NZ714812A - A method of laying new chip seal surfacing - Google Patents

Abstract

The present invention provides a method of laying new chip seal onto a surface in a high demand section of chip seal roading to provide a skid resistant surface, the method including the steps of: applying a ?rst layer of a ?rst binder to the surface; applying a ?rst layer of aggregate over the surface of the ?rst binder; crushing the aggregate in the ?rst layer into the ?rst layer of binder; removing loose material from the surface of the ?rst binder/aggregate mix; applying a second layer of a second binder over the surface of the ?rst binder/aggregate mix; applying a second layer of aggregate over the second layer of binder; and embedding the second layer of aggregate into the second layer of binder to form a second binder/aggregate mix, wherein the ?rst layer of aggregate includes low polish resistant aggregate and the second layer of aggregate includes polish resistant aggregate.

Description

James & Wells ref:300388/62 A METHOD OF LAYING NEW CHIP SEAL SURFACING TECHNICAL FIELD The present invention relates to a new method of preparing new chip seal surfacing. In particular it relates to new 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 this number of layers and order of application can vary according to situation. The binder adheres to the chips and the road surface and holds the chips and the seal in place; it also acts as a waterproofing membrane which can prevent or at least limit the amount of water 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.

Chip sealing is adequate for most road surfacing situations, 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. Apart from the damage that can be done to a chip seal surface the wear can also 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 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 James & Wells ref:300388/62 the New Zealand requirements on these high demand areas the ESC must be at least 0.50-0.55 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 form a new chip seal layer over the existing one. This process may be repeated several times until too many seals have been made, in which case the chip seal is removed and replaced.

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 According to one aspect of the present invention there is provided a method of laying new chip seal onto a surface in a high demand section of chip seal roading, the method including the steps of: James & Wells ref:300388/62 applying a first layer of a first binder to the surface; applying a first layer of aggregate over the surface of the first binder; crushing the aggregate in the first layer into the first layer of binder; removing loose material from the surface of the first binder/aggregate mix; applying a second layer of a second binder over the surface of the first binder/aggregate mix; applying a second layer of aggregate over the second layer of binder; and embedding the second layer of aggregate into the second layer of binder to form a second binder/aggregate mix, wherein the first layer of aggregate includes low polish resistant aggregate and the second layer of aggregate includes polish resistant aggregate.

In a preferred embodiment the first layer of aggregate includes low polish resistant stones only.

Typically locally sourced aggregate contains low polish resistant stones. Local aggregate is generally much less expensive than polish resistant aggregate, both in material cost and transport cost (as polish resistant aggregate generally needs to be transported much further than local aggregate). Therefore use of local aggregate in the first layer of aggregate may provide considerable cost savings in comparison to using polish resistant aggregate.

In a preferred embodiment the local aggregate in the first layer is laid such that adjacent stones of the aggregate are in contact with one another. The stones of the first layer of aggregate are laid “shoulder to shoulder” to provide a firm base for the chip seal.

In a preferred embodiment the step of crushing the aggregate in the first layer includes breaking off the tops of stones in the first layer of aggregate to flatten the surface of the first aggregate/binder mix. This may have the advantage of providing a relatively flat surface to the first aggregate/binder mix onto which the second PRA aggregate/binder mix is laid.

In a preferred embodiment the step of crushing the aggregate in the first layer includes use of a steel roller.

In a preferred embodiment the step of removing loose material includes sweeping the surface of the first binder/aggregate mix.

James & Wells ref:300388/62 In a preferred embodiment the aggregate in the second layer is laid such that adjacent stones of the aggregate are in contact with one another after construction. The stones in the second aggregate layer are laid so that they end up “shoulder to shoulder” after compaction and early trafficking to provide a firm upper layer for the chip seal.

In a preferred embodiment the second layer of aggregate includes polish resistant aggregate (PRA) only.

Use of polish resistant aggregate in the second layer may provide skid resistance to the surface of the new chip seal, as required to meet the local/national standards for roading. Including low polish resistant aggregate into the second layer may diminish the performance of the second layer in this regard.

In a preferred embodiment a portion of the stones in the polish resistant aggregate extends above the surface of the second binder. It is important that a portion of the polish resistant chips extends above the binder as the exposed portion is what provides the improved wearing of the exposed chips and increased skid resistance of the surface of the chip seal.

In a preferred embodiment the second binder has greater adhesion with the aggregate than the first binder.

PRA is used in the second layer to provide polish resistance which in turn increases the grip between the tyre of a vehicle and the surface of the road. Conversely, this action increases the forces on the aggregate in the second layer tending to pull the aggregate out of the surface. For this reason a stronger binder than that used in the first layer may be used in the second layer to increase the grip on the PRA and therefore increase the useful lifetime of the surface.

The method of the present invention may provide advantages over the prior art methods, including;  providing a cost effective process for laying a new chip seal surface in a high demand section of roading by using PRA in the second/top layer only and local aggregate in the first layer.

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; Figure 3 shows another step in the method of the present invention; James & Wells ref:300388/62 Figure 4 shows another step in the method of the present invention; Figure 5 shows another step in the method of the present invention; Figure 6 shows another step in the method of the present invention; and Figure 7 shows another step in the method of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION The first step of the method of the present invention is generally indicated by arrow 1 in Fig. 1. A first layer 8 of a first binder 9 in the form of bitumen mixed with water as a binder, is laid over ground 10.

The second step of the method of the present invention is generally indicated by arrow 2 in Fig. 2. A first layer of aggregate 11 is spread over the surface of the first layer 8 of the bitumen/water mixture 9.

The stones of the first layer of aggregate are closely packed together, so that each stone is in contact (“shoulder to shoulder”) with its neighbouring stones. The aggregate in the first layer includes low polish resistant stones sourced from locally produced aggregate. The stones typically have dimensions of < 7 mm.

The third step of the method of the present invention is generally indicated by arrow 3 in Fig. 3. A heavy steel roller 12 is rolled over the first layer of aggregate to embed the aggregate 11 into the first layer of binder 8. The weight of the roller is sufficient to crush the tops of the stones in the aggregate so as to leave a relatively flat surface to the first binder/aggregate mix 13. In the process small shards of stone 14 are broken off the tops of the stones, these shards remaining on the surface of the first binder/aggregate mix 13.

The fourth step of the method of the present invention is generally indicated by arrow 4 in Fig. 4. In this step the remaining shards of stone on the surface of the first layer of binder/aggregate mix are swept off the surface with a sweeping implement, shown schematically as a broom 15 in fig. 4, to leave a clean, relatively flat surface on the first binder/aggregate layer 13.

The fifth step of the method of the present invention is generally indicated by arrow 5 in Fig. 5. A second layer 16 of bituminous binder is laid over the first binder/aggregate layer.

The sixth step of the method of the present invention is generally indicated by arrow 6 in Fig. 6. A second layer of aggregate 17 is spread on top of the surface of the first binder/aggregate layer 13. The second layer of aggregate is made up of polish resistant aggregate (PRA). The stones of the PRA typically James & Wells ref:300388/62 have dimensions < 7 mm. The stones of the PRA are closely packed together so that each stone is in contact (“shoulder to shoulder”) with its neighbouring stones.

The seventh step of the method of the present invention is generally indicated by arrow 7 in Fig. 7. In this last step a roller 18 is rolled over the second layer of aggregate to push the PRA into the second layer of binder 15 to form a second binder/aggregate layer 19. The amount of binder in the second layer of binder is chosen such that the tops of the embedded PRA are exposed above the binder in the second binder/aggregate layer. In this way the surface of the new chip seal consists of high polish resistant stones as required to provide the necessary skid resistance in a high demand section of chip seal.

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:300388/62

Claims (6)

WHAT WE CLAIM IS:

1. A method of laying new chip seal onto a surface in a high demand section of chip seal roading, the method including the steps of: applying a first layer of a first binder to the surface; applying a first layer of aggregate over the surface of the first binder; crushing the aggregate in the first layer into the first layer of binder; removing loose material from the surface of the first binder/aggregate mix; applying a second layer of a second binder over the surface of the first binder/aggregate mix; applying a second layer of aggregate over the second layer of binder; and embedding the second layer of aggregate into the second layer of binder to form a second binder/aggregate mix, wherein the first layer of aggregate includes low polish resistant aggregate and the second layer of aggregate includes polish resistant aggregate.

2. A method as claimed in claim 1 wherein the first layer of aggregate includes low polish resistant stones only.

3. A method as claimed in either one of claims 1 or 2 wherein the local aggregate in the first layer is laid such that adjacent stones of the aggregate are in contact with one another.

4. A method as claimed in any one of the preceding claims wherein the step of crushing the aggregate in the first layer includes breaking off the tops of stones in the first layer of aggregate to flatten the surface of the first aggregate/binder mix.

5. A method as claimed in any one of the preceding claims wherein the step of crushing the aggregate in the first layer includes use of a steel roller.

6. A method as claimed in any one of the preceding claims wherein the step of removing loose material includes sweeping the surface of the first binder/aggregate mix. James & Wells ref: