Technical characteristics and areas of application of fiberglass reinforcement

Metal reinforcement is considered a reliable option for forming the “skeleton” of monolithic concrete. And today its importance and necessity in construction is not in doubt, although a new type of reinforcement has appeared on the market and is steadily progressing - composite or fiberglass (FRP). The material can be called “new” quite conditionally; it came to the market 50 years ago. For Russia, fiberglass was irrelevant until recently; we have enough resources to produce our own metal at a reasonable price for construction.

At the same time, fiberglass reinforcement has caught up and surpassed metal in a number of properties, and conclusions about the strength and durability of the material can be drawn from global experience in operating spas.

Structure of composite reinforcement

A building material is made from fiberglass fiber impregnated with a polymer binder in the form of relief rods of a given size - fiberglass reinforcement. Material structure:

• Inner rod. Serves to provide basic functional characteristics. Fiberglass fibers are used in production. They are placed in the structure of the rods in parallel or in the form of braided weaving, then filled with polymer resin.
• External covering. It is performed by winding composite fibers onto an internal rod or by spraying a fine abrasive onto it.
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CONNECTION WITH CEMENT

Rice. 3. Use of fiberglass composite reinforcement

When using lightweight structural concrete, it is possible to achieve improved thermal and acoustic characteristics, reduce the weight of structures, and increase the fire resistance of the structure.

When calculating and designing reinforced concrete structures using fiberglass composite reinforcement, the principles are similar to those used during the design of reinforced concrete elements, in cases where the combination of the work of concrete and reinforcement is considered the most important element. Based on the research of Zinovkin, A.A., Masalov A.V. – the connection of fiberglass composite reinforcement with concrete is ensured due to the adhesion of cement stone with an epoxy coating, and not due to the mechanical engagement of the coils, inside the concrete matrix, as with profiled metal reinforcement

Reinforcement can be of several types: internal, external and combined, which is a combination of the first two.

Figure 4. The first concrete pedestrian bridge in Europe with fiber-reinforced concrete polymers.

Internal reinforcement can be made in the form of discrete, dispersed and mixed. Discrete reinforcement is the use of fiberglass reinforcement in the form of individual rods, flat and spatial frames, and meshes. There can also be combinations, for example, individual rods, meshes, etc. Dispersed reinforcement is an additive to the concrete mixture during mixing of chopped fibers (fibers), which are randomly placed in the concrete. Using special methods, it is possible to achieve a directional arrangement of fibers. With dispersed reinforcement, concrete is usually called fiber-reinforced concrete.

External reinforcement is especially important if structures are used in an environment that is aggressive towards concrete. In this case, the external sheet reinforcement will simultaneously have three functions: strength, protection, and act as formwork during concreting.

External reinforcement can also be divided into continuous and discrete. With continuous reinforcement, it is a sheet structure that completely covers the surface of the concrete; with discrete reinforcement, it is in the form of mesh-type elements or individual strips.

Concrete structures in fiberglass shells can be produced in several ways. For example, after manufacturing a concrete element, it is possible to dry it and then enclose it in a fiberglass shell, carrying out a multi-layer winding with glass material (fiberglass or glass tape) with layer-by-layer impregnation with resin. After polarization of the binder, the winding will take the form of a continuous fiberglass shell. And the entire element will become a pipe-concrete structure. In the second method, a fiberglass shell is first made and then filled with concrete mixture.

Depending on the type of polymer binder and fiber used in production, the resistance of fiberglass to aggressive environments may also change. During internal reinforcement, it is necessary to take into account not only the relationship of fiberglass reinforcement to the external environment, but also the nature of the interaction with concrete in the liquid state. Hardening concrete has an alkaline reaction, which can cause destruction of aluminoborosilicate fiber. For such cases, it is necessary to protect the fibers with layers of resin or use fibers with a different composition. In cases where unwetted concrete structures are used, there is virtually no corrosion of fiberglass. In the presence of wetted structures, the level of alkalinity in the concrete environment can be reduced through the use of cement with active mineral additives.

Standard sizes and parameters

The diameter of the produced spa varies in the range of 4 – 18 mm. Products are produced in the form of measuring rods or in coils.

The total length of the reinforcement in the coil depends on the technological equipment used in its manufacture. Spas with a diameter of 12 mm or more are offered to the consumer exclusively in the form of rods.

The main parameters affecting the scope of application include the weight of one meter and the diameter of the composite rod.

The winding pitch can be considered an additional characteristic, but today almost all manufacturers produce reinforcement with a pitch of 15 mm.

Features of application in different types of foundations

To choose which reinforcement is best to use for the foundation, you need to take into account all the above factors. The most common types of foundation on which composite material can be used are shallow strip, grillage and monolithic slab

For them, reinforcement is taken with a thickness of 8-12 mm and with special notches for reliable adhesion to the mortar. Smooth rods of type A1 can be used for light outbuildings and as beacons when pouring the foundation.

Features of house foundation reinforcement:

• the number of rods is calculated based on the method of laying and the depth of the reinforcing layers;
• for a strip foundation, 2 such layers are needed, for a slab foundation, one and a sand cushion under the base are enough;
• the cell pitch for fiberglass should not exceed 500 mm;
• the corners of the foundation are covered with special corner elements, because butt joints in the corners are not allowed;
• tying of reinforcement at the joints is carried out with wire, staples and a special gun or plastic clamps;
• to evenly distribute the frame in the thickness of the concrete, reinforcement clamps will be required, the distance to the surface is 1-2 centimeters;
• The columnar foundation is placed below the freezing depth (usually from 0.7 to 1.5 meters depending on the region), which eliminates its movement and ruptures.

Important! When pouring the solution into the formwork, check that all parts of the frame are hidden by concrete. Where the reinforcement reaches the surface, cracks will form and further destruction of the foundation will occur.

Areas of application

Due to the demand for fiberglass reinforcement in construction, manufacturers began to offer products not only in the traditional version - coils and rods. Fiberglass reinforcing meshes and ready-made reinforced frames have appeared on the market in various designs in shape and dimensional parameters.

Composite reinforcement is used in a number of construction works and the manufacture of building structures:

• Reinforcement of structures made of monolithic concrete: walls, wells, coatings, foundations.

• Strengthening masonry made of piece wall materials - brick, stone, as well as porous and lightweight blocks of all types.
• In the construction of road surfaces and strengthening of embankments.
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• Construction of buildings using permanent formwork technologies.
• Providing flexible connections of load-bearing, facing, reinforcing layers in the construction of multi-layer walls and other structures.

• Manufacturing of power transmission line supports and railway sleepers.
• Use as dowels for fastening thermal insulation of buildings.
• Installation of utilities, sewerage, drainage.
• Creation of reclamation systems.
• Composite products have gained particular popularity among summer residents and owners of personal plots. SPA is used on the arcs of greenhouses, to create decorative and economic fencing, and to support fruit trees.

Advantages and disadvantages of use

Reviews from builders allow us to recognize the following main advantages:

• the low weight of the products not only makes it easier for workers, but also makes the structures quite light. Therefore, it is used for cellular concrete and other materials that reduce the weight of the structure while maintaining a high level of reliability and strength;
• metal, capable of transmitting cold through cold bridges. The use of fiberglass reinforcement eliminates this possibility; this advantage is especially important in monolithic construction of buildings;
• material consumption is reduced when packaging it in coils. The lashes are produced in lengths of 12 meters, which allows for more economical cutting. This point is especially important in private construction, when every ruble spent is scrupulously calculated;
• increases the economic component, the possibility of linking without overlaps and the use of welding work;
• composite reinforcement can serve for a long time and not lose its properties, but metal reinforcement laid in a concrete slab also does not decompose;
• dielectric properties guarantee safe living in the building, but this advantage is controversial. Concrete itself is a dielectric;
• a high level of resistance to chemicals is important when performing foundation work at low temperatures. At this time, various additives are added to the concrete;
• Does not interfere with the passage of radio waves. This quality is especially important in monolithic construction; metal fittings interfere with the normal operation of mobile communications and the passage of radio signals. The use of composite reinforcement can reduce the level of radio interference in the building.

These products also have disadvantages. A specialist using this material can easily name them:

• Reinforcing fiberglass (FRP) exceeds the cost of steel reinforcement. But this disadvantage is easily offset by the possibility of using thinner reinforcement for a similar type of work;
• is subject to deformation and destruction at high temperatures, but the likelihood of such an impact inside concrete is unrealistic;
• if fiberglass reinforcement is used for a foundation with many turns, it is not possible to bend the parts for bending, but the problem is easily solved. It is enough to take a piece of steel rod, bend it at the desired angle and tie it to the main lash;
• one of the main disadvantages is the low elasticity when the rod breaks. In this case, fiberglass reinforcement is inferior to steel, but it works better in tension. Due to its low resistance to fracture, its use in capital construction is somewhat limited;
• when using it in the foundation and pouring concrete from a mixer, you need to be extremely careful. Glass reinforcement cannot be placed in a rigid frame and under high pressure its integrity may be damaged. Composite mesh is the best solution to the problem.

How to knit fiberglass reinforcement, but easier than metal. This does not require the use of different hooks. It is tied together with self-tightening plastic clamps. The operation is simple and requires a minimum of knowledge and tools.

Having considered the advantages and disadvantages, it is impossible to unequivocally answer the question of which is better - light plastic or rigid steel. Only construction engineers can do this.

Ribbed and smooth rods

The ribbed profile of the products is necessary to improve adhesion to the concrete mixture. Sometimes, for the same purpose, the surface of the reinforcement is sprinkled with sand during the hardening process.

Fiberglass rods with a smooth surface cannot have proper adhesion to concrete, which is why they are less in demand as reinforcement for concrete work.

But the price of smooth rods is much lower, so it makes sense to use them as auxiliary products with minimal load when assembling a frame for reinforcement.

Physical properties and materials used in the production of reinforcing products

The main characteristics were obtained after a series of scientific research and the introduction of the latest developments. Some properties allow it to be used for reinforcement in residential and industrial construction:

• light weight of products - steel reinforcement is an order of magnitude heavier (9 times);
• is not subject to destruction from corrosion, acids, alkalis. According to this indicator, metal fittings are inferior by 10 points;
• low level of thermal conductivity. When arranging foundations and floor slabs, the possibility of thermal insulation failure due to cold bridges is reduced to 0.
• light and flexible - this quality simplifies its delivery and work;
• does not conduct electricity, is not susceptible to stray currents;
• Due to its plasticity, it can take any shape; there is no need to use welding or cutting machines.

Thanks to these characteristics, reinforcing the foundation with fiberglass reinforcement becomes justified both in production and economic terms. Much in this matter is decided by the material used for the production of ASP. The industry produces composite non-metallic reinforcement from several types of modern plastics. They have a base made of the following materials:

1. Fiberglass.
2. Carbon fiber.
3. Basalt-plastic.
4. Made from aramid.
5. Material created on the basis of glass-reinforced polyethylene terephthalate.

The price of some materials does not allow their use in mass quantities. For this reason, 2 types of materials are most popular. These are fiberglass and basalt plastic products. The main trunk is woven from many strands of material. They are connected using thermoactive synthetic resins.

To securely connect the rod, either sand coating is applied, or the trunk is wrapped around several turns running in a spiral. When using fiberglass reinforcement, one should take into account its property of slight stretching in a concrete product. In this case, there will be very little contact with the concrete and separation of the coils or abrasive coating will occur.

Products made of basalt plastic do not have a reliable connection with concrete. The best fixation is provided by coils made of carbon fiber, applied to the fiberglass main barrel. In this case, the load is evenly distributed over the entire part and the rod is normally fixed to the concrete mass.

Advantages of composite reinforcement

Thanks to the combination of non-metallic fibers and a binder composite composition, fiberglass reinforcement has acquired additional qualities and properties that are actively used in practice:

• low specific weight, which reduces transportation costs and facilitates installation;
• no welding operations required;
• tensile strength, almost twice that of metal;
• chemical resistance;
• low level of thermal conductivity combined with a wide operating temperature range;
• high dielectric constant.

The advantages of the material itself are complemented by the features of the technological process:

• all core threads are equally stressed, which enhances the strength of the spa;
• the thread flow at the twisting stage is cleared of all kinds of contaminants, which ensures optimal consumption of components during production and helps reduce the final cost of products;
• To increase chemical resistance and enhance adhesion to concrete, the reinforcement is coated with a layer of vinyl ester resin.

Purpose

Composite fiberglass reinforcement is a type of construction reinforcement; it is produced in the form of rods of different lengths, having an external section in the form of a spiral. Made from fiberglass and binder resins. The fiber provides the necessary strength, and the resin binds the fibers together. The introduction of this reinforcement into the construction technology not only reduces the cost of work by up to 50%, but also increases the service life of the facility. The advantage of this reinforcement is its high strength and low specific weight. Therefore, such fittings are a strong competitor to simple metal fittings. Fiberglass reinforcement has a number of physical and mechanical qualities that allow it to be used in very aggressive environments. Over time, the material does not rust or collapse upon contact with concrete. Due to its advantages, composite fiberglass reinforcement has practically replaced metal reinforcement in many areas of construction: reinforcement of strip and monolithic foundations in low-rise construction, reinforcement of concrete floor screed. It has found application in many parts of our planet. It is used in the construction of skyscrapers in Eastern countries, construction sites in Europe, and in Japan it is the main type of reinforcement in the construction of buildings that are subject to increased requirements for seismic resistance.

Recommendations for choosing products

Criteria for selecting a spa for construction work:

• compliance of the product diameter with the declared values;
• quality of winding of the outer layer;
• Availability of quality certificates and material test reports.

If after a visual inspection it turns out that the color of the fittings is darker than that declared by the manufacturer, then it is not recommended to purchase such products. Darkening of the spa means a violation of the temperature conditions during manufacturing, the product is considered burnt, and its technical characteristics do not correspond to the declared ones.

Fiberglass or metal?

The main disadvantages of metal fittings:

• susceptibility to corrosion;
• creating radio interference;
• high weight;
• high thermal conductivity;
• complexity during installation (cutting, welding, unlike composite reinforcement, which is tied with wire, clamps or clamps) - the total savings on installation is about 60%.

Comparison of the weight in grams of 1 meter of fiberglass reinforcement (ASK) with steel (AZ):

Advantages of composite fiberglass reinforcement:

• the weight of the reinforcement greatly affects the weight of the structure as a whole;
• transportation - packaging in coils instead of rods of 11.7 meters and low weight of the material, which significantly reduces logistics and loading and unloading costs;
• tensile strength for ASK = 1190 MPa - for AZ = 390 MPa → 3 times higher;
• relative elongation (percentage change in the length of the rod during a tensile test, the lower the indicator, the less likely it is for cracks to appear) - for fiberglass = 2.2%, and for metal = 25%;
• density (or specific gravity) - fiberglass = 2 t/m3, and metal = 7.85 t/m3;
• linear coefficient of thermal expansion (how much the material expands when heated by one degree) - for fiberglass = 9-12 akh10-6/°С, and for metal = 13-15 х10-6/°С. Since the thermal coefficient of concrete and fiberglass reinforcement is almost the same, the product will be less susceptible to the negative influence of temperature fluctuations;
• thermal conductivity coefficient - fiberglass = 0.35 W. (m°C), and metal = 46 W/(m°C). Fiberglass reinforcement conducts heat significantly less and, unlike steel reinforcement, does not form “cold bridges”;
• radiotransparency and dielectric properties;
• corrosion resistance;
• environmental safety.

The only advantage of metal reinforcement over composite fiberglass:

The elastic modulus is the ability of a material to deform elastically. Here, steel reinforcement is superior to composite reinforcement. The modulus of elasticity of steel reinforcement is 200,000 MPa, and that of fiberglass reinforcement is only 55,000 MPa. This figure varies by almost 4 times!

The elements that work to deflect depend on the modulus of elasticity:

• beams (rectangular or T-section);
• floor slabs;
• lintels (window or door).

When using composite reinforcement for the building products listed above, it is necessary to take a larger diameter than steel. The correct recalculation is in the regulatory document Amendments No. 1 to SP 63.13330.2012 “SNiP 52-01-2003 Concrete and reinforced concrete structures. Basic provisions" .

Price and quality

The price-quality ratio when choosing between fiberglass and metal is undoubtedly higher for fiberglass, which explains the high popularity of fiberglass reinforcement!

In addition to the obvious savings on the price of the reinforcement itself, there is the possibility of savings in the long term - a long service life of objects without repair work, since concrete structures using composite reinforcement will last decades longer. And the likelihood of cracks appearing on road surfaces will be reduced.

Comparison of the characteristics of steel and fiberglass reinforcement

You should not compare and evaluate steel and composite reinforcement, dividing it into “good” or “bad” based on a set of characteristics. There are precise definitions of when fiberglass reinforcement should not be used, and when it may be the best solution.

As a rule, the justification for any choice is the technical characteristics of fiberglass reinforcement and its metal competitor.

Comparison of these types of fittings is inevitable, since they have similar parameters and areas of application, which means they can be mutually replaced if certain conditions are met.

Which reinforcement is better, metal or fiberglass?

One of the main arguments given in favor of fiberglass reinforcement when compared with metal reinforcement is its lower price. However, if you look at the price tags of metal warehouses, you will see that this is not so. The cost of metal is on average 20-25% lower than the composite.

The reason for the confusion is that plastic sellers take into account the so-called “equivalent” diameter. The logic here is this: non-metallic reinforcement is tensile stronger than construction steel. Therefore, a polymer rod with a smaller diameter will withstand the same load as thicker steel reinforcement. Based on this, the conclusion is drawn: less plastic is needed to reinforce a structure than metal. This is where the “lower” price comes from.

For a reasoned comparison of a composite with metal, a regulatory document is needed. Today such guidance already exists. This is Appendix “L” to the order of the Ministry of Construction of Russia No. 493/pr dated 07/08. 2016

In paragraph L.2.3. obscure for ordinary developers, but very interesting for professionals, contains two reduction factors for all types of composite reinforcement.

For example, consider the most common fiberglass (FRP):

• Under continuous load, its tensile strength should be multiplied by 0.3. That is, instead of 800 MPa we get 240 MPa (800x0.3=240).
• If the structure operates outdoors, then the result obtained must be multiplied by another 0.7 (240 MPa x 0.7 = 168 MPa).

Table with reduction coefficient for composite reinforcement
Table with coefficients taking into account operating conditions

Further, as required by the standard, the resulting 168 MPa must be divided by a safety factor (safety factor) equal to 1.5. As a result, we get 112 MPa.

Now you can correctly compare the strength of plastic reinforcement with metal. For example, let's take construction steel grade A500. Its ultimate tensile strength, taking into account the safety factor, is 378 MPa. For the fiberglass composite, we obtained only 112 MPa.

Our small study is clearly illustrated by a table of real, and not theoretical, equal-strength replacement of steel reinforcement with composite reinforcement. It can be used when choosing and purchasing.

Having looked at this table, it is easy to notice that for plastic to be an equivalent replacement for metal, not less, but more metal is required. Only the most expensive carbon fiber material (CF) is superior to steel of equal diameter.

Flaws

The popularity of fiberglass reinforcement is justified by a number of undoubted advantages, but the material also has disadvantages that can cancel out all the advantages.

Low modulus of elasticity

This indicator means that composite products should not be used to reinforce monolithic floors or sections thereof. If it is absolutely necessary to use SPA, it is necessary to carry out careful technical calculations.

Low thermal stability

Fiberglass reinforcement is a self-extinguishing material that cannot spread fire in concrete structures. But at high temperatures, spa products sharply lose their functional strength characteristics, which limits the scope of application of composite reinforcement.

Loss of strength

Fiberglass reinforcement reduces or loses its strength characteristics over time (polymer organic bonds are destroyed - the so-called “aging” process of organics). The process is accelerated when the reinforcement is exposed to alkaline environments. To avoid this drawback, composite products with the addition of rare earth metals should be used.

Taking into account all the listed, even unique advantages of fiberglass reinforcement rods, their use is allowed only in conditions and structures where the material will not experience destructive loads and impacts.

Pros and cons of composite fiberglass reinforcement

The reason that after its appearance on the market SPA became quite in demand were the positive qualities of this material, which include:

• light weight;
• resistance to oxidation and other types of corrosion;
• low thermal conductivity;
• long service life;
• is a dielectric (does not conduct electric current);
• Possibility of use without the use of welding equipment.

Disadvantages are also present, but they are much smaller, these are:

• relatively low thermal stability;
• low elasticity values.

Using SPA in the manufacture of foundations
Related article:

Tying reinforcement under a strip foundation is a reliable way to create a rigid metal frame for a reinforced concrete structure. We will tell you how to carry out this work correctly and without extra costs in this detailed material.

Nuances and features

As with any relatively new building material, there are many conflicting opinions about SPA in professional and amateur circles. Let's try to understand the authenticity and validity of some judgments.

About SPA bending

The need to bend reinforcement often arises during construction, directly on site. But fiberglass rods cannot be bent efficiently directly at the installation site - this is what distinguishes it from metal. Builders often consider this a disadvantage of the spa, but not critical. There are two acceptable solutions:

• Bent elements are ordered from the manufacturer in advance if there is a reinforcement design or at least an understanding of the need for bending.
• It is possible to use mixed reinforcement. In this case, composite rods are connected to corner elements made of metal reinforcement.

About the regulatory framework for the use of spas

Opponents of fiberglass reinforcement in construction argue that its use on construction sites is illegal, since there are no regulations and standards for its use. This is just a half-truth. In fact, the use of composite rods is permitted by GOST; no one has the right to prohibit the implementation of a project with expertly verified load calculations. But there is a problem - the lack of programs and approved structural calculation models for the use of composite reinforcement. But for low-rise construction there is no need for such standards and programs. It is possible to build a small house or cottage using a spa, for which you can use approximate standards and advice from knowledgeable professionals.

About the color of composite rods

The initial, standard color of the SPA is light yellowish. As a rarer option, black, if the source material is basalt. Color is intended to make composite rods attractive; this is more of a marketing move, it is not caused by necessity. But there has been some kind of information leak on the market: supposedly coloring additives in the composite improve its characteristics.

Therefore, let’s put the point straight away: color does not in any way affect the quality of fiberglass reinforcement. Perhaps color schemes play some role when using spas for household needs in dachas and gardens.

Specifications

Mesh made of fiberglass reinforcement

The reinforcing mesh is a single-layer flat frame. It consists of rods located perpendicular to each other, connected at the joints. Their main function is to increase the strength and resistance to deformation of monolithic and prefabricated structures.

Advantages of composite masonry mesh:

• strength;
• ease of installation;
• light weight;
• ease of transportation;
• durability;
• corrosion resistance;
• high adhesion strength;
• dielectric properties;
• environmental friendliness;
• resistance to deformation.

Composite mesh is used in the following cases:

• reinforcement of brickwork;
• performing screeding and leveling floors;
• pouring foundation slabs, basement walls;
• strengthening wall panels and ceilings;
• concreting roads;
• reinforcement of concrete products, gypsum sculptures, decorative elements of buildings;
• strengthening the walls of hydraulic structures;
• construction of bridges, strengthening of embankments.

The use of a composite mesh reduces the formation of transverse cracks on construction sites by 2 times. This type of reinforcing products is gradually replacing rolled metal products with similar purposes.

Let's sum it up

The advantages of composite fiberglass reinforcement over its predecessor, steel reinforcement, are undeniable in almost all respects. These advantages are especially important when building near the sea. Therefore, we can safely conclude:

Modern construction in the Primorsky Territory using composite materials!

Attention!

When purchasing fiberglass reinforcement:

remember that the cost of a quality product made from quality raw materials, subject to the technological process, cannot be low. If you are offered fittings with a suspiciously low price, is there poor quality behind this? You already significantly reduce the cost of the estimate by choosing fiberglass reinforcement instead of metal, but it’s better not to skimp on quality.