|Quality Control Guidelines - Fibre or Micro Concrete Tiles (SKAT, 1991, 79 p.)|
|3. Production process|
Why this test
The strength development of the mortar has to be tested
- to determine the best mix and to control the quality of the raw materials.
- to control if the FCR/MCR products have gained enough strength prior to demoulding (after 24 h).
In a situation where this test is too complicated it may be substituted with the Bending Test (4.3.10).
The strength development of the mortar can be controlled on
specially prepared specimens.
The specimens could be prepared for mortar produced at the end of the day.
Place a plastic interface sheet on the vibrating table and place the special prism mould on the plastic interface sheet. Press the mould down with one hand and fill it with mortar. Cut off the mortar flush with a trowel, start the vibrator and let it work for exactly 10 seconds (or the time you would normally use for casting the tiles). Press the mould down with two fingers during the whole operation.
Transfer the plastic interface sheet with the mould over to a plank or other flat surface. Cover the mould immediately with another plastic interface sheet and a plank.
Demould the two specimens after 24 hours (or according to the time you intend to demould your tiles) and test one of them immediately. Mark the second specimen with the date and store it in the curing tanks together with the FCR/MCR products produced the previous day.
The specimens tested at the age of 28 days should be cured in the same way as the FCR/MCR products, i.e. in water for at least 5 days and in air protected against sunshine and fast evaporation for one week. After the curing period the specimens may be stored dry in the workshop.
The strength test is done by placing the specimen into the strength test rig and placing the appropriate weight, 100 g for the 24 hour old specimen and 500_g for the 28 day old specimen on the edge of the specimen.
100 g weight at the age of 24 hours
500 g weight at the age of 28 days
Foreman or laboratory staff
The mortar strength test should be done once a day. The strength of the specimens should be determined after 24 hours or according to the time you intend to demould the tiles.
Record keeping: yes
If the specimen does carry the load it has a flexural strength of at least 1 MPa (N/mm2 or 10 kp/cm2 ) after 24 hours and at least 5 MPa after 28 days.
This is sufficient for a good quality tile.
If test fails
1. A specimen tested after 24 hours fails:
It can be tested again by putting the other end of the specimen into the strength test rig and applying the actual weight (100 g) on the previously broken edge. If the specimen carries the load no other action is necessary other than preparing new specimens for testing the following day.
2. The specimen also fails this second test: The demoulding of the FCR/MCR products cast the previous day should be delayed for some hours and the demoulding be made under special care. All the FCR/MCR products produced during this period should be water cured for five extra days.
Before new FCR/MCR products are produced the reasons for the low strength must be found. Prepare new test specimens and test both of them after 24 hours. If they also fail:
- change the water to cement ratio,
- or use a different type of cement,
- or increase cement quantity,
- or use a different type of sand.
3. The 28 day test fails: The regional center should be contacted for investigating the reasons for the failure.