The present invention relates to a method and apparatus for treating road surfaces or the like to reinstate or improve the surface roughness thereof. The running surfaces or wearing courses of roads are commonly formed from an aggregate, such as stones or chippings, embedded in a matrix, such as a layer or mat of tar, asphalt, asphalt mix or other bituminous material, usually incorporating fillers id/or binders, laid on a sub-layer. The aggregate .articles are set and held in the matrix so as to project from the upper surface of the latter. The surface texture necessary to obtain the required charac¬ teristics, such as skid or slip resistance, depends upon a number of factors, including the texture ^or roughness of the individual aggregate particles (micro- texture), the overall texture or roughness of the road surface (macro-texture) determined by the degree of projection of the aggregate particles from the matrix (texture-depth), and the distribution and density of the aggregate particles in the matrix.

At low vehicle speeds, skid resistance appears to be determined mainly by the micro-structure of the exposed aggregate. At high vehicle speeds, for example above 50 mph, (80 KmpH).,. the skid resistance appears mainly to be determined by the macro-structure, and for this reason a minimum average texture depth of 1.5 mm. is desirable, and is currently specified for new high speed trunk roads in Great Britain.

This minimum texture depth is difficult to achieve with new surfacing, and is extremely difficult

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to maintain over a period of time. In use, the macro- texture deteriorates due to the accumulation of detritus and other debris, such as rubber, oil, fine grit, vegetable matter, etc, in the crevices in the road surface. In addition, the matrix or substances exuded therefrom tend to infiltrate the surface crevices, the aggregate tends to be depressed into the matrix, and the individual particles of the aggregate tend to turn in the matrix to present a lower profile, thereby further reducing the surface roughness. The micro-structure also deteriorates due to polishing of the exposed aggregate by the passage of traffic.

It has previously been proposed to clean road surfaces by spraying them with water, utilising pres¬ sures of the order of 100 pounds per square inch (psi) (7.03 Kg. er square err.) . It has also been proposed to clean airport runways by spraying with water at pressures of up to 1000 psi, (70.3 Kg. er square cm). However, such spray techniques only remove some of the debris, and do not restore the surface to a roughness approaching its original roughness.

Surface dressing using chippings and a bituminous binder is often used to restore existing road surfaces but this possesses many disadvantages, and is only applicable to minor and secondary roads subjected to relatively light, low speed traffic. The only practical way of restoring the surface roughness is to strip off and re-lay the uppermost layer or layers, which involves a large expenditure, is time consuming, and is inconvenient to road users.

It is an object of the present invention to

provide a method and apparatus for increasing or reinstating the surface roughness of a roadway or the like.

According to the present invention, in its broad- est aspect, this is achieved by impacting a high kinetic energy water jet on the road surface or the like.

According to the invention a method of treating a road surface or the like to reinstate or improve the surface roughness thereof is characterised by impinging a high kinetic energy water jet on the surface from at least one nozzle, and moving the nozzle in one direction (x) longitudinally of the surface whilst oscillating the nozzle transversely (y) of that direction and adjusting the pressure

(P) of water supplied to the nozzle, the flow rate (Q) through the nozzle, the jet displacement velocity (v) and the nozzle mean height (z) from the surface to obtain the desired scarifying treatment. The critical parameters in implementing the method and apparatus embodying the present invention, in order to achieve successful roughness of the road surface, are the hydraulic power per nozzle and the hydraulic power per unit area of the road surface. If the power or energy level is too high, the jet will damage, for example erode, the road surface and possibly also the underlying sub-layer. If the power or energy level is too low, the jet will not treat or scarify the surface sufficiently well to produce the required increase in the surface slip resistance or roughness. Various factors influence

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the power or energy level of the or each water jet. The power or energy level is dependent not only upon water pressure, but also upon the flow rate, the distance of the or each jet nozzle from the road surface, the jet pattern, and the velocity of displace¬ ment of the or each jet over the road surface.

The following is a table giving a list of values which have been found to define one practical applic¬ ation of the technique embodying the present invention:- Flow rate (Q) = 1 to 12 gallons/minute,

4.55 to 54.6 litres/minute Pressure (P) = 6,000 to 15,000 psi

422 to 1055 kg. per square cm Jet Nozzle Orifice Diameter (d) = 0.5 to 2.0mm. Jet Nozzle Mean Height (z) = 0.25 to 6 inches,

0.635 to 15.24 cm Jet Displacement Velocity (v) = 100 to 500 ft/minute,

30.48 to 152.40 metre/minute. Apparatus according to the invention for carrying out the method comprises a vehicle for movement longitud¬ inally of the surface characterised by a carriage mounted for transverse oscillatory motion below a chassis of the vehicle, nozzles supported by the carriage at a predetermined height (z) from and directed downwardly towards the surface, and means for the supply of high pressure water to the nozzles.

Suitably the predetermined height of the nozzles is adjustable, and means are suitably provided for adjusting the flow rate (Q) , the pressure (P), the jet displacement velocity (v) . Means are suitably also provided for variation of the rates of traverse of the nozzles both longitudinally and transversely relative to the surface, in particular so that paths of movement of the nozzles give the required coverage of the surface and overlap.

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In order that the invention may be more readily understood, reference will now be made to the accom¬ panying drawing, in which:-

Figure 1 is a perspective view illustrating schematically the principle of the invention;

Figure 2 is a schematic side view of one embodiment of apparatus; and

Figures 3, 4 and 5 illustrate schematically various alternative traverse patterns for the jet nozzles.

Referring to Figure 1 and the previous table, a plurality of spray nozzles, one of which is shown at 1, is carried by the apparatus shown in Figure 2 at a predetermined adjustable height _z above the road surface 2 to be treated. The road surface may be a freshly laid surface of which the surface texture or roughness S is to be enhanced, or an existing road surface having a surface texture which has deteriorated with time and use, and is to be restored. The nozzles 1 are connected by a line 3 to a high pressure pump (not shown)of a known type, which supplies water at the required- flow rate Q and high pressure P.

The -apparatus advances generally longitudinally along the road surface in the direction x. The nozzles 1 are mounted for movement relative to the apparatus so that their movement- includes a transverse component in the direction y, the compound movement being such that the nozzles traverse a predetermined width of the road surface, and such that the jet impact time is substantially uniformly distributed over the road surface, as the apparatus advances. The .resultant displacement of the nozzles, at one particular instant

in time, is represented by the vector v in Figure 1.

Referring to Figure 2, the apparatus or machine, which is shown in schematic form only, comprises a self-propelled vehicle having a chassis 4 mounted on sets of wheels 5 and 6. Forward or reverse drive is applied to the set of wheels 5 through a hydraulic motor and gear box mechanism 7, and the set of wheels 6 is steered through a hydraulic actuator or cylinder mechanism 8. Mounted beneath the chassis 4 is a carriage

9 which is mounted for horizontal, transverse swing¬ ing or oscillatory motion about a generally vertical axis 10. The transverse motion of the carriage is effected and controlled by a hydraulic motor and crank mechanism 11. The nozzles 1 are directly or indirectly mounted on an arm 9_a of the carriage 9, and are supplied with high pressure water via the line 3 connected to a pump and water reservoir (not shown). The pump and/or reservoir may be mounted on, or separate from, the vehicle, and may also be used to drive the various hydraulic motors and controls.

The nozzles may be arranged so as to execute oscillatory, orbital and/or linear translational movement. Various alternative nozzle mounting arrange- ments and movements will now be described with reference to Figures 3, 4 and 5.

In the Figure 3 arrangement, two generally horiz¬ ontal heads in the form of booms or disc-like spinners 12 are provided, each approximately 20 inches, 50.8 cm ^' in diameter and having between 2 and 6 and suitably four jet nozzles 1 circumferentially equi-spaced around its rim. The spinners are mounted below the carriage

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9 shown in Figure 2, and rotate at approximately 60 to 100 rpm about generally vertical axes or centres spaced approximately 3 ft 0.914 metre apart, in the transverse direction of the roadway (i.e. in the y direction in Figure 1). The spinners may be driven by an associated hydraulic motor or motors, although drive may be provided, or augmented, by the thrust generated by the nozzles. During advance or reverse travel of the apparatus, simultaneous transverse move- ment of the carriage oscillates or reciprocates the spinners transversely in unison so as to scan or sweep over approximately a 12ft 3166 metre width of roadway. The transverse oscillation causes the spinners to follow linear transverse zig zag paths represented by the overlapping circles in Figure 3, as the nozzles orbit about the spinner axes. The speeds of oscillation and rotation of the spinners are related to the speed of advance of the apparatus so as to provide the required coverage and overlap. Advantageously, the jets impinge on the surface substantially perpendicularly thereto, and to allow for the rotation of the spinners, this is achieved by inclining the jet nozzles forwardly, i.e. in the direction of rotation, at an angle of approximately o 20 to the vertical. The axes of rotation of the spinners may also be inclined, or adjustable in inclin¬ ation, for the same reason.

In the Figure 4 alternative, the nozzles 1 are fixed to the carriage 9, for example in two banks or rows of 2 to 6 and suitably four nozzles. During advance or reverse

travel of the apparatus and simultaneous oscillatory movement of the carriage, the nozzles follow the linear transverse zig zag paths as shown.

In the Figure 5 alternative, the nozzles l° ^r groups of nozzles are mounted for oscillation on oscil¬ latory heads 13, on the carriage 9 of Figure 1 so as individually to sweep out the arcs 14 shown. During advance or reverse travel of the apparatus and simult¬ aneous oscillatory movement of the carriage 9, the or each head 13 follows the linear transverse zig-zag path represented by a line passing through the centres of the associated succession of arcs 14.

It will be understood that the number of nozzles, heads, rows or banks of heads,etc., may be varied to suit requirements, and that the heads or nozzles may follow curved or orbital paths instead of linear paths. All of the various motions may be variable in speed, and may be reversible. The water pressure may be adjustable, and the supply to each nozzle, head or bank may be controllable, and may be capable of being switched on or off. The height of the nozzles from the road surface may be adjust¬ able. These variations provide an effectively infin¬ itely variable depth of cut and quality of cleaning. The method and apparatus embodying the invention not only effectively removes debris from the crevices between the stones or chippings of the aggregate, but also removes the volatile components of the asphalt or other matrix which are exuded into the surface crevices. The power per unit area of the jets is of such a magnitude that the matrix is also forced

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down relative to the aggregate, and the force with which the jets impinge on the aggregate is sufficient to re-orientate or tilt the individual stones or chippings in the matrix, thereby further enhancing the surface roughness. Thus the method and apparatus are capable of enhancing the macro-texture and micro- texture of new and old road surfaces.

In one specific test, the apparatus was applied to a black top tar or asphalt bound road surface which, through use and the passage of time, had an initial surface roughness or texture depth (S) of 0.6 to 0.9 mm. The scarifying action of the jets improved the rough¬ ness to 1.6 to 3.3 mm. The apparatus, on average, is capable of treating or scarifying over 1400 sq.ft/ hour 30 square metre per hour and is capable of an approx¬ imate forward speed of up to 220f /hour, 67.1 metre per our through From the foregoing, it will be seen that the method and apparatus embodying the invention offers considerable savings in cost (approximately 300%) and time over existing methods of restoring, or attemp¬ ting to restore surface texture, which consist of lifting and re-laying the entire black top surface.

It will be understood that various modifications may be made without departing from the scope of the present invention. for example, the pressures, spray patterns, distances and • ^' other parameters may be modified as required, and in dependence upon the nature of the surface to be reinstated or treated.

The apparatus may form part of a self-propelled road vehicle as described, or may be a trailer. It

may incorporate its own power source, high pressure water pump, water supply, etc. The vehicle or trailer, or an associated trailer, also preferably includes means, such as a sweeping and/or suction arrangement for disposing of the displaced debris, water, etc.

Whilst the invention is particularly applicable to the reinstatement or restoration of the surface texture or roughness of road surfaces which have been subjected to heavy and/or prolonged use, it may alter- natively be applied to relatively new surfaces to enhance their roughness, slip resistance and/or drainage. The invention is applicable to surfaces other than road surfaces, for example airfield runways or other areas used for vehicles or pedestrian traffic. The invention is also applicable to other surface compo¬ sitions, for example concrete or other composite surfaces, open texture or porous surfaces such as bitumen macadam.

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