SPECIFIC GRAVITY & SPECIFIC GRAVITY & ABSORPTION ABSORPTION CAPACITY OF CAPACITY OF AGGREGATESAGGREGATES

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DensityDensityThe 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 m3

or, how many grams in 1 cubic centimetre of the

material?1 cm3

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VM

ρi.e.,

1 m3

At 4˚ C, water has a density, ρw of exactly 1000 kilograms per cubic metre

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1 cm3

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

To find the density of any material, a sample of the material is

weighed in air, Mair and then in water, Mwater.

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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

Since the volume of the material weighed is the same as the volume of water it

displaces…

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w

waterair

w

displaced waterdisplaced water ρ

MMρ

MV

, V

MρSince,

wwaterair

air

w

waterair

air ρMM

M

ρMM

Mρ

The specific gravity, G of a material is just its density relative

to the density of water:

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Specific GravitySpecific Gravity

wρρ

G

Moisture States in Moisture States in AggregatesAggregates

There are 4 distinct moisture states for aggregates:

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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

Moisture ContentMoisture Content

The moisture content of a soil or aggregate is the mass of water per

unit mass of dry material.

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Sample Dried of Mass

Sample Dried of MassSample Wet of Mass

MM

ws

w

Moisture content is often expressed as a percentage, i.e., the mass of water in grams per 100 grams of dry material.

The absorption capacity, %ABS is the moisture content of the material when it is

in the saturated surface dried state.

EA102 Absorption Absorption CapacityCapacity

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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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?

ExamplExamplee

First find the moisture content: 2.71%486.4

486.4499.6w

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.

How much?

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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

1.52.71C

( )

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.

BULK SPECIFIC BULK SPECIFIC GRAVITYGRAVITY

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.

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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.

A pycnometer is a glass vessel used to determine the volume of small-grained

loose material.

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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: CEmpty 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

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Any material placed in the oven MUST be properly identified…hence the oven tag:

Oven TagsOven Tags

CLASS: GROUP:

DATE: TEST:

MASS OF CONTAI NER:

MASS OF DRY SOI L + CONTAI NER:

EA102 CONSTRUCTI ON MATERI ALS LAB #2

A C D

For these to work, you must fill them out accurately and completely.

1NV12

42006-01-26 156.2

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.

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There are 3 different specific gravities calculated for the sand and stone:

Specific GravitiesSpecific Gravities

ASTM Bulk Specific Gravity:

SSD Bulk Specific Gravity:

Apparent Specific Gravity:

WPVS

ODASTM VV

MG

WPVS

SSDSSD VV

MG

S

ODApparent V

MG

Voids PermeableWater of VolumeV

Solids of VolumeV

Sample of Mass SSDM

Sample of Mass Dried OvenM where

WPV

S

SSD

OD