Concrete is the most widely used material for construction. Here we will be discussing about tit in full details. Reinforced cement concrete (Commonly designated as RCC) is provided with steel bars in the tension zone to take the tensile forces as the concrete is weak in tension.
To understand more about RCC we have to look at the basic ingredients and details about plain concrete that is the concrete without Steel bars as a reinforcement, after which we will be discussing more about the RCC.
Plain concrete:-
Concrete consists of mixture of various sizes of aggregates, cement, water and some other materials like admixtures which are blended together in a definite proportions and quantity. The cement acts as a binding material in concrete, and the aggregate are inert materials which acts as filler in the concrete to fill the voids. Cement in its dry state cannot act as a binding material, and therefore water must be added in order to make cement as a binding material.
Therefore the mixture of cement, water, aggregates (and admixtures if any) when allowed to cure forms a hard stone like material with good strength properties, and is used for various purposes in construction activities.
The hardening is caused by chemical reaction between water and the cement, which continuous for a long time, and consequently the concrete grows stronger with age.
Concrete making is not just mixing of ingredients required to produce it. It involves careful calculation of quantities of various ingredients to be added to produce the required strength. The final strength of the concrete is not the only criteria, it has to fulfill various requirements in fresh state also.
- The fresh concrete (in its non-hardened state, also called as plastic concrete) must be flow-able (which is defined by workability) and must be free from segregation and bleeding.
- The hardened concrete should be strong, durable, and impermeable, or it should have minimum dimensional changes.
Grades of concrete:-
Grade is one of the properties of hardened concrete. It signifies the strenght & load compressive load carrying ability.
In some construction (Like for example construction of a dam, or a bridge) very strong concrete ( that is concrete of very large strength) is required. But in some cases (like for example the construction of a compound for a house) low strength concrete is sufficient.
Hence this measurement of strength is usually done in the form of testing the compressive strength of concrete. Usually expressed as load taken by the concrete per unit area, mathematically its unit is N/mm2
One of the most important property of concrete is the compressive strength of concrete depends upon the age of concrete. In the initial stage, when the water is added to the mixture of cement and aggregate it will be having a less compressive strength and the compressive strength goes on increasing with the age of concrete.
Hence the compressive strength for the concrete is defined for 7 days 14 days, 21 days and 28 days. During the 28th day, The mix will attend nearly the maximum compressive strength and hence the compressive strength and 28 days is usually taken as the compressive strength of that particular mix of concrete.
The grade of concrete is usually designated by letter “M” followed by a number like:- M15, M20. M25 etc. Here M refers to mix and the number represents the characteristic compressive strength of 150X150X150 size cubes at 28th day.
Reinforced cement concrete (RCC):-
Concrete is strong in compression, its compressive strength as explained above ranges from 10N/mm2 i.e., M10 to modern days M80-M100 Grade like the one used in Bandra-worli sea link. Hence when compressive forces are applied the concrete can withstand it strongly. But this is not the case with the tensional forces. In a structure ( like a bridge, or a building, dam etc) not only compressional forces act but also tensional forces. The ability of the concrete to withStand the tensional forces is only 10% of that of what it can withstand compressional forces.
The solution to this problem is Steel bar or rods. Steel is strong in handling the tensional forces, but at the same time it is not as strong as concrete in handling the compressional forces. Therefore a wise usage of concrete in the compressional zone and steal in the tensional zone is what gives us the reinforced cement concrete commonly called as RCC.
There will be various types of steel bars based on their tensile strenght. Like for example the FE415 Bars. The strenght of reinforcing bars is measured by the tensile loads or the forces it can take. The mathematical expression for expressing the amount of tensile loads or the forces steel rods can take is again N/mm2.
Steel will be usually provided in the form of Steel rods, of varying diameter. The internal diameter of the Steel rod will be ranging from 10mm dia bars to 26-28 sometimes 30 mm dia bars.
These Steel will be provided on the tensile forces zone and they will be covered with concrete in the compression load acting zone.
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