CPII Material Testing 5 — Questions and Answers
Question 1: Which ASTM standard covers the Standard Specification for Concrete Aggregates?
- ASTM C 150
- ASTM C 33 (Correct answer)
- ASTM C 39
- ASTM C 94
Correct answer: ASTM C 33
ASTM C 33 specifies requirements for fine and coarse aggregates for use in portland cement concrete.
Question 2: A compaction test result shows 94% relative compaction. The project specification requires 95%. What should the inspector do?
- Accept the material since 94% is within normal testing variability
- Require the contractor to recompact and retest the failing area (Correct answer)
- Average the failing test with adjacent passing tests
- Report the result only if three consecutive tests fail
Correct answer: Require the contractor to recompact and retest the failing area
When a compaction test fails specification requirements, the contractor must recompact the failing area and pass a retest before work can proceed.
Question 3: What characteristic does the California Bearing Ratio (CBR) test measure?
- The hydraulic conductivity of subgrade soils
- The load-bearing strength of subgrade relative to a standard crushed rock (Correct answer)
- The plasticity index of fine-grained soils
- The swell potential of expansive clay subgrades
Correct answer: The load-bearing strength of subgrade relative to a standard crushed rock
CBR measures the load-bearing capacity of a subgrade soil by comparing the force required to penetrate it with the force required to penetrate standard crushed California limestone.
Question 4: Viscosity grading of asphalt binders was largely replaced by which modern grading system?
- Marshall stability grading
- Superpave Performance Grading (PG) system (Correct answer)
- Hveem stabilometer grading
- AASHTO empirical grading
Correct answer: Superpave Performance Grading (PG) system
The Superpave Performance Grading system replaced AC and AR viscosity grades, specifying asphalt binder performance over the actual temperature range at the project location.
Question 5: What does a 'plastic limit' value represent in soil classification?
- The moisture content below which soil crumbles when rolled into 1/8-inch threads (Correct answer)
- The moisture content at which soil changes from plastic to liquid behavior
- The maximum moisture content allowed for compaction operations
- The bearing capacity threshold for cohesive subgrade soils
Correct answer: The moisture content below which soil crumbles when rolled into 1/8-inch threads
The plastic limit is the moisture content below which a soil behaves as a semi-solid and crumbles when attempting to roll it into 1/8-inch diameter threads.
Question 6: When testing freshly mixed concrete, the air content measured by the pressure meter method (ASTM C 231) is applicable to:
- All concrete mixes including lightweight aggregate concrete
- Normal weight concrete only — not lightweight aggregate concrete (Correct answer)
- Concrete with w/c ratios above 0.50 only
- Concrete placed in cold weather conditions only
Correct answer: Normal weight concrete only — not lightweight aggregate concrete
ASTM C 231 (pressure method) applies only to normal weight concrete; porous lightweight aggregates absorb pressure and give inaccurate readings requiring the volumetric method (ASTM C 173).
Question 7: A pipe joint leakage test requires maintaining 4.0 psi for 15 minutes with no drop. The gauge reads 4.0 psi at start and 3.6 psi at 15 minutes. The correct conclusion is:
- The joint passes because the drop is within equipment calibration tolerance
- The joint fails and must be repaired and retested (Correct answer)
- The joint passes if the average pressure over 15 minutes exceeds 4.0 psi
- No conclusion can be drawn without also measuring flow rate
Correct answer: The joint fails and must be repaired and retested
Any pressure drop below the specified minimum during the required hold time constitutes a failure; the joint must be repaired and retested until it maintains pressure.
CPII Material Testing 5
Which ASTM standard covers the Standard Specification for Concrete Aggregates?