NETTCP Material Specifications 4 — Questions and Answers
Question 1: Which AASHTO soil classification group is generally considered unsuitable as a subgrade material without treatment?
- A-7-6 (Correct answer)
- A-1-a
- A-3
- A-2-4
Correct answer: A-7-6
A-7-6 soils are highly plastic clays with poor load-bearing characteristics and are generally unsuitable as subgrade without stabilization or replacement.
Question 2: For structural steel used in highway bridges, which ASTM grade is most commonly specified for rolled W-shapes?
- ASTM A709 Grade 50 (Correct answer)
- ASTM A36
- ASTM A514
- ASTM A572 Grade 65
Correct answer: ASTM A709 Grade 50
ASTM A709 Grade 50 is the bridge-specific structural steel specification most commonly used for rolled W-shapes in highway bridges.
Question 3: What is the purpose of specifying a maximum water-to-cementitious-material (w/cm) ratio in bridge concrete?
- To limit permeability and improve durability against chloride intrusion (Correct answer)
- To increase workability for placement
- To reduce the heat of hydration
- To lower the unit weight of concrete
Correct answer: To limit permeability and improve durability against chloride intrusion
A lower w/cm ratio reduces concrete permeability, limiting chloride ion penetration and protecting reinforcing steel from corrosion.
Question 4: According to AASHTO M 29, what is the standard specification for fine aggregate (sand) used in bituminous mixtures?
- It covers natural sand, manufactured sand, and screenings meeting specific gradation and quality requirements (Correct answer)
- It specifies only naturally occurring river sands
- It sets minimum angular particle requirements only
- It applies exclusively to recycled concrete aggregate fines
Correct answer: It covers natural sand, manufactured sand, and screenings meeting specific gradation and quality requirements
AASHTO M 29 covers fine aggregate from natural or manufactured sources used in asphalt mixtures, including gradation and quality limits.
Question 5: Fly ash used as a supplementary cementitious material in concrete must conform to which ASTM standard?
- ASTM C618 (Correct answer)
- ASTM C150
- ASTM C595
- ASTM C989
Correct answer: ASTM C618
ASTM C618 specifies requirements for natural pozzolans and fly ash used as supplementary cementitious materials in concrete.
Question 6: For highway guardrail, which ASTM specification covers the W-beam rail element material?
- ASTM A36 or A572 (Correct answer)
- ASTM A307
- ASTM A325
- ASTM A490
Correct answer: ASTM A36 or A572
W-beam guardrail is fabricated from steel meeting ASTM A36 or A572 requirements for structural carbon steel.
Question 7: What characteristic distinguishes a Superpave SP-12.5 mix designation from an SP-19 mix?
- SP-12.5 has a nominal maximum aggregate size of 12.5 mm versus 19 mm for SP-19 (Correct answer)
- SP-12.5 requires higher asphalt content than SP-19
- SP-19 is used only for surface courses while SP-12.5 is for base
- SP-12.5 uses a softer PG binder grade than SP-19
Correct answer: SP-12.5 has a nominal maximum aggregate size of 12.5 mm versus 19 mm for SP-19
The number in a Superpave mix designation (SP-12.5, SP-19) refers to the nominal maximum aggregate size in millimeters.
NETTCP Material Specifications 4
Which AASHTO soil classification group is generally considered unsuitable as a subgrade material without treatment?