E702.3
Designing Concrete Structures:
Acceptance of Concrete Compressive
Strength Test Results According to
ACI 318-19
ACI E702.3-21
Designing Concrete Structures: Acceptance of
Concrete Compressive Strength Test Results
According to ACI 318-19
Reported by ACI Committee E702
Kimberly Kramer, Chair
John Aidoo
Bryan Castles
Om Dixit
Claude Goguen
Todd Hawkinson
Carl Larosche
Lei Lou
Katelyn Low
William Rushing
Luke Snell*
Lawrence Taber
Jairo Uribe
Kari Yuers
*Primary author
ACI E702.3-21 Designing Concrete Structures: Acceptance of Concrete Compressive Strength Test Results
According to 318-19.
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Owner, design professional, and concrete repair contractor.
It is not intended to relieve the user of this guide of responsibility for a proper condition assessment and structural
evaluation of existing conditions, and for the specification of
concrete repair methods, materials, or practices by an experienced engineer/designer.
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ACI E702.3 Example Problem
Acceptance of Concrete Test Results
Luke M. Snell
Example Problem: Acceptance of Concrete Compressive Strength Test
Results According to ACI 318-19, “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 3500 psi at 28 days.
Given Information
Table 1 provides a set of 15 test results performed on 6 x 12 in. cylinders at 28 days.
Table 1
Test
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Cylinder 1 (psi)
4100
4320
4310
4420
4200
4250
3880
3570
3570
3780
3680
3300
3470
2770
3200
Cylinder 2 (psi)
4320
4190
4310
4380
4160
3810
4040
3680
3210
3780
2980
3740
3210
2750
3480
Assumptions
Sampling frequency is adequate; the minimum frequency is:
a. Once a day for a given class
b. Once for every 150 yd3
c. Once each 5000 ft2 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
Certified field-testing technicians performed the tests on the fresh
concrete
Certified laboratory technicians performed all required laboratory tests
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Reference
ACI 318, 26.12.2.1(a)
ACI 318R, 26.12.2.1(a)
ACI 318R, 26.12.2.1(a)
ACI 318R, 26.12.2.1(a)
ACI 318, 26.12.1.1(d)
ACI 318, 26.12.1.1(e)
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ACI E702.3 Example Problem
Acceptance of Concrete Test Results
Calculations
Reference
Concrete strength is considered satisfactory as long as averages of any three
ACI 318,
consecutive compressive strength test results (arithmetic average) remain above fc′ 26.12.3.1(a)(1)(2)
and as long as no individual strength test (ST) falls below fc′ by more than 500 psi
when fc′ is 5000 psi or less, or by more than 0.10fc′ when fc′ is greater than 5000 psi.
Determination of Compressive Strength
Strength test results calculation is the average strength of at least two 6 x 12 in. or
at least three 4 x 8 in. cylinder tests from the same batch tested at 28 days or at test ACI 318,
26.12.1.1(a)
age designated for determination of fc′.
For 6 x 12 in. cylinders:
Cylinder 1 + Cylinder 2 = Strength test result
2
•
Note: For 4 x 8 in. cylinders, the equation becomes:
•
Cylinder 1 + Cylinder 2 + Cylinder 3 = Strength test result
3
Strength Test Results
• Strength test No. 1:
4100 + 4320 = 4210
2
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
(psi)
4100
4320
4310
4420
4200
4250
3880
3570
3570
3780
3680
3300
3470
2770
3200
Cylinder 2
(psi)
4320
4190
4310
4380
4160
3810
4040
3680
3210
3780
2980
3740
3210
2750
3480
Strength Test
(ST) Result (psi)
4210
4255
4310
4400
4180
4030
3960
3625
3390
3780
3330
3520
3340
2760
3340
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Arithmetic Average of Strength Test Calculation
ACI 318,
26.12.3.1(a)(1)
ST1 + ST2 + ST3 = Arithmetic Average
3
Arithmetic Average of Strength Test Results
•
•
Using the first three strength test results:
4210 + 4255 + 4310 = 4258 psi
3
Thus, the arithmetic averages for the tests are shown (Table 3):
Table 3
Test
Cylinder 1
(psi)
1
4100
2
4320
3
4310
4
4420
5
4200
6
4250
7
3880
8
3570
9
3570
10
3780
11
3680
12
3300
13
3470
14
2770
15
3200
Cylinder 2
(psi)
4320
4190
4310
4380
4160
3810
4040
3680
3210
3780
2980
3740
3210
2750
3480
Strength Test
(ST) Results (psi)
4210
4255
4310
4400
4180
4030
3960
3625
3390
3780
3330
3520
3340
2760
3340
Arithmetic
Average (psi)
—
—
4258
4322
4297
4203
4057
3872
3658
3598
3500
3543
3397
3207
3147
Determination of Value to Verify Strength Test Results are Acceptable
Specified strength is 3500 psi; therefore, to be acceptable, no strength test result
can be below fc′ – 500, or 3500 – 500, which is equal to 3000 psi.
Each strength test (ST) result in Table 2 is to be compared to 3000 psi.
Test Results Evaluation
Determine if the arithmetic average of the strength test results fail to meet
satisfactory strength levels.
•
ACI 318,
26.12.3.1(a)(2)
Arithmetic averages (Table 3) for Tests 13, 14, and 15 are below fc′.
Strength test results (Table 2) for Test 14 are below 3000 psi (fc′ – 500).
Note: Test 9 has one cylinder test result below 3500 psi (3210 psi). The average
of the two cylinders tested is 3390 psi (the strength test result), which is above
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3000 psi, so the concrete is acceptable.
Test 11 has a cylinder test result of 2980 psi. The strength test result is 3330 psi,
so the concrete is acceptable.
ACI 318,
26.12.3.1(b)
Steps to be taken because the arithmetic averages were low (arithmetic average of
Tests 13, 14, and 15) and because the strength in the Test 14 strength test result
was below fc′ by more than 500 psi:
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, ASTM C31, and ASTM C39.
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 in the Area Represented by Test 14 Strength
Test Result
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:
a) In-place testing
b) Strength testing of cores, in extreme cases
ACI 318,
26.12.3.1(c)
ACI 318R,
26.12.6
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
the structure, they are of value primarily for comparisons within the same
structure, rather than as quantitative estimates of strength. In-place tests
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include probe penetration (ASTM C803), rebound hammer (ASTM C803), 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 fc′ by more than the limit allowed for acceptance (ASTM
C42).
• Concrete represented by cores is considered structurally adequate if
the average of the three cores equals or exceeds 85 percent of fc′ with
no single core being less than 75 percent of fc′.
• 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 318
Chapter 27 for the questionable portion.
ACI 318,
26.12.6.1(a)
ACI 318,
26.12.6.1(e)
ACI 318,
26.12.6.1(f)
ACI 318,
26.12.6.1(g)
Note: For fc′ of 3500 psi, the average core strength must exceed 85 percent of
3500, or 2975 psi. No single tested core can be below 75 percent of 3500 psi, or
2625 psi.
Conclusions:
1. Steps must be taken to increase the average of the strength results.
2. Concrete in the area represented by strength Test 14 must be investigated and
evaluated.
3. Concrete in all other areas (except concrete in Strength test areas number 14) is
considered to have met code requirements.
Additional Reading
•
•
•
•
•
ACI 214R-11—Guide to Evaluation of Strength Test Results of Concrete
ACI 228.1R-19—Report on Methods for Estimating In-Place 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-19—Strength Evaluation of Existing Concrete Buildings
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