30/06/2012
Let us look at the most ubiquitous actor in the building drama- THE BURNT CLAY BRICK. This tiny element of the building industry has for centuries, been most misunderstood. Today, the brick is considered a building material having universal application and standards. The sole determining factor is the crushing strength of the brick. However, the performance criterion around which the crushing strength has been formulated is often relegated to the background or has been long forgotten. Analyzing the established thumb rule for crushing strength throws up a contradiction. Since the soil bearing capacity of most soils is a mere 2 Kg. / sq.cm., then the reason for using bricks of crushing strengths of 150 to 200 Kg./ sq.cm. is open to question. It seems highly illogical to use material of such high strength when the soil that the building is to rest on is of a lower crushing strength.
Yet the practice of achieving high crushing strengths for bricks is correct for an entirely different reason. The rationale is very simple: the strength determining factor for the brick is a direct consequence of its surface requirements. To ensure non-erodability, clay must be burnt adequately. Suitable non-erodability is achieved when there is a crushing strength of above 150 Kg./sq. cm. If the strength achieved is lower, then the brick wall would require additional surface treatment such as cement plaster. In blocking off the natural porosity of the brick, one is confronted with the additional problem of having created a heat trap, apart from having used an unnecessary expensive material.
Another aspect of the brick that requires rationalizing is the size itself. There is a basic error in standardizing the size of a brick at 3"X 4.5'X 9" for the entire country. The physical aspect of clay and its content varies from region to region. In attempting to standardize this building element we are actually trying to standardize the quality of clay that the earth yields. This is clearly not possible and in order to obtain a standard product, set technological solutions such as High Draft Kilns are invented. This further leads to consumption of coke that aggravates the fragile ecological balance. However, the bricks of yesteryear were of excellent quality in terms of strength and surface requirements. This was because the clay of the region determined the thickness of the brick and the final decision was that of the potter working in that area.
Thin bricks used for masonry
The brick seems to be the most widely used walling component and the most misunderstood. The fundamental error in crushing strengths of bricks was discussed with a view to rationalize material use. Before going back to the brick and any possible alternatives, let us establish the criterion for good walling elements. It is a misnomer that walling elements require great strength. This first assumption is where the basic approach to materials really goes wrong. Walling elements must essentially be non-erodable and this must be the main criterion. Low thermal conductivity is the next priority as well as the least amount of consumption of "processed material". Economy, colour and texture as intrinsic elements are other criteria that must be met.
The high benchmark of load-bearing capacity for brick was established to ensure its non-erodability. It is also an established fact that the denser the burnt clay brick, the greater is the strength and non-erodability achieved. Conversely, greater density of bricks increases its thermal conductivity. This results in higher internal temperatures resulting in the vicious cycle of expensive cooling systems. The essential criterion of a good walling material thus seems to be a non-erodable surface and a lean back up material.
This brings us to the concept of surface engineering. This refers to the creation of a permanent, non-erodable surface diaphragm composed of waste material. Integration of this diaphragm with a lean back-up material like mud or fly ash enables a walling block with a non-erodable surface and a body with low thermal conductivity. This surface diaphragm can also be made in the form of a tile with a wedge that can be integrated with the body material in the mould while casting the walling block. Tiles can be used on both sides of blocks for a permanent finish on the interior and exterior.
