Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
1998-06-08
2003-03-25
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S500000, C428S213000, C106S607000, C156S094000, C156S382000, C501S146000, C501S148000
Reexamination Certificate
active
06537676
ABSTRACT:
TECHNICAL FIELD
This invention relates to a waterproofing material suitable for waterproofing ponds, lakes, lagoons or comparable sites whereby water is retained, or wherein waste is deposited and the ground beneath has to be protected against leakage of aqueous or other liquid. The material can also be used in relation to water proofing structures, covering contaminated land to prevent flow of water into such contaminated land and lining trenches which separate contaminated areas from clear areas. The material can also be used as roofing material on flat or sloping roofs.
PRIOR ART
Several materials have been proposed in the past which include a layer of swellable smectite such as montmorillonite and/or saponite incorporated within the material to act as the sealing agent. The montmorillonite has been carried by a support layer or base which has been provided in various ways. A support layer acts as protection but also gives additional strength within the material.
European patent number 59625 (CLEM) describes a waterproofing material which is a laminate comprising a fabric base, particles of montmorillonite adhered to the base and a scrim adhered over the montmorillonite particles to retain them on the base.
In European patent application 246 311 (McGROARTY) a lower sheet comprises a base and montmorillonite and an overlaid sheet comprises a base and montmorillonite. The bases are of solid plastics non-venting and impermeable material so one of the bases forms a non-water transmissive layer between the two layers of montmorillonite, thus giving a very good seal. However, the McGROARTY construction does have several practical difficulties. Firstly, the bases are made from a thick, impervious and essentially solid plastics material, described in the specification as HDPE (high density polyethylene). Secondly, the granules of montmorillonite are adhered not only to the base but also to each other.
Waterproofing materials of this kind are usually supplied in rolls and have to be unrolled and placed to lie in the pond, lagoon or storage space. With the bases made from HDPE the McGROARTY material is less flexible than when using a fabric (non-woven or woven) for the base. This means that the product is much more difficult to handle and the montmorillonite is likely to crack during folding and unfolding. Further, because of the nature of an HDPE plastic sheet the adhering of the montmorillonite to its surface is not easy. Quite large quantities of very strong glue have to be used.
A further waterproofing barrier material is disclosed in GB 2 202 185 (NAUE) in which a layer of montmorillonite is sandwiched between a pair of layers of non-woven textile material and the two layers are united by needling, the needles passing through the layer of montmorillonite and uniting all three layers. Again, because the montmorillonite is not adhered to the layers, as the material is unfolded, folded and manhandled during installation, the montmorillonite can move relative to the two layers leaving voids and/or more permeable thinner areas in the montmorillonite layer.
There is a further disadvantage in that all these earlier materials tend to use particulate montmorillonite which may be from 2-5 mm, usually about 3 mm in size. Although finer material can be poured to fill gaps between the larger granules, such larger size granules tend to make up the bulk of the montmorillonite layer in the waterproofing material. As the waterproofing material is only relatively thin, for example containing only perhaps one or two layers of montmorillonite granules, problems can arise in connection with foreign bodies in the montmorillonite used. In its natural state montmorillonite is found alongside shale and other impurities. Whilst the montmorillonite can be quite highly purified, it is not unusual for a low percentage of shale particles to remain in the final sized and graded montmorillonite. An unfortunate result of the use of relatively large granules of montmorillonite is that granules of impurities can also become incorporated in the material. The chemical nature of shale and some other impurities have the effect that not only are they not montmorillonite (and therefore do not swell upon contact with water), but, when wetted, act to inhibit swelling in adjacent montmorillonite granules. Thus, a single granule of shale in a layer of waterproofing material can form a small area (perhaps 10 mm in diameter) which does not swell upon being contacted with water. Such areas are generally water impermeable, but medium and larger such areas allow water to pass through the sheet. When water pressure is high this flow can cause significant wash out of adjacent montmorillonite leading to failure of the sealing system. Although the percentage of impurities is small, and although the failure rate is small, when a large area is sealed using sheet material incorporating such impurities it needs only a single leak for the whole system to have failed. A pond or lagoon which has a single leak is no pond or lagoon at all!
U.S. Pat. No. 2,277,286 (Bechtner) is primarily concerned with formation of a blanket of dry “in-situ” bentonite which has all the disadvantages noted above, and is also difficult to distribute evenly. However, it also mentions the possible formation of a putty-like mass form 50-60% water and 40-50% clay, which is sufficiently cohesive to adhere to rough or smooth surfaces, such as a wall which is to be sealed against leakage from outside earth.
Particulate montmorillonite has also been mixed with various organic components to form a thick putty (see U.S. Pat. No. 4,534,925). Typical components are polypropene and polybutene. This material has been extruded in the form of rods and sheets, usually being stored between layers of release paper. Such material has been used for sealing ground foundations and similar structures. It has not, however, being extruded so as to become united with a carrier sheet and be capable of use in large rolls for covering large areas. Indeed, the polypropene and polybutene used is intended deliberately to give the extruded material a rubbery or formable consistency enabling it to be moulded by hand around small areas such as chimneys, at joints in concrete panels, or where drains penetrate foundations. These materials are also quite expensive and prohibitively so for use in relation to large area sheets.
U.S. Pat. No. 5,116,413 (Nooren) teaches the mixing of bentonite clay with a hydrophobic substance such as bitumen or vaseline, with addition of only a small amount of water or alcohol, namely 0-4% (see column 4 line 44), to provide a sealing agent which is mouldable and useful for production of watertight bushings. Cellulose compounds or polyacrylates are mentioned as alternative water swellable or swollen high-molecular substances to the bentonite clay.
U.S. Pat. No. 5,132,021 (Alexander) is primarily concerned with use of dry, particulate bentonite clay sandwiched between outer sheets. At column 7, line 26 to 33 it mentions that polar activators such as 75-98% methanol or ethanol and 25-2% water can be “included with (absorbed by)” the clays, the amount of such activator being from 10-40% relative to the dry weight of the clay. Partial hydration of the clay should result from the aforesaid addition. However, there is no teaching at all of the mixing of the two constituents, or kneading same, to provide a substantially homogeneous deformable mass. Without this, a reliable waterproofing layer is not formed. The mere pouring of water onto the “in situ” dry clay will be quite inadequate in most applications, as discussed above.
U.S. Pat. No. 5,237,945 (White et al) teaches the application of a bentonite clay/water paste (preferably about 30% clay) to the top surface of a loose fibrous mat in which powdered clay has been deposited. The paste is subsequently compressed into the mat, which in practice is likely to prove difficult, and certainly will not provide a truly homogenous hydrated layer, nor retain or hydrate the loose particles.
Calcium montmorillonite is sometimes
Carter Glyn C.
Flynn Bryan N.
Oliff & Berridg,e PLC
Rawell Group Holdings Limited
Tarazano D. Lawrence
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