METHOD AND DEVICE FOR THE TREATMENT OF AN ASPHALT STRUCTURE WITH A LIQUID AGENT

Abstract

 The present invention relates to a method for the treatment with a liquid agent of an asphalt structure, in particular an asphalt structure which comprises a porous asphalt surface course, using an air flow directed at the aforesaid asphalt structure, wherein said treatment comprises the following steps:
i) spraying a liquid binder onto the surface course of the aforesaid asphalt structure;
ii) directing a concentrated air flow at the liquid binder sprayed onto the aforesaid surface course in step i), wherein step ii) is carried out in such a manner that the spraying according to step i) and the directing of the air flow according to step ii) are carried out as separate steps, so that the aforesaid liquid binder will penetrate through the surface course, forming a sealing layer of binder in the aforesaid surface course in a region near the bottom side of the surface course.

Description

[0001] The present invention relates to a method and a device for the treatment of an asphalt structure with a liquid agent. More in particular, the present invention relates to a method and a device for the treatment with a liquid agent of an asphalt structure, in particular an asphalt structure comprising a porous asphalt surface course, wherein use is made of an air flow directed at the aforesaid asphalt structure.

[0002] Porous or open courses have been used for years as surface courses or upper layers of road surfaces. These layers, whose advantages are known, provide significant benefits both for the road user and for the environment. Rainwater is absorbed in the porous layer, so that rainfall will not result in water splashing up from the road, possibly blocking the road user's view. In addition, because of the porosity the noise produced by vehicle tyres is absorbed and reduced, resulting in less noise nuisance from the road traffic in the vicinity of the road. A special form of a porous road surface is a two-layer porous asphalt surface. It consists of two superposed layers of porous asphalt; the lower layer is a coarse-grained layer with large pores which allow good flow-through of water into and through the layer, and on top of said layer a relatively thin fine-grained surface course is installed, which surface course has been optimised for reducing traffic noise.

[0003] From US patent application US2014-0076199 there is known a cationic emulsion which is used for the so-called fog seal process. According to the fog seal technique, a liquid binder is sprayed onto the road surface using a large amount of air in the spray fog so as to realise an optimum distribution of the binder on and in the surface course.

[0004] Bitumen emulsions are known per se, they are for example disclosed in US patents US 6,840,991 and US 7,918,624 and in International application WO 2011-034425.

[0005] US patent publication US 2005/265784 discloses a method for the treatment of an asphalt structure wherein use is made of a special composition for realising both internal protection and surface protection. Such a treatment is in particular desirable with a view to preventing the ingress of water into asphalt, which would result in the porosity of the asphalt layer being completely lost. To carry out such a treatment, an apparatus is used by which the special composition is sprayed onto the surface of the asphalt structure, after which a brush rotating at high speed forces the composition thus sprayed onto the asphalt structure into the asphalt.

[0006] From French publication FR 2 680 806 there is known a method for the treatment of an asphalt structure, in which publication mention is in particular made of effecting rapid breaking of the emulsion. Such breaking of the emulsion, upon which the process is conditional, takes place by first pre-treating the asphalt surface with a low-pressure hot air flow, after which the emulsion is sprayed onto the surface and finally a low-pressure hot air flow is used again. The emulsion broken using such a method provides a dense binder course on the asphalt surface thus treated with a hot air flow, as a result of which the asphalt surface thus obtained must be considered to be non-porous.

[0007] From German publication DE 21 54 133 a method for the treatment of an asphalt surface is known wherein use is made of an installation wherein first a reduced pressure is applied to the asphalt for pre-treating the asphalt as such. After the application of the reduced pressure, an overpressure is used for forcing an impregnation agent into the underlying surface.

[0008] From German publication DE 673 645 there is known a similar method wherein use is also made of a reduced pressure for subjecting an asphalt structure to a surface treatment.

[0009] From European publication EP 1 396 580 there is known a method for the installation of porous asphalt, wherein so-called asphaltic concrete is installed on a road surface, which asphaltic concrete includes a bitumen emulsion.

[0010] Usually cracking and fraying occur soonest at places where strips of asphalt touch, after all, the seam is a vertical seam. A major cause is the temperature difference between the existing asphalt and the newly installed layer of asphalt. For this reason a strip of cold bitumen is placed against the upright edge of the asphalt. It is also possible, however, to clean the upright edge of the asphalt first using a hot air lance, after which a layer of hot polymer-modified bitumen is applied to the vertical contact surface. After the new layer of asphalt has been installed, a bond is formed which is claimed to prevent cracking and fraying.

[0011] It is further known to conserve asphalt with a so-called asphalt coating that protects the asphalt against motor oil, road salt and various types of weather influences such as frost, rain and ultraviolet (UV). Such an asphalt seal coating makes the asphalt impervious to water and causes the water to be drained to a drainage pit or to the roadside. It is assumed that UV rays cause binders such as bitumen to dry out, as a result of which asphalt will become very coarse and obtain an open structure and stones will come loose in the asphalt. Furthermore, evaporation and damage to the binder can affect the flexibility of the asphalt, which may lead to the formation of cracks.

[0012] A problem that occurs in the use of macroporous, open surface courses is that it is not possible to apply such an impermeable layer afterward. After all, the macroporous surface course is at that stage already present on top of the dense layer that would have to be provided with such an impermeable surface course. If a problem exists as regards the quality of the underlying dense layer, it will be necessary to remove the open surface course first, after which the impermeable layer can be installed, and finally a new open surface course will have to be installed in that case. This means a major destruction of capital.

[0013] Porosity of porous or open courses, such as porous asphalt, is in general realised by the selection of the mineral structure in the road surface mixture. In the case of asphalt, for example, a particular stone gradation is selected and a limited amount of mortar is used for durably binding this stone fraction together. The mortar consists of the fine fractions in the mixture, such as sand and aggregate, and in addition to that bitumen as a binder material which binds the entire asphalt mixture together. Upon compaction of the asphalt mixture during the installation process, the stone fraction in the mixture is pressed together, so that a stable stone skeleton having a high load-bearing capacity is formed, while sufficient open pores still remain present between the mortar-envelopes stones for providing the required porosity.

[0014] A consequence of the use of such a porous surface course on the upper side of a pavement structure is that the drainage of rainwater and any road salts takes place in a different manner than usual. In the case of conventional dense surface courses, the drainage of water takes place over the surface of the pavement. The pavement is for that purpose given sufficient cross-fall, so that the water can drain in transverse direction to the verge of the road.

[0015] When porous surface courses are used, the water first penetrates vertically into the course and then flows over an underlying dense layer to the verge of the road as a result of the cross-fall of the road. Because the water thus flows between the stone grains at the bottom of the porous layer to the verge of the road, drainage is retarded. As a result, the upper side of the underlying dense layer remains wet longer after a rain shower, whilst in addition, in contrast to a dense road surface, no sunlight reaches said underlying dense layer and car tyres do not have a drying effect at that location.

[0016] Dense surface courses such as dense asphaltic concrete or crushed stone asphaltic concrete are protected against weather influences by their dense structure. The granular structure of minerals and bitumen as the binder prevent the ingress of water and air into the surface course. In particular in frost conditions, the ingress of water can create expansion forces in the asphalt, as a result of which the cohesion thereof decreases or is even lost altogether. Ingress of air into an asphalt layer causes oxidation of the binder, resulting in loss of flexibility of the asphalt and hardening of the binder. A hard and brittle binder can lead to cracks when the road surface is subjected to loads, which cracks in turn accelerate the above process.

[0017] The ageing process as described above will occur sooner if the porosity of such a dense surface course is higher. However, this porosity is not the same as the aforesaid porosity of open surface courses such as porous asphalt. Both as regards extent and as regards pore size, the porosity of dense surface courses is one order of magnitude lower than that of porous asphalt, for example. In the present description, the term "macroporosity" is used in relation to porous asphalt and the term "microporosity" is used in relation to dense surface courses.

[0018] The microporosity in dense surface courses can be caused by incorrect compaction of the course at construction, but it may also develop with the passage of time as a result of ageing and weathering. Furthermore, the presence of road salts in the draining rain water has a negative effect on this deterioration process.

[0019] It is therefore of paramount importance that the dense layers present beneath macroporous open surface courses exhibit a high degree of density. The effects of water and salt are intensive and prolonged and any damage that occurs in this underlying layer will also cause the overlying open surface course to deteriorate.

[0020] A special impermeability requirement applies to bridge decks. Ingress of water and salt into the concrete deck of a bridge or flyover will adversely affect the concrete, resulting in a loss of bearing capacity of the bridge, which may thus become critical. If a macroporous open surface course is used on a bridge deck, a dense (asphalt) layer is often installed first beneath said open surface course, with maximum requirement being applicable as regards the hollow space in the mixture after compaction (max. 5%). This is done so as to ensure absolute impermeability.

[0021] Upon renovation of the asphalt structure on an existing concrete flyover, the existing asphalt layers are first removed up to the concrete and two new layers of asphalt are installed within the shortest possible time. First the dense lower layer of, for example, dense asphaltic concrete is installed so as to seal and protect the concrete, after which, once the lower layer has cooled, the surface course of porous asphalt is installed. Because it is often more difficult to create relief roads at flyovers and the width of the road in relation to phasing of the work is often limited, this work is usually carried out under high pressure of time. Determining whether the dense lower layer meets the applicable impermeability requirements can only be done afterwards in those cases. If it appears upon sampling that the density is insufficient, which is a real risk due to the high pressure of time of the work, a correction measure must be taken. This may for example comprise the removal of the newly installed porous asphalt layer, the application of a sealing layer and the subsequent installation of a new porous asphalt surface course. The consequence is a great deal of nuisance and high cost.

[0022] In the case of two-layer porous asphalt, it is especially the thin, fine surface course that is subject to wear caused by traffic. The lower coarse-grained porous asphalt layer is not exposed to traffic influences. A possible renovation method concerns the replacement of only the fine surface course. As a result, the porous asphalt lower layer can last for a period of twice the life of the surface course, for example 2 x 10 = 20 years.

[0023] The underlying dense cover layer (generally crushed stone asphaltic concrete) must in that case be capable of withstanding the effects of water thereon without any quality problems during this double life span. This is often doubtful. When normal, single-layer porous asphalt is replaced, the underlying dense layer is exposed and correction measures can be taken. This can be done either in the form of a renovation or by the application of a sealing layer.

[0024] The aforesaid possibility is not available upon replacement of the surface course of two-layer porous asphalt. If problems with the underlying dense asphalt layer are nevertheless expected during the second life cycle of the surface course, a correction measure can only be taken if the lower porous asphalt layer is removed as well. This, too, involves high cost, destruction of capital and additional construction time and nuisance.

[0025] It is an object of the present invention to provide a solution to the above problem.

[0026] Another object of the present invention is to provide a method for the treatment of an asphalt structure of the open type, wherein a durable sealing layer is applied whilst the advantageous properties of the open asphalt structure are retained.

[0027] Yet another object of the present invention is to provide a method for the treatment of an asphalt structure of the open type, wherein, in particular in the case of an old open surface course, hair cracks in the mastic and the adhesive bridges between the grains are corrected over the entire height of the course and the whole is strengthened.

[0028] Accordingly, the present invention provides a method for the treatment with a liquid agent of an asphalt structure, in particular an asphalt structure which comprises a porous asphalt surface course, using an air flow directed at the aforesaid asphalt structure, which method is characterised in that said treatment comprises the following steps:

i) spraying a liquid binder onto the surface course of the aforesaid asphalt structure;

ii) directing a concentrated air flow at the liquid binder sprayed onto the aforesaid surface course in step i), wherein step ii) is carried out in such a manner that the spraying according to step i) and the directing of the air flow according to step ii) are carried out as separate steps, so that the aforesaid liquid binder will penetrate through the surface course, forming a sealing layer of binder in the aforesaid surface course in a region near the bottom side of the surface course.

[0029] Using such a method, one or more of the aforesaid objects are achieved. By directing a concentrated air flow at the road surface directly after spraying of the liquid binder has taken place, the liquid binder is blown to the bottom of the open surface course, against the dense underlayer, during its liquid phase. The concentrated air flow functions as a means of transport for the liquid binder. The speed of movement of said liquid binder during spraying is inhibited by the contact with the stone grains of the open surface course in the road surface, as a result of which the liquid binder remains "suspended" at the top of the open surface course. As a result of the air flow, the macropores of the open surface course are blown open and the functionality, viz the drainage of water and the absorption of sound, is retained.

[0030] It should be noted that the present invention is essentially different from the above-discussed so-called "fog seal" technique. In the method according to the present invention, the spraying of the liquid binder and the positioning of the air flow are carried out as separate steps, whilst in the so-called "fog seal" technique the binder is atomised in the air flow. In other words, carrying out in the present method the two operations in succession, viz spraying binder onto the surface course according to step i) and subsequently subjecting the binder present on the surface course to a concentrated air flow, achieves that both the liquid binder and the air are transported through an open surface course to a deeper layer, whilst the surface is blown clear. Furthermore, in this way the binder is prevented from dispersing into the environment, which is an actual danger indeed when the so-called "fog seal" technique is used.

[0031] In a special embodiment, it is preferable that step i) and step ii) are carried out using a vehicle construction that moves over the asphalt structure to be treated, wherein the period of time for the liquid binder, i.e. the time that passes between the moment when the aforesaid liquid binder is sprayed and the moment when the liquid binder thus sprayed onto the aforesaid surface course is subjected to the aforesaid concentrated air flow, is at most 5 seconds, in particular at most 3 seconds.

[0032] If a period of more than 5 seconds is used, the liquid binder cannot penetrate the layer to a sufficient extent, for example due to a change in viscosity, which is undesirable. A change in viscosity can occur due to curing of the bitumen emulsion or due to cooling of a hot binder.

[0033] It is further preferable that step ii) further comprises the use of an additional air flow, in which additional air flow a pressure lower than the concentrated air flow is used.

[0034] Such an additional air flow leads to an improved transport of the liquid binder through the surface course. The present inventor assumes that the impact of the concentrated air flow, which is directed at the surface course, will decrease as a result of the air flow "colliding" with the surface course and the liquid binder, so that the aforesaid additional air flow is desirable in particular for transporting the binder further into the surface course in order to attain the desired result. The liquid binder is to migrate through the surface course, which migration is in particular realised by the use of the concentrated air flow. The additional air flow as used in the present application in particular functions to break the emulsion, also called curing. The additional air flow is thus preferably a hot air flow, whereas, quite the opposite, the concentrated air flow is not.

[0035] In addition to that it is desirable from the viewpoint of an enhanced transport effect that an air flow volume higher than the air flow volume of the concentrated air flow be used in the aforesaid additional air flow.

[0036] The present method is further carried out in such a manner that the aforesaid additional air flow is preferably positioned in such a manner relative to the aforesaid concentrated air flow that the liquid binder sprayed in step i) is first brought into contact with the aforesaid concentrated air flow and then with the aforesaid additional air flow.

[0037] In order to obtain accelerated drying of the liquid agent, it is desirable in certain embodiments that the temperature of the aforesaid additional air flow be higher than the temperature of the aforesaid concentrated air flow. Said accelerated drying will in that case take place after the liquid agent has been transported to the desired location, viz at the bottom of the course, mainly by means of the concentrated air flow, so that it is fixed in the correct position and will not flow to the verge of the road under the influence of the cross-fall. By using a temperature which is slightly higher, the aforesaid adverse effect is mitigated, so that the binder can take up the desired position in the surface course. It is also assumed that when an emulsion is used for the liquid binder, the emulsion can break, resulting in seriously retarded mobility of the binder, which interferes with the transport of the binder through the surface course. In addition to that it is assumed that a higher temperature has an advantageous effect on the curing process of the binder. In certain embodiments it is desirable that the temperature of the concentrated air flow be low, i.e. ambient temperature. In such an embodiment, an ordinary compressor can be used for the concentrated air flow.

[0038] The amount of liquid binder to be sprayed onto the surface course in step i) preferably ranges between 0.5 - 5 kg/m², in particular 1 - 5 kg/m², more in particular 0.5 - 4 kg/m², preferably 1 - 3 kg/m², more preferably 2 - 3 kg/m².

[0039] Examples of the liquid binder include one or more compounds selected from the group of bitumen, bitumen emulsion, polyurethane (PUR) and epoxy resins.

[0040] According to the present method it is preferable that the aforesaid porous asphalt surface course is present on a lower layer, wherein the sealing layer of binder thus formed in the aforesaid surface course abuts the aforesaid lower layer.

[0041] It is in particular desirable that step i) be carried out in such a manner that breaking of the emulsion of the liquid binder during its transport through the aforesaid surface course is prevented. Undesirable breaking will lead to an increase of the viscosity, which interferes with the transport through the surface course. In addition, such undesirable breaking will result in an immobile product.

[0042] The present invention further relates to an asphalt structure, in particular an asphalt structure comprising a porous asphalt surface course, obtained by carrying out the above-described method, wherein a sealing layer of binder is present in the aforesaid surface course in a region near the bottom side of the surface course.

[0043] Preferably, a lower layer, in particular a dense underlayer of dense asphaltic concrete, is present beneath the aforesaid porous asphalt surface course, wherein in particular the aforesaid sealing layer of binder abuts the aforesaid lower layer.

[0044] In the asphalt structure obtained by means of the present method, hair cracks in the mastic of the porous asphalt surface course and adhesive bridges between the stones are corrected over the height of the course and the whole is strengthened. Said correction and strengthening is in particular desirable in the case of old open surface courses and is realised in that the liquid binder is transported through the surface course under the influence of the air flow directed at the asphalt structure. During the aforesaid transport of binder through the surface course, strengthening of the adhesive bridges between the stones occurs. In addition, any hair cracks in the mastic of the porous asphalt surface course can be sealed.

[0045] The invention further relates to a device for the treatment of an asphalt structure, in particular an asphalt structure which comprises a porous asphalt surface course, using an air flow directed at the aforesaid asphalt structure, wherein the aforesaid device is a vehicle construction that moves over the asphalt structure to be treated, comprising an element for spraying a liquid binder onto said surface course and an element for directing a concentrated air flow at said surface course so as to cause the aforesaid liquid binder to penetrate through the surface course for forming a sealing layer of binder in the aforesaid surface course in a region near the bottom side of the surface course.

[0046] It is further desirable that the device comprise an element for providing an additional air flow, in which element an air pressure is used which is lower than the air pressure in the aforesaid concentrated air flow element, wherein the additional air flow element is preferably positioned in a vehicle construction that moves over the asphalt structure to be treated, not being the vehicle construction that comprises the aforesaid element for spraying a liquid binder onto the aforesaid surface course and the aforesaid element for directing a concentrated air flow.

[0047] The aforesaid additional air flow element is preferably located downstream of the aforesaid concentrated air flow element.

[0048] In a special embodiment, the device further comprises means for increasing the temperature of the air used for the aforesaid additional air flow element and/or the aforesaid concentrated air flow element, in particular for increasing the temperature of the air used for the aforesaid additional air flow element.

[0049] The device furthermore in particular comprises means for increasing the temperature of the aforesaid liquid binder to be sprayed onto the surface course of the aforesaid asphalt structure.

[0050] In a preferred embodiment of the present invention, a so-called "air knife" is provided directly behind the spray beam used for spraying the liquid binder. Said air knife is a very concentrated air flow which, using little volume but a high pressure, scrapes the liquid binder off the stone grains at the surface and forces it down into the course. In this way the liquid binder is prevented from being swirled up and dispersed into the environment under the influence of the large amount of air.

[0051] In another embodiment, two types of air flow can be employed in succession. The first one is to be employed in the embodiment comprising the air knife and a second one, which employs a somewhat lower pressure and a higher volume, is employed for achieving an optimum transport effect deeper in the open course.

[0052] In another embodiment, air flows having a higher temperature can be used. Using a higher temperature in particular for the latter air flow achieves that the liquid binder, when used, will dry at an accelerated rate. After drying, such a binder is no longer liable to being washed out by rain.

[0053] In another embodiment, tyre rollers comprising rubber tyres are employed in addition to the air flow for forcing any residual binder off the stones at the surface of the road so as to prevent the road surface exhibiting insufficient skid resistance in relation to traffic safety after treatment.

[0054] In another embodiment, a granular chipping material is spread over the road surface after blowing so as to bind the last remnants of the binder to the road surface and also to prevent the aforesaid skid resistance problems.

[0055] The result of the present invention shows in the presence of a sealing layer at the bottom of the open surface course, between the lowermost stone grains of the porous asphalt layer in and around the points of contact of the lowermost stone grains with the underlying dense layer. At the same time, cavities, cracks and porous spots in the underlying dense layer are filled and sealed. Water and road salts can thus no longer penetrate into the underlying dense layer and the quality will remain at a sufficient level during the life of the open surface course.

[0056] The present inventor also assumes that cracks and microporosity in the binder layer or the layer of mortar around the stone grains in the open surface course are corrected over substantially the entire height of said open course. The adhesive bridges that bond the stones in the open surface course together are also strengthened as a result of this. This has a positive effect in particular on an old open surface course whose quality has decreased as a result of internal deterioration caused by moisture, frost, road salt and traffic influences.

[0057] The present invention will now be explained in more detail by means of a number of examples, which examples must be regarded as illustrative rather than limitative.

Figure 1 is a cross-sectional view of a renovated asphalt structure on a concrete fly-over;

Figure 2 is a cross-sectional view of a renovated asphalt structure of the two-layer porous asphalt type.

Example 1: Making an asphalt structure on a concrete flyover impermeable.

[0058] Within the framework of maintenance to be carried out, the asphalt structure of a number of flyovers must be renovated, with the upper layer of the asphalt structure to be renovated consisting of porous asphalt. The impermeability is realised by means of a dense structure in the lower asphalt layer, which is to be achieved by intensive road rolling during construction. The work comprises the removal of both old asphalt layers by milling, so that the concrete of the bridge road becomes exposed. Then an adhesive layer is applied as a bonding layer and the lower, dense asphalt layer is installed and compacted by road rolling. Immediately after that the porous asphalt layer is installed. Upon inspection afterward it was unfortunately found that the first, dense asphalt layer had been insufficiently compacted. Because impermeability has not been achieved, the road operator demands complete replacement of the asphalt structure. Although the upper asphalt layer (porous asphalt) does meet all the requirements, it must be removed as well in order to be able to replace the lower layer. This means a major destruction of capital and a great deal of extra traffic nuisance.

[0059] According to the method of the present invention, the aforesaid destruction of capital is prevented by subsequently, during the next night, applying an impermeable layer at the bottom side of the porous asphalt layer.

[0060] This is done by spraying an amount of 2.5 kg/m² of a bitumen emulsion onto the porous asphalt layer, viz a 3.5 m wide lane, immediately after which this liquid binder is blown to the bottom of the layer using a concentrated air flow. The bitumen emulsion is a water-emulsified straight-run bitumen having a penetration value between 45 and 100 Pen and a bitumen content in the emulsion of 30 to 70%. It is possible to control via the composition, in particular the coagulant, how rapidly and under what conditions the bitumen emulsion will break. It is thus preferable to choose a stable emulsion, viz an emulsion that will not break but will remain stable (and thus liquid) during said concentrated blowing. However, if use is made of the additional air flow, it is desirable in certain embodiments to use hot air.

[0061] The process conditions for the concentrated air flow are as follows: flow < 0.5 m³ per sec, temperature about 20 °C, pressure between 0.5 and 1.5 bar. The bitumen emulsion is then cured (breaking of the emulsion and egress/evaporation of the water) using a hot air flow under the following process conditions: flow between 5 and 10 m³ per sec, pressure between 0.05 and 1.5 bar, temperature 300 - 500 °C (but also 200 - 400 °C in a special embodiment), so that the emulsion will not be carried along by road roller water or by rain shortly after its application, causing it to drain to the side of the flyover. The speed at which the vehicle used for this purpose is moved over the road surface ranges between 3 and 8 km/h. The time that passes between the moment when spraying of the aforesaid liquid binder takes place and the moment when the liquid binder thus sprayed onto the aforesaid surface course is subjected to the aforesaid concentrated air flow ranges between 0.6 and 1 second.

[0062] Upon examination of a cylinder drilled from the total asphalt structure it was found that the insufficient density of the underlying layer was compensated by an impermeable layer on top of said underlayer. The aforesaid cylinder was subjected to water pressure and its permeability tested in a laboratory test arrangement. It was found that the asphalt structure met the permeability standard yet, which had been achieved by injecting and blowing in the impermeable layer in accordance with the present invention.

[0063] In figure 1 the renovated asphalt structure, which is schematically indicated at 1, comprises stones 2 between which cavities or pores 3 are present, with a sealing layer 4 of binder in the region near the bottom side of the surface course. The surface course is present on top of a dense asphalt layer 8, for example dense asphaltic concrete or crushed stone asphaltic concrete. The impermeable layer 4 of the injected binder is present at the bottom, between the stones of the porous asphalt on the dense underlayer 8.

[0064] In the embodiment of example 1 (on a bridge deck) the concrete of the bridge deck lies beneath the dense asphalt layer (which has approximately the same thickness as the porous asphalt layer).

Example 2: Making impermeable an underlayer beneath two-layer porous asphalt to be renovated.

[0065] Because of the increasing noise nuisance by road traffic, use is increasingly made of a sound-absorbing surface course of two-layer porous asphalt. The upper layers of such an asphalt structure in that case consist of two layers of porous asphalt on top of each other: a coarse-grained porous asphalt lower layer for sound absorption and water drainage and a fine-grained very open surface course for reducing tyre noise. Disposed under said two-layer porous asphalt is a dense asphalt layer as the substrate layer, in particular for transporting rainwater to the verge of the road via cross-fall (transversal slope), which underlayer is also impermeable.

[0066] According to a usual existing method, the thin, fine-grained 25 mm thick porous asphalt surface course is removed by milling. In this way the underlying coarse porous asphalt layer is exposed. Present under said porous asphalt lower layer is the dense underlayer. Core drilling has shown that the underlying dense asphalt layer is no longer in optimum condition. In order to be sure that no frost damage problems will arise in the underlying, water-draining dense layer during the second stage of life (the life of the new fine porous asphalt surface course, being about 10 years), the entire coarse porous asphalt lower layer must be removed, after which a new impermeable layer can be applied. Then a new porous asphalt lower layer and a new porous asphalt surface course must be installed. This means a major destruction of capital and a great deal of extra traffic nuisance.

[0067] According to the method of the present invention, the aforesaid destruction of capital is prevented by spraying a liquid binder through the exposed coarse porous asphalt lower layer, so that an impermeable layer is formed at the bottom side of said coarse porous asphalt layer.

[0068] In this embodiment, an amount of 2.0 kg/m² of bitumen emulsion is sprayed onto the layer, viz a 3.5 m wide lane, immediately after which the liquid binder is blown to the bottom of the layer using a concentrated air flow. The bitumen emulsion is then cured (breaking of the emulsion and egress/evaporation of the water) using a hot air flow, so that the emulsion will not be carried along by road roller water or by rain shortly after its application, causing it to drain to the side of the flyover. The type of bitumen emulsion as well as the process conditions correspond to those described in example 1. It has been found that residual bitumen emulsion within the coarse porous asphalt layer provides an additional positive effect on the life of said layer in that the old adhesive bridges between the stones in said layer are enveloped in new bitumen and thus strengthened. After these rapidly carried out operations according to the present method, the new fine-grained porous asphalt surface course is installed.

[0069] It has been found that rainwater that penetrates through the two porous asphalt layers will no longer flow over the underlying aged asphalt layer to the verge of the road, but over the newly applied impermeable layer. In this way the asphalt structure can remain intact without any problems during its second stage of life.

[0070] In figure 2 the renovated asphalt structure, which is schematically indicated at 7, comprises a fine-grained, very open surface course of stones 5 and an underlying coarse-grained porous asphalt layer of stones 6, both of which layers contain cavities or pores 3, with a sealing layer 4 of binder in the region near the bottom side of the aforesaid layer. The surface course lies on top of a dense asphalt layer 8, for example dense asphaltic concrete or crushed stone asphaltic concrete. The impermeable layer 4 of the injected binder lies at the bottom, between the stones of the porous asphalt on the dense underlayer 8.

Claims

1. A method for the treatment with a liquid agent of an asphalt structure, in particular an asphalt structure which comprises a porous asphalt surface course, using an air flow directed at the aforesaid asphalt structure, characterised in that said treatment comprises the following steps:

i) spraying a liquid binder onto the surface course of the aforesaid asphalt structure;

ii) directing a concentrated air flow at the liquid binder sprayed onto the aforesaid surface course in step i), wherein step ii) is carried out in such a manner that the spraying according to step i) and the directing of the air flow according to step ii) are carried out as separate steps, so that the aforesaid liquid binder will penetrate through the surface course, forming a sealing layer of binder in the aforesaid surface course in a region near the bottom side of the surface course.

2. A method according to claim 1, characterised in that step i) and step ii) are carried out using a vehicle construction that moves over the asphalt structure to be treated, wherein the period of time for the liquid binder, i.e. the time that passes between the moment when the aforesaid liquid binder is sprayed and the moment when the liquid binder thus sprayed onto the aforesaid surface course is subjected to the aforesaid concentrated air flow, is at most 5 seconds, in particular at most 3 seconds.

3. A method according to one or both of claims 1-2, characterised in that step ii) further comprises the use of an additional air flow, in which additional air flow a pressure is used which is lower than the pressure of the concentrated air flow.

4. A method according to claim 3, characterised in that an air flow volume higher than the air flow volume of the concentrated air flow is used in the aforesaid additional air flow.

5. A method according to one or both of claims 3-4, characterised in that the aforesaid additional air flow is positioned in such a manner relative to the aforesaid concentrated air flow that the liquid binder sprayed in step i) is first brought into contact with the aforesaid concentrated air flow and then with the aforesaid additional air flow.

6. A method according to one or more of claims 3-5, characterised in that the temperature of the aforesaid additional air flow is higher than the temperature of the aforesaid concentrated air flow, in particular that the temperature of the aforesaid concentrated air flow is low, for example ambient temperature.

7. A method according to any one or more of the preceding claims, characterised in that the amount of bitumen emulsion to be sprayed onto the surface course in step i) ranges between 1 - 5 kg/m², preferably between 2 - 3 kg/m².

8. A method according to any one or more of the preceding claims, characterised in that the liquid binder is selected from the group of bitumen, bitumen emulsion, polyurethane (PUR) and epoxy resins, or one or more combinations thereof.

9. A method according to any one or more of the preceding claims, characterised in that the aforesaid porous asphalt surface course is present on a lower layer, wherein the sealing layer of binder thus formed in the aforesaid surface course abuts the aforesaid lower layer.

10. A method according to any one or more of the preceding claims, characterised in that step i) is carried out in such a manner that breaking of the emulsion of the liquid binder during its transport through the aforesaid surface course is prevented.

11. An asphalt structure, in particular an asphalt structure comprising a porous asphalt surface course, obtained by carrying out the method according to one or more of the preceding claims, characterised in that a sealing layer of binder is present in the aforesaid surface course in a region near the bottom side of the surface course.

12. An asphalt structure according to claim 11, characterised in that a lower layer, in particular a dense underlayer of dense asphaltic concrete, is present beneath the aforesaid porous asphalt surface course, wherein in particular the aforesaid sealing layer of binder abuts the aforesaid lower layer.

13. An asphalt structure according to one or more of claims 11-12, characterised in that hair cracks in the mastic of the porous asphalt surface course and adhesive bridges between the stones are corrected over the height of the course and the whole is strengthened.

14. A device for the treatment of an asphalt structure, in particular an asphalt structure which comprises a porous asphalt surface course, using an air flow directed at the aforesaid asphalt structure, characterised in that the aforesaid device is a vehicle construction that moves over the asphalt structure to be treated, comprising an element for spraying a liquid binder onto said surface course and an element for directing a concentrated air flow at said surface course so as to cause the aforesaid liquid binder to penetrate through the surface course for forming a sealing layer of binder in the aforesaid surface course in a region near the bottom side of the surface course.

15. A device according to claim 14, characterised in that the device further comprises an element for providing an additional air flow, in which element an air pressure is used which is lower than the air pressure in the aforesaid concentrated air flow element, wherein the additional air flow element is preferably positioned in a vehicle construction that moves over the asphalt structure to be treated, not being the vehicle construction that comprises the aforesaid element for spraying a liquid binder onto the aforesaid surface course and the aforesaid element for directing a concentrated air flow.

16. A device according to one or both of claims 14-15, characterised in that the aforesaid additional air flow element is located downstream of the aforesaid concentrated air flow element.

17. A device according to one or more of claims 14-16, characterised in that the device further comprises means for increasing the temperature of the air used for the aforesaid additional air flow element and/or the aforesaid concentrated air flow element, in particular for increasing the temperature of the air used for the aforesaid additional air flow element.

18. A device according to one or more of claims 14-17, characterised in that the device further comprises means for increasing the temperature of the aforesaid liquid binder to be sprayed onto the surface course of the aforesaid asphalt structure.

19. A device according to one or more of claims 14-18, characterised in that the aforesaid element for directing a concentrated air flow is an air knife.

Drawing