CVG 2141 Lecture Notes - Lecture 2: Tricalcium Aluminate, Pascal (Unit), Gypsum

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Aggregates
Aggregates are a granular material used a cementing medium or as foundation material/fill
Pros of Aggregates:
Can be used as filler and reduces cost
Greater volume stability than paste (less shrinkage)
Amount of aggregate should be maximized
Sources:
Natural Aggregates: pits, rivers, lakes, seabed. Mixture of rocks and minerals, sand and gravel,
oRounded and smooth texture
Crushed Stone: collected by crushing large rocks, boulders and gravel (e.g.granite, sandstone,
limestone)
oAngular and rough
Classification by Size:
Fine Aggregate: Each particle < 5mm, Natural Sand and crushed stone
Coarse Aggregate: > 5mm (usually 10-40mm), gravel and crushed stone
Classification by Density:
Lightweight: From natural (volcanic material) or manufactured
oSG = 0.2 – 2.5
oFine aggregates < 1120 kg/m^3 Coarse Aggregates: <880 kg/m^3
Normal Weight: From crushed stone, gravel, sand
oSG = 2.6 – 2.85
o1520 – 1680 kg/m^3
Heavy weight: From iron ores
oSG = 4-5
o2400-3040 kg/m^3
Classification by Shape:
Angular, rounded, flaky, elongated
Avoid flaky an elongated due to easy breakage and compacting in thin layers
High friction = Angular and rough = strength and stability
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Low friction = rounded and smooth = workability
Moisture Conditions of Aggregates:
Moisture Content: Amount water in an agg particle
Absorption Capacity: Maximum amount of water that 1
particle can retain.
When MC > AC there is free moisture on each particle, will provide
more water than needed = higher than expected w/c ration.
When MC < AC each particle will absorb any water added, more water is needed, if not lower
w/c = low workability.
Effective Absorption: Amount of water needed to bring MC condition from AD to SSD
Surface Moisture: Amount of water on the surface of a particle
Bulking:
% increase of volume of an aggregate over its dry volume
oCan by affected by the moisture content and particle size
Finer particles have a larger % increase
Largest % increase at 5% MC
Specific Gravity (Relative Density):
Density of the aggregate compared to water
Bulk Specific Gravity: SG with all pores included
Apparent Specific Gravity: SG with impermeable voids only included
o
Porosity: Volume of pores in the total volume, affects the absorption, freezing, strength
Bulk Unit Weight:
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