CCIL Concrete Compressive Strength Testing 4 — Questions and Answers
Question 1: What is the maximum number of uses permitted for a neoprene pad cap before it must be retired per ASTM C1231?
- 25 uses
- 50 uses (Correct answer)
- 100 uses
- 200 uses
Correct answer: 50 uses
ASTM C1231 limits neoprene pad caps to a maximum of 100 uses; however, pads must be inspected after each test and discarded if they show excessive wear.
Question 2: A concrete cylinder breaks with a Type 5 fracture pattern (side fracture at top or bottom). What does this likely indicate?
- Excellent load distribution and uniform specimen quality
- Poor end condition or misalignment of the loading platen (Correct answer)
- The concrete achieved higher than expected strength
- The specimen was over-consolidated during casting
Correct answer: Poor end condition or misalignment of the loading platen
Type 5 fractures typically result from poor end conditions, eccentric loading, or platen misalignment causing stress concentration at the specimen end.
Question 3: What is the required standard curing temperature range for concrete cylinders in the moist curing room or water storage tank per ASTM C31?
- 15°C ± 2°C (59°F ± 3.6°F)
- 23°C ± 2°C (73°F ± 3.6°F) (Correct answer)
- 20°C ± 3°C (68°F ± 5.4°F)
- 27°C ± 2°C (81°F ± 3.6°F)
Correct answer: 23°C ± 2°C (73°F ± 3.6°F)
ASTM C31 specifies standard moist curing at 23°C ± 2°C (73°F ± 3.6°F) in the curing room or water tank.
Question 4: When reporting compressive strength results per ASTM C39, to what nearest value should the result be rounded?
- Nearest 1 psi (0.01 MPa)
- Nearest 5 psi (0.05 MPa)
- Nearest 10 psi (0.1 MPa) (Correct answer)
- Nearest 50 psi (0.5 MPa)
Correct answer: Nearest 10 psi (0.1 MPa)
ASTM C39 requires compressive strength results to be reported to the nearest 10 psi (0.1 MPa).
Question 5: Which information is NOT required to be reported with compressive strength test results per ASTM C39?
- Specimen diameter and length
- Type of fracture pattern
- Name of the concrete mix designer (Correct answer)
- Age of the specimen at time of test
Correct answer: Name of the concrete mix designer
The mix designer's name is not a required data element in ASTM C39 reporting; specimen geometry, fracture pattern, and test age are required.
Question 6: What effect does testing a concrete cylinder in a wet or saturated condition have on measured compressive strength compared to testing it in a dry condition?
- Wet testing increases strength by 10 to 15%
- Wet testing reduces strength by approximately 10 to 15% (Correct answer)
- Wet testing has no significant effect on strength results
- Wet testing doubles the coefficient of variation
Correct answer: Wet testing reduces strength by approximately 10 to 15%
Saturated concrete typically yields compressive strengths 10 to 15% lower than oven-dried concrete due to reduced internal friction and lubrication of crack planes.
Question 7: Under ASTM C39, what maximum variation in diameter is allowed along the length of a concrete cylinder before it is considered non-conforming?
- 0.25 mm (0.01 in)
- 0.5 mm (0.02 in) (Correct answer)
- 1.0 mm (0.04 in)
- 2.0 mm (0.08 in)
Correct answer: 0.5 mm (0.02 in)
ASTM C39 requires that the diameter not vary by more than 0.5 mm (0.02 in) along the length of the specimen.
CCIL Concrete Compressive Strength Testing 4
What is the maximum number of uses permitted for a neoprene pad cap before it must be retired per ASTM C1231?