Precast reinforced concrete strip foundation: materials, characteristics, device

Any construction project must start with the construction of a solid and long-lasting foundation. Precast reinforced concrete strip foundations are one common option. This kind of foundation ensures stability over time and provides a sturdy base to support the weight of the structure above.

The advantages of prefabricated concrete components and the sturdiness of steel reinforcement are combined in precast reinforced concrete. The end product is a foundation that is reasonably simple to install and strong. Precast components shorten the construction period and improve consistency in foundation quality.

If you intend to use a precast reinforced concrete strip foundation, it’s critical to comprehend the components used, the essential qualities that make this kind of foundation efficient, and the construction process. Every one of these elements is essential to the project’s overall success.

Materials for precast reinforced concrete foundation

The very definition of the house’s foundation (base) requires that this design be given extra consideration. Since it is impossible to choose the wrong materials when building a structure of this kind, the primary attributes of the materials that comprise the precast reinforced concrete strip foundation will be discussed in this chapter.

Reinforced concrete foundation slabs

The purpose of reinforced concrete foundation slabs is to transfer the weight from the structure’s walls to the foundation’s soil base.

The subterranean portion of the foundation is built using concrete slabs, which are composed of heavy concrete with a density of 2200–2500 kg/m3. These slabs can be built on both dry and water-saturated soils, with an acceptable air temperature of up to –40°C (cm. table).

Strip foundations with reinforced concrete slabs (GOST 13580 85) are categorized into four groups based on the weight and thickness of the walls that rest on them.

The product’s alphanumeric marking designates each of these groups:

1. Product name — FL and slab width in decimeters.
2. Foundation slab length in decimeters.
3. A number indicating the group number according to the bearing capacity of the product.
4. A letter indicating the value of concrete permeability.

The concrete permeability parameter is typically indicated for reinforced concrete slabs used in environments where they are subjected to aggressive factors.

1. N — low permeability.
2. P — reduced permeability.
3. O — especially low permeability.

As an illustration, consider the following: a reinforced concrete foundation slab measuring 2380 mm in length and 1600 mm in standard width, with a load-bearing wall thickness of 160 mm, is identified by the following marking: FL16.24–2. The same slab appears as FL16.24–2–N (low permeability) when viewed through the lens of the concrete permeability index.

Foundation blocks for precast foundations

Blocks of reinforced concrete for the foundation When constructing a building’s foundation, FBS works in tandem with reinforced concrete foundation slabs; however, the slabs only serve as a base, or cushion, and the foundation blocks serve as the building’s load-bearing walls in the basement and subterranean areas. They can also be employed in the construction of industrial building and structure enclosures.

When compared to traditional monolithic foundations, the construction and installation of a building can be completed considerably faster when precast reinforced concrete foundation technology is used.

While it is true that the total cost of building such a structure will be higher than that of a ready-made monolithic foundation, the prefabricated option appears to be more cost-effective when considering the installation time of ready-made enlarged elements of a prefabricated foundation as well as the overall time required to pour and gain the design strength of a monolithic foundation.

FBS blocks with the following modifications are typically utilized for individual construction:

• made of heavy concrete;
• made of silicate concrete;
• from expanded clay concrete.

Any kind of foundation block should have an average density of at least 1800 kg/m3 (see table).

Based on their design, foundation blocks fall into three categories and are produced in compliance with GOST 13579 78 and building codes.

1. Solid foundation block (FBS).
2. Solid foundation blocks with openings for laying communications and cutouts for laying lintels (FBV).
3. Hollow foundation block (FBP).

Similar markings are found on FBS and FL, or foundation slabs. For instance, the block is 2380 mm long, 400 mm wide, and 580 mm tall on average; it is solid – FBS24.4.6-T.

Hints: the choice of the necessary parameters of the foundation blocks is regulated by the design documentation. Based on the planned load on the foundations of the building, the necessary design and the brand of the block is selected.

This video will teach you more about strip reinforced concrete foundations:

Preparatory stages for constructing strip foundations

It takes a number of technological steps to prepare the construction site and excavate the area designated for construction before building a strip foundation out of concrete blocks.

1. Clearing the construction site: removing debris, uprooting trees and bushes, moving utility networks (if necessary).
2. Soil cutting near the construction site.
3. Conducting geological studies of the soil within the boundaries of the future building.
4. Carry out a geodetic breakdown of the building’s foundation with the removal of the building’s axes in nature and securing them at the construction site.
5. Laying temporary water and electricity networks.
6. Carry out excavation work to construct a pit or trenches for the construction of a prefabricated strip foundation.
7. If necessary – equip the fence of the construction site.

It is advised to work on the investigation of the building site’s soils even while the structure is being designed. Because: the conclusions drawn from geological analyses of the soil in the vicinity of the building that is currently under construction will determine the depth of the future foundation.

It is preferable to get in touch with a specialized organization in order to perform geological studies of the soil situated inside the future structure’s boundaries. It will expertly carry out tests and give the client an overview report on the state and kinds of soils on the building site.

Cutting off topsoil and marking the axes of the future building

During the preparation phase, removing the topsoil and saving it for use on the individual plot is a crucial environmental procedure.

The organic inclusions in the soil layer are abundant (remains of roots, grass, etc.). Fungi can grow when these materials rot and damage wooden structures inside and outside of buildings if they are not removed within the bounds of the new construction.

Soil cutting can be done by hand without the need to mobilize specialized equipment, depending on the area of the building under construction. The size of the prepared construction site should be 1.5 meters greater than the total size of the building that is currently being built.

Once the aforementioned tasks are finished, you can start designating the building’s axes. The building’s main axes are removed and brought to the construction site to start the pit’s breakdown for the reinforced concrete strip foundation.

The building’s axes are marked and removed using specialized geodetic tools, such as a theodolite and level, which enable you to complete the full scope of declared work with expert precision and high quality. If these tools are not available, you can still construct the building with the most basic tool you can make yourself.

You can use the following methods to mark the major axes of your own home’s foundation:

1. From even planed slats, we construct a right-angled triangle with side dimensions of 3, 4 and 5 m. On the site, we mark the top of one of the future corners of the building with a peg, and apply a measuring tool made by hand to this mark.

1. After this, parallel to the sides of the triangle, using a cord, we set aside the distances of the corresponding walls of the building, and using pegs we fix these points on the ground.
2. We repeat this procedure with the remaining, unmarked fourth corner of the building.
3. The correctness of the marking is checked by measuring the diagonals between the opposite marks of the corners of the building (the values ​​​​should be the same).

Reminder: Keep in mind that marking is done along the building’s axes. As a result, you must set aside the wall’s design thickness in directions other than these axes in order to determine the actual wall dimensions.

We equip a formwork (an extension) after marking the building’s main axes, parallel to the finished layout axes and two to three meters away from the pit’s edge. The formwork is made up of edged boards that are nailed to wooden posts that are at least 1.0 m high and shaped like the letter "P." The board used for the extensions’ crossbars needs to be at least 40 mm thick.

Mark the main layout axes in the center of the crossbars of the formwork. Number and fasten the markings with cuts or nails. Mark the thickness of the building’s walls to the left and right of the main axis.

During the entire construction phase, the formwork serves as a reference point for the building’s dimensions. Once the above-ground portion of the foundation is constructed, the formwork is moved to the building’s base. You can now build trenches or a pit for the strip precast reinforced concrete foundation as the marking of the foundations is finished.

Earthworks

For buildings with a cellar or basement, reinforced concrete strip foundation composed of FBS blocks is typically utilized during construction. The entire excavation process involved in installing a foundation pit needs to be accompanied by, and it is preferable for it to be completed by, a specialized organization with qualified staff and specialized equipment.

The horizontality of the base and the depth of the open foundation with the thoroughfare level must be monitored and controlled while the excavator is excavating the soil. Taking into consideration the manual soil refinement at the locations where the reinforced concrete plates (FL) of the prefabricated foundation are to be laid, the junction of the pit should be 15–30 cm shallower than the design depth.

The last stage of pit refinement for installation is done by hand, and it is necessary to confirm that the base is horizontal and that the breakdown of the building’s main axes is accurate.

Precast reinforced concrete strip foundations are a common option for building projects because of their strength, longevity, and simplicity of installation. This kind of foundation, which is made of steel-reinforced precast concrete sections, has a high load capacity and can support a variety of building styles. It is intended to disperse a structure’s weight uniformly, lowering the possibility of it settling or cracking with time. An enduring and trustworthy foundation for your project is guaranteed when premium materials and appropriate installation methods are used.

Calculation of the strip foundation

The device of foundations from prefabricated reinforced concrete

The primary technological process in building and structure construction is the installation of reinforced concrete foundation structures. The building’s durability and appearance are greatly impacted by the caliber of the installation job.

The amount of time needed to install prefabricated components determines how quickly the remaining tasks must be completed and, in turn, when the facility must be fully commissioned.

Installation of reinforced concrete foundation slabs

A 100 mm-thick layer of sand is the base for a concrete slab foundation. If there is loose soil at the foundation’s base, it needs to be removed, and then rammed in place with a mixture of crushed stone and sand. The breadth and length of the sand cushion are extended by 20 to 30 centimeters in order to keep the foundation slabs from hanging from the sand base.

Using a plumb line at the intersections of the main axes, the corners of the foundations at the bottom of the pit are identified by pulling a cord or metal strings between the formwork. Metal moorings, or pegs, are used to mark these locations. They are positioned 2-3 mm away from the precast reinforced concrete strip foundation’s closest side edge.

Utilizing a truck crane, foundation slab installation is done. In order to prevent the soil from collapsing, it shouldn’t be placed too close to the pit’s edge.

The sand base’s surface cannot be damaged during the installation of a reinforced concrete slab; slings can only be removed once the foundation slab is fully positioned in its designated location.

A two-meter rack level is used to measure the horizontal level of the slab installation (rule). The rule’s edge ought to align levelly and snugly with the base of the foundation slab made of reinforced concrete. A sledgehammer is used to secure the foundation slab mounting loops to the base, and concrete mortar is used to fill the joints and monolithic areas between the slabs.

Installation of foundation blocks of basement walls

The surface of the reinforced concrete slabs is leveled with mortar and reinforced with reinforcement following the installation of the foundation sole. Roll material is used to lay horizontal waterproofing after the reinforced layer has dried.

The inner portion of the waterproofing is next to the basement floor waterproofing, while the outer protruding portion is wrapped around the vertical walls and connects with the vertical insulation.

The required tools must be ready before foundation blocks are installed. After laying two or three blocks, position the mortar box so that it doesn’t move, diverting the crane’s attention from more work.

Guidelines and suggestions for installing a precast reinforced concrete strip foundation:

1. Assembly of a strip precast reinforced concrete foundation begins with laying corner (beacon) foundation blocks at the intersection points of the load-bearing walls. The solution is laid out using a shovel, but it is better to level the solution with a metal or wooden lath. In this case, it is possible to maintain the thickness of the layer and achieve a perfectly smooth surface.

1. The blocks are lifted by two mounting loops using a truck crane and placed in the designated place on the prepared layer of mortar.
2. After laying the lighthouse foundation blocks, a mooring cord is pulled along the edges of the prefabricated foundation strip, raising it to the height of the outer edge of the foundation blocks. Then all the other blocks are laid along the cord, not forgetting to leave holes for laying utilities (electricity, water supply, etc.).
3. After laying a number of blocks, the horizontality of the surface is checked, and if it is broken, the block is raised again and repositioned.
4. The gaps between the reinforced concrete foundation blocks planned by the project, as well as the junction points of the foundation blocks of the transverse and longitudinal walls, are filled with concrete mixture.

The next stage of installing a prefabricated reinforced concrete foundation is vertical waterproofing, which is completed after the foundation blocks for the subterranean portion of the foundation are installed.

Vertical adhesive waterproofing of prefabricated strip foundations

If the walls of a reinforced concrete strip foundation are not shielded from this effect by vertical roll-on waterproofing, the foundation will become saturated with moisture when it comes into contact with the ground.

Using special gas burners, rubber-bitumen mastic (one option) is applied to the foundation’s outer walls to adhere rolled waterproofing (aquaizol, waterproof, etc.).

The following is the sequence of steps for installing vertical roll waterproofing on basement walls:

• clean the surface of the walls from dust, dirt and mortar residues;
• seal the seams and eliminate all irregularities in the surface of the foundation walls;
• prime the surface of the base of the walls with a special primer;
• roll out a roll of waterproofing and cut sheets of the required length based on two layers of insulation coating;
• using a spatula, a thin layer of mastic is applied to the primed base, and on it, from bottom to top (overlapping), using a gas burner, the prepared sheets of waterproofing are fused;
• the height of the vertical waterproofing is determined by the level of the blind area or sidewalk.

Backfilling the pit sinuses with soil is done from the outside of the foundation once the foundation structures have been completed and the foundation walls have been covered with vertical waterproofing (see photo).

Backfilling needs to be done in layers (30–50 cm), with pneumatic or electric rammers used to compact each successive layer of soil.

Material	Characteristics and Device
Concrete	Forms the main body of the foundation, providing strength and durability. Typically, a concrete mix with a specific grade is used to ensure proper load-bearing capacity.
Steel Rebar	Embedded within the concrete, steel rebar reinforces the structure, enhancing its resistance to tension and preventing cracking under stress.
Gravel or Crushed Stone	Used as a base layer under the foundation, it ensures proper drainage and stability by preventing the concrete from settling or shifting.
Waterproofing Membrane	Applied to the exterior surface of the foundation to protect it from moisture, reducing the risk of water infiltration and potential damage.
Formwork	Temporary molds that shape the concrete while it cures, ensuring that the foundation maintains its desired dimensions and shape.

For many building projects, precast reinforced concrete strip foundations provide a sturdy and long-lasting solution. They are a popular option for both residential and commercial applications because of their modular design, which expedites the building process.

These foundations are renowned for their durability, strength, and resistance to environmental elements. An enduring foundation can be guaranteed by utilizing premium materials and appropriate installation methods.

The unique properties of precast reinforced concrete, such as its load-bearing capacity and compatibility with your overall design, should be taken into account when planning your project. To fully reap the rewards of this kind of foundation, careful preparation and implementation are essential.

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