0Cement Concrete
| Cement |
Predetermined proportions.
|
| Fine Aggregate | |
| Coarse Aggregate | |
| Water |
When water is added, chemical reaction will occur, which is very much slow and requires time (setting time) and favourable temperature for its completion,
This setting time can be divided into 3 distinct phases known as:
| Initial set | 30-60 minutes |
| Final set | 5-6 hours) |
| Progressive hardening (increase in strength) |
|
Concrete has enough strength in compression but has little strength in tension, so obviously concrete is weak in Bending, Shear and Torsion.
So, to use Cement Concrete in structures which will be having tensile loads (Beams, Slabs etc.) steel bars may be placed at tensile zones of the structure.
The steel bars (steel reinforcement) takes the tensile stresses & Concrete so obtained is known as reinforced cement concrete (R.C.C)
Grades of concrete:
IS 456:2000 specifies 15 grades of concrete.
|
Group |
Grade Designation | Specified characteristic compressive strength of 150 mm cube at 28 days (N/mm2) |
|
Ordinary concrete | M10 | 10 |
| M15 | 15 | |
| M20 | 20 | |
|
Standard Concrete | M25 | 25 |
| M30 | 30 | |
| M35 | 35 | |
| M40 | 40 | |
| M45 | 45 | |
| M50 | 50 | |
| M55 | 55 | |
|
High Strength Concrete | M60 | 60 |
| M65 | 65 | |
| M70 | 70 | |
| M75 | 75 | |
| M80 | 80 |
Letter M refers as the Mix and the number to the Specified Characteristic Strength ( ) of 150 mm cube at 28 days (in N/mm2).
Characteristic Strength:
i. It is the strength of the material below which not more than 5 % of the test results are expected to fall.
ii. As per IS 456:2000 minimum grade of concrete shall not be less than M 20 in RCC.
