A particularly important technical field for use of the method according to the inven- tion is for bridge decks, and the invention will below be described especially with ref- erence to this area of use. It should however be understood that the inventive princi- ples and therefore also the inventive method and layer construction may be applied to other constructions where corresponding problems are to be alleviated.

The traffic surface on bridge decks and in particular bridges made from reinforced concrete are replaced at intervals due to wear, erosion and corrosion which may no longer be kept at bay by normal and ordinary maintenance works on the traffic sur- face.

Traditionally, the traffic surface on a bridge deck made from reinforced concrete nor- mally comprises a multi-layered construction which has a thickness of 10-15 cm. The layer construction consists of water permeable materials of bitumen based asphalts or in older constructions, concrete and asphalts which are arranged on a thin membrane for example made from a roofing felt or the like or a liquid membrane such as for ex- ample an epoxy based membrane which will harden in place. The purpose of the mem- brane is to avoid water and in particular water containing salts and chlorides in gaining access to the reinforced concrete. The bitumen based asphalt layer is usually made up of a number of layers such that permeability of the top asphalt layer is bigger than the lower asphalt layer which may also act as a drain. In this manner, water which would build up in the asphalt layer may be drained away on top of the liquid impervious membrane to wells arranged in the membrane.

It has been shown repeatedly that membranes used in constructions as described above do not remain impervious. The horizontal forces which are transferred to the traffic surface by vehicles travelling on the surface when the vehicles change speed or direc-

tion have to be transferred to the reinforced concrete structure through the membrane and in particular by the adhesive used to attach the membrane to the top of the rein- forced concrete surface.

When applying membranes to the concrete surface, it is more or less impossible to achieve a full adhesion between the membrane and the concrete layer. Thereby, the adhesion will be non-existing or neglible in smaller or larger areas. Especially in the zones between adhered membrane areas and non-adhered membrane areas, tension and shear forces will rise which will have a tendency to exceed the ultimate stress of the membrane whereby the membrane will rupture such that water and in particular salt containing melting water will gain access and be able to penetrate into the rein- forced concrete structure.

The percolating water and salt water causes substantial damage to the reinforced con- crete structure. As the salt water's ingress in the reinforced concrete structure occurs the rebars will corrode, and the corrosion products will expand and thereby produce stresses in the concrete. As these stresses increases due to the corrosion, the concrete will crack which in turn will create further ruptures in the membrane such that more salt water will gain access to other areas of the reinforced concrete structure and thereby substantially increase the possibility of corrosion processes which again will disintegrate and destroy the reinforced concrete structure. It is therefore necessary to renovate the construction and also replace the damaged membrane.

In a construction where the membrane has ruptured such that water may ingress into the underlying reinforced concrete structure and thereby induce corrosion processes in the reinforcement, the construction as such provides a certain resistance against the water's ingress into the construction. As soon as the traffic surface, i. e. the asphalt layers and the membrane, has been removed, even small amounts of water, for exam- ple in the shape of rain showers and the like, will create a substantial moisturization of the concrete layers. As the concrete is moisturized, the electric conductivity of the reinforced concrete construction increases dramatically whereby the chloride induced corrosion processes around the reinforcement bars will increase dramatically. These processes are further accelerated as the access to oxygen dissolved in the rain water

and in the air on the surface of the concrete structure will be further accelerating this process.

It is therefore an object of the present invention to provide a method for renovating these types of structures wherein the exposure to extra moisture is avoided such that the accelerated deterioration of the reinforced concrete construction may be avoided and at the same time provide a renovated structure which avoids the drawbacks of the prior art methods and provide a long lasting moisture impervious structure.

This problem is addressed and solved by a method which is particular in that the struc- ture which is to be renovated comprises a reinforced concrete carrying structure on which a membrane is arranged and on top of which a surface layer such as bituminous asphalt is arranged, where the method comprises the following steps: a) the area to be treated is protected against precipitation, for example by the erection of a tent; b) the asphalt and the membrane is removed; c) the upper concrete layer is removed, such that the surface of the ex- posed concrete appears substantially without cracks, and substantially level; d) a ventilation layer is arranged on the dry concrete surface; e) a liquid impervious membrane is placed on top of the ventilation layer; f) a drainage mat is arranged on top of the membrane; g) a layer mixed from gravel, sand and/or other inorganic materials is placed on top of the drainage mat, and said layer is compacted and lev- elled; h) concrete pavement blocks are arranged as closely together as possible on top of the compacted and levelled layer, and joints between concrete pavement blocks are filled with sand; i) a bituminous based traffic surface layer is placed on top of the pave- ment blocks.

When renovating this type of constructions according to prior art methods, the con- crete layers which are infected with chlorides or which are deteriorated to such a de- gree that the integrity of the concrete structure is not sufficient in order to provide the

strength necessary in order to render the structure safe, or where the reinforcement is so badly affected by corrosion that they need to be replaced, the upper concrete layers are usually removed for example by hammering whereby the reinforcement may be exposed. Usually, a substantial part of the reinforcement is removed and replaced by new reinforcement and also concrete surrounding the reinforcement has to be removed in order to assure that a chloride free, i. e. non-infested, concrete environment may be provided around the newly installed reinforcement bars. Therefore, after removing the necessary concrete and reinforcement bars, new reinforcement bars arranged in place of the old. According to normal practice, the old concrete layer is moisturised in order to provide good adhesion between the old and the new concrete layers.

This entire process takes a relatively long time and necessitates that the traffic surface on which the renovation works take place is sealed off from traffic during a substantial amount of time. Also during this substantial amount of time, the bridge deck may be exposed to precipitation in the shape of rain or snow whereby the detrimental corro- sion effects as described above may give rise to further destruction of the reinforced concrete structure before the renovation works are carried out.

The present invention however by protecting the area to be renovated or treated against precipitation maintains the work site in dry condition during the entire process.

One example of means for keeping the work site dry is the erection of a tent. A suit- able tent for this use is disclosed in DE 19724294 or DEU8204892.

After erecting the tent, the asphalt and the membrane is removed. Hereby, the surface of the concrete is exposed. Had no protection against precipitation been provided, the concrete may now have been exposed to rain or snow such that the harmful and detri- mental corrosion processes driven by the chlorides in the concrete have accelerated.

However, by providing protection against precipitation, the surface of the concrete is maintained in a dry state, and furthermore work may be carried out substantially re- gardless of the weather and the season.

Hereafter, the top layer of the concrete is removed. In most cases, it is only necessary to remove the concrete which is disintegrated or severely cracked which will normally only be the concrete cover layer. By removing the concrete which is severely cracked

or disintegrated, this will usually expose the reinforcement which has been exposed to the most severe corrosion attacks. Hereafter, it is possible if necessary to replace the rebars in order to achieve a sound load-carrying structure.

Without casting a fresh concrete, a ventilation layer is arranged on the dry concrete surface. It should in this context be understood that the upper concrete layer which is removed should leave a substantially level and not jagged top surface. On top of the ventilation layer, the liquid impervious membrane whether it be a traditional roof membrane or a liquid membrane is placed without adherence to the concrete layer as the ventilation layer will insulate the liquid impervious membrane from direct contact with the underlying concrete layer.

On top of the liquid impervious membrane, a drainage mat is arranged. In the prior art, the asphalt layers are built up with increasing permeability away from the surface such that the button part of the asphalt layer will function as a drainage layer. It has shown however that it is advantageous to arrange a dedicated drainage mat on top of the membrane in order to make sure that the drainage structure in the asphalt layer is not clogged up over time whereby by providing a dedicated drainage mat, it is assured at all times that the water may be drained away from the traffic structure.

On top of the drainage mat, a layer mixed from gravel, sand and/or other inorganic materials is placed. This is a rather thin layer which main purpose is to create a smooth and level surface for the concrete pavement blocks which are arranged closely together on top of this compacted level layer. The joints between the different pave- ment block are filled with finely grained sand for example beach sand as is common for this type of pavement structures.

Finally a bituminous based traffic surface layer for example in the shape of asphalt is placed on top of the concrete pavement blocks. The construction above the liquid im- pervious membrane corresponds to the applicant's earlier patents published as EP 0505359 and EP 0570373.

The provision of the ventilation layer serves a number of purposes. Firstly, it ensures that the liquid impervious membrane does not come into contact with the concrete

layer. In this manner, any horizontal/lateral forces on the traffic surface do not result in ruptures in the liquid impervious membrane. Furthermore, the ventilation layer al- lows moisture in the underlying concrete construction to evaporate and leave the entire structure through the ventilation layer. Therefore, should any moisture be trapped in the concrete structure which could give rise to corrosion processes around the rebars, this moisture may leave the structure through this ventilation layer. Thereby, over time any corrosion which might be taking place in the concrete may be stopped in that the relative humidity in the overall construction may be lowered. As no new moisture is provided to the concrete construction, the relative moisture content and thereby the ability of the chloride to create corrosion around the rebars will be substantially nill.

With the traditional methods for renovating this type of surfaces where the renovated concrete structure is provided with an adhered on membrane, the membrane seals the concrete surface and thereby traps the moisture inside the concrete. It is therefore pos- sible that further corrosion processes may continue in the concrete structure as both a certain amount of oxygen and moisture is present such that the chloride driven corro- sion processes may carry on. Therefore, in the art it has been common to further pro- vide cathodic protection which is both a costly and labour intensive installation in or- der to maintain a status quo around the rebars. With the present invention, this extra insurance may be alleviated in that the ventilation layer assures that the moisture con- tent in the concrete structure will be lessened over time.

In a further advantageous embodiments, the method is further improved such that after step c) and before step d) one or more holes per m2 are drilled in the concrete layer, and that removable stoppers are arranged in the holes, and further that after step d) and before step g) apertures are made in the layers corresponding to mechanical load trans- fer members, at the positions where the stoppers are present, which load transfer members, after removal of the stoppers, are fastened in the holes in the concrete layer, where the load transfer members projects from the concrete surface, but not above the concrete pavement block layer, where the pavement blocks are arranged around the load transfer members, and that the liquid impervious membrane is shaped to cover the load transfer members in a liquid impervious manner, after which an expanding cement based material is cast in the volume between the load transfer members and

the concrete pavement blocks to a level substantially flush with the upper side of the concrete pavement blocks.

The mechanical load transfer members are fastened in the holes provided in the exist- ing concrete layer of the for example bridge deck in such a manner that they will be able to transfer lateral forces from the newly constructed traffic surface to the underly- ing concrete structure. The load transfer members may for example be fastened to the concrete layer by bolts going through the load transfer member into the holes drilled in the concrete layer. Furthermore, the load transfer members projects from the concrete surface in such a fashion that they project through the ventilation layer. For this pur- pose, apertures corresponding in size and shape to the circumference of the load trans- fer members are provided at appropriate places. The stoppers which are arranged in the holes for the following layers and applied to the concrete surface will indicate where these apertures for the load transfer members are to be placed. Corresponding apertures are provided in the liquid impervious membrane.

In order to maintain a liquid impervious membrane, the load transfer members may be covered by patches of liquid impervious membrane which patches are fastened to the surrounding liquid impervious membrane in such a manner that it is impossible for liquids to penetrate through the assembly. The assembly may be carried out by appro- priate adhesives or by welding or any other suitable means alternatively the liquid impervious membrane may be sealed against the surface of the load transfer members.

The load transfer members may advantageously project through the drainage layer and the sand and/or gravel layer placed on top of the drainage layer. Advantageously, the load transfer members projects up to and flush with the over side of the course of con- crete pavement blocks. Depending on the type of concrete pavement blocks which are used, the space between the projecting load transfer members and the surrounding concrete pavement blocks, may be filled with an expandable cement-based mortar such that lateral forces in the traffic surface may be transferred from the concrete pavement blocks to the load transfer members and thereby to the underlying concrete carrying structure. As the upper side of the concrete pavement blocks and the load transfer members optionally with help from casting an expandable cement based mor-

tar, will be substantially flush, it is possible to apply the bituminous based asphalt over the entire surface.

As is evident from the construction of the different layers, the lateral forces will be transferred via the load transfer members to the load carrying concrete structure for example constituting the main part of the bridge deck. Therefore the liquid impervious membrane is not exposed to lateral forces which may rupture and thereby render the membrane useless. Due to wear and tear arising from traffic on a traffic surface which will give rise to lateral forces in the different layers, it may be necessary from time to time to renovate the structure. This may easily be done by removing the bituminous asphalt layer only and applying a fresh asphalt layer on top of the course of concrete pavement blocks. It is foreseen that the lateral forces are assimilated by the concrete pavement blocks and transferred by the load transfer members to the underlying con- crete structure such that both the ventilation layer, the impervious membrane and the drainage layer will only be exposed to neglible lateral forces whereby the chances of any of these layers become useless is avoided.

In a further advantageous embodiment of the invention, the ventilation layer is in the shape of a woven or non-woven fabric in order to provide an easy to place and handle ventilation layer.

In a further advantageous embodiment, the ventilation layer is pulled up and at least partly covers upstanding concrete constructions adjacent the traffic surface. By pulling the ventilation layer upwards along and in some instances over adjacent concrete con- structions, it is assured that the ventilation area will be exposed to a different air pres- sure such that factual ventilation will take place in the ventilation layer such that the advantageous properties of providing a ventilation layer on top of the exposed con- crete surface will be achieved.

In a further advantageous embodiment, the structure is a bridge deck, and the upstand- ing concrete structures adjacent the decks surface are side beams arranged for load carrying and transferring purposes in the bridge construction. By covering the side beams and optionally applying a ventilation layer and an impervious membrane placed over the side beams, it is in this manner possible to also protect the side beams from

the harmful moisture and chloride attacks such that also the side beams of the bridge deck may be provided with the advantages which the present invention provides.

The invention also relates to a layered construction as mentioned above comprising the following layers from the bottom up: a renovated concrete layer, load transfer members attached to the concrete layer and projecting from said concrete layer through a ventilation layer, a liquid impervious membrane and a sand and/or gravel layer, where said impervious membrane is shaped to cover the load transfer members, a course of concrete pavement blocks and a bitumen based asphalt layer.

With this layered construction, the advantages and long-time advantageous properties may be provided to any appropriate concrete construction.

The invention will now be explained with reference to the accompanying drawing, wherein Fig. 1 illustrates a cross-section through a layer construction according to the inven- tion, Fig. 2 illustrates a cross-section through a concrete construction having an adjacent upstanding concrete member, and Fig. 3 illustrates a Gannt-diagram for carrying out renovation work.

In fig. 1, a cross-section through a typical layered construction according to the inven- tion is illustrated. The reinforced concrete substructure 1 has in this illustration been worked down to a sound and substantially level surface such that all disintegrated and cracked concrete has been removed. Hereafter, the ventilation layer 3 is arranged on top of the dry concrete 1.

On top of the ventilation layer 3, the liquid impervious membrane 4 is loosely rolled out such that there is no connection between the impervious membrane 4 and the ven- tilation layer 3. On top of the impervious membrane 4, a drainage layer 5 is arranged which may be in the shape of a woven or non-woven layer. The drainage layer is typi- cally made from hydrophilic material and is well-known in the art. On top of the drainage layer 5, a relatively thin layer of sand or gravel 6 is arranged which layer has

a relatively even top surface, and which layer may be compacted. This layer is suitable for placing the course of concrete pavement blocks 7 on top of which the finished traf- fic surface, for example bituminous asphalt 9, may be provided.

In order to transfer the lateral forces applied to the traffic surface 9 which by adhesion to the course of concrete pavement blocks 7 transfers these forces down into the lay- ered construction, the load transfer members 2 are fastened to the concrete layer 1.

Fastening of the load transfer members 2 to the concrete layer 1 may be done in any suitable manner but for example bolt connections bolting the load transfer member 2 firmly to the concrete layer 1 may be used. The load transfer members must project enough from the concrete surface 1 such that at least a part of the load transfer mem- ber 2 projects into the course of concrete pavement blocks 7. This is done in order to be able to transfer the lateral forces from the course of concrete pavement blocks to the concrete construction 1. In order to provide a stable construction, in particular with relation to the lateral forces being transferred from the traffic surface 9 to the course of pavement blocks 7 and on to the load transfer members 2, the space around the load transfer members 2 is filled with an expanding cement based mortar 8, such that a firm connection is provided between the load transfer members 2 and the concrete pave- ment blocks 7. In the joints between the separate concrete pavement blocks, fine sand may be filled in, in order to avoid relative movement between the concrete pavement blocks and thereby may have a detrimental influence on the traffic surface layer 9.

Turning to fig. 2, the layered construction illustrated in fig. 1 is applied to a concrete structure 1 having an adjacent upstanding concrete member 1'. As may be seen, the ventilating layer 3 as well as the impervious liquid membrane 4 is carried on in order to partly cover the upstanding concrete section 1'as illustrated. In order to further pro- tect the impervious membrane and the ventilation layer, a shielding construction 10 has been provided. In this context, it should be noted that any type of shielding con- struction 10 may be used. In this manner, the ventilation layer is provided with access to the ambient air such that air pressure differences at different ends of the ventilation layer, for example different sides of the bridge, may create an airflow through the ven- tilation layer which will remove any moisture evaporating from the underlying con- crete construction 1, 1' and thereby lower the relative humidity inside the concrete of the concrete construction 1.

It is known in the art that if the relative humidity in a concrete construction is lowered below a certain limit, approximately 65% relative humidity, all reactions relating to chloride or other salts will not be able to take place. As the ventilation layer 3 is shielded from the influence of moisture but still has an opening towards the ambient air, no new moisture will be transported with the air flowing through the ventilation layer such that over time, a continuous drying out of the underlying construction 1 will take place.

In fig. 3, a schedule for carrying out a renovation of a concrete structure is illustrated.

With the inventive method as described above, it is possible to carry out and finish an entire section in the span of 12 hours as illustrated for example between 1800 hours at night and 700 hours in the morning. For bridge decks, roads and the like, this is usu- ally the period of time when there is least traffic and therefore the least amount of in- convenience will be inflicted on the users. Therefore, part of the first hour, for exam- ple from 1800 to 1900 is used in order to install traffic redirection measures in order to guide the traffic around the work site. During this period, erection of the tent which serves as protection against precipitation and the provision of work lights are initiated.

From around half past seven till almost 2200 hours, removal of the traffic surface, for example by grinding, may be carried out. The grinded material may, by means of con- veyors as known in the art be loaded directly onto trucks which will carry the removed traffic surface away for safe storage. After a substantial part of the traffic surface has been removed, the cleaning operation may proceed. The cleaning is done in order to remove dust and other loose items as well as levelling any notches which are still re- maining. After the removal of the traffic surface and the cleaning and levelling of the exposed concrete surface is carried out, a substantially level but not absolutely flat surface is provided.

Under normal circumstances with the prior art methods where the impervious liquid membrane is fastened to the lower concrete surface, an absolutely flat concrete surface is necessary in order to be able to create a long lasting connection between the imper- vious membrane and the concrete surface. For this purpose, usually a new concrete layer is cast on top of the old concrete layer. This new concrete layer is traditionally cast wet in wet, which means that the old concrete is watered before the new concrete is applied. Often a cement slurry is applied prior to casting the concrete in order to

provide sufficient adhesion between the two concrete layers. By adding the extra moisture, i. e. by watering the old concrete surface, harmful chloride reactions may occur if the removal of the old concrete has been insufficient. These harmful reactions will occur almost instantly, but at the same time, the new concrete will be applied such that it will be very difficult to detect that these harmful reactions are in fact taking place. According to the new methods however, no water is applied and no new con- crete is cast which in this manner provide two distinct advantages. Firstly, the risk of creating new harmful chloride reactions which may be detrimental to the old concrete layer and in particular the rebars is avoided. Secondly, by not having to cast a new concrete layer, there will be no waiting time for the concrete to harden before any fur- ther layers may be applied in that the old concrete layer according to the present in- vention may be used directly by applying the ventilation layer which is loosely applied to the old concrete surface.

An additional advantage achieved by not having to water and/or cast concrete and by providing protection against precipitation (rain and snow) is the fact that no water is added to the construction. Furthermore, the ventilation layer makes sure that any water trapped or still in the construction may escape. With the prior art methods, any mois- ture in the construction would remain there due to the adhesion of the impervious membrane.

Before the ventilation layer is applied, the placement of the holes and stoppers is measured out, and the holes are drilled. This takes place between 2100 hours for a duration of approximately 2 hours.

As soon as the first part of the area to be renovated in cleaned and levelled, the holes may be drilled and the stoppers may be applied. At the same time or immediately fol- lowing the drilling of the holes, the ventilation layer and the impervious membrane may be installed in the areas which have been cleaned levelled and provided with holes and stoppers. After the ventilation layer and the impervious membrane are in- stalled, the stoppers may be removed, the cut-outs for the load transfer members may be provided, and these load transfer members may be installed. This work can be car- ried out concurrently with the cleaning and levelling, measuring and installation of

stoppers. Therefore, this work may be carried out from around 2100 hours to 200 hours in the morning.

As soon as a section has been created including the ventilation layer and the imperme- able membrane as well as the load carrying members, work with the drainage layer and the sand/gravel layer as well as the course of concrete pavement blocks may be initiated. Usually, this work may start around 2330 hours and will be finished around 330 hours.

At the rate that the concrete pavement blocks are arranged around the load carrying members, the casting of the expandable cement based mortar between the load transfer member and the concrete pavement blocks may be initiated. This may typically be started around 200 hours and may typically be finished by 400 hours. As the casting around the load transfer members is finished, the preparation for applying the traffic surface, i. e. the bituminous asphalt, may be initiated.

As may be understood from the description above, all works relating to the other lay- ers should be finished just before 400 hours in the morning which leaves the time from just before 400 hours to 530 hours for applying the asphalt to the finished layered con- struction. From 530 to just before 700 hours, the tent and light installation will be re- moved as well as the traffic redirection installations will be dismantled such that the bridge deck will be open for normal traffic by 700 hours.

The time schedule illustrated above is applicable for renovation of areas of up to be- tween 100 and 200 square meters, but it should be noted that as the crew working with this type of work becomes better trained and more used to the working procedures, larger areas may be carried out. Furthermore, more than one site may be erected such that more areas may be renovated simultaneously.

Although the invention has been described above with reference to particular applica- tions, the invention as such is not limited, and the invention is therefore only limited by the scope of the appended claims.