WO1998044046A1

WO1998044046A1 - Road surfacing composition

Info

Publication number: WO1998044046A1
Application number: PCT/GB1997/000884
Authority: WO
Inventors: Paul Phillips; Chris Whitworth
Original assignee: Aggregate Industries UK Ltd
Current assignee: Aggregate Industries UK Ltd
Priority date: 1997-03-27
Filing date: 1997-03-27
Publication date: 1998-10-08
Anticipated expiration: 1999-09-27
Also published as: GB2338486A; GB2338486B; GB9922370D0; AU2171997A

Abstract

An asphaltic road surfacing composition, which is particularly suitable for motor racing circuits, comprises 92.4 to 93.6 % by weight of an aggregate and filler component and 6.4 to 7.6 % by weight of a binder component, wherein the aggregate and filler component comprises from 58 to 78 % by weight of crushed rock having a particle size greater than 2 mm, from 20 to 30 % by weight of crushed rock fines and natural sand having a particle size less than 2 mm and from 2 to 12 % by weight of a filler, and the binder comprises bitumen having a penetration of from 50 to 100 pen and dry organic fibres containing at least 70 % by weight of cellulose, said fibres being present in an amount which is from 0.3 to 1.5 % by weight of the total road surfacing composition. A hot mixing process for the preparation of the surfacing composition, a method of laying road surfaces and a road surface are also provided.

Description

ROAD SURFACING COMPOSITION

The present invention relates to an asphaltic road surfacing composition which can be used to lay motor racing circuits having improved skid resistance, spray reduction and durability, to road surfaces laid with said composition, and to processes for preparing said composition and laying said road surface.

Motor racing circuits have been surfaced with a variety of bituminous products in the last fifty years, the majority of which have followed airfield or highway material specifications. Most of these are asphaltic concretes, traditional macadams or hot rolled asphalts. Additionally, there is Delugrip™, a modified macadam having a special aggregate, which was developed by Lees-Dunlop and is the only surface which has been introduced as a proprietary system. In fact Delugrip™ has been the preferred option for the past 20 years. During that period of time no alternative has been developed even though materials technology has advanced in bituminous products.

There is a need to develop a new generation of road surfacing for motor racing circuits with improved properties. There a four main areas which are of importance when assessing the performance of a road surface.

(i) Safety. There are two main elements which must be evaluated, skid resistance and spray reduction. Maximising the grip and minimising the spray generated in wet conditions is critical for circuits used by high performance cars.

(ii) Durability. Resistance to wear with persistent use, particularly against rutting and fatigue damage, is absolutely vital, as wear to motor racing circuits is one of the chief causes of accidents.

(iii) Environment. The main area of concern here is noise pollution generated by tvre/surface contact. Conservation of raw materials is also a sienificant factor. ->

( IV) Cost. Chief areas of cost include the price of raw materials and the ease of laying of the road surfacing (and hence the amount of time and labour involved)

High durability stone mastic asphalt thin surfacings have been known for some time These have only been used on public roads We have now developed a modified stone mastic asphalt thin surfacing which is particularly suitable for use on high-speed motor racing circuits This new surfacing shows good performance in all four of the main performance areas outlined above

In a first aspect of the present invention, there is provided an asphaltic road surfacing composition comprising 92 4 to 93 6% by weight of an aggregate and filler component and 6 4 to 7 6% by weight of a binder component, wherein d) the aggregate and filler component comprises from 58 to 78% by weight of crushed rock having a particle size greater than 2 mm, from 20 to 30% by weight of crushed rock fines and natural sand ha\ ing a particle size less than 2 mm and from 2 to 12% by weight of a filler, and

(ύ) the binder comprises bitumen having a penetration of from 50 to 100 pen and dry organic fibres containing at least 70% by weight of cellulose, said fibres being present in an amount which is from 0 3 to 1 5% bv weight of the total road surfacing composition

The bitumen used in the present invention has a penetration of from 50 to 100 pen. as determined according to British Standard Specification (B S ) 3690, Part 1 (published in 1989 bv the British Standards Institute) the contents of which are incorporated herein by reference thereto (the test is based on a viscositv ranking test, 1 pen = 0 1 mm) Preferably, the bitumen should have a penetration of 50 pen

The bitumen mav be modified with ethvlene-vinvl acetate copolymer, stvrene- butadiene-styrene block copolymer, styrene-butadiene rubber or natural latex Modification with these polvmers results in a surfacing composition which is both more elastic, making it less prone to cracking in cold weather, and more viscous, making it less likely to soften in hot weather Preferablv the polvmers should be present in an amount from 6 to 8% bv weight of the total binder

The cellulosic fibres should contain at least 70% bv weight of cellulose and be present in an amount of from 0 3 to 1 5% b\ weight preferablv 0 45% by weight, of the surfacing composition Pelletised cellulosic fibres mav be used, in which case they should comprise at least 0 45% bv weight of the total surfacing mixture Examples of suitable fibres include Topcel™ and Technocel™ obtainable from Cellulose Fulstoff Fabπk, Fleenwerg, Moenchengladbach Typically, the fibres are obtained from recycled paper

The inclusion of cellulosic fibres in the binder provides a thick binder film, which acts as a strong adhesive and lubricant, facilitating compaction and integrity of the asphaltic surfacing The asphaltic road surfacing composition of the present invention has a strong skeletal structure, leading to improved rut resistance and load bearing properties Motor racing circuits laid with the surfacing of the present invention show increased resistance to permanent deformation with use and improved durability The road surfacing of the present invention has a micro texture which results in a considerable increase in skid resistance It also has good spray reducing characteristics in the wet due to its favourable macro texture and it reduces noise generation caused b\ tyre surface contact These and other properties are discussed further and exemplified below

The crushed rock used in the present invention is the coarse aggregate element and refers to the particles whose size exceeds 2 mm, as tested using the appropriate British Standard test sieve It is obtained from the quarry process of blasting, crushing and screening of a mineral deposit The crushed rock used can be any conventionally used in the production of stone mastic asphalts e g limestone andesite and granite

Examples of suitable crushed rock for use in the present invention include crushed rock from Bardon Hill Quarry Leicestershire, and other sources with properties similar thereto in terms of Polished Stone Value and Magnesium Sulphate Soundness (measured according to Parts 1 14 and 121 respectively of British Standard Specification 812, 1989, the contents of which are incorporated herein bv reference thereto), and Aggregate Abrasion Value (measured according to Part 1 13 of British Standard Specification 812. 1990. the contents of which are incorporated herein bv reference thereto)

The crushed rock fines are particles whose size is less than 2 mm. as tested by the B S test sieve size 2 36 mm, and are obtained from the same quarry process as that used to obtain the crushed rock

Natural sand is a fine aggregate which is not the result of a primary activity such as quarry crushing/blasting, nor as the result of secondary aggregate production such as the crushing of demolition waste It is generally obtained from pit, dune or marine deposit exploitation, as dug and is screened without crushing

Together, the crushed rock fines and the natural sand form the fine aggregate element Preferably, this fine aggregate element should comprise no greater than 50% by weight of natural sand

A preferred specification for the crushed rock, the crushed rock fines and natural sand mixture is as follows

B.S. Sieve Size Percentage Passing ( m) B.S. Sieve Size

14 100

10 90 - 100

6 3 58 - 78

2.36 20 - 30

0 08 7 - 1 1

The fillers used are those conventionally used in the production of stone mastic asphalts They are generally powders whose particle size is substantially less than 75 μm as tested by the appropriate British Standard test sieve. Examples of suitable fillers include the product of milling limestone aggregate, hydrated lime and Portland cement. Preferably 2% by weight of filler is added. Ideally, the fillers used should comply with the requirements of British Standard Specification 594, Part 1 (published in 1992 by the British Standards Institute), the contents of which are incorporated herein by reference thereto.

The asphaltic road surfacing composition of the present invention is prepared using a conventional hot mix plant. In a further aspect of the present invention there is provided a process for preparing an asphaltic road surfacing composition comprising hot mixing, at a temperature of from 150 to 190^CC, 92.4 to 93.6% by weight of an aggregate and filler component and 6.4 to 7.6% by weight of a binder component, wherein: (i) the aggregate and filler component comprises from 58 to 78% by weight of crushed rock having a particle size greater than 2 mm, from 20 to 30% by weight of crushed rock fines and natural sand having a particle size less than 2 mm and from 2 to 12% by weight of a filler; and

(ii) the binder comprises bitumen having a penetration of from 50 to 100 pen and dry organic fibres containing at least 70% by weight of cellulose, said fibres being present in an amount which is from 0.3 to 1.5% by weight of the total road surfacing composition.

Preferably, the hot mixing should take place in accordance with the requirements of British Standard Specification 4987, Part 1 (published in 1993 by the British Standards Institute), the contents of which are incorporated herein by reference thereto. The crushed rock should, ideally, be in a surface dry condition before mixing. The cellulose fibres should be introduced carefully into the mixture to ensure complete dispersal.

In a further aspect of the present invention, there is provided a method for laying the surface of a road comprising laying on a pre-prepared surface, preferably at a temperature of from 80 to 90°C and an average thickness of from 30 to 40 mm, an asphaltic road surfacing composition comprising 92.4 to 93.6% by weight of an aggregate and filler component and 6.4 to 7.6% by weight of a binder component, wherein:

(i) the aggregate and filler component comprises from 58 to 78% by weight of crushed rock having a particle size greater than 2 mm, from 20 to 30% by weight of crushed rock fines and natural sand having a particle size less than 2 mm and from 2 to 12% by weight of a filler, and

(n) the binder comprises bitumen having a penetration of from 50 to 100 pen and dry organic fibres containing at least 70% by weight of cellulose, said fibres being present in an amount which is from 0 3 to 1 5% bv weight of the total road surfacing composition

When laying a motor racing circuit using the asphaltic road surfacing composition of the present invention, the existing road surface should ideally first be cleaned using steel brooms, suction sweeping or similar means The surface may be moist but not wet and no standing water may be present Typically, the tack coat (a bituminous primer) is Kl-40 catiomc bitumen complying with British Standard Specification 434, Part (published in 1989 bv the British Standards Institute), the contents of which are incorporated herein bv reference thereto

The asphaltic road surfacing composition of the present invention is usually laid in accordance with the requirements of Specification for Highway Works (SHW) Clause 901, published by HMSO for the UK Department of Transport, 7th Edition, Dec 1991, (the contents of which are incorporated herein by reference thereto) at an average thickness of from 30 to 40 mm The surfacing is typically applied at a composition temperature of from 80 to 90°C The surfacing is compacted immediately, typically using at least two steel wheeled rollers, with a minimum mass of 3 tonnes per paver Preferablv, one roller should be a tandem drum roller

The present invention also provides road surface laid according to the method outlined above

The asphaltic road surfacing composition of the present invention gives road surfaces having an improved macro texture and micro texture The road surfaces are highly compact with a reduced air void content In a preferred embodiment of the invention, the road surfaces have an air void content of from 1 to 4% by volume This compact structure improves the durability of the road surface in use at the motor racing circuit The macro texture of the road surface of the present invention is of great importance both to the grip and the spray reduction provided. The road surface of the present invention has an average texture depth of 0.8 mm ± 0.2 mm This gives both excellent grip (the road surface preferably having a Sideways Force Coefficient of 0.50) and improved spray reduction (the road surface preferably having a hydraulic conductivity of 0.03 to 0.05 ms^"2).

As stated above, the four main areas of importance when evaluating the performance of a road surface suitable for motor racing circuits are safety, durability, environmental factors and cost. We have found that road surfaces laid with the asphaltic road surfacing composition of the present invention are superior to those laid with conventional compositions in some areas and equivalent in the others.

Safety

(i) Skid Resistance (Grip)

One of the primary objectives of the development of the asphaltic road surfacing composition of the present invention was the provision of a motor racing surface that consistently produces a high quality of grip. A series of skid resistance tests performed on road surfaces laid to specifications suitable for motor racing circuits has shown that they show average levels of skid resistance after the equivalent of 12 months of daily use which is well above the requirements set out in Road Note 27 (published by HMSO for the UK Road Research Laboratory in 1983), the contents of which are incorporated herein by reference thereto, where minimum values of 65 are specified for difficult sites. Road surfaces laid with the composition of the present invention gave values of between 68-76, with an average figure of 72. (ii) Spray Reduction

The skid resistance is mainly a function of the micro texture of the road surface. However, the safety of a surfacing material is not just dependent on its micro texture, it is equally important to take into account its macro texture which has a significant effect on its ability to dissipate rain fall. The asphaltic road surfacing composition of the present invention provides a road surface with a rugous surface texture which, through its interconnecting conduits, assist in the lateral displacement of water, thus reducing spray from tyres under wet conditions. Durability

The road surfacing of the present invention is highly durable and thereby resistant to rutting and fatigue damage Tests have shown that in both respects the road surfacing of the present invention is superior to conventional motor racing surfaces

Reduction of Surface Noise

Whilst design of the surfacing can in no way reduce engine noise, we have managed to reduce the noise generated by tyre/surface contact Road surfacings of the present invention have a negative texture, 1 e it is not ultra smooth, does not have protuberances and it has a texture integral to the product which offers no significant resistance to the tyre but has a oid structure to dissipate noise generated Evaluation has shown a reduction of 2 dB(A) in comparison to Marshall Asphalts (conventional macadams) and 4 dB(A) in comparison to Hot Rolled Asphalt Wearing Course (HRA WC)

Cost

The raw materials used to prepare the surfacing composition of the present invention are cheaper than those used to prepare conventional surfacing compositions Furthermore, the time and labour required to lav circuits with the surfacing composition of the present invention are significantly lower than for conventional surfacing compositions

Joints in the final surface can be a source of weakness and should be minimised Ideally the surfacing of the present invention should be laid by pavers working in echelon, such that longitudinal joints may be virtuallv eliminated

The present invention may be further understood bv means of the following non- hmiting example

A one mile test track was laid, at an average thickness of from 30 to 40 mm and a composition temperature while laving of from 80 to 90°C, using the following composition of the present invention, to determine whether the material had the required performance levels of durability and safety ( 1 ) 91% by weight of a mixture of crushed rock, crushed rock fines and natural sand conforming to the following specification

B.S. Sieve Size Percentage Passing (mm) B.S. Sieve Size

14 100

10 90 - 100 6.3 58 - 78 2 36 20 - 30 0 08 7 - 1 1

(2) 2% by weight of a filler: and

(3) 7% by weight of a binder comprising bitumen having a penetration of 50 pen and dry organic fibres containing at least 70% by weight of cellulose, said fibres being present in an amount which is 0 45% by weight of the total composition.

The raw materials used in this asphaltic road surfacing composition were as follows

This test track was compared with a track laid with the industry standard Delugrip¹ The wet skid resistance of the two test tracks was determined using the pendulum test (an on-site measurement of dry skid resistance developed by the UK Transport Research Laboratory, involving the measurement of frictional resistance of a standard mass brought into contact with the road surface by a standard swing). Measurements were made on trafficked material, where the mineral aggregate had been exposed at the surface, along the racing line at the corners of the test tracks and also on the untrafficked material. All skid tests were conducted in accordance with the procedure described in Road Note 27, published by HMSO for the UK Road Research Laboratory in 1983.

The results of the tests conducted are recorded in Tables 1 and 2 below. The values of the skid resistance under wet conditions given in the tables were corrected to 20°C to take account of the effects of the temperature on the resilience of the rubber slider used in the test apparatus.

Table 1 - Skid Resistance Values for the Test Track Laid with the Surfacing Composition of the Present Invention

Location of Test Corrected Skid Condition of Surface at Test Location Resistance Value

Turn 1, outside rip 71 mineral aggregate exposed on racing line Turn 1. middle rip 76 mineral aggregate exposed on racing line Turn 1. inner rip 76 mineral aggregate exposed on racing line Turn 2. inner rip 69 mineral aggregate exposed on racing line Turn 2. inner rip 68 mineral aggregate exposed on racing line Turn 2, inner rip 64 binder film intact off racing line Turn 2, inner rip 62 binder film intact off racing line Table 2 - Skid Resistance Values for the Delugrip™ Track

Turn 1 inner πp 66 binder film intact on new material

Turn 1 inner πp 76 binder film intact on new material

Turn 1 , inner πp 75 binder film intact on new material

Exit Turn 1, inner πp 85 mineral aggregate exposed old material

Exit Turn 1, outer πp 76 mineral aggregate exposed old material

The skid resistance under wet conditions measured on the trafficked areas of both the test track laid with the composition of the present invention and that laid with Delugrip™ was consistently above the minimum required level of 65 The surfacing composition of the present invention clearly shows equivalent performance in skid resistance to the industry standard Delugrip™

The skid resistance under wet conditions of the test circuit laid with the composition of the present invention was also assessed bv measurement of the Sideways Force Coefficient (SFC) during a simulated controlled brake using a Grip Tester obtained from Findlay Irvine Limited of Bog Road, Penicuik, Midlothian, U K The test track was found to have a SFC of 0 50 This compares with a minimum required value of 0 40 and provides the high levels of grip required by high performance cars on racing circuits

The spray reduction properties of the test track laid with the composition of the present invention were determined by hydraulic conductivity tests conducted in accordance with Specification of Highway Works (SHW) Clause 940, 7th Edition, published bv HMSO for the UK Department of Transport. December 1991, the contents of which are incorporated herein bv reference thereto It is generally accepted that a hydraulic conductivity of greater than 0 02 ms ^" provides a significant contribution to sprav reduction The test track of the present invention was found to have a hydraulic conductivity of 0 03-0 05 ms ^", indicating excellent sprav reduction properties Circuits laid with Delugrip™, by contrast have a hydraulic conductivity of zero The composition of the present invention thus provides a significant improvement in safety over the industry standard in wet-weather racing

The rut resistance of the test track was measured using the wheel tracking test laid out in British Standards Specification (B S ) 598, Part 100 (published in 1996 by the British Standards Institute), the contents of which are incorporated herein by reference thereto It was found that the rut resistance values for the test track were less than 1 5 mm This compares very favourably with the most stringent specification for Hot Rolled Asphalt Wearing Course of 2 0 mm

The void content of the surface of the track was measured using the test laid out in Draft for Development (DD) 228 (published in 1995 by the British Standards Institute), the contents of which are incorporated herein by reference thereto It was found to be from 1 to 4% by volume of the surface

Claims

CLALMS

1 .An asphaltic road surfacing composition comprising 92.4 to 93 6% by weight of an aggregate and filler component and 6 4 to 7 6% by weight of a binder component, wherein: (i) the aggregate and filler component comprises from 58 to 78% by weight of crushed rock having a particle size greater than 2 mm, from 20 to 30% by weight of crushed rock fines and natural sand having a particle size less than 2 mm and from 2 to 12% by weight of a filler; and

(ii) the binder comprises bitumen having a penetration of from 50 to 100 pen and dry organic fibres containing at least 70% by weight of cellulose, said fibres being present in an amount which is from 0 3 to 1 5% by weight of the total road surfacing composition.

2. An asphaltic road surfacing composition according to Claim 1 wherein the bitumen is modified with a polymer chosen from ethylene-vinyl acetate copolymer, styrene-butadiene- styrene block copolymer, styrene-butadiene rubber and natural latex.

3 An asphaltic road surfacing composition according to Claim 2 wherein the polymeric material is present in an amount from 6 to 8% by weight of the binder component

4 .An asphaltic road surfacing composition according to any one of Claims 1 to 3 comprising 0 45% by weight of cellulosic fibres

5 An asphaltic road surfacing composition according to any one of Claims 1 to 4 wherein the amount of natural sand present is less than or equal to the amount of crushed rock fines

6 .An asphaltic road surfacing composition according to any one of Claims 1 to 5 wherein the crushed rock and crushed rock fines are predominantly comprised of andesite 14

7 An asphaltic road surfacing composition according to any one of Claims 1 to 6 wherein the particle size distribution of the element comprising the crushed rock, the crushed rock fines and the natural sand is as follows

itish Standard Specification Percentage Passing British Standard

Sieve Size (mm) Specification Sieve Size

14 100

10 90 - 100

6.3 58 - 78

2 36 20 - 30

0 08 7 - 11

8. An asphaltic road surfacing composition according to any one of Claims 1 to 7 wherein the average particle size of the filler is less than 75 μm

9 An asphaltic road surfacing composition according to any one of Claims 1 to 8 which comprises 2% by weight of filler.

10. An asphaltic road surfacing composition according to any one of Claims 1 to 9 wherein the filler is chosen from the product of milling limestone aggregate, hydrated lime and Portland cement

1 1. A process for preparing an asphaltic road surfacing composition comprising hot mixing, at a temperature of from 150 to 190°C, 92.4 to 93 6% by weight of an aggregate and filler component and 6 4 to 7 6% by weight of a binder component, wherein:

(li) the binder comprises bitumen having a penetration of from 50 to 100 pen and dry organic fibres containing at least 70% by weight of cellulose, said fibres being present in an amount which is from 0 3 to 1 5% by weight of the total road surfacing composition

12 A method for laying the surface of a road comprising laying on a pre-prepared surface an asphaltic road surfacing composition according to any one of Claims 1 to 10

13 A method according to Claim 12 wherein the asphaltic road surfacing composition is laid at an average thickness of from 30 to 40 mm

14 A method according to Claim 12 or Claim 13 wherein the asphaltic road surfacing composition is laid at a composition temperature of from 80 to 90°C

15 A road surface obtainable according to the method of any one of Claims 12 to 14

16 A road surface according to Claim 15 having an air void content of from 1 to 4% by volume

17 A road surface according to Claim 15 or Claim 16 having an average texture depth of 0 8 mm ± 0 2 mm

18 A road surface according to any one of Claims 15 to 17 having a Sideways Force Coefficient of 0 50

19 \ road surface according to any one of Claims 15 to 18 having a hydraulic conductivity of from 0 03 to 0 05 ms^"2

20 .An asphaltic road surfacing composition substantially as described herein

21. A process for preparing an asphaltic road surfacing composition substantially as described herein.

22. A method for laying the surface of a road substantially as described herein.

23. A road surface substantially as described herein.