FR2808522A1 - FIBER REINFORCED COMPACT ROUND CONCRETE COMPOSITION AND METHOD FOR PRODUCING A PAVEMENT FROM SAID COMPOSITION - Google Patents

Abstract

The present invention relates to a fiber-reinforced compacted rolled concrete composition and a process for producing continuous pavements and industrial areas without joints from said composition, the metal fibers being constituted by substantially cylindrical wires (10) comprising a longitudinal central (11) substantially rectilinear extending on each side via an intermediate portion (13) of a curved end portion (12), said wires having a diameter (d) of between 0.38 and 1.05 mm, a total length of between 19 and 80 mm, a length (l, l') of the end parts of between 1.5 and 4 mm, a transverse offset (h, h') of at least 0.75 mm, an obtuse angle (alpha, alpha') less than or equal to 160 degrees between each intermediate portion and the central part, an obtuse angle between each intermediate portion and end part, and a minimum tensile strength of 900 N / mm2, and said composition it comprises, per cubic meter of concrete, between 180 and 400 kg of hydraulic binder, between 90 and 150 liters of water, and between 25 and 60 kg of metal fibers.

Description

The present invention relates to a compacted rolled concrete composition

  reinforced with fibers and a process for producing continuous pavements and industrial areas without joints, from said composition. Compacted rolled concrete compositions differ from conventional poured or perverted concrete by the fact that, for similar mechanical properties, they require a reduced cement dosage as well as a reduced water content. This lower water content makes it possible to obtain sufficient bearing capacity to use the material with road vehicles in order to compact it using a vibrating compactor and a tire compactor, then to return it to circulation without delay. The consistency of poured concrete requires implementation with traditional techniques of sliding formwork machine or vibrating rule and allows recirculation only after a sufficient setting time which is generally at least

7 days.

  In the two types of conventional concrete mentioned above, it is known to insert metallic fibers. The metallic fibers used in industrial paving are most often drawn fibers generally comprising wires of 1 mm in diameter. The different existing fibers differ from each other by the type of active anchoring in the concrete matrix. There are fibers manufactured with a so-called deformable anchor, for example hook fibers such as those sold by the company Bekaert under the brand "Dramix" or wavy fibers such as those sold by the company Trefil Arbed. This company also manufactures a fiber sold under the brand "Twincone" which has a non-deformable cone at each of its ends. This type of anchor is much more rigid than the anchor obtained by hooks or

  undulations, hence its name of fibers with so-called total anchoring.

  After reinforcement with steel fibers, traditional perverted or poured concrete makes it possible to produce industrial pavements (often covered and therefore less subject to weathering and temperature variations than pavements) of large size reaching up to 2000 m2 without joints , the properties of the fibers making it possible to space the joints. On the other hand, these concretes have so far been unable to be used effectively for the production of continuous pavements without joints, despite the advantage presented by such an application. Indeed, the relatively high dosages in cement and water generate in these

  Concrete hydraulic shrinkage to which is added thermal shrinkage.

  The mechanical stresses are such that the fibers fail to control them. As a result, the phenomena of shrinkage of the concrete lead to a significantly greater cracking than in paving, having an unacceptable degree of opening generally exceeding 1 mm of opening. Thus it is necessary to practice joints in these pavements in pervibrated fiber concrete in order to localize the effects of shrinkage and reduce the crack openings, which makes lose the economic advantages of a continuous and brakes pavement.

  considerably the development of fiber concrete in pavement.

  To produce a durable pavement in seamless poured concrete, a process is known, known as the continuous reinforced concrete (BAC) process, in which steel bars, generally 16 mm in diameter, are connected to each other continuously. along the entire length of the roadway. Once the steel bars are laid, the concrete is applied, usually using a sliding formwork machine. Continuous reinforced concrete remains a heavy technique to implement

work and expensive.

  Due to the advantages brought by compact rolled concretes compared to traditional poured, pervibred or extruded concretes, various compact concretes reinforced with fibers have been proposed in which the composition has been suitably adapted and the fibers selected in order to obtain a pavement or continuous industrial concrete area where cracking is regularly distributed and

limited opening hours.

  The results of a comparative study of the cracks observed on parts of the roadway carried out on the one hand with a compact concrete reinforced with fibers "Twincone" with total anchorage, and on the other hand with a compact concrete reinforced with wavy fibers, in comparison with continuous reinforced concrete, are presented in the following table I:

TABLE I

  Reinforced concrete Compacted concrete with Continuous compacted concrete Corrugated fibers Twincone fibers Number of cracks over a length of 60 11 15 linear meters Average space between 20 15 cracks (m) Average opening 1 2.5 1 of cracks (mm) Total crack openings over a length of 200 60 27.5 15 linear meters (mm) Continuous reinforced concrete, which is the benchmark for continuous concrete without joints, presents a fine and close cracking. With compacted concrete reinforced with corrugated fibers, the cracks are spaced but wide. When "Twincone" fibers are used, the sum of the crack openings is 30% lower than that observed in the case of wavy fibers. In view of this study, it appears that the behavior of concrete reinforced with fibers with total anchoring is similar to that of continuous reinforced concrete, this fiber

  allowing a more efficient anchoring than that of corrugated fiber.

  Within the framework of the study which is the subject of table 1, the tests have shown that the evolution of cracks in compacted rolled concrete reinforced with i5 fibers "Twincone" is equivalent to that of cracks in continuous reinforced concrete. Furthermore, FIG. 1 of the appended drawings illustrates the results of a comparative pull-out test (“Pull-out test”) of a “Twincone” fiber A with total anchorage and of a fiber with deformable anchorage B, the two fibers with an identical diameter of 1 mm. When looking at this graph, it turns out that the use of fully anchored fibers is

  necessary for the realization of continuous pavements without joints, these

  to better limit cracks.

  Thus, patent application FR 2 684 397 defines a concrete composition for producing seamless pavements, having a determined composition which includes fibers with non-deformable anchoring such as those described in the patent applications

European EP 130 191 and EP 098 825.

  With this in mind, in order to improve the anchoring of cylindrical fibers with so-called first generation hooks used in poured concrete, the hooks of said fibers have been flattened. Such fibers are sold in particular under the brand "Dramix FL 45/50" and

  are the subject of patent application WO 97/11239.

  Thus the current trend is to use fibers with total anchorage or with very strong anchorage for the production of continuous lo pavements without joints, fibers with weak anchorage such as corrugated or hook fibers being used only in concrete compositions. perverted for the production of industrial pavements or

sprayed concrete.

  The purpose of the present invention and to provide a composition of rolled compacted concrete reinforced with fibers making it possible to limit the presence of cracks while ensuring control of

the opening of the cracks.

  This object is achieved by the fact that the composition of compacted rolled concrete reinforced with fibers according to the invention, comprising aggregates, a hydraulic binder and metallic fibers, is characterized in that the metallic fibers consist of substantially cylindrical wires comprising a substantially rectilinear longitudinal central part extending on each side by means of an intermediate portion of a curved end part whose shape is of the type which prohibits the attachment of two neighboring fibers, said wires having - a diameter between 0.38 and 1.05 mm, - a total length between 19 and 80 mm, - a length of the end parts between 1.5 and 4 mm, - a transverse offset between the central part and each part of at least 0.75 mm, - an obtuse angle (ca, ac ') less than or equal to 160 between each intermediate portion and the central part, - an obtuse angle between each portion interlayer and end part, and, a minimum tensile strength of 900 N / mm2, and said composition comprising a content of hydraulic binder between 180 and 400 kg per cubic meter of concrete, a water content between 90 and 150 liters per cubic meter of concrete, and a dosage of metallic fibers between 25 and 60 kg per cubic meter

of concrete.

  Unexpectedly, the fibers which have been selected in the present invention to be inserted into a composition of compacted rolled concrete, have led to better results in terms of limitation and control of cracking. The use of fibers as defined above, having curved end portions, substantially cylindrical over the entire length, in a composition of compacted rolled concrete, allows, surprisingly, to obtain a fair balance between the limitation of the number of cracks and limitation of

  the opening of the cracks present.

  Fibers with total or very strong anchoring have a

  strong anchoring resistance up to a crack opening of 1 mm.

  However, if the crack opens further, there is a break in the fibers and a very rapid drop in the sewing effect of the edges of the crack. Up to a crack opening of 1 mm, the fiber according to the invention provides a strong anchoring effect, practically equivalent to that of the fiber with total anchoring. On the other hand, the performance of the anchoring is kept at much larger crack openings of up to 3 to 4 millimeters. The composition according to the invention has a much more secure ductility plateau than the breaking effect observed beyond I mm with a fiber with total anchoring, for example in the case of localized subsidence of the platform. the pavement and

  a crack opening which could exceed 2 mm.

  Advantageously, the threads constituting the fibers have a diameter between 0.65 and 0.85 mm and a total length / diameter ratio between 65 and 85. In particular, the fibers have a total length / diameter ratio of the order of 80. According to a particular feature, each curved end part is formed of a rectilinear part connected to the central part by said inclined part.

comprising at least two elbows.

  Advantageously, the fibers used in the present invention are fibers of 0.75 mm in diameter, with a total length of 60 mm and with a tensile strength of at least 1100 N / mm2. This fiber also has the advantage, with an equal dosage by weight in concrete, of a number of fibers double that of the number of fibers of diameter of 1 mm traditionally used. Due to a hardening pushed further to the wire drawing, the thinner wire moreover has a 1o higher elastic limit which makes it more efficient than a wire of 1 mm

of diameter.

  The cracking observed in concretes obtained from the composition according to the invention remained limited to values between 0.3 and I mmn. With such a crack limitation, it follows that the aggregates of the concrete forming the irregular surface of the walls of the crack remain embedded between them and held in position, the embedding effect being ensured by the fibers anchored in the matrix of the concrete. on either side of the crack. This mutual locking of the aggregates with one another and of the fibers which ensures a "seam" of the edges of the crack means that the crack thus controlled does not significantly weaken the overall structure of the pavement. The crack is not active, in the sense that it does not evolve under the constraints of heavy traffic during the service life of the roadway. Furthermore, the edges of the crack remaining mechanically embedded by the intergranular contacts between the constituents of the concrete, the fibers are consequently less stressed.

  in fatigue, which ensures good durability of the pavement.

  Furthermore, in the case where the opening of the cracks remains less than 1 mm, it has been shown that the water possibly loaded with de-icing salt does not penetrate into such a crack even if it opens on the surface. Risks of corrosion of fibers in the crack

are thus limited.

  The aggregates used comprise from 70 to 100% of crushed materials, having sharp angles and a shape close to the square, and a particle size between 0 and 14 mm so as to avoid the phenomena of segregation, that is to say of separation of large elements. The concrete composition also preferably comprises a plasticizing aid which facilitates compaction by intergranular lubrication and makes it possible to obtain a density in the region of 2400 kg / m3 of concrete with favorable consequences, such as higher strength and the possibility of reducing the dosing with hydraulic binder s The optimal water content is determined by the test

  Modified Proctor and varies between 4 and 6% of the dry constituents of concrete.

  Advantageously, the composition comprises a content of hydraulic binder in the region of 250 to 300 kg per cubic meter of concrete, a water content of 4 to 6% of the weight of the dry constituents of the concrete, ie to approximately 100 to 150 liters of water per meter. concrete cube, a dosage of metallic fibers between 25 and 50 kg, preferably between 30 and kg, per cubic meter of concrete. For example, the composition includes 280 kg of hydraulic binder and 110 liters of water per meter

concrete cube.

  Advantageously, the composition also comprises a plasticizer content varying between 0.3 and 1.8% of the weight of the hydraulic binder. The concrete composition according to the invention can be used for making or reinforcing road structures or industrial areas having to support high rolling loads, such as those produced by frequent passage of trucks, vehicles

  heavy or large aircraft for example.

  The composition according to the invention allows a layer of concrete having a continuously variable flexural strength over an extended crack opening range, for example from 0 to 4 mm, and without breaking the fibers. According to one characteristic, the variation in resistance over said range is less than 20% less than

its nominal value.

  The processing of the material according to the invention is carried out by means of a heavy table finisher, which is a material generally used for processing bituminous materials, or by means of a grader. The concrete is then densified by a compactor of several tonnes comprising one or two vibrating rollers. This compaction can then be followed by a kneading effect provided by the action of a tire compactor applying for example

  a load of 3 to 5 tonnes per wheel.

  The fiber-reinforced compacted concrete can then be directly covered with a bituminous wearing course, the cure for

  concrete can be made by an emulsion of gravel bitumen.

  A pavement consisting of a concrete base layer according to the invention, then covered with a bituminous wearing course has the advantage of a separation of functions, the cement concrete ensuring a long service life for the structure under heavy traffic, and the bituminous mix making it possible to obtain a carpet having high specific qualities, for example a draining mix which absorbs rainwater and / or an acoustic mix which limits the rolling noise. The concrete layer can also be covered with a highly proportioned micro-concrete in cement, made up of a mixture of three components, namely cement, a fillerized sand (comprising a significant part of fine elements), and a sand containing little fine, fillerized sand comprising at least

  minus 10 to 20% of fine elements less than 0.080 mm.

  Beyond its application for producing continuous new pavements without joints with very good durability conditions, the rolled compacted concrete reinforced with fibers according to the invention can be used in reinforcing pavements. Simultaneously with reinforcement, this process can also resolve the problem of rutting of bituminous pavements by adding a thin layer of 5 to 18 cm,

  covered with a thin or very thin bituminous mix.

  The invention will be better understood, and other objects, details, characteristics and advantages will become more clearly apparent during the course of the invention.

  detailed explanatory description which follows of an embodiment

  currently preferred particular of the invention, with reference to the drawing

diagram attached.

  In this drawing - FIG. I is a diagram illustrating the prior art and representing the results of pull-out tests of a fiber with total anchorage and a fiber with deformable anchorage; - Figure 2 is a partial schematic side view of a fiber usable in a composition according to the invention; and FIG. 3 is a diagram illustrating bending tests of several prisms obtained from a composition according to

  the invention in comparison with compositions according to the prior art.

  According to FIG. 2, the composition according to the invention comprises metallic fibers constituted by wires 10 provided with curved end portions 12. The wires are substantially cylindrical over their entire length L and comprise a central portion 11 substantially rectilinear extending from each side by an inclined intermediate portion 13 which is extended by said end portion 12. Each portion 12 is formed of a straight portion connected to the central portion 1 1 by said inclined intermediate portion 13 comprising at least two elbows. The wires have a diameter d l0 between 0.38 and 1.05 mm, a total length L between

  19 and 80 mm, and a minimum tensile strength of 900 N / mm2.

  The two end portions 12 of a wire can have a different or similar shape. The length e, t ′ of the rectilinear parts of the end parts 12 can be different or similar and is between 1.5 and 4 mm. The inclined portion 13 of each end part forms with the rectilinear central part 11 an angle oc or at an obtuse angle equal to or greater than 160. The two angles ca, a 'thus defined can be identical or different. One of the intermediate portions of an end portion is not necessarily in the plane formed by the other intermediate portion and the central portion 11. Furthermore, each end portion is not necessarily in the plane constituted by its intermediate part and the central part. The transverse offsets h, h 'between the central part 11 1l and each end part

  may be the same or different and are at least 0.75 mm.

  In the example described here, the composition according to the invention comprises fibers sold under the brand "Dramix 80/60". The "Dramix 80/60" fiber is a fiber which is characterized by a total length L of 60 mm for a diameter d of 0.75 mm, ie an X ratio of 80, and a tensile strength of at least 1100 N / mm2. The two angles cc Oa 'are substantially identical and the intermediate portions, the end portions and the central portion 11 are substantially in the same plane. Different compositions were carried out according to Table II, compositions 1, 2 and 4 differ from each other only by the nature of the fibers that they contain. Composition 1 comprises “Twincone” fibers of the fully anchored type, composition 2 comprises “Dramix FL 45/50” fibers of flattened hook ends and

  composition 4 according to the invention comprises "Dramix 80/60" fibers.

  In these three compositions, the fibers are dosed at 30 kg / m3. Composition 3 includes "Dramix FL 45/50" fibers such as

  composition 2 but these are dosed at 35 kg / m3.

TABLE II

  Composition I Composition 2 Composition 3 Composition 4 Fiber "Twincone" Fiber "Dramix Fiber" DRAMIX Fiber "Dramix

FL 45/50 "FL 45/50" 80/60 "

  Gravel 5/15 1103 1103 1103 1103 Sand 0/5 735 735 735 735 rCiment (*) 400 400 400 400 Total water 160 160 160 160 e Superplasticizer 6 6 6 6 Fibers 30 30 35 30 W / C ratio

0.4 0.4 0.4 0.4

  (water / cement) (*) cement CPA-CEM I 52.5R The formulation of the compositions was defined so as to satisfy a criterion of resistance to compression of the order of 50 to MPa, while respecting the spindle of particle size in force for roller compacted concrete (NF P 98128). The compressive strength measured on cylinders of dimension 16x32 cm,

  in accordance with the standard in force, is given in table III.

  The tests were carried out on three cylinders for each composition 1 to 4.

TABLE III

  Cylinder i Cylinder 2 Cylinder 3 medium Composition 1 50 MPa 54 MPa 50 MPa 51.3 MPa Composition 2 52 MPa 52 MPa 52 MPa 52.3 MPa Composition 3 61 MPa 59 MPa 57 MPa 59.0 MPa Composition 4 58 MPa 57 MPa 52 MPa 55.7 MPa I To characterize the contribution of the fibers in terms of the capacity to maintain a residual charge during a mechanism of cracking of the material, tests in bending on a prism were carried out. Prisms have been tested in circular bending. Given the size of the fibers, large prisms were chosen, with a length of 70 cm, a height of 20 cm and a width of 15 cm. The distance between the support points during bending was 60 cm and the distance between the points of application of the load 20 cm. Each prism was previously notched in central 0o section in order to locate the crack. A sensor bridged this notch and made it possible to pilot the tests directly on the opening of the crack. FIG. 3 shows the results of the comparative bending tests carried out to assess the performance of the different fibers in controlling

cracking of concrete.

  Curves 1 to 4 correspond respectively to compositions 1 to 4 defined above. The crack appears under a load level of around 25 kN for the

different compositions.

  The prism obtained with composition 1 comprising “Twincone” fibers has a pressure drop after the appearance of the crack up to approximately 0.2 mm of opening, then the fibers allow a resumption of effort. From a millimeter of crack in bending, corresponding to the maximum bearing capacity, the fibers begin to break, which results in successive jumps of load and a

  very rapid decrease in the bearing capacity of the prism.

  The prism of composition 4 according to the invention exhibits a slight pressure drop at the appearance of the crack and then a resumption of effort. The maximum bearing capacity is obtained for a crack opening between 1 and 1.5 mm. Bearing capacity decreases

then very gradually.

  For composition 2 comprising "Dramix FL / 50" fibers dosed at 30 kg, the prism displays a very large pressure drop (of the order of 50%) after the appearance of the crack. Beyond a certain crack opening of the order of 1.8 mm, load jumps are visible on the curve. These jumps reflect breaks in

  fibers as in the case of composition 1.

  For composition 3, comprising "Dramix FL / 50" fibers dosed at 35 kg, the results are similar to those obtained with composition 2, only the increase in the dosage of fibers allows a

higher load capacity.

  The capacity to recover from stress after cracking is substantially of the same order of magnitude for compositions 1, 3 and 4. The fibers have substantially the same potential with regard to cracking for openings restricted to 1 mm. Beyond this, the intrinsic behavior of the fibers, leading to a break or a tearing out, modifies the behavior of a cracked section. The fully anchored fiber shows the strongest strength of the anchor up to a crack opening of 1 mm. However, if the crack opens further, there is a break in the fibers and a very rapid drop in the sewing effect of the edges of the crack. Up to a crack opening of 1 mm, the fiber according to the invention shows a slightly lower anchoring resistance, of the order of 7%, than that obtained with a fiber with total anchoring. On the other hand, the performance of the anchoring is preserved at much larger crack openings ranging from 3 to 4 millimeters, which is not the case when using

  fully anchored fibers or other fibers.

  Although the invention has been described in connection with a particular embodiment, it is obvious that it is in no way limited thereto and that it includes all the technical equivalents of the means described as well as their combinations if these come under

the invention.

Claims (10)

  1. Composition of compacted rolled concrete reinforced with fibers, comprising aggregates, a hydraulic binder and metallic fibers, characterized in that the metallic fibers consist of substantially cylindrical wires (10) comprising a substantially rectilinear longitudinal central part (11) extending on each side by means of an intermediate portion (13) of a curved end portion (12) whose shape is of the type which prohibits the attachment of two neighboring fibers, said wires having - a diameter (d) between 0.38 and 1.05 mm, - a total length between 19 and 80 mm, - a length (e, e ') of the end portions between 1.5 and 4 mm, - a transverse offset (h, h ') between the central part and each end part of at least 0.75 mm, - an obtuse angle (ct, o') less than or equal to 160 between each intermediate portion and the central part , - an obtuse angle between each intermediate portion and p end piece, and a minimum tensile strength of 900 N / mm2, and said composition comprising a content of hydraulic binder of between 180 and 400 kg per cubic meter of concrete, a water content of between 90 and 150 liters per cubic meter of concrete, and a dosage of metallic fibers between 25 and 60 kg per cubic meter of concrete.   2. Composition according to claim 1, characterized in that the threads (10) constituting the fibers have a diameter (d) of between 0.65 and 0.85 mm and a ratio (X) total length / diameter (L / d ) between 65 and 85.   3. Composition according to claim 2, characterized in that the fibers have a ratio (X) total length / diameter of the order of 80. 4. Composition according to claim 3, characterized in that the wires have a total length of 60 mm, a diameter of the order   0.75 mm and a minimum tensile strength of 1100 N / mm2.   5. Composition according to one of claims 1 to 4,   characterized in that each curved end part (12) is formed by a rectilinear part connected to the central part (11) by said   intermediate part (13) comprising at least two elbows.   6. Composition according to one of claims 1 to 5,   characterized in that it comprises a content of hydraulic binder of between 250 and 300 kg per cubic meter of concrete, a water content of 4 to 6% of the weight of the dry constituents of the concrete, ie approximately 150 liters of water per cubic meter of concrete, a dosage of fibers   1o metallic between 25 and 50 kg per cubic meter of concrete.   7. Composition according to one of claims 1 to 6,   characterized in that it comprises a plasticizer content of 0.3 to   1.8% by weight of the hydraulic binder.   8. A method of producing continuous pavements or industrial areas without joints, characterized in that it comprises a step of producing a layer of compacted rolled concrete reinforced with fibers to   starting from the composition according to one of the preceding claims, from   so as to obtain a layer of concrete having a continuously variable flexural strength over a range of crack openings   extended, for example from 0 to 4 mm, and without breaking the fibers.   9. Method according to claim 8, characterized in that the variation in resistance over said range is less than less   % compared to its nominal value.   10. The method of claim 8 or 9, characterized in that said concrete layer is covered with a bituminous wearing course or a microbeton made of a mixture of three components, namely cement, fillerized sand comprising at least 10 to% of fine elements less than 0.080 mm and sand containing few fines. 1l. A method according to claim 8 or 9, characterized in that said step consists in producing said layer of compacted rolled concrete reinforced with fibers with a thickness of 5 to 18 cm for the   reinforcement of bituminous pavements or anti-rutting treatment.