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Title:
STABILISING SURFACES WITH MAGNESIUM CEMENTS
Document Type and Number:
WIPO Patent Application WO/2003/002820
Kind Code:
A1
Abstract:
A method for the provision of a stabilised surface, characterised by the steps of: a) blending magnesium oxide and either magnesium chloride or magnesium sulphate and water to form slurry; and b) applying the slurry to a surface to be stabilised or sealed. The method is intended to seal or stabilise surfaces such as unsealed roads, road bases, drains, culverts and other civil engineering constructions. The composition (claimed separately) may also contain aggregates and waterproofing agents such as bitumen emulsion, styrene butadiene rubber, toll oil pitch and acrylic or latex emulsions.

Inventors:
Kerr, Robert Gregory (22 Greenmount Rise, Greenmount, Western Australia 6056, AU)
Application Number:
PCT/AU2002/000846
Publication Date:
January 09, 2003
Filing Date:
June 28, 2002
Export Citation:
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Assignee:
SUNHAWK PTY LTD (1310 Hay Street, West Perth, Western Australia 6005, AU)
Kerr, Robert Gregory (22 Greenmount Rise, Greenmount, Western Australia 6056, AU)
International Classes:
C04B9/00; C04B28/30; C09K17/10; E01C7/36; (IPC1-7): E01C7/36; E02D3/12; C09K17/10; C09K17/14; C04B9/02; C04B9/04; C04B28/30
Domestic Patent References:
WO1994029233A11994-12-22
WO1992018437A11992-10-29
Foreign References:
US3482493A1969-12-09
AU1041932A
AU135709B
AU5571573A1974-11-21
US5276255A1994-01-04
US3956900A1976-05-18
US5110361A1992-05-05
US4838941A1989-06-13
GB1381290A1975-01-22
Other References:
DATABASE WPI Derwent World Patents Index; Class L02, AN 2001-390714/42
DATABASE WPI Derwent World Patents Index; Class A93, AN 1991-119820/17
DATABASE WPI Derwent World Patents Index; Class A93, AN 1983-01028K/01
DATABASE WPI Derwent World Patents Index; Class P61, AN 1991-189953/26
DATABASE WPI Derwent World Patents Index; Class K07, AN 2000-315719/27
DATABASE WPI Derwent World Patents Index; Class Q49, AN 1983-700224/27
DATABASE WPI Derwent World Patents Index; Class L02, AN 1999-076696/07
DATABASE WPI Derwent World Patents Index; Class E33, AN 1989-278722/39
Attorney, Agent or Firm:
WRAY & ASSOCIATES (Level 6, 239 Adelaide Terrace Perth, Western Australia 6000, AU)
WRAY & ASSOCIATES (Level 4, The Quadrant 1 William Stree, Perth W.A. 6000, AU)
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Claims:
Claims
1. A method for the provision of a stabilised surface, the method characterised by the method steps of: blending the components magnesium oxide, either magnesium chloride or magnesium sulphate and water to form slurry ; and applying the slurry to a surface to be stabilised or sealed.
2. A method for the provision of a stabilised surface according to claim 1, wherein the slurry is applied to the surface within about 16 hours after blending.
3. A method for the provision of a stabilised surface according to claims 1 or 2, wherein the components are blended in a tanker or other suitable receptacle and transported to the surface to be stabilised or sealed.
4. A method for the provision of a stabilised surface according to any one of the preceding claims, wherein the components are combined on the surface to be stabilised and mixed in situ by means of a motor grader, rotary hoe, road stabiliser/scarifier or similar means.
5. A method for the provision of a stabilised surface according to any one of the preceding claims, wherein the surface to be stabilised is mechanically rolled after application to create a suitable, well compacted surface.
6. A method for the provision of a stabilised surface according to any one of the preceding claims, wherein the mass ratio of magnesium oxide to either magnesium chloride or magnesium sulphate is between about 0.5 : 1 and 4: 1.
7. A method for the provision of a stabilised surface according to any one of the preceding claims, wherein the mass ratio of magnesium oxide to either magnesium chloride or magnesium sulphate is between about 0.5 : 1 and 1.5 : 1.
8. A method for the provision of a stabilised surface according to any one of the preceding claims, wherein the components may further comprise aggregate.
9. A method for the provision of a stabilised surface according to any one of the preceding claims, wherein the water is present in such an amount to provide between about 15 to 40 % of the total mass of the components in the absence of any aggregate.
10. A method for the provision of a stabilised surface according to any one of the preceding claims, wherein the magnesium chloride is used in its solid form.
11. A method for the provision of a stabilised surface according to any one of claims 1 to 9, wherein the magnesium chloride is used as an aqueous solution.
12. A method for the provision of a stabilised surface according to any one of the preceding claims, wherein bitterns is used as the source of magnesium chloride.
13. A method for the provision of a stabilised surface according to any one of claims 1 to 9, wherein the magnesium sulphate is used in its solid form.
14. A method for the provision of a stabilised surface according to any one of claims 1 to 9, wherein the magnesium sulphate is used as an aqueous solution.
15. A method for the provision of a stabilised surface according to any one of the preceding claims, wherein the components are mixed with a waterproofing agent prior to application to the surface to be stabilised.
16. A method for the provision of a stabilised surface according to claim 15, wherein the waterproofing agent comprises between 40 % and 70 % by weight solids.
17. A method for the provision of a stabilised surface according to claims 15 or 16, wherein the waterproofing agent comprises 50 % by weight solids.
18. A method for the provision of a stabilised surface according to any one of claims 15 to 17, wherein the waterproofing agent is an acrylic or latex polymer.
19. A method for the provision of a stabilised surface ac according to any one of claims 15 to 18, wherein the waterproofing agent is a cationic emulsion.
20. A method for the provision of a stabilised surface according to claim 19, wherein the cationic emulsion is selected from the group of bitumen emulsion, styrene butadiene rubber, toll oil pitch or similar.
21. A method for the provision of a stabilised surface according to any one of claims 15 to 20, wherein the waterproofing agent comprises less than about 10 % by weight of the slurry.
22. A method for the provision of a stabilised surface according to any one of claims 15 to 21, wherein the waterproofing agent comprises less than about 5 % by weight of the slurry.
23. A method for the provision of a stabilised surface according to any one of claims 15 to 22, wherein the waterproofing agent comprises less than about 2.5 % by weight of the slurry.
24. A magnesium cement composition characterised by comprising magnesium oxide and either magnesium chloride or magnesium sulphate and water.
25. A cement composition according to claim 24, wherein the mass ratio of magnesium oxide to either magnesium chloride or magnesium sulphate is between about 0.5 : 1 and 4: 1.
26. A cement composition according to claims 24 or 25, wherein the mass ratio of magnesium oxide to either magnesium chloride or magnesium sulphate is between about 0.5 : 1 and 1.5 : 1.
27. A cement composition according to any one of claims 24 to 26, wherein the composition further comprises aggregate.
28. A cement composition according to any one of claims 24 to 27, wherein the water is present in such an amount to provide between about 15 to 40 % of the total mass of the composition in the absence of any aggregate.
29. A cement composition according to any one of claims 24 to 28, wherein the magnesium chloride is used in its solid form.
30. A cement composition according to any one of claims 24 to 28, wherein the magnesium chloride is used as an aqueous solution.
31. A cement composition according to any one of claims 24 to 30, wherein bitterns is used as the source of magnesium chloride.
32. A cement composition according to any one of claims 24 to 28, wherein the magnesium sulphate is used in its solid form.
33. A cement composition according to any one of claims 24 to 28, wherein the magnesium sulphate is used as an aqueous solution.
34. A cement composition according to any one of claims 24 to 33, wherein the composition further comprises a waterproofing agent.
35. A cement composition according to claim 34, wherein the waterproofing agent comprises between 40 % and 70 % by weight solids.
36. A cement composition according to claims 34 or 35, wherein the waterproofing agent comprises 50 % by weight solids.
37. A cement composition according to any one of claims 34 to 36, wherein the waterproofing agent is an acrylic or latex polymer.
38. A cement composition according to any one of claims 34 to 37, wherein the waterproofing agent is a cationic emulsion.
39. A cement composition according to claim 38, wherein the cationic emulsion is selected from the group of bitumen emulsion, styrene butadiene rubber, toll oil pitch or similar.
40. A cement composition according to any one of claims 34 to 39, wherein the waterproofing agent comprises less than about 10 % by weight of the composition.
41. A cement composition according to any one of claims 34 to 40, wherein the waterproofing agent comprises less than about 5 % by weight of the composition.
42. A cement composition according to any one of claims 34 to 41, wherein the waterproofing agent comprises less than about 2.5 % by weight of the composition.
43. A method for the provision of a stabilised surface substantially as hereinbefore described with reference to any one of the accompanying Examples.
44. A magnesium cement substantially as hereinbefore described with reference to any one of the accompanying Examples.
Description:
STABILISING SURFACES WITH MAGNESIUM CEMENTS Field of the Invention The present invention relates to a method and composition for stabilising a surface.

More particularly, the method and composition of the present invention relate to the use of magnesium oxychloride and magnesium oxysulphate cements as dust palliatives and particularly in the stabilising or sealing of unsealed granular aggregate, surfaces and as cementatious binders of granular aggregate bases.

Background Art Magnesium cement is a term used to refer to various compositions having as basic ingredients magnesium oxide (MgO), magnesium chloride (MgCI2) and water. It is also variously known as"Sorel Cement".

Sorel Cement is variously described as having formulas 2MgO. MgCI2. 4H20, 3MgO. MgCI2. 8H20,5MgO. MgCI2. 8H20 and 9MgO. MgCi2. 5H20. Typically, Sorel Cement consists of magnesium oxide (also known as calcined magnesia) mixed with an aqueous solution of magnesium chloride.

It is known in the prior art that cement, with the addition of aggregate (various sands, gravels and native soils-either naturally occurring or manufactured) and water is used to prepare concrete, which has a vast number of uses in the modern world. The most commonly used cements for concrete preparation are"Portland Cement"and"Asphalt Cement". Portland cement suffers from slow setting characteristics and substantial curing times.

Despite careful selection of cement and aggregate, virtually all cementatious surfaces are prone to cracking, pitting, oxidisation and the formation of other deformations and imperfections. Various methods have been used to repair broken concrete surfaces. Traditional methods involve applying more concrete to the affected area. This is unsatisfactory when using Portland cement as the concrete shrinks on curing, thereby weakening the bond between the two surfaces. More recently, resin or epoxy-type materials have also been used.

Their success has been limited by their deterioration by heat and ultraviolet radiation.

Asphaltic cement is mixed with various aggregates to form an asphaltic concrete pavement. It has the advantage over Portland cement based concrete in that it is much less prone to cracking and doesn't need to have expansion joints incorporated into its design. It does, however, usually require specialized application equipment and is best applied as a hot mixture. It is also a non- renewable petroleum product with attendant environmental issues such as the release of hydrocarbons into the environment.

Sorel cement has been used in the repairing of Portland concrete surfaces (US Patent 5110361). Sorel cement offers advantages over Portland cement in that it sets much faster, has high structural strength and suffers from less shrinkage on curing.

Various Sorel cement compositions have been used in the repair of Portland concrete surfaces (US Patent 4838941). Advantageously, salt lakes have been found to be a good source of magnesium chloride, unexpectedly resulting in a cement composition with higher strength than when using known solutions of magnesium chloride. It is expected that the existence of salts other than magnesium chloride in the salt lake solutions"synergistically"react with the magnesium oxide, although this remains simply an empirical observation.

Further sources of magnesium chloride are known to be bitterns (US Patent 4838941), the concentrated saline solutions remaining after the evaporation of the major water content and the extraction of the bulk of the common salt content of sea water.

Dust emission from unpaved roads is a significant expense. Dust palliatives are known to be used extensively on these surfaces to reduce dust emission and surface erosion. A dust palliative is a compound applied to dust particles to coat individual particles and to bind such particles together to prevent them becoming airborne.

For many reasons it may be uneconomic for unpaved roads to be stabilised with relatively expensive materials, including asphalt concrete pavements. Asphalt concrete pavements must be applied and transported whilst hot, resulting in dangerous working conditions and a dangerous goods classification with respect to transport. Further, asphalt concrete pavements suffer from incompatibility with high silica soils and a tendency to"strip"or'fall off'. Hence, there is a desire to form a relatively cheap, viable alternative.

Traditional methods of coating roads or other surfaces include the use of acrylic, chlorides, emulsions, enzymes, lignins, organic oils, polymers, resins and surfactants. Such surface treatments often strip, crack, separate or disintegrate with exposure to the elements to release fugitive dust and permit undesirable erosion. Solutions of magnesium chloride alone can be used as a dust palliative but these suffer from a tendency to form slick surfaces in the presence of clay or water, creating a potential hazard. Other known palliatives may release toxic and undesirable elements into the environment.

There is a need for a dust palliative and stabiliser that provides a useful alternative to those already known in the industry. It would be an advancement in the art to provide a dust palliative and stabiliser that provides both a high degree of stability for unpaved or unsealed surfaces, whilst overcoming the abovementioned problems associated with the prior art.

The preceding discussion of the prior art is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge in Australia as at the priority date of the application.

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

Disclosure of the Invention In accordance with the present invention there is provided a method for the provision of a stabilised surface, the method characterised by the method steps of: blending the components magnesium oxide, either magnesium chloride or magnesium sulphate and water to form a slurry ; and applying the slurry to a surface to be stabilised or sealed.

Preferably, the slurry is applied to the surface and the surface shaped and compacted within about 1-6 hours.

The components may be blended in a tanker or other suitable receptacle and transported to the surface to be stabilised or sealed but preferably will be blended at the site in order to minimize the risk of the components reacting within the mixing tank.

The components may also be combined on the surface to be stabilised and mixed in situ by means of a motor grader, rotary hoe, road stabiliser/scarifier or similar means.

Preferably, the surface to be stabilised is mechanically rolled after application of the slurry to create a suitable, well compacted surface.

Preferably, the mass ratio of magnesium oxide to either magnesium chloride or magnesium sulphate is between about 0.5 : 1 and 4: 1.

Preferably still, the mass ratio of magnesium oxide to either magnesium chloride or magnesium sulphate is between about 0.5 : 1 and 1.5 : 1.

The method may further comprise the addition of aggregate. The proportion of aggregate is carefully controlled, depending on the nature and gradation of the aggregate and the specific surface to which it will be applied.

Preferably, water is present in such an amount to provide between about 15 to 40 % of the total mass of the components in the absence of any aggregate.

Magnesium chloride may be used in its solid form or as an aqueous solution.

Preferably, the magnesium chloride is used as an aqueous solution. Bitterns may be used as the source of magnesium chloride.

Magnesium sulphate may be used in its solid form or as an aqueous solution.

Preferably, the magnesium sulphate is used as an aqueous solution.

The components may be mixed with a waterproofing agent prior to application to the surface to be stabilised.

The waterproofing agent preferably comprises between 40 % and 70 % by weight solids. Most preferably, the waterproofing agent comprises 50 % by weight solids.

Preferably, the waterproofing agent is either an acrylic or latex polymer or a cationic emulsion. The cationic emulsion may be selected from the group of bitumen emulsion, styrene butadiene rubber, toll oil pitch or similar.

The waterproofing agent preferably comprises less than about 10 % by weight of the slurry.

Still preferably, the waterproofing agent comprises less than about 5 % by weight of the slurry.

Still further preferably, the waterproofing agent comprises less than about 2.5 % by weight of the slurry.

In accordance with the present invention there is further provided a magnesium cement composition characterised by comprising magnesium oxide and either magnesium chloride or magnesium sulphate and water.

Preferably, the mass ratio of magnesium oxide to either magnesium chloride or magnesium sulphate is between about 0.5 : 1 and 4: 1.

Preferably still, the mass ratio of magnesium oxide to either magnesium chloride or magnesium sulphate is between about 0.5 : 1 and 1.5 : 1.

The cement composition may further comprise aggregate. The proportion aggregate within the composition is carefully controlled, depending on the nature of the aggregate and the use of the cement.

Preferably, water is present in such an amount to provide between about 15 to 40 % of the total mass of the cement in the absence of any aggregate.

Magnesium chloride may be used in its solid form or as an aqueous solution.

Preferably, the magnesium chloride is used as an aqueous solution. More preferably, bitterns may be used as the source of magnesium chloride.

Magnesium sulphate may be used in its solid form or as an aqueous solution.

Preferably, the magnesium sulphate is used as an aqueous solution.

Preferably, the magnesium cement further comprises a waterproofing agent.

The waterproofing agent preferably comprises between about 40 % and 70 % by weight solids. Most preferably, the waterproofing agent comprises 50 % by weight solids.

Preferably the waterproofing agent is an acrylic or latex polymer or a cationic emulsion. The cationic emulsion may be selected from the group of bitumen emulsion, styrene butadiene rubber, toll oil pitch or similar.

The waterproofing agent preferably comprises less than about 10 % by weight of the composition.

Even more preferably, the waterproofing agent comprises less than about 5 % by weight of the composition.

Most preferably, the waterproofing agent comprises less than about 2.5 % by weight of the composition.

Best Mode (s) for Carrying Out the Invention The method and composition of the present invention will now be described, by way of example only, with reference to two embodiments thereof.

The composition may either be used as a surface treatment, or preferably, incorporated into the surface with a motor grader, rotary hoe, road stabiliser/scarifier or similar means. Before being completely cured, the slurry is rolled in the normal manner to provide a suitable stabilised road surface.

Alternatively, the slurry may be mixed with an aggregate in a pug mill mixer prior to application to the surface.

The cement composition of the present invention is prepared to efficiently bind the existing surface, but not so that it has insufficient flexibility and resistance to deleterious cracking. The strength may be adjusted by changing the amount of water present in the composition or by the percentage of slurry to aggregate- normally 1 %-15% by weight.

The method of the present invention can be seen to provide an effective method of stabilising or sealing otherwise improving materials used in civil engineering construction, including roads, road bases and sub-bases, road shoulders, batters, median strips, drains and culverts, backfill, floodways, driveways, pathways and similar by the addition of magnesium cement into or onto that surface.

In one embodiment of the invention, magnesium oxide (3000 kg; 94.5 % purity) and an aqueous solution of magnesium chloride (3500 L; 1.22-1. 32 gmL~1) are combined in a mixing tank comprising a mechanically powered agitation shaft.

After the magnesium oxide powder and the magnesium chloride solution were thoroughly mixed, a waterproofing agent was added to assist in the final waterproofing of the cement. The waterproofing agent was 2.5 % by weight of a cationic acrylic co-polymer emulsion (50 % solids content).

The resultant slurry was blended at the site to be stabilised and removed from the inside of the tank before it hardened and applied to the unsealed surface at a desired rate. The desired rates are exemplified in the following non-limiting Examples. The surfaces that were treated in the Examples were small sections of untreated truck and bus pullouts. All of the surfaces were scarified by known means prior to application of the magnesium cement composition.

Example 1 Dimensions of stabilised surface: Length 200 m Width 2 m Depth 75 mm Area 400 m2 Volume 30 m3 Weight of material treated 72000 kg Weight of slurry applied 3515 kg Ratio of slurry to material to be treated 5 % The slurry was hand sprayed onto the top of the surface to be stabilised. After application, the entire surface was again scarified, then graded and compacted with steel and rubber tyred rollers.

The following day, the surface was visibly hard. Over a period of 8 months, the surface remained smooth, compact and tightly bound. The boundary between the bitumen seal and the cement shoulder showed little or no wear along the entire length and the boundary between the stabilised surface and the untreated gravel remained clearly evident.

Example 2 Dimensions of stabilised surface ; Length 280 m Width 2 m Depth 75 mm Area 560 m2 Volume 42 m3 Weight of material treated 100800 kg Weight of slurry applied 3128 kg Ratio of slurry to material to be treated 2. 5 % The slurry was hand sprayed onto the top of the surface to be stabilised. After application, the entire surface was again scarified, then graded and compacted with steel and rubber tyred rollers.

Over a period of 8 months, it became evident that insufficient binder to consolidate the gravel had been used and that the shoulder had been subject to unravelling.

Example 3 Dimensions of stabilised surface; Length 180 m Width 2 m Depth 75 mm Area 360 m2 Volume 27 m3 Weight of material treated 64800 kg Weight of slurry applied 4860 kg Ratio of slurry to material to be treated 7. 5 % The slurry was hand sprayed onto the top of the surface to be stabilised. After application, the entire surface was again scarified, then graded and compacted with steel and rubber tyred rollers.

The following day, the surface was visibly hard. Over a period of 8 months, the surface remained smooth, compact and tightly bound. The boundary between the bitumen seal and the cement shoulder showed little or no wear along the entire length. The boundary between the cemented surface and the untreated gravel remained clearly evident.

Example 4 In accordance with a second embodiment of the invention, a 150 mm thick layer of blue metal gravel was placed and shaped by a"bobcat"on a hard-stand area in a truckyard. The gravel was treated with a slurry comprising magnesium oxide mixed into a 30% magnesium chloride solution. The resultant 3050kgs of slurry was calculated to be 7% of the total weight of the blue metal.

The slurry was mechanically sprayed onto the surface to be stabilised and incorporated by a rotary hoe. A small, steel-drum roller was used to compact and flatten the blue metal gravel. In order to achieve a smooth, sealed surface a final slurry was sprayed on top of the final surface and left to set. The resultant hard- stand has been in constant use by forklift and truck traffic without visible signs of wear.

Dimensions of stabilised surface : Length 11 m Width 12 m Depth 150 mm Area 132 m2 Volume 19. 8 m3 Weight of material treated 43600 kg Weight of slurry applied 3050 kg Ratio of slurry to material to be treated 7 % Modifications and variations such as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.