ATT Organic Impurities Assessment 2

Question 1

Which ASTM standard governs the colorimetric test for organic impurities in fine aggregates for concrete?

Accepted Answer

ASTM C40

Answer

ASTM C40 is the standard test method for organic impurities in fine aggregates for concrete using the colorimetric method.

Question 2

What does a color darker than the reference standard No. 3 organic plate indicate about a fine aggregate sample?

Accepted Answer

The aggregate contains harmful levels of organic matter

Answer

A color darker than the reference standard No. 3 organic plate indicates potentially harmful organic impurity levels requiring further investigation.

Question 3

In the ASTM C40 test, what solution is added to the sand sample before comparing to the color standard?

Accepted Answer

3% sodium hydroxide (NaOH) solution

Answer

A 3% sodium hydroxide (NaOH) solution is added to the sand and shaken, then allowed to stand before color comparison.

Question 4

How long must the sand and sodium hydroxide mixture stand before the color comparison is made in ASTM C40?

Accepted Answer

24 hours

Answer

The mixture must stand for 24 hours before the color of the solution is compared to the organic plate reference standard.

Question 5

If a fine aggregate fails the ASTM C40 organic impurities test, what is the most appropriate next step?

Accepted Answer

Run ASTM C87 mortar strength test

Answer

ASTM C87 (mortar strength test) can determine if the organic impurities actually affect concrete strength, allowing the aggregate to potentially still be used.

(ATT) ACI Aggregate Testing Technician Practice Test

(ATT) ACI Aggregate Testing Technician Practice Test

ATT Organic Impurities Assessment 2