Unit Weight
Unit Weight
Significance and Use
• Often used to determine bulk density values used in selecting proportions for concrete mixes
• Also used for mass/volume relationships for conversions in purchase agreements
• Also used annually for inventory control and verification
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Unit Weight
Definition
• Unit Weight is the weight per unit volume of a material. Unit Weight = Weight of Material
Volume of Material
Example:
U.W. = 103.2 lbs = 103.2 pcf
1 cf
Loose Unit Weight
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Loose Unit Weight
Loose Unit Weight
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Loose Unit Weight
Loose Unit Weight
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Dry Rodded Unit Weight
Test Procedure
• For nominal maximum size of 1½” (37.5 mm) or less, use rodding procedure.
• For nominal maximum size greater than 1½” (37.5 mm), use jigging procedure.
• Record weight of empty bucket (to the nearest 0.1 lbs or 0.05 kg).
• Dry aggregate sample to a constant mass.
• Fill bucket ⅓ full with dried aggregate.
• Level surface with fingers.
Dry Rodded Unit Weight
Test Procedure
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Dry Rodded Unit Weight
Test Procedure
Dry Rodded Unit Weight
Test Procedure
• Rod 1st aggregate layer.
– Use 25 strokes of the tamping rod.
– Evenly distribute the strokes over the surface.
– Do not allow rod to strike bottom of bucket forcibly.
• Fill bucket ⅔ full with dried aggregate.
• Repeat leveling and rodding procedure.
– Use more vigorous effort than on 1st layer, but
– Do not cause tamping rod to penetrate to previous layer.
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Dry Rodded Unit Weight
Test Procedure
Dry Rodded Unit Weight
Test Procedure
• Fill bucket to overflowing.
• Repeat leveling and rodding procedure.
• Level final aggregate surface with fingers or a straight edge.
– Make any slight projections of larger pieces of aggregate approximately balance the larger voids in the surface.
• Record weight of bucket and sample.
• Calculate unit weight and % voids of dry rodded aggregate.
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Dry Rodded Unit Weight
Test Procedure
Dry Rodded Unit Weight
Test Procedure
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Dry Rodded Unit Weight
Test Procedure
Dry Rodded Unit Weight
Test Procedure
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Dry Rodded Unit Weight
Test Procedure
Dry Rodded Unit Weight
Test Procedure
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Unit Weight Bucket Calibration
• Volume of bucket must be calibrated at least once per year.
– Place a thin layer of grease around the rim of the bucket to prevent water leakage.
– Record combined weight of empty bucket and plate glass (to the nearest 0.1 lbs or 0.05 kg). Unit Weight Bucket Calibration
• Bucket volume calibration, cont’d – Fill bucket with water and cover with plate glass.
• Leave no bubbles or excess water.
• Wipe off any overflow water.
– Record combined weight of bucket, water, and plate glass (to the nearest 0.1 lbs or 0.05 kg). 11
Unit Weight Bucket Calibration
• Bucket volume calibration, cont’d.
– Record temperature of water (to the nearest 1 °F or 0.5 °C).
– Use Table 1 to determine correct unit weight of water at the recorded temperature. – Calculate the volume of the bucket (same as volume of just the water).
Unit Weight Bucket Calibration
Table 1
Water Temperature, °F
Unit Weight of Water, pcf
60
62.366
65
62.336
70
62.301
73.4
62.274
75
62.261
80
62.216
85
62.166
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Unit Weight Bucket Calibration
• Bucket volume calibration, cont’d.
A = Weight of empty bucket + plate B = Weight of water‐filled bucket + plate C = Unit Weight of water at measured temperature
Bucket Volume = B – A
C
Unit Weight
Bucket Calibration
• Example:
– Weight of empty bucket + plate = 1.8 lbs
– Weight of water‐filled bucket + plate = 34.2 lbs
– Temperature of water in bucket = 70 °F
• UW of water at 70 °F = 62.301 pcf (from Table 1)
Bucket Volume = (34.2 lbs – 1.8 lbs)
62.301 pcf
Bucket Volume = 0.52 cf
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Adjusted Unit Weight
% Moisture
• Record weight of wet aggregate sample
• Dry sample to a constant mass
• Calculate %moisture of sample:
– %Moisture = (Wet Wt. – Dry Wt.) x 100
Dry Wt.
Adjusted Unit Weight
% Moisture
• Example:
– Weight of wet sample = 125.0 lbs
– Weight of dry sample = 117.9 lbs
% M = (125.0 lbs – 117.9 lbs) x 100
117.9 lbs
% Moisture = 6.0%
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Adjusted Unit Weight
% Moisture
• Adjust the dry‐rodded unit weight for moisture
• Example:
– Dry‐rodded unit weight = 101.2 pcf
– % Moisture = 6.0%
– Adjusted U.W. = 101.2 pcf x 1.06
– Adjusted U.W. = 107.3 pcf
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