Field of the Invention

The present invention relates to a settable composition that may be used for coating substrates such as cementitious substrates. The invention also relates to a method of repairing or rehabilitating degraded concrete and in particular degraded concrete sewer mains, and to a shaped article formed from the composition.

The settable composition of the invention is particularly suitable for coating or repairing the interior surfaces of concrete sewer mains, and the invention will be described with particular reference to this application. However, it is to be understood that the settable composition of the invention may be suitable for coating a variety of substrates and no limitation is intended thereby.

Background of the Invention

Settable compositions based on Portland cement have been extensively used for many years. Such compositions have been favoured for their low cost and desirable mechanical properties. However, Portland cement based compositions, such as concrete, are prone to cracking during the curing process, have a relatively slow curing time, and are particularly susceptible to degradation through chemical attack. Environments where concrete may be subjected to chemical attack include chemical plants, storage tanks, smoke stacks, sewer mains and sewer pipes.

The limitations of Portland cement based compositions can be highlighted by way of reference to the problem of acid induced degradation of concrete sewer mains. This problem is of particular concern in most developed countries, and results from hydrogen sulfide that is liberated from sewage effluent being converted into sulfuric acid by microorganisms that are prevalent in sewer systems. The acid' so-formed in turn attacks ionisable calcium constituents of the concrete causing degradation that manifests itself as a reduction in the thickness of the pipe wall and subsequent reduction in its mechanical properties. As a result of such acid attack, the life expectancy of sewer pipes and tunnels can be significantly reduced. There have been numerous attempts to address the problem of acid induced degradation of concrete sewer mains. One approach has involved attempting to control hydrogen sulfide liberation by adding chemicals such as caustic soda to increase the pH of the effluent. However, such techniques have only a temporary effect and must be repeated on a regular basis, making them particularly labour intensive and uneconomic. Other attempts have targeted the sulfuric acid producing microorganisms by incorporating biocides into the concrete or dosing the effluent with biocides. However, biocides incorporated into the concrete will eventually be leached and, as with the addition of caustic soda to the effluent, dosing the effluent with biocides must be repeated on a regular basis and is uneconomic. Furthermore, the addition of biocides to the effluent can adversely effect downstream processing of the sewage.

Another approach has been to provide concrete pipes and mains with acid resistant plastic liners. However, the cost of these liners is prohibitive for many municipalities. Furthermore, degradation of the pipes can still occur where effluent seeps between any gaps between the liner and the concrete. Alternate approaches have been to use adhesives to adhere the liner to the concrete. However, this adds an additional step to the process and additional cost. Still further, installation of plastic liners does not significantly improve the mechanical properties of severely degraded concrete and is generally considered to be a preventative measure only.

In many cases, the level of degradation of the pipes is such that there is a real danger of mechanical failure. In such cases, it is too late to attempt to minimise further degradation and the pipe must be either replaced or repaired. Replacement or repair of many miles of sewerage pipe by conventional means is expensive, labour intensive and logistically difficult in view of the fact that sewage flow must normally be diverted during replacement or repair.

It has been proposed to rehabilitate degraded sewer pipes by coatiffg the degraded interior surfaces of the pipes with conventional Portland cement based settable compositions. However, apart from coating the pipes with a composition which itself will be susceptible to acid degradation, such compositions are generally difficult to apply so as to achieve an effective coating. Furthermore, the conventional compositions are susceptible to cracking during the curing process and have a relatively slow curing time. The curing time of the coating composition can be a particular problem given that the composition should be fully cured before sewage is re-introduced into the pipes. In other words, the longer the curing time, the longer the sewage needs to be diverted.

Accordingly, there remains a need to provide a settable composition that can overcome or alleviate at least some of the disadvantages associated with the aforementioned conventional settable compositions.

Summary of the Invention

The present invention provides a settable composition comprising an expansive inorganic binder, pozzolanic material, a first water dispersible polymer or prepolymer comprising epoxy functionality, water, and a source of hydroxide ions.

The invention also provides a cured composition formed by blending together an expansive inorganic binder, pozzolanic material, a first water dispersible polymer or prepolymer comprising epoxy functionality, water, and a source of hydroxide ions.

The settable composition has been found to be useful as a coating for cementitious substrates, particularly as a coating to repair degraded cementiteous substrates.

The invention therefore further provides a method of repairing a degraded cementitious substrate, the method comprising applying the composition of the invention to the substrate and allowing the composition to cure. In a preferred embodiment, the method is employed for repairing cementitious substrates that are subjected to acidic environments and which have a surface(s) that has been degraded by acid attack.

In performing the method of the invention, the composition of the invention will typically be applied to the degraded surface of the cementitious substrate.

The invention also provides a shaped article formed by locating the composition of the invention in a mould and allowing the composition to cure to form said article. Without wishing to be limited by theory, it is believed that the settable composition of the invention exhibits unique mechanical and cohesive properties through the operation and interaction of at least three binding mechanisms involving the expansive inorganic binder, the pozzolanic material, and the first water dispersible polymer or prepolymer. In particular, curing of the expansive inorganic binder through uptake of water, curing of the pozzolanic material through reaction with hydroxide ions to form a geo-synthesised mass, and curing of the water dispersible polymer or prepolymer through reaction of the epoxy functionality is believed to result in a complex matrix of inorganic and organic polymeric species that in combination provide a cured product having an increase in mechanical and cohesive properties compared with those properties capable of being attained by the expansive inorganic binder, pozzolanic material, or first water dispersible polymer or prepolymer when used alone.

By the term "settable" composition is meant that upon mixing the components of the composition together, the composition will undergo a curing reaction to thereby solidify or set. Accordingly, it will be appreciated that prior to mixing the composition to promote the curing reaction, the components will be isolated in an appropriate manner so that they do not prematurely cure. To prevent such premature curing, the components of the composition will typically be provided in a multi part pack. Further details in relation to such multi part packs are discussed below.

The settable composition in accordance with the invention can advantageously be formulated to minimise cracking during the curing process, the constituents of the composition are relatively inexpensive, and the composition can also be formulated to have a relatively fast curing time. Furthermore, the composition of the invention can, and preferably is, formulated with a minimum amount of, or substantially no, common cement products, and can therefore exhibit excellent acid resistant properties.

Detailed Description of the Invention

As used herein, the expression "expansive inorganic binder" denotes an inorganic material which expands in volume upon being exposed to water through the uptake of water as water of crystallisation. Accordingly, upon being exposed to water an expansive inorganic binder will in effect become hydrated. The expansive property of the binder is believed to minimise, if not eliminate, undesirable contraction and cracking of the composition as it cures. Such an inorganic material must of course also be capable of functioning as a binder in the sense that it can cohesively bond to itself and/or other materials.

Preferably, the expansive inorganic binder is an expansive inorganic binder which, when mixed with water, hardens by chemical and/or physical reactions to form a solid article within a curing time of less than Portland cement and modified Portland cement compositions under comparable curing conditions. In other words it has a substantially fast curing rate relative to Portland cement and modified Portland cement. Preferred curing times of the expansive inorganic binder are within about 6 hours, more preferably within about 2 hours. By "curing time" is meant a time after which immersion in water may be tolerated without substantial erosion of the composition.

The curing time of the settable composition in accordance with the invention is preferably no longer than that of the expansive inorganic binder.

Typically, the expansive inorganic binder will be present in the composition in an amount ranging from about 10 wt % to about 45 wt%, relative to the total weight of the composition. Preferably, the inorganic binder is present in the composition in an amount ranging from about 15 wt% to about 35 wt%, more preferably about 20 wt% to about 25 wt%, relative to the total weight of the composition.

A preferred example of the expansive inorganic binder is, but is not limited to, calcium sulphate. A preferred form of calcium sulphate is calcium sulphate hemihydrate. A more preferred form of calcium sulphate hemihydrate is calcium sulphate alpha-hemihydrate, also known as alpha-plaster.

The composition in accordance with the invention also comprises pozzolanic material. As used herein, the term "pozzolanic material" refers to siliceous or siliceous and aluminous materials which in themselves possess little or no binder value but may, in a finely divided form, chemically react with hydroxide ions to form a solid mass possessing cementitious properties. Examples of pozzolanic materials include finely divided amorphous silica, such as silica fume, microsilica, pumice, perlite, diatomaceous earth, metakaolin, blast furnace slag, fly ash, and combinations thereof. The particle size of the pozzolanic material is preferably less than about 20 microns. Preferred pozzolanic materials include, but are not limited to, metakaolin, fly ash or a mixture of two or more thereof. A particularly preferred pozzolanic material is a low carbon fly ash having an average particle size of less than about 20 microns. The compositions of the invention will typically include between about 2 wt% to about 30 wt%, preferably between about 5 wt% to about 20 wt%, more preferably between about 10 wt% to about 15 wt%, pozzolanic material.

The source of hydroxide ions is provided to render the overall composition alkaline. As discussed above, it is believed that the hydroxide ions in the composition promote curing of the pozzolanic material to afford a geo-synthesis mass. To promote curing of the pozzolanic material the hydroxide ions will generally be provided at a concentration to provide the settable composition with a pH of at least 10, preferably at least 12.

Those skilled in the art will appreciate that any source of hydroxide ions will also comprise a counter cation. The counter cation may be an organic or inorganic cation. To provide the requisite pH for curing of the pozzolanic material, the source of the hydroxide ions should have a high solubility in water. Preferably, the source of the hydroxide ions has a solubility in water at O0C of greater than about 0.2 g/100 cc water, more preferably greater than about 1 g/100 cc water.

Although it may be possible to formulate a composition where the source of the hydroxide ions is generated in situ, it is preferable that a direct source of the hydroxide ions is added to the composition as a separate entity.

A particularly convenient source of hydroxide ions may be obtained from alkali metal hydroxides such as sodium and/or potassium hydroxide. Given that the presence of calcium ions in the composition can render it more susceptible to acid attack, it is preferred that the source of hydroxide ions is not calcium hydroxide. An example of a suitable "organic" hydroxide ion sources includes, but is not limited to, tetrabutylammonium hydroxide.

The composition in accordance with the invention also comprises a first water dispersible polymer or prepolymer comprising epoxy functionality. By being "water dispersible" the polymer or prepolymer will generally be provided in the form of an aqueous emulsion, with water being the continuous phase and the polymer or prepolymer being the discontinuous phase. Those skilled in the art will appreciate that such emulsions also comprise one or more additives such as surfactants that function to maintain or stabilise the polymer or prepolymer in a dispersed state (i.e. to prevent or minimise coagulation).

By the water dispersible polymer or prepolymer "comprising epoxy functionality" is meant that the polymer or prepolymer has two or more epoxy groups. It will be appreciated that such epoxy groups should be capable of reacting with one or more components of the composition. During curing of the composition in accordance with the invention, the epoxy groups are believed to react at least with the pozzolanic material to contribute to the complex matrix of the cured composition.

As used herein, the term "prepolymer" denotes monomeric and/or oligomeric materials that are capable of subsequent reaction to form polymer.

The epoxy functionality will generally be in the form of a terminal epoxy group.

CH-CH2 O

The epoxy groups may be present in their own right or they may be formed in the composition (i.e. in situ) through reaction of appropriate functional groups. For example, a person skilled in the art would appreciate that a halohydrin group

CH CH2

OH X , where x = Cl, Br or I

will form a terminal epoxy group under alkaline conditions. The first water dispersible polymer or prepolymer used in accordance with the invention may have a molecular structure which incorporates the epoxy functionality in various ways. For example, the polymer or prepolymer may be a copolymer or pre-copolymer wherein the epoxy functionality is incorporated as pendant groups that extend from a backbone polymer chain. In this case, the polymer or prepolymer may be prepared through emulsion polymerisation of an ethylenically unsaturated monomer comprising epoxy functionality, or precursor thereto, and one or more other ethylenically unsaturated monomers. Polymers or prepolymers of this type are disclosed in US 4,710,526, the content of which is incorporated herein by cross reference.

The polymers or prepolymers disclosed in US 4,710,526 are essentially acrylate copolymers which comprise (a) about 25% to 99.5% of a hydrolytically-stable acrylate monomer, (b) about 0.5 to 15% of an alkaline-curable cationic quaternary ammonium salt monomer, (c) 0 to 70% of a hydrolytically-stable monomer other than (a) or (b), and (d) 0 to 30% of a hydrolytically-unstable monomer other than (a) or (b) with the percentages being by weight and totalling 100%; the acrylate units in the polymer being represented by the formula

and the alkaline-curable cationic quaternary ammonium salt units in the polymer being represented by the formula

R

-CH,

O= R^

■(CH2)n-N+ CH2 CH CH2 Y"

R3 OH where R is hydrogen or a methyl group; R1 is a C1-C12 alkyl group or a C6-Ci2 cycloalkyl group with the proviso that R1 is not Ci or C2 when R is H; R2 and R3 may be the same or different and are a methyl or ethyl groups; A is -O- or -NH-; X is chlorine, bromine, or iodine; Y is an organic or inorganic monovalent anion; and n is 2 or 3.

Typical alkyl or cycloalkyl acrylates or methacrylates include methyl methyacrylate, ethyl methacrylate, propyl acrylate or methacrylate, butyl acrylate or methacrylate, amyl acrylate or methacrylate, hexyl acrylate or methacrylate, 2-ethylhexyl acrylate or methacrylate, n- octyl acrylate or methacrylate, decyl acrylate or methacrylate, lauryl acrylate or methacrylate, and cyclohexyl acrylate or methacrylate. These can be used alone or in combination. If necessary, other monomers which can be copolymerised with the above- described monomers can be included. These include hydrolytically-stable monomers such as styrene and its derivatives, acrylonitrile or methacrylonitrile, acrylic acid or methacrylic acid, vinyl pyridine, vinyl pyrrolidinone, hydroxyalkyl acrylate or methacrylate and its derivatives, alkyl amino acrylate or methacrylate, N,N'-dialkyl acrylamide or methacrylamide, dimethylaminopropyl acrylamide or methacrylamide in amounts up to about 70 wt%. Hydrolytically-unstable monomers such as methyl acrylate, ethyl acrylate, vinyl acetate, vinyl chloride, and vinyl ethers may also be used in amounts which do not effect the hydrolytic stability of the polymer, eg., up to 30% by weight.

The expression "hydrolytically-stable monomer", as used herein, means a monomer which does not substantially hydrolyse at a pH above 1 1.

Preferred polymers of the type disclosed in US 4,710,526 contain about 40-60%, most preferably 50% methylmethacrylate or styrene, 40-60%, most preferably 50%, butyl acrylate, 1 -10% of the cationic monomer, and optionally 2-ethylhexyl acrylate, with the percentages totaling 100%.

In US 4,710,^26, suitable alkaline-curable cationic quaternary ammonium monomers are defined as adducts of an epihalohydrin and a dialkylaminoalkyl acrylamide or methacrylamide (where A is -NH-) or acrylate or methacrylate (where A is -O-). Such cationic halohydrin-containing monomers are described in U.S. Pat. No. 3,095,390 and U.S. Pat. No. 3,694,393. Typical adducts include adducts dimethylaminoethyl acrylate or methacrylate, diethylaminoethyl acrylate or methacrylate, dimethylaminopropyl acrylate or methacrylate, diethylaminoethyl acrylamide or methacrylamide, diethylaminopropyl acrylamide or methacrylamide, and the like. The monomers are typically used in the salt form, and a variety of salts are suitable. Typical inorganic anions include chloride, bromide, sulfate and nitrate. Typical organic anions include acetate, benzosulfonate and lauryl sulfonate. The preferred monomers are the chlorides or nitrates of dimethylaminoethyl methacrylate, dimethylaminopropyl methacrylate, and dimethylaminopropyl methacrylamide. The amount of quaternary ammonium salt monomer used is preferably 0.5-15%, preferably 1-10%, by weight of the total polymer.

The polymers or prepolymers disclosed in US 4,710,526 are dispersed in water and thus form an emulsion. The preferred particle size of the dispersed polymer or prepolymer phase is 0.1-1 micron. The polymer content (i.e. solids) of the emulsion is preferably 20- 70% by weight. The glass transition temperature (Tg) of the acrylate copolymers is essentially controlled by the carbon chain length of the alkyl group (i.e. R1) in the acrylate or methacrylate monomer. The polymer or prepolymer should have a Tg below 1 O0C, preferably below 0°C, and most preferably -100C or below.

However, acrylate or methacrylate copolymers having a Tg above 100C can be used if sufficient plasticiser is added so that the apparent Tg of the plasticised polymer composition is lowered to below 1 O0C. For the purposes herein, these plasticised aqueous polymer emulsions are considered the equivalent of the non-plasticised polymer emulsions containing polymers have the required Tg. The plasticiser can be added during manufacture of the copolymers or can be added after the polymerisation reaction has been completed. The preferred plasticisers include di-butyl phthalate, dioctyl phthalate, trimethyl penta diol mono-iso-butyrate, trimethyl penta diol di-iso-butyrate, and butyl carbitol. The amount of plasticiser used is generally below 20 wt%, based on the total weight of the polymer. It is preferable to minimise the amount of plasticiser used.

Tg values referred to herein are calculated Tg's. The Tg of a copolymer may be calculated by way of the following Fox equation:

l/Tg = W,/Tg(1) + W2/Tg(2) wherein Wi and W2 are the weight fraction of monomeric units 1 and 2, respectively; Tg(i) and Tg(2) are the Tg (in degrees Kelvin) of homopolymers of monomeric units 1 and 2, respectively.

The first water dispersible polymer or prepolymer used in accordance with the invention may also conveniently be based on conventional epoxy resins. Such epoxy resins will generally be a glycidyl epoxy resin, and the glycidyl epoxy resin will preferably be a glycidyl-ether epoxy resin.

Those skilled in the art will appreciate that glycidyl epoxy resins are typically prepared via a condensation reaction of an appropriate hydroxy compound and epichlorohydrin.

Suitable glycidyl-ether epoxy resins include, but are not limited to, those formed through a condensation reaction between a hydroxy compound such as bisphenol A, bisphenol-F, hydrogenated bisphenol-A (i.e. bisphenol-H), glycerol, and combinations thereof, and epichlorohydrin, or formed through the condensation reaction between a phenolic novolac resin and epichlorohydrin.

Of the suitable glycidyl-ether epoxy resins, those formed through the condensation reaction of bisphenol-A and epichlorohydrin are preferred. Such resins are generally referred to as being difunctional (i.e. having two reactive terminal epoxy groups per molecule), and can be made with varying molecular weights. A generalised structural representation of this family of epoxy resins can be depicted by the following formula:

Resins of the type depicted directly above are commonly referred to as DGEBA resins. Commercial DGEBA resins typically have a degree of polymerisation (i.e. value of n) ranging from greater than O to about 25. Preferred DGEBA resins used in accordance with the invention have a value of n ranging from greater than O to about 5. A particularly preferred DGEBA resin used in accordance with the invention has n = 0.2 (i.e. equivalent to a molecular weight ranging from about 300 to 350 in commercial products).

Multifunctional (i.e. more than two reactive epoxy groups per molecule) DGEBA resins may also be used in accordance with the invention. Such resins provide a means to achieve higher crosslinked densities which can improve at least the chemical resistance of the settable composition.

In contrast with the type of polymers disclosed in US 4,710,526, water dispersed glycidyl epoxy resins are not generally prepared by emulsion polymerisation techniques, but instead the resin is first prepared via a condensation reaction and the resulting product is subsequently emulsified. Those skilled in the art will appreciate the techniques used to emulsify such epoxy resins. In general, an epoxy resin is loaded into a high-speed disperser and an appropriate suitable surfactant(s) is added. A defoamer is also generally added to prevent excessive aeration, and high shear mixing is employed. Water is then slowly added to the epoxy resin composition. At this stage, the epoxy resin composition presents as the continuous phase and the water as the dispersed phase. As the water content increases, the ratio of the dispersed phase to the continuous phase increases until a phase inversion occurs. The inversion generally occurs at about 65% volume ratio of dispersed to continuous phase and is accompanied by a rapid reduction in viscosity. Water addition is then continued until the desired solids concentration is achieved. Additional additives and modifiers can be incorporated into the formulation at this stage. The resultant water dispersed epoxy resin typically has a particle size ranging from about 0.5 to 3 microns. The solids content of the dispersion typically ranges from about 30 to about 65 wt% and has a viscosity ranging from about 2,000 to about 12,000 cps, preferably in the range from about 2,500 to about 3,500 cps, as measured using a Brookfield HAT Viscometer (spindle #3 at 20 rpm).

The water dispersed epoxy resins should be stable in terms of the polymer and the dispersion under alkaline conditions. In other words, the epoxy resin should be hydrolytically stable and be maintained as a dispersion under alkaline conditions. While it is believed that the epoxy functionality of the first water dispersible polymer or prepolymer reacts at least with the pozzolanic material, it may also be desirable to include in the composition of the invention a curing agent to further promote reaction of the epoxy functionality. Curing agents suitable for this purpose may be conveniently selected from those curing agents conventionally used with such resins. Common curing agents used with epoxy resins include amines, polyamides, polyamidoamines, phenolic resins, anhydrides, isocyanates, polymercaptans, and combinations thereof.

Suitable amine curing agents include, but are not limited to, mono or poly functional amines, such as methylamine, ethylamine, n-propylamine, isopropylamine, the isomeric butylamines, pentylamines, hexylamines and octylamines, n-dodecylamine, n-tetradecylamine, n-hexadecylamine, n-octadecylamine, cyclohexylamine, the isomeric methylcyclohexylamines, aminomethyl-cyclohexane, dimethylamine, diethylamine, dipropylamine, diisopropyl-amine, dibutylamine, diisobutylamine, bis-(2-ethylhexyl) amine, N-methyl- and N-ethylcyclohexylamine, dicyclohexylamine, hydrazine, ethylenediamine, 1 ,2-diaminopropane, 1 ,4-diaminobutane, 2-methylpentamethylene diamine, 1,6-diaminohexane, 2,2,4- and 2,4,4-trimethylhexamethylene-diamine, 1 ,2- diaminocyclohexane, l-amino-3,3,5-trimethyl-5-arninomethylcyclohexane (isophoronediamine, IPDA), 4,4'-diaminodicyclohexyl-methane, pyrrolidine, piperidine, piperazine, (3-aminopropyl)trimethoxy-silane, (3-aminopropyl)triethoxysilane and (3- methylamino)propyltri-methoxysilane, amino-alcohols such as 2-aminoethanol, 2- methylamino-ethanol, 2-(dimethylamino)ethanol, 2-(diethylamino)ethanol, 2-dibutyl- amino)ethanol, diethanolamine, N-methyl-diethanolamine, triethanolamine, 3-amino-l- propanol, 3-dimethylamino-l-propanol, l-amino-2-propanol, l-dimethylamino-2-propanol, l-diethylamino-2-propanol, bis-(2-hydroxypropyl)amine, bis-(2- hydroxypropyl)methylamine, 2-(hydroxyethyl)-bis-(2-hydroxypropyl)amine, tris-(2- hydroxypropyl)amine, 4-amino-2-butanol, 2-amino-2-methylpropanol, 2-amino-2-methyl- 1 ,3-propanediol, 2-amino-2-hydroxypropyl-l,3-propanediol and N-(2- hydroxyethyl)piperidine, ether-amines, such as 2-methoxyethylamine, 3- methoxypropylamine, 2-(2-dimethylaminoethoxy)ethanol, and l,4-bis-(3-aminopropoxy) butane, diethylenetriamine, triethylenetetramine, dimethylaminopropylamine, diethylaminopropylamine, amine-glycidyl adducts, amine-ethylene oxide adducts, cyanoethylation products, m-Phenylenediamine, diaminodiphenylmethane, diaminophenyl sulphone, piperidine, triethylamine, benzyldimethylamine, dimethylaminomethylphenol, tri(dimethylamino methyl)phenol, tri-2-ethylhexoate salt of tri(dimethylaminomethyl) phenol, and combinations thereof.

Typically, the curing agent will be used in a stoichiometric ratio of epoxy resin to curing agent ranging from about 2: 1 to about 1 : 1.

The composition in accordance with the invention generally comprises between about 5 wt% to about 25 wt%, preferably between about 10 wt% to about 25 wt%, more preferably between about 15 wt% to about 20 wt% of the first water dispersible polymer or prepolymer on a solids content basis (i.e. on the basis of the weight of polymer or prepolymer in the emulsion, not the weight of the emulsion per se).

Those skilled in the art will appreciate that the choice of the first water dispersible polymer or prepolymer, and curing agent if used, may effect the properties of the settable composition when cured. In particular, through variation of the crosslink density that can be derived from the epoxy functionality, properties such as chemical resistance, flexibility, and hardness can be altered. Depending on the intended application of the settable composition, it may be desirable to control one or more of such properties through the appropriate selection of the first water dispersible polymer or prepolymer and/or a curing agent (if used).

For example, if it is desirable to render the cured settable composition more flexible, one approach may be to enhance the toughness of the cured first water dispersible polymer or prepolymer. In this case, enhancing the toughness of the polymer or prepolymer could be achieved by one or a combination of (i) chemical modification of the polymer or prepolymer backbone to make it more flexible, (ii) increasing the molecular weight of the polymer or prepolymer, (iii) reducing the crosslink density of the resulting cured polymer or prepolymer, and (iv) incorporating a dispersed toughener phase (i.e. a flexibiliser) within the cured polymer matrix. Alternatively, flexibility of the cured settable composition may be enhanced through incorporating a second water dispersible polymer or prepolymer in the composition. The second water dispersible polymer or prepolymer will not comprise epoxy functionality that can react with one or more components of the composition, and will preferably not comprise epoxy functionality at all. Generally, the second water dispersible polymer or prepolymer will be a polymer formed by emulsion polymerisation of one or more ethylenically unsaturated monomers selected from typical alkyl or cycloalkyl acrylates or methacrylates such as methyl methacrylate, ethyl methacrylate, propyl acrylate or methacrylate, butyl acrylate or methacrylate, amyl acrylate or methacrylate, hexyl acrylate or methacrylate, 2-ethylhexyl acrylate or methacrylate, n-octyl acrylate or methacrylate, decyl acrylate or methacrylate, lauryl acrylate or methacrylate, and cyclohexyl acrylate or methacrylate, styrene and its derivatives, acrylonitrile or methacrylonitrile, acrylic acid or methacrylic acid, vinyl pyridine, vinyl pyrrolidinone, hydroxyalkyl acrylate or methacrylate and its derivatives, alkyl amino acrylate or methacrylate, N,N'-dialkyl acrylamide or methacrlyamide and dimethylaminopropyl acrlyamide or methacrylamide. Possible alternative ethylenically unsaturated monomers include those described in US 6,890,983 and US 6,858,299, the contents of which are incorporated herein by cross reference.

The second water dispersible polymer or prepolymer should also be hydrolytically stable under alkaline conditions, and the stabiliser(s) used to maintain the polymer or prepolymer as a dispersion should be capable of functioning as a stabiliser under alkaline conditions.

Bearing in mind that the second water dispersible polymer or prepolymer should be hydrolytically stable under alkaline conditions, it may nevertheless be possible to prepare the polymer or prepolymer using a proportion of hydrolytically-unstable monomers such as methylacrylate, ethylacrylate, vinyl acetate, vinyl chloride, and vinyl ethers provided that the amount used does not effect the net hydrolytic stability of the resulting polymer. In this case, the hydrolytically-unstable monomers will generally be used in an amount which does not exceed 30 wt% of the total monomers polymerised. Preferably, the second water dispersible polymer or prepolymer is a water dispersible acrylic polymer, more preferably a water dispersible acrylic copolymer of methylmethacrylate, butyl acrylate and acrylic and/or methacrylic acid. Such an acrylic copolymer preferably has a non-volatile solids content by weight of about 50%, a specific gravity of about 1.06 kg/L, a Brookfield viscosity (LVT, #2 spindle at 30 rpm) in the range of about 1 to 500 cP, a pH in the range of about 8 to about 9, a polymer density(dry) of about 1.12 kg/L, and a volatile organic content (VOC) in the range of 0 to about 5 g/L, and comprises a non-ionic surfactant.

As mentioned above, the second water dispersible polymer or prepolymer may be used in combination with the first water dispersible polymer or prepolymer to manipulate the properties of the cured settable composition. It has been found that the second water dispersible polymer or prepolymer can be particularly effective at increasing the flexural properties (i.e. reducing the brittleness) of the cured settable composition. It is believed that the Tg of the second water dispersible polymer or prepolymer plays an important role in modifying the flexural properties of the cured settable composition.

It will be appreciated from the foregoing that water dispersible polymers of the type disclosed in US 4,710,526 may be prepared using monomers that not only provide the requisite epoxy functionality but also create a backbone structure that imparts desired flexural properties to the cured settable composition. Accordingly, when water dispersible polymers or prepolymers of this type are used there will often be less need to employ a second water dispersible polymer to modify the properties of the cured settable composition.

In contrast, the aforementioned glycidyl epoxy resins are not generally commercially prepared using monomers that can modify the polymer or prepolymer backbone such that the resin can impart enhanced flexural properties to the cured settable composition. Variation in the crosslink density afforded by such polymers or prepolymers can modify the flexural properties of the cured composition to some extent, but this will often be of limited scope. Accordingly, where glycidyl epoxy polymers or prepolymers are employed and flexural properties of the cured composition are desired beyond that which can be afforded by the glycidyl epoxy resin alone, it is preferable that the settable composition of the invention comprises a second water dispersible polymer or prepolymer.

Where the settable composition in accordance with the invention comprises a second water dispersible polymer or prepolymer in combination with the first water dispersible polymer or prepolymer, the total amount of first and second water dispersible polymers or prepolymers present in the composition will generally range from 5 wt% to about 25 wt%, preferably from about 10 wt% to about 25 wt%, more preferably from about 15 wt% to about 20 wt% on a solids content basis. The ratio of the first to the second water dispersible polymer or prepolymer in such a composition will generally range from about 1 :0.5 to about 1 :12, preferably from about 1 :2 and about 1 :9, on a weight percent basis relative to the solids content of the dispersions. In adjusting the ratio of the first and second water dispersible polymers or prepolymers, it may be necessary to vary the amount of other components present in the composition, and/or the application thickness of the composition, to optimise curing. This can be achieved through simple experimentation and testing.

As mentioned above, the Tg of the second water dispersible polymer or prepolymer can be important in enhancing the flexural properties of the cured composition. The appropriate Tg of the second water dispersible polymer or prepolymer will vary depending on the intended application of the composition. Where a more hard or rigid composition is required, the Tg will typically range from about 0°C to about 2O0C, preferably from about from about 50C to about 20°C, more preferably from about 1O0C to about 200C. Where a more soft or flexible composition is required, the Tg will typically range from about -2O0C to about O0C, preferably from about from about -100C to about O0C. The particle size of the dispersed polymer or prepolymer in the second dispersion is preferably about 0.1 to 1 micron, and the solids content of the emulsion is preferably about 20 wt% to about 70 wt%.

Without wishing to be limited by theory, it is believed that where the first water dispersible polymer or prepolymer is used in combination with a second water dispersible polymer or prepolymer which has been prepared using one or more monomers having a functional group that is capable of reacting with an epoxy group, a fourth bonding mechanism may operate in the settable composition to afford the complex cured matrix. In other words, it is believed that the epoxy functionality of the first water dispersible polymer or prepolymer may react with both the pozzolanic material and the second water dispersible polymer or prepolymer.

Monomers that may be used in the preparation of the second water dispersible polymer or prepolymer that have functional groups capable of reacting with the epoxy groups include, but are not limited to, ethylenically unsaturated monomers comprising carboxylic acid groups such as acrylic acid, methacrylic acid, beta-acryloxypropionic acid, ethacrylic acid, α-chloroacrylic acid, α-vinylacrylic acid, crotonic acid, α-phenylacrylic acid, cinnamic acid, chlorocinnamic acid, and β-styrylacrylic acid. Preferred ethylenically unsaturated monomers comprising carboxylic acid groups are acrylic acid and methacrylic acid. Possible alternative ethylenically unsaturated monomers that have functional groups capable of reacting with the epoxy groups include those comprising phosphate, phosphonate and sulfonic acid groups as described in US 6,890,983, the contents of which are incorporated herein by cross reference. Such monomers will generally be used in an amount ranging from about 0.5 to about 10 wt%, preferably from about 1 wt% to about 7 wt%, more preferably from about 1 wt% to about 5 wt%, most preferably from about 1 wt% to about 3 wt%, relative to the total amount of monomers used in the preparation of the second water dispersible polymer or prepolymer.

The composition of the invention also comprises water. It is believed that the water plays a role in functioning as a fluidizing medium and as a chemical reagent. The amount of water required in the composition is believed to be dependent upon a number of factors. Such factors include the amount of water necessary to emulsify the first polymer or prepolymer and where used the second polymer or prepolymer, the amount of water to permit geo-synthesis hydration of the pozzolanic material, and the amount of water needed for hydration, preferably complete hydration, of the expansive inorganic binder.

The source of hydroxide ions may also be provided in the form of an aqueous solution. In determining the amount of water that is to be used in the composition, consideration also needs to be given to the degree of fluidity/viscosity required for the desired application of the composition. For example, the amount of water for a sprayable formulation will differ from a trowel-on formulation. Those skilled in the art could readily determine the amount of water required to obtain a desired fluidity for a given application.

Typically the total amount of water in the composition will range from about 5 wt% to about 15 wt%, preferably from about 10 wt% to about 15wt%.

The composition of the invention may also comprise an aggregate material. An example of an aggregate that may be used in the settable composition includes, but is not limited to, any inorganic substance which is substantially acid resistant. Specific examples of suitable aggregates include, but are not limited to, sand, silica flour, crushed rocks or stones of quartz, granite, feldspar, gneiss, basalt and combinations thereof. The choice and relative amount of aggregate may depend upon the desired application of the composition, for example whether the composition is to be used as an acid resistant liquid coating to minimise degradation, or as a mortar and repair agent for severely degraded pipes, or as a shaped article. A preferred aggregate is silica based sand with a preferred particle size of below about 500 mesh. A typical composition includes up to about 50 wt%, preferably between about 30 wt% to about 45 wt% aggregate.

The composition of the invention may also comprise optional additives such as other polymers, surfactants, extenders, pigments and dyes, pearlescents, adhesion promoters, dispersants, defoamers, leveling agents, optical brighteners, UV stabilizers, coalescents, preservatives, biocides, antioxidants, viscosity modifiers, rheology modifiers, associate thickeners, and common organic polymer based modifiers. Examples of such modifiers/thickeners include, but are not limited to, alkyl and hydroxyalkyl cellulose ethers (methylcellulose, hydroxyethylcellulose, methylhydroxy ethyl cellulose, ethyl- hydroxyethylcellulose, propylcellulose, hydroxypropylmethyl cellulose, hydroxybutylmethylcellulose) acrylamide polymers or copolymers, alkyl and hydroxyalkyl cellulose ethers (methylcellulose, hydroxyethylcellulose, methylhydroxy ethyl cellulose, ethyl-hydroxyethylcellulose, propylcellulose, hydroxypropylmethyl cellulose, hydroxybutylmethylcellulose) acrylamide polymers or copolymers, (polyacrylamide, polymethacrylamide, acrylamide/methacrylamide copolymer), (polyacrylamide, polymethacrylamide, acrylamide/methacrylamide copolymer), and attapulgite.

If used, the modifiers/thickeners will generally be incorporated in the composition in an amount ranging from about 0.05 wt% to about 10 wt%, preferably from about 1 wt% to about 7 wt%, more preferably from about 1 wt% to about 5 wt%, most preferably from about 1 wt% to about 3 wt%, relative to the total mass of the composition.

Where the composition of the invention is to be used in applications which require low "slump" or high "hangability" properties, incorporation of viscosity and/or rheology modifiers in the composition will generally be preferred. Incorporation of such modifiers can be particularly useful in applications where the composition is spray coated onto vertical surfaces such as onto the interior of sewer pipes.

A preferred modifier that may be used to improve the compositions slump or hangability properties is attapulgite. Attapulgite is a magnesium aluminium silicate of very fine particle size and is also known as palygorskite or Fullers Earth. Use of attapulgite in the composition of the invention has been found to impart thixotropic character to the composition to thereby enhance its slump and hangability properties. It has also been found that this function of the attapulgite may be enhanced by first subjecting attapulgite that has been wet out with water to high shear forces to promote separation of the layered clay structure and then incorporating this sheared slurry into the settable composition (i.e. in contrast with adding attapulgite powder direct to the composition). It is believed that the application of shear to the attapulgite increases the surface area of the material that may be exposed to the composition. In addition to functioning as a thixotrope, it is believed that when the composition begins to cure the attapulgite may also become chemically bound into the pozzolan geo-synthesis mass. Attapulgite will typically be used in the composition in an amount of about 0.5 wt%, relative to the total mass of the composition.

Prior to the settable composition of the invention curing to form a solid mass, it will be appreciated that the composition should maintain sufficient fluidity in order to be used in the intended application. Accordingly, it will be important on combining the components of the composition that a substantially uniform suspension or slurry of the components in the mixture is maintained, that is, that one or more of the components do not substantially flocculate or coagulate to form a relatively non-homogenous distribution throughout the mixture.

The negative effect of flocculation or coagulation in the composition may be an important factor to consider when selecting suitable components for use in accordance with the invention. For example, those skilled in the art will appreciate that additives used to stabilise the water dispersible polymer or prepolymers should be selected so that they are compatible with each other and components in the composition such as the hydroxide ions. Those skilled in the art will also appreciate that the particle size of the polymer or prepolymer in such dispersions can be an important factor to consider when the dispersions are combined with "non-stabilised" particulate materials such as fine inorganic particles.

The composition of the invention will typically be provided in the form of a mullti pack product. For example, as a 2 pack product, Part A will generally comprise the first water dispersible polymer or prepolymer, the second water dispersible polymer or prepolymer (if required), water, pozzolanic material, curing agent (if required), and the source of hydroxide ions, and Part B will generally comprise the expansive inorganic binder and an aggregate (if required). In this case, Part A may begin to cure on standing and the composition will generally need to be prepared and used on demand, for example in spray applications. As a 3 pack product, Part A will generally comprise the water dispersible polymer or prepolymer, the second water dispersible polymer or prepolymer (if required), water, and pozzolanic material, Part B will generally comprise the curing agent (if required), water and the source of hydroxide ions, and Part C will generally comprise the expansive inorganic binder and aggregate (if required). In this case, the 3 part pack will generally have a good shelf life.

The cured product formed from the settable composition of the invention will exhibit excellent physical and chemical properties. Preferably, the cured product exhibits one or more of a compressive strength, as measured in accordance with AS2350.6 (see example 2) or AS 1012.9, ranging from about 5 to about 30 Mpa, preferably from about 15 to about 30 Mpa, an adhesive bond strength, as measured in accordance with AS 1012.9, ranging from about 1 to about 3.5 MPa, an indirect tensile strength, as measured in accordance with AS1012.10, ranging from about 0.8 to 1 MPa, a bond in shear (over concrete), as measured in accordance with AS 1640, ranging from about 0.8 to about 1.5 MPa, a flexural strength, as measured in accordance with AS1012.11, ranging from about 3 to about 5 MPa, and an acid resistance capable of passing the "Redner Cell Test" (i.e. sample does not soften, bubble, crack or delaminate after being submersed in 10% sulfuric acid for 12 months).

In certain applications it may be desirable that the cured product formed from the settable composition exhibits a high degree of compressive strength. In this case, it has been found that the compressive strength of the cured product can be further enhanced through incorporating in the composition one or more inorganic additives selected from ground glass, preferably having an average diameter of less than about 20 microns, sodium or potassium silicate, micaceous iron oxide and ilmenite. Such inorganic additives will generally be used in the composition in an amount up to about 5 wt%, preferably up to about 1 wt%, relative to the total mass of the composition.

In certain applications it may be desirable that the cured product formed from the settable composition has a high degree of acid resistance. As mentioned above, in this case it is preferable that the composition comprises a limited amount of or substantially no, ionisable calcium ions. Those skilled in the art will appreciate that although an expansive inorganic binder such as calcium sulfate contains calcium ions, they are not readily ionisable in an acidic aqueous medium and as such present little if no concern in terms of the cured products acid resistance. In contrast, the presence of common cement products in the composition will typically result in the cured product comprising ionisable calcium ions and thereby render the product susceptible to acid degradation. Accordingly, it may be preferable to minimise the amount of common cement products that might be incorporated in, or substantially exclude such products from, the composition of the invention. Preferably, the composition of the invention comprises no more than about 3 wt% of common cement products, more preferably no more than about 1 wt%. For some applications, it may be particularly preferred that the composition of the invention contains substantially no common cement products.

As used herein, the expression "common cement products" is intended to mean Portland cements and aluminous cement. As used herein, the expression "Portland cements" is intended to include those cements normally understood in the art to be "Portland cement" or "modified Portland cement" such as those described in ASTM Standard C 150.

As used herein, the expression "aluminous cements" is intended to include those cementitious materials normally understood in the art to contain as the cementitious constituent, mono calcium aluminate (CaO x Al2O3). This would include high alumina cement (HAC), calcium aluminate cement, and many other commercially available alumina cements. High alumina cement is normally understood in the art to contain greater than 15 wt% of mono calcium aluminate.

As discussed above, it is believed that a cured product formed from the settable composition forms a complex matrix through at least 3 binding mechanisms. Without wishing to be limited by theory, it is also believed during the process of curing, water that is initially associated with the water dispersible polymer and pozzolanic material disassociates to at least be partially absorbed as water of crystallisation by the expansive inorganic binder. Interestingly, it has been found that compositions of the invention typically require more water than can be theoretically absorbed by the expansive inorganic binder (i.e. up to about 25 wt% more). Given that shrinkage of the composition during cure remains negligible, being suggestive that water is not lost through evaporation, the fate of this "extra" water is not entirely clear. However, it is believed that the "extra" water may form novel hydrates that could possibly contribute to the unique physical and chemical properties of the cured settable composition.

A preferred composition in accordance with the invention comprises calcium sulphate alpha-hemihydrate as an expansive inorganic binder (typically in an amount ranging from about 10 wt% to about 45 wt %, preferably about 25 wt%), metakaolin and fly ash as pozzolanic material (typically in a total amount ranging from about 2 wt% to about 30 wt %, preferably about 15 wt%), a water dispersed DGEBA resin having a molecular weight of approximately 300 to 350 as a first water dispersible polymer or prepolymer, a water dispersed acrylic polymer, preferably an acrylic copolymer of methylmethacrylate, butyl acrylate and acrylic or methacrylic acid, as a second water dispersible polymer or prepolymer (typically in a total amount of DGEBA and acrylic polymer ranging from about 5 wt% to about 25 wt %, with the ratio of DGEBA to acrylic polymer ranging from about 1 :0.5 to about 1 : 12, preferably in a total amount of about 15 wt%, with the ratio of about 1 :9 (solids)), water (typically in an amount ranging from about 5 wt% to about 15 wt %, preferably about 10 wt%), alkali in the form of sodium or potassium hydroxide as a source of hydroxide ions (preferably to provide the composition with a pH of about 12), silica sand as an aggregate (typically in an amount up to about 50 wt%, preferably about 40 wt%), attapulgite as a viscosity and/or rheology modifier (typically in an amount ranging from about 0.5 wt% to about 10 wt %, preferably about 4 wt%), and triethylenetetramine as a curing agent (typically in an amount ranging from about 0.8 wt% to about 3 wt %, preferably about 1 wt%).

A further preferred composition in accordance with the invention comprises calcium sulphate hemihydrate as an expansive inorganic binder (typically in an amount ranging from about 10 wt% to about 45 wt %, preferably about 25 wt%), metakaolin and fly ash as pozzolanic material (typically in a total amount ranging from about 2 wt% to about 30 wt %, preferably about 15 wt%), a water dispersed alkaline curable resin as described in US 4,710,526 as a first water dispersible polymer or prepolymer (typically in an amount ranging from about 5 wt% to about 25 wt % (solids)), water (typically in an amount ranging from about 5 wt% to about 15 wt %, preferably about 10 wt%), alkali in the form of lime as a source of hydroxide ions (preferably to provide the composition with a pH of about 12), silica sand as an aggregate (typically in an amount up to about 50 wt%, preferably about 40 wt%), methylcellulose as a viscosity and/or rheology modifier (typically in an amount ranging from about 0.05 wt% to about 10 wt %, preferably about 4 wt%), and triethylenetetramine as a curing agent (typically in an amount ranging from about 0.8 wt% to about 3 wt %, preferably about 1 wt%). Certain compositions of the invention are particularly suitable as a settable composition that may be used to rehabilitate degraded concrete sewer mains. The application thickness typically corresponds to the depth of concrete lost by degradation and may be applied up to a thickness of about 5mm to about 125mm.

Alternatively, the composition may be used for providing an acid and/or chemically resistant protective and/or rehabilitative coating to a substrate. A particularly preferred substrate is a concrete sewer main. The coating composition may be applied to the interior of a concrete main prior to installation of the main to provide a protective lining or coating against hostile acidic and/or corrosive environments. In this case, the composition may be applied to a thickness of between about 100 to 250 microns to about 1 mm.

The composition in accordance with the invention can be conveniently applied to a substrate using techniques known in the art such trowelling and spraying.

The compositions of the invention can provide a low cost yet effective composition for coating or repairing substrates which are susceptible or have been damaged by acid or chemical corrosion. Such substrates include pipes, smoke stacks, flooring which is subject to damage from chemical or acid spills and storage tanks. The composition of the invention may also be used to form an acid resistant article.

Still further, the settable composition may be moulded to form a shaped article, independent of a substrate. Examples of shaped articles include liners for mains and even roof tiles.

A further advantage of the composition of the invention is the degree of surface preparation required as compared to conventional coatings and rehabilitative compositions. For example, prior to applying a conventional polymer coating to a sewer main, the surface must be carefully cleaned to remove debris and loose particles. In contrast, compositions of the invention can be applied to less stringently cleaned surfaces or over wet or damp surfaces.

Still further, the settable composition of the invention has a fast curing time when compared to standard Portland cement materials. Rapid curing time is an important consideration when rehabilitating sewer mains where flow through the main must be stopped or diverted to allow worker access.

By way of example only, the present invention will now be described with reference to the following non-limiting examples:

Example 1

A settable composition in accordance with the invention was prepared according to the following two-part formulation:

Ingredient wt% Part A (Liquid) Water 5.99 Calcined kaolin 0.40 Flyash 9.92 Polymer A* (solids) 12.12 Methylcellulose 0.04 Curing agent** 0.88 KOH 0.1 1

Part B (Solids) Sand 44.08 Calcium sulfate alpha-hemihydrate 26.45 * Polymer A is an alkaline curable acrylate monomer as described in US4714526 having a solids content of about 50 wt%. ** triethylenetetramine

Parts A and B were mixed and observed to set in about 1 to 2 hours.

The cured material was observed to have superior acid^resi stance properties when compared to conventional Portland cement. In particular, the material was not found to soften, bubble or crack after being submerged in 10% sulfuric acid for more than 2 years. Furthermore, it was also observed that under similar conditions Portland cement based concrete cured in not less than about 24 hours. The cured material was subjected to mechanical testing. Results from the test are shown below in Table 1.

Table 1 - Mechanical test data for the cured material produced in Example 1.

Example 2

A settable composition in accordance with the invention was prepared according to the following three-part formulation:

Ingredient wt% Part A (Liquid) Water 1 1.1 Calcined kaolin 0.6 Flyash 10.6 Polymer A* (solids) 7.0 Polymer B** (solids) 0.6 Attapulgite 0.5

Part B (Xiαuid) Water 2.7 Curing agent*** 0.1 KOH 0.1 propylene glycol 0.3

Part αCSolids) Sand 41.6 Calcium sulfate alpha-hemihydrate 22.9 Portland cement 1.9 * Polymer A is an acrylic emulsion polymer (Rohm & Haas) having a solids content of about 50 wt%. ** Polymer B is a water dispersed digycidyl ether of bisphenol-A (DGEBA) epoxy resin (Huntsman) having a solids content of about 40 wt%. *** triethylenetetramine

Parts A-C were mixed and the mixture was observed to cure in about 30 minutes.

The cured material was observed to possess vastly superior acid resistance properties when

compared to conventional Portland cement cured materials. Whereas a fully cured Portland

cement product was observed to completely disintegrate within a matter of hours in a 20%

solution of sulfuric acid at 700C, a sample of this Example survived undamaged for over 9

months.

The cured material was subjected to various mechanical tests. Results from the test are

shown below in Table 2.

Table 2 - Mechanical test data for the cured material produced in Example 2.

* AS2350.6-1980 adapted for 50 mm cubes

** In house test method performed by CTI Consultants Pty Ltd of 4 Rothwell Avenue, Concord West NSW 2138, Australia. Example 3

A settable composition in accordance with the invention was prepared according to the following three-part formulation:

Ingredient wt% Part A (Liαuid) Water 16.5 Calcined kaolin 0.6 Flyash 11.3 Polymer A* (solids) 6.2 Attapulgite 0.4

Part B (Liquid) Water 1.2 Curing agent** 0.4 KOH 0.1 propylene glycol 0.3

Part C (Solids) Sand 44.1 Calcium sulfate alpha-hemihydrate 18.9 * Polymer B is a water dispersed digycidyl ether of bisphenol-A (DGEBA) epoxy resin (Huntsman) having a solids content of about 40 wt%. ** triethylenetetramine

Parts A-C were mixed and the mixture was observed to cure in about 6 hours.

It will be understood that various changes and modifications may be made to the invention as described therein without departing from the spirit and scope thereof.

Throughout this specification, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia or elsewhere.