AU1633801A - Surface covering material - Google Patents

Description

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): FOSROC GROUTING PTY LIMITED A.C.N. 084 965 962 Invention Title: SURFACE COVERING MATERIAL The following statement is a full description of this invention, including the best method of performing it known to me/us: 2 SURFACE COVERING MATERIAL FIELD OF THE INVENTION The present invention relates to a surface covering formulation and is particularly suitable for use in the mining industry to coat and thus stabilise roofs, walls and floors of mining tunnels, shafts, open cut pits, etc and to cover mining bolts and plates etc. However, it should be appreciated that the invention is not limited to these applications and can be used in the construction industry etc.

BACKGROUND ART Surface coating and covering formulations and materials are known in the art for use in the mining and construction industries. Examples of such materials are shown in US 4849018, DE 3302440, ZA 85/7733, EP 89113048, JP 60258349, JP 4300231, JP 70/119318 and WO 98/58886.

These formulations are based around a cement binding material that is primarily an ordinary portland cement (hereinafter "OPC").

OPC requires suitable ambient conditions in the construction industries for appropriate curing, otherwise it develops structural defects. In addition, the presence of OPC can negatively effect the speed of setting and also ooeee: S"the flexibility of the resulting cured surface covering material. However, the bulk of covering formulations have relied on OPC because of its excellent binding properties, particularly when cement-polymer formulations are provided (the polymer providing additional flexibility to the cured sprayed on material) JP 84/206847 discloses a cement-based coating composition including a cement and synthetic resin emulsion mixture. Cements other than OPC are disclosed.

The cement, however, comprises the bulk of the 3 composition, as this is necessary when coating concrete buildings.

JP 89/315748 also discloses a cement composition for use in repairing concrete structures. In this document a latex copolymer is combined with ultrafine waste particles such as silica fume, blast furnace slag or pulverised flyash. The resultant "cements" are not however optimum from a structural strength viewpoint, particularly if they were to be used in mining surface covering applications.

Similarly, JP 80/050958 discloses a moulded cement product which includes either portland cement or a flyash, silica or slag cement, mixed with a synthetic polymer. Again, the resulting non-OPC formulations would not provide high structural integrity. In addition, the cement is in greater proportion than the polymer as a result of its use in moulding applications. Yet again, JP 83/199948 discloses a joint sealing material which can include cements other than OPC, in conjunction with a polymer, but again the cement is necessarily in greater proportion than the polymer in this application.

Finally, JP 60158269 discloses a film forming composition for use in the construction industry to provide a thick coating film on structures, to protect and ooeee waterproof the same. The document teaches the mixing of a polymer with a non-OPC cement component based on a calcium aluminate that must include gypsum at a fixed ratio.

Gypsum is essential to the cement in order to overcome the quick setting problems of known calcium aluminate/polymer mixtures. As a result, it is understood that the formulation is difficult to handle and spray, and this problem would be particularly exacerbated if the formulation was attempted to be used in the constricted and structurally unstable situations occurring in the -4 mining industry. Furthermore such a formulation would be relatively expensive and cumbersome to produce.

SUMMARY OF THE PRESENT INVENTION The present invention provides a surface covering formulation including a substantially OPC-free aluminous cement and a water dispersible polymer that is present in greater weight proportion than the cement.

It is most preferred that the water dispersible polymer is a polymeric ester material. It has been surprisingly observed that polymeric esters when used in conjunction with aluminous cements can eliminate the need for other additives including OPC and gypsum. In addition, such formulations demonstrate surprising sprayability, early strength, film-forming capacity, setting/curing performance, and long term stability.

When the terminology "substantially OPC-free" is used in the present specification, it indicates that the cement is preferably entirely OPC-free, but may contain OPC S..amounts up to as high as about 5-10%. It should be appreciated, however, that the OPC does not primarily contribute to the enhanced performances of the formulation and might only be added in some applications for economic (cost) reasons or because of ease of availability.

The term "aluminous cement" includes both calcium sulpho aluminates and high aluminous cements, and includes calcium aluminates, di-calcium aluminates, tri-calcium aluminates, mayenite, tetracalcium aluminoferrite, regulated set cement, calcium sulphoaluminate, calcium ferroaluminates and analogues of the aforementioned cements. Typically the term "aluminous cement" refers to a cement containing 30-50% of lime, 30-50% of alumina, and not more than 30-50% of silica, iron oxide etc. The most preferred cement for use in the invention is a calcium 5 sulpho aluminate cement.

The polymer preferably includes polymeric esters, especially polymeric vinyl esters, such as ethylene vinyl acetate. However, when the term "water dispersible polymer" is used in the present specification it can include polymers as disclosed in US 4849018, including methylcellulose, hydroxyethylcellulose, polyvinyl alcohol, styrene, divinylstyrene, methylmethacrylate, co-polymers of styrene and methylmethacrylate or maleic anhydride, acrylic and acrylic ester resins, emulsions of vinyl acetate homopolymer, vinyl acetate-acrylic copolymers, internally plasticised and externally plasticised vinyl chloride copolymers, polyacrylic emulsions, styrene butadiene copolymers, vinyl chloride-vinylidene chloride copolymers, vinyl copolymers, vinyl chloride vinylidene chloride acrylic terpolymers, copolymers of methylmethacrylate with methacrylic acid, acrylic acid, crotonic acid, itaconic acid or similar unsaturated carboxylic acids, copolymers of methyl methacrylate with ethyl acrylate, ethyl hexyl acrylate, butyl acrylate or similar esters of acrylic acid and acids of the same, copolymers of vinyl acetate with esters of acrylic acid, methacrylic acid, crotonic acid or similar unsaturated acids, optionally modified to include carboxyl groups, copolymers of vinyl acetate with acrylic acid, methacrylic acid, crotonic acid and similar unsaturated acids or salts thereof, copolymers of vinyl pyrrolidone with acrylic acid, methacrylic acid, crotonic acid or similar unsaturated acids, which may also include as monomers esters of these acids, copolymers of anhydrides of unsaturated acids, such as maleic acid, with suitable unsaturated monomers such as styrene, di-isobutylene, methyl vinyl ether, partially hydrolysed polymers and 6 copolymers of acrylamide, methacrylamide and acrylonitrile, graft polymers of polyethylene oxide with copolymers of acrylic acid, methacrylic acid etc., methylacrilade, methylamethatricade etc.

Notably, however, the inventors have discovered that a polymer including a polymeric ester, such as a vinyl ester, gives very surprising performance results when combined with aluminous cements. Also, the inventors have discovered that the overall strength and flexibility of the cured material in surface covering applications is enhanced when the polymer present in the formulation is greater in weight than the cement.

Most preferably the formulation is prepared from an emulsified form of the polymer which is mixed with the cement. Alternatively, the polymer can be supplied in the ."form of a powder and mixed with cement powder prior to the addition of water. Hereafter, any polymer referred to S"will usually be in an emulsified form.

oO When the polymer is an ethylene vinyl acetate copolymer emulsion, a typical and suitable solids content range (based on the emulsion) is from 5 to 80wt%, and preferably at least 25wt%. Effective performances are obtained with solids content ranging from 30-75wt%, and most preferably around 55wt%. The preferred pH range for the emulsion is 4.5-6.5. The preferred emulsion glass transition temperature is around 0°C. Preferably the emulsion viscosity ranges from 1500-2500 cps, and typically the molecular weight of the emulsion is around 7 million mwu.

Such vinyl esters surprisingly provide quick set and high early strength characteristics, which are desirable in the highly humid and stagnant atmosphere found in mining tunnels, shafts etc.

7 Preferably the vinyl esters are: when an emulsion, selected from the range of DA 100 to DA 103H vinyl esters; or (ii) when in powdered form and prior to formulating, selected from the range of DA 1200 to DA 1420 vinyl esters.

Such polymers are provided by the Dairen Corporation (hence the DA prefix) either as emulsions, or as powders.

DA 101 has been found to be particularly suitable in the present invention.

Preferably the cement includes either or both of a sulpho-aluminate or high alumina cement, in conjunction with a calcium sulphate. Preferably the sulpho-aluminate cement is a calcium sulpho-aluminate cement. Such cements are quick setting and can develop high early strength *"which is particularly advantageous in mining applications.

Furthermore, their dependency of hydration speed on ambient temperature is low, and they have an excellent capacity for absorbing water out of the polymer emulsion in which they are employed.

Whilst calcium sulphate is not essential to the invention it is most preferably added to the formulation to promote the formation of a crystalline compound known as ettringite, being a highly water absorbent form of cement, and thus quick setting with high early strength.

S. The present inventors have surprisingly discovered that the ettringite developed in the present formulations has the capacity to absorb at least eight times as much water as OPC based cements. The calcium sulphate can be provided in the form of gypsum, plaster or anhydrite, most preferably as anhydrite.

Preferably the material further comprises lithium carbonate. The inventors have observed that lithium 8 carbonate aids the reaction of cement with calcium sulphate by forming nucleation sites which accelerate the formation of the crystal structure ettringite.

The formulation preferably further comprises viscosity control agents and reinforcement particles.

Typically the viscosity control agents include citric acid, guar gum and super plasticising agents. Citric acid had the added benefit of functioning as a set (cure) control agent. Typically the reinforcement particles include synthetic fibres, such as nylon, polyethylene, polyamide, glass fibres etc. Because the formulation is substantially OPC-free, less alkali resistant glass types (ie. than might otherwise have been required) can be employed.

An anti foaming agent is also preferably added to prevent foaming and consequent trapping of air during mixing (which otherwise can result in a reduction in S" strength of the final cured material) Typically the cement comprises 40-80wt% of the formulation and typically the calcium sulphate comprises 0-60wt%. In the cement itself, it is most preferred that the aluminous cement is present at about 66wt% and the calcium sulphate is present at about 33wt%.

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Preferably the lithium carbonate, viscosity control agents, reinforcement particles and/or anti-foaming agents comprise 0-2wt% of the cement.

Typically the ratio of polymer (as emulsion) to cement ranges from about 2:1 to 3:1 and preferably is about 2.5:1, but other ratios can still provide a sufficiently flexible result in the subsequently cured material.

In a second aspect the present invention provides a surface covering formulation including a cement and an 9 ester based polymer that is capable of developing high early strength in conjunction with the cement.

It has been particularly observed that certain ester based polymers assist in the surface covering material reaching a high early strength and degree of curing at an early stage after spraying, thus overcoming adverse atmospheric conditions prevalent in mining applications.

In the second aspect the ester based polymer can be used in a formulation that has a cement portion comprising OPC, although it is usually employed with a cement that is substantially OPC-free. The cement and polymer of the second aspect are typically in all other respects the same as those defined for the first aspect.

MODES FOR CARRYING OUT THE INVENTION Preferred examples of the present invention will now *"be described with reference to substantially OPC-free cements. It should be appreciated, however, that high S"early strength ester based polymers, especially the particular ethylene vinyl acetate copolymers disclosed, can also be employed with cement portions that include at least some OPC.

S" EXAMPLES Surface covering materials were prepared by mixing up different cements as follows: .6 a .0 a 10 Cement Example 1 *r

S

Component Mass Percent (kg's) Calcium sulpho-aluminate 600 60.0% Anhydrite calcium sulphate 298 29.8% Ground granulated blast furnace slag 91.2 9.12% Guar gum 6 0.6% Citric acid 1 0.1% Glass fibres (25mm length) 0.8 0.08% Super plasticiser 1 0.1% Lithium carbonate 2 0.2% Total: 1000kg 100% Cement Example 2: Component Mass Percent (kg's) Calcium sulpho-aluminate 660 66.0% Anhydrite calcium sulphate 328 32.8% Guar gum 7 0.7% Citric acid 1 0.1% Glass fibres (25mm length) 0.1 0.01% Super plasticiser 1 0.1% Lithium carbonate 2 0.2% Total: 1000kg 100% In cement Example 1, the addition of grodnd granulated blast furnace slag provided a reactive filler function and thereby enhanced the control of cement reactivity and set. In particular, the blast furnace slag slowed down the reaction time and lowered the viscosity of the cement (thus enhancing sprayability). Also, whilst 11 calcium sulpho-aluminate cements were preferred, satisfactory results were obtained with various other aluminous cements defined above.

The cements 1 2 were then formulated with a number of water dispersible polymers (as defined above). Aqueous emulsions of vinyl esters, especially ethylene vinyl acetate copolymers, were found to provide high performance surface covering formulations (ie. high early strength and set, and excellent sprayability). A preferable EVA was that supplied under the trade name DA 101 by Dairen Chemical Corporation, having a solids content of around Polymer solids contents ranging from 30-75% were also observed to be quite satisfactory.

Specific characteristics of a preferred EVA polymer emulsion were as follows: solids content about 55%, pH of emulsion glass transition temperature Tg about 0C, viscosity ranging from 1500-2500 cps, molecular weight around 7 million mwu.

The polymeric emulsion was employed in a greater mass than the cement, and in the preferred formulation was used at a weight ratio of 2.5:1 to the cement. In further examples coating formulations were developed where the ratio of polymer to cement was 3:1 and 2:1, and sufficiently flexible coating products resulted. In addition, Dairen EVA emulsions in the range of DA 100 to DA 103H (and EVA powders in the range of DA 1200 to DA 1420) were found to be highly effective.

As stated above, a dry polymer powder can also be mixed with the cement prior to adding water to the resultant powder mixture. Thus, a manufacturer can supply to an end user (eg. a mine) a powder premix of the polymer and cement and, at the point of use the premix, can then 12 have water added thereto to redisperse the polymer and cement.

As stated above, anhydrite calcium sulphate was preferred and was observed to promote the formation of ettringite. Thus, whilst some amount of calcium sulphate was preferred in the inventive formulations, it was observed that formulations without calcium sulphate could be prepared and used. Although these latter formulations showed slow strength gain, they were observed to be advantageously extremely elastic once cured.

Guar gum, citric acid and super plasticiser were added to enhance and control viscosity, which was particularly important when spraying the formulation on to surfaces. Citric acid was observed to provide the added benefit of set (or cure) control, thus preventing too early or too late a curing of the formulation either "in S•the pot" or once applied.

S"Glass fibres were added to provide reinforcement, and fibres of 25mm length were observed to be efficacious.

Other fibrous materials were also trialed including nylon, polyethylene, polyamide etc. Glass of higher alkali oooo resistance was preferred, although by using a substantially OPC-free formulation, glass of lesser alkali S"resistance was then able to be used.

As stated above, lithium carbonate was observed to be catalyst to the formation of ettringite and was thus preferably included in the formulations. Lime was also added to the formulations which, in conjunction with the lithium carbonate, assisted in the formation of ettringite.

Accordingly, whilst preferred formulations were based on the combination of an aluminous cement with a polymer, the additional components exemplified herein enhanced the 13 performance, control and use of the formulation, particularly when used as a spray in mining applications.

The resulting formulations were then sprayed onto mining tunnel roofs and walls and displayed excellent adhesion, early curability, high early strength, high subsequent cured strength and excellent flexibility once cured.

In particular, some of the advantageous properties observed of the preferred formulations included: an initial set of 50-60 minutes at 20 0 C, a tensile strength of 2.5-3.0 MPa at 24 hours curing time, and 4 to 5 MPa at 7-28 days curing time, and an elongation of between 20 to of original length once cured. The formulations, when applied to a rock surface, were observed to seal the surface against moisture degradation and to stabilise the surface. The formulations also accommodated any stresses and movement in the rock because of their high degree of elongation. A preferred formulation thickness achieved in practice ranged from 3-7 mm.

Whilst the invention has been described with reference to a number of preferred embodiments, it should be appreciated that the invention can be embodied in many other forms.

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Claims (16)

1. 2. A formulation as claimed in Claim 1 wherein the polymer is ester based.
2. 3. A formulation as claimed in Claim 1 or 2 wherein the polymer is a vinyl ester polymer.
3. 4. A formulation as claimed in any one of the preceding claims wherein the polymer is an ethylene vinyl acetate copolymer. S" 5. A formulation as claimed in any one of the preceding claims wherein the polymer is an ethylene vinyl acetate copolymer emulsion having a polymer solids content range (based on the emulsion) of around
4. 6. A formulation as claimed in claim 5 wherein the pH range for the emulsion is 4.5-6.5, the emulsion glass transition temperature (Tg) is around 0 0 C, the emulsion viscosity ranges from 1500-2500 cps, and the molecular weight of the emulsion is around 7 million mwu.
5. 7. A formulation as claimed in any one of Claims 4 to 6 wherein the ethylene vinyl acetate copolymer has quick set and high early strength characteristics, and is: 15 when in the form of an emulsion, selected from the range of DA 100 DA 103H ethylene vinyl acetate copolymers (as herein defined); (ii) when in powered form and prior to formulating, selected from the range of DA 1200 to DA 1410 ethylene vinyl acetate copolymers (as herein defined).
6. 8. A formulation as claimed in any one of the preceding claims wherein the cement includes either or both of a sulpho-aluminate or high alumina cement, optionally in conjunction with a calcium sulphate.
7. 9. A formulation as claimed in claim 8 wherein the sulpho-aluminate cement is a calcium sulpho-aluminate cement. b.
8. 10. A formulation as claimed in Claim 8 or 9 wherein the calcium sulphate is in the form of gypsum, plaster or anhydrite.
9. 11. A formulation as claimed in any one of Claims 8 to wherein, in the aluminous cement itself, the sulpho- aluminate or high alumina cement is present at about 66wt% and the calcium sulphate is present at about 33wt%.
10. 12. A formulation as claimed in any one of the preceding claims further including lithium carbonate, viscosity control agents, reinforcement particles, and/or an anti foaming agent.
11. 13. A formulation as claimed in Claim 12 wherein the viscosity control agents include citric acid, guar gum and 16 super plasticising agents, and the reinforcement particles include synthetic fibres, including nylon, polyethylene, polyamide and/or glass fibres.
12. 14. A formulation as claimed in Claim 12 or 13 wherein the lithium carbonate, viscosity control agents, reinforcement particles and/or anti-foaming agent are present at 0-2wt% of the cement.
13. 15. A formulation as claimed in any one of the preceding claims wherein the cement comprises 40-80wt% of the formulation.
14. 16. A formulation as claimed in any one of the preceding claims wherein the ratio of polymer (as emulsion) to cement ranges from about 2:1 to 3:1. S" 17. A formulation as claimed in Claim 16 wherein the ratio of polymer is about 2.5:1.
15. 18. A surface covering formulation including a cement, and an ester based polymer that is capable of developing high early strength in conjunction with the cement. o
16. 19. A surface covering formulation as claimed in Claim 18 .*.wherein the cement and polymer are as defined in any one of claims 1 to 17. A surface covering formulation substantially as herein described with reference to the Examples. 17 Dated this 18th day of January 2001 FOSROC GROUTING PTY LTD. By its Patent Attorneys GRIFFITH HACK so 0 *ago *so