EP1382795A1 - Tunnel lining comprising a layer of refractory mortar - Google Patents

Abstract

The prefabricated tunnel arch (1) consists of a main layer (4) of strengthened, pre-stressed or fibre-reinforced concrete, and a secondary layer (5) of a refractory mortar that has a 28-day mechanical resistance of over 25 MPa, a thermal conductivity of below 1W/m.K at 20 deg C, and a resistance to temperatures as high as 1300 deg C for two hours. One face (2) of the main layer is designed to go against the inner wall of the tunnel, while the refractory mortar layer is fitted against the inner surface (6) of the main layer by threaded rods (12) and mechanical fixings. The refractory mortar can be made from an alumina cement containing granules of expanded minerals, clay, schist or slag.

Description

The invention relates to a precast concrete part comprising a layer main in reinforced, prestressed or fiber-reinforced concrete and a secondary layer in refractory mortar ensuring both additional mechanical strength and fire protection, as well as a method of making such a room.

The invention finds in particular, but not exclusively, an application in the tunnel segments having to withstand very high temperatures, especially during a fire.

We already know refractory mortars able to withstand 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 tunnel tunnel segment traffic (cars, trucks, trains).

These projected refractory mortars generally have a low resistance mechanical, the pre-existing structure having the required mechanical strength. he 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 withstand handling, which makes them unsuitable for their integration from the start of the manufacturing process cycle tunnel segments, produced off site. Such mortars therefore do not allow the production of segments comprising a layer of structure and a layer of protection assembled to each other before the installation of the segment in the tunnel.

We also know refractory mortars to be put in place from the manufacturing process of the segments, so as to produce segments comprising a main layer and a protective layer assembled together to the other before the installation of the segment in the tunnel.

Document WO 99/28596 describes such a refractory mortar, cast or sprayed in a mold so as to form a protective layer. After a certain drying time, but before complete hardening, a main layer is placement 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 includes many cavities, for example obtained by adding polystyrene, which gives said mortar with good insulating properties. However, the presence of these cavities leads to obtaining a mortar of low mechanical resistance. 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 ensures the mechanical strength of the segment. So it is not possible to reduce the thickness of the main layer. Therefore, the thickness total segment including 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 layer main in reinforced, prestressed or fiber-reinforced concrete and a secondary layer in refractory mortar ensuring both additional mechanical strength and fire protection, said mortar having resistance mechanical at 28 days greater than 25 MPa, thermal conductivity less than 1 W / m.K at 20 ° C, and resistance to very high temperatures up to 1300 ° C, for 2 hours.

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

The invention also relates to a method for producing a part made of precast concrete.

a) réaliser une couche principale en béton armé, précontraint, ou fibré dans un moule ;

b) après durcissement, décoffrer la couche principale ; et

c) appliquer une couche secondaire en mortier réfractaire sur l'une des faces de la couche principale.

According to an important characteristic according to the invention, the method comprises the following steps:

a) make a main layer of reinforced, prestressed or fiber-reinforced concrete in a mold;

b) after hardening, release the main layer; and

c) apply a secondary layer of refractory mortar on one of the faces of the main layer.

The method may further comprise the step of assembling the layers main and secondary using connection keys and mechanical fixings.

The invention also relates to a mortar comprising at least one cement refractory, artificial aggregates of selected particle size and density and of the water.

The proportions of the components of the mortar are chosen so that said mortar has a mechanical strength at 28 days greater than 25 MPa, thermal conductivity less than 1 W / m.K at 20 ° C, and resistance to very high temperatures up to 1300 ° C, for 2 hours.

Thus, refractory cement gives the stability function to very high temperatures while the aggregates of selected particle size and density confer the function of mechanical resistance and thermal insulation.

Cement belongs for example to the group formed by molten cements aluminous.

The aggregates are for example light aggregates, and can be expanded mineral aggregates. For example, they belong to the formed group by clays, shales, slag.

According to another characteristic, the mortar can also comprise fibers fuses with a diameter of a few micrometers and / or with a length of around 12 mm.

• la figure 1 est une vue en coupe longitudinale d'un voussoir de tunnel, comprenant une couche se structure et une couche de protection réalisée à partir d'un mortier selon l'invention ;
• la figure 2 représente le fond d'un moule apte à la réalisation de la couche de structure du voussoir de la figure 1, ledit fond étant vu depuis l'intérieur du moule ;
• les figures 3 à 5 représentent schématiquement les différentes étapes de réalisation du voussoir de la figure 1.

Other characteristics and advantages of the invention will appear in the light of the description which follows, 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;
• FIG. 2 represents 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;
• FIGS. 3 to 5 schematically represent the different stages of production of the segment of FIG. 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 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.

• une première couche 4 s'étendant depuis l'extrados 2 vers l'intrados 3, sur une épaisseur de l'ordre de 40 cm à 50 cm, représentant environ 80 à 90 % de l'épaisseur totale du voussoir 1 ;
• une deuxième couche 5 s'étendant depuis la face 6 de la première couche 4 opposée à l'extrados 2, vers l'intrados 3, sur une épaisseur de l'ordre de 3 à 10cm.

Segment 1 includes:

• 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 3 to 10 cm.

The first layer 4, or main layer, is made of concrete traditionally used to manufacture tunnel segments, and ensures much of the mechanical strength of the segment 1.

The second layer 5, or secondary layer, is made with a mortar refractory 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 (Figure 3), the main layer 4 is made by pouring in a mold 7 the concrete 8 intended to constitute said main layer 4. The 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 portion of cylinder, 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 impede the flow of the concrete 8 and avoid the existence of inaccessible areas leading to a poor distribution of the concrete at the bottom 9 of the mold 7. In the production shown, the reservations 10 are distributed along a checkerboard pattern.

Reservations 10 allow the layers to be assembled main 4 and secondary 5, in particular by increasing the area of contact and by the pyramid shape of said reservations 10, which ensures mechanical maintenance of the secondary layer 5. This is rendered possible without the need to provide a mold 7 whose bottom 9 has a complex and elaborate form.

The mold also has lateral reservations 11 allowing provide a space not filled with concrete 8, 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 of the bottom 9 of mold 7, and extend inside 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 the handling of said main layer 4 is not hindered by the rods 12, these being housed in the spaces 13 formed by the reservations 10.

Secondly (Figure 4), once the main layer 4 is poured onto the desired thickness and hardened, said main layer 4 is stripped and then returned, 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 attached to the ends rods 12 located in the spaces 13, so as to protrude above the main layer 4.

Finally, in a third step (Figure 5), the secondary layer 5 is put in place, for example by pouring or spraying, refractory mortar 15 on the main layer 4 already hardened.

Thus, a segment 1 is obtained comprising a main layer 4 produced in a classic 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 layer main 4, opposite the upper surface 2, and acting as an interface with the layer secondary 5. The adhesion of the layers to each other is effected by bonding and by roughness.

The manufacture of the main layer 4 can be carried out in a continuous cycle, the secondary layer 5 being made out of cycle, so as not to constitute an obstacle to the manufacturing 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, to allow main layer 4 to maintain its integrity and mechanical properties, without degradation due to temperature.

On the other hand, the secondary layer 5 also plays a structural role, due to its relatively high mechanical resistance. Since the diaper secondary 5 contributes to the mechanical resistance of segment 1, the thickness of the segment 1 can be very close to the thickness of monolayer segments conventional, 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 resistant to handling, it can be put in place during manufacturing segment 1.

The implementation of a secondary layer 5 with a thickness of the order of 5 cm protects the main layer of the tunnel segments in the application of a modified hydrocarbon type fire at 1300 ° C for 2 hours.

• de 250 à 380°C à l'interface 6 entre les deux couches 4, 5 (suivants les épaisseurs des couches) ;
• de 110 à 250°C dans la couche principale, à 25 mm de l'interface 6.

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 250 ° C in the main layer, 25 mm from the interface 6.

• possibilité de décoffrage à 6 heures, ce qui correspond à une résistance à la compression de l'ordre de 15 MPa. ;
• limitation des épaufrures lors de la manutention et du stockage sur les cales, ce qui correspond à une résistance de l'ordre de 10 MPa ;
• résistance caractéristique à 28 jours de 25 MPa (par comparaison, cette valeur est de l'ordre de 40 à 50 MPa sur cylindre pour le béton de structure) ;
• nécessité de résister aux contraintes générées par les déformations dues à une éventuelle ovalisation de l'anneau du tunnel.

The secondary layer according to the invention has a compressive strength making it possible to comply with the following conditions:

• formwork possible at 6 o'clock, which corresponds to a compressive strength of around 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.

• possibilité d'appliquer une ventouse de manutention (correspondant à une résistance de l'ordre de 0,2 MPa) ;
• solidarité maintenue entre les deux couches pendant l'incendie ;
• adhérence satisfaisante pendant la durée de service de l'ouvrage, supérieure à 30 ans.

The main 4 and secondary 5 layers are assembled with a certain adhesion, so as to respect the following conditions:

• possibility of applying a 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, greater than 30 years.

The shrinkage value of the secondary layer is of the same order of magnitude than that of a B50 type structural concrete (concrete with resistance mechanical 50 MPa), i.e. 200 to 400 µm / m, in order to avoid separation between the two layers or propagation of cracks in the refractory mortar decreasing its effectiveness as a coating concrete.

The secondary layer also verifies durability parameters making it possible to justify a coating function, namely gas permeability with an order of magnitude from 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 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 resistance in order to obtain a secondary layer refractory 5 able to be assembled with the main layer 4 and to protect this last against a modified hydrocarbon fire at 1300 ° C 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 case adjuvants.

According to a possible embodiment, the mortar comprises from 25 to 35% of cement refractory, 20 to 30% first aggregates, 25 to 35% second aggregates, and from 10 to 20% of water, the percentages being expressed by weight per relative to the total weight of the mortar.

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 1290 ° C on pure paste. The density of the cement is in the range of 3.2 to 3.3 t / m ³ .

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 1130 ° C, whose apparent bulk wet density is of the order of 1 t / m ³ , whose actual density is 1.8 to 1, 78 t / m3 and whose water absorption coefficient is around 4.2 to 4.7%. The fraction 0/4 mm can be chosen relatively constantly.

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 wet bulk density is of the order of 0.8 t / m ³ , whose real density is 1, 50 to 1.33 t / m ³ and whose water absorption coefficient is around 5.7 to 8.1%.

The first and second aggregates make it possible to lighten the mortar, and give it good resistance to temperature. At very high temperatures, for example at 1150 ° C, 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, with good compactness, and therefore good resistance. It is not necessary to have aggregates of the same nature. 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 admixture or plastic likely to give off harmful vapors during an increase in temperature.

According to one possible embodiment, the composition of refractory mortar according to the invention may 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 200 ° C, thus creating channels in the protective layer made from 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 m ³ of mortar.

The fibers are present in a very small amount (of the order of 0.1% in weight), and play no structural role.

• ciment :   520 kg/ m³,
• fibres de polypropylène :   2 kg/ m³,
• granulat léger GRANULEX 0/4 :   460 kg/ m³,
• granulat GRANULEX 4/8 :   550 kg/ m³,
• eau totale :   240 à 255 kg/ m³.

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 / m ³ ,
• polypropylene fibers: 2 kg / m ³ ,
• GRANULEX 0/4 light aggregate: 460 kg / m ³ ,
• GRANULEX 4/8 aggregate: 550 kg / m ³ ,
• total water: 240 to 255 kg / m ³ .

Fresh mortar thus has a density of the order of 1.8 t / m ³ (compared to 2.4 t / m ³ for structural concrete and 1 t / m ³ for known refractory mortars).

The refractory mortar has a thermal conductivity less than 1W / .m. ° K at 20 ° C (against 1.40 W / .m. ° K for structural concrete).

• on introduit les deux granulats et les fibres de polypropylène ;
• on produit un malaxage d'une minute ;
• on introduit le ciment puis l'eau ;
• on malaxe de façon complémentaire pendant deux minutes.

In practice, the manufacture of mortar includes the following stages:

• the two aggregates and the polypropylene fibers are introduced;
• one minute mixing is produced;
• the cement and then the water are introduced;
• 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 compressive strength at 28 days 30 to 40 MPa Average compressive strength at 5 hours 20 to 25 MPa (without steaming) Average splitting resistance at 28 days 3 MPa Young module at 28 days 21,000 MPa Adhesion to traditional concrete type B40 (interposed wire mesh) 1.5 to 2.5 MPa
1.0 to 1.5 MPa Plastic withdrawal at 24 hours 473 µm / m Withdrawal after taking at 28 days 297 µm / m Oxygen permeability 2.84 10 ^-16 m ² Water permeability 4.3 10 ^-11 m / s Specific heat at 50 ° C 878 J / kg. ° K Thermal conductivity 0.82 W / .m. ° K at 20 ° C Thermal conductivity 0.77 W / .m. ° K at 200 ° C Thermal conductivity 0.38 W / .m. ° K at 1250 ° C

The mortar forming a secondary layer is here a compromise between the insulation thermal and mechanical resistance.

Mechanical resistance of the secondary layer made from mortar is around 30 to 35 MPa. On the one hand, during manufacturing, the steps handling and cleaning can be done without risking damage the diaper. On the other hand, in service, the secondary layer is strong enough to not be damaged, for example easily by cars traveling 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 realization load-bearing structures, regardless of cost issues. Conversely, certain known refractory mortars lead to obtaining structures having a mechanical resistance of less than 5 MPa.

Claims (9)

Precast concrete part comprising a main layer (4) of concrete reinforced, prestressed or fiber-reinforced and a secondary layer (5) in mortar refractory ensuring both additional mechanical resistance and fire protection, said mortar having resistance mechanical at 28 days greater than 25 MPa, thermal conductivity less than 1 W / m.K at 20 ° C, and resistance to very high temperatures up to 1300 ° C, for 2 hours. 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 joined to the main layer (4) at a second face (6) of said main layer (4), opposite to said first face ( 2). Method for producing a precast concrete part according to claim 1 or 2, characterized in that it comprises the following steps: a) producing a main layer (4) of reinforced, prestressed or fiber-reinforced concrete in a mold (7); b) after hardening, release the main layer (4); and c) apply a secondary layer (5) of refractory mortar on one of the faces (6) of the main layer (4). Method according to claim 3, characterized in that it further comprises the step of assembling the main (4) and secondary (5) layers using connection keys and mechanical fasteners. Refractory mortar used in the process for producing a precast concrete part according to claim 3 or 4, characterized in that it comprises at least: refractory cement; artificial aggregates of selected particle size and density; some water. Mortar according to claim 5, characterized in that the cement belongs to the group formed by fused aluminous cements. Mortar according to either of Claims 5 and 6, characterized in that the aggregates are mineral expanded aggregates. Mortar according to any one of Claims 5 to 7, characterized in that the aggregates belong to the group formed by clays, shales, slag. Mortar according to any one of Claims 5 to 8, characterized in that it also comprises fusible fibers with a diameter of a few micrometers and / or having a length of the order of 12 mm.

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