1. SPECIFIC GRAVITY & ABSORPTION CAPACITY OF AGGREGATES
EA102
SPECIFIC GRAVITY & ABSORPTION CAPACITY OF AGGREGATES

2. The density, ρ of any material is the mass per unit of volume:
EA102
Density
The density, ρ of any material is the mass per unit of volume:
i.e.,
For example, how many kilograms in 1 cubic metre of the material?
1 m3
or, how many grams in 1 cubic centimetre of the material?
1 cm3

3. EA102
At 4˚ C, water has a density, ρw of exactly 1000 kilograms per cubic metre
1 m3
At 4˚ C, water has a density, ρw of exactly 1 gram per cubic centimetre
1 cm3
At 20˚ C (standard), water has a density, ρw of gram per cubic centimetre

4. EA102
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:

5. EA102 ,
Since,
Since the volume of the material weighed is the same as the volume of water it displaces…

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

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

8. EA102
Moisture Content
The moisture content of a soil or aggregate is the mass of water per unit mass of dry material.
Moisture content is often expressed as a percentage, i.e., the mass of water in grams per 100 grams of dry material.

9. EA102
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.

10. EA102
Example
The %ABS of stock sand is 1.5% and we need 8 kg of sand in the SSD condition to make concrete. A gram sample of the stock sand was dried over a bunsen burner to a constant mass of grams. How much of the sand should be used?
First find the moisture content:
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. APPROXIMATELY, an extra 2.71-1.5 = 1.21% of the required SSD mass.
EA102
How much?
APPROXIMATELY, an extra = 1.21% of the required SSD mass. ( )
The mathematically correct version of this % correction is:
This translates to x = an extra or kg of sand.
This means an extra kg of water will be brought into the mix, so the mixing water should be reduced by kg to compensate.

12. EA102
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 gram sample of sand at SSD.

13. Fill to calibration mark with water and weigh: B
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A pycnometer is a glass vessel used to determine the volume of small-grained loose material.
Fill to calibration mark with water and weigh: B
neck
Place entire g sample into pyc., cover with water, vacuum, fill to calibration mark and weigh: C
calibration mark
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
bulb
scale

14. EA102
Oven Tags
Any material placed in the oven MUST be properly identified…hence the oven tag:
1NV12 4
156.2
624.3
For these to work, you must fill them out accurately and completely.
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
Specific Gravities
There are 3 different specific gravities calculated for the sand and stone:
ASTM Bulk Specific Gravity:
SSD Bulk Specific Gravity:
Apparent Specific Gravity: