ATT Specific Gravity & Absorption 3

Question 1

A coarse aggregate sample has an OD mass of 4,856 g, SSD mass of 4,921 g, and submerged mass of 3,057 g. What is the absorption (%)?

Accepted Answer

1.34%

Answer

Absorption = ((4921 - 4856) / 4856) × 100 = (65 / 4856) × 100 ≈ 1.34%.

Question 2

What is the primary reason that aggregates with high absorption values can be problematic in concrete?

Accepted Answer

They may absorb mixing water, effectively lowering the water-cement ratio

Answer

High-absorption aggregates can draw water from the paste, reducing effective w/c ratio and potentially causing workability loss.

Question 3

In the wire basket method for coarse aggregate (ASTM C127), what is the purpose of the wire basket?

Accepted Answer

To hold the aggregate submerged while its mass is determined in water

Answer

The wire basket is suspended in water on a balance to obtain the submerged (buoyant) mass of the aggregate.

Question 4

If apparent specific gravity is 2.71 and bulk OD specific gravity is 2.61 for the same aggregate, what can be inferred?

Accepted Answer

The permeable pore volume is significant

Answer

A larger difference between apparent and bulk OD specific gravity indicates a greater permeable pore volume within the particles.

Question 5

Which aggregate characteristic directly affects the calculation of batch weights in mix design using specific gravity?

Accepted Answer

Volume of aggregate per unit mass (reciprocal of specific gravity)

Answer

Mix design uses specific gravity to convert between aggregate mass and volume, so it directly affects batch weight calculations.

(ATT) ACI Aggregate Testing Technician Practice Test