Transcript SPECIFIC GRAVITY & ABSORPTION CAPACITY OF AGGREGATES

EA102
SPECIFIC GRAVITY &
ABSORPTION CAPACITY
OF AGGREGATES
EA102
Density
The density, ρ of any material
M
ρ

i.e.,
is the mass per unit of volume:
V
For example, how many
kilograms in 1 cubic metre of
1 m3
the material?
or, how many grams in 1 cubic
centimetre of the material?
1 cm
3
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1 m3
1 cm3
At 4˚ C, water has a density,
ρw of exactly 1000 kilograms
per cubic metre
At 4˚ C, water has a density,
ρw of exactly 1 gram per
cubic centimetre
At 20˚ C (standard), water
has a density, ρw of 0.99823
gram per cubic centimetre
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To find the density of any material, a
sample of the material is weighed in
air, Mair and then in water, Mwater.
The difference between the mass in
air and water is the mass of the
water displaced by the material when
placed in the water:
Mwater displaced  Mair  Mwater
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M
,
Since, ρ 
V
Vwater displaced 
Mwater displaced
ρw
Mair  Mwater

ρw
Since the volume of the material weighed is
the same as the volume of water it displaces…
Mair
Mair
ρ

 ρw
Mair  Mwater Mair  Mwater
ρw
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Specific Gravity
The specific gravity, G of a material
is just its density relative to the
density of water:
ρ
G
ρw
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Moisture States in
Aggregates
There are 4 distinct moisture
states for aggregates:
Saturated Surface
Air
Dried
Free
Oven
Moisture
Dried
Dried, SSD
(Water
(Hygroscopic
between
(No Moisture)
Moisture)
particles)
Voids
Water
Moisture
Filled
Permeable
with
fromWater
Air
Voids
Particle coated with water
Aggregate Particle
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Moisture Content
The moisture content of a soil or
aggregate is the mass of water per
unit mass of dry material.
Mw Mass of Wet Sample  Mass of DriedSample
w

Ms
Mass of DriedSample
Moisture content is often expressed as a
percentage, i.e., the mass of water in grams
per 100 grams of dry material.
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Absorption Capacity
The absorption capacity, %ABS is the moisture
content of the material when it is in the
saturated surface dried state.
We need to know the %ABS of the sand and
stone used to make concrete because if they
are drier than SSD then they will absorb some
of the mixing water.
On the other hand, if there is free moisture in
the aggregate then there will be too much
water in the mix.
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Example
The %ABS of stock sand is 1.5% and we need 8 kg of
sand in the SSD condition to make concrete. A 499.6
gram sample of the stock sand was dried over a
bunsen burner to a constant mass of 486.4 grams.
How much of the sand should be used?
First find the moisture content:
w
499.6  486.4
 2.71%
486.4
This means that if we weighed out 8 kg of the sand,
we’d get less than 8 kg of sand at SSD and extra
(free) water.
We therefore must weigh out extra sand in order to
get 8 kg at SSD.
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(
How much?
APPROXIMATELY, an extra 2.71-1.5 = 1.21% of
the required SSD mass.
The mathematically correct
version of this % correction is:
2.71  1.5
C
 1.192%
101.5
This translates to 0.0121 x 8.000 = an extra
0.0968 or 0.097 kg of sand.
This means an extra 0.097 kg of water will be
brought into the mix, so the mixing water should
be reduced by 0.097 kg to compensate.
)
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BULK SPECIFIC GRAVITY
In order to calculate volumes of the concrete mix
components, we need to know the Bulk SSD Specific
Gravities of the sand and stone, the specific gravity
of Portland Cement and the density of water.
Bulk SSD Density is calculated by dividing the mass
of the material at SSD by the bulk volume of the
material.
For sand (Lab 2 part A), a pycnometer is used to find
the bulk volume of a 500.0 gram sample of sand at
SSD.
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A pycnometer is a glass vessel used to
determine the volume of small-grained loose
material.
neck
calibration mark
Fill to calibration mark with
water and weigh: B
Place entire 500.0 g sample
into pyc., cover with water,
vacuum, fill to calibration
mark and weigh: C
Empty contents of pyc.,
into oven container of
known mass; after 18 h
bulb
scale
at 110°C find mass of
container and sample and
then dried sample: A
EA102
Oven Tags
Any material placed in the oven MUST be
properly identified…hence the oven tag:
EA102 CONSTRUCTION MATERIALS LAB #2
CLASS:
DATE:
1NV12
2006-01-26
4
GROUP:
TEST:
MASS OF CONTAINER:
MASS OF DRY SOIL + CONTAINER:
A
C
D
156.2
624.3
For
these
work,
you must
them
out
When
you to
have
finished,
file fill
them
in the
accurately
andclass
completely.
box with your
code in the drawer at
WS 8 (208). Use the paper clip to keep all
3 of your tags together.
EA102
Specific Gravities
There are 3 different specific gravities
calculated for the sand and stone:
ASTM Bulk Specific Gravity: G
ASTM
SSD Bulk Specific Gravity:
Apparent Specific Gravity:
MOD

VS  VWPV
GSSD 
GApparent
MSSD
VS  VWPV
MOD

VS
where MOD  OvenDried Mass of Sample
MSSD  SSD Mass of Sample
VS  Volume of Solids
VWPV  Volume of Water  Permeable Voids