Technical characteristics of the concrete floor on the ground, the subtleties of filling, pros and cons of

For many construction projects, concrete floors placed directly on the ground provide a sturdy and adaptable solution. These floors offer a strong foundation for a variety of activities and structures, and they are frequently utilized in commercial, industrial, and residential settings.

The filling process is one of the most important parts of ground-level concrete flooring. This entails leveling and excavating the ground surface in order to properly prepare it before pouring the concrete mixture. The final floor’s functionality and longevity are greatly influenced by the caliber of this preparation.

The technical attributes of concrete floors are important in determining their suitability for use on the ground. The strength and longevity of the floor are determined by various factors, including thickness, curing methods, and reinforcement. Comprehending these attributes facilitates builders’ and homeowners’ decision-making regarding their construction endeavors.

There are benefits and drawbacks to using concrete floors for construction, just like any other method. Positively, they resist heavy use-related wear and tear and offer excellent durability. In addition, they offer thermal mass, which lowers energy expenses and aids in controlling interior temperature. However, issues like the requirement for adequate drainage and the possibility of cracking due to ground movement need to be properly thought out and handled.

Black screed design features

One such reinforced supporting constructive element that serves numerous crucial purposes is the ground floor’s concrete screed.

• Serves as a tough basis under the final floor for the first floor of the building.
• Effectively distributes external permanent and temporary loads for the purpose of their subsequent distribution along the compacted soil base.
• Prevents the formation of uneven settlements and tilting of the floor structure, which, as a rule, is separated from the foundations and other elements of the building by an expansion joint.
• If there are heated floors, it serves as the basis for their hidden installation.
• In the case of wet rooms with a ladder for draining water, the screed is made with a slope to direct its flow during operation of the structure.
• Protection for polystyrene foam insulation boards installed under floors on the ground.

In order to prevent shrinkage cracks and deformations, reinforced concrete screed is a load-bearing and enclosing impermeable structure that must be poured according to design using heavy, high-quality concrete.

Is it always made of concrete??

The most common material for ground floor screed is concrete, but other creative, highly durable, weather-resistant, or more economical designs are occasionally permitted, including:

• Reinforced concrete, in the presence of soft soils, karst sinkholes or increased operational loads.
• Hydrophobic polymer concrete, if there is wet soil under the floors, or if the groundwater level rises high during the season.
• Expanded clay concrete, provided that the ground floors are operated without the application of large external loads. This material significantly increases the heat transfer resistance of the building envelope.
• Prefabricated reinforced concrete slabs, subject to the presence of solid, non-subsidence and non-heaving soils in the base and high quality piece reinforced stone elements with formed edges for interlocking.
• Innovative clay concrete mixtures that are used for solid and semi-rocky foundations, eliminating high concentrations of water, as well as deformation under loads.

Typically, a knitted flat frame constructed of steel rods in the lower portion of the structure or a concrete screed reinforced with road mesh is utilized as a rough foundation for the ground floor.

Understanding ground-level concrete floors requires delving into their technical facets, from the nuances of pouring to weighing their benefits and drawbacks. This article addresses potential issues like maintenance and environmental impact while also highlighting the practical considerations associated with installing these floors and emphasizing their affordability and durability. Through an analysis of the advantages and drawbacks, readers will obtain a thorough understanding to enable them to make well-informed decisions regarding their building and remodeling endeavors.

Requirements

Unlike most other forms of rough covering used to finish slabs of horizontal surfaces, floor screed on the ground is a multifunctional structure that serves both enclosing and load-bearing purposes at the same time. As a result, regulatory documents govern the requirements for it:

• GOST 31358-2019 “Dry construction floor mixtures”.
• SP 29.13330.2011 “Floors. Updated edition".
• SP 63.13330.2018 “Concrete and reinforced concrete structures”.
• SP 71.13330.2017 “Insulating and finishing coatings”.

These documents state that the following design and operational requirements apply to screeds beneath floors on the ground:

• Mechanical strength – the screed must withstand all design permanent and temporary loads.
• The absence of cavities, chips, potholes, cracks and other mechanical defects on the surface of the screed after it has hardened, which indicates the high quality of the materials and compliance with the technology for their installation.
• Uniformity of concrete composition, equal fraction of fine and coarse aggregate.
• Availability of reinforcement, according to static calculations and design requirements.
• The thickness of the screed must prevent the formation of through shrinkage cracks and deflections during settlement of the compacted base.
• Waterproofness and frost resistance, depending on the hydrogeological features of the base, as well as the operating conditions of the structure.
• Brand of cement – hydraulic binder in the screed, which must meet the required class of concrete.
• The screed must be compacted before curing immediately after installation to reduce porosity.
• The maximum difference in height of the screed laid under floors on the ground should not exceed 0.3 – 0.5 mm/m.
• The height of the screed must fully satisfy the space-planning solutions of the building and mark 0.000 appointed by the architect.
• If there are different types of finishing coatings on the ground floor floors, the screed height is made with differences to ensure a constant surface level in the rooms.
• If there are heaving soils under the floors along the ground, an additional layer of hydro and thermal insulation from polystyrene foam boards and technoelast is installed.

The quality of the material, as attested to by certificates of conformance for batches of goods sold, and adherence to the technological map during installation and maintenance of reinforced concrete structures are the two main determinants of all screed requirements.

Professionals frequently use non-destructive methods to control the class of concrete and also use geodetic as-built surveying to verify the level installation plane of the base beneath the finished floor on the ground in order to ensure the strength of the finished structure once it reaches a certain stage of hardening.

Technical characteristics and parameters

Screed installed in public or private buildings with ground-level floor designs possesses the subsequent technical attributes and specifications:

• Non-reinforced screed is allowed for non-heaving soils with a deformation modulus of 30 MPa and above.
• The reinforced screed must have a minimum thickness of 70 mm.
• The optimal thickness of the screed in floors on the ground is 120 mm for residential buildings and 200 mm for public, commercial or industrial buildings, provided that there are no specialized technological processes in them.
• In the case of laying hidden utilities in the body of the screed, its thickness depends on the diameter of the pipes and can be increased to 250 – 300 mm, either on the entire plane or locally.
• For standard operating conditions in residential or office premises, the class of concrete for screed can be B12.5 – B15, and for increased loads in shops or industrial buildings, it increases to B20 – B25 and higher.
• The waterproof grade of concrete for floor screed under floors on the ground is W4 – W6, and frost resistance is from F75 and higher, since such structures relate to foundations and zero cycle, which implies aggressive operating conditions.
• The fraction of granite crushed stone in a concrete screed under floors on the ground ranges from 5-20 mm, with a thickness of up to 100 mm, and 15 – 30 mm, with a thickness of over 100 mm.
• For the screed, construction quartz washed sand with granule dimensions from 1 – 2 to 3 – 5 mm is used.
• The Portland cement used to prepare concrete for this design has a strength grade of at least M300, but most experts are inclined to use M400 – M500.
• The screed is reinforced with a road mesh with a cell of 100 x 100 mm or 100 x 200 mm, with a rod thickness of 5 to 6 mm, or with bar reinforcement of a periodic profile of class A500s with a diameter of 6 – 10 mm, with a cell of 150 x 150 mm – 200 x 200 mm , as well as with local reinforcements in areas of high loads or weak soil foundations.
• If necessary, aramid fiber fiber is added to a screed with a thickness of less than 100 mm, which provides continuous reinforcement and increases the crack resistance, as well as the deformable properties of the reinforced concrete structure.

Based on space-planning solutions, applied loads, and static calculations of ground-level floors, the working design establishes all final technical features as well as the geometric parameters of the screed. Materials are chosen using technical and physical-mechanical indicators, and a thorough specification for the project drawings is then created.

Layers of the cake

Ground level screeded floors are a relatively complex reinforced concrete structure made up of the following layers, arranged from bottom to top:

• Continental foundation soil.
• Ring drainage for groundwater drainage.
• A layer of sand and gravel mixture, compacted to a degree of at least 0.95 – 0.98.
• Waterproofing layer made of fiberglass with bitumen impregnation.
• Expanded polystyrene boards with a density of at least 40 kg/m 3 and a thickness of 50 mm or more.
• Sewer outlets from the building.
• Reinforced reinforced concrete slab with a thickness of 70 to 250 – 300 mm (according to the strength calculation of the structure for the project).
• In the body of the slab there is a heated floor structure, as well as other pipe or cable communications.
• A layer of self-leveling floor or a thin leveling screed with polymer additives.
• Finish floor covering from selected materials.

Due to the high cost of overly complex structures and the fact that their use is often impractical, property owners often turn to basement construction as a solution. Therefore, all layers laid in the screed must be justified by the actual soil conditions and operational parameters of the structure’s design.

As a result, the pie mentioned above only applies to general situations; the layers are assigned separately for each design.

What brand of composition is used??

In residential or public buildings, heavy concrete with the following properties and composition is used for traditional floor screeds on the ground (based on 1 m 3 of the finished mixture):

• Portland cement with a grade of M300 and higher – from 250 to 300 kg.
• Quartz sand, medium size, medium density, mass fraction of moisture – no more than 10% – 12% – 750 – 850 kg.
• Granite crushed stone with a granulometric composition of 15 – 30 mm – 1050 – 1150 kg.
• Water for obtaining the finished mixture with mobility P2 – P3 – 180 – 220 l.
• The final density of concrete class B15, F75, W4 is from 2350 to 2400 kg/m2, which is easily checked on standard scales in a 10-liter container (the weight of such a bucket is 23.5 – 24 kg).

It is permissible to use densely crushed limestone and expanded clay gravel in areas without groundwater for building construction. Concrete is treated with plasticizer and antifreeze additives if building is required during the winter.

Proportions and cooking technology

According to the information above, the ratio of C: P: W is 1: 2.4: 4.3 to prepare concrete for screeding beneath ground floor levels, and water is added based on consistency. Before placing such plastic material in the structure, it must be properly mixed. To do this, follow these steps:

• A trough for mixing concrete is prepared, or a mixer with an electric motor is rented.
• Sand is mixed with crushed stone in the required proportions until a completely homogeneous composition is achieved.
• Cement is added to the mixture, portionwise, after opening each new bag, the building composition is constantly mixed.
• Water is added in parts, with an interval of 20 – 30 seconds.
• When the concrete reaches the desired consistency, the water supply is stopped, after which the mixture is mixed for another 5 – 10 minutes to evenly distribute all components throughout the structure of the plastic material.

It should be mentioned that the instantaneous reaction between the water and cement in the hydrated concrete causes the liquid material to set in 1.5 to 2 hours. In order to guarantee the appropriate design strength of the material after hardening, the resultant concrete mixture needs to be incorporated into the structure within the first hour of mixing.

Additional materials

Certain additional materials, or parts of them, are also needed to create such a screed beneath floors on the ground:

• Ready-made road reinforcement mesh, steel bar reinforcement, or composite materials to strengthen the structure.
• Anti-frost additives for concreting screeds in the cold season, at temperatures less than +5 o C.
• Plasticizers, if necessary, to maintain the mobility of the concrete mixture and delay the setting period of the material, in the case of long-term concreting of the screed structure.
• Fiber fibers for structural strengthening of a concrete slab, when conventional reinforcing mesh is not enough.
• Expanded polystyrene balls, if necessary, to reduce the density of a concrete structure and enhance its thermal properties.
• Water repellents that effectively close pores with viscous polymers to prevent moisture from entering the body of a concrete structure, as well as eliminating capillary suction of groundwater when the base under the house is wet.

The quantity of ingredients and building materials needed for them is determined by a number of factors, including the region in which the facility is being built, the season, the physical and mechanical properties of the soil base, and the design specifications for the structure and project.

Guide to installation in a private home

Rough concrete floor screed applied while adhering to several significant technological guidelines and while running a specific algorithm:

• In the ground, between the foundation walls or pillars, a trough is prepared for the installation of floors on the ground.
• All weak base is removed for the purpose of its subsequent replacement with a layer of ASG.
• Continental soil is compacted using vibratory rammers.
• A sand and gravel mixture is prepared with a humidity of up to 15% – 20%.
• The ASG is laid in the trough in layers, with the thickness of each filling no more than 200 – 250 mm.
• Each layer of ASG is compacted with vibrating plates until a compaction degree of 0.95 – 0.98 is achieved.
• It is recommended to pour clean tap water over the compacted soil, then compact it again.
• The top mark of the sand and gravel cushion layer is removed, if necessary, the mixture is added until the base is completely leveled.
• A roll waterproofing is laid over the sand and gravel cushion, which is fused in the overlap areas by at least 100 mm along the length of the roll.
• When the melted areas cool down, a layer of insulation is laid out from extruded polystyrene foam boards with a locking joint in the end parts.
• The polystyrene foam boards are foamed with chemical insulating compounds – mounting foam.
• After installing the insulation, spacers are installed on top of the resulting plane for laying the reinforcement mesh, and an elastic damper tape is glued along the perimeter of the foundation walls or pillars to prevent the transfer of operational loads to building structures, as well as to ensure the correct functioning of the floating floor.
• Next, reinforcement of the future screed under floating floors is arranged, taking into account areas of high stress, according to the detailed design drawings.
• The body of the future structure includes utilities – underfloor heating pipes, water supply, sewerage, as well as cable products in corrugations with a wire broach.
• The flange formwork is leveled.
• The concrete mixture is prepared in accordance with a pre-selected recipe.
• The structure is concreted until the desired level is reached.

It is important to remember that concrete is a weak structural material that can shrink. In order to account for the movement of the concrete mixture during installation, vertical cut-offs and expansion joints are necessary if one of the room’s dimensions is greater than 6000 mm.

If there is a temperature and disposal seam in the trading or other public building, it should be fully replicated by screed under the floors.

Reinforcement

As previously stated, a screed for ground floor applications is an enclosing and load-bearing structure that is hardly ever utilized without reinforcement due to the weak structure of concrete when it bends. Several significant details are considered when reinforcing screeds:

• The screed is reinforced only in the stretched concrete zone. Considering that this design does not have a rigid seal around the perimeter, this zone almost never occurs in the support areas in the upper zone, which requires laying reinforcement only in the lower part of the screed.
• In addition to working in tension, the reinforcement also prevents the formation of shrinkage cracks in concrete, which requires its installation in the required quantity, according to the minimum percentage of reinforcement according to SP. Thus, this reinforcement has a rod diameter of at least 6 mm and a pitch of rods in a cell of at least 200 – 250 mm.
• It is recommended to use reinforcement only with a periodic profile.
• At the bottom of the slab, a protective layer of concrete of at least 15 mm must be maintained to prevent corrosion or cracks in the screed from the ground side.
• The mesh is rolled out with an overlap between the cards of at least 1 cell.
• The rod reinforcement is joined along the length with a value of at least 35 – 40d.
• In one cross-section, it is allowed to join no more than 50% of the rods, and the distance between adjacent overlaps must be at least 100 d to ensure an equally strong section.
• Longitudinal and transverse reinforcement rods are fixed to each other with annealed knitting wiring, but, at the same time, the mesh can be welded, factory-made.
• If it is necessary to lay reinforcement in local areas, it is recommended to install additional rods strictly in the direction of laying the background reinforcement, so that double layering of flat frame elements does not occur.
• Supporting elements to ensure a distance between the insulation or soil base should be exactly as much that the reinforcing rods or the mesh does not bend between these point supports.
• If there are traces of corrosion on the reinforcing bars, it is necessary to treat them with acid compounds, as well as with steel brushes.
• The ends of the reinforcing bars must lag behind the wall structures at a distance of at least 10 mm.
• If it is necessary to install a vertical cutoff for a break in concreting, the reinforcement is tied to the entire structure at once, or when constructing the frame, outlets are left outside the fine-grained mesh so that continuous reinforcement of the screed is subsequently achieved.

Purchasing fittings made solely of premium steel A500c that shows no signs of deep corrosion or bending is advised. Because coil reinforcement cannot be straightened into straight rods, it is not appropriate for building a flat frame.

Possible difficulties

The screed device, which is placed beneath floors on soil, is a responsible construction and installation operation that calls for specific expertise from the master. In this sense, certain issues that could come up during the pouring of this structure and need to be addressed right away to prevent damage to the load-bearing foundation beneath the ground’s floors include:

• Poor quality compaction of the base – the sand and gravel cushion under the screed must be compacted to a degree of 0.95 – 0.98 using special vibration platforms that ensure the transfer of a load of at least 5000 kg.
• The presence of weak foundation soils under a reinforced concrete structure – before starting design, construction and installation work, it is necessary to carry out engineering-geological surveys under the proposed construction site with the preparation of a detailed report on the physical and mechanical characteristics of the soil foundation, after which a decision can be made on the complete or partial replacement of clayey soils , or dusty soils.
• Insufficient thickness of the screed – the power of the structure should fully satisfy the static calculation of the construction structure for 2 groups of maximum states, from the calculation of ensuring the strength and stability of this element of the building.
• Insufficient reinforcement of the structure – when assigning the amount of steel to reinforce concrete in a tensile zone, it is necessary to be guided by the required minimum percentage of reinforcement, as well as stress isofields, based on the calculation results and drawing up diagrams.
• Insufficient protective layer – all reinforcement installed in the lower part of the concrete screed must be distanced from the base by 15 mm or more.
• The presence of cold bridges in the finished structure – when installing floors on the ground in the freezing zone of the base, the installation of polystyrene slabs is required to prevent heaving and ensure the required energy efficiency of the building.
• Uneven surface of the screed – after pouring, before the start of the concrete setting process, it is necessary to smooth and level the upper surface, and, after hardening, perform a geodetic executive survey and, if necessary, refine the reinforced concrete structure.

It is advised that you become familiar with master classes from professional installers before pouring screed beneath floors on the ground in a residential or public building on your own. These installers frequently post their videos online for other users to watch.

Rules for care after work

According to the joint venture schedule, concrete is a unique kind of building material that is poured into formwork in liquid form and strengthens in at least 28 days. Accordingly, unique conditions must be established during the hardening process to guarantee all operational attributes, specifically:

• Immediately after laying and setting, the structure is covered with a flexible fabric or polymer material with a high level of heat transfer resistance to avoid loss of heating energy, which is concentrated during the chemical reaction of cement with water.
• Considering that cement is a hydraulic binder, after it hardens, it is necessary to pour water onto the material, since the structure hardens better at maximum humidity.
• When the outside air temperature is less than +5 o C, it is necessary to add antifreeze additives to the concrete mixture to prevent rapid crystallization of water before the end of the chemical reaction and setting.
• If the outside air temperature is below 0 o C, it will additionally be necessary to install a TMO, as well as a PNSV cable in the body of the reinforcement cage to ensure uniform heating of the concrete without slowing down the chemical reaction.

In order to stop moisture from penetrating the concrete body and causing localized or structural screed destruction, it is advised to fill in any shrinkage cracks that appear on the surface of the concrete right away using a non-shrinkable cement mortar of the NTs type.

Advantages and disadvantages

In practically every construction, if the working design calls for this design solution, a rough floor screed is installed beneath floors on the ground since there are numerous benefits to this method of construction.

• A reliable base under the final floor on the ground.
• The floating structure excludes the roll and transfer the efforts to the foundations of buildings.
• The full distribution of any spot external loads on the ground soil.
• Durability – the design can serve for more than 50 years without the need to repair or replace.
• Complete water resistance, when choosing the right brand of concrete, as well as a reliable roll bitumen waterproofing.
• Reliable protection against freezing, provided that laying polystyrene plates under a plate made of reinforced concrete.
• The possibility of a design of any thickness and configuration.
• The possibility of choosing a concrete mix with various physical and mechanical characteristics.
• The minimum volume of production and repair operations when finalizing the structure after hardening.
• The reliable structure practically does not spread the shock sound wave and structural noise.
• Possibility of masking all utilities in the body of a reinforced concrete screed slab.

However, this design is not without its drawbacks, which is why some builders, designers, and landowners would rather use insulated foundation slabs or other load-bearing structures beneath a building’s first floor:

• Large number of wet processes.
• The need for concrete maintenance.
• Large labor and material costs for manufacturing the structure.
• The need for lengthy preparation before pouring the structure.
• Difficulty in carrying out work in winter.
• Risk of defects due to the large number of manual work operations.
• Large mass of the structure, which requires a reinforced base.
• Without insulation, reinforced concrete has extremely low thermal conductivity, which can cause freezing of building premises.
• High risk of corrosion of reinforcing steel.
• The need to attract a large number of professional gasoline or electric units.

It is advised to plan the project ahead of time, evaluate the technical and financial indicators, and create an investment plan that will assist in selecting the best design before deciding whether to install screed beneath the soil floors of the building.

Useful video

Furthermore regarding the device:

Technical Characteristics	The concrete floor on the ground is typically a slab poured directly onto soil or a compacted base. It"s designed to support the intended loads and provide a stable foundation.
Subtleties of Filling	Preparing the ground properly is crucial. This involves leveling, compacting, and possibly adding a layer of gravel or sand for drainage and stability before pouring the concrete.
Pros	Durable and long-lasting, resistant to moisture when properly sealed, can be reinforced for added strength, suitable for various types of flooring finishes.
Cons	Susceptible to cracking if not properly installed or if the ground shifts, can be costly depending on the area and depth, may require professional equipment and expertise.

A ground-level concrete floor’s longevity and usability are determined by a number of important factors that must be taken into account during construction. The subbase’s appropriate preparation is one of the most important components. It is necessary to level and compact this foundational layer thoroughly in order to give the concrete a stable surface. Inadequate preparation can lead to long-term problems like settlement and cracking, which weaken the floor’s structural integrity.

The mix design is important when it comes to filling the concrete. The concrete’s strength and workability are determined by the proportions of cement, aggregate, and water. Adequate mixing and placement are crucial for guaranteeing strength and homogeneity across the floor. By paying close attention to these details, problems such as segregation or insufficient strength in different areas of the floor can be avoided.

The longevity of a concrete ground floor is one of its main benefits. It can effectively resist wear and tear and support heavy loads when installed and maintained correctly. Because of this, it offers a durable flooring option that is appropriate for high-traffic areas in both residential and commercial settings.

On the other hand, ground level concrete floors have disadvantages just like any other construction technique. One significant issue is the possibility of cracking, particularly in cases where the concrete mix or subbase preparation are subpar. Cracks may need to be repaired in order to stop future damage over time because they can let moisture in. Furthermore, depending on the size of the project, the initial installation of a concrete floor may need specialized equipment and be labor-intensive.

In conclusion, even though ground-level concrete floors are highly durable and adaptable to a range of settings, their advantages and lifespan can only be fully realized through careful concrete mixing, appropriate subbase preparation, and continuous maintenance. When selecting this kind of flooring for their construction projects, homeowners and builders can make more informed choices if they are aware of these technical features and factors.

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