ACI Certification Aggregate Properties and Testing 3

Question 1

The absorption capacity of aggregate is important because it affects what aspect of concrete?

Accepted Answer

The effective water available for cement hydration — high-absorption aggregate soaks up batch water, reducing the water available for the cement reaction

Answer

Only the aggregate's weight

Answer

The color of finished concrete

Answer

The aggregate's resistance to freezing

Question 2

What does petrographic examination (ASTM C295) reveal about an aggregate?

Accepted Answer

The mineralogical composition, physical characteristics, and potential durability issues of the aggregate through microscopic examination

Answer

Only the aggregate's color

Answer

The aggregate's weight per cubic foot

Answer

Only whether the aggregate contains clay

Question 3

Why is the soundness test performed on concrete aggregates?

Accepted Answer

To evaluate the aggregate's resistance to disintegration from repeated cycles of wetting and drying or freezing and thawing — simulating weathering

Answer

To measure how much noise aggregate makes

Answer

To test if aggregate is solid enough to walk on

Answer

To determine the speed of sound through aggregate

Question 4

How does aggregate shape and texture affect concrete performance?

Accepted Answer

Angular, rough-textured aggregates improve bond with cement paste (increasing strength) but reduce workability; rounded, smooth aggregates improve workability but may reduce strength

Answer

Shape only affects appearance

Answer

Only rounded aggregates should be used

Answer

Shape has no effect on concrete properties

Question 5

What is the significance of the amount of material passing the No. 200 sieve in concrete aggregate?

Accepted Answer

It measures the amount of very fine dust, silt, and clay particles that can coat aggregate surfaces, weaken the paste-aggregate bond, and increase water demand

Answer

It indicates the aggregate's color

Answer

It only matters for road base, not concrete

Answer

More fine material always improves concrete

Question 6

A concrete supplier's aggregate source changes slightly. Which test results should be monitored most closely?

Accepted Answer

Gradation (sieve analysis), fineness modulus, specific gravity, absorption, and minus-200 content — all can shift with source changes and affect mix performance

Answer

Only the color

Answer

Only the delivery ticket weight

Answer

The temperature of the aggregate pile