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SPECIFIC GRAVITY. aka Relative Density. How specific is gravity anyway?. or How dense are your relatives?. What is Specific Gravity?. The density of any material is just its mass divided by its volume. It’s just the density of any material relative to (divided by) the density of water.

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slide1

SPECIFIC GRAVITY

aka Relative Density

How specific is gravity anyway?

or How dense are your relatives?

what is specific gravity

What is Specific Gravity?

The density of any material is just its mass divided by its volume

It’s just the density of any material relative to (divided by) the density of water

We measure the volume of any material by finding its mass in air and water

back in 200 bc in greece

Back in 200 BC in Greece…

Archimedes figured out how to find the volume of any weird-shaped object…

its volume is equal to the volume of water that it displaces when immersed in water

…its volume is equal to the volume of water that it displaces when immersed in water

In the lab we can weigh an object in air and then in water or use a pycnometer

for coarse aggregate

For Coarse Aggregate:

and then calculate:

we measure:

A = Oven dry mass of the sample (kilograms)

B = Mass of SSD sample in air (kilograms)

C = Mass of SSD sample in water (kilograms)

slide6

NOTE:

for specific gravity, divide density by the density of water...

the ssd mass in air is also just

The SSD mass in air is also just...

=

+

the oven dried mass in air, PLUS

A

B - A

B

the mass of water in the water permeable voids

g ssd and g astm

are “Bulk” Specific Gravities

GSSD and GASTM

The “Bulk” volume includes the water permeable voids:

This is because the “Bulk” volume of the material is used in the calculation

B - C

NOTE: the SSD sample does not absorb any water when its weighed in water

for the apparent specific gravity g apparent

For the “Apparent” Specific Gravity, GAPPARENT,

The volume excludes the water permeable voids:

A - C

for fine aggregate

For Fine Aggregate:

and then calculate:

we measure:

500.0 grams of SSD sample

A = Oven dry mass of the sample (grams)

B = Mass of the pycnometer + water (grams)

C = Mass of pycnometer + sample + water (grams)

instead of the a b c s let s use some meaningful nomenclature

Instead of the A, B, C’s let’s use some meaningful nomenclature:

The SSD mass of the sand or stone in air is thenMS + the mass of water absorbed, MWABS

Let the oven dried mass of the sand or stone (i.e., mass of solids in air) beMS

The Bulk Volume is the volume of solids VS +the volume of water absorbed VWABS

bulk volume

Since ρw = 1 g/cm3

Therefore, Bulk Volume =

Bulk Volume

Mpyc

+ Mwcal

+ MS

+ MWABS

- Mpyc

- Mwexcal

- MS

- MWABS

C = Mpyc + Mwexcal + MS + MWABS

B = Mpyc + Mwcal

500 = MS + MWABS

Mpyc

calibration mark

Mass of water displaced by SSD sample = B + 500 - C

Mwcal

Mwexcal

-

+

MS + MWABS

(500 grams)

apparent volume

Therefore, Apparent Volume =

Apparent Volume

Mpyc

+ Mwcal

+ MS

- Mpyc

- Mwexcal

- MS

- MWABS

B = Mpyc + Mwcal

A = MS

C = Mpyc + Mwexcal + MS + MWABS

Mwcal – Mwexcal is the bulk volume of all the sand particles in the sample

Mass of water displaced by solids = B + A - C

Since this includes the volume of the water-permeable voids in all the sand particles,subtracting theMWABSwill leave the volume of the solid parts of the sand particles only

slide14

Now we can examine the relationships among these different versions of specific gravity and the absorption capacity.

If masses are in grams and volumes in cm3, then

OR

for example we can find an expression for g ssd in terms of g apparent and w a

For example, we can find an expression for GSSD in terms of GAPPARENT and wa:

Substituting:

Cancelling Ms’s:

and Rearranging:

similar relations can be determined for any of the four parameter in terms of any 2 of the others

Also, given any 2 of the parameter values, the other 2 can be determined.

Example: If GASTM =2.605 & GAPPARENT = 2.718, find the GSSD and wa.

Similar relations can be determined for any of the four parameter in terms of any 2 of the others.

Basing the calculations on 100 g of oven dried material,