The present invention relates to a composition and method for controlling water content of particulate aggregate surface layers. More particularly, the inven- tion relates to improving water balance of surfaces such as gravel roads or other similar particulate constructions.

Background art

In the northern hemisphere seasonally changing weather causes a variety of challenges for construction materials used. Air humidity and large annual fluc- tuations in temperature, especially around zero degrees Celsius, have a negative impact on materials, and cause severe economic losses. One of the most typical issues in the northern regions is rain water penetrating into the structures resulting in freeze-thaw cycle and deterioration of structures.

The construction and maintenance of unpaved roads, i.e. earth roads or gravel roads, meet two major challenges: the deterioration of road due to water and the loss of surface cohesion and compaction due to traffic.

Water causes the unpaved road structure a variety of problems. In the beginning of the frost time wet road structures will freeze and cause frost damage, which greatly complicate the use of road in the spring. In cold weather, mois- ture that penetrates the base layers of roads freezes and rips cracks into the road substrate that seriously undermine the load bearing capacity and longevity of the roadway. Likewise, in milder weather, when water seeps into the base layers of roads the result is softening and erosion that cause potholes that are expensive and recurring problems. When the road structure has dried it starts to dust and fine adhesive particles of road aggregate are disappearing. In autumn, rain water starts again wetting the structure which in turn will freeze later when temperature drops below 0°C.

The problems typically associated with unpaved roads are surface deterioration and surface deformation. An example of surface deterioration is loss of fi- ne binder particles from road surfaces. This can be seen as dust and the loss of fine particles leads to other types of road distress such as loss of cohesion and compaction of the road fill material and reduced capacity to maintain the requisite moisture in the road structure.

Surface deformations in turn include ruts, corrugations, depressions, and potholes. Both surface deterioration and deformation are caused by the harmful effects of water and high moisture content; the lack of surface cohesion and resulting loss of road compaction caused by loss of fine particles, dust and the heavy traffic loads exerted on roads.

There is a need for useful low-cost capillary barrier systems for limiting water infiltration and controlling seepage at solid waste landfills. The application in wet regions can be problematic due to loss of water-impermeable properties under high-frequency precipitation. A potential solution is to alter soil grain surfaces to become water repellent by mixing or coating the soil cover material.

Mines, the rest of the industry and power plants have a variety of fields and landfills where water absorption and subsequent dissolution of various materials cause problems. Dust is also a very typical problem in these areas.

Industry has provided various chemical additives to impart water resistance of unpaved road structures with variety of success and environmental impacts.

Water repellent chemicals are, however, not binders and load bearing capaci- ty, stability, and frost resistance are not improved. In many cases, dust can be also separately reduced by applying chemical additives, "dust suppressors" or "dust control agents", which draw moisture from air to improve fine aggregate cohesion. So called "soil stabilizers" which are chemicals designed to act as binders and coalesce forming bonds between the soil or aggregate particles, have shown promise in greatly improving the load bearing and traffic capacity of the road.

Existing soil stabilizing solutions and dust control agents are difficult to apply and use in cold climates. They tend to have long curing times, short life-cycles and do not provide the required protection against water damage; particularly excessive moisture content resulting from capillary action.

A variety of chemical agents have been developed to balance the water content of aggregate surface and to reduce dust problems. Typically dust binding agents are hygroscopic chloride salts, such as calcium or magnesium salts, and for example forestry by-products from lignosulfocarbonate. One of the most recent developments within hygroscopic materials comprises biodegradable salt of formic acid, such as potassium formate. Furthermore, there is a variety of mineral oil based polymer products, such as acrylic and methacrylic- based polymers. The purpose of these chemicals is to bind the particles of earth material together and thereby reduce fines in the formation of dust. Mineral oil based polymers are often a problem for their environmental impact and high price. Potassium formate in turn is clearly more expensive than traditional chloride salts and its rapid biodegradation and high water solubility prevents extensive use as gravel road dust-binding agent.

Furthermore, commonly used and efficient but highly soluble chloride salts must typically be reapplied approximately 2-3 months after the previous treatment. This will incur additional costs, and the chloride pollution into the envi- ronment increases.

As a result, there is a great need for an improved method of maintenance of unpaved roads or other similar constructions to effectively control water balance in particulate aggregate surfaces layers.

Summary of the invention One object of the present invention is to provide a method for enhancing the control of water balance in particulate aggregate surface layers which are required to withstand load and wear, such as traffic.

Another object of the present invention is to provide a composition and method for decreasing the amount of damage caused by ambient temperature varia- tions around freezing point of water to particulate aggregate surfaces, such as the road network.

Yet, another object of the present invention is to provide a composition and method for decreasing the environmental load caused by dusting of particulate aggregate surfaces or surface layers. The present invention provides a method for treating particulate aggregate surface layers, for example unpaved road surfaces. Moreover, compositions for use in the method are provided, as well. The use of the method and the compositions provided by the present invention will reduce the time, costs and environmental impacts associated with conventional maintenance of, for example, unpaved roads.

Detailed description of the invention By a biopolymer is meant polymers which are naturally found in nature. Like polymers biopolymers are chain-like molecules made up of repeating chemical blocks and can be very long in length. The prefix bio means that they are produced by living organisms and thus are biodegradable. Biopolymers contain monomeric units that are covalently bonded to form larger structures. By particulate aggregate surface layer is meant a surficial layer of a thickness of about 0-0.1 m, preferably about 0.05 m, from the surface towards the bulk. This layer is typically called wear or abrasion course or layer, in particular, when the surface is a road surface, a gravel road surface, for example.

By man-made, constructed surface is meant deliberately constructed surface, optionally a horizontal surface, for a purpose to use said surface as a base or ground for action taking place on said surface such as traffic. Typically said area suffers from lowered load bearing capacity, stability, and frost resistance and action thereon causes dusting arising from said damaged surface.

By unpaved or paved surface is meant surface of a pathway or a field suitable for traffic which is typically coated for obtaining a more suitable surface to operate on. Such surface may be prone to generate or contain dust i.e. small size particles easily air born due to damage to said surface by harsh ambient conditions such as frost. .In the first aspect, the present invention provides a method for controlling the water content of a man-made, constructed, unpaved and paved particulate aggregate surface layer suitable for traffic comprising roads, passage ways and landfill areas. In this method a composition comprising from 3 to 50% by weight of a biopolymer is applied onto the particulate aggregate surface layer. The biopolymer forms a film on said surface and aids in binding the particulates on said surface together i.e. increasing the surface cohesion and providing a surface resistant to leaching by water.

This composition may be used in dry form, or preferably as a solution, such as an aqueous solution. The amount of the biopolymer is in weight percentage of active material. The commercially available materials may be of technical grade i.e. containing impurities. Commercial grade biopolymer may comprise e.g. 10-20% by weight impurities such as salts, or moisture, or water.

By man-made constructed unpaved or paved areas comprising roads, pathways and landfill areas is meant surfaces which require building the underlying ground for a certain application or purpose such as traffic. A landfill area may be coated by the inventive composition for environmental reasons, for safety, hygienic or health reasons, for protection of vehicles operating thereon from malfunctioning. The composition may be used on a pathway, such as a playing ground or sports ground, or typically, on roads for traffic, such as vehicle traffic. Preferably, the man made construction is a road, such as a gravel road. The application methods may include any suitable apparatus typically used for applying solid materials or aqueous solutions onto planar surfaces comprising particulate aggregates or dusting particles.

The surface may comprise any location suffering from surface deterioration, deformation and dusting. The method of the present invention is particularly useful for unpaved surfaces, such as road surfaces, comprising sand, gravel or other earth materials. Preferably, this composition is applied onto gravel roads

In addition to roads the composition of the present invention may be applied at port areas, such as paved areas at ports prone to dusting due to traffic, on the streets to decrease street dusting, on the road constructions for tunnels, and on permanent or temporary road construction of building sites.

The method of the present invention is also useful for football fields, sports fields, parking places, yards, playgrounds, maneges and horse tracks.

In an exemplary embodiment, the composition of the present invention is used for landfills requiring load bearing capacity, and which landfills originate from by-products of construction sites, industrial processes, and mining.

Preferably, the solid content of the composition comprising the biopolymer is from 3 to 100% by weight i.e. it may be applied as particulate material, essentially as a solid composition, or as an aqueous mixture, such as dispersion or solution. More preferably, the solid active material content of the composition comprising the biopolymer is from 3 to 50% by weight, the balance being water. Biopolymers may be classified into three groups, depending on the nature of the repeating unit. They may comprise polynucleotides, which are long polymers composed of nucleotide monomers; polypeptides, which are short polymers comprising amino acid chains; and polysaccharides i.e. sugars, which are polymeric carbohydrate structures comprising long chains of monosaccharide units bound together by glycosidic linkages.

Polysaccharide based polymers can be linear or branched, and they are typically joined together with glycosidic bonds. The exact placement of the linkage can vary, and the orientation of the linking functional groups is also important, resulting in a- and β-glycosidic bonds with the numbering being definitive of the linking carbons' location in the ring. Many saccharide units may further undergo various chemical modification reactions. Preferably, the biopolymer of the present invention comprises a polysaccharide. Polysaccharides are generally occurring plant biopolymers and industrially applicable and commercially readi- ly available. More preferably, the polysaccharide is selected from the group consisting of cellulose derivatives and starch. Cellulose and starch and derivatives thereof are well-known polymers. They are easily globally available as products of food and forest industry, low cost and easy to modify and use.

Starches are glucose polymers in which glucopyranose units are bonded by alpha-linkages. It is made up of a mixture of amylose and amylopectin. Amyl- ose consists of a linear chain of several hundred glucose molecules and amylopectin is a branched molecule made of several thousand glucose units. Starches are insoluble in water but they can be digested by hydrolysis. Potato, rice, wheat, and maize are major sources of starch. The starch of the present invention may comprise tapioca starch, wheat starch, oak starch, potato starch, corn starch or rice starch. Most preferably, the starch of the present invention is potato starch, such as native waxy potato starch, or corn starch, such as native waxy corn starch. Waxy potato starch and corn starch are readily available and comprise pure amylopectin starch without am- ylose. High amylopectin content enables a composition with good product stability. Furthermore, waxy starches have less retrogradation i.e. the changes taking place are irreversible resulting in a more stable product. In one embodiment the biopolymer comprises starch having an amylopectin content of at least 50% by weight, preferably more than 70%, more preferably more than 90%, or even more than 95%.

In another embodiment the starch is produced from potato or corn waste or by- product material. This waste material may originate from potato producers, and typically comprises potato peals or the like. Recycled use of this waste product enables to reduce the environmental load caused by additional processing for destroying the undesired by-products by conventional ways.

Cellulose is a polymer made with repeated glucose units bonded together by beta-linkages. The structural components of plants are formed primarily from cellulose. Wood is largely cellulose and lignin, while paper and cotton are nearly pure cellulose. It is the most abundant carbohydrate in nature. Humans and many animals lack an enzyme able to break the beta-linkages, so they cannot digest cellulose. Cellulose is insoluble in water but yields glucose in hydrolysis. The hydroxyl groups of cellulose can be partially or fully reacted with various reagents to produce a variety of derivatives with a wide range of useful properties, like cellulose esters and cellulose ethers.

Preferably, the cellulose derivative to be used in the present invention comprises nanocellulose, carboxyl methyl cellulose, sodium carboxy methyl cellu- lose (NaCMC), hydroxyl propyl methyl cellulose (HPMC), hydroxyl ethyl cellulose (HEC) or hydroxyl propyl cellulose (HPC). These are most common cellulose derivatives, globally available and technically capable of efficiently forming a polymer film. Some of the most developed and tailored versions of cellulose derivatives, like HPC, can form durable and elastic polymer film without the use of any further additives. They are, however, quite expensive which limits their large scale use. Moreover, e.g. HPC is well suited for crosslinking. Solubility is one concern; depending on the carbon chain length the resulting product may become highly viscous posing constraints to the application apparatus. In one embodiment the amount of HPC of the biopolymer is at least 50% by weight, preferably more than 70% by weight, and more preferably more than 90% by weight, such as 98% by weight. In another embodiment the biopolymer comprises NaCMC and the amount of NaCMC is at least 50%, preferably more than 70%, most preferably more than 90%, such as from 95 to 100% by weight.

In another embodiment the biopolymer comprises nanocellulose and the amount of nanocellulose of the biopolymer is at least 50%, preferably more than 70% most preferably more than 90%, such as from 95 to 100% by weight. Nanocellulose is typically very effective, and a smaller amount will suffice.

In another embodiment the biopolymer is produced from cellulose waste or byproduct material originating from the forest industry or the pulp and paper pro- duction processes. Preferably, the biopolymer is produced from cellulose waste, more preferably from cellulose waste fiber, such as zero fiber. Zero fiber is fiber having the fiber length too short for it to be used in cellulose processing i.e. the fiber has come to the end of its use in the paper making process. Fiber slurry may comprise branch reject, primary slurry, secondary slurry or mixed slurry. Zero fiber contains possibly also calcium and/or kaolin clay. This material is disposable waste and the disposal thereof may incur costs. By reusing said material recycling is promoted. Moreover, the material cost may thus be minimized. In one embodiment the present invention provides use of cellulose zero fiber for controlling the water content of a man-made, construct- ed, unpaved and paved particulate aggregate surface layer suitable for traffic comprising roads, passage ways and landfill areas.

Preferably, a further composition comprising a hygroscopic metal halide is applied onto the particulate aggregate surface layer, in combination with the composition comprising the biopolymer. The halide is used to maintain the moisture content, to provide better elasticity to the surface layer and to increase cohesion between aggregate materials.

The hygroscopic metal halide of the present invention preferably comprises alkali metal halides or alkaline earth metal halides. Preferably, the halide is chloride. Most preferably the metal halide is highly hygroscopic and low cost CaC^ or MgC or iron chloride, such as ferrous or ferric chloride, or a mixture thereof. The dust binding ability of calcium chloride is particularly high, especially when the relative humidity is high.

In one embodiment the composition comprising a hygroscopic metal halide and the composition comprising a biopolymer are mixed together prior to appli- cation onto the particulate aggregate surface layer. In this manner the treatment of the present invention can be made at the same time saving on labour costs and decreasing the amount of traffic disturbance. Especially, if only one treatment round is due, this type of application is a good solution. In one embodiment, the amount of the biopolymer in the method and composition of the present invention is from 3.5 to 45% by weight, preferably from 4 to 40%, more preferably from 4.5 to 35%, such as from 5 to 20%, or even from 5 to 10% by weight. The upper limit is determined by the solubility of the used material and the lower limit is due to the film forming properties. The lower val- ues are economically more feasible ones. In another embodiment the method of the present invention is carried out by first applying the composition comprising a hygroscopic metal halide onto the particulate aggregate surface layer to be treated, and subsequently applying on top of the resulting surface the composition comprising a biopolymer. Using the separate treatments more freedom to formulate biopolymer solutions is provided ensuring higher stability to the biopolymer solution Preferably, the amount of the biopolymer when used in combination with the metal halide is less than 30% by weight the balance being water. More preferably the amount is from 3 to 20% by weight, most preferably from 3 to 10%, such as from 3 to 5%. The final ratio of formulation between the biopolymer and the halide is optimized on the basis of technical requirements such as durability and efficiency, and by environmental and cost reasons. Typically biopolymers are at least an order of magnitude more expensive than the preferred halides, calcium and magnesium chloride. Moreover, the use of metal halide enables more appropriate environment for the bi- opolymer film formation resulting in faster film formation and better film properties which in turn decrease highly soluble halides from leaching into the environment.

In one embodiment aqueous solution of halide and biopolymer, preferably calcium chloride and/or magnesium chloride in an amount of from 20 to 40% by weight, and starch and/or CMC in an amount of from 3 to 20% by weight, is preferably manufactured at the production facility of the halide. Most preferably, CMC or starch can be dissolved in a warm halide solution to produce different ratios of halide and biopolymers. In this case it is possible to use production facilities, utilities, storage tanks and other equipment of the halide pro- duction unit, already available at the site. Product is later supplied as prefabricated mixtures to the final destination, and the already existing logistics set up can be utilized. Liquid mixture is easy to apply with high accuracy on the dusting surface layers. The final ratio of formulation between the biopolymer and the halide is optimized on the basis of technical requirements such as durability, efficiency and by environmental and cost reasons. Preferably, the amount of the metal halide, preferably calcium chloride, magnesium chloride or iron chlorides, when used together with the composition comprising the biopolymer is less than 97% by weight, preferably from 0.1 to 90%, more preferably from 0.5 to 80% by weight, most preferably from 1 to 60%, or even from 5 to 50%, by weight of dry matter. In one embodiment the method of the present invention includes the use of a composition consisting of 3-10% by weight of biopolymer and 20-40% of MgCl2 or CaC^, the balance being water, for controlling the water content of a particulate aggregate surface layer.

In one embodiment the method of the present invention includes the use of a composition consisting of from 3 to10%, preferably from 3 to 6%, more preferably from 3 to 5% by weight of biopolymer and from 0.1 to 5%, preferably from 0.5 to 5%, more preferably from 1 to 5%, of CaC^ or iron chloride, such as ferric or ferrous chloride, the balance being water, for controlling the water content of the surface layer. Without being bound by any theory, it has been found that the halide functions as a crosslinking agent. It provides better durability, hydrophobicity and enhanced water resistance to the formed film. Moreover, a lower halide content composition is an environmentally friendly alternative.

In one embodiment the biopolymer and the metal halide are both essentially in solid form. Composition consisting of from 5 to 40% by weight of biopolymer and from 60 to 95% of MgC^ or CaC^ is applied as a solid mixture. The solid application has the advantages that the mixing is easy, better availability of solid spreading systems and easier logistical solutions and better global availability of solid halides. A solid mixture can be made in the facility of halides industrial production process. After mixing the solid mixture can be placed in varying size of packagings or supplied as a bulk. The solid product mixture is then logistically easy to transfer to the final destination. Solid mixture is also easy to spread on the aggregate surface by utilising existing spreading systems and equipment. The final ratio of the solid formulation between the biopolymer and the halide is optimized on the basis of technical requirements. In an exemplary embodiment the solid mixtures comprising the biopolymer and the halide such as MgC or CaC^ may either be used as such or dissolved into suitable water solution, preferably prior to application, such as in situ at the point of use. The preferred viscosity of the aqueous composition comprising the biopolymer is less than 2000 cP, more preferably from 10 to 1000 cP, most preferably from 50 to 500 cP, to comply with readily available application equipment.

Typically, a degradable plastic is defined by ASTM and ISO as material which undergo a significant change in chemical structure under specific environmen- tal conditions. This degradation results from the action of naturally occurring microorganisms such as bacteria, fungi and algae. In general, biodegradable is taken to mean to be consumed by microorganisms and returned to compounds found in nature. Some microorganisms have a naturally occurring, microbial catabolic diversity to degrade, transform or accumulate a wide range of com- pounds including hydrocarbons.

In the present invention controlled biodegradability is measured by the ability of the biopolymer to remain intact and perform its desired function. Preferably, the functionality of the slowly biodegradable polymer composition of the present invention remains unchanged for at least 3 months, more preferably at least 4 months, possibly for a year. Once dissolved into ambient a swift degradation of the polymer takes place. Especially, the close presence of the metal halide was found to decrease the degradation rate of the polymer. Once leached from the surface layer and aparted from the halide, the degradation rate of the polymer is increased in the less halidic soil surroundings. Thus, the use of the combined compositions according to the present invention provides a self-controlling effect on the degradation behaviour.

In one embodiment the biopolymer of the present invention comprises a slowly biodegrading biopolymer, maintaining its functionality from 3 to 12 months.

In another embodiment the composition comprising the biopolymer further comprises a binder. Binders enhance the effective adherence of the polymer film to particulate aggregates. The selected binder has a clear effect on the technical characteristics, such as waterproofness, colour, hardness, elasticity, biodegradability and longevity, of the forming film. Binders can be emulsions and/or dispersions based on the following chemicals: polyvinyl alcohol, styrene-butadiene, vinyl acetate, vinyl versatate, ethylene, acrylic acid, polyacrylate, polyester resins, silicon based binders, and mixtures, and/or monomers, and/or polymers and/or copolymers thereof. Pref- erably, the binder is polyester resin, vinyl acetate, vinyl versatate, the mixture or polymer, monomer or copolymer thereof.

Optionally, biopolymer and/or binder can be applied as their monomeric compounds for making in situ polymerization.

In one embodiment of the present invention the binder comprises polyester such as polyester resins, vinyl acetate, vinyl versatate or mixtures thereof or copolymers thereof. These can be made from renewable plant-based materials, and were found particularly suitable for use in the present combination of biopolymers and metal halides. The aliphatic biopolyesters can be polyhydrox- yalkanoates (PHAs), like the poly-3-hydroxybutyrate (PHB), polyhydroxy- valerate (PHV) and polyhydroxyhexanoate (PHH). Vinyl acetate based products are commercially available (e.g. Wacker's Vinnapas, DPX-271 and EP 400). An example of vinyl acetate and versatate copolymer (VACA/eoVA) is for example redispersible polymer powder (e.g. AP-2080, Shanghai Rongou Chemical Technology). Vinyl acetate, and vinyl acetate and versatate copoly- mer are globally available, cost-efficient and very capable of making a strong bonds.

In one embodiment the binder comprises a polymer or a copolymer capable of film forming and bonding in situ after water evaporation from the film after application onto the particulate aggregate surface layer. In another embodiment the binder comprises monomeric compound or compound undergoing polymerisation in situ once applied onto the particulate aggregate surface layer.

This film forming preferably takes place within less than 48 h, more preferably less than 24 h, most preferably less than 12 h. Possibly even in a few hours. Film forming is highly dependent on the rate of water evaporation level, in optimal conditions the film can be formed in a few hours. Crosslinking agents, binders and initiators may have a favourable impact on the rate of film forming and final properties of the film, such as colour, adhesion to an aggregate, hardness, flexibility and waterproof ness. Preferably, the amount of the binder is less than 10% by weight. More preferably the amount is from 0.1 to 5% by weight, most preferably from 0.1 to 2.5% by weight, such as from 0.1 to 1 % by weight. Binder amount is optimised into as low level as possible in order to avoid extra cost and possible environmen- tal load.

In one embodiment the composition comprising a biopolymer further comprises a crosslinking agent. Possible crosslinking agents include aldehydes, such as glyoxal or glutaraldehyde, urea formaldehyde resins, melamine formaldehyde resins, glyoxylated polyacrylamide resins, zirconium based compounds, such as ammonium zirconium carbamate (AZC), polycarboxylic acids, such as citric acid, phosphoric compounds, such as trimetaphosphate or polymetaphos- phate, metals in ionic form, such as calcium, iron, aluminium or zinc. Preferably, the crosslinking agent of the present invention comprises glyoxal, zirconium-compounds, polycarboxylic compounds and metal based cross-linking agents. Most preferably the crosslinking agent comprises glyoxal, ammonium zirconium carbonate (AZC), metal halides, such as calcium chloride and ferric chloride and metal oxides, such as colloidal iron oxides. Glyoxal and AZC are specifically effective CMC and starch crosslinking agents. By the use of a crosslinking agent the resulting polymer film can be formed faster and at lower temperatures. Furthermore, the weather resistance of the formed film may be improved.

The amount of the crosslinking agent is preferably: less than 5% by weight, more preferably 0.01-3% by weight, most preferably 0.05-2.5% by weight, such as from 0.1-2.0%. For cost and environmental reasons amount of cross- linking agent is as low as possible.

In one embodiment Ca ²⁺ and Mg ²⁺ , especially in the form of CaC^ or MgC^ is used as a crosslinking agent.

In another embodiment iron chloride, such as ferric chloride or ferrous chloride is used as a crosslinking agent. In another embodiment iron oxide, such as colloidal ferric oxide, is used as a crosslinking agent. Preferably, the composition comprising the biopolymer further contains at least one a plasticizer. Plasticizers assist in balancing the forces coming from traffic or other external and internal sources, such as ground freezing. The plasticizer may include carboxylic acid derivatives, glycols, glycerol, sorbitol and poly- ethers, organophosphates and polymeric plasticizers. Preferably, the plasticizers of the present invention comprise carboxylic acid derivatives like dibutyl sebacate, dioctyl sepacate and dioctyl adibate, and/or glycols like propylene glycol and/or glycerol or sorbitol. Most preferred plasticizer comprises glycerol or sorbitol which are easily available and effective in the low concentrations to give elastic properties for the film.

The composition comprising the biopolymer may yet further contain a water repellent. These agents reduce water (in liquid form) penetration into the polymer film, and therefore increase the water resistance of the film. Preferred hydrophobic agents comprise fatty acids, such as oleic or stearic acids and their derivatives. As an example, vegetable based stearine and stearites may be used. Stearites are advantageously salts of magnesium, calcium, sodium and zinc.

In addition, the composition of the present invention comprising the biopolymer may yet further contain biocides or preservatives, which may be used to im- prove storage stability of solution and hinder the biodegrability of the formed polymer film. Preferred biocides include biodegradable or food preservation agents like sorbic acid and its salts, citric acid and its derivatives, benzoic acid and its salts, propionic acid and its salts like calcium propionate, sodium nitrite, sulfites such as sulfur dioxide, sodium bisulfite, potassium hydrogen sulfite, and traditional industrial biocides like sodium hypochlorite. Moreover, cationic polymers, such as polyDADMAC (diallyl dimethyl ammonium chloride) or poly- amine-based products may be used as microbe flocculating agent. For long term protection of biopolymer film, for example, DCOIT (dichloroctylisothiazoli- non) based formulation can be applied. DCOIT has a very good affinity for starch and cellulose based biopolymers.

Moreover, initiators may be used to initiate the polymer reactions. On the road surface or near the surface layer, it is advantageous to accelerate the polymer film formation and possibly photolysis may be utilised, as well. Preferred initiators include metal iodides, metal alkyls, or azo compounds. The composition of the present invention may further comprise an emulsifying, wetting, biopolymer stabilizer, defoaming and/or a colouring agent. The emulsifying agent can be for example PVA and polyvinyl alcohol, and the surfactant can be for example fatty alcohol sulfate, FAS, polyether, or polyethyleneglycol, PEG. Moreover ethylene diamine alkylene oxide adduct (such as Genapol ED 3060 from Clariant) is an environmentally beneficially multi-functional ingredient for waterborne biopolymer solution, being able to act as a wetting agent, film strength enhancer, stabilizer and defoaming agent.

In one embodiment the amount of biopolymer is from 5 to 20% by weight and it further comprises PEG or ethylene diamine alkylene oxide adduct from 0.1 to 2.0% by weight as a surfactant and defoaming agent. This enables deeper penetration of aqueous biopolymer solution to the aggregate surface layer and less foaming during the manufacturing process.

In the method of the present invention the composition comprising the biopol- ymer is applied onto the particulate aggregate surface layer, preferably in an amount of from 10 to 500 g/m ² , preferably from 10 to 250 g/m ² , calculated based on the solid content. Even small dosages from about 1 to 20 g/m ² may be applied. The dosage is dependent on the properties of the particulate aggregate surface layer, as well. For long-term applications higher dosages, like 100-500 g/m2 are recommended. For the retreatment or short-term applications smaller dosages like 10-100 g/m2 can be applied. Weather conditions (rain, moisture content and temperature), aggregate surface properties and traffic conditions also influence in the need of the dosage. The composition may be easily diluted to a desired concentration. In an exemplary embodiment, for short term application in the streets or other paved areas very small dosages like 1-20 g/m ² may be applied.

The biopolymer film forms on the surface layer, and to some extent, such as into 0.1 m, or at least 0.05 m into the layer below the surface. The formation of the polymer film takes place within a few days, preferably within 48 hours, more preferably within 24 hours, depending on the ambient conditions, aggregate surface and the quality and quantity of the biopolymer. The formed polymer film prevents the penetration of water from total rainfall into the aggregate structure. Preferably, the biofilm is formed at a time with little or no rain water. Furthermore by partially penetrating deeper into the surficial layer of aggregate structure and strengthening the structure thereof the biopolymer treatment gives better durability for wear and abrasion structure

The endurable film formed by application the composition of the present invention withstands high load and long term usage. It is able to function as a capil- lary barrier system and provides load bearing capacity, stability, and frost resistance to the surface layer. In particular, the additional use of crosslinking agent provides enhanced durability. The use of plasticizer enhance the elasticity of biopolymer film further giving long-term durability for the film.

In one embodiment a composition comprising a biopolymer from 3 to 20% by weight and a plasticizer from 1 to 2% by weight, and optionally crosslinking agent from 0.1 to 3.0% by weight, is used on gravel roads to prevent road structure from aggressive winter time deterioration and deformation by preventing excessive water from penetrating and thus saving road structure from harmful freeze-thaw cycle and frost heaves or surficial frost heaves. In another embodiment the composition comprising a biopolymer from 3 to 20% by weight and a halide from 60 to 90% by weight, and preferably a plasticizer from 1 to 2% by weight, and optionally crosslinking agent from 0.1 to 3.0% by weight, is used on gravel roads to maintain the desired moisture content in the road structure during warm and dry weather conditions and to pre- vent fine particles to detach from road surface and to form dust.

In another embodiment the composition comprising a biopolymer from 3 to 20% by weight and preferably a plasticizer from 1 to 2% by weight, and optionally crosslinking agent from 0.1 to 3.0% by weight, is used on mine landfill areas to prevent surface dusting during warm and dry weather conditions. By forming a water-proof polymer film it is possible to prevent rain water from penetrating inner to the landfills and thus prevent hazardous or harmful material leaching into the environment.

In an exemplary embodiment, the present invention provides a method for controlling the water content of a man-made, constructed, unpaved and paved particulate aggregate surface layer suitable for traffic comprising roads, passage ways and landfill areas, wherein a composition comprising from 3 to 50% by weight of biopolymer and a crosslinking agent is applied onto said surface and which composition is able to form a film on said surface. The surfaces treated with the compositions according to the present invention remain moist and non-dusting for a long period. The treated surface becomes water repellent and the rain water is removed from the treated surface without being absorbed into the particulate bulk. Especially, the combination of metal halide and the polymer was found particularly resistant and unaffected by ambient condition changes.

The method of the present invention does not include harmful chemicals which would have negative effects on ambient flora or fauna. Moreover, the composition is economical even in large quantities. The method of the present inven- tion enables maintaining the particulate surface and bulk moist for a long period and the film formed by the biopolymer is water resistant decreasing dusting and hygroscopic halide or harmful chemicals leaching into the surroundings. The film formed on the surface binds effectively the aggregates and particles and due to heavy loads the disrupted film provides fewer fines than a surface without the biofilm. Advantageously, the biofilm is flexible enough to withstand well the load and stress due to heavy traffic.

The advantages of the present invention further include savings in the maintenance work, materials and labour cost. In addition the use of the scarce natural resources like gravel and sand can be decreased. Unpaved roads are in better condition enabling fluent traffic and reduced dust formation improves human health and the comfort of living.

In the second aspect, the present invention provides a composition for controlling the water content of a man-made, constructed, unpaved and paved particulate aggregate surface layer suitable for traffic comprising roads, passage ways and landfill areas. This composition comprises i. a metal halide comprising CaC .MgC^ or iron chloride preferably in an amount of from 1 to 95% by weight dry matter, more preferably from 15 to 95%, most preferably from 50 to 95%, and

ii. a biopolymer comprising NaCMC or starch or a mixture thereof, prefera- bly in a total amount of from 3 to 90% by weight of the dry matter, preferably from 3 to 30%, most preferably from 3 to 20%, and

iii. optionally, a plasticizer comprising glycerol, preferably in an amount of from 0.5 to 30% by weight of the dry matter, more preferably from 1 to 25%, most preferably from 1 to 20%, and iv. a binder comprising polyester resins or vinyl acetate polymer or copolymer, preferably in an amount of from 0.1 to 30%, preferably from 1 to 20%, more preferably from 5 to 15%, by weight of the dry matter, and v. optionally, a crosslinking agent comprising glyoxal or AZC or metal oxide, preferably iron oxide, and preferably in an amount of from 0.1 to 30%, preferably from 1 to 20%, more preferably from 5 to 15%, by weight of the dry matter.

More preferably, the metal halide comprises alkali metal halide, such as CaC or MgC , in an amount of 60-95% by weight of the dry matter. In another embodiment the present invention provides a composition for controlling the water content of a man-made, constructed, unpaved and paved particulate aggregate surface layer suitable for traffic comprising roads, passage ways and landfill areas, comprising i'. a biopolymer in an amount from 3 to 20% by weight, preferably Na CMC or starch, more preferably waste cellulose from pulp and paper industry or starch waste from potato or corn industry,

ii'. metal salt or metal oxide in an amount from 0.1 to 20% by weight, preferably calcium chloride, iron chloride or iron oxide, more preferably calcium chloride, ferric chloride or ferric oxide in an amount from 1-5% by weight.

Preferably, the balance is water.

The composition of the present invention may further contain an additive selected from emulsifying and wetting agent, defoaming agent, initiator, hydrophobic agent, colouring agent and/or biocide. The additives may be used for enhancing solubility and stability of monomers and polymers, to initiate and accelerate polymer film forming in ambient conditions, to increase hydrophobi- city and waterproofness of polymer film, to use colour as marking agent for better visibility and separation of layers and for preserving biopolymer solutions from microbial growth and biopolymer film from too fast biodegradation. In one embodiment the composition comprises an aqueous mixture of starch 3-10% by weight and calcium chloride 20-40% by weight. This mixture can be produced by utilizing a nearby halide production unit or separately in other location. Liquid mixture is easy to apply with high accuracy on the aggregate surface layers. In another embodiment composition comprises an aqueous mixture of CMC 3- 10% by weight and calcium chloride 20-40% by weight. This mixture can be produced by utilizing a nearby halide production unit or separately in other location. Liquid mixture is easy to apply with high accuracy on the aggregate surface layers.

In another embodiment composition comprises an aqueous mixture of starch 3-10% by weight and magnesium chloride 20-40% by weight. This mixture can be produced by utilizing a nearby halide production unit or separately in other location. Liquid mixture is easy to apply with high accuracy on the aggre- gate surface layers.

In another embodiment composition comprises an aqueous mixture of CMC 3- 10% by weight and magnesium chloride 20-40% by weight. This mixture can be produced by utilizing a nearby halide production unit or separately in other location. Liquid mixture is easy to apply with high accuracy on the aggregate surface layers.

In one embodiment composition comprises a solid mixture of starch 5-35% by weight and calcium chloride 65-95% by weight. A solid mixture can be made in the facility of halides industrial production process. After mixing the solid mixture product can dosed into different size of packages or supplied further as a bulk. Solid mixture is then logistically easy to transfer to a destination. Solid mixture is also easy to spread on the aggregate surface by utilising existing spreading systems. This solid mixture may be either used as such or dissolved into suitable water solution prior to application. This solid mixture may be either used as such or dissolved into suitable water solution prior to application. In one embodiment composition comprises a solid mixture of CMC 5-35% by weight and calcium chloride 65-95% by weight. A solid mixture can be made in the facility of halides industrial production process. After mixing the solid mixture product can dosed into different size of packages or supplied further as a bulk. A product mixture is then logistically easy to transfer to a destination. Solid mixture is also easy to spread on the aggregate surface by utilising existing spreading systems. This solid mixture may be either used as such or dissolved into suitable water solution prior to application.

In one embodiment the composition comprises a solid mixture of starch 5-35% by weight and magnesium chloride 65-95% by weight. A solid mixture can be made in the facility of halides industrial production process. After mixing the solid mixture product can dosed into different size of packages or supplied further as a bulk. A product mixture is then logistically easy to transfer to a destination. Solid mixture is also easy to spread on the aggregate surface by utilis- ing existing spreading systems. This solid mixture may be either used as such or dissolved into suitable water solution prior to application.

In one embodiment the composition comprises a solid mixture of CMC 5-35% by weight and magnesium chloride 65-95% by weight. A product mixture can be made in the facility of halides industrial production process. After mixing the solid mixture product can dosed into different size of packages or supplied further as a bulk. A product mixture is then logistically easy to transfer to a destination. Solid mixture is also easy to spread on the aggregate surface by utilising existing spreading systems. This solid mixture may be either used as such or dissolved into suitable water solution prior to application. In a preferred embodiment the composition of the present invention comprises a biopolymer comprising starch 5% by weight, a binder comprising poly vinyl acetate 1 % by weight, a crosslinking agent FeCb, which is preferably pH adjusted by NaOH to a value about 7, thus producing at least partly colloidal ferric oxide thereof, 1 .5% by weight and plasticiser comprising glycerol 1 .5% by weight and optionally, a hydrophobic agent comprising vegetable stea- rin/stearate 0.1 % by weight and/or a halide comprising calcium chloride 32% by weight. In yet another embodiment, the composition further comprises in addition an emulsifying agent comprising polyvinyl alcohol 0.05% by weight and a biocide comprising sodium hypochlorite 0.5% by weight. In another preferred embodiment the composition of the present invention comprises a biopolymer comprising CMC 5 % by weight, a binder comprising poly vinyl acetate 1 % by weight, a crosslinking agent CaC½ 1 .5 % by weight and plasticiser comprising glycerol 1 .5 % by weight and optionally, a hydrophobic agent comprising vegetable stearin/stearate 0.1 % by weight and/or a halide comprising calcium chloride 32 % by weight. In yet another embodiment, the composition further comprises in addition an emulsifying agent comprising polyvinyl alcohol 0.05 % by weight and a biocide comprising sodium hypochlorite 0.5 % by weight. The invention is further illustrated by the following non-binding examples.

Examples

Example 1

A mixture was prepared consisting of 5% by weight of potato starch derivative (AVEBE, GF-107), 0.5% by weight of a dispersion of vinyl acetate polymer including an emulgator (WACKER, VINNAPAS DPX 271 ), 0.1 % by weight of vegetable based stearine/stearate (AVEBE, GLISSOFIL EXTRA) and the balance water. A 20 g sample of this mixture was poured onto a gravel road sample (10 cm x 10 cm x 5 cm) and the treated sample was dried at 40°C for 1 .5 hours. The gravel surface of the sample was hardened and water resistance increased significantly compared to untreated samples.

Example 2

A mixture was prepared consisting of 3% by weight of sodium carboxymethyl cellulose (CP Kelco, Finnfix 5), 0.3% by weight of dispersion of vinyl acetate and ethylene polymers (WACKER, VINNAPAS EP 400), 1 .0% by weight of glycerol and 0.1 % by weight of vegetable based stearin/stearate (AVEBE, GLISSOFIL EXTRA) and the balance water. A 20 g sample of this mixture was poured onto a gravel road sample (10 cm x 10 cm x 5 cm) and the treated sample was dried at 60°C for 48 hours. The gravel surface of the sample was hardened and water resistance increased significantly compared to untreated samples. Plasticizing glycerol was observed to modify polymer film more elastic compared to the treated sample of example 1 .

Example 3

A mixture was prepared consisting of 3% by weight of hydroxypropyl cellulose (Ashland, Klucel E), 0.3% by weight of crosslinking glyoxal (Brenntag, Sequa- rez 755), 32% by weight of calcium chloride and the balance water. A 20 g sample of this mixture was poured onto a gravel road sample (10 cm x 10 cm x 5 cm) and the treated sample was dried at 60°C for 48 hours. The gravel surface of the sample was hardened and water resistance increased significantly compared to untreated samples. After drying the hygroscopic calcium chloride was observed to draw new moisture into the sample. Example 4

Four cylinder-shaped sample containers (end point area 80 cm ² ) were prepared and to each of them was added 10 cm authentic sample of gravel road. Samples of 20 g of water controlling solutions from the examples 1-3 were mixed uniformly to three gravel road cylinders. One cylinder was kept untreated reference sample without solution addition. Subsequently, all samples were allowed to stand at room temperature for 7 days.

Next, all samples were wetted with water simulating summer total rainfall so that a total of 168 grams of water was irrigated into the surface of the samples. Water absorption was monitored immediately after irrigation, and the next inspection was carried out after one week. In the reference sample water was absorbed immediately and with other three samples the surface was still wet a week after the water addition.

Example 5 Four cylinder-shaped sample containers (end point area 80 cm ² ) were prepared and to each of them was added 10 cm authentic sample of gravel road. Next, 20 g samples of calcium chloride (32% by weight) solution were poured to all cylinders. A week later samples of biopolymer solutions (listed in the examples 1-3, but without calcium chloride in the sample 3) were added to three gravel road cylinders. One cylinder remained as a reference sample without biopolymer solution addition. Subsequently, all samples were allowed to stand at room temperature for 7 days.

Next, all samples were wetted with water simulating summer total rainfall i.e. a total of 168 grams of water was poured onto the surface of the samples. Water absorption was monitored immediately after irrigation, and the next inspection was carried out after one week. In the reference sample water was absorbed immediately and with the other three samples the surface was still wet a week after the water addition.

Example 6 Samples from the tests described in the example 5 were taken to perform the long term weather durability test for 3 months. A test cycle of wetting (1 week), drying (1 week), freezing (1 week) and wetting (1 week) was applied. After the test the reference sample without polymer addition behaved like a sample with no treatment. All the calcium chloride was dissolved by leaching and column surface started to dust immediately when getting in dry conditions. After wetting clear deformation on the surface structure could be seen and freezing test further increased this deformation.

All the biopolymer treated samples showed with good weather durability. Surface of the columns were firm and no dust formation took place, and no significant deformation was observed during the test period.

Example 7 A mixture was prepared consisting of 5% by weight of sodium carboxy methyl cellulose (CP Kelco, Finnfix 5), 1 .5% by weight CaCI2 crosslinking agent and the balance being water. A 20 g sample of this mixture was poured onto a gravel road sample (10 cm x 10 cm x 5 cm) and the treated sample was dried at 60°C for 48 hours. The surface of the sample was hardened and water re- sistance film was formed on the upper layer of about 50 mm of the road sample.

Example 8

A mixture was prepared consisting of 5% by weight of potato starch derivative (AVEBE, GF-107), 1 .5% by weigh FeCI3 crosslinking agent and the balance being water. Next pH of the solution was adjusted up to 7 by using 0.2 mol/l NaOH. A 20 g sample of this mixture was poured onto a gravel road sample (10 cm x 10 cm x 5 cm) and the treated sample was dried at 60°C for 48 hours. The surface of the sample was hardened and water resistance film was formed on the upper layer of about 50 mm of the road sample. Example 9

A mixture was prepared consisting of 10% by weight of zero fibre (Pulp&Paper mill), 3% by weight CaC^ crosslinking agent, 2.5% by weight of dispersion of polyvinyl acetate) (W ACKER, VINNEX), 1 .0% by weight of glycerol and the balance being water. A 20 g sample of this mixture was poured onto a gravel road sample (10 cm x 10 cm x 5 cm) and the treated sample was dried at 60°C for 48 hours. The surface of the sample was hardened and water resistance film was formed on the upper layer of about 50 mm of the road sample.