NZ521650A - Dust Suppressant for use on roads, containing saponified tall oil pitch - Google Patents

Abstract

A dust suppressant composition for application to a substantially soil particle laden surface including (i) a saponified tall oil pitch, and (ii) a salt, wherein said composition is an emulsion characterized in that the salt is present in an emulsion destabilizing amount, is disclosed. Also disclosed is a method of use of a dust suppressant composition, wherein said substantially soil particle laden surface is coated with at least a monolayer of described dust suppressant composition sufficient to cause particles to substantially agglomerate.

Description

521650 PATENTS FORM NO. 5 Fee No. 4: $250.00 PATENTS ACT 1953 COMPLETE SPECIFICATION DUST SUPPRESSANT l/WE Econ Products Limited, a New Zealand company, of 79 Foundry Road, Silverdale, Auckland, New Zealand hereby declare the invention, for which I/We pray that a patent may be granted to me/us, and the method by which it is to be performed to be particularly described in and by the following statement: 1 26991/37 LK DUST SUPPRESSANT TECHNICAL FIELD This invention relates to a dust suppressant and in particular, though not solely, this invention relates to a composition and method for reducing dust generation or 5 evolution from roads and/or generation of airborne dusts.

BACKGROUND ART The dust generated from unsealed rural and forestry roads due to vehicular traffic creates not only the obvious visibility hazard for other road users, but also an environmental hazard for surrounding vegetation and buildings. The coating of dust 10 on vegetation effectively reduces the amount of arable or cultivatable land available as plants are inhibited in their growth by such dust layers. This significantly affects both the quality and quantity of horticultural produce, particularly with sensitive produce such as kiwifruit, berry fruit or flowers, rendering them fit only for local sales or waste. Buildings and the vehicles themselves are often coated in a layer of fine 15 dust detracting from their appearance and requiring more frequent and therefore expensive cleaning. In vehicles, brakes and filters will require more frequent replacement as a result of dust ingress.

Currently, heavy traffic removes the aggregate from a road surface up to a depth of around 70mm per annum which results in a significant on going maintenance cost 20 to replenish this aggregate and maintain roads to an acceptable level of service for the community. The increasing trend towards environmental controls has seen an emerging interest in the use of dust suppressants. A greater concern for health and economic costs of dust output are catalysts for roading and controlling authorities to take more positive measures to control dust emissions. 2 It is therefore an object of the present invention to provide a dust suppressant which will go at least some way towards addressing the foregoing problems or which will at least provide the industry and/or public with a useful choice.

It is desirable to develop a dust suppressant formulation that is cost effective, durable, 5 meets with environmental requirements and is an effective substitute for materials that are currently used.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors 10 assert, and the applicants reserve the right to challenge the accuracy and pertinence of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

It is acknowledged that the term 'comprise' may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term 'comprise' shall have an inclusive meaning - ie that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or 20 elements. This rationale will also be used when the term 'comprised' or 'comprising' is used in relation to one or more steps in a method or process.

DISCLOSURE OF INVENTION For the purposes of this specification the term "soil" is used to refer not only earth or dirt, but also incorporates any other materials or fillers commonly used in roading 25 and/or civil construction. 3 Accordingly, in a first aspect the invention consists in a dust suppressant composition suitable for application to a substantially soil particle laden surface comprising a saponified tall oil pitch.

Preferably, said dust suppressant includes tall oil pitch.

Preferably, said dust suppressant includes mineral oil.

Preferably, said dust suppressant includes an aqueous component, such as water.

Preferably, the dust suppressant diluted with an aqueous component to a dilution of about 1 part dust suppressant composition: 1 parts aqueous component or less.

Preferably, the dust suppressant diluted with an aqueous component to a dilution of 10 about 1 part dust suppressant composition: 2 parts aqueous component or less.

Preferably, the dust suppressant diluted with an aqueous component to a dilution of about 1 part dust suppressant composition: 25 parts aqueous component or less.

Preferably, the dust suppressant diluted with an aqueous component to a dilution of about 1 part dust suppressant composition: 50 parts aqueous component or less.

Preferably, the dust suppressant diluted with an aqueous component to a dilution of about 1 part dust suppressant composition: 100 parts aqueous component or less.

Preferably, said dust suppressant is diluted with said aqueous component to a dilution of about 1 part dust suppressant composition: 250 parts aqueous component or less.

Preferably, said dust suppressant is diluted with said aqueous component to a dilution 20 of about 1 part dust suppressant composition: 1000 parts aqueous component or less.

Preferably, said dust suppressant is diluted with said aqueous component to a dilution of about 1 part dust suppressant composition :more than 1000 parts aqueous 4 component.

Preferably, the pH of the dust suppressant is buffered to greater than pH 7. Preferably, the pH of the dust suppressant is buffered to be about pH 11.

Preferably, said dust suppressant composition includes a salt.

Preferably, wherein said salt is present in an emulsion destabilising amount. Preferably, said salt is an inorganic salt.

Preferably, said salt is selected from one or more of the following: lime, slaked lime, KOBM slag, cement, fly ash, gypsum, bassinite, anhydrite, or calcium salts.

Preferably, said dust suppressant composition includes a soil stabiliser.

Preferably, said soil stabiliser is selected from one or more of the following: lime, slaked lime, KOBM slag, cement, fly ash, gypsum, bassinite, anhydrite, calcium salts.

Preferably, the soil stabiliser includes KOBM slag, and one or more initiators.

Preferably, said initiators are selected from the following group potassium chloride, sodium silicate (water glass), calcium hydroxide (slaked lime), sodium metasilicate 15 (anhydrous), sodium carbonate (soda ash), sodium hydroxide (caustic soda), lime oxide.

Preferably, the soil stabiliser is a soil stabiliser as claimed in New Zealand Patent No. 332204.

In a second aspect, the invention consists in a method of use of a dust suppressant 20 composition, wherein said substantially soil particle laden surface is coated with at least a monolayer of dust suppressant composition according to the first aspect enabling said soil particles to substantially agglomerate.

Preferably, the dust suppressant composition is blended with and emulsion destabilising salt prior to application to the soil particle laden surface.

Preferably, said method also comprises the steps of: spreading an emulsion destabilising amount of a salt onto a soil particle laden 5 surface, and spreading the dust suppressant composition onto said salted surface.

Preferably, said method further includes the step of: mixing said emulsion destabilising salt and the soil particle laden surface together.

Preferably, said mixing step is performed by a stabiliser machine and/or grader.

BRIEF DESCRIPTION OF DRAWINGS Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which: Figure 1 is a graph illustrating the surface area to mass contributions of particles making up Bosher Road, Figure 2 is a graph illustrating the surface area to mass contributions of particles making up Horseshoe Bush Road, Figure 3 is a graph illustrating the cumulative weight of particles generated as dust from the trial conducted on Bosher Road of different dust suppressing materials, Figure 4 is a graph illustrating a comparison between Northland Road and Bosher Road of the cumulative weights of particles generated for different dust suppression trials, and 6 Figure 5 is a graph illustrating a theoretical dust particle settling rate for dust particles in air over a range of particle sizes.

BEST MODES FOR CARRYING OUT THE INVENTION A dust suppressant composition in accordance with a preferred embodiment of the 5 present invention will now be described with reference to the above figures.

A dust suppressant composition may substantially increase the strength of a soil material and/or substantially reduce dust emissions from a surface containing said soil material (a soil particle laden surface).

Processing of crude tall oil (CTO) from the wood pulp industry can produce a high 10 molecular weight material termed "pitch" (or a tall oil pitch). The processed CTO produces the tall oil pitch which contains fatty acids, resin acids, terpene acids, esters of sterol and various other components.

Tall oil pitch material will "set" and bind to most materials in a way similar to bitumen although the applicant has discovered that tall oil pitch can be processed to form a 15 composition which can be readily handled and used as a component of or as a dust suppression agent.

The tall oil pitch produced is processed in a modification (saponification) reaction to form a stable emulsion (which may be referred to as a stabilised tall oil pitch and is the basis of a dust suppressant composition), of which approximately 5% of the tall oil 20 pitch is converted in the saponification reaction. The dust suppressant may also be an emulsion containing the saponified tall oil pitch and non-saponified tall oil pitch. Mineral oils may also be used and combined with the saponified tall oil pitch to provide an emulsion.

Dilution of this stabilised tall oil pitch emulsion with an aqueous component to form a 25 stable aqueous emulsion, for example with water or a solution of sodium hydroxide 7 may be used to obtain a desirable dilution suitable to the dust suppressant requirements of a soil laden surface. For example, a more concentrated dust suppressant composition will provide a greater affinity for soil particles to agglomerate together, being less likely to become airborne and therefore a potential dust hazard.

Preferably the pH of the stabilised emulsion is buffered and/or maintained at greater than 7, though most preferably at about pH 11. The pH may be adjusted to help maintain the stability of the stabilised emulsion as it may be advantageous for the pH of the dust suppressant to remain at around 11 for improved storage durability.

The dust suppressant composition may optionally utilise other components. These 10 other additional components may be salts used as emulsion breaking or destabilising agents, soil stabilisers, aqueous components, or pH adjusters. The combination of the dust suppressant composition with such other components may yield in an enhanced strength dust suppressant mix which assists in reducing dust release from a soil particle laden surface.

Salts for breaking (or destabilising) the emulsion may already be contained in the soil surface material being treated, and if so minimal if any additional breaking agent may be required (Calcium ions may be used for destabilising the emulsion). The sodium soap produced during the saponification reaction is the stabilising component of the emulsion (that is, the saponified tall oil pitch dust suppressant). It may be that 20 aggregate materials in roads already have higher free calcium ion reserves and can be utilised for this purpose, such as limestone soil materials. Aggregates with calcium reserves or those which are calcium 'rich' are also suitable, indeed any material able to destabilise the emulsion may be used.

Other suitable salts which may be sources of, for example, calcium ions which 25 perform the emulsion destabilising function may be lime or calcium compounds such as lime, burnt lime, slaked lime or calcium hydroxide, cement, slag, fly ash will act as 8 emulsion breakers. Also, gypsum, bassinite or plaster of paris, anhydrite and lime flour can be used. It is also likely other calcium salts will have similar effect, for example, calcium chloride, calcium acetate, calcium nitrate (Ca2+ releasing compounds).

Added soil strength may also be provided by utilising soil stabilisers in the dust suppressant composition, such as lime, slaked lime, burnt lime, KOBM slag (referred to as Kontinuous Oxygen Blast Maxiite, a by-product of the iron and steel making process), cement, fly ash as these form calcium clays which aggregate better. Gypsum, bassinite, anhydrite and/or a triple blend (TB), such as a blend of KOBM, 10 ordinary Portland cement and burnt lime may also be used to increase the strength properties of the soil the dust suppressant composition is applied to.

KOBM and or one more initiators may also be used, where such initiators may be potassium chloride, sodium silicate (water glass), calcium hydroxide (slaked lime), sodium metasilicate (anhydrous), sodium carbonate (soda ash), sodium hydroxide 15 (caustic soda), lime oxide.

Preferably, there is a method of determining a proposed application rate of dust suppressant and required breaking agent (such agent for example being one or more of KOBM binder, Durabind™, lime oxide, cement, kiln dust, potassium chloride, sodium metasilicate pentahydrate).

The contents of New Zealand Patent number 332204 is hereby incorporated by reference, and generally relates to compositions which may be used as soil stabilisers.

A methodology has been invented for the application of the dust suppressant composition to ensure it is efficiently and effectively applied. In a first aspect, this 25 methodology may preferably involve the spreading of the breaking agent onto pavement surface, the monitored application of the dust suppressant into the in-situ 9 material and the mixing of the materials by in-situ mixing with a stabilizer machine or grader with attachments.

A stabiliser may be a large piece of civil construction equipment that is used to pulverise and mix materials on site as opposed to plant mixing off site and 5 transporting to a project. It is similar to a large grader but in place of the central grading spade there is a stabilising rotor. The rotor is a large cylindrical drum with many spade shaped tips and when rotated by the machines drive at high revolutions per minute the tips preferably pulverise and mix the materials the rotor is placed into.

Application of the dust suppressant composition may also be via a water-cart type 10 operation spraying directly onto the surface with an option to further mix the product into the host material by grading the material back and forth.

Properties of the Material to which the Dust Suppressant/Soil Stabiliser is Applied The dust suppressant system may be for any unsealed surface including stockpiles, and may be uniquely formulated to suit regional road geology and/or climactic 15 conditions, producing maximum dust suppression and/or reduced road surface wear. The system's "active" ingredient is the stable emulsion which is manufactured and blended with other additives (for example, aqueous components such as water, NaOH) to form an aqueous emulsion.

The dust suppressant may be applied and/or incorporated into the roading surface in 20 such a way as to balance the performance as a dust suppressant and its price. As the dust suppressant composition may preferably include soil stabilisers, this may help to increase the strength of the road/soil agglomerates, and may be useful as a soil conditioning step prior to road sealing, for example with bitumen or asphalt.

The components making up the road, and moisture content of the soil particles/road 25 also need to be considered prior to application of the dust suppressant, as these factors can affects the wetting and spreading of the dust suppressant over the soil particles.

The adsorption of the dust suppressant onto "dusts" taken from existing roads where the dust is known to cause a problem was measured via a "titration" of the dust with 5 excess suppressant followed by assay of the remaining suppressant. After determining the coating rate on various dusts, a criterion for acceptable coating has been developed, and related to the coating rate.

This has indicated acceptable dilutions for application, leading to an indication of the financial viability of the system in managing the dust nuisance both in forming roads 10 prior to surfacing, and in the maintenance of dirt roads where traffic is not high enough to warrant sealing, but is still of a volume that generation of dust by traffic is categorised as a nuisance.

The dust suppressant may act in two ways to reduce dust emission from a pavement. Firstly the dust suppressant is strengthened and plasticity reduced so the material is 15 less prone to moisture fluctuations causing erosion of the surface materials by swelling and shrinkage together with the binding action resisting the forces wanting the particles to move. Secondly the dust suppressant causes the smaller particles to agglomerate together so their effective size increases, and the wind speed required to lift particles also increases to a point where a limited number of particles are now able 20 to be liberated.

The dust suppressant has been designed to maintain dust reduction on a treated site for a period of 3 - 4 months during which time on going maintenance is expected to be minimal although six months and longer of acceptable level of service and dust reduction may be achievable in some material types. 11 Properties of the Road Surface after Application of Dust Suppressant The major properties that mark a successful dust suppressant are related to the effective lifetime of the material, and to minimal environmental impact. The effective lifetime is based on the extent to which the material resists wash-off ("washability") 5 during rainfall and abrasion during road use.

This portion of the work was based upon relating "washability" of the dust suppressant from the surface of dust, and relating this to the dust type and the time between application and subsequent washing (such as might represent rainfall). The criterion for acceptability was the performance equivalent to resistance to wash-off within 4 10 hours of application.

Application of the Product The application methodology may incorporate the addition of road surfacing materials which are carefully blended to 'match' the specific properties of the road surface being treated together with a controlled mechanical process which thoroughly combines the 15 dust suppressant with the road surface additives and which is then contoured and rolled.

Preferably the unique properties of this dust suppressant composition are: It may be 'formulated' (i.e. by varying the amount of dust suppressant/aqueous emulsion to breaking agent and use of soil stabilisers, as well as diluting with aqueous 20 components to a desired custom formulation) to suit specific regional road surface geology, has an ability to resist abrasion and 'wash-off' because of its carefully controlled mechanical application and combination of products (especially in areas with higher average rainfall), and is relatively cost-effective in terms of its ability to substantially reduce overall road surface wear and maintenance costs.

Properties of the dust suppressant material 12 Sensitivity of Cold/Hot Storage Jars of the stable emulsion diluted with water in dilutions of 1:25, 1:50 to 1:100 were stored at 20°C and 40 ± 2°C for several weeks and compared with solutions stored at ambient. We elected to track changes by measuring kinematic viscosity, with Table 1 5 listing the viscosity of the samples at the beginning of the experiment.

Table 1: Variation of the viscosity of stored samples Viscosity of stored samples mPa.s °C Dilution 1:25 1:50 1:100 Start 1.010 1.076 0.922 These values are only slightly different from the value for water (being 0.960 mPa.s at 25°C), but appear rather variable. Viscosity is very sensitive to structure within the 10 liquid so we assume the variation is due to micelle formation.

By the end of the first week there was minor separation of the samples. A faint layer had occurred on the surface, and this would have interfered seriously with the measurement of viscosity. The situation worsened to the extent that at four weeks the material had begun to separate.

It was concluded that separation occurs, and the diluted aqueous emulsions are not stable for periods of longer than about two to three weeks.

Bacterial Decomposition of Samples at 35°C Experiments were conducted by Landcare Research in Hamilton (New Zealand), to determine carbon dioxide effusion rates with time when the dust suppressant was 13 applied to Bosher Road (in the Rodney District near Wellsford of New Zealand) aggregate and a control. The trial was run for three weeks and the rate of effusion was linear throughout. The roading aggregate showed a higher efflux than the control soil but the soil may have been affected by the high alkali residue in the pitch 5 (pH~11). The loss of the dust suppressant over 21 days was about 0.3 %.

There are two consequences of this. The first is that in wet conditions the dust suppressant may slowly loose capacity to bind dust on the road surface. However the second but more advantageous corollary to the bacterial decomposition is that there is likely to be little long term contamination from runoff if the new road suffers from 10 heavy rainfall immediately after application of the dust suppressant.

Containers of dust suppressant have shown little or no sign of deterioration over a six month period, and in that respect they are relatively similar to conventional roading emulsions. They can be assumed to have a shelf life approximately equal to the "high season" for road works, but will be unlikely to survive storage between seasons. The 15 "high season" is generally the period of time in a country where weather conditions permit substantially increased road work activities.

Our original criterion for acceptable performance was no significant (less than 10%) deterioration on 12 months storage. This target has not been met for diluted material and consequently the dust suppressant has a limited shelf life. However, 20 deterioration in use is very slow and should be sufficient for the length of time period (3-4 months) over summer. The minor bacterial decomposition of the diluted dust suppressant on soil suggests that there will be little problem with runoff.

Application to the Road Surface The original intention of this project was to add the diluted dust suppressant to the 25 road surface and then hoe it into the top 100 mm of road bed. The principal modification to this strategy was to add a triple blend which may for example be in the 14 following quantities, and it is to be noted that this is only one particular example of a blend, KOBM slag (2%), ordinary Portland Cement (0.5%) and burnt lime (0.5%) by weight of the aggregate is utilised. Other triple blend compositions may be suitable. The blend was applied and the dust suppressant added as the blend was hoed into 5 the road surface.

KOBM slag (Kontinuous Oxygen Blast Maxiite) is a by-product of the iron and steel making process. It is generally regarded as a waste material, with use as a roading material or soil stabilising material. When the slag is recovered from the steel plant it is in a molten form which solidifies as a solid mass. Weathering of the slag, for as 10 long as 6 weeks, causes it to become friable. This material is screened and used. The finer material and/or fines (material that is less than 2.9 mm in diameter) can be used as the stabiliser of soils or aggregates for roading.

These proportions were duplicated in the laboratory in the initial work by producing compacted cylinders which were allowed to dry and the firmness and cohesion of 15 material noted. The cylinders were formed by loading 1kg dry solid and 100g of liquid to a mixer, mixing for 1 minute, and then standing for 5 min. The paste was then loaded into a cylinder mould, and vibrated for 1 min before extruding and standing for air drying. We used liquids formed from 1:10 dust suppressant in water and 1:1000 dust suppressant in water as well as some control cylinders with no added dust 20 suppressant.

The aggregate/dust suppressant cylinders were generally firm, with the 1:10 formulations giving quite strong compacts. These, and the 1:1000 compacts weaken when wetted. The materials containing little clay adhered better with the addition of the dust suppressant than the control cylinders, so the dust suppressant does 25 improve cohesiveness in the case of low clay materials.

Coating of Dust Particles The surface area that the dust suppressant is required to coat was assessed by measuring the particle size distributions by a laser scattering technique. The particle size data can then be used to calculate the contribution of a particle size band to the total surface area of the sample. The distributions for Bosher Road material are given 5 in Figure 1.

As expected most of the surface area of the roading material is contributed by the fines. In our measurement there is a discrepancy in the region around 700 jum where the estimates of the particle sizes of the larger and smaller fractions are made by two different methods. This discrepancy is related to the shape of the particles. The form 10 of the discrepancy suggests that the particles are probably "platelike" (that is, approximately plate shaped particles), not equi-axed, and suggesting much of the finer material is clay. This is also supported by the behaviour of the fines as they undergo ultrasonic agitation, breaking down to even finer particle sizes.

Different materials also have greatly different particle size distributions. Horseshoe 15 Bush Road (in the Rodney District near Silverdale, New Zealand) material has the peak in the particle size distribution moved toward lower values. It is possible that there is a bimodal distribution in the Horseshoe Bush Road material (Figure 2) with peaks around 10 and 1 micron while the Bosher Road material has its main peak at about 50 microns.

The surface area of the Bosher Road material is about 50m2.kg'1 or 0.05 m2.g"1 (if the particles are treated as smooth surfaced spheres). This is quite a low surface area, and the description as a smooth sphere is not a very good one. However if the clays are largely kaolinites or related materials, as would be expected given the geothermal origins of most of the materials in the Northland region of New Zealand, it is not an 25 unreasonable value as the clay on its own tends to have surface areas around 0.5 to 2.4 m2.g"1 (W Eitel, The Physical Chemistry of the Silicates, A III, 31 University of Chicago, 1954). New Zealand cements have a typical particle size around 10 to 15 16 l-im, corresponding to a specific surface area of 0.115, although their actual measured value is around 1 m2.g"1 or around 10 times that of a smooth sphere of equivalent diameter. We also note that the value of the surface area is for the particles as received, that is dry, and strongly agglomerated. The surface area for a 5 sodium montmorillonite, the extreme case for surface area, is about 750 m2.g"1 (H van Olphen, An Introduction to Clay Colloid Chemistry, p254, Wiley, New York, 1977).

Requirements to Coat all Particles with a Monolayer Underlying our work on this material is the belief that if small particles are coated with a material such as an oil, they will agglomerate and become sufficiently large to not 10 entrain in air. The amount required to coat all particles can be estimated by calculating the surface area and then calculating the amount of material needed to coat this with a monolayer of dust suppressant.

Tall oil pitch is largely made up of esters of sterols, and terpene acids, the saponification process to solubilize it converts only about 5% of the material to the 15 stable emulsion used as the dust suppressant. Since this estimate is simply to determine the point at which the material is covered by a monolayer, we have made the assessment using several assumptions, most of which are driven by a lack of data for this and similar materials. These assumptions can be examined in the light of the results of the calculation to see if the errors they introduce are material.

The standard material used in the discussion of films is stearic acid. Typical Langmuir experiments show that stearic acid has a surface area of about 20.5 A2 per molecule. This converts (using the Avagadro number of 6 x 1023 mol"1, and a molecular weight of 284) to 43 m2.g"1. That is a gram of stearic acid will cover an area of 43 square meters. The Bosher Road material has a calculated surface area of 25 under 0.1 m2.g"1.so would be covered in a monolayer of stearic acid by 1/430 g of 17 stearic acid. That is a dosing of 0.23% should cover most of the roading materials we used in a monolayer.

If we assume that the dust suppressant behaves in the same way as stearic acid, then the dilution corresponding to that dosage rate can be calculated. Our dust trial 5 showed that around 660ml of water was required to achieve a moisture content that would make the 12kg charge of aggregate workable. The dosage rate of 0.23% corresponds to a value of about 2.8g of pitch solids (by pitch solids it is meant undiluted (i.e. non-aqueous) saponified tall oil pitch, that is dust suppressant with no aqueous component) or 4.7g of dust suppressant (at nominal 60% pitch solids (i.e. 10 40% aqueous component(s) making up the balance), so the dilution to give a monolayer is 4.7g in 660g or approximately 1:150.

Dust suppressant solids may generally be the amount of saponified tall oil pitch in water suspension not lost after drying at 105°C. It may not be solids per se but contain high boiling liquid pitch.

This is quite a similar dilution to the lowest dilution of 1:100 used in these experiments, so we need to examine the assumptions made in arriving at that figure. The assumption that requires the biggest leap is the parallel drawn between stearic acid on a water surface and fatty esters adsorbed onto a solid surface. Certainly the stearic acid will be strongly aligned on the water surface with the polar end group on 20 the water surface and the fatty esters of the dust suppressant pitch are more likely to lie flat, thus underestimating the concentration required for the monolayer.

There is a second issue in the estimate of surface area. The values for surface area for an aggregate will depend very strongly on the aggregate type with high clay materials requiring more suppressant, and aggregates based on gravels or crushed 25 rock requiring less. These aspects are discussed in slightly more detail under the results for the dustability trials. 18 DUSTABILITY TRIALS Laboratory Trials No standard laboratory testing regimes for assessing the performance of dust suppressants on unsealed roads have been discovered. Our original method was 5 based on a technique for sampling particulates from a smokestack, drawing the air across a glass filter for subsequent weighing of the dust. The pressure drop across the system was so great that we were unable to collect much dust so we discarded this method in favour of one using "generic vacuum cleaner bags" as the filter. These are cheap, readily available and very consistent in performance. We elected to use a 10 roller to represent the movement of vehicles on a road. This should be effective at dusting up the surface of the road bed, tending to drag up fines to the surface if it has a set of spikes to cut the surface. We therefore arranged the equipment on the basis that on a country road there would be 50 to 100 vehicles per day, so that 100 strokes with the roller would represent about one day of use.

The wind speed across the bed is the major factor in entraining dust. Average wind speeds are generally low, about 8km/hr in Kaitaia, and 11km/hr in Auckland, while the wind under a car must be near the speed of the car. Consequently the wind speed is selected as near as possible to 50 km/hr.

The in-house method was developed using a ply wood enclosure of approximate 20 dimensions 2 x 0.8 metres to contain a simulated road bed. The box has side mounted suction from a large capacity fan (3000 m3.hr°1). A network of perforated pipes in the base of the box allows compressed air to be flowed through the newly formed bed to dry it prior to the dust trial. About 100mm of graded pea gravel is laid in the box first to distribute the air as evenly as possible through the "road bed" which 25 is laid on top. 19 Each aggregate bed comprises about 12kg of roading aggregate which has been passed through a jaw crusher producing a maximum particle size of about 15mm. A triple blend (TB) comprising 240g of KOBM slag and 60g each of burnt lime and cement was blended with the aggregate before any liquid was added. To this was 5 added 660ml of the undiluted dust suppressant. This was prepared in three concentrations 1 part pitch to 10, 20 and 40 parts water. No further water was added except in the "blank" runs. An additional trial was done using a higher pitch solids (HS) content which had added terpenes at a dilution of 1:20. The bed was tamped into place and allowed to dry with flowing air passing through the bed for at least 36 10 hours.

Laboratory Dustability Results The dusting regime involves running a spiked roller, whose length fills the entire width of the box, up and down the length of the box making 20 return strokes per minute for timed periods between 0.5 and 2 minutes. At the end of each period the dust bag 15 was weighed and the cumulative mass recorded. The spikes penetrate approximately 8-10 mm into the surface. The "dusting regimes" are continued until the quantity of dust per run became constant or became too small to measure accurately. A decrease in dust production usually coincided with "road bed" surface being destroyed by the spiked roller. The cumulative masses of total available dust were plotted 20 against time. Table 1 gives the raw data for the dustability runs, where TB refers to Triple Blend, DNZ refers to dust suppressant, and the ratio refers to the dust suppressant to water ratio. HS refers to "high solids" (i.e. the undiluted saponified tall oil pitch) content dust suppressant.

Table 1: Dustability Trials for Bosher Road material cumulative dust collected 25 from surface Cumulative dust (grams) Time (sec) TB only DNZ 1:10 DNZ 1:20 DNZ 1:40 HS 1:20 Water only 2 0.47 0.6 0.47 0.63 1.6 60 2.11 1 0.7 0.85 2.2 90 2.74 0.89 1.3 120 3.39 0.93 1.2 2.97 150 1.27 180 3.95 1.46 3.61 240 4.66 1.47 270 1.92 300 1.89 4.3 360 .66 1.79 480 6.65 2.35 Figure 3 shows that the addition of the dust suppressant lowers the dust output from traffic, even at high dilutions, below the two blanks where either only water, or water plus the triple blend (TB) was applied. The comparison between the runs with water alone and with the triple blend indicates that the fine materials included in the triple 5 blend may contribute to the dusting intensity unless the dust suppressant was applied at the same time. It is significant that there is little difference in the dustability behaviour of the trial beds, suggesting that the application rates used here are higher than the minimum rates required.

A second aggregate from the Northland region was assessed briefly. On this 10 aggregate, dust suppressant improved the "dustability" of the aggregate by comparison with the "blank" but the effect is much smaller than for the Bosher Rd aggregate (see Figure 4). Where BR refers to the Bosher Road data points for dust suppressant at a given ratio, N refers to Northland data points for dust suppressant at 21 a given ration, N Blank refers to no dust suppressant used and BR + TB refers to Bosher Road plus triple blend data points.

The extent of the laboratory trials demonstrates that dust suppressant works well in reducing the total available dust from a road surface. It is unclear at this stage how 5 much needs to be applied as the limited runs within the scope of this project did not demonstrate that applying more concentrated dust suppressant resulted in less dust. The corollary of this is that we may have been applying dust suppressant at a rate that exceeded the required value. The previous discussion of the requirements to form a monolayer on the surface of the aggregate suggests that the critical dilution is 10 1:150.

The data for dustability suggest that there is little variation in the dustability over the fivefold range represented by the range of dilutions from 1:20 to 1:100, and this also points to the likelihood that excess coating material was present. The lowest concentration is approaching the limit suggested by our calculation, but gives a slight 15 margin for poor mixing, and so provides some balance between the operational factors (such as poor mixing), cost factors (which require minimum loading with dust suppressant) and performance (which requires a perfect wetting, and maximum agglomeration of fines).

It may never be possible to eliminate surface dust completely by this technique since 20 the dusting is most certainly a function of the wind speed. However, there may be a relationship between the maximum wind speed and the minimum dust suppressant required to prevent pickup of dust in that wind.

Suspension of Dust in Air For a particle to remain suspended in air, the upward component of velocity should 25 exceed the downward component of the falling velocity. In the simplest case of a downward falling particle in upward moving air, we can calculate the terminal velocity 22 of the particle by balancing the downward force due to gravity and the upward force due to flotation of the particle in the air, and the viscous drag on the particle as the air moves past it.

The general equation for the terminal velocity of a particle is Ui = a)i~1 3 PgCd J where Ut = the terminal velocity g = force due to gravity dp = diameter of the falling particle pd = density of the particle pg = the density of the gas Cd = drag coefficient Assigning values to the variables permits us to evaluate the terminal velocity of particles as a function of size. Figure 5 shows the relationship between the particle size and setting velocity.

On the basis of the particle size distribution (Figure 1), it is clear that small amounts of material have settling velocities in the range 1 to 10 cm/sec (corresponding to wind speeds of less than 1 km/hr. Clearly the wind speeds over our artificial road bed were much greater than this, indicating that the entrainment of the dust into the surrounding air is greatly affected by a boundary layer at the road surface.

The values also show why dust is so persistent. Nearly 0.5% of the mass in these roading materials has a particle size under 1 micron, and thus a settling rate in air of less than 1 cm/s, so that particles of this size (not the smallest in the sample) will take slightly over a minute and a half to fall through a distance of 1 meter on a still day. 23 On a day with a gentle (10 km/hr) breeze, the dust will have drifted about 160 m in that time.

Washability Early in the experimental work a tentative thesis was developed that the dust 5 suppressant emulsion would be broken on contact with the soil and the view was formed that this emulsion breaking would help control washability. If the breaking of the emulsion could be deferred, it would probably reduce the power demand for the blending process, but it should occur fast enough that a newly formed road surface would be unaffected by subsequent rain (perhaps within 4 hours).

Possible mechanisms for breaking the emulsion were change in pH or perhaps conversion of the sodium soap used to stabilise the emulsion to a calcium soap. As well as providing some added strength to the road surface, the triple blend may provide free calcium ion to advance this process, and if this were so, it would provide a very useful mechanism in sandy soils and high volcanic glass soils. Triple Blend (TB) may enhance soil properties necessary for reaching a near maximum soil stability. It also enhances dust suppression from a surface. The term Ordinary Portland Cement (OPC) is used as a generic term for the purposes of this specification. It was also possible that many high clay soils would be dominantly Sodium ion rich soils, having little spare Calcium ion reserve.

This thesis was tested with a washability test on three aggregate/triple blend/emulsion mixtures. Bosher Road, Horseshoe Bush Road and GAP 25 aggregates, with triple blend in the proportions above, and dust suppressant at 1:20 dilution were prepared in vibrated cylinders and dried overnight at 40°C. The cylinder was broken, and soaked in static water for 2 hours before the fluid was decanted off.

As result of this treatment GAP 25 showed no sign of frothing or soapiness. Both other materials show weak foaming and colouring/cloudiness in the water column 24 even after standing for two weeks. After that period of time the colouring is likely to be caused by the dust suppressant rather than the clay. This suggests that GAP 25 has adequate calcium ion to destabilise the dust suppressant, but that there is little free calcium ion in either Bosher Road or Horseshoe Bush Road material.

GAP 25 and GAP 20 are general all passing aggregates with a maximum stone size of 25 or 20 mm. It is a common term to describe aggregate that meets certain grading and size requirements but are generally not able to meet higher standard specifications.

This is the first indication that the roading materials are likely to behave differently 10 according to the source. We then took each of the fluids and attempted to extract the dust suppressant from the liquids with a hydrocarbon solvent (heptane). None of the materials had released dust suppressant into the aqueous phase, suggesting that at least in these cases the dust suppressant had adsorbed onto the clay, and the low concentration of soap required to make the emulsion stable was too low to help wash 15 the dust suppressant off the roading material once it has dried.

Experiments were also carried out to control the pH of the dust suppressant so that it became much less stable. It was hoped that this would perhaps modify the material so that it would work more effectively on very sandy materials. The pH of as delivered pitch in a 5% solution in water is around 11, and our target value was a pH of 7. 20 Modifying the pH with acid easily dropped the pH to any desired value, but almost always, on continued stirring, the diluted emulsion separated to give globules of saponified tall oil pitch (i.e. dust suppressant with no aqueous component) which was judged to be too difficult to handle while blending into the roading material. This line of enquiry was discarded, but it was noted that there is still the possibility of applying a 25 weak acid wash to roading materials that are very low in clay.

Undiluted emulsions suspension is at pH 11 and can be stored at this pH for an extended period. Dilution with water only slowly destabilises the emulsion as the pH drops. There can be extra sodium hydroxide added to maintain pH and stability.

EXAMPLES Tauhoa Road Characteristics The objectives of the trial was to evaluate the effectiveness of the product in reducing dust emissions on a full scale "live" (i.e. a road open to traffic) unsealed road, to a level that was acceptable to the local residents, and determine if the layer will perform adequately to become stage 1 of a staged seal extension programme The location for this trial was Tauhoa Road which is approximately 5km north of Warkworth running off the end of Kaihakatea Flats Road of the North Island of New Zealand. The trial section was 1.1km in length commencing at route position (RP, which is the position or distance along a particular road) and ending at a different RP and was split into 2 sections. The first 550m section started at the end of the existing 15 seal was the trial section and the second 550m section was the control section. A bridge with short sealed approaches was in the middle separating the 2 sections.

The area is mainly farmland and predominantly flat and low lying which results in drainage problems such as surface water after rain events with the trial length in rolling country with a number of shallow curves along the alignment which is able to 20 be safely driven at 65 kilometres per hour (km/hr). It has a typical mix of traffic between light vehicles and heavy logging traffic with a vehicle count of average annual daily traffic (AADT, which is used to describe the volume of traffic expected on a road) of 180 vehicles per day (vpd). The section has five residential houses along the frontage of the road which provided a suitable number of residents to assess the 25 performance of the product. 26 The scope of the trial was to identify a suitable road to perform the trial on, construct the test sections using agreed techniques and products, monitor test sections using agreed techniques and produce a report with conclusions and recommendations of the performance.

The pavement was designed to be undertaken in 100mm depth sections to gauge the suitability of these particular depths, as there were no particular design criteria in terms of the structural strength of the pavement or its contribution to a possible future life as part of a staged seal extension. The trial sections had the following parameters: treatment length each section 550 metres average width 6.0 metres cross fall (most section in superelevation) 6% roadside drainage maintain that which was on site previously Pavement Material Properties The pavement consists of a firm orange brown silty clay with adequate shape overlayed by 50 - 100 mm dense GAP 20 greywacke/limerock blended aggregate acting as a pavement / wearing course layer.

As the site only has intermittent vegetation along the route it is exposed to the drying action of wind which also takes any subsequent dust onto the surrounding properties.

Following treatment of the site with the dust suppressant system, the extent was delineated with marker posts and information signs to advise travelling vehicles of the section.

The pavement consists of material that is able to be broken down under the passage of loaded vehicles and reduces the particle size to a point where it is prone to movement and, as discussed earlier, this movement is carried by several factors 27 present during the passage of a vehicle. The dust suppressant system improves the likelihood of particles bonding together causing the effective wind speed required to lift the now larger particles off the ground to be raised and thereby generally reducing the total volume of dust released.

As each pavement material has unique requirements in terms of increasing strength and effective wind speed together with decreasing plasticity, a number of laboratory tests have been undertaken to determine the appropriate dust suppressant blends and concentrations required to achieve the desired results.

The preliminary works that were undertaken to set up the trial site included installation 10 of permanent sign detailing the trials start and end and excavation of test pits to establish depth of existing pavement. Once established on site, the construction was commenced as no upgrading of the pavement shape or watertable was required and was completed as per the agreed methodology which ensured a fully monitored and accurate application rate together with full blending of the system with the host 15 material.

Monitoring and Performance Monitoring was undertaken by regular visual assessment and scoring on a number of predetermined attributes and it was not restricted to the engineering and physical properties, it also involved local residents in an opinion survey of its effectiveness.

An experienced pavement team assessed the performance of each section of the trial section. The factors considered under each evaluation were dust reduction, skid resistance; number and depth of potholes, surface rutting and severity, amount of material moved to the shoulders and general ride comfort to objectively rank each performance. 28 The evaluations were undertaken on each fortnightly anniversary of the trials construction to ensure a regular and uniform time period for each assessment.

This application process that was undertaken used the following sequence (1) Sample host material for type, grading, strength, plasticity index, clay index 5 and water content. (2) Determine proposed application rate of dust suppressant and required breaking agent (such agent being one or more from KOBM binder, Durabind™, lime oxide, cement, kiln dust, potassium chloride, sodium metasilicate pentahydrate). (3) Undertake minor reshaping with no additional aggregate onto existing pavement. (4) Minor watering as required to bring host material to an approximate or desired moisture content. (5) Spread salt / emulsion breaking or destabilising agent(s) onto pavement surface. (6) Inject dust suppressant into stabiliser rotor and monitor application rates. (7) Assess moisture content of host material with added dust suppressant and other components behind stabilizer and add water with dust suppressant via water cart spray bars to lift water content to the desired moisture content. (8) Compact and trim for shape with all additional water added containing dust suppressant. (9) Water with dust suppressant as surface dressing to create slurry of surface material.

Stabilise and Mix into Host Material 29 This process will introduce the dust suppressant to the host material or surfaces via direct spraying from the water cart. While less effective, this methodology will be suitable for yards and stockpile areas in the mining, quarrying, construction and roading situations where a more robust long term treatment is not desired.

Condition Two Weeks Trial Section The trial section exhibited adequate dust reduction and presents a surface that is safe, has no loose aggregate and providing good skid resistance. It was noted that, with some very minor work, the pavement surface condition would be suitable to seal. 10 The pavement is very compact and has no defects such as potholes, rutting or corrugations. A small 40m section is generating dust due to some running course that was spread inadvertently by contractors.

An initial heavy rain event two days after the treatment has not affected the performance of the product and has demonstrated the dust suppressant resists 15 leaching out during rainfall. Several light rain events since then have confirmed this aspect further.

It was noted that the minor volume of dust generated dissipated quickly upon the passage of the vehicle.

Control Section The control section has been regraded since the initial treatment. The surface is covered in a thin layer of loose aggregate and has only moderately less traction than the trial section with no potholes or other defects evident.

However as the aggregate has been recently regraded the dust generation is extreme. During photographing of a vehicles passage and the dust generated, it was often dangerous as visibility completely disappeared. Significant volumes of dust were dispersed and the dust tended to linger for some time after the vehicles departure. It was estimated that the dust generated was several times greater than the treated section.

Although the surface had been regraded, loose aggregate was noted as being retained in the watertable and will be lost prior to the next regrade with a subsequent need for aggregate replacement.

Condition Six Weeks Trial Section The section still exhibits adequate dust reduction and presents a surface that is safe, with very little loose aggregate and provides good skid resistance. The pavement is dense and compact and shows no signs of rutting, corrugations or defects.

The trial section had 6 potholes present with a depth of 25mm on the right hand size of the carriageway approximately 2.0m from the centreline. However overall 15 pavement shape has been maintained and no rutting was evident along the length.

Control Section The control section exhibits dust generation at approximately double that of the trial. As the surface was regraded some four weeks ago the loose aggregate has now migrated into four separate windrows which present a traffic hazard should a car 20 travel into them. The loose aggregate is also a hazard in terms of flying debris for oncoming windscreens and is often lost into the watertable prior to the next regrade with a subsequent need for aggregate replacement. 31 The pavement has corrugations in several areas of a total length of 120m and has 26 potholes. Due to the corrugations and windrows of loose aggregate the overall pavement shape is now poor and well outside requirements.

Condition 12 Weeks 5 Trial Section The section has had continuous rain for a period of ten days and presents a surface that is safe, with very little loose aggregate and provides good skid resistance under wet conditions. The pavement is dense and compact and shows limited signs of rutting for a length of 50m to a depth of 20mm The trial section had 19 potholes present with a depth of 25mm on both sides of the carriageway generally 2.0m - 2.5m from the centreline.

Control Section Due to the above mentioned rain there is also no dust generated on the control section. The loose aggregate has been retained in four separate windrows which 15 present a traffic hazard should a car travel into them. The pavement has corrugations in several areas of a total length of 80m and has 42 potholes. Rutting is evident on approximately 400m of the length to a depth of 80mm representing a significant safety aspect.

Due to the rutting, corrugations and windrows of loose aggregate the overall 20 pavement shape is now poor and well outside requirements.

Further Various Dust Suppressant Characteristics A number of dust suppressant properties and characteristics may be determined from these experiments, such as: 32 • Application of the dust suppressant to an unsealed road surface reduces the rate of dusting by approximately factor of three to four.

• The current formulations improve physical road bed stability, as well as reducing dusting.

• The dust suppressant does not seem to wash out in water after it has dried on the roading material.

• Rate of consumption of the dust suppressant composition by biota is slow and it is unlikely to be consumed during dry periods when it is required most.

• The long term stability of diluted emulsion is poor. Diluting the emulsion to form 10 the dust suppressant just prior to use is essential.

• The more dilute emulsions while providing good initial dust prevention, limit the life of the road bed.

• Performance of dust suppressant is improved by using a HS content emulsion.

• A good balance between performance and cost is provided by a dilution of 15 around 1:100 to result in a dosage rate of around 0.3% of dust suppressant solids on the aggregate, but this dosage will vary with aggregate type.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof. 33

Claims (27)

WHAT WE CLAIM IS:

1. A dust suppressant composition for application to a substantially soil particle laden surface including (i) a saponified tall oil pitch, and (ii) a salt, wherein said composition is an emulsion characterised in that the salt is present in an emulsion destabilising amount.

2. A dust suppressant composition as claimed in any one of the preceding claims, wherein said dust suppressant includes mineral oil.

3. A dust suppressant composition as claimed in any one of the preceding claims, wherein said dust suppressant includes an aqueous component, such as water.

4. A dust suppressant composition as claimed in any one of the preceding claims, wherein the dust suppressant is diluted with an aqueous component to a dilution of about 1 part dust suppressant composition: 1 parts aqueous component or less.

5. A dust suppressant composition as claimed in any one of the preceding claims, wherein the dust suppressant is diluted with an aqueous component to a dilution of about 1 part dust suppressant composition: 2 parts aqueous component or less.

6. A dust suppressant composition as claimed in any one of the preceding claims, wherein the dust suppressant is diluted with an aqueous component to a dilution of about 1 part dust suppressant composition: 25 parts aqueous component or less.

7. A dust suppressant composition as claimed in any one of the preceding claims, wherein the dust suppressant is diluted with an aqueous component to 34 a dilution of about 1 part dust suppressant composition: 50 parts aqueous component or less.

8. A dust suppressant composition as claimed in any one of the preceding claims, wherein the dust suppressant is diluted with an aqueous component to 5 a dilution of about 1 part dust suppressant composition: 100 parts aqueous component or less.

9. A dust suppressant composition as claimed in any one of the preceding claims, wherein the dust suppressant is diluted with said aqueous component to a dilution of about 1 part dust suppressant composition: 250 parts aqueous 10 component or less.

10. A dust suppressant composition as claimed in any one of the preceding claims, wherein the dust suppressant is diluted with said aqueous component to a dilution of about 1 part dust suppressant composition: 1000 parts aqueous component or less. 15

11. A dust suppressant composition as claimed in any one of the preceding claims, wherein the dust suppressant is diluted with said aqueous component to a dilution of about 1 part dust suppressant composition: more than 1000 parts aqueous component.

12. A dust suppressant composition as claimed in any one of the preceding 20 claims, wherein, the pH of the dust suppressant is buffered to greater than pH 7.

13. A dust suppressant composition as claimed in any one of the preceding claims, wherein, the pH of the dust suppressant is buffered to be about pH 11. 35

14. A dust suppressant composition as claimed in any one of the preceding claims, wherein, said salt is an inorganic salt.

15. A dust suppressant composition as claimed in any one of the preceding claims, wherein, said salt is selected from one or more of the following: lime, 5 slaked lime, KOBM slag, cement, fly ash, gypsum, bassinite, anhydrite, or calcium salts.

16. A dust suppressant composition as claimed in any one of the preceding claims, wherein, said dust suppressant composition includes a soil stabiliser.

17. A dust suppressant composition as claimed in any one of the preceding 10 claims, wherein, said soil stabiliser is selected from one or more of the following: lime, slaked lime, KOBM slag, cement, fly ash, gypsum, bassinite, anhydrite, calcium salts.

18. A dust suppressant composition as claimed in any one of the preceding claims, wherein, the soil stabiliser includes KOBM slag, and one or more 15 initiators.

19. A dust suppressant composition as claimed in any one of the preceding claims, wherein, said initiators are selected from the following group potassium chloride, sodium silicate (water glass), calcium hydroxide (slaked lime), sodium metasilicate (anhydrous), sodium carbonate (soda ash), sodium hydroxide 20 (caustic soda), lime oxide.

20. A dust suppressant composition as claimed in any one of the preceding claims, wherein, the soil stabiliser is a soil stabiliser as claimed in New Zealand Patent No. 332204. 36

21. A method of use of a dust suppressant composition, wherein said substantially soil particle laden surface is coated with at least a monolayer of dust suppressant composition as claimed in any one of the preceding claims sufficient to cause particles to substantially agglomerate. 5

22. A method as claimed in claim 21, wherein the dust suppressant composition is blended with an emulsion destabilising salt prior to application to the soil particle laden surface.

23. A method as claimed in claim 21 or claim 22 wherein, said method also comprises the steps of: 10 i. spreading an emulsion destabilising amount of a salt onto a soil particle laden surface, and ii. spreading the dust suppressant composition onto said salted surface.

24. A method as claimed in any one of claims 21 to 23, wherein said method further includes the step of: 15 iii. mixing said emulsion destabilising salt and the soil particle laden surface together.

25. A method as claimed in any one of claims 21 to 24, wherein said mixing step is performed by a stabiliser machine and/or grader.

26. A dust suppressant composition substantially as hereinbefore described and 20 with reference to any one of the accompanying examples.

27. A method of use of a dust suppressant composition substantially as hereinbefore described and with reference to any one of the accompanying examples. 37