Transcript Lecture No. 06

Lecture No. 06
Subject: Sources of
Aggregates
Objectives of Lecture
• To explain the sources of aggregates
used for making concrete.
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 ⅜ and 1½ in.
Fine Aggregates
Coarse Aggregates
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.
• 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.
Lightweight Aggregates
• Expanded clay (left)
• Expanded shale
(right)
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
Range of particle sizes found in
aggregate for use in concrete
Making a sieve analysis test of
coarse aggregate in a Lab
• Amount of cement
paste required in
concrete is greater
than the volume of
voids between the
aggregates.
Fine aggregate grading limits
Type of aggregate and drying
shrinkage
Harmful materials in aggregates
• Aggregates can
occasionally contain
particles of iron oxide
and iron sulfide that
result in stains on
exposed concrete
surface.
Cracking of concrete from alkali
silica reactivity
Influence of Adding mineral admixture on
alkali-silica reactivity (ASR)
Heavily reinforced concrete is
crushed with a beam-crusher
Recycled-concrete aggregate
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.
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.
• 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.
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.
Sample #
Name of quarry
Location
Mineralogical composition, % by weight
Calcium carbonate
(CaCO3)
Quartz (SiO2)
1
Al-Suhaimi
Abu-Hadriyah
99.0
1.0
2
Al-Osais
Abu-Hadriyah
95.0
5.0
3
Al-Moosa
Hofuf
80.0
20.0
4
Al-Aflaq
Hofuf
75.0
25.0
5
Al-Muneer
Riyadh road
85.0
15.0
6
Al-Summan
Riyadh road
75.0
25.0
Table 2.
Materials finer than ASTM # 200 sieve in
the selected coarse aggregates.
Sample #
Name of
quarry
Location
Material finer than
ASTM No. 200
sieve, %
Acceptable
value, %
[ASTM C
33, Saudi
Aramco]
1.0
1
Al-Suhaimi
Abu-Hadriyah
0.50
2
Al-Osais
Abu-Hadriyah
0.65
3
Al-Moosa
Hofuf
0.46
4
Al-Aflaq
Hofuf
0.17
5
Al-Muneer
Riyadh road
0.20
6
Al-Summan
Riyadh road
0.44
Table 3.
Sample #
Specific gravity and water absorption for the
selected coarse aggregates.
Name of
quarry
Location
Specific
Absorption,
gravity
%
1
Al-Suhaimi
Abu-Hadriyah
2.52
2.32
2
Al-Osais
Abu-Hadriyah
2.53
2.4
3
Al-Moosa
Hofuf
2.43
1.80
4
Al-Aflaq
Hofuf
2.45
1.2
5
Al-Muneer
Riyadh road
2.59
1.06
6
Al-Summan
Riyadh road
2.6
1.1
Acceptable
value, %
[Saudi
Aramco]
2.5
Table 4.
Sample
#
Loss on abrasion in the selected coarse
aggregates.
Name of
quarry
Location
Loss on
abrasion,
%
1
Al-Suhaimi
Abu-Hadriyah
32.40
2
Al-Osais
Abu-Hadriyah
33.20
3
Al-Moosa
Hofuf
35.05
4
Al-Aflaq
Hofuf
25.89
5
Al-Muneer
Riyadh road
23.66
6
Al-Summan
Riyadh road
22.60
Acceptable value,
% [Saudi
Aramco]
40
Table 5.
Sample #
Name of
quarry
Chloride and sulfate concentrations in the
selected coarse aggregates.
Location
Chloride
concentration,
%
Allowable
chloride
concentrati
on, %
[Saudi
Aramco]
0.03
Sulfate
concentratio
n, %
1
Al-Suhaimi
Abu-Hadriyah
0.066
2
Al-Osais
Abu-Hadriyah
0.028
0.059
3
Al-Moosa
Hofuf
0.026
0.083
4
Al-Aflaq
Hofuf
0.011
0.035
5
Al-Muneer
Riyadh road
0.017
0.059
6
Al-Summan
Riyadh road
0.022
0.067
Allowable
sulfate
conce
ntration
,%
[Saudi
Aramc
o]
0.206
0.4
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.
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.