ACI Certification Concrete Mix Design 2 — Questions and Answers
Question 1: What does the fineness modulus (FM) of fine aggregate indicate?
- The percentage of material passing the No. 200 sieve
- An index of the overall coarseness or fineness of the aggregate (Correct answer)
- The specific gravity of sand
- The absorption capacity of fine aggregate
Correct answer: An index of the overall coarseness or fineness of the aggregate
FM is computed by summing cumulative percentages retained on a specified series of sieves and dividing by 100; higher values denote coarser material.
Question 2: According to ACI 211.1, as the fineness modulus (FM) of fine aggregate increases, the recommended bulk volume of coarse aggregate per unit volume of concrete:
- Decreases
- Remains the same regardless of FM
- Increases (Correct answer)
- Drops to zero
Correct answer: Increases
Coarser fine aggregate (higher FM) has fewer small particles, allowing a greater volume of coarse aggregate while still maintaining adequate workability.
Question 3: What is the primary purpose of preparing trial batches during concrete mix design?
- To verify that the calculated mix proportions meet specified requirements under actual conditions (Correct answer)
- To determine the unit weight of aggregate alone
- To establish the compressive strength of neat cement paste
- To calculate the water absorption of aggregates
Correct answer: To verify that the calculated mix proportions meet specified requirements under actual conditions
Trial batches confirm that calculated proportions achieve required fresh properties (slump, air content) and hardened strength before full-scale production.
Question 4: Which ACI document provides the standard practice for selecting proportions for normal, heavyweight, and mass concrete?
- ACI 318
- ACI 301
- ACI 211.1 (Correct answer)
- ACI 305R
Correct answer: ACI 211.1
ACI 211.1, 'Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete,' provides the absolute volume method for mix design.
Question 5: The saturated surface-dry (SSD) condition of aggregate is used as the reference state in mix design because:
- It requires no moisture correction to batch water calculations (Correct answer)
- It requires the most additional water to be added
- It represents the driest possible state of aggregate
- It eliminates the need to measure aggregate specific gravity
Correct answer: It requires no moisture correction to batch water calculations
Aggregate at SSD neither absorbs water from nor contributes free water to the mix, making it the ideal baseline for calculating batch proportions.
Question 6: In concrete production, 'batch weights' refer to:
- The weight of cement only in one batch
- The weight of mixing water per batch
- The actual quantities of all ingredients loaded into the mixer for one production batch (Correct answer)
- The weight of one cubic yard of hardened concrete
Correct answer: The actual quantities of all ingredients loaded into the mixer for one production batch
Batch weights are the plant-ready quantities of cement, water, aggregates, and admixtures used to produce one mixer load of concrete.
Question 7: According to ACI 318, the maximum w/cm ratio for concrete subjected to deicing chemicals (severe freezing-and-thawing exposure) is:
- 0.50
- 0.45
- 0.40 (Correct answer)
- 0.55
Correct answer: 0.40
ACI 318 limits w/cm to 0.40 for severe freezing-and-thawing exposure involving deicing chemicals to minimize concrete permeability and deterioration.
ACI Certification Concrete Mix Design 2
What does the fineness modulus (FM) of fine aggregate indicate?