NZ714813A - Surface treatment of asphalt - Google Patents

Abstract

The method of the present invention di?ers from the prior art methods in that only the surface of A a demand section of asphalt is modi?ed/repaired, as against removal and replacement of the entire asphalt layer in both the high demand section and a 40 m section of asphalt before the high demand section. There is provided a method of resurfacing an asphalt layer to provide skid resistance in a high demand section of asphalt, the method including the steps of: applying a surface preparation to roughen the surface of the asphalt layer in the high demand section; applying a binder to the roughened surface; applying a layer of Polish Resistant Aggregate (PRA) chips over the binder; and compacting the PRA chips into the binder to form a modi?ed surface layer in which a portion of the PRA chips extends above the binder.

Description

James & Wells ref: 300389/62 SURFACE TREATMENT OF ASPHALT TECHNICAL FIELD The present invention relates to a new method of repairing asphalt surfacing. In particular it relates to repair of an asphalt surface for high demand sites where skid-resistant surfaces are required.

BACKGROUND ART Hot mix asphalt surfacing is used extensively around the world for creating generally smooth surfaces for roads, pavement, shoulders and embankments. Hot mix asphalt is a mixture of aggregate (typically between 85 % and 95 %) with a bituminous binder filling the voids between the stones of the aggregate.

For cost reasons (both cost of aggregate and transport costs) local aggregate (local sand and gravel) is used. This is adequate for most road surfacing, but in high demand areas such as the approach to a traffic light, a sharp curve or a steeply inclined section of road, the surface of the road surfacing can wear more quickly due to braking/acceleration and shear stresses of turning vehicles. This wear can expose the aggregates at the surface which are then subject to polishing by the tyres of the passing vehicles. The polishing can significantly reduce the skid resistance of the surface thus increasing the likelihood of skidding or increased stopping distances.

Recently many transport authorities have introduced specifications to address this problem. In New Zealand, for example, the New Zealand Transport Authority has introduced the NZTA T/10 Specification for State Highway skid resistance management which provides limits for the skid resistance and texture of road surfaces. The skid resistance of the State Highway network road surface is measured annually by a scrim machine to provide an Equilibrium Scrim Coefficient, or ESC, for every 10m section. To meet the New Zealand requirements on these high demand areas the ESC must be at least 0.55 on each 10m section of each lane.

Most local aggregates with low polish resistance tend to polish quickly in high demand conditions and therefore are unlikely to meet the ESC requirement. When this is the case special Polish Resistant Aggregate (PRA) must be used. PRA, which can typically (without limitation) be some natural aggregates, minerals, slag or calcined bauxite, and metal for example, which have high polish resistance, is generally more expensive than those local aggregates which have low polish resistance. There will be additional costs if the PRA needs to be transported a large distance to the location of the site where aggregates with high demand are needed to treat the hot mix asphalt surface.

James & Wells ref: 300389/62 When the surface of a section of high demand asphalt deteriorates (i.e. no longer provides the required level of skid resistance) the traditional method of repair is to remove the asphalt from the entire road in the high demand section (typically around 50-60 m by 10 m by 0.04 m for a two lane road) as well as a section of road approximately 5060 m by 10 m by 0.02-0.04 m in the approach to the high demand section. Once the asphalt is removed over the entire 100-120 m by 10 m by 0.02-0.04 m (20-50 cubic metres) section of road, a new asphalt layer is applied. The repair process creates 20-50 cubic metres of waste asphalt, and uses 20-50 cubic metres of new asphalt.

Furthermore, in the high demand section PRA is used throughout the asphalt layer to provide the required skid resistance at the surface of the layer. This process of removing the old asphalt layer over the entire road (i.e. all lanes on each side of the road) and replacing it with new asphalt is expensive, wasteful and time consuming. The requirement to use PRA throughout the layer in the high demand section adds further to the cost and waste.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

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 assert, and the applicants reserve the right to challenge the accuracy and pertinency 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.

Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise”, “comprising”, and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of “including, but not limited to”.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

DISCLOSURE OF THE INVENTION The method of the present invention differs from the prior art methods in that only the surface of the high demand section of asphalt is modified/repaired, as against removal and replacement of the entire James & Wells ref: 300389/62 asphalt layer in both the high demand section and a 40 m section of asphalt before the high demand section.

According to one aspect of the present invention there is provided a method of resurfacing an asphalt layer to provide skid resistance in a high demand section of asphalt, the method including the steps of:  applying a surface preparation to roughen the surface of the asphalt layer in the high demand section;  applying a binder to the roughened surface;  applying a layer of Polish Resistant Aggregate (PRA) chips over the binder; and  compacting the PRA chips into the binder to form a modified surface layer in which a portion of the PRA chips extends above the binder.

It is important that a portion of the PRA chips extends above the binder as the exposed portion is what provides the increased skid resistance.

In a preferred embodiment the PRA chips are pre-treated prior to application with a material to increase the adhesion of the PRA chips within the surface region of the asphalt layer.

The pre-treatment of the PRA chips may increase the ease with which the PRA is pushed into the binder as well as to increase the adhesion of the PRA to the binder to provided longer lifetime to the modified surface of the asphalt (i.e. lower the occurrence of individual PRA chips being loosened from the modified surface layer as it wears).

In a preferred embodiment the step of compacting the PRA chips into the binder includes use of a roller.

Use of the present method may have several advantages over prior art methods, including:  significant reduction in material and labour costs as the present method is applied to the surface region of the asphalt layer in the high demand section (typically 50-60 m by 3.5 m by 0.005 m, i.e. 1.05 cubic metres) only as against the prior art method of replacing the whole asphalt layer over the entire width of the road in the high demand section and 50-60 m before the high demand section (100-120 m by 10 m by 0.02-0.04 m, i.e. 20-50 cubic metres), with the high demand section requiring use of high cost PRA throughout the asphalt layer;  cost and environment savings as the existing layer of asphalt is retained, only the surface of the asphalt layer in the high demand section is removed thus significantly reducing the amount of James & Wells ref: 300389/62 waste material produced as well as significantly reducing the cost of new materials; and  significant reduction in the time required to replace the worn section of high demand asphalt as only the surface of the high demand section is modified in the present method whereas previously the entire asphalt layer at and before the high demand section had to be removed and re-laid.

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 shows schematically the region of an asphalt layer replaced in a prior art method; Figure 2 shows a step in the method according to one embodiment of the present invention; Figure 3 shows schematically another step in the method according to the embodiment shown in Fig.1; and Figure 4 shows schematically another step in the method according to the embodiment shown in Fig. 1 and Fig. 2.

BEST MODES FOR CARRYING OUT THE INVENTION A high demand section of asphalt that requires treatment to improve skid resistance is indicated schematically in plan view (for a two lane section of asphalt road), by the rectangle ABCD in Fig. 1. The amount of asphalt that has to be removed and replaced according to a method of the prior art is indicated by the rectangle AEFG. In the method of the present invention the surface layer only of the asphalt in the rectangle ABCD is treated which may provide several major advantages over the prior art method, as discussed above.

The first step of the method of a preferred embodiment of the present invention is generally indicated by arrow 1 in Fig. 2, which shows a cross sectional view through the upper portion of the asphalt layer in the high demand section. In this step the surface 2 of the high demand section (ABCD) is prepared by removing a relatively thin layer of the surface of the existing asphalt layer so as to leave a roughened surface 3. This may be done by any of the methods that are well known in the art, including, without limitation, use of a milling machine, bob cat, scabbling machine or other mechanical device.

James & Wells ref: 300389/62 The second step of the method is generally indicated by arrow 4 in Fig. 3. In this step a binder 5, in the form of a modified polymer binder, is applied to the roughened surface. The binder is chosen to increase the adhesion of the PRA to the roughened surface 3 and withstand the significant shear imparted by traffic.

The third step of the method is generally indicated by arrow 6 in Fig. 4. In this step pre-treated PRA (PPRA) chips 7 are applied over the binder 5 by spreading of the chips from each side of the high demand area (ABCD).

The fourth step of the method is generally indicated by arrow 8 in Fig. 5. In this step the layer of pre- treated PRA (PPRA) chips 7 is rolled into the binder by a roller 9 so that a portion 10 of the PPRA chips extends from the surface of the binder 5. The pre-treatment of the PRA may increase the ease with which the PRA is pushed into the binder 5 as well as to increase the adhesion of the PRA to the binder layer to provide longer lifetime to the modified surface of the asphalt (i.e. lower the occurrence of individual PRA stones being loosened from the modified surface layer as it wears).

The entire disclosures of all applications, patents and publications cited above and below, if any, are herein incorporated by reference.

Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in the field of endeavour in any country in the world.

The invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features.

Where in the foregoing description reference has been made to integers or components having known equivalents thereof, those integers are herein incorporated as if individually set forth.

It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be included within the present invention.

James & Wells ref: 300389/62 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 of the appended claims.

James & Wells ref: 300389/62

Claims (3)

WHAT WE CLAIM IS:

1. A method of resurfacing an asphalt layer to provide skid resistance in a high demand section of asphalt, the method including the steps of: applying a surface preparation to roughen the surface of the asphalt layer in the high demand section; applying a binder to the roughened surface; applying a layer of Polish Resistant Aggregate chips over the binder; and compacting the PRA chips into the binder to form a modified surface layer in which a portion of the PRA chips extends above the binder.

2. A method as claimed in claim 1 wherein the Polish Resistant Aggregate chips are pre-treated prior to application with a material to increase the adhesion of the Polish Resistant Aggregate chips within the surface region of the asphalt layer.

3. A method as claimed in either one of claims 1 or 2 wherein the step of compacting the Polish Resistant Aggregate chips into the binder includes use of a roller. Jeff Waters, John Forrest and Fulton-Hogan Limited By their Attorneys JAMES & WELLS