The present invention relates to an asphalt composition and a process for preparing such a composition. The invention also relates to a mastic composition that can be used in the preparation of the asphalt composition and to a road surface comprising such an asphalt composition.

Asphalt compositions, sometimes also called asphalt concrete, comprise bitumen- containing bituminous binder material and aggregates. The binder material can be bitumen, but it may also contain polymers and other organic material to provide a good adhesion of the binder material to the aggregates. The aggregates are typically mineral aggregates, such as fine filler, sand, gravel or optionally ground stones. The asphalt compositions are commonly used in the preparation of road surfaces.

Bitumen is a dark-coloured solid or viscous liquid that occurs in nature or is obtained as a residue in petroleum refining. It is a mixture of paraffinic and aromatic hydrocarbons and heterocyclic compounds containing sulphur, nitrogen and oxygen. It tends to be soluble in carbon disulfide and trichloroethylene. It softens when it is heated. With filler and aggregates it forms asphalt. Bitumen may be modified to alter its properties. Polymers may be used to modify bitumen. Known polymers that are used for this purpose include natural rubber, styrene-butadiene rubber (SBR), styrene-butadiene-styrene block copolymer (SBS) and ethylene vinyl acetate copolymer (EVA). Also crumb rubber, i.e. recycled rubber from automotive and truck scrap tires, may be used to modify the properties of bitumen. When filler, i.e. aggregates with a particle size of smaller than about 63 pm, is combined with bitumen, mortar is obtained. When sand, i.e. aggregates with a particle size ranging from about 63 pm to about 2 mm, is added to bitumen mortar mastic, or in short mastic, is obtained.

Asphalt compositions for road applications are to fulfil a number of requirements.

Evidently, the road surface should have a satisfactory durability or life expectancy. One of the requirements that has a growing interest is the noise performance of the road surface. Dense asphalt concrete is frequently used as road surface. The traffic noise on this type of road surfaces have become a subject of study in view of the unacceptable level of noise, especially in densely populated areas. Dense asphalt concrete tends to be very durable. In a dense asphalt concrete aggregates with a variety of particle sizes are present such that the resulting construction of aggregates and bituminous binder have a low amount of voids. In porous asphalt compositions, the proportion of relatively large aggregates is higher so that the voids are less filled by small aggregates. The porous asphalt compositions have as advantage the excellent drainage performance for rain. Further, the obtained voids absorb traffic noise well. The highest noise reduction is obtained when road surfaces are porous, flexible and have a fine surface texture. Porosity can be obtained by use of a gap-graded mineral fraction, implying that mineral particles, i.e. aggregates or fillers, with a certain size are largely absent. The mineral particles having sizes that are above the gap will form a granular skeleton. This skeleton provides stability to the mixture. The minerals with particles sizes that are below the gap, have a larger specific surface than the minerals in the skeleton. As a result, when minerals are mixed with the bituminous binder most of the binder will adhere to the particles that are below the gap, to form mastic. The mastic in these mixtures will bind the particles in the skeleton to form porous asphalt. The surface texture is controlled by selection of the mineral grading.

In an alternative investigation it was found that when a bituminous binder material was modified with a polymer, the bitumen properties could be altered, and the life expectancy could be prolonged. Therefore, several studies were undertaken to investigate whether the addition of polymers to the bituminous binder would have an effect on the life expectancy of road surfaces that have a good noise reducing performance. Polymer-modified bitumen is used as the binder for producing porous open-textured asphalt. The polymer can be a rubber, for example styrene butadiene rubbers or ground tire rubber. In the preparation of this polymer-modified bitumen small droplets or particles of polymer material are mixed with the heated bitumen under severe stirring such that a completely homogeneous mixture is obtained.

An example of the preparation of a polymer-modified bitumen is provided by WO

201 1/074003. This document discloses a modified bitumen composition that comprises bitumen, a minor amount of crumb rubber, a small amount of FCC spent catalyst and optionally another low-value polymer. The ingredients are mixed at elevated temperature whilst homogenizing, to yield a modified bituminous binder. The polymer-modified bitumen tends to be very cohesive and relatively flexible.

The use of polymer-modified bitumen enables the design of a very porous asphalt mixture with a high effective void percentage. The resulting road surface shows a reasonably good acoustic performance.

An alternative method for obtaining good noise performance can be obtained by using layered porous asphalt. In this case a porous asphalt composition with relatively uniform but large aggregates is used as the lower layer, providing large voids for excellent drainage performance. On top of the layer with large aggregates, a layer of smaller aggregates with a uniform particle size is placed. The resulting road surface with these two layers yield an improved noise reduction, that is mainly due to the fine texture of the upper layer which incurs less noise caused by tires etc. , and the increased thickness of the two layers which provide a better noise absorption.

So-called Poro-Elastic Road Surfaces (PERS) show very good noise reducing properties. In PERS mineral aggregates are completely or partially replaced by much softer particles, often obtained from scrap tires. The binder in PERS mixtures is a synthetic polymer binder, such as polyurethane. An example of such a road pavement is described in US 2004/0044104. According to this US patent application, waste rubber particles with a size of 2 to 8 mm were mixed with an epoxy or urethane binder material and with stone aggregates having particles sizes in the range of less than 0.5 mm to about 30 mm. The resulting mixture was used as elastic top coat on a pavement surface. The specification teaches that when the size of the waste rubber particles is below 1 mm, the elasticity is insufficient and the noise reduction is unsatisfactory. When the particle sizes are 10 mm or bigger, the durability of the pavement is too low.

In addition to the high costs of such a pavement due to the use of expensive binder material, the workability of the mixture is also short. Owing to the curing time of the polyurethane or epoxy polymers, the workability time is limited, say in the order of 10 to 30 minutes. This is often regarded as too short for road surface manufacture. Further, it appeared that such pavements have a very short life expectancy.

Another proposed solution to obtain a high level of noise reduction on pavements is described in JP 2007-154539. According to this application an elastic paving material, comprising bitumen and an ethylene vinyl acetate copolymer as binder, aggregate, and rubber chips or rubber powder, is used to fill the voids of a porous pavement. However, by filling the voids, the drainage performance is reduced and thereby the reduction of the voids content tends to increase the noise level. Hence, this solution is also unsatisfactory and does not add any advantage over the teachings of US 2004/0044104.

Further it has been found that the life expectancy of PERS remains too short for practical application. Failure mechanisms that are reported for current day PERS focus on:

- durability, i.e. disintegration of the material under the influence of weather and traffic; - delaminating, i.e. the adhesion between the PERS and the bituminous asphalt

underlying structure is lost; and

- skid resistance, i.e. especially in wet conditions the rubber particles of PERS provides limited skid resistance.

Therefore, it is an objective of the present invention to obtain an asphalt composition having a proper balance between the noise-reducing performance on the one hand and not having the drawbacks of PERS, such as limited skid resistance, delamination and

disintegration of PERS or at least to a lesser extent, on the other hand. It has now surprisingly been found that such a proper balance can be obtained when the asphalt composition contains a bituminous binder and gap-graded solid particles composed of elastic particles and mineral aggregates.

Accordingly, the present invention provides an asphalt composition comprising a bituminous binder material and solid particles composed of mineral aggregates and elastic particles, which elastic particles have a maximum particle size of at most 2.8 mm, and which solid particles are gap-graded, wherein the upper limit of the gap is bigger than the maximum particle size of the elastic particles, and wherein the mineral aggregates include particles with particle sizes above the upper limit of the gap as defined in claim 1.

In the invention the solid particles composed of mineral aggregates and elastic particles, the latter having a maximum size of at most 2.8 mm, are gap-graded. Such a gap is defined by a lower and upper limit. In the asphalt composition solid particles having a size within the gap are substantially absent. Due to the gap-graded solid particles and to the mineral aggregates with sizes above the upper limit of the gap, porosity is introduced into the road surface that is produced from the asphalt composition. This has a positive effect on the noise performance of such road surface. The mineral aggregates are bound to each other by means of a mastic that comprises the bituminous binder material and the fine particles, i.e. mineral aggregates with a size of 2.8 mm or less and the elastic particles. Without being bound by theory, it is believed that the elastic particles are present between the coarse aggregate particles and ensure that a direct mutual contact of coarse aggregate particles cannot develop. Furthermore, the elastic particles tend to soften the mastic. These two effects result in a softening of the links between individual coarse mineral aggregates, allowing easier movement upon application of a load and thus lowering the mechanical impedance. If the maximum size of the elastic particles would be more than 2.8 mm, e.g. 4 mm in view of the series of standard sieves according to EN 12697-2 used for grading, then the coarse mineral aggregates above the gap would have a size e.g. up to 16 mm resulting in a rough surface structure and consequently insufficient noise reduction.

The elastic particles introduce elasticity into the mastic. Elasticity is the tendency of solid materials to substantially return to their original shape after being deformed. Solid objects will deform when forces are applied on them. If the material is elastic, the object will return to its initial shape and size when these forces are removed. Hereto the solid particle fraction with sizes below the gap comprise softer elastic particles as a complete or partial replacement for mineral aggregates. These softer elastic particles may act as bumper material that is present between the skeleton formed by the larger aggregates. As a result the PERS related problems with respect to skid resistance are overcome. This is because the fraction above the gap, which is responsible for the surface texture, is formed by mineral aggregate particles similar to existing porous asphalt.

Due to the use of a bituminous binder the delamination and disintegration properties of PERS using polyurethane or epoxy polymers as a binder do not occur. This has a positive effect on the durability and life expectancy of the resulting road surface. The mastic content (bituminous binder and solid particles less than 2.8 mm) of the asphalt composition according to the invention may be increased by 20% compared to a common porous asphalt composition without loss of void ratio and porosity, e.g. if a common porous asphalt composition comprises 20% mastic, then the asphalt composition according to the invention may comprise up to 24% mastic, while void ratio and porosity are maintained at a similar level. It is assumed that this finding proofs the function of the elastic particles in the composition according to the invention for enlarging the distance between the coarse aggregates having sizes above the gap. A higher content of mastic also contributes to a longer service life.

The elastic particles may be formed from any material that has a lower stiffness than the mineral aggregates, stiffness being the extent to which a body resists deformation in response to an applied force. The elastic particles in the present invention are in the form of distinct particles, suitably having a particle size of 2 μιη to 2.8 mm, more preferably from 63 μιη to 2 mm.. Preferably, the elastic particles are elastic polymer particles that comprise an elastomer material.

It is emphasized that the elastic polymer particles that are preferably present in the asphalt composition of the present invention, are present in a different shape from the polymers that are present in polymer-modified bitumen compositions. In the latter compositions, polymers are heated and homogenised so that a homogeneous mixture of polymer and bitumen is obtained. The polymer chains form a matrix for the bitumen molecules and in this way alter the properties of the bitumen binder. In contrast therewith, the elastic polymer particles in the present invention are in the form of distinct particles, suitably having a particle size of 2 μίτι to 2.8 mm, more preferably from 63 m to 2 mm.

The term gap-graded solid particles refers to solid particles having a particle size distribution that is characterized by gap-grading, gap-grading being defined as particle size distribution for the solid particles wherein particles of certain sizes are substantially absent. The particle sizes that are absent, form the gap, and the gap is characterized by a lower and an upper limit. For the present invention the upper limit of the gap is bigger than the maximum size of the elastic particles, which upper limit thus may be bigger than 2.8 mm. By increasing the difference between the upper limit of the gap and the maximum size of the polymer particles the voids become larger, so that the drainage performance of the asphalt composition and its noise-reduction performance improve. Therefore, the upper limit of the gap and the maximum particle size of the polymer particles is selected such that their difference is preferably from 1 to 5 mm, more preferably, from 2 to 4 mm. Also included are embodiments wherein the lower limit of the gap is bigger than the maximum size of the elastic particles, e.g. at least one millimetre bigger. More preferably, the grading is such that the lower limit of the gap is at least equal to the maximum size of the elastic particles. In this way, the resulting asphalt composition lacks a certain grade of aggregates which facilitates the formation of voids and at the same time the elastic particles can easily be taken up in the bituminous binder and provide the mastic to bind the larger aggregates that form a skeleton, as described above. The asphalt composition according to the present invention yields a road surface comprising the asphalt composition according to the present invention, wherein the aggregates are bound by means of the bituminous binder material into which the relatively small elastic, preferably elastic polymer, particles have been incorporated. Since the solid particles are gap-graded, they provide for a level of voids, which is beneficial for the noise reduction. Moreover, since the bituminous binder material contains small elastic particles, these elastic particles function as bumper material that prevents direct contact between the coarse mineral aggregates in the skeleton and at the same time, due to their elasticity, provides resilience between the aggregates. In this way the stiffness and also the mechanical impedance of the road surface is reduced, which has a beneficial effect on the reduction of the noise level. Since a bituminous binder is used and since no use is made of an additional polymer such as a polyurethane, as a separate binder, there is no risk of undue disintegration or delamination. The present invention therefore also provides road with such surfaces.

The preferred elastic polymer particles comprise an elastomer material. This material may be similar to those that are known to be included in polymer-modified bitumen compositions. The latter materials may suitably be selected from a variety of rubber types. These rubber types may also be used in the composition according to the present invention. These rubber types include natural rubber, which comprises a polymer of isoprene. Synthetic rubbers include polybutadiene and polychloroprene. Copolymers of conjugated dienes and aromatic vinyl compounds are also suitable. These types include especially block copolymers of styrene and butadiene or styrene and isoprene. Other types of synthetic rubber materials include acrylonitrile-butadiene copolymers ('nitrile rubber'), copolymers of isoprene and isobutylene ('butyl rubber'), polysiloxane ('silicone rubber'), ethylene-propylene-diene (EPDM) rubber, polysulphide rubber. Polyolefins and polyurethanes may also be given elastomer properties. Other elastomer materials may also be used. Examples thereof include polyvinylchloride and poly(meth)acrylates. All these materials may be used in the asphalt composition of the present invention. Some polymers have some preference. Accordingly, the asphalt composition according to the present invention preferably comprises polymer particles comprising an elastomer material, selected from the group consisting of natural rubber, styrene-butadiene copolymers, polychloroprene, nitrile rubber, butyl rubber, polysulphide rubber, polyisoprene, EPDM rubber, silicone rubber, polyurethane rubber, polyolefins rubber, and mixtures thereof.

Although natural rubber and the above-mentioned synthetic polymers are preferred, it is also feasible to use other natural polymeric material. A suitable example is provided by cork particles. These particles are buoyant, elastic and fire resistant. Cork comprises suberin, a rubbery material that consists of a polyaromatic and a polyaliphatic domain. Aromatic monomers include hydroxycinnamic acid and derivatives, and the aliphatic monomers include unsaturated α-hydroxyacids and α,ω-diacids having 18 carbon atoms. Cork is used in concrete and may be used in asphalt compositions according to the present invention.

To give the elastic polymer particles greater durability the elastic polymer particles preferably comprise an elastomer material that has been subjected to crosslinking. The crosslinking may be effected in a variety of ways, dependent on the type of the elastomer. It is well known to crosslink rubber-type materials by vulcanization with sulphur. The vulcanization is especially suitable for elastomer material that has been obtained from the polymerization with at least one diene. Vulcanization of natural rubber, polyisoprene, polybutadiene, styrene butadiene rubber, styrene isoprene copolymers and chloroprene may suitably be effected with sulphur. Suitably, the elastomer material comprises vulcanized natural rubber. For other polymers different crosslinking agents may be used, such as peroxides, metal oxides, quinones or nitrobenzene compounds.

The elastic polymer particles may comprise additional components in order to increase their durability. Such additional components may comprise polymer fibres providing reinforcement to the particles. Carbon, chlorine compounds and metal compounds may also be added to provide additional wear resistance. It is advantageous to employ crumb rubber as polymer particles in the present invention. By crumb rubber is understood ground car and lorry tires, in particular used car and lorry tires. The use thereof has the advantages that the ground tires comprise vulcanized rubber. Tires have commonly been reinforced by means of carbon and fibres. Thus the resulting particles have also a good wear resistance. Moreover, by applying crumb rubber in the present invention, the invention provides a useful destination for waste material.

The bituminous binder material that is used in the asphalt composition according to the present invention comprises bitumen. The bitumen can be selected from a variety of bitumen types. Dependent on the ultimate purpose of the asphalt composition, the skilled person may opt for the selection of a rather soft bitumen, i.e. a bitumen with a high penetration, or a relatively hard bitumen, i.e. a bitumen with a low penetration. Suitable bitumen types include those with a penetration up to 220 dmm, e.g. from 40 to 220 dmm, measured in accordance with EN 1426. When selecting the type of bitumen advantageously the skilled person will ensure that the bitumen will allow a relatively low processing temperature. The temperature at which the bitumen will be processed is preferably such that it is below the melting temperature of the elastomer material in the elastic polymer particles. If the temperature would be higher, there is a risk that elastic polymer particles will be homogenised and more or less be dissolved in the bitumen thereby possibly reducing their resilience function between the coarse aggregates.

In this context it is observed that the skilled person may also select a polymer- modified bitumen as bituminous binder material, i.e. a binder material that material contains bitumen and, in addition, a polymer that has been homogenized in the binder material. In such a case the bitumen has been modified in advance by the addition of one or more polymers separately from any addition of polymer particles, prior to the preparation of the asphalt composition. Such polymers may be elastomers as described above, including styrene butadiene rubber, styrene butadiene block copolymers, linear or star-shaped; styrene isoprene block copolymers, linear or star-shaped, and EPDM rubber. Alternatively thermoplasts may be added, such as, polyvinylchloride, ethylene vinyl acetate; copolymers of ethylene and methyl or butylene (meth)acrylate, polyethylene or atactic polypropylene.

The bituminous binder material may comprise further other materials that are also known in conventional bituminous binders. Such compounds include waxes, heavy oil fractions and plasticizing compounds, such as fatty oils, tallow oil etc. The addition of such compounds may have the purpose of adjusting the resilience properties or thermal properties of the bituminous binder material.

The aggregates in the asphalt composition according to the present invention can be selected from any known mineral aggregates that are known in the art. The aggregates tend to be granular and have a variety of sizes, and thus a variety of diameters. The aggregates may be subdivided in at least three groups; one first group with a diameter of at least 2.8 mm; one second group with a diameter ranging from at most 2.8 mm to 63 pm and a third group having granular particles with a diameter of at most 63 Mm. Suitably, the aggregates may be subdivided in three groups; one first group with a diameter of at least 2 mm; one second group with a diameter ranging from at most 2 mm to 63 pm and a third group having granular particles with a diameter of at most 63 pm. The same subdivision may be applied to all solid particles, including the elastic particles. The finer filling material, e.g. having a maximum diameter of 63 pm, may be defined as a formally dosed artificial fines or as a separate form of aggregate. The maximum diameter of the particle size of the aggregates in the first group generally does not exceed 32 mm. Asphalt compositions typically contain aggregates from all three groups. In the asphalt compositions according to the present invention the solid particles are gap-graded. That typically may result in the absence of aggregates with intermediate particle sizes. Suitably, the gap is 1 to 5 mm, preferably 2 to 4 mm. That may result in an asphalt composition that for instance substantially lacks particles within a particle size range of about 2 to about 7 mm, preferably from about 2 to 5 or 6 mm. It is emphasised that the lower limit of the gap may be lower, e.g. 1 mm, so that aggregates with a particle size in the range of about 1 to about 5 mm, preferably about 1 to about 4 mm, are substantially absent in the composition according to the present invention.

Generally, the lower the maximum size of the coarse aggregates, the lower the lower limit and upper limit of the gap, as well as the narrower the gap should be. Moreover, as the gap limits are low and the gap width is small, the requirements for the maximum allowable amount of solid particles having a size in the gap (accidentally present caused by the sieves used for grading) will become more stringent. By substantially absent is typically understood that the relative proportion of the substantially absent fraction is present in an amount of at most 10 %vol, preferably 5 %vol, more preferably less than 0.5 vol%, based on the volume of the total aggregates and elastic particles. Such is obtained by employing the sieves for particle selection in accordance with a standard that is customary employed in the field of road pavements. Suitably, aggregates comprise mineral material selected from sand, gravel, crushed stone, slag and ground concrete.

In this context it is observed that the particle sizes in aggregates and thus also for the elastic particles or elastic polymer particles are determined in accordance with the standard that is typically applied in field of road pavements, i.e. EN 12697-2. This standard defines the sieves and the procedures to be used for the various fractions of aggregates.

It is not necessary to use fresh virgin aggregates. From an environmental point of view it is advantageous to use reclaimed asphalt aggregates. In US 3999743 a process for the recycling of reclaimed asphalt aggregates is described wherein reclaimed asphalt lumps are crushed and separated into coarse particles and fine particles, the coarse particles are heated in a hot temperature zone of a drying and heating drum, and the fine particles are heated in a cooler temperature zone of the same drum. The heated coarse and fine particles are combined and may be used in the production of an asphalt composition. A similar process is described in US 4096588. Preferably, the present asphalt composition also contains at least partly reclaimed asphalt aggregates as mineral aggregates, with the proviso of the gap- grading discussed above.

In addition to particulate mineral aggregates, the asphalt composition according to the present invention also comprises elastic particles with a maximum particle size of 2.8 mm. That means that at least part of the aggregates of the second and third group has been replaced by elastic particles. It is possible to replace all these aggregates by elastic particles. However, it is not necessary to replace all aggregates of the second and/or third group by elastic particles. The elastic particles are suitably selected from the sizes of the second group only, suitably having a particle size within the range of 63 μηι to 2.8 mm. If the elastic particles are smaller than this lower limit, the contribution of the elasticity of the elastic particles is diminished. Suitably, the asphalt composition contains aggregates in all sizes in addition to the polymer particles, with the exception of sizes within the gap. The amount of elastic particles in the present asphalt composition is preferably in the range of 3 to 20 %vol, such as 3 to 18 %vol, based on the volume of the bituminous binder material, aggregates and elastic particles. If the amount is less than 3 %vol, then the noise reduction may be insufficient. If the content is more than 20%, then the voids may become occupied by the elastic particles thereby affecting porosity. The amount of mineral aggregates is

advantageously in the range of 90 to 65%vol, such as 90 to 70 %vol, based on the volume of the bituminous binder material, aggregates and elastic particles. The aggregates suitably include aggregates from all three groups. The relative distribution of the aggregates from these three groups can be determined by the skilled person, i.a. dependent on the desired porosity of the resulting road pavement. As indicated above, the skilled person may choose for the use of rather uniform coarse aggregates if an open porous road surface is desired. Typically, the asphalt composition according to the invention comprises solid particles, composed of mineral aggregates and elastic particles, in the range of 70 to 85 %vol of the first group, 2.5 to 10 %vol of the second group and 2.5 to 7 %vol of the third group, based on the volume of the aggregates and elastic particles, wherein the groups represent the mineral aggregates and elastic particles with a particle size of≥ 2.8 mm, of 63 μηι to 2.8 mm, and of <63 μιη, respectively. In the invention the first group having a particle size of≥ 2.8 mm only comprises mineral aggregates. At least a part of the solid particles in the second group consists of elastic particles. Suitably, the elastic particles comprise 50 to 100 %vol of the second group, based on the volume of the second group. It is also possible to replace mineral aggregates in the third group by elastic particles. Such replacement may also be for 50 to 100 %vol, based on the volume of the third group. It is particularly advantageous to ensure that the second group consist for substantially 100 %vol of elastic particles. The amount of bituminous binder material in the present asphalt composition is preferably in the range of 9 to 17.5 %vol, based on the volume of the bituminous binder material, aggregates and elastic particles.

The present asphalt composition may be prepared in a conventional way.

It is, however, advantageous if the processing temperature is kept relatively low especially when elastic polymer particles are used in order not to melt the elastomer material in the elastic polymer particles. Methods for preparing asphalt compositions at relatively low temperatures are known in the art, for example providing a bituminous binder material, and a solid particles fraction according to the specifications discussed, heating the bituminous binder material to an elevated temperature, e.g. in the range of 150 to 190 °C, optionally preheating the mineral aggregates from the solid particles fraction for drying and preheating purposes such as to a temperature of e.g. about 1 10 °C and combining the heated bituminous binder material with the solid particle fraction including relatively cold elastic particles.

Thus, the aggregates, optionally after drying and heating, may be mixed with heated bitumen and the elastic particles. It is to be ensured that the resultant temperature of the mixture is such that the physical shape of the polymer particles is at least to an extent retained. Therefore the temperature is suitably at most 150 °C, more preferably in the range from 100 to 145 °C.

A suitable example of a process for preparing the composition according to the invention is taught in EP 1767581. This patent describes a method for preparing an asphalt mix wherein at a temperature in the range of 75 to 1 10 °C foamed bitumen and aggregate material are contacted and mixed, wherein the moisture content of the aggregate material when it is contacted with the foamed bitumen is less than 0.5%wt, based on the mass of the aggregate material. A variation of this method can be applied when the skilled person also adds polymer particles to the aggregate material that is being contacted with the foamed bitumen. Since elastomer material generally will not melt at a temperature in the range of 75 to 1 10 °C, this known method can be used for the preparation of the present asphalt composition, also when elastic polymer particles are used. Foamed bitumen may be obtained by the method described in GB 1325916. According to this method water is injected into hot bitumen to obtain a desired open structure and low viscosity.

Thus, a preferred method for producing the asphalt composition according to the present invention uses foamed bitumen. Accordingly, the present invention provides a process for preparing an asphalt composition comprising a bituminous binder material and solid particles composed of aggregates and elastic particles,

in which process the bituminous binder material is heated to an elevated temperature; the heated bituminous binder material at elevated temperature is passed to an expansion chamber;

water is passed to the expansion chamber to contact the heated bituminous binder material to form steam, thereby forming foamed bitumen; and

the foamed bitumen is combined with the solid particles, wherein the elastic particles have a maximum particle size of at most 2.8 mm, and which solid particles are gap-graded, the gap being defined by a lower and an upper limit, wherein solid particles of a size between the lower and upper limit are substantially absent, wherein the upper limit of the gap is bigger than the maximum particle size of the elastic particles, and wherein the aggregates include particles with particle sizes above the upper limit of the gap, yielding an asphalt composition.

The bituminous binder material is heated to an elevated temperature. The temperature is selected such that at the prevailing conditions water will evaporate to form steam and thus cause the foaming of the bitumen. Whereas the process is suitably carried out at ambient pressure, the temperature of the bituminous binder material is suitably above the standard boiling point of water. Preferably, the bituminous binder material is heated to a temperature in the range of 125 to 230 °C, preferably from 150 to 190 °C.

Although it is possible to heat the water also, it is most cost effective to pass the water to the expansion chamber at ambient temperature, i.e. typically in the range of 15 to 25°C. The amount of water that is passed to the expansion chamber is suitably such that foaming of the bituminous binder material will be accomplished whereas the remaining amount of water in the foamed bitumen does not get too high. Suitably, the added amount of water is in the range of 2 to 4, more preferably from 2.5 to 3%wt, based on the combination of bituminous binder material and water. The solid particles may comprise material from all three groups, i.e. the mineral aggregates with a particle size of≥ 2.8 mm, mineral aggregates and elastic particles of 63 μπι to 2.8 mm, and of <63 μιη, respectively. Preferably, the subdivision of the aggregates is according to the particles size of≥ 2 mm, of 63 μηπ to 2 mm, and of <63 μηπ, respectively. The aggregates having a particle size of at least 2.8 mm is suitably heated to a temperature in the range of 100 to 180 °C. This will allow an easy mixing process when it is brought into contact with the foamed bitumen, which may have a temperature in the range of 60 to 145 °C, preferably from 75 to 110 °C. Moreover, this will ensure that the aggregates will be essentially dry so that no additional water is added to the foamed bitumen. The finest fraction may also be heated to the temperature of the more coarse aggregates. However, suitably the finest fraction, i.e. aggregates with a particle size of less than 63 μιη, has ambient temperature when it is combined with the foamed bitumen.

The amount of mineral aggregates with a particle size of 63 μηη to 2.8 mm, may be small or even be zero. At least a significant part thereof will suitably be taken by the elastic particles. If such mineral aggregates are being used, they may also be heated in the same or similar way like the more coarse aggregates.

The elastic particles are typically not heated. They are suitably at ambient

temperature, i.e. at 15 to 25 °C, combined with the mineral aggregates and foamed bitumen by mixing in an asphalt mixer. Since the temperature of the asphalt mixer will be relatively low, in general not exceeding 145 °C, the elastic particles essentially retain their shape.

In the process described above, the aggregates are suitably heated. Suitable temperatures of the aggregates are in the range of 100 to 170 °C. These temperatures ensure that the bituminous binder material can conveniently be mixed with the aggregates.

In the step wherein the foamed bituminous binder material is combined with the solid particles, additional binder material may be added. Such binder material may include additional bitumen or other such as heavy oils, waxes, resinous polymers, fatty oils etc.

Especially when the aggregates contain reclaimed aggregates it may be advantageous to add a rejuvenating agent. There is a myriad of products that are presently being used and marketed as rejuvenating agents for recycled road pavement. Such products are generally classified as flux oils, viscosity graded asphalt and a large variety of proprietary formulations. A potential rejuvenating agent is a shale oil modifier. Commonly used are crude oil fractions, preferably having a viscosity of at least 200 cSt at 60 °C, animal oils, vegetable oils and mixtures thereof. The viscosity is determined in accordance with NEN-EN 12595. The use of relatively light crude oil fractions has an environmental drawback in that it evaporates and thus produces hydrocarbonaceous vapours that are undesirable from an environmental point of view. Therefore, the rejuvenating agent is preferably a vegetable oil, more preferably selected from soybean oil, sunflower oil, rapeseed oil, corn oil, peanut oil, olive oil, coconut oil, palm oil, palm kernel oil and mixtures thereof, more preferably palm oil or palm kernel oil. The use of such oils is more sustainable and also shows a low volatility and thus has an long- lasting effect on the bitumen.

The present invention also enables the skilled person to prepare the starting suspension of bituminous binder material and elastic particles. Therefore, the present invention also provides a mastic composition, comprising a bituminous binder material and elastic particles, which comprises a suspension of elastic particles having a maximum particle size of 2.8 mm, preferably 2 mm, in the bituminous binder material. Preferably the elastic particles are elastic polymer particles, wherein the polymer particles comprise an elastomer material. This mastic composition differs from known conventional mastic compositions in that it is in the form of a suspension of elastic polymer particles in a bituminous binder. Also when the elastic particles are elastic polymer particles, it is different from a polymer-modified bituminous binder composition in that the polymer-modified bituminous composition comprises homogenized polymer, whereas the mastic composition according to the present invention contains identifiable particles, e.g. polymer particles, in a matrix of bituminous binder. The mastic composition according to the present invention may comprise mineral aggregates in addition to the elastic particles. These mineral aggregates advantageously also have a maximum particle size of at most 2.8 mm, preferably 2 mm. Suitably, the mastic composition comprises a proportion of the elastic particles in the total volume of aggregates and elastic particles in the range of 25 to 65 %vol, based on the volume of the elastic particles, aggregates and bituminous binder. In this way the mastic composition can be used as if it were a conventional mastic composition, whereas the elastic particles will provide the desired elasticity and thus noise reduction, to the eventual road surface.

The amount of bituminous binder material in the mastic composition is preferably from 30 to 75 %vol based on the volume of the bituminous binder material, elastic particles and, optionally, aggregates. The mastic composition is different from the asphalt composition according to the present invention at least in that the aggregates have a maximum particle size of at most 2.8 mm. Moreover, the mastic composition suitably has a different viscosity from that of the asphalt composition. The shear modulus determined by means of a dynamic shear rheometer of the mastic composition at 10 °C is suitably in the range of at most 350 MPa, preferably 25 to 200 MPa, such as 100 to 200 MPa at a loading frequency of 10 Hz.

The invention will be further elucidated by means of the following examples.

EXAMPLE 1

In order to show that the mastic of the asphalt composition according to the invention has a lower stiffness than a similar mastic wherein no elastic material is present, two mastic compositions were prepared. The first mastic composition ("Mastic 1") consists of 22.0 %vol of dust, i.e. mineral aggregates having a particle size below 63 pm, 23.4 %vol of sand, i.e. sand mineral aggregates having a particle size of 63 Mm to 2 mm, and 54.6 %vol of a standard penetration grade bitumen, having a penetration of 70/100. The second mastic composition ("Mastic 2") contained the same levels of dust and bitumen but contained 23.4 %vol of recycled rubber crumbs from scrap tires, having a particle size of 63 pm to 2 mm instead of sand.

The shear modulus of the two mastic compositions was determined in a dynamic shear rheometer (DSR). The complex shear modulus is an indicator of the stiffness or resistance of asphalt binder to deformation under load. The tests were carried out at a cylindrical sample having a diameter of 6 mm and a height of 20 mm. These specimens end in 4 mm high steel rings. The steel rings allow the specimens to be damped into the DSR and effectively reduce the specimen height to 12mm. The cylindrical test sample was put upright and an oscillating torsion load was applied. Hereto the specimen is clamped and fixed at the bottom and loaded by torque applied via the upper ring. Tests are done in the linear visco- elastic range of the material. The shear strain and applied torque was measured. The number of load cycles per second is called the loading frequency. For each loading frequency, the ratio between the applied shear load and the measured shear strain provides the shear modulus of the material. The tests are done at various temperature and frequencies and on the basis of the obtained data a stiffness master curve is constructed which provides a stiffness fingerprint of the tested mastic. At 10 °C the shear stiffness as listed in table 1 are obtained.

For bituminous materials a higher shear modulus is typically obtained at high loading frequency and at a low loading frequency a lower shear modulus is obtained.

The results of the determinations is shown in Table 1 below.

Table 1

The results show that the shear modulus for Mastic 2 is considerably lower than that of Mastic 1. This provides proof that the mastic composition according to the invention is significantly less stiff than the typical mastic composition. Since the mastic composition provides a mastic layer between mineral aggregates in a road surface, the less stiff mastic results in more flexible connections between the mineral aggregates above the gap. This results in a softer material with lower mechanical impedance and thus less noise that is created by traffic. EXAMPLE 2

Three asphalt compositions according to the invention were made as shown in below Table 2 and compared to a conventional porous asphalt (PA) 5 asphalt composition (a very open asphalt composition) having a gap between 0,63 pm to 1 mm. In mixtures INV the sand fraction (63 pm - 2 mm) was replaced by rubber crumbs taking into account the difference in density between the sand and rubber. The mastic is based on a polymer modified bitumen. In mixtures INV 2 and INV 3 the mastic fraction is 110%, respectively 120% compared to INV 1 = PA 5 = 100%. The mixtures were compacted with a gyrator at 30 rpm resulting in a compacting degree of about 100%.

Table 2.

The above results of PA 5 and INV 1 show that upon introduction of resilient particles the distance between the coarse aggregates is increased, and the void % is increased. The "extra" space can be used for incorporation additional mastic, while maintaining the void % at the level of PA 5 as is apparent from INV 2 and INV 3.