WO2011067744A1

WO2011067744A1 - Fibrous open stone asphalt composition for use in hydraulic engineering works and method for manufacture thereof

Info

Publication number: WO2011067744A1
Application number: PCT/IB2010/055597
Authority: WO
Inventors: Jelle Van Bogaert
Original assignee: Dec N.V. (Deme Environmental Contractors)
Priority date: 2009-12-04
Filing date: 2010-12-06
Publication date: 2011-06-09
Also published as: BE1019062A3

Abstract

The present invention relates to asphalt compositions. The present invention relates particularly to a fibrous open stone asphalt composition for use in hydraulic engineering works. The asphalt compositions according to the invention comprise a bitumen emulsion. The invention also relates to a method for preparing such asphalt compositions and the use thereof for stabilization in hydraulic engineering applications.

Description

FIBROUS OPEN STONE ASPHALT COMPOSITION FOR USE IN HYDRAULIC ENGINEERING WORKS AND METHOD FOR MANUFACTURE THEREOF

Technical Held The present invention relates to asphalt compositions. The present invention relates particularly to a fibrous open stone asphalt composition for use in hydraulic engineering works.

Prior art

Asphalt is a mixture of mineral components with a bituminous binder. The mineral components are further subdivided into a stone fraction, a sand fraction and a filler fraction. There are different types of asphalt mixture, which differ from each other in respect of composition and raw materials and additives used. In general the type of asphalt is determined by the ratio of the asphalt mastic, the mixture consisting of the bituminous binder, the filler fraction and optionally the sand fraction, and the stone fraction, in addition to the precise composition of the asphalt mastic and the particle size of the stone fraction. There are therefore overfilled, filled and underfilled mixes. In an overfilled mix so much mastic is present that there is no longer a mineral skeleton. The sand and stone as it were float in the filler material. The mastic must in this case have sufficient load-bearing capacity. In the case of a filled mixture the coarse mineral aggregate does now form a skeleton, wherein the hollow space in the skeleton is largely filled with mastic. The pores in this type of asphalt are not in open connection with each other. An advantage of filled pores is that the coarser constituents of the mix adhere better to each other, thereby increasing lifespan. In an underfilled mixture the hollow space in the mineral skeleton is not fully filled, whereby the pores are connected to each other. The most important advantage hereof is the improved water permeability. Such an asphalt mixture is also referred to as an open asphalt mixture. An example of underfilled asphalt is very open asphalt concrete, or ZOAB. This type of asphalt is characterized by a high percentage of hollow spaces or pores.

Use is made in hydraulic engineering and other works of an open asphalt structure. Use is often made of open stone asphalt. This forms an erosion-resistant covering with a high percentage of hollow space. The asphalt hereby becomes water-permeable, thereby preventing the buildup of water overpressures. Such an open structure moreover allows the growth of vegetation thereon.

Fibrous open stone asphalt (GOSA) is a visco-elastic material suitable for hydraulic engineering works. Such works require that the total pore volume, i.e. the porosity of the material defined in hollow space, comprises at least 10 to 30% of hollow space. The thickness with which such a layer is arranged is generally 12 to 30 cm, depending on the hydraulic load. GOSA meet these requirements since it is characterized by a porosity of 25%. For this purpose GOSA is composed of about 80% limestone chippings and about 20% fibrous mastic. The fibrous mastic itself consists of about 60% sand of a specific size, 20% very fine limestone powder as filler, about 20% bitumen and about 0.40% inert fibres. Industrial cellulose fibres are used as inert fibres.

The described asphalt compositions are produced and processed at high temperatures. An alternative to hot mix asphalt compositions are cold mix asphalt compositions. Such asphalt compositions are generally prepared by means of a bitumen emulsion. The use of cold mix asphalt compositions is however limited to providing water-impermeable layers, surface treatments or repairs to existing asphalted substrates, such as sealing cracks in a damaged road surface. Cold mix asphalt compositions have not been employed heretofore to provide new and structural stabilizing ground coating, ground covering or slope revetment, least of all in hydraulic engineering works.

In light of the foregoing, there is therefore still a need for new asphalt compositions with improved properties and a wider field of application. The present invention therefore has for its object to provide these.

Summary

The present invention relates to a water-permeable asphalt composition for use in hydraulic engineering works. The invention relates particularly to an open stone asphalt composition, such as a fibrous open stone asphalt composition. The asphalt composition according to the invention comprises 80 to 97% by weight of granulates, 0 to 12% by weight of sand, 0 to 5% by weight of filler, 0 to 0.09% by weight of fibres and 3 to 6% by weight of bitumen, wherein the bitumen is provided as a bitumen emulsion comprising 50 to 70% by weight of bitumen.

In an embodiment the joint concentration of sand, filler and fibres is lower than about 12% by weight. The inventors have found that a higher combined sand, fibre and filler concentration results in asphalt mixtures which are too dry and so do not allow a good enclosure and homogenization. In a further embodiment the ratio or proportion (on the basis of mass) between the combined sand, filler and fibre fraction on the one hand and bitumen on. the other is less than 2. The inventors have found that a higher ratio results in asphalt mixtures which are too greasy and are thus too soft, with an increased risk of subsidence.

In an embodiment the granulates comprise limestone chippings having in an embodiment a granulometry of 14/20, a granulometry of 20/40 or a granulometry of 14/40. In another embodiment the sand fraction has a granulometry of 0/2. Asphalt compositions with such a granulometry of the granulate and sand fraction are discontinuous compositions. Granulates with a size between the granulate and sand fraction (so between 2 mm and 14 mm) are essentially absent. Such a discontinuous granulometric distribution also contributes toward the here described advantages of the asphalt compositions according to the invention.

In a further embodiment the filler is basic. In yet another embodiment the fibres are cellulose fibres. Addition of such fibres to the mastic allows the use of more bitumen, whereby the adhesion, the erosion resistance, the flexibility and other properties are improved without the internal stability of the mixture being compromised. An advantage of the compositions according to the invention is that they have the property of being stable on steep slopes and resistant to high wave action and current, and so have a high resistance to erosion as well as elastically following the settling of the ground, whereby the forming of fissures is avoided. The compositions according to the invention are characterized by a modulus of elasticity which is higher than that of the conventional asphalt compositions. The modulus of elasticity of the asphalt compositions according to the invention is particularly 10000 to 20000 MPa at 5 ° C, preferably about 16000 MPa. Contrary to expectation, the use of a bitumen emulsion in an open stone asphalt results in a good homogenization and adequate enclosure and adhesion of the aggregates with the mastic. Where it might be expected that the use of a bitumen emulsion for producing an open stone asphalt with high water-permeability would result in subsidence of the bitumen emulsion, thus resulting in a poor homogenization and enclosure of the granulates, the inventors have surprisingly found that the asphalt composition according to the invention is indeed suitable for use as hard top, particularly in hydraulic engineering operations, wherein asphalt structures are often placed on slopes (such as dikes or embankments).

In an embodiment the bitumen emulsion of the asphalt composition according to the invention is a slow-breaking bitumen emulsion. In a further embodiment the bitumen emulsion is a cationic bitumen emulsion. The inventors have found that a fast-breaking emulsion does not allow sufficient time to realize a thorough homogenization and enclosure of the granulates, in contrast to the use of a slow-breaking emulsion. The use of a cationic bitumen emulsion and/or a basic filler moreover helps prevent the subsidence of the bitumen emulsion. In an embodiment the bitumen in the bitumen emulsion has a degree of penetration of 50-70 pen. In contrast, bitumen with a degree of penetration of 70-100 pen is generally used in hydraulic engineering applications. The inventors have however found that bitumen with a higher degree of penetration is too soft a bitumen for the proposed applications of the asphalt compositions according to the invention. It has been found that bitumen with a degree of penetration of 50-70 maintains the perfect balance between on the one hand a good miscibility or homogenization capacity, and thus enclosure of the granulates and the adhesion of the mastic to the granulates, and on the other minimization of subsidence of the bitumen emulsion in the asphalt composition according to the invention. On the other hand bitumen with a degree of penetration of 70-100 is generally used in hydraulic engineering applications.

The invention also relates to a method for preparing the asphalt composition as described herein. The method relates particularly to the method of mixing the separate components of the asphalt composition according to the invention, wherein in a first phase the granulates are mixed with the bitumen emulsion to form a first mixture and the sand is mixed with the filler and the fibres to form a second mixture, after which in a second phase the first mixture is mixed with the second mixture. It has been demonstrated that a better homogenization is obtained by first mixing the granulates with the bitumen emulsion before adding the other components, wherein the enclosure of the granulates and the adhesion of the mastic to the granulates is improved, this optimizing the cohesion between the aggregates. Breaking will here be delayed until a good enclosure is obtained and will be initiated by addition of the

sand/filler/fibre mixture.

As a result the pore volume of the asphalt mixture is likewise more homogeneous, which enhances the structural properties, such as water-permeability but also stability, of the asphalt composition.

In an embodiment the bitumen emulsion/granulate mixture, the sand/filler/fibre mixture and the final mixture of the two are cold-mixed. A cold mixing of the asphalt composition according to the invention is a more economic, cost-effective application in terms of energy consumption and technical requirements.

The inventors have found that, contrary to usual practice, cold-mix asphalt

compositions, particularly those as described here, can be used to asphalt "naked" ground surfaces and not only to repair or strengthen already asphalted ground surfaces. The structural requirements of an asphalt composition are particularly important in hydraulic engineering works, since for instance a permanently strong wave action or current has a highly erosive effect.

In an embodiment the bitumen emulsion/granulate mixture and the sand/filler/fibre mixture are mixed together before breaking of the emulsion occurs, and mixing takes place until breaking occurs. When the emulsion breaks the adhesion of the bitumen to the granulates begins, and curing of the asphalt composition will begin. The risk of subsidence of the emulsion is hereby limited to a minimum. The inventors have found that the sand/filler/fibre mixture must be added to the bitumen emulsion/granulate mixture before breaking of the emulsion occurs; if not, the coherence of the asphalt composition will be adversely affected.

The invention also relates to the use of the asphalt composition as described for stabilizing hydraulic engineering works, and to a method for stabilizing hydraulic engineering works, wherein an asphalt composition according to the invention is provided on a ground surface, which asphalt composition is spread and levelled. In an embodiment the ground is here excavated before the asphalt composition is provided. In a further embodiment the asphalt composition is provided here on geotextile and/or a sand asphalt layer.

An advantage of the asphalt compositions according to the invention is that the visco- elastic properties are improved without the internal stability of the mixture being compromised. An increased visco-elasticity allows highly flexible use of the asphalt compositions according to the invention for a wide range of applications, particularly in hydraulic engineering works. In contrast to the known asphalt compositions, no extensive and time-consuming ground preparation (such as placing additional, for instance stabilizing (asphalt) layers or foundations) need be carried out with the asphalt compositions according to the present invention. It suffices to excavate or scrape off the ground surface for asphalting, after which the asphalt composition is spread thereover. A layer of sand asphalt can optionally first be provided. For wet applications

(particularly applications wherein water seepage is a factor) the ground can be provided with geotextile, onto which the asphalt is poured. Such an application safeguards the ground against erosion.

Detailed description

The present invention is described in more detail hereinbelow. Different aspects or embodiments are shown. Each aspect or embodiment can be combined with another aspect or embodiment according to the invention, unless expressly stated otherwise. In particular any feature which is shown as being advantageous or preferred can be combined with any other advantageous or preferred feature. Unless stated otherwise, all terms used herein, such as scientific and technical terms, have the normal meaning as understood by a skilled person. Determined technical terms are elucidated on the basis of definitions for the purpose of elucidation. The term "about" as used herein with reference to a measurable parameter, such as a quantity, percentage, period of time and the like, comprises variations of +/- 10% or less, preferably +/- 5% or less, more preferably +/- 1% or less in the stated parameter. It will be apparent that the value with which the term "about" is associated is most preferred.

The present invention relates to an asphalt composition, in particular an open stone asphalt, for use in hydraulic engineering works, wherein the asphalt composition comprises the following components (shown as percentage by weight relative to the overall composition):

- 80 to 97% by weight of granulates;

- 0 to 12% by weight of sand;

- 0 to 5 % by weight of filler;

- 0 to 0.09% by weight of fibres;

- 3 to 6% by weight of bitumen, wherein the bitumen is provided as a bitumen emulsion comprising 50 to 70% by weight of bitumen.

In an embodiment the combined concentration of sand, filler and fibres is lower than about 12% by weight, preferably lower than about 11% by weight and more preferably about 10% by weight or lower. In a further embodiment the ratio (on the basis of mass) of the combined sand, filler and fibre fraction on the one hand and bitumen on the other is lower than 2.

"Hydraulic engineering works" are understood in the present invention to mean all hydraulic engineering-related works, more particularly dike or embankment (protection) works as well as erosion protection works adjoining waterways.

"Open stone asphalt" is understood to mean a material composed of stone chippings (as mineral granulates) and asphalt mastic with a high percentage of hollow spaces, preferably from 10 to 30%. This porosity volume is achieved in that the mixture comprises a relatively large amount of coarse granulate, for instance stone chippings, and relatively few finer constituents. "Granulates" are understood to mean the coarse mineral fraction or the mineral fraction of the asphalt composition which is larger than the sand fraction. Granulates are also understood to mean (coarse mineral) aggregates. In an embodiment the granulates comprise stone chippings, preferably limestone chippings. In an embodiment the granulates are limestone chippings with an average diameter greater than 14 mm. In a preferred embodiment the granulates are limestone chippings with a granulometry of 14/20. In a further preferred embodiment the granulates are limestone chippings with a granulometry of 20/40. In another preferred embodiment the granulates are limestone chippings with a granulometry of 14/40. For example for a granulometry of 14/20, this means that the granulates are held back on a screen with mesh of 14 mm and not held back on a screen with mesh of 20 mm. In other words, these are calibrated stone chippings with an average size between 14 mm and 20 mm, between 20 mm and 40 mm or between 14 mm and 40 mm. At least 85% of the aggregates will typically not be held back on a screen with mesh of respectively 20 mm (for granulometry 14/20) and 40 mm (for granulometry 14/40 or 20/40), and a maximum of 20% of the aggregates will not be held back on a screen with mesh of respectively 14 mm (for granulometry 14/20 or

14/40) and 20 mm (for granulometry 20/40). In an embodiment about 80, 81 , 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96 or 97% by weight of granulates is used. In a further embodiment 80 to 90% by weight of granulates is used. In a preferred embodiment the granulates are dust- free or substantially dust-free.

"Sand" is understood to mean the fine mineral aggregates. In an embodiment the sand fraction has an average diameter of less than 2 mm. In a preferred embodiment the sand fraction has a granulometry of 0/2. This means that the sand fraction is not held back on a screen with a mesh of 2 mm. In an embodiment about 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 1 1 or 12%) by weight of sand is used. In a further embodiment 5 to 10% by weight of sand is used.

"Filler" is understood to mean the finest (mineral) fraction. Non-limitative examples of fillers which can be used according to the present invention are fly ash, limestone powder or clay minerals such as kaolinite. The average grain size of the filler is typically less than 0.063 mm. The fraction not held back by a screen of 0.063 mm is generally deemed to be filler. The filler fraction generally comprises more than 85% particles smaller than 0.063 mm. In an embodiment the filler is basic. As non-limitative example use can be made of Duras Filler (Ankerpoort). Basic is also understood to mean alkaline. In this context this means that the pH in solution is higher than 7. In an embodiment the filler is a filler of type lb. In an embodiment about 0; 0.5; 1; 1.5; 2; 2.5; 3; 3.5; 4; 4.5; or 5% by weight of filler is used. "Fibres" are understood to mean inert fibres which can be used as additive in the production of asphalt compositions. Such fibres have the purpose of optimizing the viscosity of the bitumen compositions. In a preferred embodiment the fibres used are (industrial) cellulose fibres. As non-limitative example cellulose fibres with the brand name Technocel® can be used. In an embodiment about 0; 0.01 ; 0.02; 0.03 ; 0.04; 0.05; 0.06; 0.07; 0.08; or 0.09% by weight of fibres is used.

"Bitumen emulsion" is understood to mean an emulsion of bitumen in water. In addition to bitumen and water, such emulsion can also comprise other components, such as emulsifiers, stabilizers and the like. The preparation of bitumen emulsions and different types of bitumen emulsions are sufficiently known to the skilled person. A bitumen emulsion can in general be described as a liquid product in which bitumen is dispersed in the form of separate droplets through the entire continuous water phase. The droplets are held in suspension by electrostatic charges generated by an emulsifier. In an embodiment the concentration of bitumen in the bitumen emulsion is about 50; 52.5; 55; 57.5; 60; 62.5; 65; 67.5; or 70% by weight. In a preferred embodiment the concentration of bitumen in the emulsion is about 60% by weight. In an embodiment the concentration of bitumen is about 3; 3.25; 3.5; 3.75; 4; 4.25; 4.5; 4.75; 5; 5.25; 5.5; 5.75; or 6% by weight of the overall composition. The concentration of bitumen is preferably more than about 4% by weight of the overall composition. In an embodiment the bitumen emulsions according to the invention are slow-breaking emulsions. The breaking of a bitumen emulsion is understood to mean destabilization of the emulsion due to the separation of bitumen and the liquid in which it is emulsified. The point in time at which a bitumen emulsion breaks can for instance be visually determined. A colour change will for instance thus occur in the emulsion/asphalt composition when the emulsion breaks (brown before breaking and black after breaking). In an embodiment a cationic bitumen emulsion is used. The preparation of cationic bitumen emulsions and different types of cationic bitumen emulsions are sufficiently known to the skilled person. A cationic emulsion generally has a positive electrical charge. By way of example cationic bitumen emulsions can be obtained by addition of an acid, which ensures a positive charge. In an embodiment breaking-retardant components are added to such cationic bitumen emulsion.

In an embodiment the bitumen used in the bitumen emulsion according to the invention has a degree of penetration of 50/70 pen. The degree of penetration describes the penetration characteristics of bitumen. This parameter is related to the viscosity of bitumen and is associated with the hardness of bitumen. Determining the degree of penetration is sufficiently known to the skilled person. The degree of penetration (or penetrability) is specified according to European bitumen specification BS EN 12591 and can be determined in accordance with ASTM D5-97. In an embodiment use is made of Trinidad bitumen.

The asphalt composition according to the invention is characterized by a modulus of elasticity between about 10000 and 20000 MPa at 5 °C. In an embodiment the modulus of elasticity is about 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000 or 20000 MPa at 5 °C, preferably about 16000 MPa at 5 °C.

In an aspect the present invention relates to a method for preparing the asphalt composition according to the invention as described herein, wherein in a first phase the granulates are mixed with the bitumen emulsion to form a first mixture and the sand is mixed with the filler and the fibres to form a second mixture after which in a second phase the first mixture is mixed with the second mixture. It will be apparent that, in compositions without sand and/or filler and/or fibres, these components are not involved in the mixtures.

In an embodiment both the bitumen/granulate mixture, the sand/filler/fibre mixture and the mixture of the two are cold-mixed. Cold-mixing is understood to mean that the mixing or preparation takes place at ambient temperatures (normally between 0° and 40 °C). This in contrast to classic hot asphalt mixes, which are typically prepared and mixed at a temperature above 100°C.

In an embodiment the sand/filler/fibre mixture is added to the granulate/bitumen mixture before breaking of the bitumen emulsion occurs, and the two mixtures are finally mixed until breaking of the bitumen emulsion occurs.

The mixing times of the different mixtures can be determined empirically. The most important condition is that the mixing time of the bitumen/granulate mixture is sufficiently long to achieve complete mixing, but is short enough to prevent breaking. Mixing times of about 15", 30", 60", 90", 120", 150", 180" or longer can be applied as guide values. After addition of the sand/filler/fibre mixture to the granulate/bitumen mixture the mixing time must be sufficiently long to achieve homogenization of all components and the mixing must be discontinued at the moment of breaking of the bitumen emulsion in order to prevent premature curing (before the asphalt composition is spread onto a surface to be treated). Mixing times of about 15", 30", 60", 90", 120", 150", 180" or longer can be applied as guide values. It will be apparent that the indicated guide values can vary depending on the mixing equipment used, as well as on the quantities which have to be mixed.

The present invention also relates to the use of the asphalt compositions as described herein according to the invention for hydraulic engineering works, particularly for stabilizing hydraulic engineering works such as dikes, roadsides or embankments, and underwater ground structures.

In another aspect the present invention relates to a method for stabilizing hydraulic engineering works, wherein an asphalt composition as described herein according to the invention is provided on a ground surface, the asphalt composition being spread and levelled. In an embodiment the ground is excavated before the asphalt composition is provided. In a further embodiment the asphalt composition is provided on geotextile or on a sand asphalt layer.

According to the invention an open asphalt structure is likewise provided in hydraulic engineering works on dikes, embankments or as ground covering, wherein mutually adjoining strips of asphalt material according to the invention as described herein are provided. Such asphalt strips are assembled by first providing the ground surface with a ground filter layer. A first option herefor consists of covering the ground surface with geotextile. These strips of geotextile are placed parallel to each other and with a certain overlap, and the asphalt material is provided thereon. A second option consists of providing the ground surface with a layer of sand asphalt consisting of 4-8% bitumen and 96-92% sand fraction, on which the asphalt material is provided. Such ground filter layers have the purpose of safeguarding the ground against erosion (allow the water through but hold back the ground parts).

Examples

Table 1 shows examples of asphalt compositions which can be used according to the invention. These asphalt mixtures are characterized by a good enclosure,

homogenization, curing, water-permeability and structural strength.

It has moreover been established that the described characteristics of the asphalt compositions are better if in a first phase the granulates are mixed with the bitumen emulsion to form a first mixture and the sand is mixed with the filler and the fibres to form a second mixture, after which in a second phase the first mixture is mixed with the second mixture.

Table 1

Claims

1. Asphalt composition for use in hydraulic engineering works, comprising 80 to 97% by weight of granulates, 0 to 12% by weight of sand, 0 to 5% by weight of filler, 0 to 0.09% by weight of fibres and 3 to 6% by weight of bitumen, wherein the bitumen is provided as a bitumen emulsion comprising 50 to 70% by weight of bitumen.

2. Asphalt composition as claimed in claim 1, comprising 80 to 97% by weight of granulates.

3. Asphalt composition as claimed in claim 1 or 2, comprising 5 to 10%) by weight of sand.

4. Asphalt composition as claimed in any of the claims 1-3, wherein the granulates comprise limestone chippings.

5. Asphalt composition as claimed in any of the claims 1-4, wherein the granulometry of the granulates is 14/40.

6. Asphalt composition as claimed in any of the claims 1-5, wherein the granulometry of the sand is 0/2.

7. Asphalt composition as claimed in any of the claims 1 -6, wherein the filler is basic.

8. Asphalt composition as claimed in any of the claims 1-7, wherein the fibres are cellulose fibres.

9. Asphalt composition as claimed in any of the claims 1-8, wherein the bitumen emulsion is a slow-breaking bitumen emulsion.

10. Asphalt composition as claimed in any of the claims 1-9, wherein the bitumen emulsion is a cationic bitumen emulsion.

1 1. Asphalt composition as claimed in any of the claims 1-10, wherein the bitumen has a degree of penetration of 50-70 pen.

12. Asphalt composition as claimed in any of the claims 1-11 , wherein the total combined quantity of sand, filler and fibres amounts to a maximum of 12% by weight of the overall composition.

13. Method for preparing the asphalt composition as claimed in any of the claims 1 to 12, wherein in a first phase the granulates are mixed with the bitumen emulsion to form a first mixture and the sand is mixed with the filler and the fibres to form a second mixture, after which in a second phase the first mixture is mixed with the second mixture.

14. Method as claimed in claim 13, wherein the first mixture, the second mixture and the mixture of the first and second mixture are cold-mixed.

15. Method as claimed in either of the claims 13 or 14, wherein the first mixture is mixed with the second mixture before breaking of the emulsion occurs, and wherein the mixtures are mixed until breaking of the emulsion occurs.

16. Use of the asphalt composition as claimed in any of the claims 1 to 12 for stabilizing hydraulic engineering works.

17. Method for stabilizing hydraulic engineering works, wherein an asphalt composition as claimed in any of the claims 1 to 12 is provided on a ground surface, which asphalt composition is spread and levelled.

18. Method as claimed in claim 17, wherein the ground is excavated before the asphalt composition is provided.

19. Method as claimed in claim 17 or 18, wherein the asphalt composition is provided on geotextile.

20. Method as claimed in claim 17 or 18, wherein the asphalt composition is provided on a sand asphalt layer.