Aggregates Flashcards
Uses of Aggregates
- Foundations and pavements
- Embankments and Erosion Protection
- Major ingredient in Portland Cement Concrete and Asphalt Concrete
Sources of Aggregates
Natural and Industrial
Natural Sources
- Gravel pits
- River run deposit
- Rock quarries
Industrial Sources
- Slag waste
- Expanded Shale
- Recycled asphalt and Portland Cement Concrete
Which type of aggregate is undesirable?
Flat and Elongated particles because they have a tendency to break during construction and under traffic
What type of device is used to measure the aggregate dimensional ratio?
A proportional caliper
What two types of geometric properties are there?
Round and Angular
What does Angularity affect?
Interlocking
What does texture affect?
Bonding to binder material and interparticle friction
Higher void content =
higher angularity and texture
Geometric Properties Affect
Aggregate packing (Stability) and mobility of particles with binders (workability)
What is Soundness?
The ability for the aggregate to withstand weathering (freeze/thaw resistance) using the sulfate soundness test.
What is the sulfate soundness test?
percent loss of materials from an aggregate blend by exposing the aggregate to saturated solutions of sodium or magnesium sulfate followed by oven drying
What is toughness and Abrasion resistance?
Resistance to crushing, degradation, and disintegration when stockpiled, mixed with portland cement or asphalt binder, compacted, and exposed to loads. Measured using the LA Abrasian Test (max allow. loss 35 to 45 %)
What are deleterious materials?
Clay, shale, organic matter, and coal
How is clay measured?
Using a graduated cylinder with a floculating solution which forces the clay to separate from the sand.
What is the sand equivalent value?
Ratio of the sand height to clay height
Unit Weight
Weight of Material/volume of material
Density
mass of material/volume of material
Moisture conditions
bone dry, air dry, saturated surface-dry, saturated surface-wet
Weight of water displaced by aggregate
Dry weight - Submerged weight
Bulk Volume of the Aggregate
Weight Saturated Surface Dry - Submerged Weight
Apparent Specific Gravity (Gsa)
Wdry/(Wdry-Wsubmerged)
Bulk Dry Specific Gravity (Gsb dry)
Wdry/(Wssd-Wsubmerged)
SSD Specific Gravity (Gssd)
Wssd/(Wssd-Wsubmerged)
The unit weight increases as the void content
decreases
% Voids
(1-(DRUW)/(Gsb dryUnit weight))100
sieves
is the number of openings per linear inch
Coarse and Fine Aggregate Sieves are separated by
4.75 mm
Maximum Aggregate Size
smallest aggregate size with 100 % passing
Nominal Maximum Aggregate Size
Smallest sieve through which most of the aggregate passes (85 to 95 %)
Asphalt Concrete NMAS
One size larger than the first sieve to retain more than 10 %
Asphalt Concrete Max
One size larger than NMAS
What is the maximum density line?
Represents gradation that will yield highest density and lowest void content
maximum design line equation
p = 100*(d/D)^n, p = % passing, d = diameter of interest, D = max aggregate size, n = 0.45 according to the FHWA
Why does finer aggregate require more cement paste?
Because finer aggregate has more surface area
Review Gradation Blending
Review Gradation Blending
