Assess the Quality of Concrete to Ensure a Strong Home
The strength of your home depends on the quality of the concrete your builder uses for construction. Concrete is the essential building material used for structural elements like pillars, slabs and footing of a home. Read through the article to know about certain features and requirements of concrete for home construction.
As we all know, concrete is a mixture of cement, water, sand and aggregates. It is an excellent construction material having easy mouldability, long durability, and high compressive strength. Here are some details on the strength of the concrete.
Grades and types of concrete
The strength of the concrete is termed by grade. The grade reflects the compressive strength which is the characteristic strength of concrete after 28 days. It is depicted by a letter M followed by a number. For instance, if the grade of the concrete is said to be M20, it means that the concrete mix (M) has a compressive strength of 20 N/mm2. Various grades of concrete are used for different applications in home constructions.
Different types of concrete including ordinary, standard and high strength concrete include use of various grades. Ordinary concrete includes grades of M10, M15 and M20. The standard ones include M25, M30, M35, M40, M45, M50, and M55. The high strength concrete includes M60 and M80 grades. Generally M10 and M15 grades of concrete are used for leveling course, and bedding for footings. Standard concrete and concrete of grade M20 is applicable for Reinforced Cement Concrete (RCC) works for slabs, beams, columns and so on. The high strength concrete has its applications for high rise buildings.
The proportion of the materials in the concrete mix also varies for different applications. For instance, a proportion of 1:2:4 (1 part of cement, 2 parts of sand, and 4 parts of aggregates) is used for footings of pillars and raft foundations. It is even used for RCC works in lintel shelves and other small works. The quantity of water required for this proportion per bag of cement (50 kg) is about 30 liters. However, for RCC work in beams, pillars, walls and others, a proportion of 1:1.5:3 is used which requires about 25 liters of water per bag of cement.
Quality of concrete
The stress applied on the concrete footings, pillars, and slabs affects the strength of the building. Therefore you should not compromise on the quality of concrete or materials used for these key elements. The quality of concrete depends on the quality of cement, sand, aggregates and water used in the mixture.
Good quality cement is greenish gray in color without any lumps or dust. You should feel a cool finish when a pinch of cement is rubbed between your fingers. Coming to sand, it should be free of grass, leaves, and other foreign organic matter. Too much clay and silt content of the sand also affects its quality.
The other component of concrete is aggregates. Clay or dirt coating on the aggregates prevents the adhesion of cement to aggregates. This in turn slows down the setting and hardening process, reducing the strength of concrete. Therefore ensure that quality aggregates are used. Good quality aggregates are dense, inert, hard and durable. They are capable of maintaining well bonding with the cement paste. Grades of aggregates are expressed in terms of BIS test no. 480, 240, 120, 60, 30 and 15.
Here are some features of quality aggregates that you should check.
They should be angular but not flat. Mud and other impurities should not be there. They also must not contain marks of layers of any other color. As the components of concrete are mixed by water, it is necessary to even use good quality water for mixing. It should be clean and fresh. It should be devoid of dirt and unwanted chemicals as they affect the strength of concrete.
Factors affecting quality of concrete
The quality of concrete also depends on the way of its mixing, placing, compacting, finishing and curing. Also, it is just not enough to use quality elements; they should also be added in proper proportions. The water-cement ratio is another factor which affects the strength of concrete. It is the ratio of minimum quantity of water to the weight of cement required for desirable consistency and workability of concrete mix. With increase in this ratio, the added water once evaporated leaves behind small voids. This weakens the concrete in turn. So, the strength of concrete decreases with increase in water-cement ratio.
Assessing the quality of concrete
However, it is not possible for a common man to know or check the quality of concrete prepared at the construction site. Only a construction supervisor can know its quality by certain compression and slump test methods. However, these days ready mix concrete is being used for construction which reduces the labor force and the chances of errors in quality concrete. Many manufacturers provide ready mix and reinforced cement concrete tested for quality at laboratories and sent to the site.
Ask your builder or contractor to make sure that concrete is tested before usage.