Saturated Surface Dry COndition.ppt

SSD Pavement Material a collected copy

1. SPECIFIC GRAVITY &
ABSORPTION CAPACITY
OF AGGREGATES
EA102

2. Density
The density, ρ of any material
is the mass per unit of volume:
For example, how many
kilograms in 1 cubic metre of
the material?
1 m
3
or, how many grams in 1 cubic
centimetre of the material?
1 cm
3
EA102V
M
ρ
i.e.,

3. 1 m
3
At 4˚ C, water has a density,
ρ
wof exactly 1000 kilograms
per cubic metre
EA102
1 cm
3
At 4˚ C, water has a density,
ρ
wof exactly 1 gram per
cubic centimetre
At 20˚ C (standard), water
has a density, ρ
wof 0.99823
gram per cubic centimetre

4. To find the density of any material, a
sample of the material is weighed in
air, M
airand then in water, M
water.
EA102
The difference between the mass in
air and water is the mass of the
water displaced by the material when
placed in the water:waterairdisplaced water
MMM 

5. Since the volume of the material weighed is
the same as the volume of water it displaces…
EA102w
waterair
w
displaced water
displaced water
ρ
MM
ρ
M
V


,V
M
ρ Since,w
waterair
air
w
waterair
air
ρ
MM
M
ρ
MM
M
ρ 





6. The specific gravity, Gof a material
is just its density relative to the
density of water:
EA102
Specific Gravitywρ
ρ
G

7. Moisture States in
Aggregates
There are 4 distinct moisture
states for aggregates:
EA102
Oven Dried
Aggregate Particle
Water Permeable Voids
(No Moisture)(Hygroscopic Moisture)
Air Dried
Moisture from Air
Saturated Surface
Dried, SSD
Voids Filled with Water
Free Moisture
(Water between particles)
Particle coated with water

8. Moisture Content
The moisture content of a soil or
aggregate is the mass of water per
unit mass of dry material.
EA102Sample Dried of Mass
Sample Dried of MassSample Wet of Mass
M
M
w
s
w


Moisture content is often expressed as a
percentage, i.e., the mass of water in grams
per 100 grams of dry material.

9. The absorption capacity, %ABS is the moisture
content of the material when it is in the
saturated surface dried state.
EA102
Absorption Capacity
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.

10. EA102
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?
Example
First find the moisture content:2.71%
486.4
486.4499.6
w 


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.

11. How much?
EA102
APPROXIMATELY, an extra 2.71-1.5 = 1.21% of
the required SSD mass.
The mathematically correct
version of this % correction is:1.192%
101.5
1.52.71
C 

 ( )
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.

12. BULK SPECIFIC GRAVITY
In order to calculate volumes of the concrete mix
components, we need to know the Bulk SSD Specific
Gravitiesof the sand and stone, the specific gravity
of Portland Cement and the density of water.
EA102
Bulk SSD Densityis 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.

13. A pycnometer is a glass vessel used to
determine the volume of small-grained loose
material.
EA102
neck
calibration mark
scale
bulb
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
at 110°C find mass of
container and sample and
then dried sample: A

14. EA102
Any material placed in the oven MUST be
properly identified…hence the oven tag:
Oven TagsCLASS: GROUP:
DATE: TEST:
MASS OF CONTAINER:
MASS OF DRY SOIL + CONTAINER:
EA102 CONSTRUCTION MATERIALS LAB #2
A C D
For these to work, you must fill them out
accurately and completely.
1NV12 4
2006-01-26
156.2
624.3
When you have finished, file them in the
box with your class code in the drawer at
WS 8 (208). Use the paper clip to keep all
3 of your tags together.

15. EA102
There are 3 different specific gravities
calculated for the sand and stone:
Specific Gravities
ASTM Bulk Specific Gravity:
SSD Bulk Specific Gravity:
Apparent Specific Gravity:WPVS
OD
ASTM
VV
M
G

 WPVS
SSD
SSD
VV
M
G

 S
OD
Apparent
V
M
G  Voids PermeableWater of VolumeV
Solids of VolumeV
Sample of Mass SSDM
Sample of Mass Dried OvenM where
WPV
S
SSD
OD



