TECHNICAL FIELD

The present invention relates to aqueous dispersions su itable for use as additives to cement to improve the flexibi lity and strength of the resulting concrete. In particular, the present invention relates to aqueous dispersions that can be util ised in cement-stabilised infrastructure and for im proving the mechanical performance of soils for the construction or rehabilitation of subgrades and pavements.

BACKGROUND ART

The use of concrete as a construction material is com mon, indeed, concrete is used in a majority of civil engineering projects. One important aspect of the use of concrete in civil engineering projects, and particularly where a concrete slab or the like is required, is that the soil under the concrete slab m ust be heavily compacted and solid so as to provide the necessary support for the concrete slab. Compressible soils can result in the concrete slab suffering forms of stress - such as tensile or shear stress - which the slab is not designed to resist, leading to cracking or other fractures. Improper compaction of the soil layer can also foul the setting process of the concrete slab, leading to edge projection which can complicate the later stages of the project.

Other civil engineering projects, such as road construction and repair or borehole dril ling, may also require that the soil be hardened and stabil ised prior to operation .

For exam ple, roads having a soil layer that is insufficiently com pressed and hardened may exhibit deflection under load that is outside acceptable parameters. Repeated traffic will result in plastic deformation of the road due to the compressible soil layer, contributing to increased road wear, development of potholes and other traffic hazards and ultimately an increased need for maintenance. In respect of boreholes and soil-cement piles, the process of hardening the soil or the soil compositions is well known and in general involves the addition of a cementitious binder to the soil. In the event of a cementitious binder being used, however, it is often desirable to further introduce additives to offset the substance's known deficiencies, which are shrinkage during curing, low flexibility, decreased performance under tension or shear load and extended curing times.

Previous attempts to develop cement additives have suffered from myriad issues. One well-known product is disclosed in Australian patent no. AU 1993035121, which discloses a cement additive to increase the flexibility of the resulting concrete and offsets the shrinkage that occurs during setting. However, the product disclosed in this prior patent consists of two main components, being a mixture of chloride salts and an alkali silicate (also known as waterglass). The two components are pre-mixed in the desired ratio and then added to the cement mixture. However, these chemicals begin reacting with one another immediately upon mixing, resulting in the silicate mixture undergoing premature setting and reducing its efficacy.

This rapid onset curing requires additional machinery to be transported to the construction site so as to allow for the pre-mixing to be conducted as late as possible in the construction process in order to alleviate the issue of the rapid setting of the two components of the additive. This is particularly disadvantageous for construction projects that are located in remote areas or in locations that are difficult to access, because of the need for additional maintenance, power and transport to these locations.

Furthermore, waterglass is rated as a hazardous substance. It has a number of risk and safety phrases associated with it as defined in Annex IV of the European Union Direction 67/548/EEC and requires safety precautions taken during transport as well as on-site. A further additive is disclosed in International PCT publication no. WO 2008/098843, which describes a mixture of materials for curing construction materials, in particular concrete. The mixture increases the flexibility of concrete and reduces shrinkage of the concrete mix during curing. The mixture comprises 1-8% xanthan gum; 1-6% water-containing apparent viscosity thickener; 2-10% liquefier; 20-50% cement compatible synthetic resin; 0.1-3% foaming agent; 30-70% hardening accelerator; and 0.2-4% conserving agent, wherein the total weight of all components of the material mixture must be 100% by weight.

The hardening accelerator that is present in the additive in an amount between 30-70% is selected from the group of calcium formate, calcium chloride or calcium aluminate cement. At this concentration range, calcium chloride is classified as hazardous, which is undesirable, particularly because of the additional regulations for the transport of the material, such as the need for protective procedures and training.

A previous non-hazardous cementitious additive is described in Australian patent no. AU 1997202209, which discloses a non-hazardous dispersion to improve the elasticity and shrinkage of concrete. However, the dispersion is predominantly water, which makes the product uneconomical to transport. This is important as dispersions for improving the flexibility of concrete are often used in locations that are significant distances from established commercial centres, so reducing transport logistic issues, and in particular transport costs is an important consideration for such products.

An alternative non-concentrated, non-hazardous cementitious additive is described in International PCT publication no. WO 2010/018020. This dispersion has a high percentage of water, which makes the dispersion non-economical to transport in bulk quantities. The dispersion is for use in a concrete mix and contains 85.0-95.0% by weight, based on the total weight of the dispersion, of water; 0.5-2.0% by weight, based on the total weight of the dispersion, of cellulose; 0.1-0.3% by weight, based on the total weight of the dispersion, of sodium hydroxide; 0.9-1.5% by weight, based on the total weight of the dispersion, of calcium chloride; and 5-10% by weight, based on the total weight of the dispersion, of styrene-butadiene, where the total weight of all components of the dispersion has to add up to 100% by weight.

It is desirable to provide an alternative additive to overcome the known deficiencies of cementitious binders in soil and concrete mixtures, which include shrinkage, low flexibility, cracking and extended curing times.

It is also desirable to provide an alternative additive which is rated as not being dangerous and which is generally recognized as being safe for the environment.

Further, it is desirable to provide an alternative additive which reduces the transport and storage costs associated with transporting dilute products, but which avoids the additional costs and hazards associated with highly concentrated products with component concentrations exceeding hazard thresholds.

DISCLOSURE OF INVENTION One aspect of the invention provides an aqueous dispersion comprising calcium chloride, synthetic latex, a biocide preservative, sodium hydroxide and water, wherein the calcium chloride comprises less than twenty percent of the mass of the aqueous dispersion and wherein the synthetic latex comprises from about four to about fifty percent of the mass of the aqueous dispersion. The aqueous dispersion as described may also contain additional components, including but not limited to a hydrophobic emulsion and a colouring agent.

According to a first embodiment, the present invention relates to an aqueous dispersion containing :

less than 20wt% calcium chloride;

4wt% - 50wt% synthetic latex;

less than 0.5wt% biocide preservative

less than 0.5wt% sodium hydroxide; and

water whereby the total weight of all components of the dispersion add up to 100wt%.

Preferably, the synthetic latex contains 40wt% to 60wt% polymer solids. Most preferably, the synthetic latex contains 46 wt% polymer solids.

It is preferred that the polymer solids comprise one or more of the following polymer types: acrylic-based polymer or co-polymer, styrene-based polymer or co-polymer. However, most preferably, the polymer solid is an acrylic-based co- polymer.

Preferably, the calcium chloride is in the form of an aqueous solution. Preferably, the biocide preservative is isothiazolinone-based.

In a particularly preferred embodiment, the aqueous dispersion of the present invention comprises:

19.97wt% calcium chloride;

18.60wt% synthetic latex;

0.10wt% biocide preservative;

0.092wt% sodium hydroxide; and

water to 100wt%

In accordance with another aspect of the present invention, the aqueous dispersion further comprises:

lwt% to 15wt% hydrophobic emulsion; and

at least one colouring agent.

Preferably, the hydrophobic emulsion of the aqueous dispersion contains 30wt% to 60wt% wax particulates.

In a particularly preferred embodiment, the aqueous dispersion according to this aspect of the invention comprises:

1.99wt% calcium chloride;

4.36wt% synthetic latex; 9.40wt% hydrophobic emulsion

0.13wt% biocide preservative;

0.02wt% sodium hydroxide; and

water to 100wt%

Preferably, the aqueous dispersion of the present invention further contains a thickener selected from either xanthan gum or a cellulose-based thickener.

Another aspect of the invention concerns a method for utilising the aqueous dispersion to stabilise a soil layer, which comprises the step of combining the aqueous dispersion, water, a cementitious binder and the existing soil in a ratio determined by the soil's structural properties that include but are not limited to its Atterberg Limits, optimum moisture content and particle size distribution. Preferably, the method for soil stabilisation as part of a construction project comprises the steps of:

determining the geotechnical properties of the soil through geotechnical testing;

utilising gathered geotechnical data to develop pavement design, further taking into account project goals such as traffic volume, loading and other factors;

adding dry cementitious binder to the soil;

injecting the aqueous dispersion according to claim 1 into water;

combining the water and aqueous dispersion mixture with the soil and cementitious binder;

mixing the combination of water, aqueous dispersion, soil and cementitious binder such that each are equally dispersed; and

compacting, grading and/or trimming the stabilised soil.

Another aspect of the invention concerns a method for utilising the aqueous dispersion to stabilise the walls of a shaft bored into soil or otherwise substantially naturally-occurring material, which comprises the step of combining the aqueous dispersion with water and cement and lining the shaft walls with the resulting mixture to an extent determined by the soil's structural properties that include but are not limited to its Atterberg Limits, optimum moisture content and particle size distribution .

Preferably, the method for stabil ising the shaft of a bore hole drilled into soi l comprises the steps of:

determin ing the geotechnical properties of the soil, particle size distribution and opti mum moisture content of the bore hole shaft;

injecting the aqueous dispersion accord ing to claim 1 into water;

combining the dispersion and water with cementitious binder; and lin ing the bore hole shaft wal l with the resulting mixture.

Another aspect of the invention concerns a method for utilising the aqueous dispersion in the construction of soi l-cement piles, which com prises the step of injecting the aqueous dispersion, water and a cementitious binder in a ratio determined by the soil's structural properties that include but are not limited to its Atterberg Li mits, optimum moisture content and particle size distribution, as well as the requirements of the relevant construction project.

Preferably, the method for forming soil-cement piles comprises the steps of: determin ing the geotechnical properties of the soi l;

developing a pi le design using the determ ined geotechnical properties;

injecting the aqueous dispersion according to claim 1 into water;

combining the dispersion and water with cementitious binder; and injecting the cementitious binder and the di luted aqueous dispersion using a piling rig .

MODES FOR CARRYING OUT THE INVENTION

In accordance with a first embodiment of the present invention, the aqueous dispersion com position of the present invention comprises a mixture primarily consisting of calcium chloride and synthetic latex dispersed in an aqueous solution such as water, in combination with small amounts of other additives, including a biocide preservative and a base. The calcium chloride accelerates the hydration of the cement and the setting and curing process associated with the cement. The synthetic latex increases the mechanical performance of the dried cement to which the dispersion of the present invention is added and serves to reduce or inhibit crack propagation. The synthetic latex further makes the resultant mixture more resilient, stronger and more flexible. The biocide preservative controls the growth of organisms may cause damage to the resultant mixture. The base serves to maintain the correct pH of the aqueous dispersion of the present invention. The synthetic latex component is preferably selected so as to increase the water resistance of the dried cement. The synthetic latex component is further preferably selected for compatibility with cements. The synthetic latex component is further preferably selected for compatibility with a wide range of soil types and other cement filling agents, including but not limited to organic and inorganic soil, sand, clay or other substantially naturally-occurring ground constituents; recycled cementitious material; recycled road material; bauxite; laterite; vulcanised ash; and all forms of material that are generally regarded as typical cement filling agents. The synthetic latex component may further be preferably selected for resistance to the detrimental effects caused by environment-specific variables such as temperature range, typical climate and ultraviolet light exposure.

The synthetic latex component of the present invention is typically an aqueous dispersion of polymer solids, wherein the polymer solids consist of at least one of a number of polymer and copolymer classes with a concentration ranging from about 40% to about 60% by weight. There are a number of suitable classes of polymers and copolymers that can be used in the formulation of the synthetic latex. These classes include, but are not limited to, styrene polymers or copolymers (including styrene-butadiene co-polymer) and acrylic polymers or co-polymers. It is preferred that the synthetic latex is present in the aqueous dispersion of the present invention such that its concentration is between about 4% to about 50% by weight. One suitable synthetic latex is marketed under the name Duramul 607C and is an aqueous dispersion of acrylic polymers with a concentration of about 46% by weight.

It is preferred that the calcium chloride is added such that its final concentration in the aqueous dispersion of the present invention is less than twenty percent by weight. The calcium chloride component, for ease of combining with the other ingredients, may be added in the form of an aqueous solution of calcium chloride. According to one preferred embodiment of the invention, this aqueous solution is 32% by weight calcium chloride. The preferred form of the biocide preservative is that of an isothiazolinone-based biocide that does not contain formaldehyde.

One suitable form of biocide is marketed under the name of THOR MicrocarelT and is a standard CIT/MIT biocide. The chemical composition of the example biocide is a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one and 2- methyl-4- isothiazolin-3-one.

It is generally understood that only minute quantities of biocide are required and thus it is generally preferred that the concentration of the biocide does not exceed one half of a percent by weight.

The base is preferably selected for suitability in pH correction.

The preferred form of the base is that of an aqueous solution containing sodium hydroxide. In order to preserve the desired non-hazardous nature of the product it is generally preferred that the concentration of sodium hydroxide does not exceed one half of a percent by weight.

In another embodiment of the invention, a hydrophobic emulsion and a thickener are added. The hydrophobic emulsion is preferably selected so as to increase the water resistance when in use. It is preferred that the hydrophobic emulsion consists of hydrophobic particulate suspended in an aqueous solution such that the hydrophobic particulate forms from about thirty percent by weight to about sixty percent by weight of the hydrophobic emulsion with the remainder being water. It is further preferred that the hydrophobic particulate consists of waxes and/or paraffins. One commercially-available product that may be used is marketed under the name Freemulsion 786S, which comprises a hydrophobic emulsion of wax particulate wherein the wax particulate is about 50 percent by weight of the emulsion and the remainder is water. The hydrophobic emulsion is generally added to the aqueous dispersion of the present invention such that it is present from about one percent by weight to about fifteen percent by weight depending on the ultimate needs of the product.

It is preferred that the thickener is a cellulose-based thickener or xanthan gum- based thickener, although it should be understood that there are other potential thickeners.

The aqueous dispersion of the present invention is classifiable as a non- hazardous substance through application of NOHSC Criteria. As a non-hazardous material, the aqueous dispersion of the present invention can be transported and used without extraordinary safety measures.

The aqueous dispersion of the present invention utilises minimal amounts of water in its production, such that the aqueous dispersion is concentrated, allowing for the dispersion to be transported long distances in an economical manner without undergoing undue separation.

Other ingredients can also be added to the aqueous dispersion of the present invention as per demands of particular projects in which the dispersion is being utilised. One example of such an additive is a water-soluble or otherwise liquid-soluble colouring agent. The use of colouring agents in the dispersion of the present invention is desirable in preferred embodiments of the invention. The use of a colouring agent serves two primary purposes. Firstly, specific colouring agents can be utilised for specific product identification, with particular colours being used different versions of the aqueous dispersions of the present invention. Secondly, the use of colouring agents can be useful for particular applications where there is a need or desire for colouring treated soils.

Composition Examples

One tested composition of the aqueous dispersion of the present invention consists of 19.97wt% calcium chloride, 18.60wt% synthetic latex, 0.10wt% biocide preservative, 0.092wt% sodium hydroxide and water to 100wt%. This composition was utilised in a number of trials.

According to another aspect of the invention, a second preferred composition that has been tested comprises 1.99wt% calcium chloride, 4.36wt% synthetic latex, 9.40wt% hydrophobic emulsion, 0.13wt% biocide preservative, 0.02wt% sodium hydroxide and water to 100wt%. This composition was found to offer improved performance relative to other possible forms of the present invention when utilised in hygroscopic environments. Comparative Results

The present invention offers numerous advantages over road construction utilising cement mixtures that lack any form of additives. · Pavements and roads constructed using the aqueous dispersion of the present invention as an additive to the construction mixture are more durable than ones constructed without the additive.

When the aqueous dispersion has been added to cementitious material, the resulting construction mixture cures far more rapidly than construction mixtures lacking the additive. This reduces the need for rework and repairs following inclement weather during the curing process.

• Roads constructed from mixtures utilising the aqueous dispersion of the present invention as an additive have exhibited superior strength characteristics.

• Pavements and roads constructed utilising the aqueous dispersion of the present invention are rapidly trafficable and do not require extended setting times following the final compaction process. This reduces the length of time that traffic flow is disrupted by construction.

• Construction mixtures utilising the aqueous dispersion of the present invention as an additive have improved workability and compaction compared to non-additive mixtures.

• Cement mixtures containing the aqueous dispersion of the present invention as an additive can contain recycled or lower-grade material for filling agents without sacrificing the resulting structure's strength or durability.

The present invention also exhibits benefits and advantages over the additives disclosed within the prior art.

• The aqueous dispersion of the present invention remains stable even at high concentration. This reduces the need to heavily dilute the mixture for transport, thus reducing overall construction costs.

• The aqueous dispersion of the present invention is injected into the water added to the cement mixture, preventing the need for additional premixing stages to ensure adequate dispersal of the additive.

• The aqueous dispersion of the present invention also provides a protective function when utilised as an additive to cement. The result of this protective function of the aqueous dispersion is that the cement can be used for stabilisation in areas with material types normally not suitable for cement stabilisation due to the materials being toxic to cement. · The aqueous dispersion of the present invention is generally non- hazardous. This is particularly the case where the aqueous dispersion of the present invention is measured relative to other cement additives.

• The aqueous dispersion of the present invention is not known to have a negative environmental impact.

Road Repair Trial Data

The aqueous dispersion of the present invention was trialled in a 293m segment of road requiring rehabilitation and repair, as a sub-section of an already existing road rehabilitation program .

One aim of the trial was to exhibit the ability for the present dispersion to enable the rehabilitation of existing road through recycling the road material and avoiding the need to import extra material to be brought to the construction site from a remote location, which was located a significant distance away from the site. The majority of the local rock type (a form of rock known as scoria) was not generally regarded as suitable for road construction through traditional methods. A number of sources of material were located nearby the construction site and were utilised during the trial. These local gravel sources provided extra filling material.

The aqueous dispersion of the present invention was used to form a road cement mixture (the test mixture) for approximately half of the allocated road segment, with a road cement mixture without curing additives (the control mixture) used for the remaining half. The strip of road being repaired was originally 6.4m wide, and part of the reparation process involved widening this existing road by 0.8m. The composition of the aqueous dispersion of the present invention utilised in the trial was as follows: a. 62.40 wt% calcium chloride solution comprising 32 wt% CaCI2;

b. 18.60 wt% synthetic latex comprising 46% acrylic-based copolymer;

c. 0.10 wt% THOR MicrocarelT isothiazolinone biocide preservative;

d. 0.02 wt% sodium hydroxide; and

e. 18.88 wt% water. An initial geotechnical sampling of the trial repair site was carried out so as to determine the Atterberg Limits of the local soil along with other necessary soil properties. The Atterberg Limits are a basic measure of the critical water contents of a fine-grained soil, such as its shrinkage limit, plastic limit, and liquid limit, which can be used to distinguish between silt and clay, as well as different types of silts and clays.

The geotechnical sample data was compared with data covering a range of soil types so as to determine the appropriate concentration of the present invention to be added to the road cement mixture for optimum function.

These properties are in Table 1 below.

Table 1 It was thus determined that the soil required increased plasticity for optimum stabilisation and additional gravel so as to improve the soil strength through mechanical interlock. The road cement mixture was produced through combining the cementitious binder with the filling agent and water. The cementitious binder was added to the road cement mixture so as to be 2.8% GP cement by mass. The filling agents utilised in the trial consisted of a mixture of recycled road material, Scoria (a type of local rock) and crushed rock with a mean size of 40mm and a PI of 15 which was subjected to further screening so as to remove materials differing from the mean size by 19mm or more.

For the relevant section of road, the present invention was added to the road cement mixture such that when spread to a depth of 250mm, the concentration of the present invention would be 0.35 L/m2. This formed the testing mixture. The properties (as tested through sampling in a laboratory environment) of the resulting road cement mixtures are shown in Table 2 below.

Table 2 The resilient modulus of the associated road cement mixtures was determined through further laboratory testing. These results are shown in Tables 3a and 3b below.

Table 3b

As shown in the above tables, the addition of the present invention into the road cement mixture resulted in the resilient modulus of the mixture being approximately 1000 MPa higher at seven days than without using the present invention as an additive. Even at twenty-eight days the road as produced through the test mixture still offered ten percent higher mechanical performance over the control mixture. The representative profile - that of rapid gain in the resilient modulus followed by a plateau, to which the normal road cement mixture eventually approaches - supports the purpose of the present invention, that being a cement mixture that cures rapidly thereby alleviating the disruption to traffic flow.

Testing undertaken after concluding the repair process determined that the section of road repaired using the mixture containing the present invention had an improved performance in further road-specific properties.

For example, although both repaired road sections showed improved deflection distances, the section that was repaired using the mixture containing the present invention showed an even greater improvement in deflection distance. The deflection and road curvature properties were tested through a PaSE assessment carried out approximately four months after conclusion of the trial's construction phase. A PaSE assessment is a non-destructive method of analysing the strength of a section of pavement using a deflectograph.

The control mixture exhibited an overall 24.4% reduction in deflection distance in comparison to the original road; in comparison, the testing mixture exhibited 38.6% reduction in deflection. The control mixture exhibited an overall 55.1% reduction in the characteristic curvature of the repaired road. In comparison, the testing mixture was found to exhibit 66.2% reduction in the characteristic curvature.

Relative to the control mixture, the testing mixture has thus been found to exhibit 60% further improvement in deflection and a further 20% improvement in characteristic curvature.

Filling Agent Toxicity Experiment During research and development, a form of the aqueous dispersion of the present invention was tested regarding compatibility with filling agents which would normally be toxic to cement.

Three concrete mixtures were produced, which each contained 20 kg of cement and 5 litres of water. Mixture 1 contained 100 litres of commercially available building sand as a filling agent, Mixture 2 contained 100 litres of excavated native soil taken from a building site as a filling agent and Mixture 3 contained 100 litres of ash from a combustion plant as a filling agent. The concrete mixtures were intensively premixed in a concrete mixing machine and then mixed in a vat with a litre of the dispersion and placed into a mould, in which the concrete mixtures set to form a slab.

A visual assessment of the concrete slabs showed that the shrinkage of the concrete mixtures was low in all cases during setting. The slabs were also subjected to a number of different mechanical testing procedures, which included tests to measure the slab's resistance to pressure, the ductility and the surface hardness. The results of these tests indicated that the mechanical characteristics of the concrete slabs was satisfactory.

It is believed that the aqueous dispersion of the present invention will provide similar mechanical performance when used to produce cement with filling agents normally regarded as toxic. Application Example: Roadworks

In a first example, the dispersion of the present invention is utilised in the construction or rehabilitation of a road or the like. The first step in the process of using the dispersion of the present invention for such a project is to complete a geotechnical analysis of the area in which the dispersion will be used. This geotechnical analysis will include, but is not limited to, preparing a soil description, which may include factors such as Atterberg Limits (a basic measure of the critical water contents of a fine-grained soil, such as its shrinkage limit, plastic limit, and liquid limit), particle size distribution, optimum moisture content, and California Bearing Ratio (the penetration test for evaluation of the mechanical strength of road subgrades and base courses).

Where the project relates to the construction or rehabilitation of a road or the like, the next step in the process of using the dispersion of the present invention is to estimate the design life and traffic type, volume, and loading that the road will be subject to over its lifecycle. This data is used to determine pavement depth and the cement, dispersion, and water application rates, based on empirically determined relationships.

The next step is for there to be a rough preparation of the soil. This step may include the removal of organic materials from the soil, shaping of the soil to which the dispersion will be added (particularly where the soil mixture will be used as a road base for example), the possible inclusion of additional materials in the soil, and modifying the moisture content if and when necessary.

The dispersion of the present invention is then diluted with water in accordance with the required rate to form a desired concentration. Dry cement is then spread on the roughly prepared surface at the specified rate preferably using a computerised cement spreader apparatus. A stabiliser/reclaimer machine is then used to mix the in-situ and imported soils and cement powder while simultaneously injecting the aqueous dispersion of the present invention and water in a controlled manner.

The area is then compacted with a combination of pad/sheep's foot, smooth drum, and multi wheel compactors, preferably with and without vibration. The area is then trimmed and shaped with a grader as required. If necessary, additional water is added where required.

Alternative application methodologies include manual materials placement and compaction, the use of a pug-mill or similar for mixing the soil, cement, dispersion and water, and the use of manual or tractor pulled stabiliser/reclaimer equipment.

Where the project relates to the construction or rehabilitation of a road or the like, the surface of the pavement that has been stabilised with the dispersion of the present invention in combination with a cementitious binder may be sealed with a conventional wearing course. Alternatively, the surface can be directly used as the wearing course for low traffic applications. A road or pedestrian pavement can typically be trafficked immediately after the appl ication process of the dispersion of the present invention has been completed .

Application Example : Borehole Stabil isation

In a second example, the dispersion of the present invention is uti lised in the stabilisation of a dri lli ng bore hole.

Cementitious materials are often used to stabil ise the walls of dril ling holes in oi l and gas, water, min ing, and exploration appl ications. The dispersion of the present invention is mixed with the cementitious materials prior to appl ication to rapidly set the cementitious lin ing, wh ile also improving lin ing resil ience from reduced permeabil ity and increased strength and flexibility. The first step in the process of using the dispersion of the present invention for the stabilisation of a drill ing bore hole is to complete a geotechnical analysis of the area in wh ich the dispersion will be used . This geotechnical analysis wi ll include, but is not limited to, preparing a soil description, which may include factors such as Atterberg Limits (a basic measure of the critical water contents of a fine-grained soil, such as its shrinkage limit, plastic limit, and liquid l im it), particle size distribution, optim um moisture content, and, if relevant for the project, measure a California Bearing Ratio (the penetration test for evaluation of the mechanical strength of road subgrades and base courses) . Once the geotechnical analysis of the borehole has been com pleted, the dispersion of the present invention is then di luted with water in accordance with the required rate to form a desired concentration .

As the dril ling bore hole is completed, the walls of the bore hole are lined with cement and the dispersion of the present invention . It is preferable that the dispersion is sprayed onto the boreholes walls using conventional borehole spraying techniques.

Alternative application methodologies include manual placement of the dispersion on the borehole wall, but this is only possible in relatively li m ited circumstances where the diameter of the borehole allows for such manual application.

Application Example 3 : Soil-Cement Piling

In a third example, the present invention is utilised in the construction of soil- cement piles, which may be used in soil stabilisation projects. Soil-cement piling may be used as in-situ method of soil stabilisation wherein cement, concrete or similar is injected into boreholes in soil so as to increase the stability, strength and other assorted mechanical properties of the local soil.

It is thus desirable to use the aqueous dispersion of the present invention so as to improve the strength and the setting time of the soil-cement piles. The first step in the process of using the dispersion of the present invention for the construction of soil-cement piles is to complete a geotechnical analysis of the area in which the dispersion will be used. This geotechnical analysis will include, but is not limited to, preparing a soil description, which may include factors such as Atterberg Limits (a basic measure of the critical water contents of a fine- grained soil, such as its shrinkage limit, plastic limit, and liquid limit), particle size distribution, optimum moisture content, and, if relevant for the project, measure a California Bearing Ratio (the penetration test for evaluation of the mechanical strength of road subgrades and base courses). Once the geotechnical analysis of the local area has been completed, it is combined with loading data to create a piling design (involving elements such as cement content, additives, pile depth and width, among others) to satisfy project requirements. The dispersion of the present invention is then diluted with water and combined with cement in accordance with the required rate to form a desired concentration. The resulting mixture is then injected into the soil through the use of a piling rig.

While the invention has been described with reference to preferred embodiments above, it will be appreciated by those skilled in the art that it is not limited to those embodiments, but may be embodied in many other forms. In this specification, unless the context clearly indicates otherwise, it should be understood that the aqueous dispersion of the present invention is compatible with agents that may also be added into cement mixtures for a range of purposes and as dictated by the needs of the project, such as lime.

In this specification, unless the context clearly indicates otherwise, the word "comprising" is not intended to have the exclusive meaning of the word such as "consisting only of", but rather has the non-exclusive meaning, in the sense of "including at least". The same applies, with corresponding grammatical changes, to other forms of the word such as "comprise", etc.

INDUSTRIAL APPLICABILITY

The dispersion can be used in conjunction with cementitious binders in new construction or rehabilitation of general civil engineering applications. Suitable civil engineering applications may include, but not limited to, pavements, hardstands, laydown yards, and related areas, either full depth or in selected layers, such as subgrade, sub base, and base; soil stabilisation or similar; drainage and drainage channel formation; crane mats, piling mats, and similar; railway subgrade and formation layers; cementitious piling; airport runways, aprons, and related areas; and drilling and bore hole stabilisation . The present invention may also relate to the production of construction material, such as slabs or stones, from concrete mixtures, which comprise the dispersion according to the invention.