Rules for reinforcing a monolithic floor slab
Creating a reinforcing frame can be called one of the responsible moments (read more about the reinforcement of the foundation slab), so when performing the process, it is important to follow a few rules:
- The optimal material for reinforcing the floor slab is a hot-rolled steel reinforcement of A3 class with a diameter of 8-14 mm.
- It is recommended to lay the reinforcement in two layers: the first is placed in the bottom of the slab, the second. in its upper part. In this case from the lower and from the upper edge of the slab to create a gap of 20-25 cm. For this purpose special plastic clamps are used, which are preferably installed at the joints of the reinforcing bars.
- The distance from the walls of the formwork to the outermost bars of the reinforcement must be more than 2 cm. However, remember that the mesh reinforcement must necessarily go over the walls. And if the walls are built of brick the overlapping distance may be more than 15 cm to the walls of aerated concrete blocks the grid can go to 25 cm or more.
- Use a special tying wire to bind the bars.
- The mesh size of the mesh reinforcement depends on the floor area. Standard sizes are 1515cm, for smaller slabs you can use meshes with a mesh of 2020 cm.
- If the length of the rod is insufficient, it is possible to perform the extension. In this case you should make an overlap, the length of which is approximately equal to 40 diameters of the rod.
The installation of formwork and concrete pouring takes 1-2 days. The rest of the time falls on hardening of the concrete. At different times of the year, the liquid mass hardens differently. On average 30 % of the concrete sets in the first 3 days. In the next 2 weeks the mortar sets by 80% and only after a month (28-30 days) the floor can be considered as ready.
Depending on the air temperature the times may vary. For example, if the installation of the slab took place in summer at a temperature of 30-35 degrees, then after 5 days you can remove the forms from the formwork. If the temperature outside reaches 25 degrees, curing occurs within a week.
In winter, at the level of the mercury column of 10 degrees, the floor is ready in average 2 weeks. At zero temperature only after a month.
Causes of defects and cracks
Various shortcomings that may appear on the monolith, largely related to the quality of materials and non-compliance with the technical norms of installation when working with consumables.
Purchase elements for the monolith (concrete mixture metal reinforcement) is best from proven manufacturers who are able to provide consumers with quality certified products.
The main defects of monolithic slabs are considered:
- Appearance of cracks. Poorly compacted and vibrated areas, unsuitable temperature for work, poor composition with a lot of water and sand.
- Burning of the reinforced parts of the framework. The thickness of the monolith was not sufficient, not enough mortar was poured.
- Voids and cavities. Related to the quality of the pouring, irregularities in the pouring and distribution of concrete on the formwork.
- Apparent presence of foreign inclusions. Caused by inaccurate proportions and the use of unscreened or unsuitable material.
- Irregular joint arrangement. The work was not performed according to the scheme of the plan, due to which the geometry of the surface became incorrect.
- The presence of unconsolidated areas. In the process of pouring there were no stages of the evenness of the creation of the overlap.
Occur all these deficiencies also at:
- Unprepared soil base;
- Lack of concrete proportions;
- using more sand and water than required;
- Poor compacting and vibration distribution of the composition;
- Lack of compliance with the required thickness of the slab;
- Overconsumption of concrete mix.
To prevent defects, it is necessary to accurately perform the steps of installation and preparation for it, according to the project documentation. Identified by the available deficiencies foreman, after a thorough visual inspection and carrying out the necessary measurements.
Any imperfections can be corrected by reinforcing the concrete surface. For this purpose, a layer of concrete is put on a reinforced mesh. If there are large cracks, they are further tightened with an anchor, over which a mortar poured.
The main areas of application of cast-in-place ceilings are buildings with load-bearing walls of brick, masonry or concrete panels, as well as domed houses. The requirements for the monolithic nature of the slab can be determined by
- non-standard building plan;
- the need to significantly increase the load-bearing capacity of the floor;
- higher requirements for hydro and noise insulation;
- The need to provide a free layout;
- reducing the cost of interior finishing.
The casting is usually carried out after the first floor walls have been completed. However, variants of casting cast-in-place ceilings are possible in buildings with a roof, if weather or other conditions require it. In such a case, on the masonry of the lower floor mount I-beams and along the perimeter of the load-bearing walls pour the vein at the height of the slab. Also, to strengthen the mechanical ties, on the inner side of the crown release 4050 cm of embedded reinforcement. Its total cross-section cannot be less than 0.4% of the cross-section of the longitudinal cut of the crown.
For an independent device of monolithic slab formwork builder does not need to know the world trends in the creation of formwork systems. But some information may well be useful, since the principle of the device formwork common to both small houses and high-rise buildings.
Slab formwork is erected with the help of:
- wooden, aluminum or composite beams
- Plywood or other durable sheet material;
- Supports of various designs;
- Various accessories and auxiliary devices.
Horizontal formwork is divided into several types:
Telescopic props can be used when the height of the overlap does not exceed 4.6 m.
Volumetric formwork provides for the erection of slabs up to a height of 12 m, with a monolith thickness of up to 1 m. It can be used for flat and transom formwork, variable-thickness capitals, freestanding bollards. By design, volumetric props are similar to the inventory of metal scaffolding masons, plasterers and painters. where very often used after the completion of monolithic work.
For structures up to 20 m in height, framed formwork is used. It accepts a load of up to 5 tons per axis, and the thickness of the slab can reach 2 meters.
For high-rise buildings, wedge-shaped scaffolding is required.
Assembling the reinforcement scaffold
When building a slab with your own hands, do not forget about laying the reinforcement, without which its operation is impossible. To create a framework is used:
At least 1.5 cm from the formwork, the first layer of framing is laid. The size of its cells no more than 20×20 cm. It is desirable that the length of each rod is sufficient from wall to wall. If the fitting is short, connect 2 bars with an overlap of 40 times their diameter.
The framework will be weakened if the location of joints of short rods in adjacent rows will coincide. It is necessary to ensure that the joints are as far apart from each other as possible. Gaps between the bars are allowed only in the place where an opening in the slab is envisaged. By the way, the reinforcement should border the perimeter of the future hole. Under the other edges of the framework there must be load-bearing structures. The second layer of the monolithic slab framework is laid in the same way. It is located at a certain height above the first layer, but the grid must be recessed into the thickness of the concrete at a depth of 1.5-2 cm.
It should be said that steel pipes, laid parallel to each other between 2 frameworks, will facilitate the weight of the monolithic floor slab. Their cross-section depends on the distance between the bars. If both ends of the pipes will be supported by the walls, the construction will gain additional rigidity. The pipes must not reach the side panels of the formwork. For laying in the framework it is not necessary to use new products.
Technological solutions for monolithic slab on strip foundation
When the place for construction is characterized by unstable soil, it is advisable to erect a combined type of foundation. a monolithic slab on the strip.
All the features of the technology of building a monolithic slab on a strip foundation, the sequence of laying the foundation, as well as possible options for the arrangement of the floor are described in the article.
Before pouring concrete into the formwork, it is necessary to check its reliability, check the presence of all technological holes. The latter include chimneys, ventilation ducts, openings for pipes, cables. boxes, embedded parts and other solutions are provided for all.
Concrete mixture, as a rule, is fed through the distribution hose of the concrete pump. Before delivering concrete to the site, it is necessary to find out whether the auto mixer set has a hose of sufficient length.
Two people are required to take the concrete: one feeds the hose with concrete in the right place of the formwork, the other levels the mixture at a predetermined mark. If the plasticity of concrete mixture is low, the operator can add a little water in it, it will not affect the quality of concrete, and it will be much easier to level and feed the mixture into the farthest corners.
Compaction of concrete is done with a depth vibrator, it can be rented, the cost is small, especially considering that it is needed for a few hours.
After pouring the entire formwork, the concrete is finally levelled and smoothed.
Concrete Monolithic slab for beginners how to diy step by step part 1 of 2 Dirt Boss
Caulking of joints between panels up to 30 cm wide
All of the above is designed for monolithic sections of a width of 30 cm or more. Regulatory requirements imply that the slabs are laid virtually butt to butt, with an allowable gap of 15 mm.
Important! In the range from 15 to 300 mm, the reinforcement of the monolithic areas between the slabs may not be performed.
Several methods are recommended for filling joints:
Plywood, planks, metal sheet at least 0.8 mm thick, OSB or other sheet sturdy material is attached to the bottom of the site. Under it, spacers are placed without any special standards, you get the simplest formwork. To be on the safe side, it is possible to perform minimal reinforcement of the site at the discretion of the contractor. Then it is filled with concrete and dismantled in 3 to 4 weeks.