EP0034296A1

EP0034296A1 - Surface treatment

Info

Publication number: EP0034296A1
Application number: EP81100755A
Authority: EP
Inventors: Philip James Deane; Arthur Roger Williams
Original assignee: Dunlop Ltd
Current assignee: Dunlop Ltd
Priority date: 1980-02-15
Filing date: 1981-02-03
Publication date: 1981-08-26
Also published as: JPS56128807A; GB2071520A; DK64381A; CA1139974A

Abstract

A method and apparatus suitable for treating a surface, e.g. that of a road, which comprises at least one aggregate (8) in a binder matrix (9). The invention resides in applying fine abrasive particles (11) each having a mean diameter of up to 500 microns so that they will be bonded only to those portions of aggregate (8) in the binder matrix (9) which will be directly exposed to wear. The method is applicable to new or old surfaces and alsoto runways, pavements and sports surfaces.

Description

This invention relates to a method and apparatus suitable for treating a surface, e.g. that of a road, and to the novel treated surface produced thereby.
In conventional road surface constructions at least one aggregate is combined in a binder matrix and applied where required by suitable means. The friction level i.e. skid- resistance of the resulting road surface generally takes the following path: a) initially there is a high level of friction provided by the fine aggregates ("fines") used in the mix. These are worn away by the action of traffic, leaving a thin film of binder covering the aggregate surface b) this binder film masks the microtexture of the aggregate and thus results in a low level of friction. c) once this binder film has worn away, the microtexture of the aggregate is exposed and the friction level rises d) further traffic action polishes the aggregate, i.e. removes the microtexture, thereby causing the friction level to fall until eventually it will reach a stage where its friction level is too low for safety.
There are thus two stages at which the friction level can fall below a safe level i.e. "b)" when the fines have been worn away but the thin film of binder is still present, and "d)" when the exposed aggregate has been polished to a low microtextural level by the action of traffic. Incidentally, the time taken for a particular road surface to reach these stages is dependent upon a number of factors including the type of aggregate and binder, the volume of traffic, the speed at which traffic travels on the road (at higher speeds a higher friction level is required for safety), the frequency of rain (wet surfaces require a higher friction level for safety)and the geometry of the site.
There are two traditional solutions to this problem. The first is to apply to the road surface a layer of hot bitumen- coated aggregate particles, usually 14 to 19 mm in size, having first spray-coated the road surface with a tack coat of bitumen. This solution, known as surface dressing, restores both microtexture and macrotexture but the resulting surface will follow the path outlined above with its two attendant disadvantageous stages "b" and "d". Furthermore the adequate retention of the aggregate particles can be a problem; they will often have no mechanical interlock with the underlying surface and will therefore only be held by the binder film. The forces applied to these large aggregate particles by the action of traffic will often be sufficient to dislodge them from the surface, resulting in considerable damage to passing traffic usually in the form of chipped paintwork and broken windscreens.
The second solution to the problem is to combine aggregate particles in an epoxy resin binder and apply this to the entire surface. Again, this improves both microtexture and macrotexture. The disadvantage of this system is the high cost involved.
The present invention aims to overcome these disadvantages by providing a relatively cheap and simple method of improving the microtextural character of aggregate particles in a binder matrix. The invention is particularly useful both in the early life of a road surface (problem stage "b)" and when the road surface has been exposed to trafficking for a time (problem stage "d)".
According to one aspect of the present invention, a composite suitable for use as the surface of a road, runway, pavement, sports surface or the like comprises at least one aggregate in a binder matrix bonded to particles, characterised in that the particles are fine abrasive particles each having a mean diameter of up to 500 microns and said particles are bonded substantially only to those portions of aggregate in the binder matrix which will be directly exposed to wear.
According to a further aspect of the present invention a method suitable for treating the surface of a road, runway pavement, sports surface or the like comprising at least one aggregate in a binder matrix is characterised in that fine abrasive particles each having a mean diameter of up to 500 microns are applied to the surface so that said particles will be held substantially only by those portions of the surface which will be directly exposed to wear.
According to yet another aspect of the present invention, an apparatus for treating the surface of at least one aggregate in a binder matrix is. characterised in that it comprises means for applying a binder to the surface and in tandem therewith means for applying to the resulting binder-coated surface fine abrasive particles each having a mean diameter of up to 500 microns.
Aggregate materials suitable for use as the fine abrasive material are those derived from aggregates having a maximum aggregate crushing value as specified in BS 812:1975 of not more than 30. Materials derived other than from aggregates, e.g. metals, must be of an equal performance to this e.g. having a hardness of at least 1 and preferably at least 2 on the Moh scale of hardness.
Preferably at least 50% by weight of the fine particles each have a mean diameter in the range 50 to 250 microns. Examples of suitable materials include crushed naturally occurring gritstones e.g. "Gilfach", "Craig-yr-Hess" and "Millstone grit", artificial aggregates, e.g. crushed calcined bauxite, slags and emeries.
Where an aggregate/binder matrix is to be coated according to the present invention and uncoated aggregate particles ,tre exposed to the surface it will be necessary to apply a fresh coating of the same or a different binder to the surface to which the fine particles will adhere.
This is also a solution to the problem of coating an aggregate/ binder matrix where the binder is in the solid, tack-free state e.g. in the case of a road surface which is not newly laid. An alternative approach to this latter operation is to soften the existing binder to a tacky state before applying the fine particles.
Examples of aggregate/binder matrices the surfaces of which may be treated according to the present invention include road, pavements, runways, sports surfaces and the like. The present invention can be used both to restore a worn or old surface and to provide a top-coat for a newly laid surface. This can be done by coating only the uppermost portions with binder as it is only where there is binder that the fine particles will remain. The apparatus of the present invention can be used to achieve this result by designing the means for applying the binder so that it is only applied to'the uppermost aggregate surfaces and/or by ensuring that the binder is sufficiently viscous not to flow over the entire surface and has sufficient tack to hold the fine particles applied thereto. This preferred method of treatment is intended to improve the microtexture, i.e. roughness, of the individual aggregate . particles.
The abrasive material can be applied in dry form or in a binder. The proportion of binder must be sufficiently great to hold the abrasive particles to each other but not so great as to mask the microtexture of the abrasive particles. If desired further dry abrasive particles may be dusted onto the resulting surface.
Preferably at least 160 g/m² of dry fine abrasive material is applied to the underlying substrate. Where the abrasive material is applied as a paste in a binder, e.g. 50/50 by weight, preferably at least 250 g/m2 is applied to give an average film thickness of 0.14 mm.
By way of example only, two embodiments of the method of the present invention, both of which relate to the top-coating of a newly laid road surface but which equally apply to top-coating a new runway, pavement, sports surface or the like, are as follows:

(i) After a road surface comprising aggregate particles in a binder matrix has been laid and while the binder (which may be of e.g. bitumen or a specialised surface dressing type such as rubberised bitumen or epoxy-bitumen) is still warm, fine particles are applied dry, warmed and in excess. The excess material may be left to be dispersed naturally or removed, e.g. by suction, where the cost of the material warrants it and/or if there is a possibility that the drainage channels either between the individual aggregate particles in the road surface or within the body of a porous road surface become blocked by excess material.
(ii) After the road surface comprising aggregate particles in a binder matrix has been laid, a film of a different binder is applied to the road surface. Fine particles are then applied to the surface and the excess material can be dealt with as described in (i). This process allows two different types of binder to be used if desired so that the properties of each can be selected to suit the requirements of different layers of the road structure.

The binder to which the fine material adheres may be selected from e.g. bitumen, tar, epoxy-bitumen, bitumen- polymer blend or an epoxy resin.
A preferred embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a simplified representation of a machine for applying binder and fine partic!.es to a new or old road or similar surface;
Figure II is a section of the resulting treated surface, and
Figure III is a sectional view of the uppermost portion of a single aggregate particle in the treated surface shown in Figure II.

Referring now to Figure I, the machine 1, which may or may not be self-propelled, includes a binder reservoir (not shown) provided with means for heating the binder to its working temperature, means (not shown) for controlling the flow rate of the binder and, in communication with the binder reservoir, a spreader bar 2 provided with an outlet 2b for applying binder to the uppermost surface of the road 3. In tandem with the binder applicator is dusting means 4 for applying fine abrasive material to the coated road surface. The dusting means may simply be (as shown) a tapered outlet 4 for the fine material in the reservoir 5. The outlet is usually provided with closure means (not shown) which would come into operation when the machine is not in use and means (not shown) for controlling the flow rate of the material. Suction means 7 may be provided to remove the excess fine material from the road surface and to transfer it back into the reservoir.
In use, the machine 1 is moved over the road surface to be treated, binder is applied to the uppermost portion of the surface by means of the spreader bar 2 and immediately following this, fine material is dusted in excess from the tapered outlet 4 onto the binder-coated road surface. The viscosity of the binder is selected so that it is sufficiently viscous not to flow over the entire road surface but has sufficient tack to hold the fine particles.
If excess fine material is to be removed, suction is applied through the suction means 7 and the excess material is thereby returned to the reservoir 5.
As shown in Figures II and III, the product of the method and apparatus described with reference to Figure I is a road surface comprising particles 8 coated with binder 9 and provided with a new coating of binder 10 on the uppermost portions, adhered to which are fine particles 11.
The invention is further illustrated by the following Examples in which the materials referred to are as follows:
The testing procedure adopted for each sample was that described for polished stone value (PSV) contained in BS 812:1975. Each sample consists of a single layer of 35 to 50 polished aggregate particles packed as closely as possible and covering an area of 90.6 x 44.5 mm, set in a thin resin mortar so that the aggregate surfaces were exposed. The samples were subjected to a polishing action to simulate that which would occur in a road surface and then the residual frictional resistance was measured using a pendulum skid- tester. Samples tested in this way were then used as described in the Examples and the final "road surface" was tested in the same way to gauge the effect of the abrasive material applied.

EXAMPLE I

Two samples of each of seven different aggregates - blast furnace slag, Wimmis, Morraine, Basalt, Diabase, Enderby and LD - were heated in an oven and then the uppermost surfaces were coated with a film of bitumen. Calcined bauxite was applied in excess and rolled into the bitumen film. As shown by the results summarised in Table 1, the mean skid resistance rose from 47 (uncoated) to 94 after coating and fell to 58 during the six hour test. The skid resistance measured for each sample was found to be independent of the substrate.

EXAMPLE II

A paste consisting of about 50% by weight resin/50% by weight calcined bauxite was applied as a relatively thick coating to the uppermost surfaces of various types of aggregate. Dry bauxite particles were then dusted over the coatings. The uncoated aggregates had PSV's in the range 44 to 79 with a mean of 61. Twelve samples were tested in all. Table 2 summarises the mean skid resistances of the coated samples. The standard deviation of the result was only 3.9, thus indicating that the result was independent of the aggregates used in the substrates.

EXAMPLE III

Four different methods of producing a total of 12 samples were employed:

(i) A thin resin film was applied to the uppermost surface of each of four aggregate samples.
(ii) A paste of resin and bauxite particles was applied as a thin coating to the uppermost surface of each of four samples.
(iii) Two samples were prepared as in (ii), but using Bridport pebble as the aggregate substrate. Bridport pebble presents a very smooth surface and therefore hindered any interlock with the surface treatment.
(iv) Two samples were made by a two stage process. Firstly, a bitumen film was applied to the uppermost surface of the aggregate and the sample was heated and then dusted with bauxite particles. An epoxy resin/bauxite paste was applied to this after the sample had been cooled.

The results of these tests are summarised in Table 3.

EXAMPLE IV

A series of fourteen samples were made:

(i) Three samples were produced by applying binder to the uppermost aggregate surface and then dusting this with bauxite particles. Thermoplastic rubber had been incorporated into the 100 penetration bitumen binder, in an amount equivalent to 10 parts by weight per 100 parts bitumen.
(ii) The binder used in (i) was used to make a paste with bauxite particles and this was then applied to the uppermost aggregate surface and then dusted with excess dry bauxite particles. Three samples were made in this way.
(iii) A paste was made from bauxite particles and a binder consisting of 95 parts bitumen/5 parts carbon black bitumen additive. This was then applied as a thin film which was subsequently dusted with dry bauxite particles. Three samples were made in this way.
(iv) A paste was made from bauxite particles and a binder consisting of 40 parts bitumen/60 parts epoxy resin. This was then applied as a thin film which was subsequently dusted with dry bauxite particles. Three samples were made in this way.
(v) A paste was made from bauxite particles and bitumen. This was then applied as a thin film which was subsequently dusted with dry bauxite particles. Two samples were made in this way.

All of these samples were subjected to polishing and measurement of their frictional properties according to BS 812. The samples were removed at different stages of the test and their skid resistance measured. The standard test consisted of polishing the samples under wet application of a coarse abrasive for three hours, followed by fine polishing for three hours. The skid resistance value at the end of the six hour test was termed the polished stone value (PSV).

TABLE 1

Results of Example I

Method of coating Thin coating of bitumen/bauxite paste followed by dusting with excess bauxite particles Number of samples : 12.

Mean Skid Resistance Values

TABLE 2

Results of Example II

Method of coating : Thick coating of epoxy resin/bauxite paste followed by dusting with excess bauxite particles.
Number of samples : 12.
Mean Skid Resistance Values

Mean Weights of Coating Applied and Lost

Claims

1. A composite suitable for use as the surface of a road, runway, pavement, sports surface or the like comprises at least one aggregate (8) in a binder matrix (9) bonded to particles (11), characterised in that the particles (11) are fine abrasive particles each having a mean diameter of up to 500 microns and said particles are bonded substantially only to those portions of the aggregate (8) in the binder matrix (9) which will be directly exposed to wear.

2. A composite according to Claim 1 characterised in that the fine abrasive particles are bonded to the aggregate in the binder matrix by means of an interlayer of an identical or different binder (10).

3. A composite according to Claim 1 or 2 characterised in that at least 50% by weight of the fine abrasive particles each have a mean diameter in the range 50 to 250 microns.

4. A composite according to Claim 1, 2 or 3 characterised in that the fine abrasive particles comprise at least one aggregate having a maximum aggregate crushing value as specified in BS 812:1975 of not more than 30.

5. A composite according to any preceding claim characterised in that the fine abrasive particles constitute a coating of at least 16₀ g/_m ².

6. A method suitable for treating the surface of a road, runway, pavement, sports surface or the like comprising at least one aggregate (8) in a binder matrix (9) characterised in that fine abrasive particles (11) each having a mean diameter of up to 500 microns are applied to the surface so that said particles will be held substantially only by those portions of the surface which vill be directly exposed to wear.

7. A method according to Claim 6 characterised in that an identical or different binder (10) is applied substantially only to those portions of the surface which will be directly exposed to wear and then the abrasive particles (11) are applied in dry form.

8. A method according to Claim 6 characterised in that the abrasive particles are combined with a binder to form a paste which is then applied substantially only to those portions of the surface which will be directly exposed to wear.

9. A method according to Claim 8 characterised in that the paste is applied in amount of at least 250 g/m².

10. A method according to Claim 8 or 9 characterised in that the average layer thickness resulting from the paste is at least 0.14 mm.

11. An apparatus (1) suitable for treating the surface of at least one aggregate in a binder matrix (3) characterised in that it comprises means (2) for applying a binder to the surface and in tandem therewith means (4) for applying to the resulting binder-coated surface fine abrasive particles each having a mean diameter of up to 500 microns.