Since the middle of the 20th century, owing to the increased interest of representatives of the construction industry in corrosion-resistant materials, the use of concrete structures reinforced with glass and plastic was enhanced. In addition, the necessity of providing non-magnetic and also dielectric properties for certain types of structures strengthened the desire of the developers to use multicomponent reinforcing bars. Moreover, it was very important to take into account the high consumption, even without already existing shortage of ore minerals used in the steel analogue.
Initially, the main base of the multicomponent reinforcing frame was continuous, alkali-resistant fibreglass having a diameter of 10-15 microns. It was absolutely inactive to the actions of an alkaline environment. The reinforcing bar was formed from fibreglass, and the resins of polyester, epoxy or other similar synthetic compounds were actively used as raw materials for the main binder.
The factories of large cities of countries of the former USSR used the technology for manufacture of non-metallic reinforcing bars resistant to alkaline environment and made of the glass. Its diameter was 6 mm, and the composition contained a very small coefficient of zirconium dioxide.
Manufacture of the first fibreglass reinforcing bar was carried out as an experiment owing to a great desire, as well as hard work of Soviet scientists. This time period covers the 1960s. According to the results of numerous practical experiments related to the bars of five-millimetre fibreglass composite, a number of its physical and technical characteristics were established:
- Initial modulus of elasticity of concrete of 50 GPa;
- Ultimate Strength 1.5 GPa;
- Ultimate Density 2 t/m³;
- Duration of the strength coefficient in the optimal temperature mode with an appropriate humidity of 65%.
At that time, a large number of organizational factors prevented from establishing a stable production of such reinforcing bars. But at the same time, construction companies had been erecting more and more buildings, facilities and structures using the fibreglass reinforcing frame. Many of them are still in operation. This was the first big step towards improving production, as well as using a non-metallic type of reinforcement.
From 1969 to 1979, the concrete cross-arms of electric power transmission lines were reinforced with fibreglass bars in many countries of the former USSR. The extensive sections of electric power lines had been created and installed in many regions of countries such as Belarus, Adzharia and Russia based on the developed experimental samples of electrically insulating cross-arm of the electric power transmission line supports. Moreover, the experts from all countries studied the fibreglass frame used for reinforcing the supports of the contact lines, as well as construction of feed risers. Also, it was used even in industrial, transport and commercial complexes of non-ferrous metal or inorganic fertilizer warehouses.
The use of this multicomponent type of the reinforcing bars when laying structures made of light-weight concrete, constructing cross-arms with no insulation, as well as foundations and coatings began in the 70s of the XX century.
But, despite the active and positive use of the fibreglass reinforced plastic frame in many areas of living environment, unfortunately, the plant production of fibreglass reinforcing frame was never carried out.
Fibreglass reinforced plastic bars were also actively used for reinforcing intermediate slabs of the technological galleries of the acid station of Svetlogorsk Artificial Fibre Plant. The bars with a diameter of 6 mm were used for reinforcement. Its ribs and plates of the transverse direction were set under tension. This method had only positive consequences and also reduced the costs.
According to the development data and analysis of the results a support line for 10-kV transmission lines with cross-arms created using the concrete reinforced with fibreglass reinforced plastic bars was put into service in 1970 near Kostroma by the Institute of Construction and Architecture of the State Committee for Construction of the Belarus Soviet Socialist Republic together with SEI “Selenergoproekt”. Stavropol glorified 1972 by putting into operation a similar facility of the electric power transmission line of 35 kV. And 1975 became important for Grodno and Soligorsk, when the electric power transmission line of 10 kV was connected. Another significant date related to installation of the electric power transmission line of 0.4 and 10 kW was in 1979 for Batumi.
Built-up, three-beam construction of the cross-arms consists of two linear, previously stressed, fibreglass elements to which three wires are attached. The base of the cross-arm was electrically insulating concrete reinforced with four bars with a diameter of 6 mm in each individual element.
Specialists of Ust-Kamenogorsk Nonferrous Metallurgical Plant mastered the production of the pre-stressed electrolysis baths for obtaining aluminium the design of which was reinforced with fibreglass bars with a diameter of 6 mm. The first wood-glued bridge was erected using 4 mm fibreglass reinforced plastic bars according to the “Bridges and Tunnels” Project developed by the department of Khabarovsk Polytechnic Institute. It dates back to 1975.
In 1976 there was a large-scale construction of movable warehouses with an unconventional design in the territory of Belarusian cities of Rogachev and Cherven. The arches of the warehouses were reinforced with multicomponent wire, the diameter of which was 6-8 mm.
Bridge over the Shkotovka River (the Far East of Russia) reinforced in 1981 with multicomponent bars, is still in use today. The span of the bridge consists of six I-beams of metal grade 45, which were pre-stressed with ties of 12 multicomponent bars with a diameter of 6 mm.
Moreover, 1989 was as well remembered by the history of the commissioning of another bridge in Khabarovsk Territory using combined reinforcement: four bundles applied tension along 24 fibreglass bars with a diameter of 6 mm. The reinforcement of the beams using a frame of classes A-I and A-II remained without significant changes.
According to the results of the studies, the pre-stressing effect for multicomponent reinforcement in bridges dated from 1975 to 1989 remained the same.
After a long break, the years of two thousand glorified Russia by new experimental results of development of the technologies for new Fibreglass Reinforced Plastic Bar samples. The experts from the scientific research centres of the Concrete and Reinforced Concrete Research Institute, as well as the Federal State Unitary Enterprise “MATI Research Centre” made a large theoretical contribution to the development of this filed together with the practical experience of Yaroslavl Plant of Composite Materials LLC. The result of their joint work was that a new promising and perspective method of non-spinning pultrusion technology has been developed.
When studying the already used bar, much attention was paid to its physical and technical characteristics such as strength, durability, corrosion resistance, as well as resistance to aggressive influences of various environments. During the research new indicators of the use of this kind of frame were derived:
- Tensile strength up to 1500 MPa;
- Initial modulus of elasticity of 50,000 MPa;
- Density 1.8-2 t/m3 with a fibre weight of glass of 80%;
- When stretched, the working diagram remains linear right up to the breaking point, the deformations edge at this moment is 2.5-3%;
- Long-term frame strength under normal temperature and humidity conditions is 65% of the ultimate resistance;
- Linear expansion coefficient 5.5-6.5*10-6.
- Also, the bending level of the binding elements of the reinforcing bars was studied under the influence of static loads.
As for the international theoretical and, of course, practical history, the use of multicomponent reinforcing bars began even before the Second World War. The aerospace industry itself has shown the true and qualitative characteristics of this kind of frame. And during the war, interest in lightweight, practical, and most importantly, durable material only increased. Thereafter, the rapidly developing US economy really needed a raw material that was not very expensive but satisfying consumer needs. This is how coaxially oriented fibre plastic, as well as composite plastic, material were produced and then used for production of golf drivers or fishing rods. And only by the 60s this material was considered as the main raw material for concrete reinforcement.
But as far back as the 50s, there was a very urgent need to change the material for speedway systems, the round-the-clock maintenance of which was very expensive. Using salt to clean ice from motor-road bridges, road services faced the problem of corrosion, as well as its negative impact on steel reinforcement. This was a good motivation to carry out the research on various protective coatings (zinc, with electrostatic spraying, polymer concrete, epoxy, as well as fibreglass reinforcing bars), according to the results of which the fibreglass reinforced plastic bars were proved to be the best option for the aggressive conditions. Nevertheless, the use of this kind of frame was not considered effective due to its high cost. For these reasons, this material was not suitable for active commercial distribution until the end of the 70s. “Use of the composite material technology in the design and construction of bridges” (Plecnik and Ahmad 1988) is an official document dated 1983, which was the first project of the US Department of Transportation. The monopolist in the initial development of fibreglass reinforcing bars in the United States was Marshall-Vega Inc. Initially, the fibreglass frame was simply perfect alternative to the steel analogue for polymer concrete due to the complete lack of compatibility of the thermal expansion characteristics between polymer concrete and steel. By the end of the 70s, another corporation entered the same market – International Grating Inc. This period is associated with the occurrence of a big problem of the deterioration of the state of bridges under the influence of corrosion caused by the action of chloride ions. The main, even the only solution to the problem of quick ageing of bridges was the reinforcement of the structure with glass and plastic. These two economic associations made a great contribution to the development of production, as well as the use of multicomponent fibreglass reinforcing bars, and completed their activities in this field closer to the 80s. The next time period was famous for the use of fibreglass reinforced plastic frame in the construction of medical institutions, centres and complexes. The need for the use of this kind of reinforcement was associated with the great influence of the steel analogue on the results of medical equipment for magnetic resonance imaging. The largest projects were Gonda Buildings of Mayo Clinic in Rochester, Minnesota, and the National Cancer Institute in Bethesda, Maryland. Thereafter, this material was used for reinforcement of bridge structures, breakwaters, basements of the reactors of electrical substations, runways and electronics laboratories. The most famous projects are bridges in Potter County, Texas, and Bettendorf, Iowa. This contributed to new thorough research in the field of non-metallic reinforcement, the results of which were gathered in the document titled “Elements Made of Fibreglass Composites and Technology for the Use of Non-Metallic Reinforcement”.
In 1986, motor-road bridge was built in Germany using fibreglass reinforcement. By the mid-90s, Japan had been already using the frame made of the Fibreglass Reinforced Plastic Bars. The results of studies of more than 100 commercial projects involving the use of fibreglass bars were described in the scientific paper “Recommendations for Design and Construction”.
The decking of the Canadian Crowchild Bridge in Calgary region of Alberta State, dated 1997, was also reinforced with fibreglass bars. The civil engineers of this country have long been working on the development of regulations for the use of non-metallic reinforcement. They secured their result with an official document – “Canadian Highway Bridge Design Code”. On its basis, series of demonstration projects was built. The most prominent and most successful of them were: Headingley Bridge in Manitoba, Kent County Road Bridge No. 10, Joffre Bridge over the Saint Francois River located in Sherbrooke (Quebec). Thus, Canada had taken a leading position in the field of construction of bridge decking.
British Columbia had used fibreglass reinforcement when constructing a winery dating back to 1998.
Today, China is the largest consumer of a multicomponent frame. Experts of the country’s construction industry use it in the construction of new structures in various fields from bridge decks to underground coatings or fastenings.