ACI Concrete Strength Testing Technician

ACI Concrete Strength Testing Technician Practice Exam Questions And Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

1. The primary purpose of concrete strength testing is to determine:

• Workability
• Durability
• Compressive strength compliance
• Air content

Correct Answer: C

Rationale: Concrete strength testing verifies whether the concrete meets

specified compressive strength requirements.

• Which ASTM standard governs compressive strength testing of

concrete cylinders?

A. ASTM C31

B. ASTM C39 1 / 4

C. ASTM C39

D. ASTM C42

Correct Answer: C

Rationale: ASTM C39 outlines procedures for compressive strength testing

of cylindrical concrete specimens.

3. ASTM C31 primarily addresses:

• Testing hardened concrete
• Strength calculation
• Making and curing concrete test specimens
• Core sampling

Correct Answer: C

Rationale: ASTM C31 covers proper molding, curing, and handling of

concrete test specimens.

4. Standard concrete test cylinders are typically:

• 4 in. × 6 in.
• 6 in. × 6 in.
• 6 in. × 12 in.
• 8 in. × 16 in. 2 / 4

Correct Answer: C

Rationale: The most common cylinder size for strength testing is 6 inches in

diameter and 12 inches in height.

5. The standard curing temperature for concrete cylinders is:

A. 10–20°C

B. 23 ± 2°C (73 ± 4°F)

C. 30–35°C

• Ambient air temperature

Correct Answer: B

Rationale: ASTM standards require controlled curing at approximately

23°C for accurate strength results.

6. The minimum number of layers for rodding a 6 × 12 in. cylinder is:

• 1
• 2
• 3
• 4

Correct Answer: C

Rationale: Cylinders are filled in three equal layers when using rodding for

consolidation.

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7. Each layer of a 6 × 12 in. cylinder must be rodded:

• 10 times
• 15 times
• 25 times
• 30 times

Correct Answer: C

Rationale: ASTM C31 requires 25 rod penetrations per layer for proper

consolidation.

8. When internal vibration is used, the vibrator should:

• Touch the mold sides
• Remain in one spot
• Be inserted vertically and withdrawn slowly
• Be used continuously

Correct Answer: C

Rationale: Proper vibration minimizes air voids without causing

segregation.

9. Over-vibration of concrete can cause:

• Increased strength
• Segregation and bleeding
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