CCI Concrete Testing & Evaluation 3 — Questions and Answers
Question 1: The Windsor probe test is used to estimate which concrete property non-destructively?
- Flexural strength
- Air content
- In-place compressive strength (Correct answer)
- Modulus of elasticity
Correct answer: In-place compressive strength
The Windsor probe system estimates in-place compressive strength by measuring the penetration depth of a hardened steel probe driven by a powder-actuated driver.
Question 2: According to ASTM C805, rebound hammer readings should be taken at a minimum of how many points on a test area to get a valid average?
- 5 readings
- 10 readings (Correct answer)
- 15 readings
- 20 readings
Correct answer: 10 readings
ASTM C805 requires a minimum of 10 rebound readings per test area, discarding any that differ from the median by more than 6 units.
Question 3: Carbonation of concrete surface affects rebound hammer readings by causing them to be:
- Lower than actual strength
- Higher than actual strength (Correct answer)
- Unaffected
- Completely unreliable regardless of depth
Correct answer: Higher than actual strength
Surface carbonation hardens the concrete surface layer, causing the hammer to read higher than the actual bulk compressive strength of the element.
Question 4: When cores are taken to evaluate structural concrete strength per ACI 318, what is the minimum number of cores required per location of concern?
- 1 core
- 2 cores
- 3 cores (Correct answer)
- 5 cores
Correct answer: 3 cores
ACI 318 requires a minimum of three cores per questionable location; the concrete is considered adequate if the average of three cores ≥ 0.85f'c and no single core < 0.75f'c.
Question 5: What correction factor is applied to a concrete core with a length-to-diameter (L/D) ratio of 1.75 when converting to the equivalent standard cylinder strength?
- No correction needed — L/D of 1.75 is standard
- Multiply by a factor less than 1.0 (Correct answer)
- Multiply by a factor greater than 1.0
- The test is invalid at this L/D ratio
Correct answer: Multiply by a factor less than 1.0
Cores with L/D below 2.0 require a correction factor less than 1.0 per ASTM C42, as shorter specimens register higher apparent strength than standard 2:1 cylinders.
Question 6: The pullout test method for in-place concrete strength measurement is governed by which ASTM standard?
- ASTM C803
- ASTM C900 (Correct answer)
- ASTM C1074
- ASTM C1202
Correct answer: ASTM C900
ASTM C900 covers the pullout strength of hardened concrete by measuring the force required to pull a pre-inserted or post-installed insert from the concrete.
Question 7: Chloride ion permeability of hardened concrete is quantified in coulombs using which ASTM test?
- ASTM C642
- ASTM C1202 (Correct answer)
- ASTM C597
- ASTM C876
Correct answer: ASTM C1202
ASTM C1202 (Rapid Chloride Permeability Test) measures the electrical charge passed through a 2-inch concrete disc over 6 hours to assess chloride ion penetrability.
CCI Concrete Testing & Evaluation 3
The Windsor probe test is used to estimate which concrete property non-destructively?