AS 1012.13:2015 Methods of testing concrete
7.3.1 Horizontal comparator
The procedure for taking the initial measurements with a horizontal comparator is as follows:
(a) At an age of seven days from moulding, remove the specimens one at a time from the lime-saturated water and wipe the surface dry with a damp cloth.
(b) Ensure that the ends of the gauge studs are clean and polished.
(c) Immediately after wiping the surface dry, place the specimen in the comparator so that its axis is aligned with the measuring anvil and its top surface, as cast, does not bear on the locating supports of the comparator. Record the micrometer reading (length difference) when the anvils are in contact with the specimen.
(d) Remove the specimen and replace it in the comparator in the same orientation. Repeat taking replicate measurements until at least five consecutive determinations have been made, all of which are within 0.001 mm of the average measurement. These readings shall be completed within 2 min of removing the specimen from the lime-saturated water. Record as the initial measurement the mean of these five determinations.
(e) Place the specimens on racks in the drying chamber so that there is a clearance of at least 50 mm on all sides, except for the necessary support.
(f) Using the reference bar, check the zero setting of the comparator after the measurement of every three specimens. Where the comparator is found to have varied by more than 0.002 mm, all readings taken since the previous reference bar check shall be repeated.
7.3.2 Vertical comparator
The procedure for taking the initial measurements with a vertical comparator is as follows:
(a) At an age of seven days from moulding, remove the specimens one at a time from the lime-saturated water and wipe the surface dry with a damp cloth.
(b) Mark each specimen to identify one end as the top. These markings shall be made on one cast face of each specimen only, and the marked face shall be the front.
(c) Before each specimen is measured, wipe both stud ends to remove any dust particles. Also wipe clean both the base anvil and the dial gauge anvil.