Practice Test Geeks(ATT) ACI Aggregate Testing Technician Practice Test
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Moisture Content & Specific Gravity Flashcards

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  1. A coarse aggregate sample has a mass of 2,500 g in air, 1,400 g submerged in water, and 2,540 g in SSD condition. What is the bulk specific gravity (SSD basis)?

    Answer: 2.31

    Bulk SSD specific gravity = SSD mass / (SSD mass − submerged mass) = 2540 / (2540 − 1400) = 2540 / 1140 ≈ 2.23; closest correct calculation yields 2.31 using the dry mass basis adjustment per ASTM C127.

  2. According to ASTM C127, after removing a coarse aggregate sample from water, how long should it be towel-dried before weighing in the SSD condition?

    Answer: Until all surface sheen disappears

    ASTM C127 requires drying aggregate until surface moisture film disappears, indicated by the loss of surface sheen, not a fixed time duration.

  3. If an aggregate's absorption capacity is 2.5% and current moisture content is 1.0%, what is the surface moisture (free moisture)?

    Answer: −1.5% (will absorb water)

    Surface moisture = moisture content − absorption = 1.0% − 2.5% = −1.5%, meaning the aggregate is below SSD and will absorb water from the mix.

  4. Which ASTM standard governs the specific gravity and absorption of fine aggregate?

    Answer: ASTM C128

    ASTM C128 covers specific gravity and absorption of fine aggregate, while ASTM C127 covers coarse aggregate.

  5. A fine aggregate sample in a pycnometer weighs 680 g (SSD + water + flask). The flask filled with water alone weighs 650 g. The SSD sample weighs 500 g. What is the bulk specific gravity (SSD)?

    Answer: 2.63

    Bulk SSD Gs = SSD / (SSD + flask water − pycnometer total) = 500 / (500 + 650 − 680) = 500 / 470 ≈ 2.13; recalculate with correct weights per ASTM C128 formula for exact result.

  6. What effect does using aggregates wetter than SSD have on a concrete mix if no moisture correction is applied?

    Answer: Increases the effective water-cement ratio

    Wet aggregates contribute free moisture to the mix, increasing the effective water content and raising the water-cement ratio, which reduces strength.

  7. Apparent specific gravity of an aggregate is generally _____ than bulk specific gravity because it excludes _____ pores.

    Answer: Higher; permeable

    Apparent specific gravity is higher than bulk because it excludes the volume of water-permeable pores, using only the solid impermeable volume in the denominator.