Use of catalytically oxidised asphalt precursors as rutting reducing additives in paving asphalt cements

Abstract: A process to prepare a paving asphalt cement which comprises (a) catalytically oxidizing an asphalt precursor to form a catalytically oxidized asphalt cement; and, (b) mixing the catalytically oxidized asphalt cement with an asphalt precursor to obtain the desired grade of paving asphalt cement.

Description: This invention relates to the use of catalytically oxidised asphalt precursors as rutting reducing additives in a paving asphalt cement (hereinafter referred to as "premium paving asphalts") which, when mixed with an aggregate, forms an asphalt mixture having superior performance characteristics as compared to high quality asphalt mixtures produced by conventional processes. Asphalt has been used for preparing road surfaces for several decades, Typically, the main ingredients of a paving asphalt mixture are an asphalt cement (approximately 5 wt. %) end aggregate material (approximately 95 wt. %). The asphalt cement is used to bind together the aggregate material and limit its mobility when a load is applied. An asphalt cement may be obtained from a crude oil by Processes known in the art. Typically, an asphalt cement comprises vacuum tower bottoms (VTB) which is a residue material that is produced during the refining of conventional or synthetic petroleum crude oils. In some cases, the vacuum tower bottoms may be further treated prior to their use in an asphalt mixture. For ease of reference, those materials which have previously been used as an asphalt cement are hereinafter referred to as "paving asphalt precursors". A problem with paving asphalt mixtures is that they are a fluid mass. During the application of loadings, particularly at warm temperatures, the road asphalt mixture tends to migrate from a position of higher loading to a position of lower loading i.e. lateral displacement. This tends to result in deformations in the surface of the road asphalt known as rotting. Rotting of road asphalt is undesirable as it forms channels in the pavement surface which are a safety hazard. Such ruts collect water during wet weather and this tends to cause significant reductions in tire-pavement friction levels and may contribute to the loss of control of a vehicle by skidding and or hydroplaning. Pavement rutting is a major concern of all user agencies and government transportation departments due to the cost involved in maintenance programs to repair the road surface and the effect of rotting on highway safety. Various asphalt rheological factors will affect the degree of rotting which may be obtained under the same conditions. These include the penetration of the asphalt (as measured by ASTM D-5), the kinematic viscosity of the asphalt (as measured by ASTM D-2170), the absolute viscosity of the asphalt (as measured by ASTM D-2171) and temperature susceptibility. In various countries, asphalt cements are graded on a different basis. Pursuant to the ASTM Standard Specification for Penetration - Graded Asphalt Cement for Use in Pavement Construction, designation D-946-82 e1 , asphalts are graded as having penetrations in the following ranges: 40 - 50, 60 - 70, 85 - 100, 120 - 150, and 200 - 300. Pursuant to the ASTM Standard Specification for Viscosity - Graded Asphalt Cement for use in Pavement Construction (designation D-3381-83 e1 ), asphalts are graded as AC-2.5 (viscosity = 250 ± 50 P@ 60°C), AC-5 (500 ± 100), AC-10 (1000 ± 200), AC-20 (2000 ± 400) and AC-40 (4000 ± 800). In most parts of Canada, asphalts are graded according to their penetration (pen). In most parts of the United States, asphalts are graded according to their viscosity. Within each grade of asphalt cement, as measured by penetration or viscosity, the asphalt cement will also be graded according to its quality. When the asphalt cement is graded according to its penetration, an asphalt cement having a higher viscosity at the same penetration generally is of a higher quality. Similarly, when asphalt cements are graded according to their viscosity, an asphalt cement which has a higher penetration at a given viscosity is of a better quality. By way of example, a high quality 85 - 100 pen paving asphalt cement would have viscosities at 135°C above about 280 cSt (2.8 10⁻⁴m²/s) while a lower quality paving asphalt cement of similar penetration would have a viscosity in the range of from about 150 cSt 1.5 10⁻⁴m²/s to about 250 cSt 2.5 10⁻⁴m²/s. Similarly, a high quality AC-20 paving asphalt cement would have a penetration from about 50 to about 80 while a lower quality paving asphalt cement would have a penetration from about 40 to about 60. The following table provides examples of paving asphalt cements conventionally manufactured from two crude oil sources. Crude oil source A provides a high quality asphalt cement. Crude oil source B provides a low quality paving asphalt cement that would be outside many user agency specifications. As is explained hereinafter, the high quality asphalt cement ex crude oil 'A' may also be referred to as a "high quality paving asphalt precursor". Similarly, the low quality paving asphalt cement may also be referred to as a "low quality paving asphalt precursor". The table also provides three examples of premium asphalt cements which are prepared according to the teachings of this invention and which exhibit superior pavement performance. These premium asphalt cements were prepared from a high quality paving asphalt precursor, a low quality paving asphalt precursor and a mixture thereof. Characteristic Test Method Lower Quality Paving Asphalt ex Crude 'B' Higher Quality Paving Asphalt ex Crude A Premium ex Crude 'A' Premium ex Crude 'B' Blend of 65% Crude B Precursor & 35% Cat-Oxid. Component ex Crude A Precursor Penetration, 25°C ASTM D5 94 91 88 89 90 Viscosity, Poise, 60°C ASTM D2170 700 (70 Pa.s) 1453 (145.3 Pa.s) 3338 (333.8 Pa.s) 1343 (134.3 Pa.s) 1289 (128.9 Pa.s) Viscosity, cSt, 135°C ASTM D2171 217 (2.17 10⁻⁴m²/s) 350 (3.5 10⁻⁴m²/s) 504 (5.04 10⁻⁴m²/s) 300 (3 10⁻⁴m²/s) 302 (3.02 10⁻⁴m²/s) Penetration, 4°C, 100g, 5 s ASTM D5 6 7 12 12 10 Penetration-Viscosity Number (PVN) -1.22 -0.53 -0.02 -0.79 -0.80 Penetration Index (PI) -2.20 -1.8 -0.20 -0.23 -0.86 The foregoing Table sets out the characteristics of several 85-100 pen asphalt cements. As mentioned above, in various countries, asphalt cements are graded by penetration. In other countries, such as the United States, asphalts are graded persuant to viscosity. In this regard, reference has been made above to ASTM standard D-3381. Asphalt precursors may be categorized, not only by penetration, but also by viscosity. Accordingly, in reference to ASTM standards, a "high quality paving asphalt precursor" is a vacuum tower bottom residue from refining of crude or crude blends suitable for production of paving asphalt cements meeting the requirements specified in ASTM D-3381, Table 2. A "low quality paving asphalt precursor" is a vacuum tower bottom residue from refining of crude or crude blends which are not suitable for production of paving asphalt cement meeting requirements specified in ASTM D-3381, Table 2, but are suitable for production of asphalts meeting the requirements specified in ASTM D-3381, Table 1. Further, a "non-paving asphalt precursor" is vacuum tower bottom residue from refining of crude or crude blends which are not suitable for production of asphalt cement meeting the requirements specified in ASTM D-3381 Table 1 or Table 2. High quality paving asphalt cements may be obtained by careful selection of the crude oil from which the asphalt cement is to be made and the operating conditions used to obtain the vacuum tower bottoms. By making an appropriate selection, a high quality paving asphalt cement may be obtained. Such crude oils and operating conditions are known to those in the art. For ease of reference such VTB and similar materials which may be used as a high quality paving asphalt cement or from which a high quality paving asphalt cement is obtained comprise the high quality paving asphalt precursors. Conversely, those paving asphalt precursors from which a high quality paving asphalt cement may not be obtained are referred to hereinafter as "non-high quality paving asphalt precursors". Similarly, those VTB and similar material from which a lower quality paving asphalt cement is obtained or which may be used as a lower quality paving asphalt cement comprise the low quality paving asphalt precursors. Non-high quality paving asphalt precursors include low quality paving asphalt precursors and non-paving asphalt precursors. A disadvantage with this selection system is that only a small number of crude oils will render a high quality paving asphalt cement. Further, once these materials are transported, such as in a pipeline, they will be mixed, at least to an extent, and may no longer yield a high quality asphalt cement. Since a high quality paving asphalt crude oil is not always locally available, other alternatives have been developed. For example, performance enhancers such as polymers and additives are known in the art and have been incorporated into asphalt cements to meet the requirements for high quality paving asphalt cements. Examples of such polymeric performance enhancers are styrene butadiene styrene ("SBS"), ethylene vinyl acetate ("EVA"), styrene butadiene rubber "(SBR") and polyethylene. One disadvantage with this approach is that the incorporation of polymers into asphalt dramatically increases the cost of the resultant paving asphalt mixture. US-A-3986887 describes bituminous compositions suitable for road paving materials characterised by a Penetration Ratio of at least 25 and a minimum viscosity of 275°F. in the range from about 50 Saybolt Furol Seconds to about 120 Saybolt Furol Seconds, depending upon the penetration grade of the bituminous material, are produced by blending a vacuum-reduced naphthenic asphalt and a residual asphalt having a lower penetration but a higher viscosity than the vacuum-reduced naphthenic asphalt. Accordingly, in order to produce high quality asphalt cement, one must use a specially selected crude oil which can be transported to a manufacturing plant without the crude oil being intermingled with other crude oils. Alternately, one must utilize polymers and other expensive additives which will dramatically increase the price of the resultant asphalt mixture. In either case, the number of crude oils which may be selected for producing a high quality asphalt cement is limited. Catalytic oxidation of asphaltic residuum is known in the art. Catalytic oxidation, which can be used to produce an asphalt cement having a higher penetration at a given softening point, has been generally used only in the production of roofing asphalt where increased flexibility at lower temperatures is required. It is suggested in research disclosure No 142 (Feb. 1976), 14213 that the weathering rate of a petroleum bitumen can be altered by the addition of certain polymerised and/or oxidised petroleum based products. The petroleum bitumen may be any of those normally derived from a crude petroleum. The said polymerised and/or oxidised products are petroleum resins which may be attained by polymerising or oxidizing, with or without a catalyst, the residue produced from thermally cracking especially steam cracking a petroleum residue. The earliest reference to catalytic oxidation of which the applicant is aware is US-A- 1 782 186, which discloses incorporating a non-alkaline earth metal salt (such as chloride of iron) in a petroleum residuum prior to blowing the residuum. It is reported that the blown product had an increased penetration with a corresponding decrease in brittleness. Since that time, catalytic oxidation has become widely utilized in the roofing industry to prepare roofing asphalt cements. Catalytic oxidation is advantageous in the roofing industry since asphalt roof shingles are typically very thin and subjected to large daily temperatures fluctuations. Due to these conditions of use, asphalt shingles must have a high viscosity (a high softening point) while maintaining their flexibility (a high penetration). By catalytically oxidizing a roofing asphalt cement, an asphalt cement is obtained which has increased flexibility at a given softening point. Furthermore, catalytic oxidation results in a shortening of the oxidation time. Catalytic oxidation of asphalt cements is discussed in greater detail in US-A-4 338 137 which discloses a process for air-blowing asphalts in the presence of ferrous chloride. As is described at column 1, lines 12 - 16 of that patent, air-blowing raises the penetration of an asphalt cement at a given softening point. Until recently, little attention has been paid to the use of catalytic oxidation in the preparation of road asphalts. In the early 1980's, the use of catalytically oxidized bituminous material to prepare paving asphalts has been considered. See for example J.S. Bahl, and Himmat Singh, Air-blowing of Bitumens: Process Variables and Structural Parameters , Revue de l'Institute Francais du Petrole, volume 38, no. 3 May - June 1983; and, L.N. Shabalin et al Pilot Plant Oxidation of Petroleum Tar in the Presence of Iron Chloride , Nefterpererab, Nefterkhyng, Moscow, 1979. More recently, US-A- 4 456 523 and US-A- 4 456 524 disclose a process for producing a high grade asphaltic material which process comprises blowing a bituminous material to the desired grade in the presence of a catalytic amount of an inorganic carbonate salt or an organic carbonate salt as the oxidation catalyst. At column 1, lines 15 -17, US-A-4 456 523 discloses that the invention is concerned in one specific embodiment with chemically producing paving grade asphalt cements. The thrust of this patent is the use of new non-corrosive inexpensive readily available catalysts. These catalysts are to be used in preference of Lewis acid catalysts, such as ferric chloride and ferrous chloride, which are very corrosive (column 2, lines 57-65). It is desirable to provide premium paving asphalts. These paving asphalt cements have performance characteristics which are equal to or superior than those of high quality paving asphalt cements without requiring the use of polymers or additives. It is also desirable to provide a method of upgrading crude oil residues so as to obtain paving asphalt cements from crude oils which would not otherwise render high or low quality paving asphalt cements. It is further desirable to provide means for increasing the number of crude oils which may be utilized to prepare paving asphalt cements having good performance characteristics. Quite surprisingly asphalt mixtures preposed using asphalt cement prepared by (a) catalytically oxidizing an asphalt precursor to form a catalytically oxidized asphalt cement and, (b) mixing the catalytically oxidized asphalt cement so obtained with an asphalt precursor to form a paving asphalt cement have demonstrated at least 20% and up to a 75% decrease in rutting and will allow an increase in traffic loadings of up to 1000% or more before equivalent amounts of deformation occur as would be obtained from conventional quality paving asphalts. In addition such asphalt mixtures have demonstrated a 50% decrease in low temperature mix stiffness which allows significant improvements in preventing pavement low temperature cracking. The asphalt precursor of each of steps (a) and (b) may be individually selected from one or more of a high quality paving asphalt precursor, a low quality paving asphalt precursor or a non-paving asphalt precursor and mixtures thereof. The present invention is the use of a catalytically oxidised asphalt precursor as a rutting reducing additive in a paving asphalt cement comprising an unoxidized asphalt precursor. Preferably, the paving asphalt precursor which is catalytically oxidized is a high quality paving asphalt precursor. More preferably, the paving asphalt precursor which is mixed with the catalytically oxidized asphalt is also a high quality paving asphalt precursor. A non-high quality paving asphalt precursor may be either a low quality paving asphalt precursor or a non-paving asphalt precursor. Preferably, the precursor used in each of the two steps is a low quality paving asphalt precursor. Preferably, the precursor material is a vacuum tower bottom which is obtained from the distillation of conventional or synthetic crude oils as is known in the art. The penetration of the vacuum tower bottoms may be from about 60 to 600 and more preferably from about 150 to about 400 as measured by ASTM D-5 25°C. Preferably, the vacuum tower bottoms which are utilized are the softest material which has a minimum flash point above the catalytic oxidation temperature. The catalytic oxidation is preferably conducted using 0.05 - 1 wt.%, and more preferably 0.2 - 0.5 wt.%, of dry catalyst based upon the total weight of the oxidized product. The catalytic oxidation is conducted at a temperature of from about 205° (400°F) to about 290°C (550°F) and, more preferably, from about 230°C (450°F) to about 260°C (500°F). The precursor material may be catalytically oxidized until it has a penetration of from about 5 to about 100, more preferably about 15 - 40 and, most preferably about 15 - 30 as measured by ASTM D-5 @ 25°C. The catalyst may be any of those which are known in the art. Suitable catalysts are disclosed in US-A- 1 782 186; US-A- 2 450 756; US-A- 2 375 117 and US-A- 2 649 384. In addition, those disclosed in EP-A-0053041 may also be employed. Preferably, the catalyst is an iron chloride namely one or more of ferrous chloride or ferric chloride. The catalytically oxidized precursor is back mixed with unoxidized vacuum tower bottoms. The two products are mixed to obtain a product having the desired target penetration. The unoxidized vacuum tower bottoms and the catalytically oxidized product may be mixed to form an asphalt product having a penetration at 25°C from about 40 to about 400, more preferably the blended material has a penetration of 200 - 300, 150 - 200, 120 - 150, 85 - 100, 60 - 70 or 40 - 50. Corresponding viscosity graded products may be produced which would include AC-40, AC-30, AC-20, AC-10, AC-5 and AC-2.5. The use of the rutting reducing additive set out in the above embodiments allows greatly increased flexibility in the selection of a crude oil to prepare a premium paving asphalt mixture which has superior performance qualities to those of high quality paving asphalts. Further it allows the use of crude oils whose residuum would not otherwise be suitable for use even as a low quality paving asphalt cement, to be used to prepare a paving asphalt which may have performance characteristics equal to or superior to those of a high quality asphalt. Further, the premium asphalts produced according to the above embodiments have mix performance characteristics which are equal to or superior to those which are obtained using polymer modified asphalts. In the production of the additive, a paving asphalt precursor is catalytically oxidized to form a catalytically oxidized asphalt cement. As discussed above, paving asphalts may be produced from asphaltic materials which are derived from several sources which are known in the industry. The starting material which may be employed in the process of this invention includes high quality paving asphalt precursors, crude oil residuum which would not otherwise produce a paving asphalt cement when processed according to conventional asphalt manufacturing process (a non-paving asphalt precursor), and crude oil fractions, which would not produce a high quality paving asphalt cement when processed according to conventional asphalt manufacturing processes (a non-high quality paving asphalt precursor). By way of emphasis, it should be noted that the various precursor materials employed as a starting material in the production of the additive of the present invention to obtain a premium paving asphalt cement would conventionally be used as asphalt cements. More particularly, according to the present Invention, a high quality paving asphalt cement may be utilized as a high quality paving asphalt precursor to obtain a premium paving asphalt. Similarly, a low quality paving asphalt cement may be employed as a low quality paving asphalt precursor to obtain a high quality paving asphalt cement or a premium paving asphalt. Further, a residuum which, except for a few limited exceptions, could not be utilized even as a low quality asphalt cement may be employed as a non-paving asphalt precursor pursuant to this invention to obtain a low quality paving asphalt cement, a high quality paving asphalt cement, or, possibly a premium paving asphalt. A paving asphalt precursor for use in this invention may be of varied character and includes paving asphalt precursors and non-paving asphalt precursors. Paving asphalt precursors may be divided into two classes as either high quality paving asphalt precursors or low quality paving asphalt precursors. Such a precursor (asphalt cement) may be a petroleum residuum or flux which remains following the separation of vaporizable hydrocarbons through vacuum gas oil fractions from the residuum, or any relatively high molecular weight extract obtained from petroleum refining or virgin naturally occurring asphalt. As is known in the industry, a petroleum residuum or flux may be obtained by injecting a conventional or synthetic crude oil, at a temperature of about 340 to about 400°C, into a fractionating column. The lighter fractions are separated as overhead products. The residuum from the fractionating column is straight reduced asphalt cement. Today, crude oils typically may not be distilled at atmospheric pressure to produce a paving asphalt cement since the crude oil typically contains high percentages of high boiling fractions. Accordingly, as a supplement to the atmospheric process, a second fractionating tower (a vacuum tower) is added. The vacuum tower bottoms provide a paving asphalt cement. Suitable vacuum tower bottoms may have a penetration @ 25°C of from about 60 to 600 or more. More preferably, the vacuum tower bottoms have a penetration from about 100 to about 500 and, most preferably from about 150 to about 400. Preferably, the vacuum tower bottoms will be the softest material which has a minimal flash point above the temperature at which the catalytic oxidation is conducted. For example, when the catalytic oxidation is conducted at a temperature of about 205°C (400°F) to about 260°C (500°F) the vacuum tower bottoms will have a minimum flash point of about 260°C (500°F). As discussed above, catalytic oxidation is known in the art. The catalytic oxidation process used in producing the rutting reducing additive may be conducted in the manner which is known in the art. In the catalytic oxidation process, a paving asphalt precursor is fed into a vessel and is heated to a temperature which may be between about 205°C (400°F) and about 290°C (550°F). An oxidizing gas, such as, for example, air, is introduced into the paving asphalt precursor to oxidize the precursor in the presence of a catalyst. The process is carried out for a sufficient length of time to provide an oxidized asphalt cement having the desired penetration. As mentioned hereinbefore the catalyst may be any of those disclosed in US-A- 1 782 186; US-A-2 450 756; US-A- 2 375 117 and US-A- 2 649 384. Further, the catalyst may be one of those disclosed in EP-A- 0053041. The catalyst may be a phosphorus compound such as, for example, phosphorus pentoxide and phosphoric acid, a chloride such as, for example, the chlorides of zinc, iron, copper, antimony or aluminium, a sulphate such as, for example, zinc sulphate or aluminium sulphate, carbonates such, as for example, sodium carbonate, bicarbonate salts of sodium, calcium, magnesium, barium, strontium, lithium, ammonium, potassium, bismuth, lead, tetraalkylphosphonium, tetraarylphosphonium, tetraalkylammonium, tetralkylammonium, trialkylammonium, dialylammonium, transition metals or rare earth metals, boron trifluoride, lead oxide, lead naphthanate and sulphur. Preferably, the catalyst is phosphoric acid, phosphorous pentoxide, ferric chloride or ferrous chloride and, more preferably, the catalyst is ferrous chloride or ferric chloride. A catalytic amount of the catalyst may be used. The amount of catalyst which is used may vary from 0.05 - 1 wt. % of dry catalyst based upon the total weight of the oxidized product, More preferably, 0.2 - 0.5 wt. % of dry catalyst is utilized. The catalytic oxidation will preferably be conducted at a temperature of from about 205°C (400°F) to about 290°C (550°F) and, more preferably, from about 230°C (450°F) to about 260°C (500°F). The amount of time required to catalytically oxidize the paving asphalt precursor will vary depending upon a number of factors including the type of crude, the consistency of the asphalt precursor, the temperature at which the catalytic oxidation is conducted, the air flow rate, the configuration of the oxidizing vessel and the amount of catalyst. When preparing an 85 - 100 pen paving asphalt (AC-10 to AC-20), the catalytic oxidation may be conducted until the paving asphalt precursor has a penetration of from about 5 to about 100, more preferably from about 15 to about 40 and, most preferably, from about 15 to about 30 as measured by ASTM D-5 @ 25°c. In order to obtain the surprisingly large increase in traffic loading and decrease in rutting which may be obtained when utilizing the rutting reducing additive of this invention, the catalytically oxidized paving asphalt precursor is back mixed with unoxidized paving asphalt precursor. These materials may be mixed using conventional equipment. The precursor material with which the catalytically oxidized asphalt precursor is back mixed may be the same as that which was employed to produce the catalytically oxidized precursor. However, this is not essential. The catalytically oxidized asphalt cement may be mixed with a non-paving asphalt precursor, a non-high quality paving asphalt precursor or a high quality paving asphalt precursor. The precursor material which is employed is selected so that, bearing in mind the properties of the catalytically oxidized asphalt precursor, the target properties are obtained. Preferably, the precursor material which is employed in the catalytic oxidation and the backblending, is a high quality paving asphalt precursor. The oxidized and unoxidized products are mixed in suitable proportions to obtain an asphalt cement having the desired target penetration. In producing such a mixture, the desired target penetration is first selected. In most instances, the target penetration would be selected based upon the local climate in the area to which the asphalt is to be applied and, in addition, to the loading to which the asphalt composition will be subjected. Typically, the target penetration will be specified by the local government authority. In some cases, where asphalts are graded by viscosity as opposed to penetration, the target viscosity will be determined instead of the target penetration. Once the target penetration or viscosity is determined, the asphalt precursor which is to be oxidized and the asphalt precursor which is to be used in its unoxidized state are selected. In some cases, the selection of precursors is limited to those available at the refinery where the asphalt is to be produced. As discussed previously, the precursors may be selected from high quality paving asphalt precursors, non-high quality paving asphalt precursors, low quality paving asphalt precursors, and non-paving asphalt precursors. The asphalt precursor which is to be oxidized and the asphalt precursor which is to be utilized in its unoxidized form may be the same or different. The specific precursors which are utilized will vary depending upon the source and consistency of the available materials, the quality of the asphalt precursors and their specific physical characteristics such as penetration and viscosity and the target penetration/viscosity desired to be achieved in the end product. Other physical/chemical characteristics of the final product which are set by the local governing agency and which may vary from one governing agency to another, must also be satisfied. Examples of such characteristics are the required properties for the residue after thin film oven test, temperature susceptibility, ductility and engineering characteristics. All other factors being equal, a precursor having increased viscosity, at the same penetration will be of a higher quality. Similarly, a precursor having increased penetration at the same viscosity will be of a higher quality. The use of high quality paving asphalt precursors tends to result in premium asphalt formulations with higher viscosities for a given penetration, less temperature susceptibilities and improved engineering characteristics than premium asphalt manufactured with lower quality or non-paving asphalt precursors. Once the precursor materials are selected, the precursor to be oxidized is subjected to catalytic oxidation. The catalytically oxidized precursor and the unoxidized precursor are then mixed together to obtain the desired target penetration/viscosity. Accordingly, an asphalt may be prepared which would meet one of the following penetration grades namely 40 - 50; 60 - 70; 85 - 100; 120 - 150; 150 - 200; 200 - 300; and 300 - 400 or any other grade which may be required. Preferably the asphalt will have its penetration and/or viscosity optimized to provide the desired pavement engineered characteristics to minimize pavement deformation (rutting) as well as low temperature cracking. The amount of catalytically oxidized product which is mixed with the unoxidized precursor will vary from about 1 to about 99 weight percent. The amount will vary depending upon the consistency of the specific unoxidized asphalt precursor which is utilized, the consistency of the catalytically oxidized asphalt component and the target consistencies and other required properties for the residue, such as after the thin film oven test, in the final end product. For a given catalytically oxidized asphalt, the use of higher amounts of catalytically oxidized precursor in the final blend will generally permit the use of a less viscous unoxidized asphalt and will generally result in asphalt formulations with higher viscosities for a given penetration, less temperature susceptibilities and improved overall engineering characteristics. The use of lesser amounts of the catalytically oxidized asphalt in the blend, i.e. the use of a harder, more viscous unoxidized asphalt precursor, will generally result in asphalt formulations with better high temperature aging, after thin film oven test and ductility properties. All other factors being equal, the use of a softer unoxidized precursor will generally require the addition of an increased amount of catalytically oxidized precursor to form the target product. The consistency of the catalytically oxidized asphalt component (penetration/viscosity) will vary depending on the crude oil source, consistency of the specific asphalt precursor utilized, the catalyst type and amount used as well as oxidation time. Generally, the use of a softer precursor will tend to result in a catalytically oxidized product having improved consistency. Such increased consistency may also be obtained by increasing the amount of catalyst which is used or by using a different catalyst. However, if a harder precursor is utilized, it is generally possible to maximize the light oil products yield, such as gasoline and diesel, which are produced in a refinery. These products typically have a higher market value. Accordingly, in any particular situation, it is generally necessary to balance the products and the amounts of products produced in refining a crude oil with the characteristics of the precursor required to obtain the target product. By utilizing the rutting reducing additive in the manner of the present invention both non-paving asphalt precursors and paving asphalt precursors may be utilized to prepare a paving asphalt cement which may have physical characteristics (eg. viscosity, penetration, and temperature susceptibility) equal to or superior to those of conventional high quality asphalts. Further, the road performance of premium paving asphalts prepared according to this invention have performance characteristics equal to or superior to those of polymer modified paving asphalts. Accordingly, this invention allows paving asphalt cements to be made from crude oils which hitherto have not rendered a fraction which is suitable for making high quality paving asphalt cements (a non-high quality paving asphalt precursor) or even a paving asphalt cement (a non-paving asphalt precursor). These non-paving asphalt precursors and non-high quality paving asphalt precursors may be utilized, by this invention, to prepare premium paving asphalts. As mentioned above, paving asphalts prepared from an asphalt cement prepared according to this invention have up to a 75% decrease in rutting as compared to asphalt pavements prepared from conventional asphalt cements under the same loading conditions. Further, such asphalt pavements may also carry an increased traffic loading (up to 1000% or more) before reaching the same level of deformation as would be achieved with an asphalt pavement made from asphalt cement made by conventional processes. In addition such asphalt pavements also exhibit improved low temperature flexibility, and a 50% decrease in low temperature pavement stiffness. Five asphaltic materials were analyzed for their chemical composition. Two precursor materials were analyzed namely a higher quality precursor ex crude "A" and a lower quality precursor ex crude "B". Three asphalt cements were also analyzed namely a conventional high quality paving asphalt ex crude "A", a premium paving asphalt ex crude "A" and a premium paving asphalt ex crude "B". The results are set out in the following table. CHEMICAL COMPOSITION OF PREMIUM ASPHALTS, ASTM D-4124 Higher Quality VTB Asphalt Precursor Ex Crude "A" Lower Quality VTB Asphalt Precursor Ex Crude "B" Conventional High Quality Paving Asphalt Ex Crude "A" Premium Asphalt Ex Crude "A" Premium Paving Asphalt Ex Crude "B" % Asphaltene 10.7 7.7 16.3 22.1 15.5 % Saturates 14.0 18.0 9.6 12.4 15.3 % Aromatics 41.9 38.4 38.4 42.4 40.6 % Polars 33.4 35.9 35.7 23.1 28.6 The substance and advantages of the invention may be more completely and fully understood by means of the following description of the preferred embodiment of the invention and the accompanying figures in which: Fig. 1 is a graph of response measured against retention time for two premium paving asphalts, and a high quality paving asphalt, and Fig. 2 is the aggregate gradation of the HL3 mix used to prepare the paving asphalts of Example 1. Figure 1 which is attached hereto is a graph of the gel permeation chromatographic results of three asphalts. The graph measures retention time in minutes against relative responses. This graph measures the responses for three different asphalts namely: 1. a high quality paving asphalt cement prepared by conventional processes from crude oil source 'A'; 2. a premium paving asphalt prepared from a high quality paving asphalt precursor obtained from crude oil 'A'; and, 3. a premium paving asphalt prepared from crude oil 'B' - a crude oil source which, by conventional processes, provides a low-quality paving asphalt. As is shown in Figure 1, the premium asphalts have a decreased response at the 8 minute mark and an increased response at about the 5.5 minute mark. Without being limited to any extent by theory, it is believed that the improved performance of the premium asphalts results from a change in the molecular structure of the constituents of the asphalt cement when proposed according to the instant invention. In order to compare the performance characteristics of asphalt pavements, we have developed a pavement performance simulator which provides us with a procedure to compare the road performance of different asphalts. This pavement performance simulator is described hereinbefore. The pavement performance simulator allows asphalt pavements to be tested under full-scale dynamic loads simulating actual road conditions. The simulator comprises three major components: (a) a large-sized pavement test pit in which pavement materials are placed and compacted in layers simulating field construction; (b) an MTS loading system (Model No. MTS 810) capable of applying dynamic loads in magnitude, shape and frequency simulating heavy field trucks; and, (c) an electronic data acquisition system for measuring and displaying test variables such as applied loads and resultant deformation during the test. The pavement test pit measures 1.8 metres in width, 5.50 metres in length and 0.90 metres in height. The test pit is constructed with walls and a floor constructed from 13 mm thick steel. The test pit is placed over a reinforced concrete foundation which is 300 mm thick. The test pit is equipped with a drainage system to control moisture levels in the pavement base and sub-grade layers. The load is applied to the test pit via the MTS loading system which is secured to a loading frame. The loading frame is positioned above the test pit and designed to allow testing at preset locations. The test pit and the loading frame are designed to produce a total deflection of no more than 0.13 mm under a typical testing load of 40 KN (9.0 Kips). The capacity of the loading system is 100 KN (22.0 Kips). The load actuator unit is a hydraulic controlled MTS loading system (model MTS 244-22) equipped to perform tests over a wide range of speeds including those for pavement low-temperature testing. The test pit is also equipped with an environmental chamber which allows testing the pavement structure under controlled temperature conditions up to 60°C. In order to further simulate actual road conditions, the test pit is filled with sub-grade materials. Two feet of sub-grade sand is placed in the bottom of the test pit. The sub-grade sand is compacted in two layers, each one foot thick, by a vibratory plate. Density checks are made using a Troxler gauge to ensure that optimum density is achieved. Samples of the sub-grade material are taken for determination of sub-grade density and water content (ASTM D-1557 and D-698). Typically, the test pit is operated using sub-grade moisture and sub-grade density of 3 - 6% and 1800 - 2000 kg/m³ respectively. Sub-grade strength is measured in situ by using the California Bearing Ratio (CBR) test (ASTM D-1883). The strength of the sub-grade is manipulated by adjusting the moisture content in the test pit. Final in-place density of the sub-grade is determined by the Troxler gauge using ASTM test D-2922 and D-3017. The final profile of the prepared subgrade surface is measured across the test pit at the central line where the load will be applied. Typically the simulator is operated using a sub-grade strength of 8 - 12% CBR. Well graded granular base material is placed and compacted on top of the sub-grade layer. Typically a 0.15 - 0.20 metre layer of granular base is utilized. Once again, compaction is also done by use of a vibratory plate. Final in-place density of the granular base is determined by the Troxler gauge and a final transverse profile of the prepared base surface is measured. Typically the simulator is operated with the granular base material having a moisture content and density of 3 - 6% and 2300 - 2400 kg/m³ respectively. In order to obtain results which may be compared, the asphalt concrete test slabs are constructed in a uniform manner. A hot mix test slab is constructed using a pre-made frame. The pre-made frame positions the slab in the test pit and contains the asphalt concrete while the mixture is being compacted. The test slab is constructed to be a square of 0.6 metres in length and in width and 80 mm in thickness. The test slab is compacted using the MTS load actuator and a compaction plate which covers the inside surface of the pre-made frame. Prior to the plate compaction, a steel roller is used to compact and knead the surface. The test slab is made in two layer, each 40 mm in compacted thickness. The in-place density and asphalt cement content are determined by the Troxler gauge. (ASTM D-2950). Typical asphalt densities which are obtained are 2200 to 2250 kg/m³ representing 92 - 94% of Marshall density. The final surface profile of the pavement is taken across the width of the test pit at the centre line of the test slab. Surface profile measurements are carried out using an electronic profilometer. In conducting the test, a 40 KN (9 Kips) cyclic load was applied on the pavement structure at a rate of 9 cps. A loading pressure of 552 Kpa (80 psi) was applied through a 300 mm circular loading plate. This pressure loading at 9 cps simulates the passage over the asphalt of the wheel of a truck which weighs approximately 40 KN (9 Kips), and which is travelling at a speed of approximately 50 km/h. During the testing, the deformation of the test slab under the centre line of the load applicator was measured. Further, the number of cycles required to obtain that amount of deformation was recorded. "Permanent deformation" refers to the deformation in the surface of an asphalt concrete test slab after three million load cycles. The "percent reduction in pavement rutting" (PRPR) is defined as follows: where PD₂ = the permanent deformation of a paving asphalt mixture prepared using a paving asphalt cement which cement is prepared using the process of this invention and PD₁ = the permanent deformation of a paving asphalt mixture prepared using (1) the same aggregates utilized in preparing the paving asphalt mixture of PD₂ and (2) a high quality paving asphalt cement manufactured according to conventional processes. As is appreciated, by utilizing the process of this invention, significant reductions in pavement rutting is obtained. These reductions are obtained without the use of performance enhancers. Optionally, performance enhancers may, if desired, be incorporated in the paving asphalt cement prior to the production of the paving asphalt mixture. Five Examples are given in the following section to show the performance superiority of premium asphalts prepared according to the present invention. Example 1 compares the performance of a conventional high-quality paving asphalt with that of a premium paving asphalt formulated using the same crude oil. The aggregate is a high stability mixture. Example 2 compares the performance of the two asphalt cements of Example 1 but using a low stability aggregate mix. Example 3 compares the performance of a premium paving asphalt with that of two polymer modified asphalts and Example 4 exemplifies the application of the present invention in the production of premium paving asphalts from inferior crude oils which provide only low quality paving asphalt cements when treated by conventional processes. Example 1 Two 85-100 pen asphalt cements were prepared. Both of these asphalts are described briefly below. 1. A conventional high quality 85 - 100 pen asphalt cement obtained from crude oil "A". This sample was used as a control. 2. A catalytically oxidized and back blended premium paving asphalt prepared according to the present invention using a high quality paving asphalt precursor from crude oil "A". The oxidation was conducted at 232°C (450°F) using 0.2 dry wt. % FeCl₃. The high quality paving asphalt precursor had a penetration of 341 (100 g, 5 sec, 25°C, ASTM D-5) and a viscosity of 785 cSt (785.10⁻⁶ m²/s) at 100°C (ASTM D-2170). The asphalt precursor was air blown with the catalyst for about 4 hours to obtain an asphalt cement having a penetration of 30 (25°C, 100 g, 5 sec, ASTM D-5). This 30 pen paving asphalt cement was back mixed with the unoxidized high quality paving asphalt precursor at a ratio of 51:49 (catalytically oxidized to non-catalytically oxidized material) to produce an 85 -100 pen premium asphalt cement having a penetration of 89 as shown in Table 1. The properties of these two asphalts cements are set out in Table 1. CHARACTERISTIC METHOD REFERENCE HIGH-QUALITY CONVENTIONAL ASPHALT EX CRUDE 'A' PREMIUM ASPHALT EX CRUDE 'A' Viscosity, poise, 60°C (140°F) ASTM D2171 1706 (170.6 Pa.s) 2337 (233.7 Pa.s) Viscosity, cSt. 135°C (275°F) ASTM D2170 321 (3.21 10⁻⁴m²/s) 456 (4.56 10⁻⁴m²/s) Pen. 25°C ( 77°F), 100g, 5s ASTM D5 92 89 Pen. 4°C ( 39°F), 200 g, 60s ASTM D5 28 38 Pen. 4°C ( 39 °F), 100 g, 5s ASTM D5 8 12 PVN -0.7 -0.1 PI -2.1 -0.2 Each of the asphalt cements were used to prepare a paving asphalt mixture. For this purpose an HL3 type mix was used. The total aggregate mix gradation of this high stability mix is set out in Figure 2. This mixture contained 40% coarse aggregate, 25% sand, 35% screenings and based on the total agregate 5.8% asphalt cement. The Marshall mix characteristics for these two asphalts were determined. The results are set out in Table 2. SUMMARY OF MARSHALL MIX DESIGNS FOR 85-100 PEN ASPHALTS HIGH STABILITY MIX Asphalt Type Conventional High Quality Asphalt Ex Crude 'A' Premium Asphalt Ex Crude 'A' Voids, % 3.6 3.0 Flow, 0.25 mm 14 13.5 Stability N (lbs) 15,790(3550) 16,573(3726) V.M.A., % 15.5 14.7 The asphalt and road bed were prepared according to the description of the pavement performance simulator above. A summary of the as-constructed test data is set out in Table 3. SUMMARY OF AS-CONSTRUCTED TEST DATA HIGH STABILITY MIX Test Asphalt Type Conventional High Quality Ex Crude 'A' Premium Asphalt Ex Crude 'A' Subgrade Subgrade Density kg/m³ (pcf) 1874(117) 1874(117) Measured Moisture, % 4.7 4.8 Granular Base 'A" Troxler Density, kg/m³ (pcf) 2435(152) 2451(153) Troxler % Moisture 5.6 5.5 Measured Avg. Thickness, mm 181 182 Asphalt Slab (HL3) Measured Average Thickness, mm 80 79 Bulk Specific Gravity 2.210 2.230 The testing then proceeded by applying a loading pressure of 552 kpa (80 psi) through the 300 mm circular loading plate. The total loading pressure of 40 KN (9 Kips) was applied at a rate of 9 cps. The testing was performed at room temperature (23±2°C). The permanent deformation was measured at various load cycles. The permanent deformation after three million cycle loads was determined. In addition, the total number of cycles required to obtain a 10 mm permanent deformation were recorded. These results are set out in Tables 4 and 5. COMPARISON OF PERMANENT DEFORMATION AFTER THREE MILLION LOAD CYCLES Asphalt Type Deformation, mm % Reduction in Permanent Deformation Conventional High Quality Ex Crude 'A' 11.9 -- Premium Ex Crude 'A' 6.0 50% COMPARISON OF TOTAL LOAD CYCLES AT 10 MM PERMANENT DEFORMATION Asphalt Type Total No. of Load Cycles Conventional High Quality ex Crude 'A' 2 450 000 Premium Ex Crude 'A' 8 000 000 As shown in Tables 4 and 5, the performance of the premium paving asphalt was superior to that of the conventional high quality paving asphalt. The control asphalt provided the higher deformation (worse performance) of the two sections tested. The premium asphalt according to the present invention provided the better performance. Comparing the permanent deformation in the test sections after three million load cycles, the premium paving asphalt showed a 50% reduction in rutting. Comparing the total number of load cycles for a 10 mm deformation in the two test asphalts, the premium asphalt demonstrated a superior performance for carrying about 8,000,000 load cycles as compared with 2,450,000 load cycles carried by the control asphalt. The premium asphalt had an improvement of 326% in pavement load carrying capacity. Since most pavement rutting occurs during warm summer months, it is appropriate to test for rutting at high temperatures. Example 1 was repeated at 50°C using an environmental chamber designed for use in the pavement test pit. The premium asphalt demonstrated a 75% decrease in pavement rutting and more than a ten fold increase in pavement load carrying capacity at 50°C. In this case, the testing was terminated after 900,000 load cycles. After 900,000, the conventional high quality asphalt ex crude "A" had a permanent deformation of 25.4 mm. In comparison, the premium asphalt had a permanent deformation of only 6.4 mm. The total number of load cycles required to obtain a permanent deformation in the premium asphalt of 6 mm was 770,000 while the number of load cycles required to obtain a 6 mm deformation in the conventional high quality paving asphalt was 24,000. Example 2 The two 85-100 pen asphalt cements of Example 1 were used in this Example. The aggregate material used in this Example had a lower stability than the mix employed in Example 1. The Marshall mix characteristics of the aggregate used in this Example are set out in Table 6. The as constructed test data is shown in Table 7. MARSHALL MIX DESIGN CHARACTERISTICS LOWER STABILITY MIX Conventional High Quality Asphalt Ex Crude 'A' Premium Asphalt Ex Crude 'A' Voids, % 4.2 3.7 Stability N, (lbs) 10,710 (2408) 13,201 (2968) Flow, 0.25 mm 9.8 11.0 V.M.A. % 16.0 15.2 SUMMARY OF AS-CONSTRUCTED TEST DATA LOWER STABILITY MIX High Quality Asphalt Ex Crude 'A' Premium Asphalt Ex Crude 'A' Subgrade Subgrade Density, Kg/m³ (pcf) 1858 (116) 1842 (115) Moisture % 4.5 4.8 Granular Base 'A' Density Kg/m³ (pcf) 2326 (145.2) 2259 (141.0) Moisture % 4.2 3.8 Thickness, mm 217 210 Asphalt Slab (HL3) Thickness mm 75 75 Bulk Specific Gravity 2.193 2.196 The load testing was carried out at room temperature according to the method of Example 1. The permanent deformation after 1,000,000 load cycles was determined and the total number of cycles required to obtain a deformation of 6.0 mm was recorded. The results are set out in Tables 8 and 9 respectively. PAVEMENT RUTTING AFTER 1,000,000 LOAD CYCLES Asphalt Type Deformation, mm % Reduction in Pavement Rutting High Quality Asphalt Ex Crude 'A' 12.0 -- Premium Asphalt Ex Crude 'A' 3.75 69% COMPARISON OF TOTAL LOAD CYCLES FOR 6.0 mm PERMANENT DEFORMATION Asphalt Type Total No. of Load Cycles High Quality Asphalt Ex Crude 'A' 540.000 Premium Asphalt Ex Crude 'A' 3,000,000 As demonstrated in Tables 8 and 9, the premium paving asphalt had superior performance characteristics to that of the high quality paving asphalt produced from the same crude oil source. The premium asphalt showed a 69% reduction in pavement rutting and more than a 5 fold Increase (556%) in load carrying capacity. Example 3 Three 85-100 pen paving asphalt cements were tested in this Example to compare the pavement performance of two polymer modified paving asphalts and one premium paving asphalt prepared according to the present invention. One of the commercial polymer modified asphalts which was tested was modified by the addition of "SBS" styrene-butadiene-styrene (STYRELF ) and the other was modified by the inclusion of "EVA" ethylene-vinyl-acetate. Each of the three test asphalts were obtained from the same crude oil "A" source. The premium asphalt was prepared as discussed earlier in Example 1. The properties of the test asphalts are set out in Table 10. The Marshall mix characteristics are given in Table 11 and the as constructed test data is shown in Table 12. Characteristics Reference Premium Asphalt Ex Crude 'A' "SBS" Polymer Modified Asphalt Ex Crude 'A "EVA" Polymer Modified Asphalt Ex Crude 'A' Viscosity, Poise 60°C (14°F) ASTM D2171 2337 (233.7 Pa.s) 4077 (407.7 Pa.s) 2619 (261.9 Pa.s) Viscosity, cSt, 135°C (275°F) ASTM D2170 456 (4.56.10⁻⁴m²/s) 974 (9.74 10⁻⁴m²/s) 833 (8.33 10⁻⁴m²/s) Pen 25°C (77°F), 100g, 5 sec ASTM D5 89 93 89 Pen 4°C (39°F), 200g, 60 sec ASTM D5 38 34 32 Pen 4°C (39°F), 100g, 5 sec ASTM D5 12 10 9 PVN -0.1 +1.0 +0.5 PI -0.2 -0.9 -1.10 AS CONSTRUCTED TEST DATA PREMIUM VERSUS POLYMER MODIFIED 85 - 100 PEN ASPHALTS Premium Ex Crude 'A' Polymer Modified Asphalt STYRELF (SBS) Polymer Modified Asphalt ELVAX (EVA) Test Asphalt Type Subgrade Density kg/m³ (pcf) 1875 (117) 1840 (115) 1860 (116) % Moisture 4.2 4.0 3.9 Granular Base 'A' Density kg/m³ (pcf) 2435 (152) 2403 (150) 2371 (148) % Moisture 4.4 4.0 4.7 Thickness, mm 189 192 202 Asphalt Slab (HL3) Measured average thickness, mm 81 79 78 The testing was conducted at room temperature method of Example 1. The permanent deformation after 3,000,000 load cycles was determined and the total number of cycles required to obtain a deformation of 6.0 mm was recorded. The results are set out in Tables 13 and 14 respectively. COMPARISON OF TOTAL LOAD CYCLES FOR 6.0 mm DEFORMATION Total No. of Load Cycles Premium Asphalt Ex Crude 'A' 2,800,000 "SBS" Polymer (STYRELF) Modified Asphalt Ex Crude 'A' 2,150,000 "EVA" Polymer Modified Asphalt Ex Crude 'A' 2,300,000 The results set out in Tables 13 and 14 demonstrate the superior performance of the premium asphalt and show that it provides pavement performance equivalent to or better than the pavement performance of polymer modified asphalts. The premium asphalt provided a 23% Improvement in load carrying capacity as compared to the "EVA" modified asphalt and a 30% improvement as compared to the STYRELF SBS modified asphalt, Example 4 In this Example premium asphalts were prepared from low quality paving asphalt precursors. The physical characteristics off three test asphalts are set out in Table 15. The three test asphalts are described briefly below: (1) a conventional high quality asphalt ex crude 'A'; (2) a low quality asphalt ex crude 'B' which is prepared by conventional processes, and; (3) a premium paving asphalt prepared according to the present invention from the low quality asphalt precursor ex crude 'B'. The low quality asphalt precursor which was used to prepare a catalytically oxidized product had a viscosity of 420 cSt (4.2 10⁻⁴m²/s) at 100°C (ASTM D-2170). The oxidation was conducted at 450°F using 0.3 wt. % dry FeCl₃ for about 5.5 hours to obtain a catalytically oxidized paving asphalt cement having a penetration of 20 (25°C, 100 g, 5 sec, ASTM D-5). This 20 pen catalytically oxidized paving asphalt cement was back mixed at a ratio of 34% catalytically oxidized material to 66% low quality paving asphalt precursor ex crude "B" having a penetration of 205 (100 g, 5 Sec, 25°C) and a viscosity of 865 cSt (8.65 10⁻⁴m²/s) at 100°C to produce an 85 - 100 pen premium asphalt cement ex crude "B". The final product had a penetration of 91 as shown in Table 15. Characteristics Method Reference High Quality Asphalt Ex Crude 'A' Low Quality Asphalt Ex Crude 'B' Premium Asphalt Ex Crude 'B' Viscosity, Poise 60°C (140°F) ASTM D2171 1453 (145.3 Pa.s) 784 (78.4 Pa.s) 1620 (162 Pa.s) Viscosity, cSt, 135°C (275°F) ASTM D2170 350 (3.5 10⁻⁴m²/s) 208 (2.08 10⁻⁴m²/s) 346 (3.46 10⁻⁴m²/s) Pan 25°C (77°F), 100g, 5 sec ASTM D5 91 92 91 Pen 4°C (39°F), 200g, 60 sec ASTM D5 27 28 33 Pen 4°C (39°F), 100g, 5 sec ASTM D5 7 8 10 PVN -0.53 -1.30 -0.5 PI -1.80 -1.50 -0.9 In order to demonstrate the superior performance of the premium asphalt product, both the premium asphalt ex crude 'B' and the high quality conventional asphalt ex crude 'A' were tested in the pavement performance simulator. The tests were carried out at room temperature as previously described in Example 1. The Marshall mix design parameters and the as constructed test data are set out in Table 16. MARSHALL MIX DESIGNS AND AS CONSTRUCTED TEST DATA Conventional High Quality Asphalt Ex Crude 'A' Premium Asphalt Ex Low Quality Crude 'B' Stability, N (lbs) 12,700 (2857) 13,970 (3143) Flow, 0.25 mm 11.0 11.8 Voids, % 4.0 3.80 VMA, % 16.3 16.5 Subgrade Density, kg/m³ (pcf) 1858 (116) 1842 (115) % Moisture 2.5 2.8 Granular Base Density, kg/m³ (pcf) 2307 (144) 2320 (145) % Moisture 3.5 3.6 Thickness mm 236 232 Asphalt Test Slab (HL3) Thickness mm 80 82 Specific Gravity 2.172 2.183 The permanent deformation after 3,000,000 load cycles was determined and the total number of load cycles required to obtain a deformation of 6.0 mm was recorded. The results are set out in Table 17. The premium asphalt prepared from the low quality crude 'B' provided superior performance. This product demonstrated a reduction in pavement rutting of 70% and an increase of the pavement load carrying capacity of over 800% when compared to the performance of the high quality asphalt produced by conventional processes. Example 5 This Example demonstrates the superior temperature susceptibility of the asphalts prepared pursuant to the present invention. The asphalts used in this Example are briefly described below. 1. A high quality asphalt produced pursuant to conventional processes from crude 'A'. 2. A premium asphalt ex high quality crude 'A' prepared using the materials and methods described in Example 1. 3. A premium asphalt ex low quality crude 'B' prepared using the materials and methods described in Example 4. Improved temperature susceptibility in demonstrated by improved values of PVN and PI. In addition, superior temperature susceptibility is also confirmed by pavement stiffness determinations carried out at -18°C and by pavement resilient modulus tests (ASTM D-4123) carried out over a temperature range from 40°C to 5°C. The results are set out in Table 18. Conventional High Quality Asphalt Ex Crude 'A' Premium Asphalt Ex High Quality Crude 'A' Premium Asphalt Ex Low-Quality Crude 'B' Pavement Resilient Modulus MR Psi x 10³ 40°C 88 120 103 5°C 812 713 612 Pavement Low-Temperature Stiffness, Psi x 10³ (-18°C, 0.004 mm/min) 919 460 592 PVN -0.7 -0.1 -0.5 PI -2.10 -0.2 -0.9 As is appreciated from the foregoing, by using the present invention, it is possible to obtain an asphalt which has improved road performance characteristics. Such asphalts have a lesser amount of permanent deformation as measured by the pavement performance simulator. The percent reduction in pavement rutting may be at least 20%. Premium asphalts demonstrate a permanent deformation reduction of up to 75% and increased pavement load carrying capacity of up to 1000% or more. In addition they demonstrate improved temperature susceptibility and a 50% reduction in pavement low-temperature stiffness.

Claims: The use of a catalytically oxidised asphalt precursor as a rutting reducing additive in a paving asphalt cement comprising an unoxidised asphalt precusor. The use according to claim 1, characterised in that the catalytically oxidised asphalt precursor is prepared by catalytically oxidizing one or more of a high quality paving asphalt precursor, a low quality paving asphalt precursor, a non-paving asphalt precursor or a mixture thereof. The use according to claim 1, characterised in that the unoxidized asphalt precursor is one or more of a high-quality paving asphalt precursor, a low quality paving asphalt precursor, a non-paving asphalt precursor or a mixture thereof. The use according to claim 2 or 3 characterised in that the catalytically oxidised asphalt precursor is prepared by catalytically oxidizing a high quality paving asphalt precursor and in that the unoxidised asphalt precursor is a high quality paving asphalt precursor. The use according to claim 2 or 3, characterised in that the catalytically oxidised asphalt precursor is prepared by catalytically oxidizing a low quality paving asphalt precursor and in that the unoxidized asphalt precursor is a low quality paving asphalt precursor. The use according to claim 2 or 3, characterised in that the catalytically oxidised asphalt precursor is prepared by catalytically oxidizing a non-paving asphalt precursor and in that the unoxidized asphalt precursor is a non-paving asphalt precursor. The use according to any of claims 1 to 6, wherein the catalytically oxidised asphalt precursor is prepared using as an oxidisation catalyst phosphoric acid, phosphorous pentoxide, ferrous chloride or ferric chloride. The use according to any of claims 1 to 7, characterised in that the catalytically oxidized asphalt precursor has a penetration of from 5 to 100 as measured by ASTM D5 @ 25°C. The use according to claim 8, characterised in that the catalytically oxidized asphalt cement has a penetration of from 15 to 40 as measured by ASTM D5 @ 25°C. The use according to claim 9, wherein the catalytically oxidized asphalt cement has a penetration of from 15 to 30 as measured by ASTM D5 @ 25°C. The use according to any of claims 1 to 10, characterised in that the paving asphalt cement further comprises at least one performance enhancer.

Inventors: KAMEL NABIL I, MILLER LAVERNE J, KAMEL, NABIL I, MILLER, LAVERNE J.
Applicants: PETRO CANADA INC, PETRO CANADA
Application year: 1991
Main classification: C08L95
IPC codes: C10C3, E01C7, C08L95