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

GRADES OF CONCRETE

 Nominal Mix Concrete:

Grades of Concrete	Mix Ratio Cement:Sand:Aggregate	Compressive strength of 150 mm cube at 28 days cured MPa (N/mm2)     Psi
M5	1:5:10	5 Mpa	725 Psi
M7.5	1:4:8	7.5 Mpa	1087 Psi
M10	1:3:6	10 Mpa	1450 Psi
M15	1:2:4	15 Mpa	2175 Psi
M20	1:1.5:3	20 Mpa	2900 Psi
M25	1:1:2	25 Mpa	3625 Psi
M30 and above	Design Mix	30 Mpa	4350 Psi

Grades of Concrete as per IS 456:

Group	Grade Designation	Specified Characteristic Compressive strength of 150 mm cube at 28 days in 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	M60	60
	M65	65
	M70	70
	M75	75
	M80	80

Note:  

(1) M5 and M7.5 Grades may be used for lean concrete bases and simple foundations for masonry walls. These mixes need not be designed.

(2) Grades lower than M15 shall not be used in reinforcement concrete.

Different Grades of Concrete -- Concrete Mix Design