ASTM C 138 Density

Question 1

The size of the measure used in determining the density of fresh concrete,
A. is based on the slump of the concrete.
B. is always 0.5 cubic feet
C. is based on the nominal maximum size (NMS) of the coarse aggregate.
D. depends on whether the concrete is consolidated using a tamping rod or vibrator.

Answer 1

is based on the nominal maximum size (NMS) of the coarse aggregate.

Question 2

It is permissible to use the bowl from the volumetric air meter to determine the density of fresh concrete when the nominal maximum aggregate size is 1 inch or less.
(T or F)

Answer 2

False

Question 3

The appropriate method of consolidation, when the slump of fresh concrete is between 1 and 3 inches, is to use
A. the tamping rod.
B. a vibrator.
C. either a tamping rod or vibrator.
D. a 24 inch long #5 reinforcing bar.

Answer 3

either a tamping rod or vibrator.

Question 4

When rodding the second and third layers of concrete in the measure, the rod should
A. strike the bottom of the measure, but not forcibly.
B. penetrate the underlying layer through half its depth.
C. penetrate the underlying layer approximately 1 inch.
D. not penetrate the underlying layer.

Answer 4

penetrate the underlying layer approximately 1 inch.

Question 5

When a vibrator is used to consolidate the concrete in the measure, fill the measure in _____ approximately equal layers
A. 1
B. 2
C. 3
D. 4

Answer 5

2

Question 6

Upon completion of the consolidation process, it is optimal to have approximately 1/8 inch of excess concrete above the rim of the measure.
(T or F)

Answer 6

True

Question 7

It is permissible to add a small quantity of representative concrete to the measure to correct a deficiency.
(T or F)

Answer 7

True

Question 8

To insure that the measure is level full with concrete, strike‐off the top surface of the concrete using
A. the tamping rod in a rolling and sawing motion.
B. the tamping rod, then use the plate at an angle for a smooth finish.
C. the plate, then use the rod in a rolling and sawing motion.
D. the strike‐off plate.

Answer 8

the strike-off plate

Question 9

In order to determine the density of fresh concrete, it is necessary to determine
A. the mass of the filled measure, the mass of the empty measure as well as the volume of the measure.
B. only the mass and volume of the filled measure.
C. only the mass of the filled measure.
D. the mass and volume of the filled measure, as well as the air content of the fresh concrete.

Answer 9

the mass of the filled measure, the mass of the empty measure as well as the volume of the measure.

Question 10

Yield represents the
A. density of a concrete mixture.
B. volume of concrete produced per batch
C. total mass of all materials batched.
D. relative air content of the batch.

Answer 10

volume of concrete produced per batch

Question 11

The gravimetric air content of a mixture is computed using the following equation, where T is the theoretical density and D is the measured density of a mixture.
A. A = (T+D) / T x 100
B. A = (T‐D) / T x 100
C. A = (T+D) / D x 100
D. A = (T‐D) / D x 100

Answer 11

A = (T‐D) / T x 100

Question 12

After consolidating a layer by vibration, tap the outside of the measure 10‐15 times with the mallet.
(T or F)

Answer 12

False

Question 13

The density of a concrete mixture is computed to be 142.568 lb/ft^3. The density should be reported as
A. 142 lb/ft^3
B. 142.6 lb/ft^3
C. 142.57 lb/ft^3
D. 142.568 lb/ft^3

Answer 13

142.6 lb/ft^3

Question 14

Report the yield of a concrete mixture to the nearest
A. 0.01 ft^3
B. 0.001 yd^3
C. 0.01 yd^3
D. 0.1 yd^3

Answer 14

0.1yd^3

Question 15

The volume of a measure is 0.510 ft^3. The net mass of concrete in the measure is 72.3 lbs. Calculate the density of the concrete
A. 72.3 x 0.510 = 36.9 lb/ft^3
B. (72.3 + 27) x 0.510 = 50.6 lb/ft^3
C. 72.3/0.510 = 141.8 lb/ft^3
D. (72.3 + 27) / 0.510 = 194.7 lb/ft^3

Answer 15

72.3/0.510 = 141.8 lb/ft^3

Question 16

The total mass of all materials in a batch of concrete is 26,520 lbs. The measured density for the mixture is 144.3 lb/ft^3. Calculate the yield in cubic yards (yd^3) for the batch.
A. 26,520 / (144.3 x 27) = 6.8 yd^3
B. 26,520 / 144.3 = 183.8 yd^3
C. (144.3 x 27) / 26,520 = 0.15 yd^3
D. (26,520 x 27) / 144.3 = 4692 yd^3

Answer 16

26,520 / (144.3 x 27) = 6.8 yd^3

Question 17

The design yield for a batch is 8.5 yd^3. The actual yield for the batch is 8.7 yd^3. Calculate the relative yield.
A. 8.7 / 8.5 = 1.02
B. 8.5 / 8.7 = 0.98

Answer 17

8.7 / 8.5 = 1.02

Question 18

The theoretical density of a mixture is 151.2 lb/ft^3. The measured density of the mixture is 142.6 lb/ft^3. Calculate the gravimetric air content for the mixture
A. [(151.2 – 142.6) / 142.6] x 100 = 6.0%
B. [(151.2 – 142.6) / 151.2] x 100 = 5.7%

Answer 18

[(151.2 – 142.6) / 151.2] x 100 = 5.7%

Question 19

Vibrator must have a minimum frequency of?

Answer 19

9000 vibrations/min (150Hz)

Question 20

Vibrator rod must be no less than….. but no more than…. In diameter

Answer 20

3/4in / 1-1/2in

Question 21

Mass should be determined to what decimal

Answer 21

.1 lb

Question 22

Volume should be determined to what decimal?

Answer 22

.001 lb

Question 23

Weight should be determined to what decimal?

Answer 23

.1 lb ft^3

Question 24

Yield should be determined to what decimal?

Answer 24

.1 yd^3

Question 25

Air content should be reported to what decimal?

Answer 25

.1%

Question 26

Relative yield should be reported to what decimal?

Answer 26

.01

Question 27

How many cubic feet are in a yard

Answer 27

27

Question 28

How to calculate density

Answer 28

Full - empty
Divided by volume .250
Equals density lbs/ft^3

Question 29

Calculate yield

Answer 29

Total mass of material in batch / density of concrete (27)

Example
34,700 / (141.8 x 27) = 9.1 yd^3