NL2010588C2

NL2010588C2 - Process for the production of reclaimed asphalt aggregates and use thereof in the production of an asphalt composition.

Info

Publication number: NL2010588C2
Application number: NL2010588A
Authority: NL
Inventors: Cornelis M A Beemt; Mathias M J Jacobs; Marinus Huurman; Ernst W Demmink
Original assignee: Konink Bam Groep Nv
Priority date: 2013-04-08
Filing date: 2013-04-08
Publication date: 2014-10-16
Also published as: WO2014168479A1

Abstract

Reclaimed asphalt aggregates are produced in a process, comprising the steps: a) providing reclaimed asphalt lumps and treating the reclaimed asphalt lumps by the use of impact to obtain reclaimed asphalt aggregates that comprise recycle bitumen; and b) separating the reclaimed asphalt aggregates into at least a coarse fraction having granular particles with a diameter of more than 2 mm and at least a fine fraction having granular particles with a diameter of at most 2 mm. The reclaimed asphalt aggregates may be separately used in a process for the preparation of an asphalt composition.

Description

PROCESS FOR THE PRODUCTION OF RECLAIMED ASPHALT AGGREGATES AND USE THEREOF IN THE PRODUCTION OF AN ASPHALT COMPOSITION

The present invention relates to a process for the production of reclaimed asphalt aggregates, in particular of granular reclaimed asphalt aggregates obtained after decomposition. It further relates to a process for producing asphalt compositions using reclaimed asphalt aggregates. In this specification by asphalt is understood the combination of bitumen and aggregates. Asphalt is sometimes referred to as asphalt concrete. Asphalt is generally used in road pavements, but other uses, e.g. in roofing felts and the like, are also possible.

There is an increasing need for road pavements based on asphalt. Asphalt from a road pavement may generally contain from 3 to 8%wt bitumen, more generally 4 to 5%wt.

The major part of asphalt is constituted of aggregates. The aggregates tend to be granular. The aggregates in asphalt commonly have a variety of dimensions and usually vary from coarse, e.g. with a minimum diameter of greater than 2 mm, and fine aggregates, e.g. with a maximum diameter of 2 mm. Finer filling material, e.g. having a maximum diameter of 63 pm may be defined as formally dosed artificial fines or as a separate form of aggregate. The largest aggregates do not have a maximum diameter that exceeds 32 mm. The aggregates are mixed together with the bitumen, spread and compacted, usually while being hot, to form a road pavement. Roads tend to age and when aged roads are being renewed, large quantities of reclaimed asphalt become available. From an environmental standpoint it is undesirable to dump the reclaimed asphalt as waste. Therefore, there is an increasing requirement to recycle reclaimed asphalt.

In practice, asphalt is already being reclaimed. In such a case typically lumps or brocks of reclaimed asphalt, that may optionally first be broken into granular pieces, are heated and mixed with fresh asphalt. Since the reclaimed asphalt comprises bitumen, the temperature to which the reclaimed asphalt may be heated is limited. If the temperature becomes too high the bitumen becomes sticky or even liquid so that the reclaimed asphalt will be difficult to handle or can even no longer be handled in an asphalt plant. Heating the reclaimed asphalt to such high temperature also results in a higher emission of volatile organic compounds, VOCs, and in more odour. The limited temperature may constitute a drawback since reclaimed asphalt generally contains a certain amount of moisture and must be dried before it can be re-used in the production of a new asphalt composition. Inter alia for this reason the proportion of reclaimed asphalt in asphalt compositions is in practice generally limited to about 50%wt.

An example of a known method for recycling asphalt is shown in a brochure by Metso Minerals Ltd (http://www.metso.com/mininqandconstruction/MaTobox7.nsf/DocsBvlD/ 97AC8AD8A245BCDBCC256C5C0080EB2B/$File/Aib031.pdf). This brochure shows how reclaimed asphalt is crushed and subsequently screened over two sieves, one with a size of 50 mm and a one with a size of 12 mm. Any retained particle from any of the screens is passed to a crusher for regrinding so that a homogeneous pile of asphalt aggregates with a maximum diameter of 12 mm is obtained. It is evident that this process provides the feed for the recycle process as described above.

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 4142803. In these patent documents reference is made to the fact that smaller particles contain more bitumen than the coarser particles. However, both patent documents are silent about the method the crushed particles are obtained.

The present inventors have found that if lumps of reclaimed asphalt is crushed in a conventional way, the amount of bitumen on the aggregates is still too high to be used in a conventional drying and heating drum. They surprisingly found that if reclaimed asphalt lumps are treated by means of impact instead of by using jaw crushers or cone crushers, and subsequently separated into at least a coarse fraction and a fine fraction, the aggregates in the reclaimed asphalt are not further crushed, and that the content of bitumen in the coarse fraction is a significantly lower than the amount of bitumen in the fine fraction.

Accordingly, the present invention provide a process for the production of reclaimed asphalt aggregates, comprising the steps: a) providing reclaimed asphalt lumps and treating the reclaimed asphalt lumps by the use of impact to obtain reclaimed asphalt aggregates that comprise recycle bitumen; and b) separating the reclaimed asphalt aggregates into at least a coarse fraction having granular particles with a maximum diameter of more than 2 mm and at least a fine fraction having granular particles with a maximum diameter of at most 2 mm.

By an impact is understood a force or shock applied for a short time period when two or more bodies collide. The force of the impact is suitably chosen so that the crushing of the aggregates themselves is minimized whilst the decomposition into the separate aggregates is optimized.

The products of the process according to the invention can advantageously be used in a process for producing a new asphalt composition, wherein the content of reclaimed asphalt aggregates can be increased to levels far above 50%wt. Moreover, the recycle bitumen that is adhered to the reclaimed asphalt aggregates can also be used, thereby reducing the need to complement the bitumen content in the asphalt to be produced with fresh bitumen. Accordingly, the invention also provides a process for the preparation of an asphalt composition comprising reclaimed asphalt aggregates, comprising the steps: a) providing at least a coarse fraction and at least a fine fraction obtained by the process of treating reclaimed asphalt lumps and separating the reclaimed asphalt aggregates as described above; b) heating at least a part of the coarse fraction to a temperature of more than 130 °C, to obtain a hot coarse fraction, c) providing fresh bitumen and heating the fresh bitumen to a temperature of at least 130 °C, to obtain hot fresh bitumen; and d) mixing at least a portion of the hot coarse fraction and, optionally, at least a portion of the fine fraction with hot fresh bitumen to obtain an asphalt composition.

The starting material for the process of the present invention comprises reclaimed asphalt lumps. It is understood that this term means the pieces of used and aged asphalt that are recovered when existing asphalt layers, e.g. road pavements, are removed. The pieces may be very large but may also be fairly small. The lumps that may be subjected to an impact treatment in accordance with the invention may typically have a maximum size of about 20 cm, preferably about 10 cm. If it is desired to have the size of the lumps reduced before being subjected to the process according to the present invention such lumps may be broken into smaller pieces by any known method, including by means of several types of crushers.

In the industry a number of different crusher types are known. Known types include jaw crushers, which comprise tapered plates that form a jaw and which due to the movement of at least one of the plates, a piece of solid material is crushed to smaller pieces; and cone crushers, wherein rocks are squeezed between an eccentrically gyrating spindle and a concave hopper, and thus crushed. According to the invention the reclaimed asphalt lumps are decomposed by the use of impact. This means that the lumps are allowed to collide with another body that has a different speed from the speed of the lumps. An example of equipment using impact, is e.g. a hammer mill.

It has been found that very good results are obtained when a different type of equipment for delivering impact is used, viz. a vertical shaft impact crusher. In this type a high-speed rotor is designed to throw lumps of material to a surface. In this way velocity is used rather than pressure to achieve size reduction. Utilizing velocity allows the size reduction to take place evenly. In this way the breaking occurs at the adhesion between coarse aggregates and bitumen, so that coarse aggregates that are substantially free from bitumen and mastic particles are obtained, mastic being defined as a mixture of bitumen and fine aggregates with a maximum diameter of at most 2 mm,. Without wishing to be bound by any theory, it is believed that via such a mechanism the advantageous products of the present invention are obtained. A main advantage of the process of the present invention resides in that the aggregates in the reclaimed asphalt lumps remain unaffected to a significant extent by the impact.

Suitably, the reclaimed asphalt lumps in accordance with the process of the present invention are decomposed in a centrifugal mill. In such a mill the lumps are accelerated and given a certain velocity that is used for the impact by means of a centrifugal force. The accelerated lumps are made to impact on an impact wall. Advantageously, the impact wall is a solid wall of the housing of the centrifugal mill or a layer of crushed reclaimed asphalt aggregates. The skilled person can adjust the configuration of the centrifugal mill (e.g. speed and the angle of impact) to achieve the optimal result.

A suitable centrifugal mill has been described in EP1335794. This mill comprises a twin-chamber rotor that is mounted in a centrifugal mill housing. Reclaimed asphalt lumps are fed into the rotor, accelerated and hurled to the outside. The lumps or blocks are thrown against a wall of the housing that serves as anvil. Alternatively, the solid material is thrown against a layer of particles that have been passed through the rotor before. By varying the rotor speed and the angle of impact, and by selecting the anvil or the layer of particles as impact wall for the reclaimed asphalt lumps, the skilled person can determine the optimal crushing strength for the reclaimed asphalt lumps. In this way the skilled person is able to optimize the breaking up of the lumps of reclaimed asphalt into coarse and fine particles, wherein the skilled person can minimize the breaking of the aggregates in the reclaimed asphalt.

The separation of the reclaimed asphalt aggregates into at least a coarse fraction and at least a fine fraction is preferably conducted by means of one or more sieves. By using the appropriate sieves, the skilled person may separate the reclaimed asphalt aggregates into the desired number of fractions. It may be advantageous to separate the reclaimed asphalt aggregates into three or more fractions. For instance, a very coarse fraction with particles having a maximum size of more than about 20 to about 50 mm can be separated. Such a fraction may suitably be recycled to the impact treatment. The separation may also be conducted such that another coarse fraction containing particles with a maximum diameter between about 2 mm and about 25 mm, is obtained which is recovered as the coarse fraction according to the invention. A fine fraction having particles with a maximum diameter of 2 mm, may suitably be recovered as the fine fraction according to the invention. The skilled person will understand that more fractions may be separated, e.g. a very fine fraction with particles having a maximum diameter of 50 to 90 pm, e.g. 63 pm. Such a fraction may be considered dust. The skilled person will also realize that the separation between the fractions may be applied differently; the cut may be e.g. at 1 mm and at 22 mm. It is possible to use the standard sieves that are commonly applied in the industry, which include 63 pm, 125 pm, 500 pm, 1 mm, 2 mm, 4 mm, 5.6 mm, 8 mm, 11.2 mm, 16 mm, 22.4 mm and 45 mm. Standard sievs have been mentioned in standard EN13043.

As indicated above, the reclaimed asphalt aggregates in the at least one coarse fraction contains very little recycle bitumen. Suitably, the reclaimed asphalt aggregates in the at least one coarse fraction contain a lower level of recycle bitumen than the used asphalt aggregates in the at least one fine fraction. The difference in recycle bitumen content between the coarse fraction and the fine fraction may such that the fine fraction contains at least three times more recycle bitumen than the coarse fraction. For instance, the reclaimed asphalt aggregates in the at least one coarse fraction suitably contain a maximum of 2,5 %wt of recycle bitumen preferably a maximum of 1.5 %wt, more preferably 1.0%wt, based on the weight of the reclaimed asphalt aggregates, whereas the reclaimed asphalt aggregates in the at least one fine fraction contain a minimum of 6%wt of recycle bitumen, preferably at least 7 %wt of recycle bitumen, based on the weight of the reclaimed asphalt aggregates in the fine fraction. Recycle bitumen contents in the fine fractions of 25%wt are attainable.

Due to the difference in bitumen content the fractions after separation can be treated differently in the preparation of asphalt compositions using these fractions. As already indicated above, the fractions may suitably be used in the production of a new asphalt composition. The coarse fraction of the above treated and separated reclaimed asphalt is heated in such a process to a temperature of at least 130 °C. Thanks to the low bitumen content it is possible to heat this coarse fraction to even higher temperatures, e.g. to at least 150 °C. Thanks to the high temperature this coarse fraction can be dried completely which benefits the preparation of the asphalt composition. Moreover, the hot coarse fraction may in this way provide at least a part of the energy that may be needed to heat the fine fraction that is optionally mixed with the hot coarse fraction and the hot fresh bitumen. The treated and separated hot coarse fraction is preferably heated to at most 240°C. At higher temperatures the bitumen that may be adhered to the reclaimed asphalt aggregates may get burned and there are no benefits gained at all. The temperature of the reclaimed asphalt aggregates in the at least one fine fraction is preferably kept below 100°C, more preferably below 75°C. Since it is most convenient to add the reclaimed asphalt aggregates in the at least one fine fraction whilst they are at ambient temperature it is most preferred to do so and to refrain from heating these aggregates at all. The excess heat of the coarse fraction or fractions and that of the fresh bitumen will provide for sufficient energy to heat also the fine fraction or fractions. The fresh bitumen that is used in the process according to the present invention can be any usual type of bitumen. Since asphalt production facilities tend to have a number of standard bitumen types available at the facilities, any of these types may be applied in the present process. 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. The type of bitumen may also be varied in accordance with the properties of the recycle bitumen that is present on the reclaimed asphalt aggregates. Dependent on the hardness of the recycle bitumen that is contained in the reclaimed asphalt aggregates, the skilled person may opt for the selection of a rather soft bitumen, i.e. a bitumen with a high penetration. The skilled person may also select a polymer modified bitumen. In such a case the bitumen has been modified by the addition of one or more polymers. Such polymers may be elastomers, such as styrene butadiene rubber, styrene butadiene block copolymers, linear or star-shaped; styrene isoprene block copolymers, linear or star-shaped, and EPDM rubber (ethylene propylene diene monomer polymer). Alternatively thermoplasts may be added, such as, polyvinylchloride, ethylene vinyl acetate; copolymers of ethylene and methyl or butylene (meth)acrylate, polyethylene or atactic polypropylene. Typically, the skilled person will strive that when the fresh bitumen and the reclaimed asphalt aggregates are mixed the kinematic viscosity of the mixed bitumen at the mixing temperature will be at most 200 cSt (200 mm2/s). This ensures that the mixing of the reclaimed asphalt aggregates and the fresh bitumen can be conducted smoothly, and that a homogeneous mixture is obtained. Such a smooth mixing may be obtained by heating the fresh bitumen to 130 °C, preferably to a temperature of at least 150°C. In order to avoid smoke from the fresh bitumen and unnecessary costs, the maximum temperature of the fresh bitumen is generally 250°C, preferably 200°C.

If desired, a rejuvenating agent may be added to the mixing step d). There is a myriad of products that are presently being used and marketed as rejuvenating agents for the recycling of asphalt compositions. 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 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 since these oils show a low volatility, their use thus has an long-lasting effect on the asphalt.

The amount of rejuvenating agent in the asphalt composition to be prepared may vary within wide ranges. The most suitable amounts can be selected by the skilled person dependent on the hardness of the recycle bitumen in the reclaimed asphalt lumps and on the intended use of the asphalt composition. Typically the amount of rejuvenating agent may be in the range of 0.5 to 5.0 %wt based on the weight of the bitumen and the reclaimed asphalt aggregates.

If desired, additives may be added to the asphalt composition. In particular it may be desirable to add virgin mineral aggregates. Therefore, the present invention also provides for the process above wherein in addition to the at least one coarse fraction of the reclaimed asphalt aggregates and the at least one fine fraction of the reclaimed asphalt aggregates, virgin coarse aggregates and/or virgin fine aggregates are added to the hot fresh bitumen. When such virgin aggregates are being added, they have suitably been heated before being added to the fresh bitumen. The temperature of the heated virgin aggregates is usually in the range of 120 to 200°C. This ensures that by the addition of the virgin aggregates the total amount of energy of the mixture that is being mixed in step d) is sufficient to keep the mixture well mixable and handleable, despite the addition of the fairly cool particles of the fine fraction.

The asphalt composition that is being produced with the process of the present invention may be used for a variety of applications. Even if it is being used for road pavement, the composition of any asphalt may be varied dependent on the requirements and wishes of the situation. Typically, the asphalt composition will be selected such that the weight ratio of bitumen, that includes fresh bitumen and recycle bitumen, to aggregates, that include the reclaimed asphalt aggregates and virgin aggregates, is in the range of 3:100 to 12:100. In general the amount of bitumen in the asphalt composition produced according to the invention will not significantly differ from conventional fresh asphalt.

As is apparent from the description above, the asphalt composition that is being produced in the process according to the present invention contains a major amount of reclaimed asphalt components. Not only the coarse and fine aggregates consist for a major part of the reclaimed asphalt aggregates, but also the recycle bitumen forms part of the recycled components. Hence, in this way the proportion of reclaimed asphalt in the asphalt composition may be significant. In addition, it is possible to add to an asphalt composition thus obtained a further portion of reclaimed asphalt. This reclaimed asphalt has not been subjected to the impact treatment and separation. The proportion of such reclaimed asphalt that is being added to the asphalt composition obtained in the process according to the invention may be as much as 50%wt, based on the combination of reclaimed asphalt and the asphalt composition produced in accordance with the present invention. This additional part of reclaimed asphalt may be added in a conventional way. This would mean that in addition the reclaimed asphalt is suitably mixed in step d) of the process. Since the proportion of reclaimed asphalt is significant a considerable amount of energy is required to bring this reclaimed asphalt into a state wherein it is smoothly stirrable to make a homogeneous asphalt composition with the other components in step d). Therefore, the reclaimed asphalt is advantageously heated before being added to the hot fresh bitumen in step d). The reclaimed asphalt contains bitumen. Therefore, the heating of the reclaimed asphalt should be such that the bitumen does not get sticky. Thus, the reclaimed asphalt will preferably be heated to a temperature that does not exceed 130°C, and is preferably lower. In view of this relatively low temperature and in view of the desired temperature in step d) of between 150 and 200 °C, it is very beneficial that the reclaimed asphalt aggregates in the coarse fraction or fractions that have been subjected to impact treatment and separation, and the fresh bitumen may be heated to a sufficiently high temperature to compensate for the low temperature of the reclaimed asphalt and the low temperature of the reclaimed asphalt aggregates in the fine fraction or fractions.

The present invention not only enables that the proportion of recycle asphalt in conventional mixtures, which is maximized to 50%wt, can be increased by the use of additional reclaimed coarse and optionally reclaimed fine aggregates, The present invention also allows for reclaimed coarse aggregates, and optionally also reclaimed fine aggregates to be added to asphalt compositions that normally would not contain any reclaimed aggregates at all. This can now be done without any loss of quality of the resulting asphalt compositions.

The skilled person will know that asphalt compositions may comprise various additives. Such additives include adhesion promoters, such as amine compounds, lime and calcium hydroxide, drip inhibitors, such as cellulose, glass fibres and rockwool, and dyes, such as iron oxide. Such additives may also be used in the asphalt compositions prepared according to the invention.

Claims

A method for the preparation of recovered asphalt aggregates, comprising the steps of: a) providing chunks of recovered asphalt and treating the chunks of recovered asphalt by the use of an impact so that recovered asphalt aggregates containing recycle bitumen are obtained; and b) separating recovered asphalt aggregates into at least one coarse fraction with granular particles with a maximum diameter of more than 2 mm and at least one fine fraction with granular particles with a maximum diameter of at most 2 mm.

The method according to claim 1, wherein the recovered chunks of asphalt are treated by means of a centrifuge mill.

A method according to claim 1 or 2, wherein the recovered asphalt is accelerated by means of a centrifugal force and is collided with an impact wall.

The method of claim 3, wherein the barrier wall is formed by a fixed wall of the housing of a centrifuge mill or a layer of compressed reclaimed asphalt aggregates.

The method according to any of claims 1 to 4, wherein the separation of the recovered asphalt aggregates into at least one coarse fraction and at least one fine fraction is carried out by means of one or more sieves.

The method of any one of claims 1 to 5, wherein the recovered asphalt aggregates in the at least one coarse fraction contain a lower content of recycle bitumen than the used asphalt aggregates in the at least one fine fraction.

The method of any one of claims 1 to 6, wherein the recovered asphalt aggregates in the at least one coarse fraction contain a maximum of 2.5% by weight of recycle bitumen based on the weight of the recovered asphalt aggregates in the coarse fraction.

A method according to any of claims 1 to 7, wherein the recovered asphalt aggregates in the at least one fine fraction contain a minimum of 6% by weight of recycle bitumen, preferably at least 7% by weight of recycle bitumen, based on the weight of the recovered asphalt aggregates in the fine fraction.

A method for preparing an asphalt composition containing recovered asphalt aggregates, comprising the steps of: a) providing at least one coarse fraction and at least one fine fraction obtained in the method of any one of claims 1 to 8; b) heating at least a portion of the coarse fraction to a temperature of more than 130 ° C, so that a hot coarse fraction is obtained; c) providing new bitumen and heating the new bitumen to a temperature of at least 130 ° C, so that hot new bitumen is obtained; and d) mixing at least a portion of the hot coarse fraction and, optionally, at least a portion of the fine fraction with hot new bitumen to obtain an asphalt composition.

The method of claim 9, wherein the recovered asphalt aggregates in the at least one coarse fraction are heated to a temperature of at least 150 ° C.

A method according to claim 9 or 10, wherein the temperature of the recovered asphalt aggregates in the at least one fine fraction is kept below 100 ° C.

The method of any one of claims 9 to 11, wherein the new bitumen has a penetration of up to 220 mm.

The method of any one of claims 9 to 12, wherein the new bitumen is heated to a temperature of at least 150 ° C.

A method according to any of claims 9 to 13, wherein, in addition to the at least one coarse fraction of the recovered asphalt aggregates and the at least one fine fraction of the recovered asphalt aggregates, fresh coarse aggregates and / or fresh fine aggregates are added to the hot new bitumen.

The method of claim 14, wherein the fresh coarse aggregates and / or the fresh fine aggregates are heated before being added to the bitumen.

The method of any one of claims 9 to 15, wherein the weight ratio of bitumen, which includes new bitumen and recycle bitumen, to aggregates involving recovered asphalt aggregates and fresh aggregates is in the range of 3: 100 to 12: 100.

The method according to any of claims 9 to 16, wherein furthermore recovered asphalt is admixed in step d).

The method of claim 17, wherein the recovered asphalt is heated before it is added to the hot new bitumen in step d).