Patent Application
20100266338
This application claims priority to Belgian Patent Application No. 2009/0179, filed Mar. 20, 2009, which is hereby incorporated by reference in its entirety.
The present invention relates to a device and method for levelling or evening out an open asphalt structure. Such asphalt structures are arranged at hydraulic engineering works, for instance for the purpose of constructing embankment bodies or dikes, embankment or dike protection works and when arranging erosion protection and the like.
Laying asphalt strips is generally performed in two phases. In a first phase an asphalt spreader will spread evenly and smooth the asphalt over a determined width, after which in a second phase a further compacting will take place through the action of rollers. Multiple layers can be laid one over the other depending on the desired final layer thickness.
Devices for spreading, levelling and compacting asphalt are known. Such asphalt spreaders always comprise a number of invariable components. The hot or cold asphalt is generally provided in an asphalt storage unit which has a determined capacity and must be refilled from time to time. Another option consists of the asphalt spreader not being provided with an asphalt storage unit, but in the asphalt being poured via cranes, trucks and the like in front of the asphalt spreader. The asphalt is fed to an asphalt spreading unit, and in the case a storage unit is present the asphalt will generally be supplied via conveyor belts. The spreading unit will distribute the supplied asphalt uniformly over a determined width. Such a spreading unit generally consists of a pair of screws or jacks mounted in opposing orientation transversely of the direction of forward movement of the asphalt spreader, as described in American patent U.S. Pat. No. 3,874,807. Spreading of the asphalt is brought about by the rotation movement of such screws.
Before being fed to the screw, the asphalt can optionally be loosened in order to minimize aggregate-forming and local compacting, as described in EP 0 693 591. Once the asphalt has been distributed over the ground surface, a screed or smoother will smooth the asphalt. This screed is mounted at a well defined height above the ground surface transversely of the direction of forward movement of the asphalt spreader, and so parallel to the distributing screws. The operation of the screed consists on the one hand of laying the asphalt at a desired thickness and on the other of removing unevenness. The screed is generally heated in order to prevent the adhesion of asphalt, and can be equipped with means which provide for vibration. The combination of smoothing and vibration already provides for a certain measure of compaction. In a first aspect the invention provides a method and a device for making objective and optimizing open asphalt operations, more particularly applied to hydraulic engineering operations.
Asphalt is a mixture of mineral components with a bituminous binder. The mineral components are further subdivided into a stone fraction, a sand fraction and a filler fraction. There are different types of asphalt mixture which differ from each other in composition and the raw materials and additives used. In general the type of asphalt is determined by the ratio of the asphalt mastic, the mixture consisting of the bituminous binder, the filler fraction and optionally the sand fraction, and the stone fraction, in addition to the precise composition of the asphalt mastic and the particle size of the stone fraction. There are therefore overfilled, filled and underfilled mixes. In an overfilled mix so much mastic is present that there is no longer a mineral skeleton. The sand and stone as it were floats in the filler material. The mastic must in this case have sufficient load-bearing capacity. In the case of a filled mixture the coarse mineral aggregate does now form a skeleton, wherein the hollow space in the skeleton is largely filled with mastic. The pores in this type of asphalt are not in open connection with each other. An advantage of filled pores is that the coarser constituents of the mix adhere better to each other, thereby increasing lifespan. In an underfilled mixture the hollow space in the mineral skeleton is not fully filled, whereby the pores are connected to each other. The most important advantage hereof is the improved water permeability. Such an asphalt mixture is also referred to as an open asphalt mixture. An example of underfilled asphalt is very open asphalt concrete, or ZOAB. This type of asphalt is characterized by a high percentage of hollow spaces or pores.
Use is made in hydraulic engineering and other works of an open asphalt structure. Use is often made of open stone asphalt. This forms an erosion-resistant covering with a high percentage of hollow space. The asphalt hereby becomes water-permeable, thereby preventing the buildup of water overpressures. Such an open structure moreover allows the growth of vegetation thereon.
In such a hydraulic engineering works an open asphalt structure is provided on dikes, embankments or as ground covering wherein mutually adjoining strips of asphalt material are provided. Such asphalt strips are assembled by first providing the ground surface with a ground filter layer. A first option herefor consists of covering the ground surface with geotextile mats. These mats are placed parallel to each other and with a certain overlap, and the asphalt material is provided thereon. Alternatively, prefabricated asphalt mats can be used which are laid adjacently of each other, for instance as underwater ground protection. A second option consists of providing the ground surface with a layer of sand asphalt consisting of 4-8% bitumen and 96-92% sand fraction on which the asphalt material is provided. Such ground filter layers have the purpose of stabilizing the ground surface relative to the asphalt material arranged thereon.
Such asphalt strips have been arranged in the past by means of generally known crane operations, and these strips have then been levelled by pressing and scraping with the blade of the crane on the arranged asphalt in order to thus obtain the required material thickness and material density. The obtained material thickness and the density was rather arbitrary and depended to a great extent on the experience of the crane driver. The required porosity was moreover also a problem since pressing with the crane shovel cannot always be performed with an appropriate downward force. Later quality control tests upon completion of the works by the client or the contractor, in particular measurements of minimal thickness and density, have usually resulted in a wide and undesirable variation.
Hydraulic engineering works are understood in the present invention to mean all hydraulic engineering-related works, more particularly dike or embankment (protection) works as well as erosion protection works adjoining waterways.
Open asphalt structures are understood to mean a material composed of mineral aggregates and asphalt mastic with a high percentage of hollow spaces, preferably from 10 to 30%. This porosity is achieved in that the mixture comprises a relatively large amount of coarse granulate, for instance stone chippings, and relatively few finer constituents.
In a preferred embodiment of the present invention GOSA® (trade name of the present invention) is applied as open asphalt material. This fibrous open stone asphalt (GOSA®) is particularly suitable for water works. Such works require that the total pore volume, i.e. the porosity of the material defined in hollow space, comprises at least 10 to 30% of hollow space. The thickness with which such a layer is arranged is generally 12 to 30 cm, depending on the hydraulic load. GOSA® meet these requirements since it is characterized by a porosity of 25%. For this purpose GOSA® is composed of about 80% limestone chippings and about 20% fibrous mastic. The fibrous mastic itself consists of about 60% sand of a specific size, 20% very fine limestone powder as filler, about 20% bitumen and about 0.40% inert fibres. Industrial cellulose fibres are used as inert fibres. Addition of such fibres to the mastic allows use of more bitumen, whereby adhesion, flow resistance, flexibility and other properties are improved without the internal stability of the mixture being endangered. GOSA® generally has the property of being stable on steep slopes and resistant to high wave action and current, and so has a high resistance to erosion. As already discussed above, GOSA® is moreover draining and plants can grow thereon.
A very important characteristic of an open asphalt structure in general, and an open asphalt structure for water works in particular is the high porosity. In order to obtain such high porosity the compacting of the asphalt material must take place very carefully. Ideally, a level asphalt structure is obtained with minimum compaction. The conventional asphalt spreaders do not however fulfil this requirement sufficiently as they are often very heavy, since in addition to spreading the asphalt they must also provide for a first compaction of the asphalt. Uniform spreading of the asphalt on the basis of a screw or jack necessitates the use of a screed for levelling purposes, resulting in an excessive compaction.
The invention provides for this purpose a device and a method, wherein the device is suitable for levelling an open asphalt structure for water works and wherein the device comprises a frame on which a drive unit is provided for driving the device; a substantially smooth propelling roller suspended from the frame at the rear relative to the direction of movement of the device; and one or two rotatable levelling shafts provided with blades at the front relative to the direction of movement of the device, wherein the height of the shafts can be adjusted independently of each other by means of a height adjuster at each outer end of the respective levelling shaft. Further provided on either side of the levelling shaft(s) are asymmetrical support elements which are likewise individually height-adjustable by means of height adjusters. The first support element is a static sliding element which is provided on already asphalted surface and comprises a sled or ski construction, with a large contact surface for an efficient distribution of the weight. The second support element is a dynamic rotating element which is provided on non-asphalted surface, and comprises a wheel or roller construction with a more limited surface, or alternatively comprises caterpillar tracks, or a combination of both. The two support elements can be disassembled and their position interchanged. With asymmetrical support elements are meant mutually different support elements positioned on either side of the levelling shaft(s).
The known asphalt spreaders in contrast are generally propelled by means of providing on both sides symmetrical (i.e. the same) propelling elements or support elements such as caterpillar tracks, or wheels if a higher propelling speed is desired. Propelling on rails is also a possibility. Height-adjustable support elements are not found in the known asphalt spreaders.
A preferred embodiment of the invention is elucidated with reference to the following figures:
a and 7b show a side view by way of elucidation of the drive for an embodiment with respectively one or two levelling elements.
Asphalt levelling device (1) for levelling an open asphalt structure comprises a frame (2) which functions as suspension for one or two levelling elements (3-3′) provided on either side with asymmetrical support elements (4, 5) and a propelling element (6). A drive unit (7) supplies the power to propelling element (6) and levelling element(s) (3-3′).
Propelling element (6) and levelling element(s) (3-3′) are mounted on frame (2) substantially transversely of the direction of movement of device (1), wherein relative to the direction of movement of device (1) the levelling element(s) (3-3′) are located at the front and the propelling element is located at the rear.
Frame (2) is preferably manufactured from metal, steel, an alloy or other durable material.
Propelling element (6) consists substantially of a rotatable smooth roller (8) preferably manufactured from metal, steel, an alloy or other durable material, which comprises a central shaft (9) which is bearing mounted on either side on frame (2). The use of a smooth roller (8) as propelling element over the full width of device (1) has the advantage of a maximum distribution of the pressure generated by the weight of device (1), with a view to causing a minimal compacting of the asphalt.
Each levelling element (3-3′) comprises a levelling shaft (10-10′) which via a central shaft (11-11′) is bearing mounted on either side on frame (2) via height adjusters (12) which are individually adjustable. The length of levelling shaft (10-10′) is preferably the same as the length of the rotatable smooth roller (8). Levelling shaft (10-10′) is provided with levelling blades or paddles (13-13′-13″) which are preferably fixed radially to levelling shaft (10). The number of levelling blades (13-13′) is preferably 5 to 15 per metre or 20 to 60 overall per levelling element (3-3′), and the blades are preferably mounted in pairs, parallel to each other, perpendicularly of the tangent plane of levelling shaft (10-10′). The mounting of levelling blades (13-13′) on levelling shaft (10-10′) is in a helical pattern, preferably in a double helix pattern made up of two alternating helices lying perpendicularly of each other, and wherein within each helix the successive pairs of levelling blades (13-13′) form an angle of 30 to 50 degrees to each other. The outer pairs of levelling blades (13″) lying closest to the respective outer ends of levelling element (3-3′) are preferably fixed at an angle to the levelling shaft such that they prevent spillage of the asphalt. The angle made by these blades (13″) relative to the lengthwise direction of levelling shaft (10-10′) provides for a funnel effect, so that the asphalt being spread by levelling element (3-3′) does not spread further than the length of the levelling element. Alternatively or additionally, side plates (14) can be provided on both outer ends of levelling element (3-3′). These are vertical plates or partitions which likewise prevent the asphalt material extending over a width greater than the length of the levelling element during spreading and levelling.
Likewise provided are nozzles (15) which are preferably mounted on frame (2) and distributed at regular intervals along the whole length of levelling element (3-3′). These nozzles (15) have the purpose of atomizing a liquid, preferably water, at a low flow rate over the whole length of levelling shaft (10-10′) and levelling blades (13-13′-13″). Nozzles (15) connect via conduits to a liquid reservoir. The purpose of atomizing a liquid over levelling element (3-3′) is to prevent the forming of residue on levelling blades (13-13′-13″). In other words, moistening the blades will prevent the asphalt remaining adhered to the blades.
The two asymmetrical support elements (4, 5) on either side of levelling element (3-3) are on the one side a static sled or ski construction (4) and on the other a dynamic wheel or roller construction (5), or alternatively a caterpillar track construction or a combination of both. The sled or ski construction (4) comprises a height-adjustable sled, ski or other sliding member (16) which is mounted on frame (2) by means of a pivot (17) which allows sled (16) to tilt freely relative to the direction of movement of device (1). The surface area of sled (16) is such that the pressure transmitted thereto by the weight of device (1) is distributed maximally. The wheel or roller construction (5) comprises a freely rotating wheel or roller (18) which is mounted on frame (2) by means of a central shaft (19) mounted in a suspension (20) which is provided with a height adjuster (21). Alternatively, a caterpillar track construction can be mounted in similar manner on frame (2). Both the sled or ski construction (4) and the wheel or roller construction (5) or the caterpillar track construction are height-adjustable independently of each other. The position of the two described support elements (4, 5) can be interchanged and each can therefore be provided at either outer end of levelling element (3-3′).
Drive unit (7) supplies the power to propelling element (6) and levelling element(s) (3-3′). Drive unit (7) is preferably, but not limited to, a diesel engine or an electric motor. The transmission (22) to propelling element (6) is provided via a drive chain wheel (23) which is driven by drive unit (7) and connected via a drive chain (24) to a chain wheel (25) mounted on central shaft (9) of propelling element (6). The transmission (26-26′) to levelling element (3-3′) is similarly provided via a drive chain wheel (27-27′) which is driven by drive unit (7) and connected via a drive chain (28-28′) to a chain wheel (29-29′) mounted on central shaft (11-11′) of levelling element (3-3′). The rotation speed of propelling element (6) and levelling element (3-3′) are both individually and variably adjustable. The rotation direction of the two is opposed to each other, so that each levelling element (3-3′) rotates in opposite direction relative to the direction of movement of device (1). If two levelling elements (3-3′) are present, these are likewise driven independently of each other so that, if necessary, a different rotation speed of the two levelling elements can be obtained.
The present invention likewise describes a method for levelling an open asphalt structure on the basis of an asphalt levelling device such as the above described preferred embodiment of such a device (1). Asphalt strips are laid over a determined length on geotextile mats, wherein the material is supplied by means of cranes and the like. Adjacent and overlapping geotextile mats form the basis for adjoining strips of asphalt. Alternatively, asphalt strips can be laid on a pre-provided layer of sand asphalt consisting of 4-8% bitumen and 96-92% sand fraction.
The levelling of the asphalt material substantially takes place in the first instance in that levelling element (3-3′), provided with levelling blades (13-13′-13″), rotates in a direction opposite to the direction of movement, whereby the arranged asphalt material (30) is pushed into a determined layer thickness by the action of levelling blades (13-13′-13″). The helical pattern of levelling blades (13-13′-13″) brings about an efficient spreading of the asphalt material, while the levelling blades themselves provide for the levelling. If a second levelling element (3′) is present, it will complete this action of first levelling element (3). First levelling element (3), at the front relative to the direction of movement, provides for a rough spreading and levelling of the arranged asphalt material, and second levelling element (3′), behind the first levelling element relative to the direction of movement, provides for a further levelling and finishing of the asphalt material. As already stated above, the manner in which the outer levelling blades (13″) are mounted on levelling shaft (10-10′), as well as the side plates (14) on either side of the levelling shaft(s), ensures that no spillage of the asphalt material occurs and the asphalt material is not spread wider than the length of levelling element (3-3′).
Of crucial importance is the adjustment of the height of levelling element(s) (3-3′), which will determine the effective layer thickness. As stated, this asphalt material is laid in strips which are then levelled to the required thickness, this with a specific pressing force which defines the final percentage of hollow space. The height of each levelling element (3-3′) is determined in the first instance by means of two height adjusters (12), each provided at an end of the shaft. The desired layer thickness can thus be adjusted when a first strip is arranged. Once the material has been spread and levelled by the action of levelling element(s) (3-3′), the method is completed by the smooth roller (8) which can smooth out possible unevenness. The device provides for both spreading and levelling of the asphalt in one movement, this with minimal compaction due to the efficient distribution of the weight over the whole length of propelling roller (8). Each strip of asphalt is moreover driven over only once, thereby also minimizing the compaction.
In a second phase the already levelled asphalt strip (30) is widened by levelling of an adjacent new asphalt strip (31). The operation of the two asymmetrical support elements (4, 5) is important for this purpose. Sled construction (4) at the one outer end of levelling element (3-3′) is placed on the already levelled asphalt strip (30) and wheel construction (5) or the caterpillar track construction at the other outer end of levelling element (3-3′) is provided on a surface (32) still to be levelled. It is important that sled construction (4) no longer affects the thickness and the amount of hollow space in the already finished asphalt strip (30), this by providing a sled or ski (14) whereby the pressure force of this support elements is distributed over a considerable surface. The layer thickness of the asphalt will in this case be ensured by setting the height of wheel construction (5) and the levelling element(s) relative to the sled construction. The layer thickness is generally determined by the setting of the different height adjusters (21, 12). If desired, a variable layer thickness can be obtained by an asymmetrical setting of height adjusters (21, 12).
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009/0179 | Mar 2009 | BE | national |
