ATT Bulk Density, Voids & Organic Impurities 1 — Questions and Answers
Question 1: What does bulk density of aggregate refer to?
- Weight of aggregate particles only
- Volume of water displaced by aggregate
- Mass per unit volume including voids (Correct answer)
- Volume of air in concrete
Correct answer: Mass per unit volume including voids
Bulk density is the mass of aggregate required to fill a container of a specified unit volume and includes the volume of the particles and the voids between them.
Question 2: Which ASTM standard covers the determination of bulk density of aggregates?
- ASTM C40
- ASTM C29 (Correct answer)
- ASTM C117
- ASTM C128
Correct answer: ASTM C29
ASTM C29 is the recognized method for measuring the bulk density and void content of aggregates.
Question 3: Why is determining void content in aggregates important?
- To determine moisture content
- To calculate absorption rate
- To estimate cement requirements (Correct answer)
- To measure particle shape
Correct answer: To estimate cement requirements
Void content helps assess the space between aggregate particles, influencing concrete workability and mix proportions.
Question 4: What is the visual indication of organic impurities in fine aggregates?
- Lighter solution than the standard
- Yellowish tint in clear water
- Dark-colored solution compared to the standard (Correct answer)
- Frothy surface layer
Correct answer: Dark-colored solution compared to the standard
A darker color in the solution during the ASTM C40 test indicates the possible presence of organic impurities that can affect concrete strength.
Question 5: Which of the following can result from excessive organic impurities in aggregates?
- Improved workability
- Increased air content
- Reduced concrete strength (Correct answer)
- Faster setting time
Correct answer: Reduced concrete strength
Excessive organic matter can interfere with cement hydration and significantly reduce the strength of hardened concrete.
Question 6: What is the correct procedure when testing bulk density?
- Fill the container randomly
- Compact the sample with a rubber mallet
- Fill using specified method such as rodding or shoveling (Correct answer)
- Use vacuum to settle particles
Correct answer: Fill using specified method such as rodding or shoveling
The container must be filled in a standard manner—loose, rodded, or compacted—depending on the type of aggregate and test requirement.
ATT Bulk Density, Voids & Organic Impurities 1
What does bulk density of aggregate refer to?