Static structures (e.g. – buildings) – Opaque stonelike module
Reexamination Certificate
1998-12-15
2001-11-06
Safavi, Michael (Department: 3635)
Static structures (e.g., buildings)
Opaque stonelike module
C106S724000, C106S802000, C106S810000
Reexamination Certificate
active
06311448
ABSTRACT:
The present invention is concerned with precast concrete plates and methods for their manufacture. In particular, though not exclusively, the present invention is concerned with concrete roof tiles, floor tiles, wall tiles and house sidings, and their manufacture.
Precast concrete roof tiles are typically produced from a concrete mortar whose consistency is such that it can be molded whilst in its green state into a design having features of shape, configuration, pattern or ornament which it will retain when cured. The tiles are usually formed of a layer or layers of green concrete molded to correspond to the desired surface appearance of the tiles. The tiles may be formed of a single layer of concrete or they may be formed of multiple layers of concrete, for example as disclosed in U.S. Pat. No. 4,789,319, U.S. Pat. No. 4,986,744 and U.S. Pat. No. 5,017,320.
Precast concrete roof tiles may have dimensions in the order of 0.42 m×0.33 m×0.012 m and can weigh about 4.5 to 5 Kg per tile. Lighter concrete roof tiles of similar dimensions can be manufactured through the use of lightweight aggregates such as pumice, scoria, fly ash, and expanded shale, clay, slate, vermiculite and Perlite, for example as described in U.S. Pat. No. 5,603,758. Artificial light weight aggregates can also be used, such as polystyrene foam particles as disclosed in U.S. Pat. No. 5,580,378. Roof tiles may also be made of a fiber reinforced concrete, such as disclosed in U.S. Pat. No. 5,108,679.
Precast concrete roof tiles are susceptible to breakage or fracture during their storage, transportation and assembly to form a roof covering.
Organic polymers are often added to mortars to alter their physical and/or chemical properties. Such polymers are often referred to as cement modifiers and are usually added to the concrete, particularly light weight concretes, to improve, for example, the strength, water-resistance and open-time of the concrete. Such cement modifiers are added to a concrete mortar, in amounts of about 2% to 6% by weight, and distributed uniformly throughout the concrete mortar. A tile manufactured from such concrete demonstrates increased resistance to flexural loadings and resistance to impact-impulse loadings. However, the quantity of cement modifier required to achieve an appropriate improvement in the strength of the tile is high.
To reduce the number of tiles which may be broken during such storage, transfer and assembly, it is disclosed in U.S. Pat. No. 4,752,520 that a high degree of resistance to flexural loadings and resistance to impact-impulse loadings on the tiles can be imparted to the tile through the use of a preformed substrate member backing comprising a substantially rigid, polymeric material, such as an epoxy resin. The preformed substrate member is preferably an epoxy resin reinforced with fiberglass in a mat form, and may be molded from a sheet to the desired form. The preformed substrate member preferably has a strength equal to or greater than the strength of the concrete layer, thereby providing fracture resistance to tensile stresses on the underside of the concrete layer, and is preferably constructed to add rigidity to bending forces applied to the concrete layer. The adhesion between the reinforced fiberglass mat and the concrete layer, however, may degrade due to the effect of the alkalinity of the concrete mix and fiberglass, eventually causing delamination of the non-homogenous layers.
Accordingly, it is the object of the present invention to provide a precast concrete tile which has a relatively high degree of resistance to flexural loadings and resistance to impact-impulse loadings in comparison to conventional concrete roof tiles without using high levels of cement modifiers and which does not suffer the problems of delamination associated with the reinforced tiles of U.S. Pat. No. 4,752,520.
In accordance with the present invention, there is provided a precast concrete plate, preferably a precast concrete tile, having a top surface and a bottom surface, and length, width and depth dimensions, the plate being adapted for arrangement with other like plates to form a decorative and/or protective covering, such as a roof, floor or wall covering; with the top surface of the plate disposed to face outwardly and the bottom surface disposed to face inwardly towards an underlying support structure, such as a roof support structure, concrete floor or wall, the precast concrete plate consisting of one or more layers of concrete and optionally one or more layers of coating compositions on said top surface and/or said bottom surface, wherein the concrete comprises in total from about 0.2% to about 5%, preferably about 0.5% to about 3%, by weight of a polymeric modifier having a Tg of above −40° C., and wherein the portion of said concrete which comprises no more than about 50% of the thickness of all said concrete which forms the plate, when measured from the bottom surface of the plate towards the top surface of the plate, includes at least about 60% by weight of said polymeric modifier.
Surprisingly, we have found that comparable improvements in break strength of precast concrete plates can be achieved through the use of significantly less quantities of cement modifiers. Further, the plates do not suffer the problems associated with the reinforced tiles described in U.S. Pat. No. 4,752,520.
Preferably, the portion of the concrete which comprises no more than about 50% of the thickness of the plate, when measured from the bottom surface of the plate towards the top surface of the plate, includes at least about 75% by weight, more preferably at least about 90% by weight, and most preferably 100% by weight, of the polymeric modifier, based on the total weight of polymeric modifier in all the concrete which forms the plate.
Preferably, the major portion, if not all, of the polymeric modifier used in said concrete is included within the portion of said concrete which comprises no more than about 33% of the thickness of all said concrete which forms the plate, when measured from the bottom surface of the plate towards the top surface of the plate.
Preferably, the major portion, if not all, of the polymeric modifier used in the said concrete is included within the portion of said concrete which comprises at least about 5%, more preferably at least about 10%, of the thickness of all said concrete which forms the plate, when measured from the bottom surface of the plate towards the top surface of the plate.
In one embodiment of the present invention, the polymeric modifier used in the concrete is uniformly distributed throughout the relevant portion of said concrete. The precast concrete plate of this embodiment may be manufactured by a process which allows plates to be obtained comprised of superimposed layers of mortars of different compositions and characteristics. For example, such a process and apparatus for performing the process are described in U.S. Pat. No. 5,017,320 and U.S. Pat. No. 4,789,319, respectively. The apparatus disclosed in U.S. Pat. No. 4,986,744 may also be used for the manufacture of such multi-layered plates. The layer of concrete which comprises the bottom surface of the plate is prepared by admixing the polymeric modifier into a conventional mortar composition to form the green concrete which, in accordance with the above process, is then extruded onto a continuous strand of moving bottom molds. Subsequently, one or more other layers of green concrete comprising substantially less or no polymeric modifier than the first formed layer are extruded onto the first layer to form the multi-layered plate. The first layer of green concrete comprises no more than about 50%, preferably no more than about 33%, of the thickness of the plate, when measured from the bottom surface towards the top surface of the plate. Preferably, the first layer of green concrete comprises at least about 5%, more preferably at least about 10%, of the thickness of the plate, when measured from the bottom surface of the plate towards the top surface of the plate.
Bowe Michael Damian
Hsin Roger Shan Chung
Rohm and Haas Company
Safavi Michael
LandOfFree
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