The steps for mixing the cement pastes are as follows:

 

1. Experimental equipment must be set up in a lab with a control temperature of 20°C (±2) and relative humidity of no less than 50%

2. Binder (in the desired proportions) along with the required quantity of water must be prepared and placed in the lab for 24h before testing to acclimatize to the lab temperature and relative humidity

3. The materials must then be placed into a mixing bowl and positioned under the an automatic mixer* 

4. Mixing commences directly after the require water quantity is added to the mixing bowl and the time of wetting must be recorded

5. Mixing takes place at a low speed and is stopped after 90s for 30s during which the paste adhering to the sides and bottom of the mixing bowl must be brought to the middle of the mixing bowl, after which a further 90s of mixing commences

6. Once mixing is completed the paste must immediately be transferred to the test specific container/mould

7. Voids are to be removed by gently tapping the container/mould against the ball of the hand

8. Excess paste is removed by a gentle sawing motion with a straight-edged instrument to leave the mould filled with a smooth upper surface.

 

*The mixer used was a Hobart A120 which conforms to SANS 50196-1:2006 and can be seen in the image below.