|Fibre Concrete (FCR) / Micro Concrete (MCR) Roofing Equipment (GTZ, 1991, 20 p.)|
Apart from a set of ordinary masonry irnplements (eg spades, measuring pans, wheelbarrows, sieves, trowels, sand and cement batching boxes, balance and the like), the production of FCR and MCR elements requires some special equipment:
· screeding machines
· testing equipment.
· This comprises a vibrating screeding
surface and interchangeable, hinged frame (for products of different shapes and
thicknesses). The machine can be a small, portable 'mini-plant', or a stationary
· The vibrating mechanism requires an energy source, which can be electricity (from a mains outlet, converted to 12 volt dc powerby a transformer-rectifier; or from a car battery), handpower (crank with pulley system or metal springs), foot-power (treadle or bicycle pedal system), or flywheel energy (hand-operated).
Advantages and problems of the various screeding machines
· Electric machines:
+ relatively quiet, do not tire out the user, produce uniform, good quality elements;
- relatively expensive, dependent on reliable power supplies for operating the machines or recharging batteries, risk of production setback due to bad battery maintenance.
· Hand-powerd machines:
+ independent of power supplies and can thus be used in remote rural areas;
- relatively noisy end tiring and needs 2 people to operate, uniformity of vibration dependent on the way the handle is turned, thus possibility of non-uniform quality of products.
· Foot-powered machines:
+more or less the same advantages and disadvantages as hand-powered machines, except that, depending on the design, the second worker can be omitted, as the hands remain free to spread the mortar duringvibration.
· Flywheel-powered machines:
+ incorporate all the advantages of electric and hand-powered machines and can be operated by a single person;
- cost about the same as electric machines.
· These can be of various shapes and sizes, depending on
the local requirements and are needed in large numbers - at least as many as the
number of components produced in two working days, because the tiles are
demoulded after 24 hours.
· The moulds can be made of different materials, such as vacuum formed PVC (polyvinyl chloride) and fibreglass. FCR and MCR producers in developing countries have devised methods of making moulds out of concrete. These are produced in 3 stages: first making a concrete 'grandmother mould', from which several concrete 'mother moulds' are formed and sold to local tilemakers, who make the actual concrete moulds themselves. More recently, plywood 'mother moulds' have been devised, eliminating the 'grandmother mould'.
· The PVC and fibreglass moulds are designed for self-stacking; in most cases, the concrete moulds are placed in special wooden racks for initial curing, but self-stacking concrete moulds (either entirely concrete or with metal frames) have also been developed.
Advantages and problems of the various types of setting
· PVC moulds:
+ produced industrially and hence uniform and of good quality, extremely lightweight and easy to handle, can be stacked airtight (vital requirement for curing) and save storage space;
- most expensive moulds, no local production in developing countries.
· Fibreglass moduls:
+ similar advantages as PVC moulds, can be produced locally if the materials and skills are available;
- tend to be less accurate than PVC moulds.
· Concrete moulds:
+ extremely cheap and can be produced by the tilemaker himself;
- heavy and less accurate than PVC, and if not self-stacking and not airtight, the rack in which they are placed has to be well covered with a plastic sheet (which is often not done carefully, causing the green tiles to crack due to non-uniform drying).
· Several tests should be carried out before, during and
after the production process to ensure that FCR and MCR products arc of
consistently good quality. The tests are generally very simple and only a few
need special equipment.
· Some FCR/MCR machines are equipped with a demoulding jig, on which the 24 hour old tiles are placed upside down, together with the setting mould, which can then be lifted off. Subsequently, the plastic sheet can be peeled off carefully and the rough edges trimmed off. A close fit of the tile and the edges being in line with those of the jig show that the tile has exactly the right shape.
· After curing and drying, random samples of tiles from each batch produced should be tested as follows:
· Ring test: holding the tile by the nib and knocking a coin on the tile - a clear metallic sound should be heard.
· Bending test: placing the tile across a gap of 35 cm between two tables and, in the centre, hanging a piece of wood (with a curved edge to fit in vertical position exactly on the tile), which can be loaded with different weights 6 mm thick tiles should resist at least 30 kg; 8 mm tiles 50 kg, and 10 mm tiles 80 kg.
· Nib tensile test: clamping the tile at the edge of a table, allowing 50 mm of the tile to project beyond the edge with the nib on the underside, and hanging a weight from the wire loop - the tile should withstand a load of at least 20 kg.
· Water tightness test: placing the tile horizontally, forming mortar barriers at the extreme ends of the channel, and after they have dried, filling the channel with water- after 24 hours, no drops should be visible on the underside.
· These and many other tests are described in greater detail in the SKAT/ILO publication, Quality Control Guidelines, which can be obtained from the Roofing Advisory Service of SKAT, Tigerbergstrasse 2, CH - 9000 St. Call, Switzerland.