DK180088B1

DK180088B1 - Crack inducer for injection moulded concrete arch in traffic tunnel

Info

Publication number: DK180088B1
Application number: DKPA201770544A
Authority: DK
Inventors: Johan Lystad Olav
Original assignee: Vik Ørsta As
Priority date: 2016-07-08
Filing date: 2017-07-03
Publication date: 2020-04-16
Also published as: DK201770544A1; IS9081A; NO20161138A1; FI20175627A; NO346342B1

Abstract

A fire retardant crack inducer (10) for grouting in a shotcrete construction (4) arranged against a combustible, draining insulation material (5) in a traffic tunnel (1) is disclosed.

Description

CRACK INDUCER FOR INJECTION MOULDED CONCRETE ARCH IN TRAFFIC TUNNEL

Background for the invention

The present invention generally relates to infrastructure in connection with traffic tunnels. More particular, the invention relates to a crack inducer for injection molded concrete arch in traffic tunnel where the crack inducer contributes to better safety during fire.

Further, the invention relates to fire retardant sealing of dilatation joints in one operation without replenishing the opening with a fire retardant grouting.

Background technique

According to prior art for traffic tunnels, draining insulating material in the form of polyethylene foam (PE-foam) is arranged on the rocky wall of the tunnel, where the main objective with said foam is to lead leaking water from the rock away from the carriageway of the tunnel and down in longitudinal roadside ditches near the transition between rocky wall and carriageway. The PE foam has good insulation ability which prevents the water freezing and thereby creating hanging ice in the tunnel.

One serious disadvantage with the PE foam is that it is inflammable and gives off smoke and gases during fire. Due to safety reasons one has found it necessary to cover the foam with concrete, which in the present case is shotcrete which is applied in suitable thickness which typically may be approx. 80 mm.

After the shotcrete has been applied, it is left to harden for a relatively long time which typically may be minimum 28 days. During the hardening the concrete shrinks with crack formation as a result. To control the crack formation, so called crack inducers are arranged in the concrete across the longitudinal direction of the tunnel with suitable spacing. The crack formation will then happen at the said crack inducers. The size of the crack at the crack inducer will change due to temperature and moisture.

An example of a crack inducer for incorporation into a concrete construction is disclosed in US 4815886 A.

Today’s solution for crack inducer comprises an l-moulding (L-shaped) which is screwed on to the PE foam with a special screw (see Figure 1). According to today’s technique, a felt is normally installed as a sliding surface under the crack inducer. The assembly happens in the following order: felt, l-moulding and reinforcement. When the l-moulding is installed and the reinforcement of the arch is finished, the lmoulding, the reinforcement and the PE foam is sprayed in with shotcrete. When the concrete has been left to harden, a crack has formed along the plastic moulding due to shrinkage of the concrete. An opening is then formed which can have access to the PE foam. Because of fire risk one cannot let the opening that has been formed be left open, as it entails a risk that a possible fire can get through the opening and set the PE foam, which lies behind the shotcrete, alight. One has therefore chosen to go back and fill the opening with fire retardant grouting.

Filling of said opening with grouting is a complicated, labour-intensive and expensive operation which also hinders the traffic in the tunnel during the rest of the installation work. As the crack formation happens over time, the need for further filling can be a hindrance for traffic or result in traffic being taken out of the tunnel. Further, the grouting has its weaknesses when the tunnel is in operation. This because the compound hardens, and when the tunnel is being washed, which is typically done by washing down with high pressure, the compound is flushed away and hence the opening is unprotected.

Hence, today’s crack inducers have several disadvantages, e.g. when it comes to security, accessibility, expenses, complexity and logistics. More specifically, there are problems with today’s solution in that a fire may travel to the PE foam. Further, the solution is complex in that it comprises both an l-moulding and fire retardant grouting which must be arranged in two steps with a time interval. The felt which is installed where the crack inducer is to be placed, provides a sliding surface, but it is not fire retardant. The solution according to prior art is complex and expensive, among other things because it comprises several elements which must be installed with the help of different methods in a sequence. The availability of the relevant tunnel is reduced both in connection with first time installation of the system, with the operation and later with maintenance. Of similar reasons the expenses will increase in the different phases during the lifetime of the tunnel.

Short presentation of the invention

The invention relates to a fire retardant crack inducer for grouting in a shotcrete construction arranged against a combustible, draining insulation material in a traffic tunnel. The crack inducer comprises a longitudinal profile with a mainly constant cross-section, where the crack inducer comprises a crack inducing part suitable to contribute to control the formation of a crack through the concrete construction by the crack inducer, and a first foot part arranged to be fastened to the insulation material, where the first foot part protrude on one side of the crack inducing part transversally to a longitudinal axis of the profile. The crack inducer comprises a second foot part protruding on the opposite side of the crack inducing part in relation to the first foot part. The second foot part is also arranged to be fastened to the insulation material.

In a preferred embodiment the solution can consist of an extruded rubber profile which has an approximately constant cross-section. The foot parts are advantageously shaped flat so that the concrete may glide along these when shrinking. The crack inducer can advantageously have a Y-shape to have a resistance against being pushed to the side when sprayed with concrete. The crack inducer can be carried out in a fire retardant rubber with or without matter that makes it expand. The Y-shaped crack inducer can advantageously comprise a connecting part between the two foot parts that will contribute to prevent the fire to get through if the rest of the crack inducer should be damaged by fire. Further, the middle foot part will prevent that the profile flattens when spraying with concrete. In the profile, holes are arranged to be able to fasten the crack inducer to the PE foam with a special screw developed for this purpose.

The crack inducer is constructed in a fire retardant material and with dimensions preventing a fire in the tunnel to spread to the insulating material.

The foot parts can advantageously provide a sliding surface for contributing to a possible relative movement between the concrete arch and the insulating material.

In a preferred embodiment, the cross dimension of the crack inducing part increases in towards the two foot parts to increase the stiffness of the crack inducer by forces affecting the crack inducing part in a transverse direction, where said increase advantageously can be to at least the double.

The crack inducing part can advantageously comprise a first and a second leg part so that the cross-section of the crack inducing part gets a y-shaped form suitable to form a long room between the leg parts, and where the two leg parts each are connected with a foot part.

The two foot parts can be arranged with an opening in between so that the long room is open in the longitudinal direction of the profile. In the long room a fire extinguishing material may be arranged.

The leg parts can advantageously be dimensioned to allow relative movement of the one foot part in relation to the other.

The two foot parts can be connected with a middle foot part between the foot parts so that the foot parts jointly form a continuous surface of contact suitable for formfitted arrangement against the insulation material.

The two foot parts and middle foot parts can have the same thickness to provide stiffness to the crack inducing part towards transverse forces and to the foot parts towards transverse forces and displacement of the foot parts in relation to each other. Alternatively, the middle foot part can be thinner than the two foot parts to give combined stiffness and flexibility to the crack inducer in that the distance between the foot parts mainly is not allowed to increase above the length of the middle foot part, but is allowed to reduce.

The crack inducer can constitute a massive body without internal room.

The crack inducer part and the foot parts can respectively be shaped with parallel lateral surfaces, where the foot parts firstly are arranged perpendicular on the crack inducer part and secondly is directly linked, so that the cross-section of the profile forms a T-shape.

The foot parts can be arranged with a plurality of holes to special screws with head and core, where the screws are to fasten the crack inducer to the insulating material, where the size of the holes are smaller than the head, but the holes are bigger than the core to provide a possibility for relative movement.

The crack inducer comprises a flexible and fire retardant material which can be rubber. The fire retardant material can expand during fire so that the fire retardant effect increases.

Problems solved by the invention

A main object with the present invention is to provide a crack inducer for traffic tunnel and methods that overcome the problems mentioned above.

The object of the invention

The present invention solves problems with today’s crack inducers.

The main object of the invention is to provide a crack inducer to control crack formation in concrete arches when shotcrete shrinks. A more specific object is to improve the control of crack formation.

A primary objective with the present solution is to arrive at a traffic tunnel with improved properties. Said properties could be related to, among other things, safety, accessibility, expenses, complexity and logistics.

A main objective is to increase safety during fire in the tunnel. A more specific objective in this connection is to prevent fire spreading from the tunnel, via cracks in the concrete arch and into underlying, flammable material in the shape of insulating, draining foam.

A further objective is by the crack inducer to provide fire-resistant joint without additional protection, for example by arranging the grouting in the joint.

Yet a main objective is to simplify the methods for installation, operation and maintenance of traffic tunnels. More specific objectives in this connection are to reduce the number of steps in the process to install concrete arches with crack inducers over underlying material.

A primary objective of the invention is to reduce costs for installation, operation and maintenance of traffic tunnels. A further primary objective is to simplify operations in connection with installation, operation and maintenance of traffic tunnels.

Yet an objective is to simplify maintenance and to increase the mechanical resilience to the solution of washing.

Means needed to solve the problems

The present invention reaches objectives mentioned above by a crack inducer for traffic tunnels as defined in the introduction to the independent claims, with the features in the characteristics of these.

A number of non-exhaustive embodiments, variants or alternatives of the invention are defined in the dependent claims.

The present invention reaches the objective mentioned above by a number of dependent claims.

Short description of the figures

The invention will in the following be described further, by reference to the figures showing several embodiment examples, and where

- Figure 1 shows a cross-section of a traffic tunnel with a concrete arch

- Figure 2 shows a cross-section of a part of a concrete arch in a traffic tunnel where a crack inducer is installed according to prior art

- Figure 3A shows a view of reinforcement of a concrete arch in a traffic tunnel as in Figure 1, where a crack inducer according to the present invention is arranged

- Figure 3B shows an enlarged view of Figure 3A where the crack inducer is arranged

- Figures 4A-C show a cross-section of a part of a concrete arch where a crack inducer according to the present invention is arranged with examples of alternative cracking by the crack inducer after hardening

- Figures 5A-C show projections of an embodiment of the present invention seen respectively obliquely from above, directly from above and directly from the side

- Figure 6 shows a detailed cross-section of an embodiment of the present invention

- Figure 7 shows a cross-section of alternative embodiments of the present invention.

Review of the reference numbers referring to the figures

Below reference numbers used in the figures are briefly presented.

Reference numbers	Description
1	Tunnel
2	Rocky wall
3	Tracks, e.g. carriageway or railway track
4	Concrete arch
5	Insulating material, e.g. PE foam
6	Safety bolt
7	Reinforcement
8	Joint
9	Grouting
10	Crack inducer
11	Crack inducing part
110	Main part of the crack inducing part
111A-B	Leg part of the crack inducing part
12A-B	Foot part
13	Middle foot part
15	Hole for securing bolt
16	Securing bolt
17	Longitudinal room

Further description of the invention with reference to figures

The invention will in the following be described further with reference to the figures showing several embodiment examples.

Figure 1 is a cross-section of a traffic tunnel (1) where a crack inducer (10) is arranged, which can be according to prior art or the present invention. In the tunnel (1), draining insulation material (5) is arranged in the form of PE foam on the rocky wall (2) of the tunnel. The main objective with said foam (5) is to lead leakage water from the rock (2) so that it does not overflow the course (3) of the tunnel (1), but is rather led down in longitudinal roadside ditches near the transition between the rocky wall (2) and the carriageway (3). The PE foam (5) has good insulation ability which prevents the water from freezing and hence create hanging ice in the tunnel (1).

The PE foam (5) is covered with concrete (4), which in the present case is shotcrete which is applied in a suitable thickness which typically may be approx. 80 mm.

After the shotcrete (4) is applied, it is left to harden for a relatively long time which typically may be minimum 28 days. During hardening the concrete (4) shrinks, with crack formation as a result. To control the crack formation, so called crack inducers (10) are arranged in the concrete transversally to the longitudinal direction of the tunnel (1) with suitable spacing. The crack formation will primarily happen at the said crack inducers (10). The figures also show bolts (6) to fasten the concrete arch to the rocky wall (2).

Figure 2 shows a mounted crack inducer (10) according to prior art, where the crack inducer (10) comprises an L-shaped profile which is screwed to the PE foam (5) with a special screw (16). Under the crack inducer (10) a felt is arranged to provide a sliding surface for the concrete arch in relation to the PE foam (5). When the lmoulding (10) is installed and the reinforcement of the arch (4) is finished, the lmoulding (10), the reinforcement and the PE foam (5) is sprayed in with shotcrete (4). When the concrete (4) is left to harden, a crack is formed along the plastic moulding (10) due to shrinkage of the concrete (4). An opening (8) is then formed with direct access to the PE foam (5). Because of the fire risk one cannot let such an opening be left open, as it entails a risk that a possible fire can get through the opening (8) and set the PE foam (5), which lies behind the shotcrete (4), alight. One has therefore chosen to go back and fill the opening (8 in Figure 2) with fire retardant grouting (9 in Figure 2).

Figure 3A shows a view of reinforcement (7) of a concrete arch in a traffic tunnel as in Figure 1, where a crack inducer (10) is arranged according to the present invention. Figure 3B shows an enlarged view of Figure 3A where the crack inducer (10) is arranged. By application of the crack inducer (10) according to the present invention, the reinforcement (7) can first be arranged continuously along the tunnel (1). The reinforcement (7) is fastened to the bolts (6). The dilatation joint can advantageously be placed centrically in relation to the fastening bolt (6) for a small movement in the reinforcement (7). Then tracks are cut in the reinforcement (7) across the length of the tunnel (1) with suitable spacing for the arrangement of the crack inducer (10). The crack inducers (10) are then typically arranged by fastening to underlying PE foam (5). The crack inducers (10) in combination with cutting of the reinforcement (7) provide a possibility for relative movement between parts of the concrete arch (4) by controlled crack formation along the crack inducers (10). By the application of crack inducer (10) according to prior art, one must firstly arrange a felt, then a crack inducer before the reinforcement (7) is arranged against the crack inducer. This can give problems by the reinforcement (7) not being arranged optimally in relation to the crack inducers (10).

Figures 4A-C show a cross-section of an embodiment of the present invention in mounted condition. Figure 4A shows a condition shortly after the spraying of concrete (4), while Figure 4B-C shows the condition after hardening of said concrete (4). The figures illustrate that the concrete (4) shortly after spraying will close around the crack inducer (10), whilst after the hardening of the concrete (4) there will be an expanded joint (8) between the concrete (4) and the crack inducer (10). This is an expected effect which contributes to control the crack formation in the concrete (4) and prevent crack formation other places than by the crack inducers (10). The expanded joint (8) may be formed on any side of the crack inducer (10) as is illustrated in Fig. 4A as an example, or also on both side of the crack inducer (10) as illustrated in Fig. 4C. The crack formation (8) may, however, have disadvantages e.g. in connection with fire safety as previously described related to prior art.

The crack inducer (10) in the illustrated example of an embodiment has mainly a Yshaped cross-section. The crack inducer (10) comprises a central crack inducing part (11) which has a main function in forming the actual crack/fracture (8) in the concrete (4), and two foot parts (12A-B). The crack inducing part (11) rises in relation to the foot parts (12) and is thus arranged to be enveloped by shotcrete (4). The foot parts (12) are arranged to lie against the PE foam (5) on one side and against the concrete arch (4) on the opposite side. The foot parts (12) of the crack inducer (10) can typically be constructed to fasten onto the PE foam (5). Further, it is essential that the foot parts (12) are dimensioned to provide sufficient fire retardant effect in relation to underlying material (5), for example in the form of PE foam, and to provide possible longitudinal sliding of the concrete arch (4) in relation to the PE foam (5). Such sliding can typically happen from a center where the crack inducer (10) is located.

The shaping of the crack inducer (10) with foot parts (12) arranged as described above, allows the crack formation to happen where it is wanted and that the cracks by the crack inducer (10) are not penetrating from the tunnel (1) and into the PE foam (5). This is important to increase fire safety by preserving fire sealing during crack formation by the crack inducer (10).

Figure 5A shows a projection of an embodiment of a crack inducer (10) seen obliquely from above. The crack inducer (10) forms a longitudinal profile suitable for arranging against the PE foam (5) along the tunnel periphery across the longitudinal direction of the tunnel. In the foot parts (12), holes (15) are arranged suitable for special screws (20) for the fastening of the crack inducer (10) to underlying PE foam (5). The crack inducer (10) is produced in a material with a flexibility which allows adaption to the curvature of the tunnel (1). This is further described below.

Figure 5B shows a view of an embodiment of the crack inducer (10) seen from straight above. Here it is illustrated that the holes (15) for the introduction of screws (20), are arranged in the foot parts (12) with suitable distance in the longitudinal direction to the crack inducers (10). Further, holes (15) are arranged in the foot parts (12) on both sides of the crack inducing part (11) of the crack inducer, where the holes (14) on both sides are arranged in parallel in the longitudinal direction in relation to each other.

Figure 5C shows a view of an embodiment of the crack inducer (10) seen straight from the side transversally to the longitudinal direction of the profile.

Figure 6 shows a cross-section of an embodiment of a crack inducer (10) across its longitudinal direction. The crack inducer (10) comprises a crack inducing part (11) with a mainly Y-shaped cross-section. Further, the crack inducer (10) comprises two foot parts (12A-B), each with a contact surface for arranging against the underlying material (5) and the overlying concrete arch (4). The crack inducing part (11) comprises two leg parts (11A-B) which make a transition into the two foot parts (12AB), and which contribute to form the Y-shaped cross-section. The crack inducing part (11) with the leg parts (11A-B) contribute at the top of its Y-shape to form a room (14 in Figure 7). The room in the embodiment of Figure 6 is open towards the PE foam, whilst there in Figure 7 is illustrated a room which is closed by a middle foot part (13).

In the cross-section of the foot parts (12) it appears that there are arranged a hole (15) for a screw (16) to fasten the crack inducer (10) to the underlying material. The screw (16) is a special screw suitable to be screwed into the PE foam. According to the present solution the holes (15) are smaller than the head of the screw, but the holes (15) are considerably larger than the core of the screw (20) so that it provides a possibility for relative movement in the form of sliding between the concrete arch (4) and underlying PE foam (5).

The Y-shape of the crack inducer part (11), possibly with a closed room (17), contributes to provide suitable stiffness for reducing the tendency of the crack inducer part (11) to bend when spraying with concrete. Further, the leg parts (11A-B) to the Y-shaped crack inducing part (11) are arranged to provide flexibility in the shape of a transverse movement in relation to the longitudinal direction of the crack inducer (11).

Figures 7A-D show a cross-section of alternative embodiments of the crack inducer (10).

Figures 7A-B show embodiments where the crack inducer part (11) is Y-shaped, and where the crack inducer comprises a middle foot part (13) which connects the two foot parts (12A-B). In both these embodiments the middle foot part (13) contributes to form a mainly closed room (17) between this and the two leg parts (11A-B). Further, the middle foot part (13) contributes, together with the foot parts (12A-B) to form a continuous contact surface for arranging against the underlying material. The middle foot part (13) can have the same thickness as the foot parts (12) as shown in Fig. 7A, which contributes to stiffness in the transverse direction for the crack inducer (10) . Alternatively, the middle foot part can have a smaller thickness than the two foot parts (12), which gives a mainly closed room (17) between the foot parts (12) and middle foot parts (13), and at the same time provides greater flexibility in a transverse direction than the solution with the thicker middle foot part (13).

The said room (17) can be utilized in alternative ways. It can as an example be filled with fire retardant material like for instance fire extinguishing foam. More alternatively, the room may also be used for carrying a fluid for instance for temperature regulation. In an alternative embodiment which is not illustrated, the crack inducer (10) is massive in the sense that there is no open room present, but that the leg parts (11A-B), foot parts (12A-B) and middle foot parts (13) make a direction transition into each other.

The figures 7C-D show alternative embodiments where the crack inducer (10) has a mainly T-shaped cross-section formed by the crack inducer part (11) and the two foot parts (12A-B).

The crack inducer’s (10) parts can have different designs. The crack inducing part (11) and the foot parts (12) can each mainly have a shape as longitudinal, rectangular parallel epipeds as illustrated in e.g. Figure 7C, or comprise bases with such a shape. The crack inducing part (11) can have a dimension in a protruding direction in relation to the foot parts (12), which is at least as big as the planned thickness of the concrete arch. The crack inducing part (11) is typically arranged orthogonally to the foot parts (12). The foot parts (12) are typically uniformly shaped. The cross-section of the crack inducer (10) is typically symmetrical round a central axis in the cross-section of the crack inducing part (11).

The crack inducer (10) is constructed to contribute to the provision of suitable properties both in the form of stiffness/flexibility, friction/stiction towards relevant adjacent materials and fire retardant properties. The combination of geometric design and choice of material contributes to the provision of such properties. The middle foot part (13) can be arranged to stretch if the concrete is stuck to one or both foot parts (12), which would contribute to the crack inducer (10) as fire retardant surface not breaking during crack formation.

The crack inducer (10) can advantageously be made from a material with suitable properties both in relation to fire retarding, resilience and flexibility. The material may be a fire retardant rubber. The rubber will typically have properties preventing fire to get through the opening and reach into the PE foam. One may also choose to use a rubber which has an additional function making it expand when affected by heat (fire) and hence also closes the opening that has emerged because of the shrinkage of the concrete.

One has now achieved to provide a crack inducer (10) which makes a joint (8) in the shotcrete (4) which is fire protected without the need to be jointed. The solution has in addition mechanical strength to endure the washing of the tunnel (1).

Further, the material is constructed to provide flexibility so as not to crack with movements in the surrounding concrete (4). The resilience in relation to crack formation has significance for fire retarding properties. The solution is further resilient for both mechanical and chemical stress during washing of the tunnel (1).

In connection with a crack inducer (10) according to the invention, a method is provided for arrangement of the crack inducer (10) where it is not necessary to refill with fire retardant grouting (9), but which all the same gives a fire resistant solution.

Further, a method is provided for installation by continuous installation of reinforcement (7) without having to end this by the joint in connection with the installation of foil under the crack inducer (10).

Claims

Fire-retardant crack indicator (10) for embedding in shotcrete construction (4) arranged against a combustible, draining insulating material (5) in a traffic tunnel (1), the crack indicator (10) forming an elongate profile with a substantially constant cross section, where the crack indicator ( 10) includes the following:

a crack indicator part (11) suitable for helping to control the formation of a crack through the concrete structure (4) at the crack indicator (10), and

- a first foot part (12A) arranged to be attached to the insulating material (5), the first foot part (12A) projecting at a side of the crack indicator part (11) across it relative to a longitudinal axis of the profile;

and wherein the crack indicator (10) comprises a second foot part (12B) projecting at the opposite side of the crack indicator part (11) relative to the first foot part (12A), characterized in that the second foot part (12B) is also arranged to be attached to the insulation material (5), and wherein the crack indicator (10) is made of a material with a flexibility which allows adaptation to the curve of the tunnel (1), and which material is sufficiently fire-retardant to counteract fire in the tunnel (1) to spread to the insulating material (5), said insulating material is preferably of PE foam.

Crack indicator according to claim 1, wherein the foot parts provide a sliding surface to assist in a possible relative movement between the concrete arch (4) and the insulating material (5).

Crack indicator according to claim 1 or 2, wherein the transverse dimensions of the crack indicator part (11) are increased towards the two foot parts in order to increase the rigidity of the crack indicator (10) by forces which act on the crack indicator part (11) in a transverse direction.

The crack indicator according to claim 2, wherein the crack indicator part (11) comprises a first and a second leg part (111A-B) such that the cross section of the crack indicator part has a Y-shape suitable for forming an elongate space (17) between the leg parts (111A), and wherein each of the two leg portions (111A-B) is connected by a foot portion (12A-B).

Crack indicator according to claim 4, wherein the leg parts (12A-B) can be arranged with an opening therebetween so that the elongate space (17) is open in the longitudinal direction of the profile (10).

A crack indicator according to claim 5, wherein a fire-extinguishing material is arranged in the elongate space (17).

Crack indicator according to claim 5 or 6, wherein the leg parts (111A-B) are dimensioned to allow relative movement of one foot part (12A-B) relative to the other.

Crack indicator according to any one of claims 1-4, wherein the two foot parts are connected to a middle foot part (13) between the foot parts (12A-B) so that the foot parts (12A-B, 13) together form a continuous contact surface suitable for shape-fitting arrangement against the insulation material (5).

Crack indicator according to claim 8, wherein the two foot parts (12A-B) and the middle foot part (13) have the same thickness to give rigidity to the crack indicator part (11) against transverse forces and to the foot parts against transverse forces and displacement of the foot parts (12A-B). in relation to each other.

Crack indicator according to claim 8, wherein the middle foot part (13) is thinner than the two foot parts (12A-B) to give combined rigidity and flexibility to the crack indicator (10) so that the distance between the foot parts (12A-B) is substantially not allowed. to increase over the length of the middle foot part (13), but is allowed to decrease.

Crack indicator according to any one of claims 1-3, wherein the crack indicator (10) forms a solid body without internal space.

Crack indicator according to any one of claims 1-2, wherein the crack indicator part (11) and the foot parts (12A-B), respectively, are formed with parallel transverse surfaces, and wherein the foot parts are primarily arranged perpendicular to the crack indicator part (11) and secondarily are directly articulated. so that the cross section of the profile is T-shaped.

A crack guide according to any one of the preceding claims, wherein the foot portions (12A-B) are arranged with a plurality of holes (15) for attaching the crack guide (10) to the insulating material (5), the size of the holes (15) allowing a possibility for relative movement between the crack indicator (10) and the insulating material (5).

A crack indicator according to any one of claims 1-13, wherein the fire retardant material is rubber.

A crack indicator according to any one of claims 1-14, wherein the fire retardant material

10 expands during fire so that the fire retardant effect is increased.