Module 2 - Aggregates Flashcards
(49 cards)
combination of sand, gravel, crushed stone, slag or other materials used in combination with a binding medium to form such materials as bituminous and Portland cement concrete, mortar, and plaster, etc. or alone as in railroad ballast, filter beds, and various manufacturing processes.
aggregates
Origins of aggregates
Natural
Crushed rock aggregates
artificial/synthetic
taken from deposits such as riverbeds, pits and exposed large rocks, without altering the mineralogical nature during processing
natural aggregates
come from quarried or excavated stones that have been crushed to a particular size and particular distribution, good for load bearing uses
crushed rock aggregates
by-products of other processes (blast furnace slag)
manufactured for the main purpose of supplying for the needs of specialized construction processes (expanded clay, shale or slate used for lightweight aggregates)
waste construction materials that have been crushed and recycled back in construction (waste portland cement concrete)
artificial / synthetic aggregates
Consists of naturally rounded particles resulting from natural disintegration and abrasion
of rock or a processing of weakly bonded conglomerate. Coarse aggregates are particles
retained on sieve #4- or 4.75-mm squares
gravel
Consists of rock particles that have been disintegrated naturally; grains are generally
granular but have been subjected to weathering. (75 micron< ___ < 4.75 mm)
sand
Product of artificial crushing of rocks, boulders, or large cobblestones, substantially all
faces of which result from crushing operation.
These aggregates should be hard, strong, durable, clean and almost cubical. Flaky and
elongate pieces are usually avoided.
crushed stone
These aggregates are manufactured from the crushing of granite or basalt rocks. This is
generally more expensive than natural sand.
artificial sand
types of aggregates
gravel
sand
crushed stone
artificial sand
sources of natural aggregates
rocks
single minerals
rocks that contain several minerals
major types of rocks
igneous
sedimentary
metamorphic
These crystalline rocks are predominantly formed by the cooling of magma.
igneous
These rocks are formed from the deposition of granular material from disintegrated preexisting rocks or from great quantities of inorganic remains of marine and animals.
deposited in layers which gives them stratified or laminated features.
sedimentary
These are sedimentary or igneous rocks that have been subjected to extreme heat or
pressure or both.
metamorphic
processing of aggregates
excavation
transportation
aggregate benefaction
crushing
sizing
processing of aggregates to meet or pass specifications
aggregate benefaction
Utilizes a suspension of water and/or ferrosilicon of fixed specific gravity so that
most deleterious materials will float.
heavy media separation / sink-float method
Soft particles can be removed by letting the aggregate fall on an inclined plane.
Poor, soft, and friable aggregate rebound at short distances, making it easier to
distinguish good aggregates.
elastic fractionation
Specific gravity method for removing light particles such as coal, lignite and sticks.
Upward pulses of air are introduced in the system to hinder the settlement of light
particles.
jigging
Blasted rocks go through three or four stages of crushing to reach the standard. Each crushing
stage produces progressively smaller sized stones
crushing
Aggregates are screened in various stages of crushing until the required sizes for commercial sale
is achieved.
sizing
geometric properties of aggregates
particle size and grading
particle shape and surface texture
the smallest sieve opening through which the
entire aggregate sample passes.
MAS (maximum aggregate size)
