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Under ASTM C39/C39M, what is the specified loading rate for testing hardened concrete cylinders during the second half of the anticipated loading phase?

35 ± 7 psi/s (0.25 ± 0.05 MPa/s)

15 ± 5 psi/s (0.10 ± 0.03 MPa/s)

60 ± 10 psi/s (0.40 ± 0.07 MPa/s)

100 ± 20 psi/s (0.70 ± 0.14 MPa/s)

to track

2026 Statistics

Key Facts: ACI Strength Testing Exam

5 yrs

Certification Validity

ACI

70%

Passing Score

60% min per section

~40

Written Exam Questions

1 hour, closed-book

ASTM Standards Tested

C39, C78, C617, C1231

$360

Typical Exam Fee

ACI chapters

CP-19

Official Workbook

25th Edition

The ACI Concrete Strength Testing Technician certification is a laboratory credential covering ASTM C39 (compressive), C78 (flexural), C617 (sulfur capping), and C1231 (unbonded caps). Candidates must pass a closed-book 1-hour written exam (~40 MC) with 70% overall and 60% per section, plus a hands-on performance exam. Certification is valid 5 years. Fees run about $360 for the complete exam at most ACI local chapters.

Sample ACI Strength Testing Practice Questions

Try these sample questions to test your ACI Strength Testing exam readiness. Each question includes a detailed explanation. Start the interactive quiz above for the full 100+ question experience with AI tutoring.

1Under ASTM C39/C39M, what is the specified loading rate for testing hardened concrete cylinders during the second half of the anticipated loading phase?

A.35 ± 7 psi/s (0.25 ± 0.05 MPa/s)

B.15 ± 5 psi/s (0.10 ± 0.03 MPa/s)

C.60 ± 10 psi/s (0.40 ± 0.07 MPa/s)

D.100 ± 20 psi/s (0.70 ± 0.14 MPa/s)

Explanation: ASTM C39/C39M specifies a loading rate of 35 ± 7 psi/s (0.25 ± 0.05 MPa/s) applied continuously and without shock during the second half of the anticipated loading phase. A higher rate is permitted in the first half so long as the load is controlled at the specified rate near failure.

2A 6 in. × 12 in. concrete cylinder tested per ASTM C39 fails at a maximum load of 113,100 lbf. What is the compressive strength, rounded to the nearest 10 psi?

A.4,000 psi

B.3,140 psi

C.5,020 psi

D.4,500 psi

Explanation: Compressive strength f'c = P / A. The cross-sectional area of a 6 in. cylinder is π × (3)² = 28.27 in². f'c = 113,100 / 28.27 ≈ 4,001 psi, which rounds to 4,000 psi. ASTM C39 requires reporting to the nearest 10 psi.

3In ASTM C39/C39M, a fracture pattern described as 'reasonably well-formed cones on both ends, less than 1 in. of cracking through caps' corresponds to which fracture type?

A.Type 1

B.Type 2

C.Type 3

D.Type 4

Explanation: Type 1 fractures are reasonably well-formed cones on both ends, with less than 1 in. (25 mm) of cracking through caps. This is the classic 'double cone' failure and typically indicates a well-capped, properly loaded specimen.

4Per ASTM C39/C39M, if a tested cylinder has a length-to-diameter (L/D) ratio of 1.75, which correction factor must be applied to the calculated compressive strength?

A.0.98

B.0.96

C.0.93

D.0.87

Explanation: ASTM C39/C39M Table 1 specifies correction factors for L/D ratios ≤ 1.75 on drilled cores or trimmed cylinders: L/D = 1.75 → 0.98, 1.50 → 0.96, 1.25 → 0.93, 1.00 → 0.87. The corrected strength is the calculated strength multiplied by the factor. Interpolation is used for intermediate values.

5ASTM C39 requires that the diameter of a cylindrical specimen be determined to the nearest _____ by averaging two diameters measured at right angles to each other at about mid-height of the specimen.

A.0.01 in. (0.25 mm)

B.0.1 in. (2.5 mm)

C.0.001 in. (0.025 mm)

D.1/16 in. (1.6 mm)

Explanation: Per ASTM C39/C39M, the diameter is measured to the nearest 0.01 in. (0.25 mm) by averaging two diameters measured at right angles at mid-height. This diameter is used to compute the cross-sectional area for the strength calculation.

6When is a diameter measurement of every individual cylinder required by ASTM C39, rather than measuring only one cylinder per lot?

A.When the difference in diameters of a randomly selected specimen within a lot is more than 2% of the average diameter

B.When cylinders are tested above 6,000 psi

C.When sulfur caps are used

D.When the specimens are larger than 4 in. in diameter

Explanation: ASTM C39/C39M allows the average diameter of a lot to be used if the difference between any two cylinders of the same lot is within 2% of the average diameter; otherwise every individual cylinder must be measured. Molds meeting ASTM C470 and produced from the same batch typically satisfy this requirement.

7According to ASTM C39/C39M, the ends of a specimen that are not plane within _____ shall be sawed, ground, or capped prior to testing.

A.0.002 in. (0.050 mm)

B.0.005 in. (0.13 mm)

C.0.010 in. (0.25 mm)

D.0.020 in. (0.50 mm)

Explanation: ASTM C39 requires that the ends of compression specimens be plane within 0.002 in. (0.050 mm). Ends that exceed this tolerance must be sawed, ground, or capped per ASTM C617 or C1231 before testing.

8Per ASTM C39/C39M, the perpendicularity of the ends of a concrete cylinder to its axis shall not depart by more than what tolerance?

A.0.5° (approximately 1/8 in. in 12 in.)

B.1.0° (approximately 1/4 in. in 12 in.)

C.2.0° (approximately 1/2 in. in 12 in.)

D.0.1° (approximately 1/32 in. in 12 in.)

Explanation: ASTM C39/C39M requires that the ends of a compression specimen not depart from perpendicularity to the axis by more than 0.5° (approximately 1/8 in. in 12 in., or about 3 mm in 300 mm). Excessive perpendicularity errors can reduce measured strength.

9A 4 in. × 8 in. cylinder fractures at 56,550 lbf. Calculate the compressive strength to the nearest 10 psi.

A.4,500 psi

B.1,770 psi

C.9,000 psi

D.5,650 psi

Explanation: Area = π × (2)² = 12.566 in². f'c = 56,550 / 12.566 ≈ 4,500 psi. ASTM C39 requires strength to be reported to the nearest 10 psi (0.1 MPa).

10Which of the following is NOT permitted to be reported as the age of a specimen in ASTM C39/C39M?

A.Age based only on when the specimen was removed from the mold

B.Age from the time water was added to the mix

C.Age from the time cement was added to the mix

D.Age counted in days with fractional part for remolded specimens

Explanation: ASTM C39 requires that the age of the specimen be computed from the time water or cement (whichever is first) was added to the mix. It is not acceptable to use the time of demolding as the age, because curing begins at the moment of mixing.

About the ACI Strength Testing Exam

ACI laboratory certification for technicians performing compressive, flexural, and related strength testing of hardened concrete. Required by ASTM C1077 and IBC for acceptance-testing labs.

Assessment

Closed-book written exam (~40 multiple-choice, 1 hour) plus a performance exam demonstrating ASTM C39, C78, C617, and C1231 procedures

Time Limit

1 hour (written) + performance exam

Passing Score

70% overall, 60% minimum per section

Exam Fee

$360 (complete exam only; $210 written-only, $250 performance-only at most ACI chapters) (American Concrete Institute)

ACI Strength Testing Exam Content Outline

35%

ASTM C39 — Compressive Strength of Cylindrical Concrete Specimens

Loading rate 35 ± 7 psi/s, fracture types 1–6, L/D correction factors, end tolerances, machine verification

20%

ASTM C78 — Flexural Strength (Third-Point Loading)

Modulus of rupture R = PL/bd², middle-third rule, 3Pa/bd² formula, span = 3× depth, reporting to 5 psi

20%

ASTM C617 — Capping Cylindrical Specimens with Sulfur Mortar

Cap planeness 0.002 in., 2-hr (<5000 psi) / 16-hr (≥5000 psi) hardening, cap thickness limits, capping plate QC

15%

ASTM C1231 — Unbonded (Neoprene) Caps

Shore A durometer 50/60/70 strength ranges, pad reuse limits, retainer ring dimensions, pad inspection

10%

General Lab Practice (ASTM C1077 / ACI 318)

Laboratory accreditation, machine verification per ASTM E4, record retention, ACI 318 acceptance criteria

How to Pass the ACI Strength Testing Exam

What You Need to Know

Passing score: 70% overall, 60% minimum per section
Assessment: Closed-book written exam (~40 multiple-choice, 1 hour) plus a performance exam demonstrating ASTM C39, C78, C617, and C1231 procedures
Time limit: 1 hour (written) + performance exam
Exam fee: $360 (complete exam only; $210 written-only, $250 performance-only at most ACI chapters)

Keys to Passing

Complete 500+ practice questions
Score 80%+ consistently before scheduling
Focus on highest-weighted sections
Use our AI tutor for tough concepts

ACI Strength Testing Study Tips from Top Performers

1Memorize ASTM C39 loading rate (35 ± 7 psi/s, so 28-42 psi/s) — heavily tested

2Memorize the L/D correction factor table: 1.75→0.98, 1.50→0.96, 1.25→0.93, 1.00→0.87

3Know all 6 C39 fracture types by description (Type 1 cones both ends; Type 5/6 common with unbonded caps)

4Master C617 cap thickness (1/4 in. avg, max 5/16 in.) and hardening times (2 hr < 5000 psi, 16 hr ≥ 5000 psi)

5Know C1231 Shore A pad hardness vs. strength: 50 duro → 1500-6000 psi, 60 duro → 2500-7000 psi

6Practice the C78 modulus of rupture formulas: PL/bd² (middle third), 3Pa/bd² (within 5% outside)

7Review CP-19, 25th Edition — ACI writes the exam directly from this workbook

Frequently Asked Questions

What does the ACI Concrete Strength Testing Technician certification cover?

The credential covers four ASTM practices for laboratory strength testing of hardened concrete: C39/C39M (compressive strength of cylinders), C78/C78M (flexural strength by third-point loading), C617/C617M (sulfur mortar capping), and C1231/C1231M (unbonded neoprene caps). It does not cover field sampling — that is the Concrete Field Testing Technician Grade I credential.

What is the ACI Concrete Strength Testing Technician exam format?

The exam has two parts. The written exam is closed-book, one hour long, and contains approximately 40 multiple-choice questions, with at least eight questions on each of the four ASTM practices and test methods. The performance exam requires the candidate to physically demonstrate C39, C78, C617, and C1231 procedures on actual equipment in front of an examiner.

What is the passing score for the ACI Strength Testing exam?

To pass, candidates need at least 70% overall on the written exam AND at least 60% on each individual ASTM practice/test method section. A candidate who scores 85% overall but only 55% on C617 would still fail. The performance exam is pass/fail — examinees must correctly complete every required step of each procedure.

How much does the ACI Concrete Strength Testing Technician exam cost in 2026?

Fees are set by local ACI sponsoring groups. Most chapters charge around $360 for the complete written + performance exam, $210 for written-only, and $250 for performance-only. Full prep packages including CP-19 workbook and a review workshop can run $460–$560.

How long is ACI Concrete Strength Testing certification valid?

The credential is valid for five years from the date of successful completion of both the written and performance exams. To maintain certification beyond five years, technicians must retake both exams — there is no continuing education renewal path.

What are the prerequisites for the ACI Strength Testing exam?

There are no formal prerequisites. Anyone can register and sit for the exam. However, realistic preparation assumes hands-on familiarity with compression machines, flexural beam test fixtures, sulfur capping equipment, and neoprene pad retainers — typical for lab technicians or QC staff.

What is the best way to prepare for the ACI Strength Testing Technician exam?

Study ACI CP-19, 25th Edition (Technician Workbook for ACI Certification of Concrete Strength Testing Technician). It contains program information, the four ASTM practices, study questions, performance checklists, and a sample exam. Supplement with practice MC questions focused on loading rates, LTD correction factors, planeness tolerances, Shore A durometer ranges, and fracture type definitions — all heavily tested on the written exam.