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close this bookQuality Control Guidelines - Fibre or Micro Concrete Tiles (SKAT, 1991, 79 p.)
close this folder3. Production process
View the document(introduction...)
View the documentMortar preparation workability test
View the documentMortar preparation mortar strength test
View the documentDemoulding / Size and shape

(introduction...)

Introduction

Beside the quality of the raw materials, careful production is the other important requisite for a high standard product.

The tests involved in the production process are:

3.1 Mortar preparation
3.4 Demoulding

Mortar preparation workability test

Fieldtest

Why this test
An easy way of controlling that the right mix proportions have been used in the mortar is to check its workability.

How
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


Figure

Who

Foreman

When

The workability of the mortar should be controlled for each mix immediately before casting the first tile and before casting the last tile.

Result

Record keeping: yes
Measure the average diameter of the mortar “pancake” that results.

Consequence

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

Mortar preparation mortar strength test

Laboratory test

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).

How

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.

Procedure:

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.


Figure


Vibrating table

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.


Figure


Figure

100 g weight at the age of 24 hours

500 g weight at the age of 28 days


Figure

Who

Foreman or laboratory staff

When

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.

Result

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.

Consequence

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.

Demoulding / Size and shape

Field test

Why this test

Only the correct size and shape of all tiles ensures a proper fixing on the roof. Poorly fitting tiles easily crack under load and wind driven water may enter the roof.

Tiles that are not square will not fit properly and the overlap will not be sufficient.

Tiles that are too thin will leak and are not strong enough.

How

Check every tile that it has the right dimensions, shape and profile during the demoulding operation. For tiles the special quality control jig developed by JPM Parry can be used.

Hold the mould on edge and place the tile against the quality control jig. Roll the mould with the tile over on the jig’s pivots until upside down. Lift the mould off. Remove the plastic interface sheet by pulling straight across from the side edge.

Run around tile edge with a knife to remove any excess flash. Check carefully that the tile fits the jig and does not wobble.

The edge of the bar should be seen, but should not have a gap showing beneath it.

If the jig is not available the test can also be done on a mould.

Always use an especially assigned mould only used for this purpose. If a plastic mould is used then it must be adequately supported to prevent flexing.

Squareness:

Test on a standard mould that the edges of the tile are parallel with the mould.

Thickness at the edges:

Check if the thickness of the upper part of the tile (a) differs from the thickness of the lower part of the tile (b). For a 6 mm thick tile it should range between 5.5 and 6.5 mm. Check on both ends of the tile.

Thickness in the middle:

Occasionally, check also the thickness of the tile in its center, by breaking the tile.


Figure


Figure

Who

Worker

When

During demoulding

Result

Record keeping: yes
The product should be within the following tolerances:

Tolerance on length

+/-

10 mm

Tolerance on width

+/-

5 mm

Tolerance on profile

+/-

3 mm

Tolerance on thickness

+/-

0,5 mm

Tolerance on squareness

+/-

3 mm

Consequence
If test fails
Discard tiles that fail the test. If the thickness varies too much the mix has to be examined and/or the worker should improve his performance.