DESCRIPTION

This invention relates to a method for strengthening concrete road pavements and methods for restoring a concrete road pavement that use the strengthening method.

Concrete road pavements are pavements constituted of a concrete slab laid on one or more base layers of cement-bound granular material and/or granular material or directly on the subgrade if this guarantees suitable load- bearing capacity. They are widely used both in Northern Europe and in North America.

In particular, there are four different structural types of concrete pavements: - pavements produced using unreinforced slabs, with relatively frequent transversal joints. The centre to centre distance of the transversal joints is approximately 4.5 to 5 m if dowel bars are not used, whilst the distance can be increased up to around 7.5 m when the bars are present. Dowel bars are metal bars that are embedded in the concrete slabs below the joints, They are also usually coated with anti-friction material, in order to allow the concrete slab to slide relative to the bars after the thermal deformations to which it may be subjected,

pavements produced using reinforced slabs of variable length from 10 to 20 m, equipped with light reinforcement distributed longitudinally and transversally. The function of that reinforcement is to hold closed the cracks generated by thermal variations inside the concrete slabs, therefore the reinforcement is positioned in the upper portion of the slab thickness;

pavements produced with continuous reinforcement, having no transversal joints except for construction joints and with the presence of relatively heavy steel longitudinal reinforcement intended to hold closed the cracks formed in the slab due to hygrothermal effects (again in this case, the reinforcement is positioned in the upper portion of the slab thickness);

- pavements produced using prestressed slabs, equipped with anchoring shoulders, in which the prestressing is guaranteed with flat jacks or with post-tensioned bars or cables.

This invention was created with reference to pavements produced using unreinforced slabs, but it may also be used for the other types if necessary. Therefore, hereinafter reference will be made exclusively to pavements of the first type.

The joints of concrete pavements may be divided, according to their function and shape, into: contraction joints, construction joints, expansion joints or movement joints. Those of interest in the context of this invention are the contraction joints.

Contraction joints may be transversal and longitudinal and constitute an interruption only in the upper layer of the concrete. Contraction joints are intended to allow thermal contraction and shrinkage of the concrete, to control cracking of the slabs and to also allow expansion, up to the original length of the slab. Structurally, contraction joints constitute sections of the slab with reduced resistance: in fact they do not extend through the entire thickness of the pavement, but are cut into the concrete with a width of 2 to 4 mm and depth of around 1 /3 to 1 /4 of the thickness of the slab. The joint is completed along the rest of the thickness by means of the cracks produced due to the point of weakness created.

Load-sharing by the slabs across the contraction joint can be guaranteed by interlocking of the aggregates of the surfaces in contact of the slabs forming the joint or, when traffic loads are high, by load transfer devices such as smooth steel bars (dowel bars) usually having a large diameter (ø 30), 500 to 700 mm long, straddling the joint below it. In the longitudinal direction, contraction joints are used to prevent the possible effects of differential sagging leaving the slab free to rotate.

In contrast, expansion joints extend through the entire thickness of the slab, and have a width that is variable depending on the filling material placed in the lower groove. The upper groove, which has a larger opening, is at least 20 mm deep. These joints must allow expansion of the slabs during the hottest periods and also act as contraction joints. They are usually located at intersections with other carriageways or if there is a variation in the laying plane. Given their breadth and the total absence of interlocking actions, expansion joints are always equipped with dowel bars housed in suitable sleeves in order to allow their movements.

In general, the joints are made by means of two cuts. The first for cutting the slab and the second for finishing off the sealant containment chamber (located at the base of the joint) and smoothing. In fact, sealing of the joints guarantees the durability of the concrete, which is protected against infiltration by water, and ensures driving comfort for users, reducing rolling noise caused by tyres passing over the interruptions formed by the cuts. However, it is know that even concrete road pavements, like all road pavements, are subject to various types of damage during their working life. In particular, the deterioration that may occur in concrete road pavements may be divided into the following categories:

- cracking;

- instability of the slab supporting surface;

- joint defects;

- surface defects;

- other damage.

The most serious types of deterioration that can affect concrete road pavements are usually caused by a variation in the conditions of the road foundation, for example due to sagging and water infiltration.

In particular, the main deteriorations usually appear at the joints. In fact, as time goes by, the sealant used to fill the joints gradually comes away from the concrete and so allows rainwater to infiltrate, washing away the earth below and consequently forming voids. Often, with heavy vehicular traffic, the presence of voids under the joints may cause first oscillations of the concrete slabs that gradually increase with the passage of each vehicle, and then the onset of cracks and breaks in the slabs.

Although after their production, concrete road pavements can guarantee a longer maintenance-free period because they are less subject to deterioration caused by climatic conditions, compared with bituminous macadam road pavements (which would make concrete road pavements the preferred choice especially in countries with relatively harsh winters), when the deteriorations described above appear, it is not currently possible to effectively remedy them with simple maintenance work. In fact, since the origin of the deterioration lies in changes in the foundations, the only way to remedy the deterioration is by the complete dismantling and then reconstruction of the pavement.

Therefore, at present, concrete road pavement managers tend to delay maintenance work as long as possible, meaning that pavements may even be used for years in dilapidated conditions that may be a risk to or at least slow down vehicular traffic.

Then, when the managers finally decide to reconstruct the pavement, on one hand the costs of the work are always very high, and on the other hand the related times taken by the work are very long.

Faced with such problems at the time of carrying out work, in many cases the road pavement managers currently decide to replace the preferred concrete pavements with bituminous macadam pavements.

In this context, the technical purpose forming the basis of this invention is to overcome the disadvantages referred to relative to concrete road pavements.

In particular, the technical purpose of this invention is to provide a method for strengthening concrete road pavements that allows alternatively the production of pavements that are less subject to deterioration, or the restoration of deteriorated road pavements without the need to work on their foundations.

The technical purpose of this invention is also to provide methods for restoring a deteriorated concrete road pavement, without the need to dismantle and reconstruct it.

The technical purpose and the aims indicated are substantially achieved by a method for strengthening concrete road pavements and methods for restoring a concrete road pavement that use it, as described in the appended claims.

Further features and the advantages of this invention are more apparent in the detailed description, with reference to the accompanying drawings which illustrate several preferred, non-limiting embodiments of a method for strengthening concrete road pavements and methods for restoring a concrete road pavement that use it, in which:

- Figure 1 is a schematic side view of a first step of a strengthening method according to this invention;

- Figure 2 is a top view of the result of the step of Figure 1 ;

- Figure 3 is a schematic side view of a second step of the strengthening method according to this invention;

- Figure 4 is a top view of the result of the step of Figure 3;

- Figure 5 is a schematic side view of a third step of the strengthening method according to this invention;

- Figure 6 is a top view of the result of the step of Figure 5;

- Figure 7 is a schematic side view of a fourth step of the strengthening method according to this invention;

- Figure 8 is a top view of the result of the step of Figure 7;

- Figure 9 is a schematic side view of the result of a fifth step of the strengthening method according to this invention; - Figure 10 is a schematic top view of what is visible in Figure 9;

- Figure 11 is a schematic front view of what is visible in Figure 9;

- Figure 12 is a schematic side view of the result of a sixth step of the strengthening method according to this invention;

- Figure 13 is a schematic top view of what is visible in Figure 12;

- Figure 14 is a schematic front view of what is visible in Figure 12;

- Figure 15 is a schematic side view of a first additional step of a first method for restoring a pavement previously strengthened in accordance with this invention;

- Figure 16 is a schematic side view of a second additional step of the first method for restoring a pavement previously strengthened in accordance with this invention;

- Figure 17 is a schematic side view of the result of a third additional step of the first method for restoring a pavement previously strengthened in accordance with this invention;

- Figure 18 is a schematic top view of what is visible in Figure 17

- Figure 19 shows a first additional step of a second method for restoring a pavement previously strengthened in accordance with this invention;

- Figure 20 shows, both together, the result of a second additional step of the second method for restoring a pavement previously strengthened in accordance with this invention, and execution of a subsequent third step;

- Figure 21 shows, both together, a first and a second additional step of a third method for restoring a pavement previously strengthened in accordance with this invention;

- Figure 22 shows the result of a third additional step of the third method for restoring a pavement previously strengthened in accordance with this invention;

- Figure 23 is a schematic rear view of a stretch of pavement strengthened and restored in accordance with this invention during its use for the circulation of vehicles on the road; and - Figure 24 is a schematic top view of a stretch of a concrete road pavement highlighting zones that are subject to strengthening work in accordance with this invention.

With reference to the strengthening method according to this invention, it should first be noticed that it may be used both on existing road pavements 1 (damaged or not), and during the production of new road pavements 1 . In accordance with this invention, it is possible to strengthen a concrete road pavement 1 by acting across one or more of the related contraction joints 2, that is to say, joints 2 extending for a depth that is less than the thickness of the layer of concrete (usually equal to one third/one quarter of the thickness).

This invention can be used both for carrying out a single piece of work at a specific position of a specific contraction joint 2, and, preferably, for carrying out either a plurality of pieces of work for a single joint 2, or a plurality of pieces of work for each joint 2 of a plurality of joints 2 (more common application when restoring damaged road pavements 1 ).

Hereinafter a description is provided of the various steps of the method according to this invention with reference to a single working zone. However, it shall be understood that in the case of work in multiple zones, the same steps must be repeated in each zone (usually located at a predetermined distance from each other along the length of the related joint 2 - normally around 50 to 200 cm).

The method comprises first the operating step of selecting a joint 2 at which the strengthening will be carried out. The joint 2 is interposed between a first portion 3 and a second portion 4 of the layer of concrete 5, where the first portion 3 and the second portion 4 are those that extend at the two sides of the joint 2, delimiting it.

In general, a first pile 7 is then vertically inserted in the ground 6 below the first portion 3 of the layer of concrete 5, and a second pile 8 below the second portion 4 of the layer of concrete 5. Preferably, those piles are inserted in the ground 6 at a distance of between 20 cm and 100 cm, preferably between 30 cm and 70 cm from a vertical plane in which the selected joint 2 lies, so that the centre to centre distance between the two piles is between 40 cm and 200 cm, and preferably between 30 cm and 70 cm.

In the case of work on existing road pavements 1 , in order to allow both insertion of the first pile 7 and of the second pile 8 in the ground 6, as well as the subsequent steps described below, a through opening 9 through the entire layer of concrete 5 is preferably made in advance. In particular, the opening is made in such a way that it extends from the first portion 3 to the second portion 4 across the selected joint 2. Advantageously, in plan view, the through opening 9 is slot-shaped.

As illustrated in Figures 1 to 6, in the preferred embodiment the through opening 9 is created by first making two holes by core drilling 10 (Figures 1 - 2), then making two cuts 11 that tangentially connect the circular holes 12 obtained with the core drilling 10 (Figure 4), and finally removing the piece 13 of the layer of concrete 5 delimited by the cuts 11 and by the holes from the core drilling 10 (Figures 5 - 6).

Both the core drilling 10 and the two cuts 11 are carried out through the entire layer of concrete 5 and if necessary any further rigid layers below. The core drilling 10 is also carried out with a diameter greater than that of the first pile 7 and of the second pile 8 to be inserted in the ground 6. The cuts 11 are preferably made with a mechanical saw 25 using a circular diamond blade (Figure 3).

As regards the steps for inserting the first pile 7 and the second pile 8 in the ground 6, advantageously, these are carried out using micropiles, that is to say, metal piles (which may be tubular or solid) having a diameter that is usually less than 250 mm, preferably constituted of a plurality of modules connected to each other axially (for example, by screwing).

Moreover, preferably the steps of inserting the first pile 7 and the second pile 8 in the ground 6 are performed by driving or rotary driving, advantageously using pressure. In particular, in the preferred embodiment the driving or rotary driving using pressure are carried out using a movable ballasted wagon 14 on which at least one hydraulic driving piston 15 is installed. However, in the case illustrated in Figure 7, the ballasted wagon 14 is equipped with two hydraulic driving pistons 15 which are positioned in such a way as to be able to drive each pile at one end of the slot defined by the through opening 9 without having to move the wagon. The two hydraulic pistons 15 can also be operated alternately, for using the entire mass of the ballasted wagon 14 as an anchor for each driving operation. A ballasted wagon 14 of this type is the subject of Italian patent application No. 102016000072862 in the name of this Applicant.

Preferably, the first pile 7 and the second pile 8 are inserted in the ground 6 in such a way that they extend in the same vertical plane perpendicular to a direction of extension of the selected joint 2, and in such a way that a first upper head 16 of the first pile 7 and a second upper head 17 of the second pile 8 are located at a height lower than a lower surface 18 of the layer of concrete 5 (preferably both at the same height).

The strengthening method according to this invention also comprises connecting the first upper head 16 of the first pile 7 inserted in the ground 6 to the second upper head 17 of the second pile 8 inserted in the ground 6, by means of a rigid element 19, such as a metal section bar, which extends transversally relative to the selected joint 2 (inserting it through the through opening 9 if this is present). In particular, in the preferred embodiment, the connection by means of the rigid element 19 fixes the first pile 7 and the second pile 8 to each other at least as regards possible movements along a horizontal direction perpendicular to the direction of extension of the selected 2 joint. In the preferred embodiment, that is achieved by means of a male - female coupling between the rigid element 19 and the first pile 7 and second pile 8, along a vertical direction. For example, if the first pile 7 and the second pile 8 are tubular, the rigid element 19 may comprise two downward projections sized in such a way that they can be inserted in the piles. Alternatively, the rigid element 19 may comprise lower hollow seats sized in such a way that they can house respectively the first upper head 16 and the second upper head 17.

Preferably, this invention comprises using a rigid element 19 having a main direction of extension and a constant cross-section perpendicularly to the main direction of extension, and making the connection between the first pile 7 and the second pile 8 by positioning the rigid element 19 with its main direction of extension horizontal and lying in the vertical plane perpendicular to the direction of extension of the selected joint 2. The rigid element 19 is also preferably provided with an anti-corrosion and anti-grip surface treatment (similar to that of the dowel bars). In fact, in this way, if necessary the concrete slab will be able to slide relative to the rigid element 19. That is particularly advantageous in the preferred embodiments of this invention, in which the rigid element 19 is connected to the first pile 7 and to the second pile 8 in such a way that it is positioned with at least a first part of it (its upper part) inside the through opening 9. In contrast, the lower part of the rigid element 19 is positioned with its lower surface at a height that is equal to or lower than the height of the lower surface of the concrete slab, in order to guarantee that the first pile 7 and the second pile 8 remain below that surface.

In the accompanying figures, the rigid element 19 has an inverted T-shaped cross-section, but in other embodiments it may have other forms, for example, it could have the shape of an I, U or H.

The strengthening method according to this invention then comprises a step of constraining the rigid element 19 to the layer of concrete 5. This is advantageously done by filling the through opening 9 again with a mortar 20, preferably an expansive mortar for grouting, in such a way that the rigid element 19 is at least partly embedded. If the strengthening method must be applied before producing the pavement, the first pile 7 and the second pile 8 can simply be inserted in the subgrade 6 (preferably in the same ways indicated above), connected to each other using the rigid element 19, then the layer of concrete 5 created and constrained to the rigid element 19. Finally, the joints 2 must be cut in such a way that they pass above the rigid elements 19.

In all of the cases described it is important that, once the work is complete, the rigid element 19 fixed to the first pile 7 and to the second pile 8 is positioned and/or constrained to the layer of concrete 5 in such a way that it constitutes an impediment to any downward movement of the layer of concrete 5.

As already indicated, this invention also relates to several methods for restoring a concrete road pavement 1 that comprises a damaged upper layer of concrete 5 and in which there are joints 2 that extend for a depth that is less than the thickness of the layer of concrete 5.

All of the various restoring methods that are the subject of this invention comprise first a step of strengthening the road pavement 1 using the strengthening method described above.

A first restoring method according to this invention, usable for pavements that have only deteriorated a little, then comprises first the step of milling with a road milling machine 21 those zones of the road pavement 1 that have been affected by the strengthening (Figure 15) to make them coplanar with the rest of the pavement, and then the step of sweeping and vacuuming the pavement debris using a suitable cleaning machine 22 (Figure 16). Finally, there is a step of cutting and sealing the joint 2 at the zones affected by the strengthening (Figure 17) in order to restore a continuity with the existing joints 2 (Figure 18).

In contrast, if the pavement is more deteriorated, after the strengthening, the restoring method may comprise first the step of milling the entire road pavement 1 with a road milling machine 21 (Figure 1 9), and then the steps of:

covering the road pavement 1 with an additional layer 23 of concrete (for example constituted of a self-levelling cement-based mortar);

making a plurality of cuts in the additional layer of concrete so as to create new joints 2 that extend above the pre-existing joints 2; and

sealing the new joints 2 created in this way.

In contrast, if the pavement surface is not excessively deteriorated, the restoring method may comprise first the step of milling the entire road pavement 1 with a road milling machine 21 , and then proceeding directly with cutting and sealing of the joints 2 at the zones previously affected by the strengthening work (Figure 21 ).

Finally, it is also possible that once the concrete pavement has been restored, it may be covered with a bituminous macadam 24 (Figure 22).

This invention brings important advantages.

First, a strengthening method was provided that on one hand allows work to restore deteriorated road pavements without the need to work on their foundations, and that, on the other hand, allows the production of concrete road pavements that are less subject to deterioration than the prior art ones. Second, thanks to that strengthening method, it has been possible to provide methods for restoring a deteriorated concrete road pavement, which allow it to be restored without the need for dismantling and reconstruction.

Finally, it should be noticed that this invention is relatively easy to produce and that even the cost linked to implementing the invention is not very high. The invention described above may be modified and adapted in several ways without thereby departing from the scope of the inventive concept.

All details may be substituted with other technically equivalent elements and the materials used, as well as the shapes and dimensions of the various components, may vary according to requirements.