Acceptance criteria of cube By Santosh Shah

1. Acceptance Criteria of Cube
BY – SANTOSH SHAH

2. Reference IS 456-2000
Amendment-1(June-2001)
Amendment-2 (September 2005)
Amendment-3 (August 2007)
Amendment-4 (May 2013)
Amendment-5 (July 2019)

3. CHARACTERISTIC STRENGTH
 Characteristic Strength :
As the strength of the
material below which
not more than 5% of the
test result are expected
to fall.
The Gaussian Distribution Curve or
The Normal Distribution curve

4.  In IS 456 – 2000 there was two clause in Table 11. 1st M -15 and 2nd is
M-20 and above. But in Amendment 4 there is only 1 clause M -15
and above. Old table was replaced by new table.
IS 456-2000 Amendment 4

5.  SPECIMEN : If we fill a cube at site 150 X 150 X
150cm for finding out the compressive strength at
28 days then this is called specimen.
 SAMPLE : If you fill three cube then this three
cubes makes a sample. 1 sample is equal to 3
cube.
 Clause 15.3 Test specimen : Three test specimens
shall be made for each sample.

6.  GROUP : Suppose we take 10 sample now take any 4 sample to create group
(1 TO 4) or (5 to 8) . Minimum requirement to create group is 4 sample.
 NON OVERLAPPING : (3 to 6) is overlapping and (1 to 4) or (5 to 8) non
overlapping.
4 Sample = 1 Group
2 31 4 65 7 98 10
3 54 6
OVERLAPPING
NON OVERLAPPING NON OVERLAPPING
2 31 4 65 7 8

7. Clause 15.4 : Test Result of Sample
The test results of the sample shall
be the average of the strength of
three specimens. The individual
variation should not be more than
± 15 percent of the average. If
more, the test result of the sample
are invalid.
Shift Cube
test
results
Average
fav
0.85
fav
1.15
fav
Acceptance
N/mm2(Min)
(M-25)
N/mm2 N/mm2 N/mm2 N/mm2
1. 19, 26,
16
20.3 17.3 23.3 Rejected due to:
Variation in strength
cubes 26 and 16 are out
of range +/-15% of
average
2. 24, 32,
28
28.0 23.8 32.2 Av = 28.0
All the cubes strength are
within +15% of average.

8. Clause 15.2.2 : Frequency
The minimum frequency
of sampling of concrete
of each grade shall be in
accordance with the
following:
Quantity of concrete in the work, m3 No 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 or part
thereof
 NOTE: At least one sample shall be taken from each shift where
concrete is produced at continuous production unit, such as
ready-mixed concrete plant, frequency of sampling may be
agreed upon mutually by suppliers and purchasers.

9. BELL CURVE
Relation between fck and fcm
The characteristic compressive
strength fck refers to the value in
the X-axis beneath 5% of the
total area under the curve falls.
As illusted in the figure, the value of
fck remains underneath fcm by an
amount identical to 1.65𝛔. Where 𝛔
denotes the standard deviation of
the normal distribution. So
fcm = fck + 1.65𝛔
Where,
fcm = mean strength
fck = compressive strength
𝛔 = standard deviation

10. Table 8 Assumed Standard
Deviation ( Clause 9.2.4.2 and
Table 11)
Table 8 Assumed Standard Deviation
(Clause 9.2.4.2 and Table 11)
Grade of
Concrete
Assumed Standard
Deviation
N/mm2
M 10
} 3.5
M 15
M 20
} 4
M 25
M 30
} 5
M 35
M 40
M 45
M 50
M 55
M 60
NOTES
1 The above values correspond to the site
control having proper storage of cement; weigh
batching of all materials; controlled addition of
water; regular checking of all materials,
aggregate grading and moisture content; and
periodical checking of workability and strength.
Where there is deviation from the above, the
values given in the above table shall be
increased by 1 N/mm2
2 For grades above M 60, the standard
deviation shall be established by actual trials
based on assumed proportions, before finalizing
the mix.

11. Acceptance Criteria
ACCEPTANCE CRITERIA
Compressive strength
 The concrete shall be deemed to comply with the strength
requirement when both the following conditions are met:
a) The mean strength determined from any group of four non-
overlapping consecutive test results, complies with the appropriate
limits col. 2 of Table 11.
b) Any individual test result complies with the appropriate limits in col. 3
Table 11.

12. Acceptance Criteria
Characteristic compressive strength compliance requirement IS: 456-2000 with amendments
Table 11 (Clause 16.1 and 16.3)
NOTE 1: In the absence of established value of standard deviation, the values given in Table 8 (IS: 456-
2000) may be assumed, and attempt should be made to obtained results of 30 samples as early as
possible to establish the value of standard deviation.
NOTE 2: For concrete quantity up to 30 m3 (where the number of samples to be taken is less than four) as
per frequency of sampling given in 15.2.2, the mean of test results of all such samples shall be fck + 4
N/mm2, minimum and the requirement of minimum individual test results shall be fck – 2 N/mm2,
minimum. However, when the number of samples is only one as per 15.2.2, the requirement shall be fck +
4 N/mm2, minimum.

13. Acceptance Criteria
Individual test :
( ≥ fck – 3 N/mm2)
IS Code says that any sample cannot be accepted whose fck value is
less than 3 that means if you test for M-30, the value is less then 27
(avg.) then you can reject it.
Mean of Group of 4 non overlapping consecutive test :
Fgm ≥ fck + 0.825 X σ
or Whichever is greater
Fck + 3
}

14.  Incase 4 sample not formed
In this case the code has given rider that fck + 3 will be
replaced by fck + 4 (Less than 30cum)
The mean of the test results of all such samples shall be fck + 4
N/mm2
Incase of Individual :
Replace fck – 3 by fck – 2 (Less than 30cum)
This will be apply only if you don’t have sample to create a group.
In case of only one sample i.e for small work between 1 to 5 cum
then fck – 3 it will replace by fck + 4