Compositions: coating or plastic – Coating or plastic compositions – Inorganic settable ingredient containing
Patent
1992-09-24
1993-12-07
Friedman, Carl D.
Compositions: coating or plastic
Coating or plastic compositions
Inorganic settable ingredient containing
106823, 52536, C04B 2434
Patent
active
052680282
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to so-called lightweight concrete products such as roof and cladding tiles and roof and cladding sheets, and more particularly to lightweight extruded concrete roof tiles.
Extruded concrete roof tiles are made from a cementitious mixture including sand and/or other aggregate, cement, colouring pigment and water plus optionally one or more other additives to facilitate extrusion, prevent growth of fungus etc. Such tiles have been produced for over forty years with apparatus including a hopper-like box which is disposed above a conveyor path and which is charged with the cementitious mixture. The flow of the cementitious mixture is assisted in the box by means of a rotating paddle disposed therewithin. A succession of pallets for moulding the undersurface of the tiles is driven along the conveyor path and beneath the box so that the cementitious mixture forms on the pallets and is compressed therein by means of a rotating roller disposed within the box upstream of the paddle and having a contour which corresponds to the upper surface of the tiles to be formed.
The cementitious mixture is further compressed on the pallets as they pass out of the box by means of a slipper which is disposed downstream of the roller and also has a contour which corresponds to that of the upper surface of the tile to form a continuous extruded ribbon of cementitious mixture on the pallets. The ribbon is subsequently cut into tile forming lengths downstream of the box by means of a suitable cutting knife and the pallets with the formed tiles thereon are conveyed to a curing location. At the curing location, the tiles are conveyed through a curing chamber which is maintained at a high relative humidity and temperature. The curing time is usually in excess of 6 hours. The tiles undergo only a partial curing in the curing chamber from whence they are conveyed to and stacked out-of-doors, to complete the curing process.
There has been the need for some years now for an extruded concrete roof tile which is lighter than ordinary concrete roof tiles made from a cementitious mixture which includes sand and/or other aggregates, for use as a roof covering, and more particularly to replace old coverings which are lighter in weight than ordinary concrete roof tiles.
In the early 1980's the Applicants commenced ,their research and development into the production of lightweight extruded concrete roof tiles which would be acceptable as replacements for the previously mentioned coverings, i.e. exhibit a weight similar to the aforementioned coverings. In the Applicant's knowledge, such a lightweight tile must also preserve those essential characteristics which have made ordinary extruded concrete roof tiles enjoy widespread acceptance throughout the world. Thus, an extruded lightweight concrete roof tile should have characteristics which are similar in value to those of ordinary concrete roof tiles. Characteristics which are pertinent are flexural strength (i.e. transverse strength), impact strength, frost resistance and low porosity.
In the early 1980's the Applicants made thinner section concrete roof tiles by replacing 10% of the cement with microsilica in the form of silica fume, but found that although the tiles produced had the benefits of being slightly thinner and lighter than ordinary concrete tiles, they were not sufficiently light to replace the coverings referred to earlier.
In an ordinary concrete roof tile the heaviest component by volume is the sand aggregate. Thus, the aim was then as it has been during the following years to replace the sand aggregate either completely or in part by an aggregate of lighter weight.
What the industry needed was a lightweight roof tile having the characteristics previously referred to. This means a tile that in performance complies with British Standards. One example would be a tile of the general type sold by the Applicants under the trade mark VANGUARD 83 but of lighweight.
During 1983 the Applicants looked at the possibility of using a lightweight aggregate, possibly
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Friedman Carl D.
Mai Lan M.
Oldcastle Inc.
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