EP2318590A1

EP2318590A1 - Load-bearing surface

Info

Publication number: EP2318590A1
Application number: EP09776242A
Authority: EP
Inventors: Bo Serwin
Original assignee: Contec International GmbH
Current assignee: Contec International GmbH
Priority date: 2008-07-18
Filing date: 2009-07-14
Publication date: 2011-05-11
Also published as: WO2010006617A1

Abstract

Load bearing surface to be arranged on a foundation layer (4), wherein the surface comprises a reinforcement in the shape of a reinforcement netting (2), which netting by means of distance keepers (3) is elevated above the foundation layer, where means are provided for improving the connection between the load bearing surface and the foundation layer, and that the surface layer consists of a layer of ultra high strength concrete or a semi-flexible cement and bitumen containing, where said layer has a thickness of between 30 and 80 mm, and where said surface layer is free of joints.

Description

Load-bearing surface

The present invention relates to a load-bearing surface placed on a sub-base.

In the art there are a number of load-bearing surfaces suggested which are to be arranged on sub-bases. Most of these however are not suitable under conditions where requirements to strength, maximum layer thickness, etc are difficult to fulfil.

One of the applicants has with his prior product, marketed under the trademark Ferroplan®, developed a solution to a number of these special problems which may arise under certain conditions.

The function of an industrial floor or industrial pavement is of crucial importance for the user. Surface damage, cracks, broken joint edges, dust, etc. can result in an uncomfortable use and damage of transportation equipment. In the food industry and with the so-called fluid tight constructions are not only the requirements of the user of importance but as well the requirements from the authorities.

In the rehabilitation or renovation of industrial floors or industrial pavements the factor time is an important key factor. Shutdown time must be minimized since every delay or break in the complex process of production, transport and storage will have immediate and possible great financial consequences for the company. The choice for a re-surfing system for the industrial floors will be mainly based on two fac- tors: the necessary shut down time and the expected service life from the new topping or overlay. Es- thetical and financial factors are of less importance as long as the new topping meets the standards and specifications from the user and the related industry.

In the case of the rehabilitation or re-strengthening of infrastructure constructions like bridges shut down time have to be absolutely minimized due the immediately impact on the economical situation and the commercial and environmental consequences. Cement based thin toppings or overlays have several important advantages compared to other materials. The advantages come into play particularly in the case of industrial flooring and paving and in the rehabilitation of civil constructions.

The Ultra Thin Heavy Reinforced High Performance or Ultra High Performance Concrete overlay marketed under the name Contec Ferroplan® System is especially developed to meet the technical standards and practical requirements for industrial floors placed with standard equipment and by traditional floor layers. The Contec Ferroplan® System is especially developed to cope with problems as: not sound or cracked concrete, sub bases from diverged materials and weak , damaged and/or under dimen- sioned constructions. Particularly in these cases the combination of a HPC or UHPC in combination with reinforcement is very interesting to produce strong and ductile "floating" overlays or to connect an extremely strong and ductile overlay to the sub base.

The Contec Ferroplan® System is an unique system that can be laid without joints in places where the quality of the existing base is not satisfactory. The system consists of a special blended High Performance Concrete or a Ultra High Performance Concrete, steel- and polypropylene fibres and welded mesh reinforcement. The final strength will depend on the amount and type of aggregates and reinforcement what will be used.

The layer can be laid as a thin overlay on a sub base where sufficient bonding cannot be secured, which is under dimensioned or where cracks and movements occur. Typical fields of application are too weak concrete, contaminated concrete, steel- and concrete bridges, piers and other constructions. The system provides a joint less chloride resistant and dense topping. The Contec Ferroplan® System can also be used to produce prefab constructions and constructions parts like panels.

The values of compressive strength and flexural strength are much higher than those of normal high quality thin overlays. The flexural strength from the system will depend on the amount of reinforcement used. Due the high content of steel, the impact resistance is extremely good and furthermore provides excellent resistance to chemicals, salts, oil, solvents, blood, fat, cleaning chemicals and acid attack. The layer also has a high heat resistance and resists hot water and steam cleaning and is absolutely frost/ thaw resistant. The layer may be applied in a relatively thin cover from 10 - 20 mm over the reinforcement.

Although this product addresses a number of the drawbacks experienced with earlier layers of this type a number of drawbacks remains.

Due to inadequate contact with the base layer, i.e. the layer on which the UHSC (Ultra High Strength Concrete) is placed, and/or movement in this layer and/or physical (and dynamic) loads applied to the layer, not taking advantage of the high compression strength of the layer, the layer has had inadequate performance when applied in particular to surfaces for vehicle traffic. In particular bridges, or other constructions which may be exposed to and move in response to dynamic loads.

The present invention addresses this in an inventive manner by providing load bearing surface to be arranged on a foundation layer, wherein the surface comprises a reinforcement in the shape of a rein- forcement netting, which netting by means of distance keepers is elevated above the foundation layer, where means are provided for improving the connection between the load bearing surface and the foundation layer, and that the surface layer consists of a layer of ultra high strength concrete or a semi- flexible ultra high strength cement and bitumen containing layer, where said layer has a thickness of between 30 and 80 mm, and where said surface layer is free of joints.

The thin layer of the load bearing surface in combination with the ultra high strength characteristics of the cement and the improved connection with the foundation layer, provides a number of advantages. The stresses occurring during use in the construction, is transferred from the load bearing layer to the foundation layer through the means for improving the connection between said two layers. In this man- ner the improving means distributes the stresses, such that the forces induced in the foundation layer are well distributed, whereby the impact on the foundation layer is drastically reduced, due to the distribution of forces. In a further advantageous embodiment at least some of the distance keepers also comprise means for anchoring the netting to the foundation layer.

By this construction, the surface is provided with an anchoring to the sub-layer. In the art it is known to anchor different constructions together, but it was hitherto not thought possible to apply this technique to USHC having very thin layer thicknesses. The conventional approach would have been to roughen the sub-surface in order to provide better grip between the two layers, or apply a thicker concrete layer in order to be able to have a sufficient concrete cover over the anchors. The anchors represent a stress concentration point, where relatively large tension forces may be generated. Generally cement-based materials exhibit very low resistance against tension compared to their ability to withstand compression. The invention has surprisingly shown that the coupling between the reinforcement netting, distance keepers and anchors creates a substantially even distribution of stresses/forces in the plane of the surface, thereby not creating stress concentrations around the anchors. The entire surface in this manner is much stronger and durable against dynamic loads, in particular loads applied in the same plane as the surface.

The reinforcement furthermore distributes the stresses such that cracking in the surface is avoided, thereby making it possible to cast relatively large surface areas without joints.

Where the top layer is a semi- flexible cement and bitumen containing layer, it may for example be of the type as described in WO 2006/074662 of the same inventor. The semi- flexible layer contains a portion of UHSC which is able to activate the reinforcement when stresses occur. The voiods in the bitumen/aggregate portion is sufficient to accommodate enough UHSC, such that connections between the reinforcement and the matrix of the semi-flexible layer may be established which are strong enough to activate the reinforcement, i.e transfer forces from the matrix to the reinforcement.

In a further advantageous embodiment of the invention the foundation layer is a roadbed, regular asphalt or concrete road construction, concrete or steel bridge deck, compacted soil or aggregate base layer, concrete layer. Due to the special ability of the layer as set out above to remain undamaged even when exposed to dynamic loading it is suitable to be applied to sub-bases or foundation layers which are not absolutely rigid or dynamic load resistant.

In a still further advantageous embodiment of the invention the ultra high strength concrete has a compressive strength of at least 65 MPa more preferably of at least 100 MPa and most preferred at least 250 MPa.

Even when applied to a relatively weak foundation, the strong surface, may take up most of the loading without being damaged. The higher the compressive strength the more it may be loaded, almost irrespective of the foundation. Of cause the foundation structures ability to carry loads and remain coherent is important, but the anchors, together with the reinforcement creates a very rigid and ductile layer. The strength measurements are related to the procedures required according to DIN standards anno 2007.

In a still further advantageous embodiment of the invention the concrete layer comprises 0 % to 12 % fibres, more preferred 2 % to 10 % and most preferred 6 % to 7 %, wherein the fibres are made from plastics, steel, carbon, glass.

All percentages are to be measured as weight-%, as opposed to for example volume-%.

The addition of fibres to the UHSC provides a very high ductility, which together with the ultra high strength provides a surface having very good properties. When applying the surface layer in the thicknesses cited above the aggregates are also relatively small. This in turn provides for a relatively high portion of smaller particles in the layer. The density stemming from a high percentage of finer particles also provides a very good bond with the fibres, such that the fibres provides a higher degree of ductility as what could have been expected for the same amount of fibre in a traditional concrete. This is particularly important over and around the anchors, where the UHSC cover is thinner. The ductility due to the addition of fibres, actively prevents cracking at these most exposed positions. Any type of reinforcement may naturally be used, but in an advantageous embodiment of the invention the reinforcement is a pre- welded netting steel reinforcement, and adjacent nets are overlapped and welded together, in order to create a coherent and uniform reinforcement.

The invention will now be explained with reference to the accompanying drawing, wherein non-limiting examples are depicted in order to illustrate possible embodiments of the invention.

Fig. 1 illustrates a cross-section through a construction including a UHSC top layer; Fig. 2 illustrates a cross-section through a construction including a semi-flexible top layer; Fig. 3 illustrates a plane view of connections in the reinforcement Fig. 4 illustrates various connectors/distance keepers

Description of an embodiment

In figure 1 is illustrated a cross section of a load bearing surface construction according to the invention. The construction comprises a layer of ultra high strength concrete 1 in which is embedded a reinforcement netting 2. The reinforcement netting 2 is kept in place by holders 3. The holders are fastened to the foundation layer 4 by means of bolts 5. In order to maintain the reinforcement netting 2 at a certain distance above the surface of the foundation layer 4 the holders 3 are shaped such that the part of the holder 3 being fastened to the surface of the foundation layer 4 is arranged between the head of the bolt 6 and the surface of the foundation layer 4. In this manner the thickness of the material from which the holder 3 is made determines the distance the reinforcement is elevated above the surface of the foundation layer 4. Additionally, the holder will also maintain the reinforcement netting 2 in its proper position during casting of the concrete 1 such that also during construction of the load bearing surface the integ- rity of the entire construction is maintained.

In figures 1 and 2 a special cross section is illustrated, namely a cross section where the load bearing surface is placed adjacent a further construction member 7. Between the further construction member 7 and the load bearing surface and in particular the ultra high strength concrete a seal 8 is placed. The seal is in this embodiment a flexible seal which will adhere to either of the construction parts 7,1 such that as the construction parts 7,1 moves relative to each other the seal will maintain a fluid tight connection between the two construction parts 7,1.

Turning to figure 2 a comparable construction is illustrated, but whereas the construction in figure 1 comprises a load bearing surface consisting of ultra high strength concrete 1 the load bearing surface according to figure 2 comprises a top layer of a semi- flexible layer 9. The remaining features are identical or comparable to the features with the same reference numbers as mentioned above with reference to figure 1.

The liquid tight seal 8 is in this embodiment provided with a flange 10 which is suitable to be in intimate contact with the load bearing surface layer 9 in order to create a reliable and strong liquid seal between the two construction parts 9, 7.

The load bearing surface layer 9 is made from a semi- flexible material. Such a material is for example disclosed in the same inventor's prior published international patent application WO 2006/074662. The material herein is a bitumen covered aggregate having sizes making it possible to relatively firmly and densely pack the bitumen covered aggregate material. The bitumen is furthermore covered with a powder composition containing among other components cement such that as water is added, the powder material will react with the water in the same manner as hardenable concrete and thereby create a very strong and rigid skeleton consisting of cement particles or other binders in the powder material. The bitumen layer will provide the matrix with a certain degree of flexibility due to the resilient characteristics of the bitumen whereas the aggregate normally being selected from relatively hard rock types will create a relatively stiff, strong and dense construction. Tests have clearly indicated that such a semi- flexible load bearing layer will be able to interact with embedded reinforcement 2 in order to activate the reinforcement once the construction is exposed to stresses, such as for example traffic and in particular braking actions from vehicles on the load bearing surface or from bridge decks which may have a tendency to vibrate or oscillate or otherwise move. The bolts 5 and the foundation structure together with the reinforcement 2 provides a very strong coherence between the load bearing surface construction whether it be ultra high strength concrete or a semi- flexible pavement such that the good bond between the two sections, i.e. the foundation 4 and the load bearing structure arranged on top of the foundation 4 will act as one and together create a relatively strong construction.

In figure 3 is illustrated a plane view of the reinforcement 2 used as part of the load bearing surface. The reinforcement of this embodiment is in the shape of a steel-netting where the individual bars 11, 12 of the netting are arranged at approximately right angles to each other such that a squared netting is achieved. In order to create a continuous reinforcement layer the sides of one net will overlap with the sides of an adjacent net such that it is possible to weld the two nets together indicated by the welding seams 13. The reinforcement netting is kept in place by the bolts 5 and holders 3. The shear characteristics of a layer, i.e. load bearing surface, may be increased or decreased depending on the number of bolts used to anchor the netting to the foundation such that depending on circumstances the number of bolts 5 per square unit may change from application to application.

In figure 4 are illustrated examples of different holders 3. Figure 4a is a holder 3 seen in an upstanding view. The holder 3 is comparable to the holder illustrated in the preceding figures 1-3. In a plane view the holder 3 will have a configuration as illustrated in figure 4b. The reinforcement bars 2 are illustrated in phantom lines as is the bolt 5. In a further configuration of the holder 3 according to figure 4a the holder may be constructed as illustrated in figure 4c such that only one arm 3' is engaging the reinforcement bars 2.

In the configuration illustrated with reference to figure 4d the holder 3 ' ' partly surrounds the bars 2 such that the lower leg of the holder 3" also serves as distance keeper from the surface of the foundation structure in use. The thickness of the material from which the holder 3" is made will in this manner be the distance keeper and indicate the distance from the top of the surface of the foundation structure to the underside of the bars 2. In a plane view the holder 3" as illustrated with reference to figure 4e will be provided will eye parts 14, 15 in either end of the holder 3" where the eye parts are suitable to be engaged by the bolt 5 and in this manner be fastened to the foundation structure.

Although the invention has been described with reference to particular embodiments, the skilled person will be able to contemplate further embodiments without departing from the scope of protection as afforded by the appended claims.

Claims

1. Load bearing surface to be arranged on a foundation layer, wherein the surface comprises a reinforcement in the shape of a reinforcement netting, which netting by means of distance keepers is ele- vated above the foundation layer, where means are provided for improving the connection between the load bearing surface and the foundation layer, and that the surface layer consists of a layer of ultra high strength concrete or a semi-flexible cement and bitumen containing, where said layer has a thickness of between 30 and 80 mm, and where said surface layer is free of joints.

2. Load bearing layer according to claim 1 wherein the means for improving the connection between the load bearing surface and the foundation layer is provided by at least some of the distance keepers comprising anchoring means, for anchoring the distance keepers to the foundation layer.

3. Load bearing layer according to claim 1 wherein the means for improving the connection between the load bearing surface and the foundation layer is provided by an adhesive, for example an epoxy based adhesive optionally comprising means for improving the mechanical connection between the load bearing surface and the foundation layer.

4. Load bearing layer according to claim 1 wherein the foundation layer is a roadbed, regular asphalt or concrete road construction, concrete or steel bridge deck, compacted soil or aggregate base layer, concrete layer.

5. Load bearing layer according to claim 1 wherein the ultra high strength concrete has a compressive strength of at least 65 MPa, more preferably of at least 100 MPa, and most preferred at least 250 MPa.

6. Load bearing layer according to claim 1 or 5 wherein the concrete layer comprises 0 weight-% to 12 weight-% fibres, more preferred 2 weight-% to 10 weight-% and most preferred 6 weight-% to 7 weight-%, wherein the fibres are made from plastics, steel, carbon, glass

7. Load bearing layer according to claim 1 wherein the reinforcement netting is pre-welded steel reinforcement bars, and that adjacent nets are overlapped and welded together or where the reinforcement netting is a coated or uncoated glass fibre net, where separate nets are locked or glued together.