ATT Unit Weight & Voids Testing 2

Question 1

When performing the unit weight test on coarse aggregate, how many layers are used when rodding a 1/2-cubic-foot measure?

Accepted Answer

3 layers

Answer

ASTM C29 requires three equal layers when rodding aggregate in a 1/2-cubic-foot measure.

Question 2

What is the purpose of striking off the surface of the measure after filling in the unit weight test?

Accepted Answer

To create a flat surface flush with the top of the measure

Answer

Striking off levels the surface flush with the rim so the volume of aggregate equals exactly the volume of the measure.

Question 3

In ASTM C29, what tool is used to strike off the surface of the measure after the final layer of aggregate is added?

Accepted Answer

A straightedge or tamping rod

Answer

A straightedge or the tamping rod is used to strike off aggregate flush with the top of the measure.

Question 4

If the unit weight of a fine aggregate is 100 pcf and the specific gravity is 2.65, what is the approximate void content?

Accepted Answer

About 39%

Answer

Void content = (1 - UW / (SG × 62.4)) × 100 = (1 - 100/165.36) × 100 ≈ 39.5%.

Question 5

Which aggregate characteristic does a high void content typically indicate?

Accepted Answer

Poorly graded or rounded particles with large interparticle spaces

Answer

High void content usually indicates poorly graded or uniform-sized aggregate, or particles with shapes that do not pack efficiently.

(ATT) ACI Aggregate Testing Technician Practice Test