2.2 The patent specification
4 The specification contains numerous typographical errors. Where the error is clear, I have corrected it in the quotes below for convenience. The field of the invention is said in the specification to relate to:
surface finishes for pathways, walls; swimming pools and other structures and more particularly relates to a surface finish which is of a cementitious nature and which includes least one aggregate type comprising glass beads.
5 In a section entitled "Background of the Invention" the specification states:
In the building industry there has been prolific use of aggregate surfaces for paving footpaths, surfacing of prefabricated building panels and slabs to provide attractive and functional facades and in and around swimming pools and the like. The known aggregate mixes have invariably utilized aggregate materials which include stones, pebbles and the like mixed in a matrix of cementitious material-selected from cement or resin.
The selection of pebbles and stones as the aggregate material usually dictates the appearance of the finish particularly with respect to its color and texture. When resins are used, the aggregate provides the final surface coloration as the cementitious resins are generally clear. An alternative surface coating may be formed by using colored mortar with pebbles and stones.
Despite the use of a wide range of aggregates to produce a variety of surface finishes successfully preparing a cementitious surface matrix using as the aggregate material glass beads either alone or with another aggregate materials selected from precious or semi precious stones, sands, quartz, marble, granites and the like has been difficult to achieve.
It was previously thought to be unsatisfactory to attempt to use other than conventional aggregates in hard-wearing surface finishes as the bonding achieved was inferior compared with conventional aggregates. In the building industry it has been considered unwise to use materials such as glass beads as aggregates as the glass is generally considered to be insufficiently porous or tough enough to establish an effective bond. The bond is also compromised by alkalinity bleeding out from the glass beads.
A number of approaches have been followed in the use of glass beads and cement formulations to provide surfaces having good light reflectivity. U.S. Patent No. 4,218,260 to Metzler discloses reflective concrete bodies in the form of slabs which can be used on road surfaces. The concrete slabs incorporate crystal balls of a uniform particle size within the range of about 0.2-0.6 millimeters. The glass balls in the reflective slabs are configured so that they are arranged in even horizontal rows through the vertical distribution of the slab. After the slabs are formed and the concrete matrix allowed to harden for a suitable period of time, for example, 29-30 days, the surface is etched with a phosphoric acidsolution to expose at least 50% of the top layer of glass balls. As an alternative to the use of glass beads of a uniform size, EP 518,854 discloses a cement formulation incorporating glass beads in which a particular particle size distribution of small and large beads is employed to ensure good reflectivity and compaction of the beads so that they are firmly incorporated into the cement matrix through the use of an adhesive agent. In EP 518,854, two particle size distributions are employed. The larger particle size component is in the range of 1.5-7 millimeters; the smaller particle size component is within the range of 1.2-1.5 millimeters. The components are employed in relative concentrations in which the smaller size component is present in a greater amount than the larger size component, preferably in a proportion of the smaller component to the larger component of about 2: 1.
Yet, another cement formulation employing glass spheres of relatively smaller particle sizes is disclosed in British Patent No. 1,397,737. Here, glass spheres approximately 0.25mm to 1.75mm in diameter, which are coated with a water-repellent material such as a silicone, are employed to form a reflectorized concrete screed laid down at a thickness of at least 1/2-inch and preferably from 1/4-inch to about 2 1/2 inches. The concrete screed can be formed from a blend of white portland cement, calcined flint particles, a titanium oxide pigment, and a binding agent which is designed to assist in preventing the reflective spheres from loosening under wear.
6 Under the heading "Summary of the Invention" the specification continues:
The present invention comprises a surface finish for application to a vertical, horizontal, or sloping surface/s of a structure or object which provides a substrate for said surface finish, the surface finish comprising a matrix formed from a combination of at least a cementitious material, water, and glass beads. The surface finish comprises a blended matrix of cementitious mortar, an aggregate of glass beads used alone or in conjunction with other aggregates selected from precious stones, semiprecious stones, or raw stones, and liquid adhesive which comprise a combination of a siliconiser and polymeriserer for enhancing the bond between the cementitious mortar and glass beads. The finish may be applied to the surface of a structure, such as a building facade as a paving surface, or to other suitable objects formed from a material capable of forming a bond with the finish.
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The cementitious material preferably is washed away such that 30-60% of the surface area of a substantial number of the glass beads on the surface of the matrix is exposed. Preferably, no more than 40% of the bead surface area is exposed at the surface of the matrix.
More specifically, in accordance with the present invention, there is provided a process for the application of a reflective surface finish to a substrate structure. In carrying out the process, there is provided a reflective cementitious composition comprising portland cement, glass beads, and a barrier-forming material selected from the group consisting of a polymerizer and a siliconizer and mixtures thereof. Preferably, the barrier forming material comprises a latex polymer. The portland cement is employed in an amount within the range of 113-213 of the total weight of the formulation. The glass beads have particle sizes within the range of 1-5 millimeters and a weight average particle size within the range of 1.5-4.5 millimeters. The beads are employed in a particle-size distribution defining a major component within a relatively large incremental size range and a minor component within a smaller incremental size range. The weight of the beads within the large incremental size range is greater than the weight within the smaller incremental size range. Preferably, this weight ratio is in the range of 2-3 and more preferably within the range of about 2-2.6. The latex polymer is present in an amount within the range of at least 2 wt% of the glass beads but less than 8 wt% of the total amount of cement and glass beads in the formulation. The cement formulation is hydrated with water in an amount to provide a water/cement ratio within the range of about 1/3-2/3 to provide a cementitious paste which is then applied to the surface of the substrate structure. Normally, the water content is near the upper end of this range to provide a water content of 65 wt.% of the cement. The paste preferably is applied to a thickness within the range of about 14-1/2-inch and, after any trowelling or other surface treatment to provide a smooth surface, is allowed to set for a time to form an initial set. Thereafter, the surface is washed with an aqueous medium to remove a small amount of cementitious material from the surface layer of the beads to form partially-exposed areas of the beads.
7 The "Detailed Description of the Invention" states that:
The present invention involves a cementitious composition comprising a mixture of glass beads in a portland cement composition together with a barrier-forming material which functions once the cementitious composition is hydrated and allowed to set to protect the glass beads from the surrounding matrix environment. While the glass beads employed in the present invention can be similar to those described previously, the present invention proceeds in a fashion directly contrary to the prior art in its distribution of glass beads along a particle size distribution which results in a relatively large bead component and a relatively small bead component which functions to provide a strong surface reflective material which is not only highly reflective but also provides good integrity. Thus, rather than using a more or less uniform particle size of beads, as in the aforementioned patent to Metzler, or a particle size distribution in which relatively small beads are employed as a major component together with somewhat larger beads, in the present invention the larger size beads provide the major bead component. The surface finish of the present invention comprises a matrix of cement, water, an adhesive, and glass beads defining an aggregate material. The adhesive can be introduced into the mix with the water to facilitate bonding between the glass beads and the mortar. As described below, known adhesives may be used such as Xycrylic polymerizer mixed with a siliconiser to provide a mechanical locking, and thus binding between the beads and the mortar. In utilizing the surface finish of the present invention, many variations of aggregate mix can be achieved to provide different aesthetic, bonding, and structural effects. The blend proportions and constituents over and above the essential constituents are primarily determined by the particular application of the surface coating and, more particularly, whether it would be used on a horizontal, vertical, or sloping substrate surface. The nature and quality of the substrate material is also a determinant of the mix.
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The polymerizer used in the present invention may be of any suitable type which is compatible with the cement, preferably while portland cement as stated above and which functions to act as a seal or barrier between the glass beads and the cement during hydration to enable good mechanical locking of the beads in place after the formulation has finally set. Polymers which are compatible with portland cement and used in special purpose concrete applications are incorporated into products commonly referred to as polymer-modified concrete (PMC) or polymer-portland cement concrete (PPCC). Such polymers can take the form of latex-type polymers which are sometimes used in so-called latex-modified concrete (LMC). Typical of such polymers are styrene butadiene rubber-type polymers, polyvinyl acetate ethylene co-polyrnerp, and polyacrylate homopolymers, including polymers of acrylic acid, methylacrylic acid, niethyl methacrylate, and butylacrylate. A particularly preferred polymerizer for use in the present invention is an acrylic hemopolymer available from Rohm & Haas Company under the designation "DRYCRYL DP-2903".
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The polymerizer functions, upon addition of water to the mixture, to coat the glass beads and protect them from attack by cement components, such sodium or potassium-based alkalies which can lead to frosting of the glass beads thus retarding their reflectability in the final product and ultimately degrading the beads. The latex polymer provides a barrier material which is interposed between the surfaces of the bead and the encapsulating matrix material. This boundary layer will not harden so long as the adjacent cementitious mixture is hydrated. Thus, the boundary layer begins to harden after the cement achieves an initial set and begins to harden. The matrix material is partially removed from the surface to expose the beads as described below.
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The siliconizer which can be employed as a optional component in the present invention includes materials which will include silicon-containing materials which are miscible with or emulsifiable in water and which functions to etch the surface area of glass beads exposed to the cement to facilitate bonding within the matrix. Suitable siliconizors include alkali metal, silicates such as potassium, silicate or sodium silicate (water glass) or other water-soluble sodium silicates such as sodium sesquisilicate, sodium orthosilicate, anhydrous metasilicate sodium, and sodium metasilicate pentahydrate. An especially suitable siliconizer for use in the present invention is sodium silicate available from Xypex, Australia, under the designation QUICKSET. This product which is conventionally used as a set accelerant for portland cement functions similarly here, but the accelerating effect of the siliconizer is offset by the polymerizer which provides a counterbalancing set-retarding effect.
The size distribution of the glass beads is important in providing relatively large beads to provide a good reflective surface area in the matrix while providing smaller beads which are interspersed within the larger beads so that they can be effectively interspersed between the relatively large beads. As described in greater detail below, the beads can be characterized as falling within two particle size distributions with the larger particle size being the predominant component. Overall the average particle size of the beads preferably will be within the range of 1.5-4.5 millimeters and more preferably within the range of about 2-3 millimeters. Although a differential particle size distribution is important in carrying out the present invention, the upper limit of the particle size distribution normally should be no more than three times the magnitude of the lower limit. While a few beads may be outside of this range, preferably at least 90% of the glass beads will fall within the designated particle size distribution. The major and minor components of the beads can he characterized in terms of average particle size values, the larger component having a average particle size greater than the midpoint of the upper and lower particle size distribution ranges and the minor component having an average particle size below this midpoint. The weight of the beads in the larger size range, as noted previously, is greater than the weight of the beads in the smaller incremental size range. Again considering the overall particle size distribution of the beads, preferably the upper value is from 2-3 times greater than the lower value and preferably no more than 2 1/2 times greater than the lower value.
The glass beads used in the present invention preferably have a size distribution within relatively narrow confines in which a major component of the beads is within a relatively large size range, termed the "large increment", and a minor component of the beads in a somewhat smaller size range, termed the "small increment". A particularly preferred particle size, distribution for the glass beads is one in which the major component of the glass beads is within a size range of about 2.5-3.5 millimeters in diameter and a minor component is within a small increment of 1.5-2.5 millimeters. The glass beads within the large increment size range are the predominant component, and preferably the weight ratio of beads within the large increment size range to those within the minor increment size range will be within the is range of about 2-3 and more preferably within the range of about 2.0 to 2.6. As described in greater detail below, where the formulation is designed for use as a "neat" cement (without the addition of aggregate), the ratio of the large increment portion of the beads to the small increment portion will be near the upper end of the range. Where it is designed for use in which it is to be mixed with an aggregate, such as sand, to form a concrete mixture, it will normally be near the lower end of this range.
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Other bead distributions which have been found to be useful in carrying out the invention are as follows: 10 wt% at 1.4 mm; 20 wt% at 1.7 mm, and 70 wt% at 2.0 mm; 10 wt% at 2.36 mm, 20 wt% at 2.0-2.8 mm, and 70 wt% at 2.36-3.35 mm; 10 wt% at 2.8 mm, 20 wt% at 2.36-3.35 mm, and 70 wt% at 2.85-4.0 mm; 10 wt.% at 2.36-3.35 mm. 20 wt% at 2.85-4.0 mm, and 70 wt% at 5.0 mm; and 10 wt% at 2-2.8 mm, 20 wt% at 2.36-3.35 mm, and 70 wt% at 2.85-4.0 mm.
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The average particle size of the glass beads employed in the present invention, ie, the average size taking into account both the small beads and the large beads, is preferably within the range of 2-4 millimeters and more preferably within the range of 2-3 millimeters. The average particle size, as referred to here, is the weight average particle size of the beads based upon the distribution of beads in the mixture. Thus, for example, for the second formulation described above and assuming an even distribution of beads across the major increment of 2.5-3.3 mm and the minor increment across the range of 1.5-2.5 mm the average particle size would be about 2.6 mm.
By providing the preferred particle size distribution in accordance with the present invention, a substantial proportion of the small beads as well as the larger beads are set within the cement matrix at the surface of the applied formulation so that the beads are mechanically locked in place by the encapsulating cement mortar. If substantial quantities of small beads, that is, those below the desired lower limit, are present in the formulation when the surface is washed to remove mortar from the beads, the removal of a substantial amount of mortar from the large beads would leave a substantially smaller bead exposed above the matrix surface throughout most of its surface area, thus exposing the small bead to removal from the matrix surface.
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The polymers used in the present invention can include those polymers which are conventionally used in polymer concrete mixtures. Typically, such polymers as used in conventional polymer-modified concrete or mortar are used to effect the final properties affecting concrete structure such as increases in flexural strength and increased resistance to degradation due to freezing and thawing cycles and to reduce the permeability of the concrete structures. Such polymers, as are used in polymer-modified concrete can be used in carrying out the present invention, although, because of the different purpose to which the polymeric additives are put in the present invention, they are used in substantially lower concentrations than used in their conventional application. The amount of polymer in the glass bead cement formulation can be characterized in terms of its concentration relative to the glass beads and its concentration relative to the portland cement component. Normally, the latex polymer will be present in an amount of less than g wt% [sic - agreed to be 8] and usually in an amount of less than 5 wt% of the total amount of the cement and glass beads in the formulation. Considering the bead content alone, the polymer preferably will be used in an amount of at least 2 wt%, usually in an amount within the range of about 4-6 wt% of the glass beads, depending upon the presence of aggregate materials such as relatively fine aggregate as described below. In terms of the amount of polymerizer relative to the portland cement component, usually it will be preferred to add the polymerizer in an amount of 3-5 wt% of the cement component.