Binding of fiberglass reinforcement strip foundation. How to knit fiberglass reinforcement

The construction market is constantly updated with interesting and modern innovations. Composite fiberglass rebar is one such newer material. At the moment, not everyone knows what it is for and how it is used correctly.

Since 2012, the interest of builders in this product has been constantly growing, since the price of this material is not so high, and the quality allows it to be used for pouring the foundation not only for residential buildings, but also for the construction of larger structures, for example, bridges. It is especially relevant in the north, since metal reinforcement is subject to corrosion, while fiberglass does not have such a problem.

SPECIFICATIONS

Fiberglass rebar is a mixture of strong fiberglass and heat-resistant resin.

In the aforementioned year, GOST was published, which clearly established the parameters of its parameters:

Diameter - from 4 to 32 mm
The temperature at which the material can be operated - from 60 degrees Celsius
The maximum tensile strength is a measure of the force with which a material is stretched and its cross-sectional area. For fiberglass reinforcement, the norm is 800 MPa.
The maximum compression strength is 300MPa.
Maximum strength - more than 150 MPa.

ADVANTAGES OF FIBERGLASS REINFORCEMENTS

This type of building material is significantly different from the usual steel and has a lot of advantages compared to it:

Corrosion resistance. Fiberglass fittings are absolutely not afraid of alkaline and acid environments.
Light weight with high strength. Its weight is 10 times less than that of steel.
Low thermal conductivity, which protects walls and foundations from freezing, which is especially important in the northern regions.
Non-conductive current and no interference.
Price. For the same price as small-diameter steel reinforcement, you can purchase larger-diameter fiberglass.
High tensile strength of the material. This figure is 3 times higher than that of steel reinforcement.
No seams. Before transportation, metal bars are cut to fit the parameters of the vehicle in which they are transported. Subsequently, the reinforced mesh has many connections, which are the weakest points in the foundation and walls. Since fiberglass rebar is supplied in coils up to 150 m, it does not need to be cut, which results in a minimum number of seams. Transportation can be carried out even in the trunk of a car.

No overpayment for the amount of material. Metal fittings are sold in the same length of 12 m, less than it can no longer be purchased, and fiberglass can be bought in the quantity that is necessary for construction.
No need to buy additional tools when installing fiberglass reinforcement, for example, a welding machine.
The coefficient of expansion that is the same as that of concrete under thermal exposure is a guarantee of the absence of cracks in the finished structure.
Despite all the advantages mentioned, fiberglass reinforcement has one main drawback - it is a high probability of fracture. For steel bars, this figure is much higher.

It is because of this indicator that fiberglass reinforcement is used only when it is necessary to comply with certain restrictions on corrosion, dielectric properties and heat conductivity. All structures that are built above certain limits are made at the risk of the builders. Manufacturers convey this information to buyers directly on branded labels.

USE OF MATERIAL IN CONSTRUCTION

Industrial construction has long and widely used fiberglass reinforcement, in contrast to low-rise ones. Judging by the advantages and disadvantages, it is possible to clearly protect the scope of fiberglass reinforcement. These are, for example, works on bank protection, construction of roads. This material is very popular in suburban construction. It is used for reinforcing walls, foundations, most often strip foundations, and aerated concrete masonry.

Important! Reinforcement of the masonry is made by a combination of steel and fiberglass reinforcement.

REINFORCEMENT PREPARATION

Before pouring the foundation, you need to properly knit reinforcement for greater strength and stability of the structure. This allows you to tie the reinforcement into a single structure, thereby creating the supporting frame of the building. The power of the overall structure of the foundation must be provided with additional stiffeners. For this you will need:

Important! The knitting wire should be round, do not take a square one, since when twisting the wire can damage itself.

There are several types of crochet hooks:

These materials must be chosen very carefully. For example, the binding wire must be fairly thick to avoid breaking when the concrete is applied to the frame. Otherwise, the ligaments may burst, and the design of the tape base will turn out to be asymmetric, which should not be allowed.

The whole process is divided into steps:

Particular care must be taken when tying corners. In hardware stores, you can buy special elements that are easily installed in place of corners.

Important! In the corners, reinforcement can only be knitted by hand, without heat exposure.

The finished frame is laid into the formwork in a horizontal position of the grids.

This method is very common among builders who knit reinforcement with their own hands. In addition to it, there are several more options for fastening reinforcement for a strip foundation:

Important! Before starting work, it is necessary to clearly determine what loads are planned for the strip foundation, and what is the scope of work.

CREATING A FOUNDATION WITH FIBERGLASS REINFORCEMENTS

After the master has finished knitting the reinforcement, you can proceed directly to the reinforcement.

For a tape-type foundation, rods are used with a diameter of 8 mm, which is comparable to metal reinforcement with a cross section of 12 mm.

Important! The foundation is performed on a perfectly flat surface.

The algorithm of actions is as follows:

Fiberglass rebar is a relatively new building product, but it has already become quite popular among those involved in private construction. In addition, fiberglass reinforcement is also carried out on an industrial scale in the construction of roads, the construction of bridges, the strengthening of banks, and construction.

Do-it-yourself knitting of reinforcement is a simple process that is easy to perform with all the necessary materials. Even an unprepared person can do it, one has only to try on several elements. This favorably distinguishes fiberglass reinforcement from steel, to create a frame from which you need a welding machine and experience with it.
1. The transverse bars of the lower layer are laid on reinforcing clamps, which are installed before work is carried out.
2. The share rods are cut and stacked at the required distance from each other, the bonding points are marked on them.
3. Jumpers are installed at right angles to the equity rods, each of which is connected in the marked places. If knitting is done with wire, then it must be folded in half and firmly fixed with a hook. If clamps are used, then each of them is tightened more tightly.

Composite reinforcement refers to modern materials designed to replace expensive rolled metal products and provide greater resistance to the negative influence of external factors. After this type of polymer rod began to be produced in Russia in 2012, the interest of builders in it began to grow every year.

The use of fiberglass materials for reinforcing monolithic concrete structures is especially important in cases of possible exposure to moisture, since polymers are not susceptible to corrosion.

Plastic rods are used at individual buildings, in the construction of large buildings and structures, for coastal fortifications and highways. In private construction, reinforcing frames for strip and slab foundations are made from it, as well as reinforced masonry from foam concrete blocks.

The material from which the plastic fittings are made is a polymer mixture of high-strength longitudinal fiberglass and a heat-resistant resin. Standard diameters of produced rods range from 4 to 32 mm. Maximum operating temperature 60˚C. Tensile strength 150 MPa.

Preparation of materials for the assembly of the reinforcing frame

To increase the overall strength of a concrete monolith, it is reinforced with a fiberglass reinforcement structure in the form of a flat mesh or a spatial frame, which is assembled from round rods of variable or constant cross section. Separate elements of such structures are interconnected using a knitting wire, fixing clamps or a special gun.

Therefore, for knitting a reinforcing frame, you must purchase:

plastic fittings of design diameters;
knitting wire or long clamps.

Unlike traditional metal rods, fiberglass rebar is supplied as a rolled coil.

Therefore, before starting the assembly of the frame, it must be unwound and cut into pieces of the required length. Cutting is done with a hacksaw or other tool that does not allow heating of the material. Marking the cut points on the surface is easy to do with an ordinary marker.

The knitting wire must be of round cross-section and with a diameter of at least 1 mm in order to provide the necessary strength of the connection and not burst when twisted. To quickly obtain pieces of wire of the length required for knitting, the entire coiled coil must be cut with a grinder into 3 or 4 parts.

To make knitting wire softer, it can be burned in a flame with a blowtorch or in a fire. Unfired wire bends worse and does not always provide a tight grip on the joint. In addition, unprepared metal has less ductility and more often breaks during operation.

Knitting with collars.

General knitting pattern.

Rebar wire tying tool

Using pliers for knitting is not very convenient. They do not provide the necessary connection coverage density and require a lot of effort. Therefore, steel wire is twisted on reinforcing bars using special hooks or a knitting gun. Tool stores offer for sale two types of hooks designed to knit reinforcement:

simple manual, which must be rotated all the time during operation;
semi-automatic screw, with a hook rotating when the handle is pressed;
plastic clamps in the form of rings and vertical racks worn on reinforcement.

You can not buy a simple hook, but make it yourself (more on how to do it -), bending it from thick steel wire and sharpening the tip. In this case, you will have something to knit a project design from rods without buying a tool.

The way you use a knitting gun makes the process quicker and easier, but this rather large tool may not provide access to certain places. In addition, such a tool leads to an overrun of the wire.

Plastic clamps are needed in order to fix the assembled reinforcing cage in the required spatial position inside the formwork before concrete is supplied.

Technology of manual wire knitting of fiberglass reinforcement

In order for the reinforcing cage or mesh to take the necessary spatial shape and not change it when pouring concrete, all individual elements must be securely connected to each other. Most often, knitting wire is used for this. Knitting is a simple and fast way of joining, which does not require high qualification skills. In addition, fiberglass reinforcement is simply impossible to connect by welding, and therefore this type of fastening is most appropriate in this case.

The whole process of how to knit fiberglass reinforcement for a foundation can be divided into the following step-by-step steps:

the rebar rolled up into a bay is unwound and cut into segments of the design length;
plastic clamps are put on the transverse bars of the lower reinforcing layer;
longitudinal rods are laid on the spaced transverse elements at a given distance from each other;
at all intersections of the reinforcement, connections are made by twisting loops from a knitting wire folded in half;
after assembling the bottom row, vertical reinforcing elements are knitted to the intersections of the outer cells;
to the upper ends or to the middle of the vertical racks, depending on the design number of rows, transverse segments are tied;
the next row of longitudinal reinforcement is laid and knitted;
the assembled frame is transferred and installed inside the formwork for the strip foundation.

The work can be greatly simplified if you combine fiberglass reinforcement with metal. Rectangular frames can be prepared in advance from steel rods and then it will not be necessary to perform a separate knitting of vertical segments.

The nuances of knitting structures for pouring a slab foundation

Reinforcement of monolithic supporting bases of slab type is carried out in the form of one or two rows of meshes, depending on the design solution. Therefore, in this design, reinforcing bars are not considered as longitudinal and transverse. To raise the lower mesh above the waterproofing layer, plastic clamps are placed on the reinforcement every one and a half to two meters. This allows you to install the reinforcing cage strictly in a horizontal plane at a given height.

An important feature of the assembly of reinforcement for a slab foundation is that it is produced on site. This is necessary because of the large size of the structure and the impossibility of subsequent movement. Therefore, during knitting, it is necessary to be extremely careful not to step on the laid reinforcing bars and not damage the structure.

In the Swedish and Finnish insulated slab (more about it in), it is necessary to provide for the intersection of the rods of the slab with the reinforcing cage of the side support tape. To do this, the rods are cut longer, let them on the vertical side reinforcing cages and tied with wire.

The nuances of knitting fiberglass frames for strip foundations

Features of the assembly of reinforcement for a strip foundation is the presence of lateral junctions, intersections and corners.

At the junction of the tapes under the inner walls, the connection of the perpendicular frame with the outer one is carried out using bent U-shaped elements.

In the corners, the reinforcement is bent at a right angle or prepared L-shaped elements are tied. The length of the overlap of the connected bars must be at least 30 cm, and at least 2 knittings are performed in this area.

Fiberglass reinforcement should be bent very carefully, without applying heat treatment. The elastic properties of the plastic make the bending procedure quite difficult. Therefore, for the assembly of corners and junctions, it is recommended to buy bent factory-made elements.

The intersections of fiberglass reinforcement under the strip foundation can be connected by straight segments or one of the intersecting structures can be assembled at the installation site.

Assembly of reinforcing cages can be carried out in an open area, away from the excavated trench. Proper laying of an already assembled structure provides for a distance of at least 25 mm from the formwork walls and the bottom.

Finally

Knitting fiberglass reinforcement for the foundation is a technologically simple process that does not require special professional skills. Even an unprepared person can quickly learn it. You just need to practice a little.

The light weight of the material greatly simplifies the work, and the large length of the reinforcing bar in the bay allows you to cut the rods of any required length. This reduces the number of joints unlike steel materials.

For more information on how to properly knit fiberglass reinforcement, you can see the following videos.

Regulatory confirmation

Composite reinforcement has many advantages and has been used in construction for many years, but it is considered a new material in the domestic market and causes controversial opinions about the effectiveness of its widespread use. Opponents of the technology of reinforcing a strip, slab or TISE foundation with non-traditional material argue that its regulatory framework remains weak, the quality has not been tested by time, and serious research in this area has not yet been conducted. Allegedly, therefore, large construction companies are in no hurry to massively use composite reinforcement in concrete structures. In fact, in Russia there are already several GOSTs related to the material. Namely:

GOST 31938-2012 - establishes the technical conditions applicable to rebar of a periodic section;
GOST 32486-2013, GOST 32487-2013 and GOST 32492-2013 - indicate methods for determining and measuring characteristics for the durability of composite reinforcement, material resistance to aggressive environments, as well as methods for establishing tensile strengths for several parameters.

State regulations specify the recommended nominal diameter of composite reinforcement from 4 to 32 mm, which, according to the requirements of SNiP 52-01-2003, can be used in the design of reinforced concrete structures. In accordance with the technical conditions announced in GOST, the cross section of the rods may have other sizes. Products with a diameter of 4-8 mm are supplied in coils (coils or on drums) according to a predetermined size, or in measured length - in segments from 0.5 to 12 meters.

Enterprises producing fiberglass reinforcement for the foundation have industry and their own technical specifications with test reports, as well as certificates. But the presence of only this documentation without confirmation of compliance with state regulations is insufficient!

Classification

Composite reinforcement for the foundation is a non-metallic rods made of fibers of various origins and binders in the form of polyester resins. The power rod is responsible for the main physical and mechanical characteristics. The anchoring layer, spirally wound around the rod, has protrusions and is intended for improved adhesion to concrete. It does not allow pulling out the reinforcement from the body of the foundation.

Depending on the reinforcing component, composite reinforcement for foundations or walls is divided into:

glass composite - has the designation ASK;
carbon composite - has the designation AUK;
basalt composite - has the designation ABK;
aramidocomposite - has the designation AAK;
combined with composite components - ACC.

It is possible to replace metal rods in the foundation structure with smooth or ribbed (spiral) fiberglass reinforcement. A special glass thread, called a rovig, is wound around the rod during the manufacturing process of the material, after which it is heat-treated. This technology makes it possible to manufacture highly reliable composite reinforcement, which makes it possible to use it in critical structures.

Distinctive features of fiberglass reinforcement

The main advantage of reinforcing the foundation with fiberglass reinforcement is the possibility of its construction on problematic soils. Besides:

the light weight of the rods makes it possible to reduce the total weight of the structure and deliver the material to the object by a conventional vehicle;
simple cutting is provided by the pliability of the material and simplifies the assembly of the frame;
the absence of corrosive processes does not allow the destruction of the structure due to rusting of the reinforcement;
technical characteristics make it possible to use fiberglass rods when installing piles TISE foundations;
low thermal conductivity eliminates the occurrence of "cold bridges" in the design;
the tensile strength of fiberglass reinforcement exceeds that of metal rods by more than two times;
the ability to pass radio waves solves the issue of shielding electromagnetic signals;
the non-conductivity of electricity makes the structure safe and protected from the action of stray currents.

We can say that outwardly fiberglass reinforcement is not much different from metal, except perhaps in color. But knitting composite rods is different, since plastic clamps in the form of special clamps are used to properly connect non-metal frames, and not welding or steel wire.

Among the negative aspects of composite reinforcement can be noted:

unsatisfactory heat resistance, significantly inferior to metal counterparts, which causes problems in case of fire;
insufficient fracture strength;
low modulus of elasticity, which does not allow the use of rods in curved structures due to the difficult fixation of reinforcement in the desired position, and in floor slabs and grillages of TISE foundations - due to the easy bending of the material, forcing concrete to work in tension.

It should be borne in mind that fiberglass reinforcement is inferior to carbon and basalt composite counterparts in several respects, but the application of a sand coating makes it stronger and more expensive at the same time.

Calculation of footage and laying of composite reinforcement

It is possible to avoid overspending of material for strip, TISE, columnar and slab foundations by performing the correct calculation. For a slab structure, it is required to know the length and width of the site, which will determine the size of the rods. Knowing their pitch in the transverse and longitudinal directions, it is possible to calculate the number of ribbed reinforcements, but it should be borne in mind that the grids in the slab must be located in the lower and upper zones. Multiplying the indicators, get the total length of the working reinforcement. Smooth rods are installed vertically. Their height depends on the height of the slab, and the number depends on the number of cells in the frame.

For a strip foundation made of fiberglass reinforcement, calculations are made in a similar way. Knitting the rods, in this case, is allowed on a separate site, followed by laying the finished spatial frames in the prepared formwork. For a strip foundation, the working rods laid along the length must necessarily have a ribbed surface.

In TISE columnar foundations and piles, the main reinforcement is located vertically. Depending on the calculations, they can contain from two to four evenly spaced ribbed rods. Their length is the sum of the depth of the well foundation drilled for TISE, or the height of the column, and the size of the releases that serve to interface with the upstream structures. As for the strip foundation, the length of the rods is multiplied by their number and the total length of the working reinforcement is obtained.

The number of transverse bars depends on their pitch, and the size depends on the diameter of the column or well. Having determined their total length in a single structure, the figure is increased by the number of concreting points and the required length of fiberglass reinforcement installed horizontally in piles and pillars is determined. Frames are prepared in a specially designated area for this. The elements are cut to size and tied together with plastic clamps. The finished frames are lowered into the wells, after which they are poured with concrete.

If the project provides for additional support of the grillage on the ground, then the metal rods of the frame can be replaced with fiberglass reinforcement.

The design of TISE foundations, which have become popular due to simple technology, versatility and speed of construction, provides for the installation of a grillage above the ground. In connection with this feature, the installation of composite reinforcement in it must be confirmed by careful calculations. Otherwise, only metal rods are used to make the frame.

Technological progress inexorably invades all sorts of spheres of modern life. He could not ignore the area of building materials. Every year, the market is replenished with new developments that make it possible to facilitate and simplify the construction process. It is thanks to new technologies that today it has become possible to lay the foundation of fiberglass reinforcement as the basis for low-rise buildings. This type of building frame, having appeared on the market not so long ago, has already managed to significantly oust the usual and popular iron and steel products. What are the main advantages of fiberglass? What is its scope?

Comparative characteristics of materials

The very name of this material contains its main characteristic. It is made from plastic or glass threads, firmly soldered together into homogeneous rods with either a smooth or corrugated surface structure and a circular cross section. The corrugated structure contributes to better adhesion to concrete and is obtained by wrapping smooth rods with fiberglass.

Products with a corrugated surface experience the brunt of the structure being erected, while smooth ones serve to connect individual parts of the frame. Unlike the usual metal products, new generation materials have a number of features due to which fiberglass reinforcement for strip foundations firmly holds the palm in the building materials market.

The main differences between fiberglass in relation to metal include:

Determination of the amount of material consumed

The calculation of fiberglass reinforcement for the foundation of a building is primarily influenced by the type of structure and its dimensions. For low-rise buildings, it is recommended to use ribbed reinforcement with a diameter of not more than ten millimeters. When calculating, it must be taken into account that the basis of the strip foundation is a two-tier frame, and the cell pitch should not exceed fifty centimeters. Its dimensions affect the total number of joints in the structure. The consumption of material also depends on the presence of load-bearing main walls in the building, since each of them requires pouring a base with a two-tier frame.

In cases where it is planned to pour the foundation with your own hands, without the involvement of professionals, it is very important to make the correct calculation of the amount of building material. It can be produced in accordance with the algorithm below.

Calculation of the size of the longitudinal frame

First of all, it is necessary to determine the perimeter of the structure, based on its dimensions, then add to the obtained value the total size of the main walls provided for by the project. If, as an example, we take a building four meters long and five meters wide, and at the same time having one load-bearing wall four meters long, the calculation result will be as follows: 4 * 2 + 5 * 2 + 4 \u003d 22 meters.

Given the need to use a two-level frame, consisting of four parallel rods, that is, two in each tier, it is necessary to increase the resulting total length of the reinforcement by four times. The result will be: 22 * 4 = 88 meters.

Since fiberglass is not subject to welding, and the joining of the frame parts is overlapped, it is necessary to allow one additional meter for each corner of the building. To do this, you need to multiply the number of external and main walls of the building by one, and then by the number of rods, that is, by four. In the accepted example, the calculation will look like this: (4 + 1) * 1 * 4 \u003d 20 meters.

The sum of the value of the total length of the walls and additional volumes for joining will give the desired value: 88 + 20 = 108 meters.

However, the calculations do not end there. Next, you need to calculate the amount of building material required to connect the frame rods into a single structure. For these purposes, smooth rods with a cross-sectional diameter of about 8 millimeters are quite suitable. They are significantly cheaper than ribbed ones and do an excellent job of connecting functions.

Calculation of the size of cross connections

Since the foundation pouring technology requires that the step between the connecting rings does not exceed half a meter, it is necessary to determine the number of required cells. To do this, you need to divide the total size of the base by fifty centimeters. In this example, the result will be: 88:0.5=44 cells. This means that 44 connector rings will need to be installed.

To calculate the consumption of building materials for one harness, you need to determine its perimeter, based on the standard parameters of 50 by 25 centimeters. The perimeter will be equal to: 0.5 * 2 + 0.25 * 2 = 1.5 meters.

The amount of material required for the connecting rings can be calculated by multiplying the perimeter by the number of rings. The desired value will be as follows: 1.5 * 44 = 66 meters.

Considering that various wastes often occur during installation work as a result of cutting, it is reasonable to add a certain percentage of the stock to the required number, from five to ten units. The result is the desired value of the order of seventy meters.

Calculation of the number of fasteners

Lastly, you need to determine the number of plastic fasteners for joining the transverse rings and longitudinal reinforcement bars. To do this, the number of connecting rings must be multiplied by the number of docking points. It turns out: 44 * 4 \u003d 176 fasteners.

In total, reinforcing the strip foundation with fiberglass reinforcement of the building from the example taken above will require the purchase of:

108 meters of corrugated reinforcement with a diameter of 10 millimeters;

70 meters of smooth reinforcement with a diameter of 8 millimeters;

176 plastic fasteners for docking the frame.

Despite some apparent cumbersomeness of the above calculation, any non-professional is quite capable of doing it on his own.

Foundation installation procedure

Despite the differences in the characteristics and features of the use of steel and fiberglass, the installation instructions for the foundation remain identical. The stages of work are general in nature and do not change depending on the type of material used.

First of all, it is necessary to build a wooden formwork of the size corresponding to the project of the building.

After preparing the base for the future foundation, it is necessary to assemble the frame from fiberglass reinforcement. To do this, the rods must be securely connected to each other using wire or plastic clamps, while observing the cell pitch required by the standards. Considering that, in contrast to steel products, fiberglass reinforcement cannot be statically fixed by welding, special attention must be paid to the bundle of rods, the susceptibility of the foundation to displacement depends on the strength of the frame. Since fiberglass rods practically do not bend, special corners from the same polymer can be used at the joints of the walls of the future building.

After the assembly of the frame is completed, the formwork is poured with concrete. Calculating the volume of the solution is quite simple. The perimeter of the base must be multiplied by its height and width. After pouring, further continuation of work is possible only after the final hardening of the concrete, which will occur no earlier than two or three weeks.

The use in construction of products from new generation materials, which can be safely attributed to fiberglass, due to their lightness, strength, reliability and durability, can significantly reduce the cost of work while improving their quality.

Recently, an increasing number of new products have appeared on the building materials market, which a non-professional cannot deal with. One such new technology is the use of fiberglass reinforcement. Manufacturers position their product as rebar, which has a lot of advantages over the usual steel rods, but is it really so?

Composite materials are a whole group of reinforcing bars that differ in the type of feedstock. The composite got its name due to the fact that it contains several elements. The first is fibers from various types of raw materials, the second is a thermosetting or thermoplastic polymer (resin). After the binder hardens, strong rods are obtained.

Depending on the origin of the fibers, several types of reinforcement are distinguished:

fiberglass;
basalt composite;
carbon composite;
aramid composite;
combined, consisting mainly of one type of fiber, but having inclusions along the entire length of another type.

The most common use of fiberglass reinforcement, it will be discussed further. The structure of fiberglass reinforcement is similar to the structure of wood. In the same way, fibers are located along the rod, which, due to the binder, form a single whole.

Advantages of application

Reinforcement with such material has the following advantages:

The ability to wind the material into coils greatly facilitates its transportation and reduces the cost of self-construction - the reinforcement can be delivered on your own vehicles.
The light weight of the products makes it easy to work with your own hands. There is no need to use a large amount of labor and lifting equipment. For comparison, the density of steel is 7850 kg per cubic meter, while a cubic meter of composite material has a mass of 1900 kg. From here it can be calculated that the mass of fiberglass reinforcement is 4.13 times less than steel.
Corrosion resistance. The main problem with steel bars is that they are prone to rust. Fiberglass is not afraid of water and various aggressive environments. Reinforcement with composite material is well suited for concrete with the addition of various modifiers (anti-frost, etc.).
Also, the advantages include the fact that fiberglass does not conduct heat well and does not conduct electricity. Concrete structures do not provide the necessary thermal insulation of the building, therefore they are always provided with a layer of insulation that prevents heat loss. In this regard, the low thermal conductivity of the composite does not play a significant role. The non-conductivity of electricity offers some advantages. But sometimes in reinforced concrete structures, rods are provided for grounding or lightning protection devices. When using fiberglass reinforcement, such measures are impossible.

Flaws and myths

The material is quite new, so it is not fully understood. The use of this type of rods in mass construction makes it impossible for there to be no regulatory framework for calculation. For fiberglass, there is only GOST 31938-2012. This is a recent and only regulatory document. GOST provides technical requirements for the material, but does not give recommendations for the calculation, manufacturers give only approximate values \u200b\u200bof the corresponding steel rods.

Composite reinforcement has the following disadvantages:

The impossibility of bending: the material can only be bent at the factory according to pre-provided schemes;
The impossibility of using welding. Usually, welding is used on large frames; in private housing construction, reinforcement is more often knitted.
Instability to high temperatures. Steel begins to lose its properties when heated to 600 degrees Celsius. In the case of a composite, the loss of bearing capacity occurs much earlier. And this means that in case of fire, concrete floors and beams will collapse faster.

In addition to the shortcomings, there are dubious points that you should be aware of.

Design characteristics

The calculation of reinforced concrete elements is carried out according to the joint venture "Concrete and reinforced concrete structures" for 2 groups of limit states (LSS).

1 GPS - calculation by bearing capacity. Check whether the element can withstand the load applied to it. The calculation is carried out taking into account the strength of the material.
2 HPS - stiffness calculation. It takes into account the deformation and the magnitude of the opening of cracks in reinforced concrete structures. The calculation is carried out taking into account the modulus of elasticity of the material.

In a reinforced concrete element, the compressive load is assumed by the concrete, and the function of the reinforcement is to prevent destruction under the action of deformations. Composite manufacturers claim high strength characteristics (Rs), but are silent about the elastic modulus (Es). It is this value that determines the deformability of the structure.

Deformability can be calculated by dividing the strength by the modulus of elasticity. For A400 steel reinforcement, Rs = 360 MPa, Es = 200,000 MPa, from here we obtain a deformability equal to 0.0018 or 0.18%. For fiberglass reinforcement Rs = 1000 MPa, Es = 50000 MPa. The deformability is 0.02 or 2%. Those. for 1 meter of the structure, the stretching of composite reinforcement is possible up to 2 cm versus 0.18 cm for steel, imagine what kind of cracks will form in the structure. The reinforcement is designed to prevent cracking and stretching. Composite copes with this function 10 times worse than steel.

This quality is especially important when reinforcing floor slabs and various beams. Here, the deformations are very large, so the reinforcement of such elements with a composite is impossible.

When used in structures with prestressing, its loss over time for steel is 20-30% (how much the stiffness of the structure is lost). For fiberglass reinforcement, this value can reach 80-90% in 5-10 years, because it is an organic material. That is, the whole point of prestressing disappears.

Please note that no manufacturer of prestressed concrete (slabs, beams) uses composite reinforcement. There are no regulatory documents for it (SP, SNiP), so it is impossible to calculate how it will behave.

Based on this, manufacturers' assurances about the high strength of the material are true, but not only strength affects the normal operation of the structure. In terms of deformability, fiberglass is significantly inferior to steel.

Reducing the weight of the structure

A small mass of material significantly reduces labor intensity, but the rods cannot provide a significant reduction in the weight of the entire structure, which is used to reduce the load on the foundation.

Numerical values are given for justification:

The load on the foundation from a slab of 6 m by 1.5 m and a thickness of 0.2 m from reinforced concrete is equal to the sum of the mass of concrete and reinforcement. The percentage of reinforcement is 3%. The volume of concrete \u003d 6 * 1.5 * 0.3 \u003d 2.7 m³. Multiplying this volume by the percentage of reinforcement, we get the volume of steel = 2.7 * 0.03 = 0.081 m³. Mass of concrete = 2.7m³ * 2000 kg/m³ = 5400 kg. Steel mass = 0.081 m³ * 7850 kg / m3 = 636 kg. Total mass of the plate = 6036 kg.
For the same slab, reinforcement is provided with fiberglass. The volume of concrete, reinforcement does not change, the mass of concrete too. Rebar weight = 0.081 m³ * 1900 kg/m³ = 154 kg. The mass of the plate is 5400 kg + 154 kg = 5554 kg.

From the above calculations, it can be seen that the total mass of the element differs by less than 500 kg. With a plate mass of more than 5000 kg, this is not a very large value. Therefore, the use of fiberglass reinforcement to reduce the load on the foundation is not economically justified, since the composite is more expensive.

Durability

You can take the word of the manufacturers of composite reinforcement that the service life of composite reinforcement is 80 years. But two facts make their words doubtful:

Steel has been used by man for many years, there is a lot of information about it, you can quite accurately determine its service life in certain conditions. Composite rods are a new material. There is no information about its operation over a long period, namely certified 80 years.
Composite rods are an organic material. Over time, polymer bonds break in any organic substance, the so-called “aging” process of organics, this leads to a loss of material properties, sometimes to destruction (for example, rubber becomes stiff and begins to crack after a certain time).

Possible applications

The previous paragraph paints everything in black colors. But when reading it, do not forget about the merits of the material. Due to its physical properties, this type of reinforcement will be a good solution for:

Masonry reinforcement. Antifreeze and other aggressive additives are often used in masonry mortars, which have a bad effect on steel products. Fiberglass is not afraid of such modifiers.
Reinforcement of the strip foundation. Laying reinforcement in a strip foundation is often constructive in nature (without calculation), therefore, fiberglass reinforcement, lightweight and resistant to chemical attack, may be suitable, but it should be used carefully, especially for massive buildings and foundations on problematic soils (high groundwater level, heaving, subsiding soil, etc.).
Reinforcement of the roadway. Reinforcement is not destroyed by contact with the ground.

Remember that there is no regulatory documentation for composite reinforcement (SP, SNiP), so no designer will be able to correctly calculate the structure with such reinforcement. There can be no question of the use of this reinforcement in slab foundations and grillage, because. tensile loads can be large.

Strip foundation reinforcement

The strip foundation, depending on the section, can be of two types:

rectangular;
t-shaped.

In the t-shaped structure of the strip foundation, the wall works only in compression, and the reinforcement is laid into it without calculation. The sole at the same time perceives the bend and is calculated. Fiberglass can be laid in the wall, but in the sole - with caution. It is suitable only for small loads.

With a rectangular section of the strip foundation, composite rods can be used. This is due to the fact that this design mainly works in compression. The working horizontal reinforcement (diameter and number of rods) is determined from the percentage of reinforcement equal, as previously given, to 2-3%. Clamps for small buildings are selected based on the design requirements in the document “Reinforcement of elements of monolithic reinforced concrete buildings. Design Guide", it also shows the minimum diameters of the working reinforcement. This document provides requirements for steel rods, there are no standards for composite, so the developer can use it at his own peril and risk.

Based on the foregoing, we can conclude that fiberglass reinforcement is a material that has not yet been fully studied. Its use today is possible only for constructive reinforcement, but this material should not be used for working reinforcement. The composite is especially not suitable for reinforcing beams, ceilings and grillages, i.e. where there are large bending and torsional moments.

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