
Each of these category will now be briefly described. It may be mentioned that it is possible to produce these products in adequate quantities and perhaps even of better quality than demanded by the building industry.
The materials required for the production of the concrete blocks are aggregates, cements and water.
The aggregates of various types have been used with varying degree of success and they include crushed stones, gravel, volcanic cinders, foamed slag, furnace clinker, etc. The aggregates are selected by considering the weight, texture or composition of the unit designed. The strength, texture and economy of the concrete block depend upon the careful grading of the aggregate. If locally available aggregate is suitable, it will help in achieving the economy.
The cement used is ordinary Portland cement. The water required is the normal potable water.
The fully automatic plants are available for the manufacture of high strength concrete blocks. These automatic machines produce superior quality concrete blocks. But they involve a large capital investment.
The manually operated machines are also available and they can be installed at project site itself which further reduce the transportation cost of the concrete blocks from the place of production to the place of actual use.
The processes involved in the manufacturing of the concrete blocks are as follows:
(i) Selection and Proportion of Ingredients:
The main criteria for the selection of the ingredients is the desired strength of the block. The greater the proportion of coarse aggregate, the greater will be the strength of the quantity of cement used.
(ii) Mixing of Ingredients:
The blending of aggregates, cement and water should be done very carefully. The mixing should preferably take place in a mechanical mixer. For hand mixing, extreme care should be taken to see that the cement and aggregates are first mixed thoroughly in dry state and the water is then added gradually.
(iii) Placing and Vibration:
The mixed concrete material is fed into the mould box upto the top level and it is ensured that the box is evenly filled. The vibration of concrete is done till it has uniformly settled in the mould box.
The block is watered after about one day of casting and it is continued for a minimum of 7 days and preferably till 28 days. The longer the curing period, the better will be the block.
The use of concrete blocks as a masonry unit can be observed on many construction sites because of the following advantages:
(i) It increases the carpet area of the building because of small width of concrete block as compared to the brick masonry wall.
(ii) It provides better thermal insulation, enhanced fire resistance and sound absorption.
(iii) It results in the saving of precious agricultural land which is used for the manufacture of bricks.
(iv) The blocks can be prepared in such a manner that the vertical joints can be staggered automatically and thus the skilled supervision is reduced.
(v) The construction of concrete block masonry is easier, faster and stronger than the brick masonry.
(vi) The perfect shape and size of the concrete block makes the work of a mason much simpler.
(vii) There is saving in construction of mortar because the numbers of joints are reduced.
(viii) The utility can be further increased by producing the Reinforced Concrete Block (RCB) masonry units. The blocks are provided two holes for placing suitable reinforcing bars and the structure with RCB units could safely resist wind and earthquakes, if so designed. The traditional beams and columns can be completely eliminated and the structure with RCB units can be given a better appearance.
In view of the advantages, the concrete block masonry technique of construction can be adopted on a large scale for mass housing and various civil engineering projects.
The fly-ash bricks are promising alternative to the conventional bricks.
The autoclaved calcium silicate bricks popularly known as the 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. The Bureau of Indian Standards code IS:4139:1989 deals with various aspects of these bricks.
Following raw materials are required for the preparation of the sand-lime bricks:
The percentage of sand in sand-lime bricks varies from 88 to 92 per cent. Hence the properties of sand-lime bricks are mainly governed by the characteristics of sand. For getting sand-lime bricks of good quality, the sand should be well-graded and it should be free from impurities such as clays, organic matter, rock minerals, soluble salts, etc.
The finely divided clay, if present in very small amount of less than 4 per cent, affords advantages of easier pressing, densification and smoother texture.
The percentage of lime in sand-lime bricks varies from 8% to 12%. The lime should be of a high calcium lime of good quality. It should neither be over-burnt nor under-burnt.
The water containing soluble salt or organic matter in excess of 0.25% should not be used for the preparation of sand-lime bricks. The sea water is unfit for the manufacture of sand-lime bricks.
To make coloured sand-lime bricks, suitable colouring pigment should be added in the mixture of sand and lime. The quantity of pigment varies from 0.2 to 3 per cent of the total weight of the brick.
Table 4-6 shows pigments for getting sand-lime bricks of different colours.
Following is the procedure of manufacturing sand-lime bricks:
(i) The sand, lime and pigment are taken in suitable proportions and they are thoroughly mixed with 3 to 5 per cent of water.
(ii) The material is then moulded in the shape of bricks in a specially designed rotary table press under mechanical pressure. The material is in a semi-dry condition and the pressure varies from 31.50 to 63 N/mm2.
(iii) The bricks are then placed in a closed chamber and subjected to saturated steam pressure of about 0.85 to 1.60 N/mm2 for 6 to 12 hours. This process is known as the autoclaving or hydrothermal treatment. An autoclave is a steel cylinder with tightly sealed ends. Its diameter and length are respectively as 2 m and 20 m.
The interaction between lime and sand is greatly speeded up by the rising temperature in the presence of high humidity. The silica of sand and calcium of lime along with water react to form a crystal like compound known as the calcium hydrosilicate. Hence these bricks are known as the calcium silicate bricks.
(iv) The bricks are taken out of chamber and they can then be dispatched for use.
Following are the advantages of sand-lime bricks:
(i) If plaster is to be provided on sand-lime bricks, the quantity of mortar required will be less as bricks are uniform in size and shape.
(ii) The calcium silicate products are available in brick, block and tile forms. They thus permit wider uses in housing and building construction.
(iii) The masonry work of these bricks offers the architects considerable flexibility to produce complex shapes, intricate designs and different surface finishes giving a pleasant visual effect.
(iv) The raw materials of these bricks do not contain any soluble salt. Hence the trouble of efflorescence does not arise.
(v) These bricks are hard and strong with compressive strength of about 10 N/mm2. It is possible to have multi-storeyed buildings with load bearing walls by using these bricks. The resistance to the seismic force, if any, can also be made by providing suitable reinforcement.
(vi) These bricks are uniform in colour and texture.
(vii) These bricks can be prepared where clay is scarce. In other words, the adoption of these bricks relieves pressure on the agricultural land.
(viii) These bricks have accurate size and shape with straight edges and true rectangular faces.
(ix) These bricks have better water repellant properties and noise reduction coefficients and they grant protection from fire.
(x) These bricks possess white colour with smooth finish and it helps in reducing effect of solar heat on exposed walls.
(xi) These bricks present a clean appearance and hence the plastering may be avoided.
(xii) The use of coloured sand-lime bricks offers permanent finish to the walls without extra cost.
(xiii) The wastage of calcium silicate products is less, say within one per cent or so.
Following are the disadvantages of sand-lime bricks:
(i) These bricks are not suitable for furnace brickwork because they will disintegrate, if exposed to heat for a long time.
(ii) These bricks are weak in offering resistance to the abrasion. Hence they cannot be used as paving material.
(iii) These bricks cannot be used for foundation work as they are less water resistant than clay bricks.
(iv) Where suitable clay for the manufacture of clay bricks is available in plenty, these bricks will prove to be uneconomical.
Factors Reducing Cost of Construction:
However it may be noted that there is reduction in cost of construction to the extent of about 40 per cent due to various factors such as:
(i) Less wastage during handling and transportation,
(ii) Reduction in cost of maintenance and avoiding the provision of facia stones,
(iii) Reduction in cost of mortar as quantity of mortar required is less as compared to the conventional clay bricks,
(iv) Reduction in wall thickness because of higher compressive strength resulting in more carpet area for every room,
(v) Saving due to cost of plastering because of smooth finish, etc.
The sand-lime bricks are used for ornamental work and they can be used in place of ordinary clay bricks in building industry. Germany has more than 200 factories producing these bricks. The other countries in which the sand-lime brick industry is well established include U.K., Netherlands, Denmark, U.S.A., Canada, U.S.S.R., Switzerland, Poland, Romania, Czechoslovakia, Mongolia, Vietnam, Bulgaria, Finland, Chile, Kuwait, Egypt, Australia, South Africa and Middle East nations.
These bricks have not yet become popular in India except Kerala State where some structures are constructed by using these bricks. The large scale production of this type of building material has not been possible in our country due to the non-availability of high capacity press.