CONCRETE SAMPLES

Sampling Procedure: 

         A random sampling procedure is adopted to ensure that each concrete batch shall have a reasonable chance of being tested i.e., sampling is done to the entire period of concreting and cover all mixing units.

Frequency:

The minimum frequency of sampling of concrete of each grade shall be accordance with the following:

Quantity of concrete in the work (m3)	Number of samples
1-5	1
6-15	2
16-30	3
31-50	4
51 and above	4 Plus one additional sample for each additional 50 m3

Strength test of concrete (IS 456):

          Samples from fresh concrete shall be taken and cubes shall be made and tested at 28 days. The test strength shall be the average of the strength of 3 specimen. The individual variation should not be more than 15 percent (+15% or -15%) of the average.

Different Grades of Concrete -- Concrete Mix Design

Different grades of Concrete:

          Based on different concrete mix proportions (or) mix ratio’s, concrete mixer is divided into different grades. As per IS 456:2000, concrete mix design has the following mix proportions:

Type of Concrete	Concrete Grade	Mix Ratio (or) Proportion	Characteristic Compressive strength of Concrete @ 28 Days in N/mm2
Ordinary concrete	M5	1:5:10	5 N/mm2
	M7.5	1:4:8	7.5 N/mm2
	M10	1:3:6	10 N/mm2
	M15	1:2:4	15 N/mm2
	M20	1:1.5:3	20 N/mm2
Standard Concrete	M25	1:1:2	25 N/mm2
	M30	Design Mix	30 N/mm2
	M35	Design Mix	35 N/mm2
	M40	Design Mix	40 N/mm2
	M45	Design Mix	45 N/mm2
	M50	Design Mix	50 N/mm2
High Strength Concrete	M55	Design Mix	55 N/mm2
	M60	Design Mix	60 N/mm2
	M65	Design Mix	65 N/mm2
	M70	Design Mix	70 N/mm2

Note:-

In Example: M5

M represents "Mix"

5 represents the compressive strength achieved after 28 days of curing.

GRADES OF CONCRETE