SOLUTIONS GRADED A+
⩥ When sampling from a truck agitator or truck mixer,.
Answer: The sample shall be taken between the 10% and 90% points of
the discharge
⩥ Grab Sampling.
Answer: The operation of securing at one point of the discharge the
required volume of representative material in as short a period of time as
possible.
⩥ Sampling for uniformity of mixed concrete includes:.
Answer: Obtaining three grab samples of concrete for comparative
purposes while the mixer is being emptied and keep the samples separate
to represent the designated portions in the batch rather than combined to
form a composite sample.
⩥ When 100 mm x 200 mm cylinders are to be cast:.
Answer: A minimum 20 L sample shall be obtained.
⩥ When 150 mm x 300 mm cylinders are to be cast:.
Answer: A minimum 30 L sample shall be obtained.
,⩥ When 150 mm x 150 mm x 535 mm cylinders are to be cast:.
Answer: A minimum 55 L sample shall be obtained.
⩥ For more than three cylinders or beams, the minimum volume shall be
increased.
Answer: By a value equal to the volume of the extra specimens, plus
10%.
⩥ Sampling shall by performed.
Answer: By passing a receptacle completely through the discharge
stream or by completely diverting the discharge into a sample container.
⩥ The sample shall be obtained, transported, and remixed.
Answer: Within 10 minutes.
⩥ The sample shall be protected.
Answer: From sun, wind, and other sources of rapid evaporation and
from contamination.
⩥ When the concrete contains aggregate larger than that appropriate for
the size of the moulds or equipment to be used,.
Answer: the sample shall be wet sieved prior to testing. For all density
tests, an unsieved sample shall be used.
, ⩥ Do not use cardboard moulds:.
Answer: When the specified concrete strength is greater than 35 MPa.
⩥ Rectangular moulds:.
Answer: Should be at least 50 mm longer than the length of the span.
Moulds shall be watertight and made of rigid, nonabsorbent material.
⩥ Tamping rod for 100 x 200 mm cylinders.
Answer: Straight steel 10 +- 1 mm in diameter and between 450 and 600
mm in length, having at least one end rounded to a hemispherical tip.
⩥ Tamping rod for cylinders 150 mm in diameter or greater.
Answer: Straight steel 16 +- 1 mm in diameter and between 450 and 600
mm in length, having at least one end rounded to a hemispherical tip.
⩥ The frequency of vibration of an internal vibrator shall be a minimum
of.
Answer: 120 Hz
⩥ The outside diameter of the internal vibrator shall be.
Answer: 20 to 40 mm