Acceptance Criteria of Concrete Cube as per IS 456:2000

 

1.  The acceptance criteria of concrete cube strength is governed by

IS 456:2000 – Plain and Reinforced Concrete (Code of Practice) and
IS 516:1959 – Method of Tests for Strength of Concrete.
 
The relevant clauses and tables referred in this article are:
• IS 456:2000 – Clause 15 (Strength of Concrete)
• IS 456:2000 – Clause 15.2.2 (Frequency of Sampling)
• IS 456:2000 – Clause 15.4 (Test Results of Concrete)
• IS 456:2000 – Table 11 (Acceptance Criteria of Compressive Strength)
• IS 516:1959 – Procedure for Compressive Strength Test of Concrete Cubes

Sampling of Cube Procedure

as per IS CODE 456:2000 Clause. 15.2.1 page-29

15.2.1 Sampling Procedure
We take concrete samples randomly, so every batch has a chance to be checked. Samples are taken different times and from all machines to make sure all concrete is good.
15.2.2 Frequency
The minimum frequency of sampling of concrete cube how many take sample concrete  quantity range follow the table.
Sr. no.	Quantity of Concrete In the work Cum	Number of Samples 1 Sample = 3 nos Cube	Number of cube in 7 Days	Number of cube 28 days	Total number of cube
1	1 to 5 Cum	1 Sample	3 Nos Cube	3 Nos Cube	6 Nos = 1 set
2	6 to 15 Cum	2 Sample	6 Nos Cube	6 Nos Cube	12 Nos = 2 set
3	16 to 30 Cum	3 Sample	9 Nos Cube	9 Nos Cube	18 Nos = 3 set
4	31 to 50 Cum	4 Sample	12 Nos Cube	12 Nos Cube	24 Nos = 4 set
5	51 to above	5 Sample	15 Nos Cube	15 Nos Cube	30 Nos = 5 set
6	Note :- Every 50 Cum plus 1 sample of cube
7	Note :-  Three cube  shall be made for each sample for testing 28 days
8	Note :-  Three cube  shall be made for each sample for testing 7 days
9	Note :-  Three cube  shall be made for each sample for testing 3 days ( If early required testing of cube )

Process of cube test

Concrete Cube Test Process.
Applied load of M25 Grade concrete Cube  680 (KN)
What is Kilonewton ( KN ) ?		What is Newton ( N ) ?
Kilonewton is a unit used to measure large force.		Newton is also a unit of force
1 Kilonewton ( KN )	=	1000 Newton ( N )
Difference In simple words
Unit	Meaning	Used For
Kilonewton (KN )	Large force	Building Loads, Structures Load etc.
Newton ( N )	Small force	Concrete cube test, material strength etc.
Applied load on Cube  680 (KN)		1 KN = 1000 N
Area of Cube 150 X 150 MM = 22,500 MM²
So, Load 680 KN = 680 X 1000 = 680000 N
Formula	( N/mm²  ) = load ( N )  ÷ Area ( mm² )
= 680000 N   ÷ 22,500 mm²
Say, 30.22 N/mm²  pass
Compressive strength of M25 Grade concrete Cube

Table 2 Grades of Concrete page no. 29

Designation of concrete M refer to Mix Design and Number Specified Compressive strength of 150 X 150 150 MM size cube at 28 days Expressed in  N/mm²

Table 2 Grades of Concrete page no. 29
(Clause 6.1, 9.2.2, 15.1.1 and 36.1 )
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
Clause 9.3 Nominal Mix
Nominal mix concrete may be used for concrete of M 20 or lower.

Assumed Standard Deviation

Table 8  Assumed Standard deviation page no. 23
(Clause 9.2.4.2,  and Table 11 )
Grade of Concrete	Assumed Standard deviation in  N/mm²	Target Strength of 150MM cube in N/mm²
M10	3.5	10 + ( 1.65 X 3.5) = 15.77 N/mm²
M15		15 + ( 1.65 X 3.5) = 20.77N/mm²
M20	4	20 + ( 1.65 X 4) = 26.60 N/mm²
M25		25 + ( 1.65 X 4) = 31.60 N/mm²
M30	5	30 + ( 1.65 X 5) =  38.25N/mm²
M35		35 + ( 1.65 X 5) = 43.25 N/mm²
M40		40 + ( 1.65 X 5) = 48.25 N/mm²
M45		45 + ( 1.65 X 5) = 53.25 N/mm²
M50		50 + ( 1.65 X 5) = 58.25 N/mm²

Acceptance Criteria of Concrete Cube Strength

as per IS CODE 456:2000 Clause. 16.1 page-29
Amendments 4 Revision May-2013
Table 11 Characteristic Compressive Strength
CRITERIA 1

Grade of Concrete M25
M Means Mix Design				25 Means 25 N/mm²
That is Called M25 Grade of concrete
Target strength use for design mix purpose
M25 + ( 1.65 X 4 ) = 31.6 N/mm²  At 28 days age
Example at 28 days test for M25 Grade 4 Cum quantity
Criteria 1
Set	Area of Cube in mm²  150 X 150MM	Compressive strength in N/mm²	Average strength in N/mm²	0.85 strength in N/mm²  ( .85 X 32.23 )	1.15 strength in N/mm²	Acceptance Criteria  25 + 4 = 29  N/mm²  ( minimum )
1	22500mm²	32.13	32.23  N/mm²	27.39  N/mm²	37.06  N/mm²	Cube pass both condition 1.Acceptance Criteria  25 + 4 = 29  N/mm²  ( minimum ) 2. more than ± 15 %  ( minimum 27.39 and maximum 37.06 all 3 cube are under the range )
	22500mm²	32.17
	22500mm²	31.86

CRITERIA 2

Example at 28 days test for M25 Grade 26 Cum quantity ( This criteria apply for below 30 cum concrete )
Criteria 2
Set	Area of Cube in mm²  150 X 150MM	Compressive strength in N/mm²	Average strength in N/mm²	0.85 strength in N/mm²  ( .85 X 32.23 )	1.15 strength in N/mm²	Acceptance Criteria  25 + 4 = 29  N/mm²  ( minimum ) Or individual fck - 2 N/mm²  25 - 2 =  23 N/mm²  minimum individual cube
1	22500mm²	31.50	31.27  N/mm²	26.57  N/mm²	35.95 N/mm²	31.27  N/mm²
	22500mm²	30.40
	22500mm²	31.90
2	22500mm²	30.90	30.87  N/mm²	26.23  N/mm²	35.49  N/mm²	30.87  N/mm²
	22500mm²	29.50
	22500mm²	32.20
3	22500mm²	30.80	30.50  N/mm²	25.92  N/mm²	35.07  N/mm²	30.50  N/mm²
	22500mm²	31.00
	22500mm²	29.70
Average of all						30.88  N/mm²
Note :-  All are cubes compressive strength within the limit + - 15% of average
Note :-  individual fck - 2 N/mm²  25 - 2 =  23 N/mm²  minimum not less than 23 N/mm²
Note :-  Acceptance Criteria  25 + 4 = 29  N/mm²  all cube average strength are above 29N/mm²
Accepted as  M25 GRADE

CRITERIA 3

Example at 28 days test for M25 Grade 65 Cum quantity ( This criteria apply for Above 30 cum concrete )
Criteria 3
Set	Area of Cube in mm²  150 X 150MM	Compressive strength in N/mm²	Average strength in N/mm²	0.85 strength in N/mm²  ( .85 X 32.23 )	1.15 strength in N/mm²	Acceptance Criteria  25 + ( .825 X 4 ) = 28.3  N/mm²  ( minimum ) Or individual fck - 3 N/mm²  25 - 3 =  23 N/mm²  minimum individual cube
1	22500mm²	31.50	31.27  N/mm²	26.57  N/mm²	35.95 N/mm²	31.27  N/mm²
	22500mm²	30.40
	22500mm²	31.90
2	22500mm²	30.90	30.87  N/mm²	26.23  N/mm²	35.49  N/mm²	30.87  N/mm²
	22500mm²	29.50
	22500mm²	32.20
3	22500mm²	30.80	30.50  N/mm²	25.92  N/mm²	35.07  N/mm²	30.50  N/mm²
	22500mm²	31.00
	22500mm²	29.70
4	22500mm²	29.90	30.57  N/mm²	25.98  N/mm²	35.15 N/mm²	31.27  N/mm²
	22500mm²	30.70
	22500mm²	31.10
5	22500mm²	30.80	31.27  N/mm²	26.57  N/mm²	35.95  N/mm²	30.87  N/mm²
	22500mm²	31.30
	22500mm²	31.70
6	22500mm²	32.10	31.17  N/mm²	26.49  N/mm²	35.84  N/mm²	30.50  N/mm²
	22500mm²	31.00
	22500mm²	30.40
Average of all						30.94  N/mm²
Note :-  All are cubes compressive strength within the limit + - 15% of average
Note :-  individual fck - 3 N/mm²  25 - 3 =  22 N/mm²  minimum not less than 22 N/mm²
Note :-  Acceptance Criteria  25 + ( .825 X  4 ) = 28.3  N/mm²  all cube average strength are above 29N/mm²
Accepted as  M25 GRADE

• Acceptance shall be based on the mean strength of a group of four

  consecutive test results AND the strength of individual cube results.

• The mean of 4 consecutive results shall be ≥ fck + 0.825 × standard deviation (σ).

• None of the individual cube results shall be less than (fck − 3 N/mm²).

Make test Report

as per IS CODE 516 Clause. 3.5.2
Cube Register

ID of cube	Discriptions of work	Grade	Quantity	Date of casting	7 days test date	28 days test date	Area of Cube in mm²  150 X 150MM	Weight of cube  grams	Strength  load (KN)	Compressive strength in N/mm²	Average strength in N/mm²
125	T-5 Ground Floor Column  Grid D-5	M-25	2.74 Cum	26-04-2025	03-05-2025		22500mm²	8286	519	23.06	22.91  N/mm²
							22500mm²	8319	502	22.31
							22500mm²	8331	526	23.37
						24-05-2025	22500mm²	8322	723	32.13	32.23  N/mm²
							22500mm²	8352	736	32.17
							22500mm²	8340	717	31.86

Witness Sign Contractor & Client
Remarks If any

Test Concrete cube

As per IS CODE 516 Clause. 3.1
If a test cube is broken or damaged, we do not test it.
If the cube inside honeycomb, it is not good.
If we still test a cube with honeycomb, we must write in the report that it had honeycomb.

Apparatus CTM Machine

As per IS CODE 516 Clause. 3.2
The test is done using a compression testing machine that follows (IS 14858)
the calibration shall be carried out at least once per year. Not later than that.
Relocation and major repair must be Re-calibration.
CTM machines are available in different load capacities, such as
1000 kN, 2000 kN, and 3000 kN
Types of CTM machines, Manual CTM, Semi-automatic CTM, Fully automatic / Digital CTM.

Age of cube test

As per IS CODE 516 Clause. 3.3
We check   the cement/concrete cube a certain age.
Most commonly check cube 7 days and 28 days old.
Some client check only 28 days old cube as project specifications.
We count the age from mix of water in dry raw material.

Number of cube

As per IS CODE 516-Part-1 Clause. 3.4
At least 3 cube (one sample) shall be tested at each selected age.

 

Procedure of cube
As per IS CODE 516 Clause. 3.5
Cube store in water  temperature  27°C ± 2°C
Wipe extra water from the cube before testing
Measure its size nearest 0.2 mm  150 X  150 X  150 MM
Weight before test weight cube 8.1KG  ( and as per design mix)
Test it within 2 hours after taking it out of water.

Loading of cube
As per IS CODE 516 Clause. 3.5.2
Load shall be applied 14 N/mm² per minutes
the maximum load indicated shall be recorded.
If one result is very different (more than ±15%), test again
If no extra sample is there, take the average of the two closest values.

Test of Specimens
Specimen means small size of concrete sample that is called Cube.
as per IS CODE 456:2000 Clause. 15.3 page-29
Testing of 28 days
Testing of 7 days
Testing of 3 days If Early required of Compressive strength of concrete.

Test result of sample
as per IS CODE 456:2000 Clause. 15.4 page-29
We test 3 cube take their average Strength. If any one cube is too high or too low  more than ± 15 % of the average. The test result invalid


Conclusion

Concrete cube compressive strength test is one of the most important quality control tests in concrete works. Acceptance of concrete should always be done strictly in accordance with IS 456:2000 to ensure safety, durability and performance of the structure

 

 

From Onsite XL