Practice Test Geeks(ATT) ACI Aggregate Testing Technician Practice Test
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Materials Finer Than No. 200 Sieve (Washing Test) Flashcards

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  1. An aggregate sample has an original dry mass of 2,012 g. After washing over the No. 200 sieve and oven drying, the retained mass is 1,966 g. What is the percent finer than No. 200?

    Answer: 2.3%

    (2012 − 1966) / 2012 × 100 = 46/2012 × 100 ≈ 2.3%, so the percent finer than No. 200 is 2.3%.

  2. Why is it important that the No. 200 sieve used in ASTM C117 be inspected and cleaned before each test?

    Answer: To prevent blinding from previous tests from reducing the effective opening size

    Clay or fines from previous tests can blind (plug) the sieve openings, causing fines to be retained rather than passing, leading to an underestimate of percent finer.

  3. Which of the following best describes 'decanting' in the context of ASTM C117?

    Answer: Pouring off the wash water carrying suspended fines over the nested sieves

    Decanting means carefully pouring the turbid wash water (carrying suspended fines) over the No. 200 sieve while keeping the coarse aggregate in the container.

  4. Per ASTM C117, what must be done with any material retained on the No. 200 sieve after washing?

    Answer: Returned to the main sample before oven drying

    Material retained on the No. 200 sieve during washing must be returned to the main sample so that the total post-wash dry mass accurately represents all particles coarser than 75 µm.

  5. For a combined sieve analysis (ASTM C136 + ASTM C117), where should the material finer than No. 200 obtained by washing be entered in the gradation calculation?

    Answer: It is added to the No. 200 pan mass from the dry sieve analysis

    The washed fines are added to the pan (material finer than No. 200) from the dry sieve analysis to determine the total amount passing No. 200.

  6. Which characteristic of aggregate makes the washing test particularly critical for evaluating concrete aggregate quality?

    Answer: Presence of clay and silt that weaken the aggregate-paste bond

    Clay and silt finer than No. 200 coat aggregate surfaces and interfere with the cement paste bond, reducing concrete strength and durability.

  7. If a technician accidentally loses some washed aggregate down the drain before drying, how does this error affect the calculated percent passing No. 200?

    Answer: It increases the calculated percent finer than No. 200

    Losing coarse material reduces the post-wash dry mass B, making (A − B) larger, which inflates the calculated percent finer than No. 200.