Swedish patent application 801663-7 describes a technigue of simplifying and cutting the price of the manufacture of concrete slabs on a solid bed. The product, which has been given the registered trademark name of Permaban, has become a great marketing success.

Permaban consists of non-tensioned reinforced concrete rails with a length of 5,1 m. They are often also re¬ ferred to as tracks. These rails are available in different heights according to the desired thickness of the concrete floor. The work using Permaban is carried out in the following way: The rails are laid out in such a way that the surface to be concreted is divided up into different sections, the widht of which corresponds to the width permitted by the equipment. A usual width of vibrators is 5 or 8 metres. The rails are levelled off and secured by means of spots of con¬ crete at a distance of about 1,7 from each other. The upper edge of the rails is levelled off to the disired position corresponding to the upper edge of the con¬ crete bed. This provides forms and glide paths for con- crete and vibrators. It is not necessary to strip forms or wait for the bay to set before starting casting work on the adjusting bay.

As this information indicates, labour is saved and quality improved by using Permaban.

As is always the case, when one problem is solved, or at least simplified, other problems turn up which are very difficult. This is also the case with the appli- cation of Permaban. Before we consider the problems, some information about the joints in concrete floors.

OMPI

Differentiation is made in concreting between working joints, contraction joints and expansion joints. The first-mentioned joint is used to provide a sharp edge at the end of the concreting bay, so that next day the concrete adheres to the earlier concrete. This problem has been solved in an excellent way by Permaban. The rails can be used to close off one section and, by using the Permaban dowel holes, you can provide a working joint that meets the highest demands.

Contraction joints are needed to absorb the contraction that results when the concrete hardens. This has proved to be yet another application for Permaban, which makes up a good crack indication and therefore pro- vides controlled contraction cracks which can be considered to be hair-fine.

Unfortunately, it has not been possible to use Permaban in order to solve the third type of joint problem. Expansion joints must absorb the movements that occur in a concrete bed resulting from tensions such as thermal stresses. Normally, when the forms are struck after concreting, some forms are left to serve as joints. Unfortunately, wood is a poor jointing material and, furthermore, dowels cannot be used in connection with this procedure. The absence of dowels means that the edge raising problem becomes more obvious. This means that the quality of the floor decreases and problems may be encountered, for example when operating fork lift trucks with heavy loads.

Another way of producing expansion joints, at a later occasion after the concrete bed has hardened, is to use special concrete saws to cut joints and then fill them with elastic material. This procedure is time-

taking and thereby expensive. It is often also diffi¬ cult to obtain straight joints. This particular in¬ vention now represents a method which eliminates problems involved in producing a concrete bed with expansion joints of good quality and for a reasonable amount of labour and thereby cost.

It has been found possible to produce an expansion joint in connection with concreting by using two long rails of non-tensioned reinforced concrete, not necessarily similar to Permaban. If two units of this type are placed close together at at least a certain minimum distance from each other, and the space created is filled with material to keep these two units tempo- rarily together, they can be used in principle in the same way as Permaban, i e as both the form and a glide path for vibrators. Later, when the concrete has hardened sufficiently, the temporary material can be replaced by suitable joint material, for example compound with good resistance to petrol (gasoline). It is also possible to consider using jointing material in the first place between the two rails.

The cross-section of the long rails is to be made up in order to meet certain mechanical demands on the joint. It has been found suitable to make up cross- sections so that the side facing the concrete has a cross-section of the tongue and groove type.

In the web of the cross-section formed by the tongue and groove, there are holes opposite each other in both rails. These holes are used for the location of dowels before concreting, the function of these dowels being to provide a connection between the two slabs and thereby eliminating the possibility of edge rising that could occur later. In order to achieve this objective, it is necessary to have a certain ^ _α T FEA f O PI

minimum length so that the dowels extend sufficiently far into both slabs. Furthermore, one end should be coated with bitumen so that it does not prevent move¬ ments. The bitumen prevents an excessively strong "bite" between the concrete and dowel. In this way, the dowels, which are thus securely attached to one slab, will accept movements in the other. It has also been found most practical for the space between the rails to be well defined. For reasons concerned with the possibility of absorbing movements, it has been found best to create the space between two flat and vertical surfaces. In this way, an elastic material can absorb movement without moving vertically. Otherwise there is the possibility of the material absorbing movement to creep up from the joint or down from the joint and causing damage.

Joint compound can have different compositions. It generally contains an elastomer. Certain compounds are sensitive to certain materials which may be handled on the floor concerned in the future.

A figure is enclosed to provide an example of the method. This figure includes the two long rails (11 and 12) of non-tensioned reinforced concrete (no reinforcing bars can be seen in the figure) as a cross-section in the final construction. The adjacent concrete slabs (4 and 3) consist of concrete that is either reinforced against cracks with mesh or steel in order to provide a structural floor. No reinforcing bars are shown in the figure. The two rails are designed in such a way that, on the upper surfaces (1 and 2) which have been made level with a fine surface in connection with production, it is possible to use compensating and vibrating machines, such as a vibrating beam finisher.

in connection with production of the slabs. In the same way, the lower parts of the rails have been made rather wider so as to create a base against the firm ground (5) below. The sides of the rails facing the concrete are designed in such a way, see the figure, that there is a connection between the base and the upper surface making up a tongue and groove, this provides the final construction with high structural strength. This is marked in the figure (10 and 9). In the same way, the side surfaces facing the space between the rails have been designed in the form of a flat and vertical surface. The intermediary space (7) created is filled - with material that has better capacity than concrete to absorb movement, i e is plastically deformable. This material may consist of various rubber compounds which have been softened by using various plasti- cizers but can also consist of polystyrene which expands to a suitable density. The figure also includes a dowel (8) in the form of a circular section bar. One end has been treated with material which makes it easy for the dowel to move in this part of the structure (6) .

It has been found to be particularly advantageous to work with an expanded form of polystyrene as the material between the rails. This can also be applied in position using adhesive in connection with the production of the rails so that, on the building site where the joint is to be located, this joint element is used in the same way as Permaban. In certain cases, the polystyrene can be permitted to remain in position in order to absorb movements or it can be removed completely or partly in order to fill the resulting cavity with another material, for example one which has greater resistance to petrol (gasoline)