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

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  1. Which ASTM standard governs specific gravity and absorption testing for fine aggregate?

    Answer: ASTM C128

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

  2. What is the significance of bulk SSD specific gravity compared to bulk OD specific gravity in volumetric mix design?

    Answer: SSD specific gravity accounts for the volume of absorbed water within particles, more closely representing aggregate behavior in a saturated mix

    SSD specific gravity includes the volume of absorbed water within permeable pores, representing aggregate volume as it behaves when fully saturated in a mix.

  3. A technician towel-dries coarse aggregate and notices that particles clump together with a damp feel. What does this indicate?

    Answer: The aggregate is still in a wet condition with surface moisture present

    Clumping and damp feel indicate free surface moisture is still present, meaning the aggregate has not yet reached SSD.

  4. In the formula for bulk OD specific gravity of coarse aggregate (ASTM C127): Gs = A / (B - C), what does 'C' represent?

    Answer: Apparent mass of the sample in water (submerged mass)

    In ASTM C127, C is the apparent mass of the saturated sample in water (submerged mass), used to determine the sample's displaced water volume.

  5. Which of the following would cause absorption results to be artificially LOW when testing coarse aggregate?

    Answer: Over-drying the aggregate surface so some evaporation of pore water occurs

    If the aggregate is over-dried beyond SSD, some absorbed pore water evaporates, resulting in a lower measured SSD mass and artificially low absorption.

  6. For a mix design using aggregate in air-dry condition, which moisture correction must be applied?

    Answer: Add water equal to the absorption capacity since air-dry aggregate is below SSD

    Air-dry aggregate contains less moisture than SSD; the mix must supply additional water equal to the effective absorption to prevent the aggregate from drawing water from the paste.

  7. What maximum coefficient of variation (precision) does ASTM C127 allow for bulk OD specific gravity between two results by the same operator on the same material?

    Answer: 0.9%

    ASTM C127 single-operator precision for bulk OD specific gravity has a maximum acceptable range of about 0.009 (roughly 0.9% for typical values near 2.65).