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Concrete Mix Design Flashcards

7 cards from real ACI Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. According to ACI 211.1, which factor most directly influences the required water content for a given slump?

    Answer: Maximum size of aggregate

    ACI 211.1 tables show that water demand decreases as maximum aggregate size increases for a given slump, due to reduced total surface area.

  2. In the absolute volume method of mix design, the sum of volumes of all ingredients for one cubic yard of concrete must equal:

    Answer: 27 cubic feet

    One cubic yard equals 27 cubic feet, so the absolute volumes of all ingredients—cement, water, aggregates, and air—must sum to 27 ft³.

  3. What is the approximate specific gravity of Type I portland cement used in absolute volume calculations?

    Answer: 3.15

    Portland cement has a specific gravity of approximately 3.15, which is used to calculate its absolute volume in mix design.

  4. A lower water-to-cement (w/c) ratio generally produces concrete with:

    Answer: Higher strength and improved durability

    Reducing the w/c ratio decreases capillary porosity in the hardened paste, resulting in stronger and more durable concrete.

  5. According to ACI 318, the maximum w/cm ratio for concrete exposed to freezing and thawing in a moist condition is:

    Answer: 0.45

    ACI 318 limits the w/cm to 0.45 for concrete subjected to freezing and thawing in moist conditions to control permeability.

  6. The target mean compressive strength (f'cr) is set higher than the specified strength (f'c) to account for:

    Answer: Normal variability in concrete production and testing

    f'cr is set above f'c to ensure that no more than a prescribed fraction of test results fall below f'c, given inherent production and testing variability.

  7. Supplementary cementitious materials (SCMs) such as fly ash are used in concrete mix design primarily to:

    Answer: Replace a portion of portland cement while maintaining or improving properties

    SCMs like fly ash partially replace portland cement, often improving workability and long-term durability while reducing heat of hydration and material cost.