Soils and Aggregates Flashcards

The California Bearing Ratio (CBR) test measures:

Answer: Resistance of subgrade to penetration relative to a standard crushed stone

CBR compares the load required to penetrate a soil specimen to the load required to penetrate a standard high-quality crushed limestone.

What is the purpose of the sand equivalent (SE) test for fine aggregate?

Answer: Measure the proportion of clay-like fines relative to sand-size particles

The sand equivalent test quantifies the relative amount of fine dust or clay-like material in fine aggregate using a flocculation procedure.

When field moisture content is above optimum during compaction, the likely result is:

Answer: Pumping and rutting of the subgrade

Compacting soil wetter than optimum moisture results in a weak, unstable subgrade that can pump and rut under roller or traffic loads.

A soil classified as A-7-6 under AASHTO is best described as:

Answer: Highly plastic clay, generally poor subgrade

A-7-6 soils are highly plastic clays with high volume change potential, considered the poorest subgrade materials under AASHTO classification.

Which aggregate property is tested using the sodium sulfate soundness test?

Answer: Resistance to weathering and freeze-thaw degradation

The sodium sulfate soundness test simulates freeze-thaw action to evaluate aggregate durability against weathering deterioration.

In USCS classification, the symbol 'ML' refers to:

Answer: Inorganic silt of low to medium plasticity

ML in the Unified Soil Classification System designates inorganic silt or very fine sand with low to medium plasticity.

What effect does excessive clay content have on aggregate base course performance?

Answer: Causes strength loss when wet and frost heave potential

Clay in aggregate base courses absorbs water, weakens under wet conditions, and increases frost susceptibility leading to heave and failure.