Lecture No' 06

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Lecture No. 06

• Subject Sources of Aggregates

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Objectives of Lecture

• To explain the sources of aggregates used for
  making concrete.

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Aggregates

• The total aggregates (fine aggregates coarse
  aggregates) are used in concrete as filler and
  generally occupy 60 to 75 of the concrete
  volume (70 to 85 by weight).
• Fine aggregates generally consist of natural sand
  or crushed stone with most particles smaller than
  0.2 in.
• Coarse aggregates consist of one or a combination
  of gravels or crushed aggregate with particles
  predominantly larger than 0.2 in. and generally
  between ? and 1½ in.

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Fine Aggregates
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Coarse Aggregates
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Sources of Aggregates

• Freshly mixed normal weight concrete (2200 to
  2400 kg/m3) can be produced using
• Natural gravel and sand are usually dug or
  dredged from a pit, river, lake, or seabed.
• Crushed aggregate is produced by crushing quarry
  rock, boulders, cobbles, or large size gravel.
• Crushed air-cooled blast-furnace slag is also
  used as fine or coarse aggregate.
• Recycled concrete, or crushed waste concrete, is
  a feasible source of aggregates and an economic
  reality where good quality aggregates are scarce.

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• Various light weight materials such as expanded
  shale, clay, slate, and slag are used as
  aggregates for producing lightweight concrete
  (1350 to 1850 kg/m3).
• Other lightweight materials such as pumice,
  scoria, perlite, vermiculite, and diatomite are
  used to produce insulating lightweight concretes
  (250 to 1450 kg/m3).
• Heavy weight aggregates such as barlite,
  magnetite and iron are used to produce heavy
  weight concrete and radiation-shielding concrete.

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Lightweight Aggregates

• Expanded clay (left)
• Expanded shale (right)

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Constituents in Naturally Occurring Aggregates

• Naturally occurring concrete aggregates are a
  mixture of rocks and minerals (see Table 5-1)
• Minerals
• Silica (ex. Quartz)
• Silicates (ex. Clay)
• Carbonate (ex. Calcite, dolomite)
• Igneous rocks
• Granite
• Basalt
• Sedimentary rocks
• Sandstone
• Limestone
• Shale
• Metamorphic rocks
• Marble
• slate

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Range of particle sizes found in aggregate for
use in concrete
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Making a sieve analysis test of coarse aggregate
in a Lab
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• Amount of cement paste required in concrete is
  greater than the volume of voids between the
  aggregates.

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Fine aggregate grading limits
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Type of aggregate and drying shrinkage
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Harmful materials in aggregates
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• Aggregates can occasionally contain particles of
  iron oxide and iron sulfide that result in stains
  on exposed concrete surface.

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Cracking of concrete from alkali silica reactivity
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Influence of Adding mineral admixture on
alkali-silica reactivity (ASR)
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Heavily reinforced concrete is crushed with a
beam-crusher
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Recycled-concrete aggregate
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Local Aggregates Sources

• Eastern Province
• Fine aggregates
• Most of the fine aggregate in the eastern
  province is dune sands with silica contents
  ranging from 79 to 98.
• Coarse Aggregates
• The coarse aggregates are limestone and they
  contain high content of calcite and some quartz.
• Central Province
• Fine aggregates
• Good quality fine aggregates are available
  throughout the central province they contain
  quartz, feldspar, and calcite. In general, the
  fine aggregates contain 82 to 99 silica.
• Coarse Aggregates
• The coarse aggregates are limestone, diorite, and
  amphibolites. These aggregates contain calcite,
  quartz, and dolomite.

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• Western Province
• Fine aggregates
• The fine aggregates contain quartz, feldspar,
  calcite, and mica. In general, the fine
  aggregates in the western region contain less
  silica (60 to 76) compared to sands from
  eastern and central regions.
• Coarse Aggregates
• The coarse aggregates are amphibolites,
  hornblende diorite, etc. They contain about 50
  SiO2.

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• Unwashed local aggregate is the largest
  contributor of chlorides in concrete in the Gulf
  region. The local aggregate in the eastern
  region of Saudi Arabia is composed of crushed
  limestone which is usually porous, absorptive,
  relatively soft and excessively dusty. The dust
  and fines are heavily contaminated with sulfate
  and chloride salts.

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The following Tables present some test results on
selected local coarse aggregates

• Table 1. Mineralogical composition of the
  selected coarse aggregates determined by X-ray
  diffraction technique.

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Table 2. Materials finer than ASTM 200 sieve in
the selected coarse aggregates.
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Table 3. Specific gravity and water absorption
for the selected coarse aggregates.
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Table 4. Loss on abrasion in the selected coarse
aggregates.
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Table 5. Chloride and sulfate concentrations in
the selected coarse aggregates.
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In conclusion

• Tests conducted on the selected coarse aggregates
  indicated that the quality of coarse aggregates
  from quarries on the Riyadh road is relatively
  better than the coarse aggregates from quarries
  in Hofuf and Abu-Hadriyah.
• The quantity of fine materials in all the coarse
  aggregates was less than the allowable value of
  1. However, the quantity of fine materials in
  the coarse aggregates from quarries in
  Abu-Hadriyah was more than that in the coarse
  aggregates from quarries in Hofuf and on the
  Riyadh road.
• The loss on abrasion in all the coarse aggregates
  was less than the allowable value of 40. The
  loss on abrasion in the coarse aggregates from
  quarries in Abu-Hadriyah was generally more than
  that in the coarse aggregates from quarries in
  Hofuf and on the Riyadh road.

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In conclusion

• The water absorption in the coarse aggregates
  from quarries in Abu-Hadriyah was more than that
  in the coarse aggregates from quarries in Hofuf
  and on the Riyadh road.
• The chloride concentration in the coarse
  aggregates from the Al-Suhaimi quarry in
  Abu-Hadriyah was two times the allowable value of
  0.03, while in other coarse aggregates, the
  chloride concentration was less than the
  threshold value.
• The sulfate concentration in all the coarse
  aggregates was less than the value specified by
  the Saudi Aramco specifications.