E702.3M
Designing Concrete Structures:
Acceptance of Concrete Compressive
Strength Test Results According to
ACI 318M-14
ACI E702.3M-18
Designing Concrete Structures: Acceptance of
Concrete Compressive Strength Test Results
According to ACI 318M-14
Reported by ACI Committee E702
Kimberly Kramer, Chair
John Aidoo
Bryan Castles
Om Dixit
Claude Goguen
Todd Hawkinson
Carl Larosche
Lei Lou
William Rushing
Luke Snell*
Lawrence Taber
Jairo Uribe
Kari Yuers
*Primary author
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ACI E702.3M-18 Designing Concrete Structures: Acceptance of Concrete Compressive Strength Test Results
According to 318M-14.
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concrete repair methods, materials, or practices by an experienced engineer/designer.
1
ACI E702.3 Example Problem
Acceptance of Concrete Test Results
Example Problem: Acceptance of Concrete Compressive Strength
Test Results According to ACI 318-14M, “Building Code Requirements
for Structural Concrete and Commentary.”
Problem Statement
Evaluate if concrete is acceptable based on compressive strength cylinder test results. The project
specification states that the concrete compressive strength is required to be 24 MPa at 28 days.
Given Information
Table 1 provides a set of 15 test results performed on 150 x 300 mm cylinders at 28 days.
Table 1
Test
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Cylinder 1 (MPa)
28.27
29.79
29.72
30.47
28.96
29.30
26.75
24.61
24.61
26.06
25.37
22.75
23.92
19.10
22.06
Cylinder 2 (MPa)
29.79
28.89
29.72
30.20
28.68
26.27
27.85
25.37
22.13
26.06
20.55
25.79
22.13
18.96
23.99
Assumptions
Reference
Sampling frequency is adequate; the minimum frequency is:
a. Once a day for a given class
b. Once for every 110 m3
c. Once each 460 m2 of surface area for slabs or walls
Samples are taken on a random basis – concrete was not to be sampled
due to appearance, convenience, or other biased criteria
Each set of cylinders was cast from a different batch of concrete
No water was added to the concrete after the samples were taken
Qualified field testing technicians performed the tests on the fresh
concrete
Qualified laboratory technicians performed all required laboratory tests
ACI 318M, 26.12.2.1(a)
ACI 318MR, 26.12.2.1(a)
ACI 318MR, 26.12.2.1(a)
ACI 318MR, 26.12.2.1(a)
ACI 318M, 26.12.1.1(c)
ACI 318M, 26.12.1.1(d)
ACI E702.3 Example Problem
Acceptance of Concrete Test Results
Calculations
References
Concrete strength is considered to be satisfactory as long as averages of any three
consecutive compressive strength test results (Arithmetic Average) remain above
f’c and as long as no individual strength test (ST) falls below f’c by more than 3.5
MPa when f’c is 35 MPa or less, or by more than 0.10 f’c when f’c is greater than 35
MPa.
ACI 318M,
26.12.3.1(b)(1)(2)
Determination of Compressive Strength
Strength test results calculation is the average strength of two 150 x 300 mm or
three 100 x 200 mm cylinder tests from the same batch tested at 28 days or at test
age designated for determination of f’c.
For 150 x 300 mm cylinders:
•
Cylinder 1 + Cylinder 2 = Strength test result
2
Note: For 100 x 200 mm cylinders the equation becomes:
•
Cylinder 1 + Cylinder 2 + Cylinder 3 = Strength test result
3
Strength Test Results
• Strength test No. 1:
(28.27 + 29.79) / 2 = 29.0 MPa
The strength test results for each of the 15 tests are as shown (Table 2):
Table 2
Test
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Cylinder 1
(MPa)
Cylinder 2
(MPa)
28.27
29.79
29.72
30.47
28.96
29.30
26.75
24.61
24.61
26.06
25.37
22.75
23.92
19.10
22.06
29.79
28.89
29.72
30.20
28.68
26.27
27.85
25.37
22.13
26.06
20.55
25.79
22.13
18.96
23.99
Strength Test
Result (ST)
(MPa)
29.0
29.3
29.7
30.3
28.8
27.8
27.3
25.0
23.4
26.1
23.0
24.3
23.0
19.0
23.0
ACI 318M,
26.12.1.1(a)
Arithmetic Average of Strength Test Calculation
ACI 318M,
26.12.3.1(b)(1)
•
ST1 + ST2 + ST3 = Arithmetic Average
3
Arithmetic Average of Strength Test Results
•
Using the first three strength test results:
(29.0 + 29.3 + 29.7) / 3 = 29.4 MPa
Thus, the arithmetic averages for the tests are shown (Table 3) with each result
compared to f’c:
Table 3
Test
Cylinder 1
(MPa)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
28.27
29.79
29.72
30.47
28.96
29.30
26.75
24.61
24.61
26.06
25.37
22.75
23.92
19.10
22.06
Cylinder 2
(MPa)
29.79
28.89
29.72
30.20
28.68
26.27
27.85
25.37
22.13
26.06
20.55
25.79
22.13
18.96
23.99
Strength Test
Results (ST)
(MPa)
29.0
29.3
29.7
30.3
28.8
27.8
27.3
25.0
23.4
26.1
23.0
24.3
23.0
19.0
23.0
Arithmetic
Average
(MPa)
29.4
29.8
29.6
29.0
28.0
26.7
25.2
24.8
24.1
24.4
23.4
22.1
21.7
Determination of value to verify strength test results are acceptable:
Specified strength is 24 MPa therefore, to be acceptable, no strength test result can
be below f’c – 3.5 MPa, or 24 – 3.5, which is equal to 20.5 MPa.
Each Strength Test Result (ST) in Table 2 is to be compared to 20.5 MPa.
Test Results Evaluation
Determine if either the arithmetic average or the strength test results fail to meet
satisfactory strength levels.
•
Arithmetic averages (Table 3) for test numbers 13, 14, and 15 are below f’c.
ACI 318M,
26.12.3.1(b)(2)
•
Strength test results (Table 2) for test number 14 are below 20.5 MPa (f’c –
3.5). Individual cylinder test results that fall below required values are not
to be used in this evaluation.
Note: Test 9 has one cylinder test result below 24 MPa (22.1 MPa). The average of
the two cylinders tested is 23.4 MPa (the strength test result), which is above 20.5
MPa, so the concrete is acceptable.
ACI 318M,
26.12.3.1(c)
Test 11 has a cylinder test result of 20.5 MPa. The strength test result is 23.0 MPa,
so the concrete is acceptable.
Steps to be taken:
1. Increase Average of Strength Test Results
Steps to be taken will be dependent on circumstances and could include one or
more of the following:
• Increase in cementitious materials content
• Reduction in, or better control of, water content
• Use of a water-reducing admixture to improve the dispersion of
cementitious materials
• Other changes in mixture proportions
• Reduction in delivery time
• Closer control of air content
• Improvement in the quality of testing, including strict compliance with
ASTM C172/C172M, ASTM C31/C31M, and ASTM C39/C39M.
Note: Changes in operating procedures or small changes in cementitious
materials content or water content should not require a formal resubmission of
mixture proportions; however, changes in sources of cement, aggregates, or
admixtures need to be accompanied by evidence that the average strength level
will be improved.
2. Investigate Low Strength Results
When the strength test results fall below acceptable levels, steps are to be
taken to ensure that the structural adequacy of the structure is maintained.
• Building official should apply judgment as to the significance of the low test
results; however, lower strength may be tolerated under many
circumstances; this is a matter of judgment on the part of the licensed
design professional and building official.
• If further investigation is deemed necessary, the following methods of
investigation may be used:
In-place testing
Strength testing of cores, in extreme cases
Note: In-place tests of concrete may be useful in determining whether a portion
of the structure actually contains low-strength concrete. Unless these in-place
tests have been correlated with standard strength test results for the concrete in
ACI 318M,
26.12.3.1(d)
ACI 318MR,
26.12.4
the structure, they are of value primarily for comparisons within the same
structure, rather than as quantitative estimates of strength. In-place tests include
probe penetration (ASTM C803/C803M), rebound hammer (ASTM C803/C803M),
or pullout test (ASTM C900).
3. Determine if concrete is adequate using coring, if required
When coring is required, three cores are to be taken for each strength test
that falls below f’c by more than the limit allowed for acceptance (ASTM
C42/C42M).
• Concrete represented by cores is considered structurally adequate if
the average of the three cores equals or exceeds 85 percent f’c with no
single core being less than 75 percent of f’c.
• Additional core testing is permitted if the core compressive test results
are considered erratic.
• If additional core tests fail to meet required strength test levels and the
structural integrity remains in doubt, the responsible authority is
permitted to order a strength evaluation in accordance with ACI 318M
Chapter 27 for the questionable portion.
Note: For f’c of 24 MPa, the average core strength must exceed 85 percent of 24
MPa, or 20.4 MPa. No single tested core can be below 75 percent of 24 MPa, or
18.0 MPa.
Additional Reading
• ACI 214R-11––Guide to Evaluation of Strength Test Results of Concrete
• ACI 228.1R-03––In-Place Methods to Estimate Concrete Strength
• ACI 228.2R-13––Report on Nondestructive Test Methods for Evaluation of
Concrete in Structures
• ACI 301-16/301M-16––Specifications for Structural Concrete
• ACI 437R-03––Strength Evaluation of Existing Concrete Buildings
ACI 318M,
26.12.4.1(a)
ACI 318M,
26.12.4.1(d)
ACI 318M,
26.12.4.1(e)
ACI 318M,
26.12.4.1(f)