Concrete – one of the most common materials used in the construction of residential buildings, industrial, administrative, social, commercial buildings, etc. an important step in the construction of certain buildings is the reinforcement of concrete. Not so long ago, the reinforcement was made with metal or steel rods. However, with the advancement of technology, they were replaced by other, superior to a number of parameters and characteristics materials.
The main types of composite reinforcement
The rods made of glass, carbon, basalt or aramid fibers and those that have undergone special processing, are called non-metallic fittings. There are several varieties. The classification is based on the fiber used:
Fiberglass
Basalt-plastic
Carbon-fiber reinforcement
Carbon-fiber reinforcement, which is a specialized material composed of several elements is now increasingly used in the construction. Carbon reinforcement is a material that consists of a base in the form of carbon fibers and resin systems: thermosetting synthetic resin. Automated technological process, which gives a reinforcement made of CFRP, is called pultrusion. With its help, without additional material costs and additional human resources, it is possible to make the composite reinforcement, which has a constant cross-sectional area.
The plant, which produces this type of products consists of a system of applying the composite fiber in a polymer bath, preforming system, hot molds (or dies), pulling and cutting machine. As polymers, the most widely used are various epoxies or vinyl resins, although in more progressive industries, there is the so-called pultrusion resin, which allows to accelerate the process up to 6 m/s.
How is carbon reinforcement made?
• Initially, graphite fiber is supplied in the plastic tub in which it is impregnated with a special polymer;
• From the bath, graphite, coated with polymer, falls into preforming device. It is given the shape of the desired future product, and the fibers align;
• From there, carbon fiber is directed into a heated die, the outer edge of which is continuously cooled with water to prevent coagulation of the polymer that is yet not solidified. Passing through the mold, in which the special heating elements create up to 6 zones with different temperatures, the polymer hardens and the output from it is cooled;
• After this carbon-fiber reinforcement is cut at a certain technological standard segments.
It seems there is nothing complicated in this process. However, just the right scientific selection of all the production parameters: feed speed, the selection of temperature of die regimes, good impregnation by the polymer and its kinetic properties, etc., will eventually make a quality product. Despite the apparent complexity of the process, the price for material such as CFRP rebar is not too high. This is the reason why this material got a certain spread.
The main properties of carbon fiber reinforcement
In appearance, this product is almost indistinguishable from its predecessor – the metal fittings. It also has the form of thin rods or rods with different diameter of the cross section (up to 20mm). The surface of the reinforcement is ribbed. That provides maximum adhesion to concrete.
The main components, which give CFRP reinforcement unique properties are the polymer and the carbon. The structure of its fibers is intermittent, and this is why the fundamental advantages that distinguish this among other fittings of composite products are achieved:
• The high strength of the products. Compared with metal reinforcement, carbon fiber can better withstand the load and pressure of compression on the kick or kink. Thanks to this quality, its consumption can be significantly reduced, as well as to make a rarer reinforced mesh. Many even use rods with a smaller diameter than metal, but the building quality does not suffer. Because of the unique durability of this product, there is a visible reduction in the construction cost;
• More lightweight. Again, compared to metal, carbon is up to 10 times lighter. This entails reduction of costs of transportation of the product, because for one time, almost 10 times more reinforcing material can be brought. If it is a construction of a country house or garden, then this valve can be easily switched in the trunk of a car, especially since it is sold along with a special packing bays;
• Resistance to corrosion and aggressive environmental factors. If metal fittings, after a certain period of time may rust, carbon fiber is not afraid of even sea water or various acids. That is why this kind of composite fittings is used in the construction of bridges;
• Low thermal conductivity. This quality is invaluable, as it will keep most of the heat in the foundation and walls. If to compare the energy saving opportunities of CFRP and steel reinforcement, it is one hundred times ahead of its predecessor!
• Resistance to extremely low temperatures;
• Good radio permeability along with shielding properties compared to electromagnetic field. And how this property of composite reinforcement will help in real life? Well, all mobile devices will work, regardless of location, without noise or signal distortion;
• High durability. According to all manufacturers of composite reinforcement, its minimum service life is about 75 years;
• And finally, the last advantage, which in importance may outweigh all the others, it is a low cost product, due to the availability of the material.
Cons of carbon fiber reinforcement
Along with the positive qualities, carbon-fiber reinforcement has a number of negative traits. First of all, it is low modulus of elasticity (4 times less than metal). It almost does not bend, and if this happens, it immediately breaks. For this reason, it is used in the construction of foundations, roads, bridges, but the use in ceilings entails potential risk.
High temperature. Thus, when heated to 600 º C, the valves made from carbon fiber begin to soften. Therefore, during construction there is a need to take the additional thermal insulation measures, in the event of a fire.
The next drawback of these fittings can be attributed not to the negative qualities but to the problematic factors. The fact that it cannot be welded by electric welding. In this regard, during production, steel lugs are fastened to the ends of the valve, which allow to carry out welding activities.
Also the shape of the carbon fiber reinforcement in the construction process cannot be changed. It is necessary to calculate the desired options and negotiate with the manufacturer in the factory, giving him the drawings.
The use of carbon fiber reinforcement
Often, carbon-fiber reinforcement is produced with a pre-applied finish. The finished material is packed in polyethylene film. Usually, it is a bunch, which includes about 50 pieces. Manufacturer gives definitely detailed product information with bullet points on the packaging. Term storage, including any warranty for the material is not more than three years. When the production of CFRP reinforcement was gaining momentum, the cost of material was too high. Today, the prices are affordable due to the low cost of the raw materials. Non-metallic fittings are displacing steel from the construction industry.
It is widely used in the following industries:
• Civil and industrial construction
• Mining industry
• Road construction
• The bridge building
• Reinforced concrete tanks and storages of treatment facilities and chemical plants
• Utilities
• Sewerage, drainage and sanitation
• Strengthening the shoreline
• Marine and port facilities
• Foundations below zero bedding level
• Catenary supports
References
Cheremisinoff, N., & Cheremisinoff, P. (1995). Fiberglass reinforced plastics. Park Ridge, N.J., U.S.A.: Noyes Publications.
Fitzer, E., & Manocha, L. (1998). Carbon reinforcements and carbon /carbon composites. Berlin: Springer-Verlag.
Shetty, M. (2005). Concrete technology. Ram Nagar, New Delhi: S. Chand.
