A common option for floors of buildings, structures and coatings in industrial premises with intense mechanical stress is concrete floor. The material from which these structural elements are created is subject to shrinkage and has low deformation resistance, resulting in cracks. In order to avoid repeated repairs, artificial cuts are created in monolithic structures. For example, an expansion joint in concrete floors, in the walls of a building, roofs, bridges.
What are they needed for?
The concrete floor appears to be a solid and durable foundation. However, under the influence of temperature fluctuations, shrinkage processes, humidity, operational loads, precipitation of the soil, its integrity is lost - it begins to crack.
To betray a certain degree of elasticity to this building structure, expansion joints are created in concrete floors. SNiP2.03.13-88 and its Handbook contain information on the requirements for designing and installing floors, indicating the need for a tearing device in the screed, underlying layer or coating, which provides relative displacement of scattered areas.
Main functions:
- Minimize sudden deformations by dividing a monolithic plate into a certain number of cards.
- The ability to avoid costly repairs with replacement of the rough and base coat.
- Increased resistance to dynamic loads.
- Ensuring the durability of the structural basis.
Main types: insulating seam
The expansion joint in concrete floors, depending on its purpose, is divided into three types: insulating, structural and shrink.
Insulation sections are made at the junction of structural elements of the room. That is, they are an intermediate seam between the walls, foundations for equipment, columns and floor. This makes it possible to avoid cracks during shrinkage of concrete in places where horizontal and vertical elements of the room fit. If we neglect their arrangement, then the screed when drying and reducing the volume during hard adhesion to the wall, for example, is most likely to give a crack.
An insulating seam is created along the walls, columns and in places where the concrete floor borders with other types of bases . Moreover, a seam is cut near the columns not parallel to the faces of the pillar-shaped element, but in such a way that a straight cut occurs at the corner of the column.
The considered type of seam is filled with insulating materials that can allow horizontal and vertical movement of the screed relative to the foundation, columns and walls. The thickness of the seam depends on the linear expansion of the screed and is about 13 mm.
Main types: shrink seam
If insulating joints prevent the deformation of a monolithic concrete floor in the places of its contact with the walls, then shrink cuts are necessary to prevent chaotic cracking of 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 hardening of the upper layer.
The device of expansion joints in concrete floors of this type occurs along the axes of the columns, where the cuts are joined with the corners of the joints along the perimeter. Cards, that is, parts of a monolithic floor, limited on all sides by shrink seams, must be square, their L-shaped and elongated rectangular shapes should be avoided. The work is carried out both during the laying of concrete with the help of forming slats, and cutting joints after the screed has dried.
The probability of cracking is directly proportional to the size of the cards. The smaller the floor area limited by shrink seams, the less chance of cracking. Sharp corners of the screed are also subject to deformation, therefore, in order to avoid concrete breaks in such places, it is also necessary to cut shrink type seams.
Main types: structural seam
Such protection of monolithic floors is created when technological interruptions occur. The exceptions are rooms with a small pouring area 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 face of such a connection is created as a thorn groove. Features of structural protection:
- The seam is arranged at a distance of 1.5 m parallel to other types of deformation demarcations.
- It is created only if concrete is laid at different times of the day.
- The shape of the ends should be made in the form of a spike-groove.
- For screed thicknesses up to 20 cm, a 30 degree cone is made on the wooden side ledges. It is allowed to use metal cones.
- Cone seams protect the monolithic floor from minor horizontal movements.
Expansion joints in concrete floors of industrial buildings
Increased requirements for wear resistance are imposed on floors laid in factories, warehouses and other industrial facilities. This is due to the appearance of the influence of different intensities of mechanical impact (the movement of vehicles, pedestrians, shock when solid objects fall) and the possible hit of liquid on the floor.
As a rule, the structural feature of the floor is a screed and coating. But under the screed is the underlying layer, which in rigid execution is laid out of concrete. A seam is cut in it in mutually perpendicular directions 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 breaks 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 the mechanical impact, coatings of different thicknesses are designed. With a thickness of 50 mm or more, a deformation seam in concrete floors (SNiP “Floors” p. 8.2.7) is created in the transverse and longitudinal directions with the elements repeating after 3-6 m. The cut is sawn through 3-5 mm wide, its depth is not less than 40 mm or a third of the coating thickness.
Requirements for creating floor deformation protection
Sawed concrete must be done with a milling cutter after two days of hardening. The depth of cuts according to the standards is 1/3 of the thickness of concrete. In the underlying layer, it is allowed to use slats treated with anti-adhesion compounds in the places of the alleged gaps before pouring concrete, which are removed after hardening the material and as a result protective seams are obtained.
The lower parts of the columns and walls to the height of the future coating thickness 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 technology of slicing begins with marking with chalk and a line of places of artificial breaks.
An indicator of timely cutting is a test seam: if the aggregate grains do not fall out of the concrete, but are cut with a cutter blade, then the correct time for creating the expansion joints is chosen.
Seam processing
The normal functioning of the joint is achieved by sealing it. Termination of expansion joints in concrete floors is carried out using the following materials:
- Waterstop is a profiled tape made of rubber, polyethylene or PVC, laid when pouring concrete screed;
- A sealing cord made of foamed polyester is laid in the slot and, when the temperature drops, maintains its elasticity, ensuring the safe movement of the concrete coating;
- Acrylic, polyurethane, latex mastic;
- A deformation profile consisting of rubber and metal guides. It is built-in or overhead.
Before sealing, the working surface of the gaps must be cleaned and purged with compressed air (compressor). Also, to increase the service life of concrete floors, it is desirable to strengthen the top layer with topping or polyurethane material.
Terms of Creation
An expansion joint in concrete floors (monolithic) becomes mandatory under the following conditions:
- Screed with a total area of over 40 m2.
- Sophisticated floor configuration.
- Operation of flooring at elevated temperatures.
- The length of the rib (just one) of the floor structure is more than 8 m.
Expansion joints in concrete floors: standards
In conclusion, the 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 in increments of 6 to 12 meters. The seam is made with a depth of 4 cm and makes up a third of the thickness of the concrete coating or the underlying layer.
With a concrete coating thickness of 50 mm or more, a deformation seam 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, the deformation gaps in the underlying layer. The width of the cut is 3-5 mm.
Propyl is carried out two days after concrete is laid. Sealing of protective cuts is carried out with special cords and sealants.