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 of bulk aggregate including the volume of the individual particles and the volume of the voids between them. m kg agg bulk density   3 V m bucket CIVL 3137 2

Unit Weight Unit weight ( n .) the weight of a unit volume of bulk aggregate including the volume of the individual particles and the volume of the voids between them. W lb agg unit weight   3 V ft bucket CIVL 3137 3

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 1 cu. ft. 1/3 cu. ft. 1/2 cu. ft. 1/4 cu. ft. 1/10 cu. ft. CIVL 3137 6

CIVL 3137 7

Dry-Rodded Unit Weight CIVL 3137 8

Dry-Rodded Unit Weight CIVL 3137 9

Question A ½-ft 3 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. V void content   100% voids V bucket

Question A ½-ft 3 bucket filled in three lifts holds 50 lb of dry aggregate. What is the void content of the aggregate? CIVL 3137 12

Volume of Voids W m agg agg V   agg RD  RD  w w V  V  V voids bucket agg CIVL 3137 13

Which Aggregate Volume? Voids + Pores Voids Alone (Net Volume) (Bulk Volume) CIVL 3137 14

Volume of Voids W agg V  agg RD  B w m agg V  agg RD  Voids Alone B w (Bulk Volume) CIVL 3137 15

Question What determines the void content of a given aggregate sample?

Effects of Particle Size 5 × 5 × 5 =125 balls 10 × 10 × 10 =1000 balls 10 in 10 in CIVL 3137 17

Effects of Particle Size 5 × 5 × 5 =125 balls 10 × 10 × 10 =1000 balls Void content = 48% Void content = 48% 4   3 V r sphere 3 CIVL 3137 20

Effects of Particle Gradation 125 large balls 125 large + 125 small balls 10 in 10 in 4   3 V r sphere 3 CIVL 3137 21

Effects of Particle Gradation 125 large balls 125 large + 125 small balls Void content = 48% Void content = 41% 4   3 V r sphere 3 CIVL 3137 23

Effects of Particle Gradation 100% CA CA:FA Blend 100% FA Void content = 48% Void content = 41% Void content = 48% CIVL 3137 25

Gravel-Sand Blend 40 Void Content (%) 30 20 0 20 40 60 80 100 Percentage of Sand in Blend CIVL 3137 26

Question A 1-ft 3 bucket holds a blend of aggregates. How much volume is occupied by the air and how much by the aggregate particles? CIVL 3137 27

Volume of Voids W W     agg agg V         agg RD  RD      B w B w A B V  V  V voids bucket agg CIVL 3137 28

Volume of Voids m m     agg agg V         agg RD  RD      B w B w A B V  V  V voids bucket agg CIVL 3137 29

Example An aggregate blend of 30% sand and 70% gravel has a dry-rodded unit weight of 125.5 lb/ft 3 . 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

Volume of Voids 3 Assume a volume of 1 ft    3  3 W 0.3 125.5 lb ft 37.65 lb ft sand    3  3 W 0.7 125.5 lb ft 87.85 lb ft gravel CIVL 3137 31

Volume of Voids 37.65 lb 3 V   0.235 ft   sand 3 2.57 62.24 lb ft 87.85 lb 3 V   0.525 ft   gravel 3 2.69 62.24 lb ft CIVL 3137 32

Volume of Voids 3 3 3 3 V  1 ft  0.235 ft  0.525 ft  0.24 ft voids 3 0.24 ft %voids   100%  24% 3 1 ft CIVL 3137 33

Gravel-Sand Blend 40 Void Content (%) 30 20 0 20 40 60 80 100 Percentage of Sand in Blend CIVL 3137 34