RAYNOR, Dean (20 Chappelfield Way, Thorpe Hesley, Rotherham South Yorkshire S61 2TL, GB)
BAGGALEY, Craig (37 Norstead Crescent, Bramley, Rotherham South Yorkshire S66 2SH, GB)
JONES, Nick (191 Wickersley Road, Rotherham South Yorkshire S60 4JP, GB)
RAYNOR, Dean (20 Chappelfield Way, Thorpe Hesley, Rotherham South Yorkshire S61 2TL, GB)
BAGGALEY, Craig (37 Norstead Crescent, Bramley, Rotherham South Yorkshire S66 2SH, GB)
| CLAIMS A high-friction coating for hard surfaces comprising an aggregate, wherein the aggregate comprises particles of an electric arc furnace carbon steel slag having a mean particle size of from 1 mm to 5 mm, eg with particle sizes of from 1 to 5 mm. A coating according to Claim 1, wherein the aggregate includes particles of EAF carbon steel slag of a size fraction selected from 1/3 mm and/or 3/5 mm. A coating according to Claim 2, comprising particles of EAF carbon steel slag from the 1/3 mm and 3/5 mm size fractions, wherein the ratio by weight of the 1/3 mm size fraction to the 3/5 mm size fraction is from 1 : 10 to 10 : 1. A coating according to Claim 1, Claim 2 or Claim 3 further comprising a binder. A coating according to Claim 4, wherein the binder comprises a curable or hardenable resin. 6. A coating according to Claim 5, wherein the resin is selected from a polyurethane, an epoxy, an acrylic, acrylate or methacrylate, or a thermoplastic resin. A coating according to any one of the preceding Claims further comprising at least one pigment, dye or other coloured substance, which imbues the coating with a desired colour. 8. A coating according to any one of the preceding Claims further comprising a reflective composition. A coating according to any one of the preceding Claims, wherein the aggregate contains particles of other slags and/or natural aggregates and/or artificial aggregates. A coating according to any one of the preceding Claims, wherein the particles of the EAF carbon steel slag make up more than 50 wt% of the aggregate. A coating according to any one of the preceding Claims having a thickness of approximately 1 to 30 mm, 1 to 25 mm, 1 to 20 mm, 1 to 15 mm, 1 to 10 mm, 1 to 9 mm, 1 to 8 mm, 1 to 7 mm, 1 to 6 mm or 1 to 5 mm, e.g. 1 to 3 mm. An area of a hard surface having applied thereto a high-friction coating according to any one of Claims 1 to 11. A road comprising a surface layer having applied thereto a high- friction coating according to any one of Claims 1 to 11. A method of coating a hard surface comprising : • selecting an area of the surface to be coated; • applying a curable or hardenable binder to the area; • depositing an aggregate comprising particles of electric arc furnace carbon steel slag having particle sizes of from 1 mm to 5 mm on the binder; and • curing or hardening the binder. A method according to Claim 14, wherein the aggregate is deposited on to the binder in excess. 16. A method according to Claim 15, further comprising the step of collecting free particles of aggregate for subsequent use. 17. A method according to any one of Claims 14 to 16 comprising pressing the particles of aggregate into the binder. 18. A method of coating a hard surface comprising : • mixing an aggregate comprising particles of EAF carbon steel slag having particle sizes of from 1 mm to 5 mm with a curable or hardenable binder, preferably a thermoplastic binder, to produce a mix; · applying the mix on to an area of the surface; and • curing or hardening the binder. A method according to any one of Claims 14 to 18 comprising the step of drying the area to substantially remove or at least minimise any moisture present in or on the surface before applying the coating thereto. A method according to any one or Claims 14 to 19 comprising the preliminary steps of: obtaining carbon steel slag produced in an electric arc furnace; drying the slag; crushing the slag; and screening the crushed slag to provide particles of aggregate within the desired particle size range. Use of electric arc furnace carbon steel slag in a high friction coating for hard surfaces. Use of electric arc furnace carbon steel slag according to Claim 21 wherein the electric arc furnace carbon steel slag comprises a particle size of from 1 mm to 5 mm, e.g. 1 mm to 3 mm. |
The present invention relates to surfaces, in particular hard surfaces such as roads, runways, walkways and the like. More specifically, the invention relates to high-friction coatings for such surfaces and, in particular, for selected areas of such surfaces.
It is known to apply high-friction coatings to roads in order to improve safety. High-friction coatings may be especially beneficial at approaches to junctions and roundabouts and on tight corners.
Road surfaces typically comprise asphalt. Once compacted, the road provides a substantially smooth waterproof surface. The surface provides a number of purposes, including sealing and improving the appearance of the road.
In contrast, a high-friction coating is a coating which is applied to standard surface in stretches where there is a high skid risk in order to improve safety on that particular stretch of road .
In relation to road surfaces, the British Board of Agrement identifies a number of suitable areas for use of high-friction surface coatings, which are set out in Table 1 below (source: Guidelines Document for the Assessment and certification of High-Friction Surfacing for Highways, March 2008).
Site definition Maximum traffic levels (commercial vehicles per lane per day)
Type 1 Type 2 Type 3
Approaches to and across major
junctions, approaches to roundabouts
Gradients of 5% to 10%, longer than
50 m 3500 1000 250
Bend radius < 500 m - dual
carriageway
Roundabout
Gradient > 10%, longer than 50 m
Bend radius < 500 m - dual 2500 750 175 carriageway
Approach to pedestrian crossing and
other high risk situations 2500 500 100
Table 1 In the UK, a high-friction road surface coating is typically expected to have an in-service lifetime of from 5 to 10 years.
High-friction coatings for roads typically contain an aggregate. The choice of aggregate is one of the variables which affect the friction characteristics, e.g. skid resistance, of the coating.
Natural aggregates such as greywacke, granite, tertiary basalt and gritstone have been used in high-friction surface coatings for roads. More recently, calcined bauxite, an artificial aggregate, has been preferred, because it may have a higher skid resistance value. Moreover, since it is artificial, its properties and characteristics may be more uniform leading to more predictable performance. However, calcined bauxite is relatively expensive due to the costs of manufacture and transportation, e.g. shipping from far-flung areas of production such as China and Guyana, and upward pressure on prices caused by periodic tightness of supply. Long haul transportation also has a deleterious impact on the environment.
It is an object of the current invention to provide a further high friction surface material which does not suffer from the problems of the prior art.
A first aspect of the invention provides a high-friction coating for hard surfaces, e.g. metal, asphalt, concrete or tarmac surfaces such as roads, comprising an aggregate, wherein the aggregate comprises particles of an electric arc furnace (EAF) carbon steel slag having a mean particle size of from 1 mm to 5 mm, e.g. from 1 mm to 3 mm and/or 3 to 5 mm. A further aspect of the invention provides a high-friction coating for hard surfaces, e.g. metal, asphalt, concrete or tarmac surfaces such as roads, comprising an aggregate, wherein the aggregate comprises particles of an electric arc furnace (EAF) carbon steel slag having particle sizes of from 1 mm to 5 mm, e.g. from 1 mm to 3 mm and/or 3 to 5 mm.
Preferably, the aggregate comprises particles of EAF carbon steel slag having a distribution with one or more maxima of from 1 mm to 5 mm, e.g. from 1 mm to 3 mm and/or 3 to 5 mm.
Preferably, the aggregate includes particles of EAF carbon steel slag of at least one size fraction, e.g. one or more of 1/3 mm and 3/5 mm.
The term size fraction will be readily understood by persons skilled in the art. For instance, in the UK, a given batch of particles is assigned to the 1/3 mm size fraction if at least 95% of the particles pass through a 3.35 mm sieve, while no more than 5% of the particles pass through a 1.18 mm sieve. The coating may comprise particles of EAF carbon steel slag from the 1/3 mm and/or the 3/5 mm size fraction. For instance, the ratio by weight of the 1/3 mm size fraction to the 3/5 mm size fraction may be from 1 : 10 to 10 : 1. Accordingly, the distribution of particles may be bi- modal. Clearly, other size fractions of particles may be utilised.
The selected distribution of particle sizes may reflect local supply and/or the demands of the intended end-use of the coating . The chemical composition of the EAF carbon steel slag may vary, depending upon the steelmaking plant and/or process from which it originates. Nevertheless, the benefits of the invention generally will be realised irrespective of the specific composition of the EAF carbon steel slag .
The coating may further comprise a binder. Preferably, the binder may comprise a curable or hardenable resin. The resin may be a polyurethane, epoxy, acrylic, acrylate or methacrylate or thermoplastic resin.
For example, a hardener comprising triethylenetetramine may be used to harden an epoxy resin.
The coating may further comprise at least one pigment to imbue it with a desired colour and/or a reflective composition to render it reflective. For instance, the particles of aggregate may be coated with a coloured and/or reflective substance. Alternatively or additionally, a dye may be dispersed within the binder. In addition to particles of the EAF carbon steel slag, the aggregate may contain other species, e.g. particles of one or more other slags and/or one or more natural aggregates and/or one or more artificial aggregates. Suitably, the other slags may include melter slag and/or basic oxygen steelmaking slag. Suitably, the natural aggregates may include greywacke, granite, tertiary basalt and/or gritstone. Calcined bauxite may be a preferred artificial aggregate.
Typically, the particles of the EAF carbon steel slag may make up more than 50 wt%, preferably more than 55, 60, 65, 70, 75, 80, 85, 90, 95 or 100 wt%, of the aggregate.
The high-friction coating may have a thickness which is approximately equal to or larger than the nominal size fraction of the aggregate. Thus, in preferred embodiments, the high-friction coating may comprise a thickness of between approximately 1 mm to 5 mm, e.g. 1 to 4 or 3 or 2 mm. In other embodiments the high-friction coating may have a thickness of 1 to 30 mm, 1 to 25 mm, 1 to 20 mm, 1 to 15 mm, 1 to 14 mm, 1 to 13 mm, 1 to 12 mm, 1 to 11 mm, 1 to 10 mm, 1 to 9 mm, 1 to 8 mm, 1 to 7 mm or 1 to 6 mm. The volume ratio of EAF particles to binder may be from 20 : 1 to 1 : 20.
A third aspect of the invention provides an area of a hard surface, preferably a metal, asphalt, concrete or tarmac surface such as a road, having applied thereto a high-friction coating according to the first aspect of the invention.
Another aspect of the invention provides a road comprising a layer of a surface, for example asphalt or a surface dressing, having applied thereto a high-friction coating according to the first aspect of the invention.
Another aspect of the invention provides a method of coating a hard surface, e.g. a metal, asphalt, concrete or tarmac surface such as a road, comprising :
• selecting an area of the surface to be coated; • applying, e.g. pouring and/or spreading, a curable or hardenable binder to the area;
• depositing, e.g. sprinkling, an aggregate comprising particles of EAF carbon steel slag having particle sizes of from 1 mm to 5 mm, e.g. from 1 to 3 mm and/or from 3 to 5 mm, on to the binder; and
• curing or hardening the binder.
The aggregate may be deposited, e.g. sprinkled on to the binder manually or by machine. The person skilled in the art will be familiar with ways of doing this. The aggregate may be deposited on to the binder in excess, which is to say in an amount in which some of the aggregate particles remain free on top of the coating after the binder has been cured . Free particles of aggregate may be collected for subsequent use, e.g. as a component of a surface coating at another location.
Additionally or alternatively, the aggregate particles may be pressed, e.g. rolled, into the binder.
Yet another aspect of the invention provides a method of coating a hard surface, e.g. an asphalt, concrete or tarmac surface such as a road, comprising : mixing an aggregate comprising particles of EAF carbon steel slag having particle sizes of from 1 mm to 5 mm, e.g. from 1 to 3 mm and/or from 3 to 5 mm, with a curable or hardenable binder, preferably a thermoplastic binder, to produce a mix; applying, e.g. extruding, pouring and/or spreading, the mix on to an area of the surface; and
curing or hardening the binder. Typically, the binder may be susceptible to moisture. Accordingly, it may be necessary to dry, e.g. using heating means such as a thermic torch, the area of the surface to be coated, in order to substantially remove or at least minimise any moisture present before applying the coating (i.e. before applying the binder or the mix). This preliminary drying step may be required even in hot, dry climates.
Similarly, it may also be necessary to dry the aggregate, prior to bringing it into contact with, e.g. by mixing with, the binder, in order to substantially remove or at least minimise any moisture present.
The aggregate may be produced by obtaining carbon steel slag produced in an electric arc furnace, drying the slag, crushing the slag, e.g. in order to break up large particles, and screening the crushed slag to provide particles of aggregate within the desired particle size range(s).
Depending on the initial characteristics of the slag, it may not be necessary to carry out all of these steps in order to produce aggregate for the coating . For instance, the dried slag may not need to be crushed prior to screening.
Beneficially, the coating of the present invention makes use of a byproduct in the form of a slag, namely EAF carbon steel slag .
A yet further aspect of the invention provides for the use of electric arc furnace carbon steel slag in a high-friction coating for hard surfaces.
Preferably, the electric arc furnace carbon steel slag comprises a particle size of from 1 to 5 mm, e.g. 1 to 3 mm and/or 3 to 5 mm.
Accordingly, high-friction surface coatings according to the present invention may be relatively inexpensive and/or energy efficient to produce in comparison with surface coatings comprising calcined bauxite. Furthermore, use of high-friction surface coatings according to the invention may have a reduced environmental impact, particularly as compared with coatings containing calcined bauxite, not least because shipping and other transportation emissions typically would be lower.
High-friction surface coatings according to the present invention may offer similar benefits over coatings comprising natural aggregates, since these will need to be extracted, e.g. mined or quarried.
Moreover, surface coatings comprising EAF carbon steel slag as aggregate may retain their high-friction properties in situ better than coatings comprising other slag types, e.g. basic oxygen steelmaking slag .
In addition, the applicant has found that improved high-friction performance may be achieved by using relatively small EAF carbon steel slag aggregate particles, i.e. having particle sizes of from 1 mm to 5 mm, in high-friction surface coatings, as compared with using considerably larger particles.
Advantageously, use of EAF carbon steel slag in combination with other aggregate species may reduce the cost of a high-friction coating, e.g. in embodiments where the EAF carbon steel slag is used in combination with calcined bauxite, since the coating may include proportionally less of a more expensive material than would otherwise be the case.
The applicant has conducted studies to demonstrate that the performance of EAF carbon steel slag as aggregate in high-friction surfaces is good enough for use on areas of road surfaces.
Three high-friction surfacing test specimens were tested according to the methods detailed in TRL Report 176 (1997) with amendments from the Guidelines Document for the Assessment and Certification of High- Friction Surfacing for Highways (British Board of Agrement, 2006).
Tests were carried out on three specimens (A, B, C) containing EAF carbon steel slag . The nominal aggregate particle size fraction for all of the samples was 1/3 mm.
An in-service lifetime of 5 to 10 years was simulated by testing the specimens using a road test machine for the equivalent of 100,000 wheel passes. After 100,000 wheel passes the specimens were assessed for changes in texture depth, erosion index and skid resistance. The test was stopped periodically to make intermediate assessments of the specimens. Texture depth was determined using the sand patch method in accordance with TRL Report 176 (1997) Appendix D with amendments from the Guidelines Document for the Assessment and Certification of High-Friction Surfacing for Highways (British Board of Agrement, 2006). The results are summarised in Table 2 below.
Table 2
After 100,000 wheel passes, the mean texture depth for the specimens (A, B, C) containing EAF carbon steel slag was 1.68 mm.
Erosion index is a visual assessment of the amount of surface erosion, i.e. aggregate loss. For all of the specimens (A, B, C), the erosion index after 100,000 wheel passes was 0, indicating no or very little aggregate loss. Skid resistance value was determined in accordance with TRL Report 176 (1997) Appendix E with amendments from the Guidelines Document for the Assessment and Certification of High-Friction Surfacing for Highways (British Board of Agrement, 2006). The results are shown in Table 3 below.
Table 3 After 100,000 wheel passes, the mean skid resistance value for the specimens (A, B, C) was above 70.
The applicant's experiments also found that the skid resistance value for specimens containing EAF carbon steel slag did not fall significantly after initial polishing. In contrast, comparative tests showed that the skid resistance value for specimens containing calcined bauxite fell more markedly after initial polishing.
Some relevant laboratory performance criteria for wear after 100,000 wheel passes, as specified by the British Board of Agrement, are set out in Table 4 below (source: Guidelines Document for the Assessment and certification of High-Friction Surfacing for Highways, 2006).
Table 4 The applicant's tests show that high-friction surface coatings comprising 1/3 mm particles of EAF carbon steel slag meet the specified requirements for Type 1, Type 2 and Type 3 road areas. For Type 2 and Type 3 road areas, in particular, such high-friction surface coatings would clearly be more than adequate.
Thus, the data suggest that EAF carbon steel slag may be fairly widely used as an aggregate in a high-friction surface coating, e.g. instead of calcined bauxite. This may achieve economic and environmental benefits, in terms of reductions in the cost of manufacture and/or transportation, lower energy consumption and increased recycling of slag .
High-friction coatings according to the invention may be applied to existing road surfaces to improve safety. Equally, the high-friction coatings of the invention may be laid down during the building of new roads or may be used to replace or repair old, worn or damaged high friction coatings. While the invention has been described in respect of roads, it is envisaged that other areas of hard surfaces, both natural and artificial, may benefit from the high-friction coating of the invention, e.g. station platforms, footpaths, pavements, walkways, step runners, cycle paths, towpaths or bridleways. For example, the high-friction coating may be applied to metal walkways, gangways, ladders and the like in industrial premises, thereby improving safety for workers.
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