FR2842553A1 - CONCRETE PIECE IN PARTICULAR TUNNEL VESSEL COMPRISING A MAIN CONCRETE LAYER AND A SECONDARY LAYER IN REFRACTORY MORTAR - Google Patents

Abstract

The invention relates to a concrete part, in particular a tunnel segment comprising a main layer of concrete (4) and a secondary layer (5) of refractory mortar ensuring both additional mechanical strength and fire protection. refractory mortar has a mechanical resistance at 28 days greater than 25 Mpa, a thermal conductivity less than 1 W / .m. ° K at 20 ° C and a resistance to very high temperatures up to 1300 ° C, for 2 hours.

Description

i The invention relates to a precast concrete part comprising a

  main layer of reinforced, prestressed or fiber-reinforced concrete and a secondary layer of refractory mortar ensuring both additional mechanical resistance and fire protection, as well as a method for producing such a part. The invention finds in particular, but not exclusively, an application in the segments of tunnels having to withstand very high temperatures,

especially during a fire.

  We already know refractory mortars capable of withstanding very high temperatures. We know on the one hand refractory mortars intended to be projected on a

  existing civil engineering structure, initially devoid of a protective layer.

  The mortar thus forms a refractory protective layer adhering to the walls of said structure, for example the walls of a segment of a tunnel of

  traffic (cars, trucks, trains).

  These projected refractory mortars generally have low mechanical resistance, the pre-existing structure having the required mechanical resistance. This results in a degradation of the protective layer as a result in particular of

  mechanical shocks caused by vehicles in circulation in the tunnel.

  In addition, these mortars do not resist handling, which makes them unsuitable for their integration from the start of the cycle of the manufacturing process of tunnel segments, carried out off site. Such mortars therefore do not allow the production of segments comprising a structural layer and a protective layer assembled together before the placement of the segment in the

tunnel.

  We also know refractory mortars intended to be put in place from the manufacturing process of segments, so as to produce segments comprising a main layer and a protective layer assembled one

  to the other before the installation of the segment in the tunnel.

  Document WO 99/28596 describes such a refractory mortar, cast or sprayed into a mold so as to form a protective layer. After a certain drying time, but before complete hardening, a main layer is put in place in contact with the protective layer, so as to obtain a

  good adhesion between the two layers.

  The mortar described in document WO 99/28596 comprises numerous cavities, for example obtained by the addition of polystyrene, which gives said mortar good insulating properties. However, the presence of these cavities leads to obtaining a mortar of low mechanical strength. Therefore, the mortar has the aforementioned drawbacks (risk of damage during

handling or in service).

  In addition, in the case of application to segments, the main layer alone provides the mechanical strength of the segment. Thus, it is not possible to reduce the thickness of the main layer. As a result, the total thickness of the segment comprising the protective layer is greater than the thickness of the segments without such a layer. It follows a decrease

  useful diameter of the tunnel, which is not desirable.

  The invention provides a solution to these problems.

  Its object is a precast concrete part comprising a main layer of reinforced, prestressed or fiber-reinforced concrete and a secondary layer of refractory mortar ensuring both additional mechanical strength and

fire protection.

  According to one aspect of the invention, the concrete part is a precast concrete segment, intended to be placed in the excavation of a tunnel, a first face of the main layer being intended to be placed against the interior wall. of the tunnel, and the secondary layer being joined to the main layer at a second face of said main layer, opposite

to said first side.

  The invention also relates to a method for producing a precast concrete part. According to an important characteristic according to the invention, the method comprises the following steps: a) producing a main layer of reinforced, prestressed, or fiber-reinforced concrete in a mold; b) after hardening, release the main layer; and c) applying a secondary layer of refractory mortar on one of the

faces of the main layer.

  Preferably, the method further comprises the step of assembling the main and secondary layers using connection keys and mechanical fasteners. The invention also relates to a mortar comprising at least: - a refractory cement; - artificial aggregates of selected particle size and density; - some water; the proportions of the components of the mortar being chosen so that said mortar has a mechanical resistance at 28 days greater than 25 Mpa, a thermal conductivity less than 1 W / m.K at 200C, and a resistance

  at very high temperatures up to 1,300 ° C, for 2 hours.

  Thus, refractory cement confers the function of stability at very high temperatures while the aggregates of selected particle size and density

  confer the function of mechanical resistance and thermal insulation.

  In practice, cement belongs to the group formed by fused aluminous cements. Preferably, the aggregates are mineral expanded aggregates. For example, they belong to the group formed by clays, shales, slag. According to another important characteristic, the mortar also comprises fusible fibers with a diameter of a few micrometers and / or having a length

of the order of 12 mm.

  Other characteristics and advantages of the invention will become apparent in the light of

  the following description, description made with reference to the appended figures

  in which: - Figure 1 is a longitudinal sectional view of a tunnel segment, comprising a structured layer and a protective layer made from a mortar according to the invention - Figure 2 shows the bottom of a mold capable of producing the structural layer of the segment of FIG. 1, said bottom being seen from inside the mold; - Figures 3 to 5 schematically represent the different stages of

  realization of the segment of figure 1.

  We now describe a tunnel segment according to the invention, as well as a method

  for manufacturing such a segment, with reference to FIGS. 1 to 5.

  A tunnel segment 1, as illustrated in FIG. 1, is shown in section

  longitudinal, substantially the shape of a ring portion.

  The segment 1 thus comprises two faces having a profile in the form of a portion of cylinder, namely a face intended to be placed against the excavation of a tunnel, called upper surface 2, and a face opposite to the upper surface 2, called lower surface 3, intended to be located opposite the axis of the tunnel, and to be visible from

inside the tunnel.

  The segment 1 comprises: a first layer 4 extending from the upper surface 2 towards the lower surface 3, over a thickness of the order of 40 cm to 50 cm, representing approximately 80 to 90% of the total thickness of the segment 1; a second layer 5 extending from the face 6 of the first layer 4 opposite the upper surface 2, towards the lower surface 3, over a thickness of the order of 5 to cm. The first layer 4, or main layer, is made of a concrete traditionally used to manufacture tunnel segments, and ensures in

  much of the mechanical strength of the segment 1.

  The second layer 5, or secondary layer, is produced with a refractory mortar which will be described in more detail below. This secondary layer 5 is intended to protect the main layer 4 against increases

  temperature, especially in the event of fire.

  The method of producing the segment 1 will now be described.

  Firstly (FIG. 3), the main layer 4 is produced by pouring the concrete 8 intended to constitute said main layer 4 into a mold 7.

  concrete 8 is of the reinforced, prestressed or fiber-reinforced concrete type.

  The mold 7, shown in Figures 2 and 3, has a bottom 9 in the form of a cylinder portion, on which are fixed reservations 10 having

  each the general shape of a square-based pyramid trunk.

  The shape of the reservations 10 is designed so as not to hinder the flow of the concrete 8 and to avoid the existence of inaccessible zones leading to poor distribution of the concrete at the bottom 9 of the mold 7. In the embodiment

  shown, the reservations 10 are distributed along a checkerboard pattern.

  The reservations 10 make it possible to promote the assembly of the main 4 and secondary 5 layers, in particular by increasing the contact surface and by the truncated pyramid shape of said reservations 10, which ensures mechanical maintenance of the secondary layer 5. This is made possible without the need to provide a mold 7 whose bottom 9 has

a complex and elaborate form.

  The mold also includes lateral reservations 11 making it possible to provide a space not filled with concrete 8, in order to allow the passage of rods and bolts ensuring the reciprocal fixing of two neighboring segments 1 in

a tunnel.

  Threaded rods 12 are fixed at some of the reservations 10 in the bottom 9 of the mold 7, and extend inside the mold 7, substantially perpendicular to the bottom 9 of said mold 7, over a height less than

  the thickness of the structural layer 4.

  The rods 12 are fixed so as not to protrude from the bottom 9 of the mold 7.

  Therefore, when the main layer 4 is hardened and stripped, the storage and handling of said main layer 4 is not hindered by the rods 12, these being housed in the spaces 13 provided by the

reservations 1 0.

  In a second step (FIG. 4), once the main layer 4 has been poured onto the desired thickness and hardened, said main layer 4 is stripped and then turned over, so as to place the spaces 13 provided by the reservations 10

  on the upper part of the main layer 4.

  Attachment means, such as bolts 14, are fixed to the ends of the rods 12 located in the spaces 13, so as to protrude above

the main layer 4.

  Finally, in a third step (FIG. 5), the secondary layer 5 is put in place, by pouring or spraying for example, of the refractory mortar 15 on the

main layer 4 already hardened.

  Thus, a segment 1 is obtained comprising a main layer 4 made of conventional segment concrete, and a secondary layer 5 produced with the

  refractory mortar according to the invention.

  The bottom 9 of the mold 7 has led to the formation of the face 6 of the main layer 4, opposite the upper surface 2, and playing the role of interface with the secondary layer 5. The adhesion of the layers to the other is by gluing and

by roughness.

  The manufacture of the main layer 4 can be carried out in a continuous cycle, the secondary layer 5 being in turn carried out out of cycle, so as not to

  hinder the production chain.

  A reinforcement cage (not shown) can also be installed in

  the main layer 4, before solidification thereof.

  The secondary layer 5 aims on the one hand to protect the main layer 4 from temperature increases, in order to allow the main layer 4 to maintain its integrity and its mechanical properties, without degradation due to the

temperature.

  On the other hand, the secondary layer 5 also plays a structural role, because of its relatively high mechanical strength. Since the secondary layer 5 contributes to the mechanical strength of the segment 1, the thickness of the segment 1 can be very close to the thickness of the conventional monolayer segments, and not increased by the thickness of the secondary layer 5. This

  is particularly advantageous in the application to the field of tunnels.

  The secondary layer 5 also allows the coating of the rods 12, and

the possible reinforcement cage.

  In addition, the refractory secondary layer 5 according to the invention constituting a product resistant to handling, it can be put in place at the time of manufacture.

segment 1.

  The covering of a secondary layer 5 with a thickness of the order of cm makes it possible to protect the main layer of the tunnel segments in the case of the application of a hydrocarbon type fire modified at 1300 ° C. for 2 hours. During a fire, the secondary layer prevents any surface chipping, thus protecting the rescue teams. In addition, the secondary layer protects the main layer by maintaining the following temperatures: - from 250 to 380 ° C. at the interface 6 between the two layers 4, 5 (depending on the thicknesses of the layers);

  - from 110 to 25,000 in the main layer, 25 mm from interface 6.

  The secondary layer according to the invention has a compressive strength making it possible to meet the following conditions: possibility of formwork stripping at 6 o'clock, which corresponds to a compressive strength of the order of 15 MPa .; - limitation of spalling during handling and storage on the holds, which corresponds to a resistance of the order of 10 MPa; - characteristic resistance at 28 days of 25 MPa (by comparison, this value is of the order of 40 to 50 MPa on a cylinder for structural concrete); - need to resist the stresses generated by deformations due to

  possible ovalization of the tunnel ring.

  The main 4 and secondary 5 layers are assembled with a certain adhesion, so as to comply with the following conditions: - possibility of applying a handling suction cup (corresponding to a resistance of the order of 0.2 MPa); - solidarity maintained between the two layers during the fire; - satisfactory adhesion during the service life of the structure,

over 30 years.

  The shrinkage value of the secondary layer is of the same order of magnitude as that of a structural concrete of type B50 (concrete having a mechanical resistance of 50 MPa), namely from 200 to 400 pm / m, in order to avoid a separation between the two layers or a propagation of cracks in the

  refractory mortar decreasing its effectiveness as a coating concrete.

  The secondary layer also checks durability parameters making it possible to justify a coating function, namely gas permeability with an order of magnitude of 10-16 m2 to 10-17 m2 for ordinary concrete B25 and water permeability with an order of magnitude from 10-10 m / s to 10-11 m / s for a

ordinary concrete type B25.

  Finally, the secondary layer has a hard and smooth surface appearance allowing the possible application of a paint and a jet cleaning under

  low pressure or with a broom during operation of the structure.

  The invention also lies in the choice and association of components forming a refractory mortar resistant to very high temperatures and having good mechanical strength in order to obtain a refractory secondary layer 5 capable of being assembled with the main layer 4 and protect the latter from a modified hydrocarbon fire at 13000C for 2

hours.

  According to the invention, the mortar comprises at least one refractory cement, artificial aggregates of selected particle size and density, water, and the case

adjuvants.

  The refractory cement comprises for example an aluminous molten cement sold under the reference "LAFARGE molten cement" by the company LAFARGE. Such refractory cement has a pyroscopic resistance of the order of 1270 to 12900C

  on pure dough. The density of the cement is in the range of 3.2 to 3.3 t / m3.

  Unlike conventional cements, refractory cement does not disintegrate

  not when subjected to very high temperatures.

  The first light aggregates have a particle size of the order of 0 to 4 mm.

  For example, the light aggregates are those sold by the company GEM (Aggregates Expanses de la Mayenne) under the reference "GRANULEX 0/4". These are cellular aggregates made from expanded shales at 11300C, with an apparent wet bulk density of the order of 1 t / rM3, s with an actual density of 1.8 to 1.78 t / m3 and whose water absorption coefficient is around 4.2 to 4.7%. The 0/4 mm fraction can be

  chosen relatively consistently.

  According to a possible variant, the light aggregates are based on a slag or

clay.

  Second gravel-type aggregates complete the composition of the mortar. These second aggregates have a higher particle size than that

  first light aggregates, for example of the order of 4 to 8 mm.

  For example, the second aggregates are "GRANULEX 4/8" sold by the company GEM, whose apparent bulk wet density is around 0.8 t / m3, whose actual density is 1.50 at 1.33 t / m3 and

  whose water absorption coefficient is around 5.7 to 8.1%.

  The first and second aggregates lighten the mortar, and give it good resistance to temperature. At very high temperatures,

  for example at 11 50C, the light aggregates become pasty.

  According to a possible variant, the second aggregates are based on a slag or clay. The fact of using aggregates of different particle sizes makes it possible to obtain a mortar as continuous as possible, having good compactness and therefore good resistance. It is not necessary to have aggregates of the same kind. Thus, the first aggregates can be based on expanded shales

  while the second aggregates may include a slag.

  In addition, the mortar does not include any admixture or plastic material capable of giving off harmful vapors during an increase in temperature. According to a possible embodiment, the refractory mortar composition according to the invention can also comprise fusible fibers, for example fibers

  polypropylene or polyolefin.

  For example, the fusible fibers are those sold by the company PIERI under

the FIBERMIX appellation.

  These fibers have the function of melting at a certain determined temperature, for example at 2000C, thus creating channels in the protective layer produced from the refractory mortar, so as to allow the evacuation of the

  water vapor and to avoid flaking of said layer under the effect of pressure.

  For example, the length of the fibers is of the order of 12 mm, and / or their diameter of the order of a few micrometers. The dosage is around 2 kg per m3 of mortar. The fibers are present in a very small amount (of the order of 0.1% in

  weight), and play no structural role.

  By way of example, the applicant has produced a protective layer based on refractory mortar according to the invention, with the following formula: cement: 520 kg / m3, - polypropylene fibers: 2 kg / m3, - GRANULEX light aggregate 0/4: 460 kg / m3, - GRANULEX 4/8 aggregate: 550 kg / m3,

- total water: 240 to 255 kg / m3.

  Fresh mortar thus has a density of the order of 1.8 t / m3 (compared to 2.4 t / m3 for structural concrete and 1 t / m3 for mortar

known refractories).

  The refractory mortar has a thermal conductivity less than 1W / .m.0K

  at 20'C (against 1.40 W / .m.0K for structural concrete).

  In practice, the manufacture of the mortar comprises the following stages: - the two aggregates and the polypropylene fibers are introduced; - a one minute mixing is produced; - we introduce the cement then the water;

  - it is mixed in a complementary manner for two minutes.

  The total time for making a batch is around four minutes

  in an automated concrete plant.

  The refractory mortar according to the invention (hardened) has the following characteristics: Average resistance to compression at 28 days 30 to 40 MPa Average resistance to compression 20 to 25 MPa (without baking) at 5 hours Average resistance to splitting at 28 days 3 MPa Young's 28-day module 21,000 MPa Adhesion to traditional concrete type B40 1,5 to 2,5 MPa (interposed wire mesh) 1,0 to 1,5 MPa Plastic removal at 24 hours 473 pm / m After removal taken at 28 days 297 pm / m Oxygen permeability 2.84 10- 'm2 Water permeability 4.3 10 _11 m / s Specific heat at 50' C 878 J / kg.0K Thermal conductivity 0.82 W /. m.0K at 20C Thermal conductivity 0.77 W / .m.0K at 2000C Thermal conductivity 0.38 W / .m.0K at 1250'C The mortar forming a secondary layer is here a compromise between insulation

  thermal and mechanical resistance.

  The mechanical resistance of the secondary layer produced from the mortar is of the order of 30 to 35 MPa. Thus, on the one hand, during manufacture, the handling and cleaning steps can be carried out without risking damaging the layer. On the other hand, in service, the secondary layer is strong enough to, for example, not be easily damaged by cars driving nearby. This mechanical resistance is fairly close to a resistance of a supporting structure of the order of 50 MPa

  for a classic concrete segment.

  The mortar according to the invention could practically be used for the production of load-bearing structures, independently of the cost issues. Conversely, some known refractory mortars lead to obtaining structures

  having a mechanical resistance of less than 5 MPa.

-6.2842553

Claims (9)

  1. Precast concrete part comprising a main layer (4) of reinforced, prestressed or fiber-reinforced concrete and a secondary layer (5) of refractory mortar ensuring both additional mechanical strength and a fire protection.   2. precast concrete part according to claim 1, constituting a segment intended to be placed in the excavation of a tunnel, characterized in that a first face (2) of the main layer (4) is intended to be placed against the inner wall of the tunnel, and in that the secondary layer (5) is assembled with the main layer (4) at a second face (6) of said main layer (4), opposite said first face (2).   3. Method for producing a precast concrete part according to claim 1 or claim 2, characterized in that it comprises the following steps: d) producing a main layer (4) of reinforced, prestressed, or fiber-reinforced concrete in a mold (7); e) after hardening, remove the main layer (4); and f) applying a secondary layer (5) of refractory mortar on one of the   faces (6) of the main layer (4).   4. Method according to claim 3, characterized in that it further comprises the step of assembling the main (4) and secondary (5) layers using   of connection keys and mechanical fixings.   5. Refractory mortar used in the process for producing a precast concrete part according to claim 3 or claim 4, characterized in that it comprises at least: - a refractory cement; - artificial aggregates of selected particle size and density; - some water; the proportions of the components of the mortar being chosen so that said mortar has a mechanical resistance at 28 days greater than 25 Mpa, a thermal conductivity less than 1 W / m.K at 200C, and a resistance   at very high temperatures up to 1300'C, for 2 hours.   6. Mortar according to claim 5, characterized in that the cement belongs   to the group formed by fused aluminous cements.   7. Mortar according to any one of claims 5 and 6, characterized in that   that the aggregates are mineral expanded aggregates.   8. Mortar according to any one of claims 5 to 7, characterized in that   that the aggregates belong to the group formed by clays, shales, dairy.   9. Mortar according to any one of claims 5 to 8, characterized in that   that it further comprises fusible fibers with a diameter of a few   micrometers and / or having a length of the order of 12 mm.