Aggregate Properties and Testing Flashcards
6 cards from real ACI Certification practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 6 Aggregate Properties and Testing flashcards as text
The absorption capacity of aggregate is important because it affects what aspect of concrete?
Answer: The effective water available for cement hydration — high-absorption aggregate soaks up batch water, reducing the water available for the cement reaction
If aggregate absorbs water from the mix, less water is available for cement hydration. Mix designs must account for aggregate absorption to ensure the correct water-cement ratio.
What does petrographic examination (ASTM C295) reveal about an aggregate?
Answer: The mineralogical composition, physical characteristics, and potential durability issues of the aggregate through microscopic examination
Petrographic analysis uses microscopy to identify minerals, assess physical properties, and detect potentially reactive or harmful constituents that could affect concrete performance.
Why is the soundness test performed on concrete aggregates?
Answer: To evaluate the aggregate's resistance to disintegration from repeated cycles of wetting and drying or freezing and thawing — simulating weathering
The soundness test (ASTM C88) simulates weathering by soaking aggregate in sodium or magnesium sulfate solution that crystallizes in pores, creating expansion pressure similar to ice crystal formation.
How does aggregate shape and texture affect concrete performance?
Answer: Angular, rough-textured aggregates improve bond with cement paste (increasing strength) but reduce workability; rounded, smooth aggregates improve workability but may reduce strength
Aggregate shape and texture affect both fresh and hardened concrete: angular particles interlock better (stronger) but create more friction (harder to work), while rounded particles flow more easily.
What is the significance of the amount of material passing the No. 200 sieve in concrete aggregate?
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
Material passing the No. 200 sieve (75 μm) is mostly silt, clay, or stone dust. Excessive amounts weaken concrete by increasing water demand and interfering with cement paste bonding to aggregate.
A concrete supplier's aggregate source changes slightly. Which test results should be monitored most closely?
Answer: Gradation (sieve analysis), fineness modulus, specific gravity, absorption, and minus-200 content — all can shift with source changes and affect mix performance
Source changes, even from the same quarry, can alter aggregate properties that directly affect concrete quality. Regular monitoring catches changes before they cause problems in the field.