|Quality Control Guidelines - Fibre or Micro Concrete Tiles (SKAT, 1991, 79 p.)|
|3. Production process|
Why this test
An easy way of controlling that the right mix proportions have been used in the mortar is to check its workability.
The workability can be measured in the following way:
Place a plastic interface sheet on the vibrating table top. Place a standard mould in the center of the table top. Press the mould down to the table and fill it with mortar and tamp the mortar 20 times with a tamper (for instance the thick end of a pencil).
Cut off the mortar flush with a trowel.
Remove the mould, start the vibrator and let it work for exactly 10 seconds or the time you would normally use when producing your tiles (should not exceed 20 seconds). For pedal driven vibrators count also the cycles, e.g. 14 each leg in approx. 10 seconds.
Fill mould with mortar
Tamp the mortar 20 times
Cut off the mortar flush
The workability of the mortar should be controlled for each mix immediately before casting the first tile and before casting the last tile.
Record keeping: yes
Measure the average diameter of the mortar pancake that results.
The bigger the diameter of the pancake, the shorter vibration time is needed for the compaction. If the workability is too high, the mortar might be overvibrated during production, i.e. the components of the mix may separate. In this case the water addition has been too high. (The sand may also be too wet). You should therefore add extra cement to the mix.
Experience tells you what the best workability for a given raw material is.
If the workability differs more than 20 % from your standard adjust the mix. If too stiff, add cement paste (a mixture of water and cement with fixed, low water to cement ratio). If too wet, add sand.
(a + b) / 2 = workability