PROCESS FOR PREPARING AN ASPHALT COMPOSITION

Abstract: The present invention provides a process for preparing a dense-graded asphalt composition which comprises adding a hard binder component to a mixture of a soft binder component and aggreagte at a temperature of less than 140 DEG C.

Description: PROCESS FOR PREPARING AN ASPHALT COMPOSITION The present invention relates to a process for preparing an asphalt composition. The temperature at which a bitumen s mixed with aggregate to produce an asphalt composition ready for 5 use on roads is normally in the range of 140 to 170 °C, although some documents, e.g. US 3,832,200, teach that even higher temperatures should be applied. Since, it is nowadays well appreciated that such hot bitumens may create potential health, safety and 10 environmental hazards, much effort is directed in this field of technology to the development of asphalt compositions which can be handled at lower temperatures . In this respect reference can be made to the 1^ application of bitumen emulsions which are prepared by mixing a hot bitumen with an aqueous emulsifier solution. These bitumen emulsions can normally be mixed with aggregate at a temperature much lower than 140 °C, in which way the above-mentioned hazards are much 0 oetter controlled. Asphalt compositions prepared from a bitumen emulsion require, however, bitumen/aggregate mixtures with relatively nigh void contents in order to allow the water to escape during breaking ol the emulsion, 2^ compaction and service. Such asphalt compositions have the drawback that they are highly permeable to water and air. As a result they lose coarse aggregate from the road surface rather easily, so-called trotting of the road surface. They further just inLerna- cohesion ) which will eventually lead to ccllapse of the material and xack of internal stability, often visible ax deformation of the road surface, _ . i- . ruttinj. Moreover, strength of these asphalts is only developed slowly . Surprisingly, it has now been found that asphalt compositions can be produced having a good resistance 5 against fretting and in addition a good creep (rutting) and fatigue performance, by adding a hard binder component to a mixture of a soft binder component and aggregate at a relatively low temperature. Accordingly, the present invention relates to a 0 process for preparing a dense-graded asphalt composition which comprises adding a hard binder component to a mixture of a soft binder component and aggregate at a temperature of less than 140 °C . Suitably, the temperature applied is less than 100 °C . 15 In accordance with the present invention both an emulsified and a non-emulsi fied soft binder component can be used, preferably a non-emulsified soft component. When an emulsified soft binder component is used it contains a small amount of water. Suitably, 0 less than 50" by volume, preferably less than 40'<> by volume. When use is made of an emulsion, the emulsion may either be a cationic or an anionic emulsion. The hard binder component is preferably added to the mixture as a powder. In that case the hard binder 25 component can very attractively be added to the mixture at a temperature of less than 50 °C, preferably at ambient temperature. If the hard binder component is used as an emulsion (or suspension) , the emulsion (or suspension) suitably contains less than 50 by volume " !() of water, preferably less than 40V, by volume. Tn that case the hard binder component can suitably be added to the mixture of a temperature of less than 100 °C, preferably at a temperature m the range of from ambient temperature to 80 °C. When use - made of an ^ emulsion, the emulsion may either be a catiυmc or an anion; c emα 1sior.. The soft binder component can suitably be added to the aggregate also at a relatively low temperature, i.e. a temperature of less than 120 °C. Suitably, the soft binder component is added to the aggregate at a temperature of at least 70 °C, preferably at a temperature in the range of from 80 to 115 °C, more preferably in the range of from 85 to 110 °C. In the context of the present invention a hard binder component is defined as a binder component having a penetration (PEN) of less than 200 dmm (as measured by ASTM D 5 at 25 °C) . The hard binder component has suitably a penetration of less than 100 dmm, preferably less than 50 dmm, and more preferably less than 10 dmm, and a softening point of less than 100 °C (as measured by ASTM D 36) , preferably less than 80 A. In the context of the present invention a soft binder component is defined as a binder component having a penetration of at least 200 dmm. Suitably, he soft binder component has a penetration of at least 500 dmm, preferably of at least 700 dmm and more preferably of at least 800 dmm. (as measured by ASTM D 5 at 25°C) . The person skilled in the art, however, usually characterizes such binder component not by its penetration value but its viscosity (as determined by ASTM D 2171 at 100 °C) . Preferably, the soft binder component has a viscosity of less than 300 mPa.s, preferably less than 200 mPa . s (as determined by ASTM 2171 at 100 °C) . Preferably, both the hard and soft binder component are bitumen components. However, in another suitable embodiment of the present invention the hard hinder component is a resin, for instance a coumarone- I ndene resin, and the soft binder component is a low viscous component (a flux) . The resins may be any of the modified resins described in EP-R-0330281 , which is hereby incorporated by reference. The binder components may suitably contain in addition a film formation improver (e.g. butyldi- oxitol) , a non-ionic emulsier (e.g. nonylphenol- ethoxylate) or an adhesion improver (e.g. an amine such as an alkylamidoamme) , preferably an alkylamidoamine . Such additional compounds are preferably added to the soft binder component, and are suitably present in an amount of less than 5° wt, preferably in an amount in the range of from 0.25 to l.O'ό wt, based on total binder content. Also mixtures of these additional compounds can suitably be used. In this way an even further improved resistance against fretting is established. The bitumen components may be naturally occurring bitumens or derived from a mineral oil. Also petroleum pitches obtained by a cracking process and coal tar can be used as well as blends of bituminous materials. Examples of suitable bitumens include distillation or "straight run" bitumens, precipitation bitumens, e.g. propane bitumens, blown bitumens, e.g. catalytically blown bitumens, and mixtures thereof. Other suitable bitumen compositions include mixtures of one or more of these bitumens with extenders (fluxes) such as petroleum extracts, e.g. aromatic extracts, distillates or residues, or with oils. The hard and soft, binder components may suitably contain any polymer modifier taught in the art, such as lor instance a thermoplastic rubber, suitably in an amount in the range of from 1 to 10', by weight. The amounts of the hard and soft binder components useo may va y between wide limits, and strongly depend on the penetration grade desired for the binder of the asphalt composition. The hard binder component can for instance suitably be present in an amount of lh to 90 wt , based on total binder . The asphalt composition prepared in accordance with the present invention is in particular suitable for use in road applications. The asphalt composition prepared in accordance with the present invention can suitably be used in the construction of base coarse materials or wearing coarse materials. The binder of the asphalt composition prepared in accordance with the present invention has suitably a penetration which varies between 10 to 300 dmm, preferably between 50 to 150 dmm (as measured by ASTM D 5 at 25 °C) . The bitumen compositions may also contain other ingredients such as fillers, e.g. carbon black, silica and calcium carbonate, stabilisers, antioxidants, pigments and solvents which are known to be useful in 5 bitumen compositions. The asphalt compositions prepared in accordance with the present invention comprise aggregate in amounts taught in the art. In the context of the present invention a dense- graded asphalt composition is defined as an asphalt composition having a void content of no more than 10", preferably a 3 to 10 ?, void content. Suitable aggregates include those normally applied in dense-graded asphalt compositions. Tne present invention will now be illustrated by 5 way cf the following Examples. Example 1 An asphalt composition was prepared in accordance with the present invention as follows. 1.04 kg of a low viscous binder component (a Bright Stock Furfural o Extract (BFE ) having a viscosity of 50 mPa . s - 100 "r ( a s determined by ASTM D 2171 ι was added to 1. i ^ kg of aggregate m a llurell mill operating at a temperature of 100 °C at aoout 35 rpm. The agqregare consisted of 7.1 ': vi filler < < 63 μm) , 36.8 w sand (63 μm-2 mm) , 15.3 w stones (2-6 mm) , 20.4 -,w stones (4-8 mm. and 20.4 w stones (8-11 mm) . Subsequently, to th- mixture so obtained 1.56 kg of a hard binder component was added in the form ol a powder at ambient temperature. The hard binder component had a penetration of 2 dmm, le up to (as determined by ASTM D 5 at 25 °C) and a softening point of 96 °C (as measured by ASTM D 36) . The powder was prepared by powdering a blown propane bitumen having a softening point of 95 °c (as measured by ASTM D 36) in a Culatti breaking mill with a sieve size of 1 mm. Solid carbondioxide was added to the hard bitumen lumps regularly to cool the mill and to avoid sticking of tne bitumen particles produced. The dense graded asphalt composition so obtained was then poured into a mould of a slao compacter, and distributed to form a homogeneously spread loose mix. The asphalt composition W s then compacted at a temperature of 100 ° C. After compaction the asphalt slab ootamed was allowed to cool down to ambient temperature and removed from the mould. Then the asphalt slab was cut and sawn into test specimens. Example 2 An asphalt composition was prepared in accordance with the present invention m a similar manner as described in Example 1 except that to a mixture of 0.9fc kg of the low -'iscous binder component and 4P9o kg of aggregate . kα of an emulsion of a hard oirider component wa_= added. Ihe- emulsion was prepared by adding 1. ^ kg of a hot (180 °C) hard binder component (a Vacuum Flasned Conversion Residue) tr 1.14 kg ol a warm (80 °C / Λ cr/emuis on solution in a Ery a mil l wnich a ipt a* " a pressure of lU atm, a temper f-ur - - 1 r L an 1 d)0' rpm. ϊt. p wut r /e ul ion huiut ion cnt-j_ned 5. < ■ f a <"om orc ia11 _ avalladle omuls liri R< rrespe r < ~ , J " w > f tinr , ard had a oil of 12. . .f ut on was al aϊ ific i υsirxi a s diαπ nvi t ι t<- s - " nn. ~ n<- nan: t j nut v . mrxun^ had . pfii cit " ' imn ,.„. < ΠI^ U'I 1 1 by IM 1 and a softening point of 90.5 °C (as measured by ASTM D 36) . The final bitumen emulsion obtained had a pH of 8.6 and a viscosity of 87 mPa . s at 100 °C (as determined by ASTM D 2171) and contained 41 ό water. 5 Example 3 An asphalt composition was prepared in accordance with the present invention in a similar manner as described in Example 2 except that 1.33 kg of a low viscous binder (a Statfjord Short Residue) having a 10 viscosity of 250 mPa . s at 100 °C (as determined by ASTM D 2171) was preblended at 100 °C with 13.3 g of WETFIX (an alkylamidoamme; ex Berol Nobel) and mixed with 44.22 kg of aggregate. Subsequently, 2.21 kg of an emulsion of the hard bitumen component was added. The 15 emulsion was prepared by adding 1.18 kg of the hot hard binder component to 1.03 kg of the warm water/emulsion solution m the Fryma mill which was operated at 3000 rpm. The water/emulsion solution contained 1.5 Jw of a commercially available emulsifier Vinsol R, 0.2 o 20 of Guar Gum, and had a pH of 12.6. The final bitumen emulsion obtained had a pH of 12.4 and a viscosity of 27 mPa.s at 100 °C (as determined by ASTM D 2171) and contained 46.7 ; water. Testing experiments ?5 The creep), fretting and fatigue performances of the dense-graded asphalt compositions prepared in Examples 1,2 and 3 were then determined in respectively the dynamic creep test, the Californian abrasian test and the three point bending fatigue test, which tests are ιo known by tne skilled person. Cylindrical test specimens (diameter Oi.ύ mm, height 6n mm) were cut for testing tne resistance to creep and fretting, wh i J > rectangular test specimens 'height 40 mm, width 30 mm, leng h 23. mm) were sawn, from the slab for tatrgue tes inα. 'In." 1 cyl in rical specimens were tested ;ι, creep .'C" f ..>rmane.> n the x-r, mi" creed test at V, md ,-:. f n'tts x performance m the Californian abrasian test at 4 and 40 °C . The rectangular specimens were tested m the three point bending test on fatigue strength at a loading frequency of 40 Hz under constant stress at a temperature of 10 °C . The performance data of the asphalt compositions are shown in Table 1. It will be clear from these data that m accordance with the present invention attractive asphalt compositions can be prepared at advantageously low temperatures. Taole 1 σ oer issmle stress for 10 b fatigue cycles 'ermiss :c^e : ra tor fatigue cycles i ure

Claims: C L I S 1. Process for preparing a dense-graded asphalt composition which comprises adding a hard binder component to a mixture of a soft binder component and aggregate at a temperature of less than 140 °C . 2. Process according to claim 1, wherein the hard binder component has a penetration of less than 100 dmm. 3. Process according to claim 1 or 2, wherein the soft binder component has a penetration of at least 500 dmm. 4. Process according to any one of claims 1 to 3, wherein the hard binder component is added to the mixture at a temperature of less than 100 °C. 5. Process according to the any one of claims 1 to 4, wherein the soft binder component is a non-emulsified 5 soft binder component. 6. Process according to any one of claims 1 to 5, wherein the hard binder component is added to the mixture as a powder. 7. Process according to claim 6, wherein the hard () binder component is added to the mixture at a temperature of less than 50 U C . 8. Process according to any one ot claims 1 - /, wnerein the sof* ~ binder component is added to the aggregate at a temperature of less than M0 °C . 5 9. Process according to claim 8, wherein the temperatur is in the range of f om 80 to 11' A. 1 u . Process according to anx one cd eMxm.- i t - 9, where. i th- haro did soft 'Oder oomrorients nif r itumei componen . 0 11. Use of an aspnal 1" c-omposil ion as prepared o »' a procesx acoor iirig t any one t ιa.m. ' i c ι_r road app 1 ication...

Inventors: HENDRIKS HENRICUS ENGELBERTUS, STOKER DIRK ADRIAAN, HENDRIKS, HENRICUS, ENGELBERTUS, JOHANNES, STOKER, DIRK, ADRIAAN
Applicants: SHELL CANADA LTD, SHELL INT RESEARCH, SHELL CANADA LIMITED, SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ B.V.
Application year: 1996
Main classification: C08L95
IPC codes: C08L95, E01C7