A common option for floors of buildings, structures and coatings in industrial premises with intense mechanical stress is a concrete floor. The material from which these structural elements are made is subject to shrinkage and has a low resistance to deformation, as a result of which cracks occur. In order to avoid repeated repairs, artificial cuts are created in monolithic structures. For example, expansion joints in concrete floors, building walls, roofs, bridges.
What are they for?
The concrete floor appears to be a strong and durable foundation. However, under the influence of temperature fluctuations, shrinkage processes, air humidity, operational loads, soil sedimentation, its integrity is lost - it begins to crack.
To give some degree of elasticity to this building structure, expansion joints are created in the concrete floors. SNiP2.03.13-88 and its Manual containinformation on floor design and installation requirements indicating the need for a break in the screed, underlayment or coating that provides relative displacement of disparate areas.
Main functions:
- Minimize sudden deformations by dividing a monolithic slab into a certain number of cards.
- The ability to avoid costly repairs with the replacement of the rough and basic coating.
- Increased resistance to dynamic loads.
- Ensuring the durability of the structural framework.
Main types: insulating joint
The expansion joint in concrete floors, depending on its purpose, is divided into three types: insulating, structural and shrinkage.
Insulating cuts are made at the junction of structural elements of the room. That is, they are an intermediate seam between walls, equipment foundations, columns and floors. This makes it possible to avoid cracks during shrinkage of concrete in the places where the horizontal and vertical elements of the room fit. If we neglect their arrangement, then the screed, when dried and reduced in volume with a rigid adhesion to the wall, for example, is most likely to crack.
An insulating joint is created along walls, columns and in places where the concrete floor borders on other types of bases. Moreover, a seam is cut near the columns not parallel to the faces of the columnar element, but in such a way that a straight cut falls on the corner of the column.
The considered type of seam is filled with insulating materials capable of allowing horizontal and vertical movement of the screed relative to the foundation, columns and walls. The thickness of the joint depends on the linear expansion of the screed and is about 13 mm.
Main types: shrink seam
If the insulating joints prevent deformation of the monolithic concrete floor in the places of its contact with the walls, then shrinkage cuts are necessary to prevent chaotic cracking of the concrete over the entire surface. That is to prevent damage caused by shrinkage of the material. As the concrete dries from top to bottom, tension appears inside it, created by the hardening of the top layer.
The arrangement of expansion joints in concrete floors of this type occurs along the axes of the columns, where the cuts are joined to the corners of the joints along the perimeter. Cards, that is, parts of a monolithic floor, limited on all sides by shrinkage seams, should be square, L-shaped and elongated rectangular shapes should be avoided. Works are carried out both during the laying of concrete with the help of forming rails, and by cutting joints after the screed has dried.
The chance of cracking is directly proportional to the size of the cards. The smaller the floor area limited by shrinkage joints, the less likely it is to crack. The sharp corners of the screed are also subject to deformation, therefore, in order to avoid concrete ruptures in such places, it is also necessary to cut shrink-type seams.
Main types: construction seam
Similar protection of monolithicfloors are created in the event of technological interruptions in work. The exceptions are rooms with a small area of pouring and continuous supply of concrete. An expansion joint in concrete floors of a structural type is cut at the joints of the screed, made at different times. The shape of the end of such a connection is created according to the "thorn-groove" type. Structural protection features:
- The seam is arranged at a distance of 1.5 m parallel to other types of deformation demarcations.
- Created only if concrete is placed at different times of the day.
- The shape of the ends should be made according to the "thorn-groove" type.
- For screed thickness up to 20 cm, a 30 degree cone is made on the wooden side ledges. Metal cones are allowed.
- Conical seams protect the monolithic floor from minor horizontal movements.
Expansion joints in concrete floors of industrial buildings
Increased wear resistance requirements are imposed on floors laid in factories, warehouses and other industrial facilities. This is due to the appearance of the influence of different intensity of mechanical impact (movement of vehicles, pedestrians, impacts when solid objects fall) and the possible ingress of liquid on the floor.
As a rule, the design feature of the floor is a screed and a coating. But under the screed there is an underlying layer, which in a rigid design is laid out of concrete. In it is cut into mutuallyperpendicular directions of the seam through 6-12 m, 40 mm deep, with at least 1/3 of the thickness of the underlying layer (SNiP 2.03.13-88). A prerequisite is the coincidence of the expansion joint of the floor with similar protective gaps in the building.
A distinctive feature of the structure of floors in industrial buildings is the creation of a top layer of concrete. Depending on the intensity of mechanical action, coatings of different thicknesses are designed. With a thickness of 50 mm or more, a deformation joint in concrete floors (SNiP "Floors" p. 8.2.7) is created in the transverse and longitudinal direction with the repetition of elements every 3-6 m. less than 40 mm or a third of the coating thickness.
Requirements for creating deformation floor protection
Concrete must be cut with a cutter after two days of hardening. The depth of cuts according to the norms is 1/3 of the concrete thickness. In the underlying layer, it is allowed to use slats treated with anti-adhesion compounds in places of alleged gaps before pouring concrete, which are removed after the material hardens and as a result protective seams are obtained.
The lower parts of columns and walls to the height of the future thickness of the coating should be glued with rolled waterproofing materials or foamed polyethylene sheet. In those places where the project provides for expansion joints in concrete floors. The slicing technology begins with chalk marking and a ruler for artificial breaks.
Test seam serves as an indicator of timely cutting:if the grains of the aggregate do not fall out of the concrete, but are cut by the cutter's blade, then the time for creating the expansion joints is correct.
Seam treatment
The normal functioning of the seam is achieved by sealing it. Sealing expansion joints in concrete floors is carried out using the following materials:
- A waterstop is a profiled tape made of rubber, polyethylene or PVC, which is laid when pouring a concrete screed;
- The sealing cord made of foamed polyester is laid in the slot and retains its elasticity during temperature changes, ensuring the safe movement of the concrete pavement;
- Acrylic, polyurethane, latex mastic;
- Deformation profile, consisting of rubber and metal guides. It can be built-in or overhead.
Before sealing, the working surface of the gaps must be cleaned and blown with compressed air (compressor). Also, to increase the service life of concrete floors, it is desirable to strengthen the top layer with a topping or polyurethane material.
Creation conditions
The expansion joint in concrete floors (monolithic) becomes mandatory under the following conditions:
- Screed, total area above 40 m2.
- Complex floor configuration.
- Exploitation of flooring at elevated temperatures.
- The length of the rib (one is enough) of the floor structure is more than 8 m.
Expansion joints in concrete floors: norms
In conclusionthe requirements for the installation of protective gaps in concrete floors according to the norms are given.
The underlying layer should have deformation cuts perpendicular to each other with a step of 6 to 12 meters. The joint is 4 cm deep and is one third of the thickness of the concrete pavement or sub-base.
With a concrete pavement thickness of 50 mm or more, a deformation joint is created in the transverse and longitudinal direction with a repetition every 3-6 m. These cuts must coincide with the seams of the floor slabs, the axes of the columns, and the expansion gaps in the underlying layer. The cutting width is 3-5mm.
The cut is carried out two days after the concrete is laid. Protective cuts are sealed with special cords and sealants.
