Organic Impurities Assessment Flashcards
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Read the first 7 Organic Impurities Assessment flashcards as text
A fine aggregate sample passes ASTM C40 but the specifying engineer still requires ASTM C87 testing. This is:
Answer: Acceptable; engineers may require additional verification
Engineers may require ASTM C87 mortar strength testing even for aggregates that pass C40 as an additional quality assurance measure.
What does the term 'supernatant liquid' refer to in the context of ASTM C40 testing?
Answer: The clear liquid above the settled aggregate after the 24-hour standing period
The supernatant liquid is the solution layer above the settled sand after the 24-hour standing period, which is compared to the color reference standard.
Which of the following field conditions would most increase the likelihood of finding elevated organic impurities in a fine aggregate?
Answer: Aggregate from a river bank adjacent to a heavily vegetated floodplain
River banks near heavily vegetated floodplains accumulate decayed plant matter (humus), which is a primary source of humic acids detected by ASTM C40.
If a technician forgets to shake the ASTM C40 bottle before the 24-hour standing period, the most likely outcome is:
Answer: A lighter-than-actual color, potentially missing harmful organics
Without shaking, the NaOH may not fully contact all aggregate surfaces, under-extracting organic compounds and producing a lighter color than is actually present.
According to ASTM C33, a fine aggregate with organic impurity test results darker than the reference standard may still be accepted if:
Answer: The aggregate produces mortar with at least 95% strength of the control per ASTM C87
ASTM C33 allows acceptance of darker-than-standard aggregates if ASTM C87 mortar strength testing shows the organic matter does not significantly impair strength.
In organic impurities testing, which aggregate fraction is tested?
Answer: Fine aggregate passing the No. 4 sieve
ASTM C40 is specifically designed for fine aggregates, which are materials passing the No. 4 (4.75 mm) sieve.
What is the significance of the 3% concentration of the NaOH solution used in ASTM C40?
Answer: It is standardized to provide consistent and reproducible color extraction results
The 3% NaOH concentration is standardized to ensure consistent extraction of organic compounds and reproducible color development across different laboratories.