NZ714814A - A method of rejuvenating chip seal surfacing - Google Patents

Abstract

The present invention relates to a method of rejuvenating an existing surface of chip seal which has been worn, for example by vehicles passing over the surface. This may lead to the stones in the upper layer of the chip seal becoming polished and the binder surrounding the stones being worn away leaving voids between individual stones in the exposed aggregate. The method entails applying modi?ed binder into the voids and embedding a polish resistant stone into the modi?ed binder so that at least a portion of the polish resistant stone is exposed above the modi?ed binder.

Description

James & Wells ref:300390/62 A METHOD OF REJUVENATING CHIP SEAL SURFACING TECHNICAL FIELD The present invention relates to a new method of rejuvenating worn chip seal surfacing. In particular it relates to rejuvenating worn chip seal surfacing for high demand sections of chip seal where skid- resistant surfaces are required.

BACKGROUND ART Chip seal is commonly used for road and pavement areas in New Zealand, particularly for sealing or rehabilitating low use areas such as rural roads and pavements. For convenience henceforth throughout this specification we will refer to chip seal applied to road surfaces only; however this should not be seen as limiting as those skilled in the art will appreciate it can be used on other surfaces such as pavements etc.

Chip sealing involves the application of a thin layer of bituminous binder onto a road surface before applying a layer of aggregate on top of the binder. The binder adheres to the chips and holds them in place; it also acts as a waterproof membrane which prevents water from passing through the chip seal into the underlying road base. Chip sealing is a relatively inexpensive and quick method for rejuvenating road surfaces. The aggregate used in chip sealing is typically sourced locally, which reduces material and transport costs. Furthermore it is environmentally beneficial (compared with other methods of forming road surfaces, such as laying asphalt) in that water is used as the binding agent for the bitumen, rather than solvents.

Chip sealing is adequate for most low use 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 road surface can wear more quickly due to braking/acceleration and shear stresses of turning vehicles. This wear can polish the aggregate (which is normally locally sourced low polish resistant aggregate) which 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 James & Wells ref:300390/62 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 0.50 or 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 skid resistance are needed to treat the chip seal surface.

When the surface of a section of chip seal in a high demand section of road deteriorates (i.e. no longer provides the required level of skid resistance) the traditional method of repair is to replace the existing section of chip seal with a new chip seal, or to form a new chip seal layer over the existing. This sometimes involved resealing the entire original length of the chip seal on both sides of the road. This involves considerable labour and capital costs in removing the existing chip seal and replacing it with a new section of chip seal. Furthermore there can be environmental costs as removal of the old chip seal increases the amount of waste to be disposed of.

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”.

James & Wells ref:300390/62 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 present invention relates to a method of rejuvenating an existing surface of chip seal which has been worn, for example by vehicles passing over the surface. This may lead to the stones in the upper layer of the chip seal becoming polished and the binder surrounding the stones being worn away, leaving exposed polished stones surrounded by voids or depressions in the surface of the chip seal. The method of the present invention may provide a simple process for binding new polish resistant aggregate into the voids/depressions to create a new skid resistant surface.

According to one aspect of the present invention there is provided a method of rejuvenating a worn chip seal surface in a high demand section of chip seal, the method including the steps of: providing a section of existing chip seal surface having exposed aggregate with voids between the individual stones of the exposed aggregate; applying a modified binder into the voids; and embedding a polish resistant stone into the modified binder so that at least a portion of the polish resistant stone is exposed above the modified binder.

One critical feature of the method is selection of an appropriate binder.

In a preferred embodiment the modified binder is a polymer modified binder. The binder used preferably has a high degree of adhesion with the aggregate, so that the stones at the surface are not easily displaced/ removed from the surface by the action of tyres passing over the surface.

Another critical feature is the size distribution of the existing voids in the surface. This needs to be established for each site before the aggregate is chosen.

Yet another critical feature is the size distribution of the polish resistant aggregate. Preferably the size distribution is chosen such that the PRA fits snugly into the existing voids in the surface such that a portion of the PRA stone extends above the binder and above the existing stones in the surface.

The present invention may have several advantages over the prior art, including: James & Wells ref:300390/62  the process is quick and relatively simple to apply; and  damaged portions of the road can be repaired without the need to replace whole sections of chip seal, thus saving material and labour costs, and significantly reducing the time taken to make the repair.

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 a step in the method of the present invention; Figure 2 shows another step in the method of the present invention; and Figure 3 shows another step in the method of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION A section of worn chip seal is generally indicated by arrow 1 in Fig.1. The existing chip seal is indicated by arrow 4. The surface layer of the chip seal, 5, consists of exposed aggregate stones 6 which have been polished due to the action of vehicles passing over the chip seal. These worn, polished stones 6 have low skid resistance, so that some remedial action is required.

In between the exposed aggregate stones 6 are a number of voids 7 where the binder of the chip seal has worn away.

In the second step of the method of the present invention, indicated by arrow 2 in Fig. 2, a thin layer of polymer modified binder 8 is poured into the voids 7 where it accumulates in the bottom of each void.

In some embodiments the polymer modified binder may be emulsified or it may be an epoxy modified binder.

In the third and final step of the method of the present invention, indicated by arrow 3 in Fig. 3, individual stones of polish resistant aggregate (PRA) 9 are placed into the polymer modified binder 8.

This causes the binder 8 to flow around the sides of the voids 7. When the binder set the PRA stones are locked in position, with the tops of the PRA stones extending above the worn surface 5 of the chip seal.

James & Wells ref:300390/62 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.

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:300390/62

Claims (4)

WHAT WE CLAIM IS:

1. A method of rejuvenating a worn chip seal surface in a high demand section of chip seal, the method including the steps of: providing a section of existing chip seal surface having exposed aggregate with voids 5 between the individual stones of the exposed aggregate; applying a modified binder into the voids; and embedding a polish resistant stone into the modified binder so that at least a portion of the polish resistant stone is exposed above the modified binder.

2. A method as claimed in claim 1 wherein the modified binder is a polymer modified binder 10 having a degree of adhesion with the aggregate so that the stones at the surface are not easily displaced/ removed from the surface by the action of tyres passing over the surface.

3. A method as claimed in either one of claims 1 or 2 including the step of measuring a size distribution of the voids between the individual stones of the exposed aggregate prior to the step of embedding the polish resistant stone into the modified binder. 15

4. A method as claimed in claim 3 including the step of selecting a size distribution of the polish resistant stones using the measured size distribution of the voids between the individual stones of the exposed aggregate, the selected size distribution of the polish resistant stones chosen such that the polish resistant stones fit snugly into the existing voids in the surface and such that a portion of the polish resistant stones extends above the binder and above the existing 20 stones in the surface. Jeffrey Carl Waters, John Rex Wallace Forrest and Fulton-Hogan Limited By their Attorneys JAMES & WELLS James & Wells ref: