CPII Material Testing 3 — Questions and Answers
Question 1: What does the term 'water-cement ratio' directly influence in concrete mix design?
- Workability only
- Strength and durability (Correct answer)
- Setting time only
- Aggregate gradation
Correct answer: Strength and durability
The water-cement ratio is the primary factor controlling concrete strength and durability — lower ratios produce stronger, more durable concrete.
Question 2: When performing a sieve analysis on fine aggregate, which sieve size defines the boundary between fine and coarse aggregate?
- No. 200 (0.075 mm)
- No. 100 (0.150 mm)
- No. 4 (4.75 mm) (Correct answer)
- 3/8 inch (9.5 mm)
Correct answer: No. 4 (4.75 mm)
The No. 4 (4.75 mm) sieve is the standard dividing line between fine aggregate (passing) and coarse aggregate (retained).
Question 3: A field density test using the sand cone method yields a wet density of 126 pcf and a field moisture of 8.5%. What is the dry density?
- 116.1 pcf (Correct answer)
- 134.5 pcf
- 117.5 pcf
- 126.0 pcf
Correct answer: 116.1 pcf
Dry density = wet density / (1 + moisture fraction) = 126 / 1.085 ≈ 116.1 pcf.
Question 4: What ASTM standard covers sampling freshly mixed concrete?
- ASTM C 138
- ASTM C 172 (Correct answer)
- ASTM C 31
- ASTM C 143
Correct answer: ASTM C 172
ASTM C 172 is the standard practice for sampling freshly mixed concrete from a truck or batch plant discharge.
Question 5: Which test determines the soundness of aggregate when exposed to freeze-thaw or wetting-and-drying cycles?
- Sodium or magnesium sulfate soundness test (Correct answer)
- Los Angeles abrasion test
- Cleanness value test
- Chip seal cohesion test
Correct answer: Sodium or magnesium sulfate soundness test
The sodium or magnesium sulfate soundness test simulates the deterioration effects of freeze-thaw cycles on aggregate by cycling immersion and oven drying.
Question 6: What is the minimum number of concrete cylinders typically cast per test set for standard acceptance testing?
- 1
- 2 (Correct answer)
- 3
- 4
Correct answer: 2
A minimum of two cylinders are cast per test set — one is broken at 28 days and one serves as a hold or early-break specimen.
Question 7: For asphalt pavement, the term 'voids in the mineral aggregate' (VMA) refers to:
- Air voids between coarse aggregate particles only
- Total void space between aggregate particles including air voids and asphalt binder (Correct answer)
- The percentage of fines passing the No. 200 sieve
- Voids created by poor compaction effort
Correct answer: Total void space between aggregate particles including air voids and asphalt binder
VMA is the intergranular void space among the aggregate particles in a compacted paving mixture, including spaces filled with air and asphalt binder.
CPII Material Testing 3
What does the term 'water-cement ratio' directly influence in concrete mix design?