One looking forward to own a building usually has a demand and that is on concrete used in the construction being of the best quality. And best quality usually means that the concrete be of the strongest variety.
But how do we define strength of concrete and how to choose the best variety that suits our requirement? Most often we feel that it is the domain of a civil engineer to comprehend these issues and all one can do is to rely on their ‘expert' advice?
Construction material expert Dr. L.H. Rao says there is a need for better public awareness about the various aspects of construction. Safety and durability of buildings can be ensured only when there is a strong public awareness about the laid guidelines and rigorous quality checks are in place during the construction.
“It is not difficult to choose the type of concrete that suits our requirement and all one has to do is to follow the guidelines laid down by the Government of India,” Dr. Rao, a technical advisor at JSW Cements, says.
According to the construction code stipulated under Indian Standard code of practice, IS 456: 2000, the concrete is graded according to its strength and the weather that a building has to endure.
Depending on their strength and durability, concretes are graded from M-10 to M-80, the higher the grade, higher the durability, Dr.Rao says.
Concrete with a grade of M-30 and above is known as high strength concretes and is used for high rise buildings. Concretes with grades M-60 and above are known as special concretes and are used in specialised and custom made constructions, he explains.
But what does the notation M-10 stands for? “For grading concrete as M-10, it has to gain strength of 100 kg per centimetre square in 28 days. Similarly, M-15 should gain a strength of 150 kg per centimetre and M-20 about 200 kg per centimetre square,” he points out.
The code also divides the type of weather that the concrete has to face into five categories: Mild, Moderate, Severe, Very Severe and Extreme, and each type of weather require different types of concrete or additional mixers that have to be used.
While IS 456: 2000 defines code of practice for plain and reinforced concretes, IS 10262: 1999 specifies the procedures that have to be followed while mixing the concrete, Dr. Rao says.
There are standards set for almost all procedures that have to be followed, right from selecting a required concrete grade, mixing the concrete and the type of curing that one has to undertake and a building will have a better life when the guidelines are followed.
“It is a common feature to see construction workers and masons mixing concrete without much of supervision.
But for creating durable concrete structures, one has to not only look into supervising part seriously, a contractor or engineer also has to see various other factors like type of cement used, maximum cement-water ratio that should be used and even the maximum temperature of the concrete at the time of construction,” he explains.
Indian Standard codes IS 456: 2000 and IS 10262: 1999 are the definitive guides for a civil engineer and the problem of lack of quality in some buildings is because the provisions delineated in these documents are not followed properly during construction, Dr.Rao adds.
