Bulk Density and Void Content Bulk Density Bulk density ( n .) the - - PowerPoint PPT Presentation

Bulk Density and Void Content

Bulk Density

Bulk density (n.) the mass of a unit volume

• f bulk aggregate including the volume of

the individual particles and the volume of the voids between them.

CIVL 3137 2

 

agg 3 bucket

m kg bulk density V m

Unit Weight

Unit weight (n.) the weight of a unit volume

• f bulk aggregate including the volume of

the individual particles and the volume of the voids between them.

CIVL 3137 3

 

agg 3 bucket

W lb unit weight V ft

Dry-Rodded Unit Weight

• 1. DRY the aggregate overnight in the oven
• 2. Select a metal mold of known volume
• 3. Fill the mold in three lifts (layers)
• 4. ROD each lift 25 times with a tamping rod
• 5. Strike off the surface level with the mold
• 6. Weigh the mold and the aggregate
• 7. Subtract the weight of the empty mold

CIVL 3137 5

Equipment

CIVL 3137 6

1/4 cu. ft. 1/10 cu. ft. 1 cu. ft. 1/2 cu. ft. 1/3 cu. ft.

CIVL 3137 7

Dry-Rodded Unit Weight

CIVL 3137 8

Dry-Rodded Unit Weight

CIVL 3137 9

Question

A ½-ft3 bucket filled in three lifts holds 50 lb of dry aggregate. What is the dry-rodded unit weight?

CIVL 3137 10

Void Content

Void Content (n.) the volume of void spaces between particles expressed as a percentage of the volume needed to contain all of the particles.

 

voids bucket

V void content 100% V

Question

A ½-ft3 bucket filled in three lifts holds 50 lb of dry aggregate. What is the void content

• f the aggregate?

CIVL 3137 12

CIVL 3137 13

Volume of Voids

     

agg agg agg w w voids bucket agg

W m V RD RD V V V

CIVL 3137 14

Which Aggregate Volume?

Voids + Pores Voids Alone

(Net Volume) (Bulk Volume)

CIVL 3137 15

Volume of Voids

Voids Alone

(Bulk Volume)

   

agg agg B w agg agg B w

W V RD m V RD

Question

What determines the void content of a given aggregate sample?

CIVL 3137 17

Effects of Particle Size

10 in 10 in

5 × 5 × 5 =125 balls 10 × 10 × 10 =1000 balls

CIVL 3137 20

Effects of Particle Size

Void content = 48% Void content = 48%

5 × 5 × 5 =125 balls 10 × 10 × 10 =1000 balls

  3

sphere

4 V r 3

CIVL 3137 21

Effects of Particle Gradation

10 in 10 in

125 large balls 125 large + 125 small balls

  3

sphere

4 V r 3

CIVL 3137 23

Effects of Particle Gradation

Void content = 48% Void content = 41%

125 large balls 125 large + 125 small balls

  3

sphere

4 V r 3

CIVL 3137 25

Effects of Particle Gradation

Void content = 48% Void content = 48% Void content = 41% 100% CA 100% FA CA:FA Blend

CIVL 3137 26

Gravel-Sand Blend

20 30 40 20 40 60 80 100 Percentage of Sand in Blend Void Content (%)

Question

A 1-ft3 bucket holds a blend of aggregates. How much volume is

• ccupied by the air

and how much by the aggregate particles?

CIVL 3137 27

CIVL 3137 28

Volume of Voids

                 

agg agg agg B w B w A B

W W V RD RD  

voids bucket agg

V V V

CIVL 3137 29

Volume of Voids

                 

agg agg agg B w B w A B

m m V RD RD  

voids bucket agg

V V V

Example

An aggregate blend of 30% sand and 70% gravel has a dry-rodded unit weight of 125.5 lb/ft3. If the sand has a bulk specific gravity of 2.57 and the gravel has a bulk specific gravity of 2.69 what is the void content of the blend?

CIVL 3137 30

CIVL 3137 31

Volume of Voids

 

 

3 3 sand

W 0.3 125.5 lb ft 37.65 lb ft

3

Assume a volume of 1 ft

 

 

3 3 gravel

W 0.7 125.5 lb ft 87.85 lb ft

CIVL 3137 32

Volume of Voids

 

 

3 sand 3

37.65 lb V 0.235 ft 2.57 62.24 lb ft

 

 

3 gravel 3

87.85 lb V 0.525 ft 2.69 62.24 lb ft

CIVL 3137 33

Volume of Voids

   

3 3 3 3 voids

V 1 ft 0.235 ft 0.525 ft 0.24 ft   

3 3

0.24 ft %voids 100% 24% 1 ft

CIVL 3137 34

Gravel-Sand Blend

20 30 40 20 40 60 80 100 Percentage of Sand in Blend Void Content (%)