ACI Concrete Materials & Mix Proportioning 3 — Questions and Answers
Question 1: What ASTM standard governs the specification requirements for normal Portland cement used in concrete?
- ASTM C150 (Correct answer)
- ASTM C494
- ASTM C33
- ASTM C231
Correct answer: ASTM C150
ASTM C150 is the Standard Specification for Portland Cement, covering all five types (I through V).
Question 2: In mix design, the 'fineness modulus' is a property of which concrete ingredient?
- Cement
- Water
- Aggregate (Correct answer)
- Chemical admixtures
Correct answer: Aggregate
Fineness modulus is an index number derived from sieve analysis of fine or coarse aggregate, indicating the average size of particles.
Question 3: Which admixture type is classified under ASTM C494 Type A?
- Air-entraining admixture
- Water-reducing admixture (Correct answer)
- Accelerating admixture
- Retarding admixture
Correct answer: Water-reducing admixture
ASTM C494 Type A admixtures are water reducers that reduce the water requirement of concrete without changing set time.
Question 4: What effect does increasing the nominal maximum aggregate size have on the water requirement of a concrete mix?
- Water requirement increases
- Water requirement decreases (Correct answer)
- Water requirement is unaffected
- Water requirement doubles
Correct answer: Water requirement decreases
Larger maximum aggregate size reduces the total surface area of aggregate, requiring less water (and cement) to achieve the same workability.
Question 5: Ground granulated blast-furnace slag (GGBFS) is classified as which type of supplementary cementitious material?
- Pozzolan only
- Latent hydraulic binder (Correct answer)
- Inert filler
- Chemical accelerator
Correct answer: Latent hydraulic binder
GGBFS is a latent hydraulic binder that reacts with water in the presence of an alkali activator (calcium hydroxide from cement hydration) to form cementitious products.
Question 6: ACI 211.1 recommends selecting the water-cement ratio based primarily on which two criteria?
- Color and texture requirements
- Required strength and durability exposure conditions (Correct answer)
- Aggregate type and cement brand
- Mixing time and placement method
Correct answer: Required strength and durability exposure conditions
ACI 211.1 selects w/c ratio based on the required compressive strength and the durability demands of the exposure environment, using the more restrictive value.
Question 7: What does 'absolute volume method' mean in ACI concrete mix design?
- Measuring ingredients by weight only
- Calculating the volume each ingredient occupies in a unit volume of concrete (Correct answer)
- Using volumetric mixers for batching
- Standardizing slump to a fixed absolute value
Correct answer: Calculating the volume each ingredient occupies in a unit volume of concrete
The absolute volume method calculates the solid volume each material (cement, water, aggregates, air) contributes so they sum to exactly 1 cubic yard or cubic meter of concrete.
ACI Concrete Materials & Mix Proportioning 3
What ASTM standard governs the specification requirements for normal Portland cement used in concrete?