CEE 311L Aggregates

What are the two main sources of aggregates?

Natural sources and manufactured/recycled sources.

Examples of natural aggregate sources

Natural sand and gravel pits, river rock, and crushed quarry rock.

Examples of manufactured/recycled aggregates

Pulverized concrete, asphalt, steel mill slag, steel slugs, expanded shale, and Styrofoam.

What aggregate material is used for heavyweight concrete radiation shielding?

Steel mill slag.

What aggregate material is used for lightweight insulating concrete?

Styrofoam.

What are the three geological classifications of rock?

Igneous, sedimentary, and metamorphic.

What is igneous rock?

Rock that was once molten and cooled to its present form.

What is sedimentary rock?

Rock formed from sediments deposited by wind, water, glaciers, or sea organisms.

What is metamorphic rock?

Sedimentary rock transformed by heat and/or intense pressure.

What properties should be checked when selecting aggregates?

Physical, chemical, and mechanical properties, plus mineralogical examination.

What are two major uses of aggregates beneath structures?

Stability and drainage.

Why is drainage important beneath foundations and pavements?

It protects the structure from frost damage.

What percentage of PCC volume is aggregate?

Approximately 60-75%.

What percentage of PCC weight is aggregate?

Approximately 80-85%.

What percentage of HMA volume is aggregate?

Approximately 80-90%.

What percentage of HMA weight is aggregate?

Approximately 90-96%.

What is coarse aggregate?

Aggregate retained on a 4.75 mm (#4) sieve.

What is fine aggregate?

Aggregate passing a 4.75 mm (#4) sieve.

What is the traditional maximum aggregate size?

The largest sieve size that allows all aggregates to pass.

What is the traditional nominal maximum aggregate size?

The first sieve retaining some aggregate, generally less than 10%.

What is the Superpave maximum aggregate size?

One sieve size larger than the nominal maximum aggregate size.

What is the Superpave nominal maximum aggregate size?

One sieve larger than the first sieve retaining more than 10% of aggregate.

What does a #4 sieve represent?

Four openings per linear inch with 4.75 mm openings.

What aggregate properties are important for mix design?

Shape, texture, soundness, toughness, moisture state, specific gravity, gradation, cleanliness, alkalinity, and asphalt affinity.

What are common aggregate particle shapes?

Angular, rounded, flaky, and elongated.

Why are flaky and elongated particles undesirable?

They break easily and make compaction difficult.

Which particle shape is preferred for asphalt mixtures?

Angular and rough particles.

Why are angular particles preferred in asphalt?

They provide high friction, strength, and stability.

Which particle shape is preferred for concrete mixtures?

Rounded and smooth particles.

Why are rounded particles preferred in concrete?

They improve workability.

What is a fractured face in aggregate evaluation?

A broken angular surface used to evaluate texture and angularity.

What ASTM test evaluates aggregate soundness?

ASTM C88.

What is aggregate soundness?

The ability to resist weathering and freeze-thaw deterioration.

How does ASTM C88 simulate freeze-thaw damage?

Using salt solutions that cause crystal growth within the aggregate.

What is measured in the soundness test?

Mass loss after repeated soaking and drying cycles.

What property does the LA abrasion test measure?

Toughness and abrasion resistance.

What ASTM standards cover LA abrasion testing?

ASTM C131 and ASTM C535.

What does the LA abrasion test simulate?

Damage during construction, traffic loading, and stockpiling.

How many revolutions are typically used in the LA abrasion test?

500 revolutions.

Name the four aggregate moisture states

Dry, Air Dry, Saturated Surface Dry (SSD), and Moist.

What is the dry moisture state?

All voids are dry and Ww = 0.

What is the air-dry moisture state?

Contains some moisture but less than SSD.

What is the SSD moisture state?

Voids are filled with water but the surface is dry.

What is the moist condition?

Aggregate contains free water on its surface.

What is absorption?

The moisture content at the SSD condition.

What is free moisture?

Moisture in excess of SSD condition.

What happens with negative free moisture?

The aggregate absorbs water to fill its voids.

What happens with positive free moisture?

The aggregate releases water to the cement paste while remaining SSD.

What is density?

Mass divided by volume.

What is the density of water in SI units?

1000 kg/m³.

What is the density of water in g/cm³?

1.0 g/cm³.

What is the density of water in Imperial units?

62.4 lb/ft³.

What is specific gravity?

The ratio of a material's density to the density of water at the same temperature.

What is the typical specific gravity of aggregate?

About 2.6.

How is specific gravity determined?

By comparing aggregate weight in air and water.

What is Gsb?

Bulk specific gravity including permeable pores.

What is Gsa?

Apparent specific gravity excluding permeable pores.

Which ASTM standard covers coarse aggregate specific gravity?

ASTM C127.

Which ASTM standard covers fine aggregate specific gravity?

ASTM C128.

What device is used for fine aggregate specific gravity testing?

A pycnometer.

What is bulk unit weight?

The weight of aggregate required to fill a unit volume.

Why is bulk unit weight important?

It helps determine aggregate quantities needed in mixtures.

How is loose bulk unit weight measured?

Fill container without compaction, strike off level, and weigh.

How is compacted bulk unit weight measured?

Fill in layers, rod each layer, strike off level, and weigh.

What is aggregate gradation?

The distribution of particle sizes within an aggregate sample.

What test is used to determine aggregate gradation?

Sieve analysis.

What is a well-graded aggregate?

An aggregate with a good distribution of all particle sizes.

Why is well-graded aggregate desirable?

It reduces voids and requires less cement or asphalt.

What is uniform gradation?

Aggregate consisting of nearly one particle size.

What is gap-graded aggregate?

Aggregate missing one or more intermediate sizes.

What is open-graded aggregate?

Aggregate lacking small particles that fill voids.

What is fineness modulus (FM)?

A measure of the fineness or coarseness of fine aggregate.

What is the typical FM range for fine aggregate?

2.3 to 3.1.

What does a larger fineness modulus indicate?

Coarser aggregate.

What is alkali-aggregate reactivity (AAR)?

A reaction between aggregates and alkalis in cement.

What problems can AAR cause?

Expansion, cracking, and popouts.

What aggregate component most commonly causes AAR?

Reactive silica.

How can alkali-aggregate reactivity be minimized?

Use low-alkali cement, keep concrete dry, use fly ash, or add limestone.

What ASTM test evaluates expansion potential of aggregate-cement combinations?

ASTM C227.

What ASTM test identifies reactive silicates?

ASTM C289.

What ASTM test identifies reactive carbonates?

ASTM C586.

What is asphalt affinity?

The tendency of aggregate to bond with asphalt binder.

What is asphalt stripping?

Separation of asphalt binder from aggregate due to water.

What aggregate type is most susceptible to stripping?

Hydrophilic silicate aggregates.

What aggregate type is least susceptible to stripping?

Hydrophobic limestone aggregates.

What ASTM tests evaluate asphalt stripping?

ASTM D1664, ASTM D3625, and ASTM D1075.

What qualities should aggregate samples have?

They should be random and representative of the stockpile.

What is quartering?

A process for reducing sample size while maintaining representativeness.

Which aggregate gradation generally produces the highest strength?

Well-graded aggregate.

How does maximum aggregate size affect strength?

Larger maximum aggregate size generally increases strength.

How does compaction affect aggregate strength?

It increases strength through friction and interlocking.

What limits the strength of concrete or asphalt?

The strength of the aggregate.

What is the typical compressive strength range of aggregates?

Approximately 5,000 to 50,000 psi.

What is resilient modulus?

A measure of recoverable deformation under loading.