The present invention relates to a method of reinforcing coatings of a material having plastic deformation properties, such as asphalt coatings, in which a reinforcement net comprised of mutually joined rods or like elements made of steel, plastic or some other rigid material, are laid side- by-side, with or without overlapping parts, and embedded in the coating material. The invention also relates to a reinforcement net for use when reinforcing such coatings.

In this description and in the following Claims, the word coating is used both alone and in compounds for the coating including possible underlying base course of a material having plastic properties, while the word asphalt is used both alone and in compounds for the mixture of bitumen and ballast or aggregate material, such as stone aggregates, normally used in the building of roads, airports, parking areas, stock yards and like structures. Coatings of this kind are subjected to dynamic and/or static loads and may also be subjected to deformations, among other things as a result of becoming frozen, ground subsidence, movements that occur in constructions in contact with the coating, and movements due to temperature variations.

These loads and movements can result in crack formations in the asphalt coating or surfacing layer. The tendency for cracks to form increases with falling temperatures, as the colder the asphalt the harder it becomes. As with concrete, crack formations can be prevented or reduced with the aid of reinforcement steel, for instance.

An asphalt reinforcement, however, does not function in the same way as a concrete reinforcement. For instance, among other things steel nets and other rigid net reinforcements

cannot be spliced or joined together in the same way as concrete reinforcement steels. The functional difference between reinforced concrete and reinforced asphalt is that concrete is not plastic whereas asphalt is plastic, even at low temperatures.

Naturally, what is said below with regard to asphalt also applies to other materials having plastic deformation properties.

Since concrete is not plastic, the tensile forces in the splices between concrete reinforcement nets can be taken up by adhesion between concrete and steel. When concrete is subjected to tensile forces, these forces are initially taken up by the concrete and then solely by the reinforcement when cracks occur, said reinforcement therewith determining the load that the concrete can withstand.

In reinforced asphalt, on the other hand, in addition to being taken up by the asphalt itself, tensile forces are primarily taken up by those reinforcement rods in a net reinforcement which extend perpendicularly to the direction of the tensile load and are transmitted from these rods through the welds in the net to those rods that extend in the direction of the tensile force.

Because the reinforcement nets are embedded in a plastic material, the transmission of forces at the edges of the net is low, since the nets are able to move in the material. Consequently, it is possible for cracks to form along the edges of the reinforcement nets and between the nets. However, because of the plastic properties of the asphalt, these cracks are smaller than they would have been if the asphalt were not plastic.

The main object of the present invention is to provide a technique which will completely eliminate or greatly reduce

the tendency of crack formation at net edges in a reinforced asphalt coating or a coating or surfacing of some other plastic material, when the structure is subjected to internal or external forces. This also includes crack formation in net splices, which in this context are to be considered as two juxtaposed, contiguous or coincidental net-edge cracks.

This object is achieved in accordance with the invention by means of a method of the kind defined in the first paragraph which is characterized by placing a net-edge net along at least one edge of a reinforcement net, either above or beneath this net, and embedding the net-edge net in the coating material together with the reinforcement net.

A thus positioned net-edge net will prevent effectively or greatly reduce crack formations in the net edges and along splicing zones between juxtaposed nets.

In this description and in the following Claims, the term reinforcement net is used to identify the main reinforcement in a coating structure, whereas the term net-edge net is merely intended to identify those reinforcing nets that are placed above or beneath the edges of nets and the splicing zones in the main reinforcement. The net splices may be open or have the form of overlapping parts. By net intersection as used in this document is meant an area in which more than two nets are mutually juxtaposed or overlap one another.

When the invention is applied to a crowned road surface or the like, it is preferred that the crown of the road is planed down and the net-edge nets are then placed on the resultant flat surface. The road surface can be flattened out with the aid of a milling machine or in conjunction with laying the surfacing material.

When applying the invention on flat surfaces, it may also be beneficial to mill or likewise cut along the net edges and

splicing zones, preferably with the aid of a miller which cuts box-like recesses, and place the net-edge nets in the cavities or recesses thus produced. This reduces the amount of fresh asphalt that would otherwise be required, since a thick layer is then required only over the net-edge nets.

The reinforcement nets are suitably placed so that their edges will overlap, such that outwardly projecting rods of one net will extend between the rods of an adjacent net, so as to obtain a so-called finger joint between the nets.

With the intention of limiting the number of reinforcing rods in the intersection points between mutually adjacent rein¬ forcement nets, it is preferred that the nets are laid out so that at most three nets will meet at one and the same intersection.

This can be achieved by placing the reinforcement nets so that those net splices that extend generally parallel with the direction of the crack formations that the nets are primarily intended to counteract will be mutually displaced generally perpendicular to this crack formation direction. This further reduces the danger of a longitudinally extending crack.

The main characteristic features of a device for use when practicing the inventive method are set forth in the follow¬ ing apparatus Claims.

The invention will now be described in more detail with reference to exemplifying embodiments thereof and also with reference to the accompanying drawings.

Fig. 1 illustrates schematically the occurrence of a net splice crack in connection with a conventional asphalt coating reinforcement.

Fig. 2 illustrates the occurrence of net-edge cracks in connection with conventional asphalt coating reinforcement.

Fig. 3 illustrates how a net splice crack shown in Fig. 1 can be stopped by means of a net-edge net in accordance with the invention.

Fig. 4 shows how net-edge cracks shown in Fig. 2 can be stopped with the aid of two net-edge nets in accordance with the invention.

Figs. 5 and 6 illustrate two embodiments of a road surface reinforced in accordance with the invention.

Fig. 7 illustrates the point of intersection of four overlap¬ ping reinforcement nets.

Fig. 8 illustrates a modified reinforcement net.

Fig. 9 illustrates the intersection of four overlapping reinforcement nets of the kind shown in Fig. 8.

Fig. 10 illustrates an intersection point between reinforce¬ ment nets that are mutually ^" displaced relative to one another.

Fig. 11 illustrates positioning of a plurality of reinforce¬ ment nets with the intention of effectively preventing the occurrence of an elongated crack.

Fig. 1 illustrates an asphalt road surface 1 in which there is embedded reinforcement nets 2 which each consist in steel reinforcing rods which are welded together to form a net having generally rectangular meshes.

In the illustrated example, the road surface 1 is subjected to a vertical force generated by the wheel 3 of an automotive

vehicle. As shown in the Figure, this force has resulted in the formation of a net splice crack 4 in the asphalt coating 1 between the two reinforcement nets 2. In the illustrated example, the nets are shown spaced apart, although a corre- sponding crack would also be liable to occur in the case of overlapping nets, because the nets are able to move in the plastic asphalt material 1 in the direction of the tensile force.

Fig. 2 illustrates an asphalt road surface or coating 1 in which a conventional reinforcement net 5 is embedded. In this case, the crack 6 caused by the wheel 3 is taken up effec¬ tively by the reinforcement net. However, the load gives rise to net-edge cracks 7 along the edges of the reinforcement net, these cracks propagating up to the road surface.

Fig. 3 illustrates how the crack 4 shown in Fig. 1 can be arrested and prevented from reaching the road surface 1. This is achieved by placing a net-edge net 8 along the splicing zone between the two reinforcement nets 2, in accordance with the present invention. The net-edge net 8 extends slightly in on the two reinforcement nets 2 and can be placed beneath these nets, as shown and preferred, or on top of the nets. The net-edge net therewith stops the crack 4 from spreading. Any edge cracks 9 that form along the edges of the net-edge net 8 are, in turn, stopped by the main reinforcement nets 2.

Fig. 4 illustrates the use of a large main reinforcement net 5 for preventing the further development of a crack 6 that forms beneath the net, as shown in Fig. 2. In this case, net- edge cracks 12 form along the edges of the net 5. To prevent these cracks from further development to the road surface 1, a net-edge net 10 is placed along both edges of the main net 5 with a certain overlap. These net-edge nets 10 therewith effectively arrest propagation of the edge cracks 12.

Figs. 5 and 6 illustrate how the technique shown in Fig. 3 can be used to reinforce the surface of crowned roads or the like. In order to reduce the amount of asphalt required and also to avoid bending the net plastically or elastically, the old asphalt coating 11 is milled down to obtain a flat surface which extends along the crown or the surface crown.. The nets 2 placed in the two halves or lanes of the road surface are arranged to meet above the flat surface on which a net-edge net 8 is placed. The nets 2 and 8 are then embedded in a fresh asphalt coating 13. The nets are not lashed together in this embodiment.

In the case of the Fig. 5 embodiment, the crown has been milled away to form a box-like cavity. This technique can also be applied when reinforcing flat surfaces, with the intention of reducing the amount of fresh asphalt required. Conventional flat milling has been applied in the Figure 6 embodiment. The configuration illustrated in Fig. 6 can be achieved readily when planing out freshly-laid asphalt. The invention can thus be applied when laying new asphalt and when re-asphalting an old surface. In both instances, the reinforcements illustrated in Figs. 5 and 6 function to eliminate or to greatly reduce the tendency for cracks to form along the centre line of the road surface.

Although not shown, net-edge nets are also used conveniently along the transverse splices between mutually adjacent reinforcement nets 2 and along the other longitudinal edges of the nets 2.

In order to further reduce the tendency towards crack formation in an asphalt coating, the main reinforcement nets 2 are placed so as to overlap one another at the splices or joins. To this end, the reinforcing rods of each reinforce- ment net 2 will preferably project freely over a relatively long _. distance, e.g. through a distance corresponding to the extension of two to five meshes in the net, along two net

edges, preferably two mutually adjacent edges. The rods may project out through a short distance along the remaining two edges of the net or may terminate at the point at which they are connected to the outer transverse rod.

Fig. 7 illustrates the overlapping of four nets constructed in this way, having rod sections 15 which project outwardly from two edges over a relatively long distance, and rod sections 16 which project from the remaining two edges over a relatively short distance. In this case, the outwardly projecting rod sections 15 extend in between those rods of a respective adjacent reinforcement net that extend parallel with said rod sections, so as to obtain an effective, overlapping splice, a so-called finger splice, between adjacent nets. Such an overlap splice, which does not increase the thickness of the net structure, will further reduce the tendencies towards crack formation in the asphalt coating.

However, the reinforcing rods located in the circle 17 illustrating the common intersection point of the four nets are so densely packed that 1) there is a risk that asphalt will be unable to penetrate between the rod interstices and effectively embed all rods; 2) it is not possible to obtain effective adhesion between new asphalt and underlying old asphalt; and 3) that the surface cannot be compacted effec¬ tively.

Fig. 8 illustrates a solution to this problem, wherein those rod sections which project relatively far out along one side of the net are shortened at one corner of the net, as illustrated at 18. The point at which the four nets intersect will not then contain more reinforcement rods than the remainder of the overlapping parts. This is illustrated in Fig. 9, which corresponds to Fig. 7 in other respects.

Fig. 10 illustrates another method of avoiding too many

reinforcing rods at an intersection point. In this case, the nets have been displaced so that at most three nets will meet at each intersection point, wherewith the number of rods in the intersection points will be the same as the number of rods in the remaining overlap regions, see the area within the circle 17.

This can be achieved, for instance, by placing the nets 2 in the manner shown in Fig. 11. In this case, the nets 2 are displaced relative to one another in a direction generally perpendicular to a line 19 which represents the direction in which crack formation is to be primarily prevented. For instance, in the case of an aircraft runway this line may be represented by the direction of transverse temperature cracks. This provides a further reduction in the tendency for elongated cracks to form in comparison with the effect that is obtained when all net rows have a net splice in line with the line 19.

The invention has been described above mainly with reference to asphalt road surfaces. However, as also mentioned in the introduction, the invention can also be applied to other surfaces that are coated with asphalt or some other plastic material. The invention can also be applied to prevent cracks and joints in a concrete coating from penetrating up through a layer of asphalt laid thereon. In addition to preventing crack formations, the invention also contributes towards improving the bearing strength of the reinforced coating. It will be understood ^' that modifications can be made within the scope of the following Claims. For instance, a net-edge net can be placed on both the underside and the upper side of a splice between adjacent reinforcement nets in the main reinforcement if this is found desirable in any demanding application.