Feb 5, 2019 in Informative

Carbon Fiber Reinforced Polymers: Reconstructing Civil Engineering

Abstract

This study gives a range of analyses of the significance and relevance of the research. Special attention goes to the structure and specific properties of the plastics that are reinforced with carbon fiber, the fabrication process of carbon fiber and potential shortcomings of its implementation in the engineering industry. The use of the polymers reinforced with carbon fiber in the field of materials of engineering undergoes analysis at the construction of bridge decks and concrete beams. This paper provides conclusion of the study and extends to propose the possible areas of study in the future.

Thesis of the Study

This study points out the advances made in materials of engineering by the construction process of concrete beams and bridge using polymers reinforced with carbon fiber. In an overview, it has given engineers good opportunities for building sustainable structures.

Introduction

Studying the intertwinement between carbon fiber and engineering industry has multiple benefits to engineering professors, engineers, scholars, and engineering students. One of its key significances is the fact that having a clear understanding of the uses of carbon fiber in engineering creates a platform for eliminating future errors that may befall construction. Whilst steel and all hard components of construction have revolutionized this industry by a large margin, there other ‘soft’ materials that can match or even surpass them in performance. The constantly expanding demands for structures also highlight the need for alternative materials for construction.

In all accounts, carbon fiber has allotted in seamlessly to fill the void left by the shortage of construction materials.  Despite being one of the newest components in Manufacturing Engineering, carbon fiber boasts a wide range of architectural qualities that, by far, ousts those of ‘hard’ materials such as metal. 

In the recent studies, engineers have backed the use of FRP in building structures, adding that it has impressive mechanical properties. In a nutshell, this draft will outline the history of carbon fiber as well as the structure and properties of plastics reinforced with it. In addition, it will narrate the process of fabrication, areas of application and limitations of FRP.

The Theory

The History

The first of carbon fiber took place in Cleveland in 1958 through a process that involved heating of rayon strands. According to Alferjani et al (45), the outcome of short of strength and its quality was below par. A few years after that, the Japanese improvised a chemical version of doing the same thing, giving rise to the standard procedure that has remained in use to date. The Japan ‘engineers’ used their quality, purity and strength to transform the rayon strands into new versions. 

At the turn of 1963, the scale production of commercial goods as well as the rise in demands for strength and quality saw Britain adopt a new production procedure. As a result, carbon fiber became commercially acceptable for application in a few special cases. By that time, the impacts of its weak structure did not fully match the values of construction requirements. The engineers also pointed out that its usage led to aerodynamic problems with the engines. In the modern era, methods of manufacturing using carbon fiber vary in details from one engineering industry to another. 

In general, the use of this material is dependent on three sources of substance - pitch PAN, or rayon. The manufacturing procedures requires large amounts of energy for attaining high temperature ranges needed for heating. This factor directly contributes to the hefty costs of producing it.

Structure and Qualities of Plastics reinforced with Carbon Fiber

The Structure

Carbon fiber has a structure that is comparable to that of a graphite. It constitutes of carbon atom units that are aligned in a systematic heptagonal structure. Engineers have extensively used both electron microscopy and x-ray spreading techniques to depict graphite fiber. Unlike graphite, carbon fiber does not have a three-dimensional structure. In PAN-based compounds, for example, the framework of linear chains undergoes modification in an effort to change them into planar framework. 

This process takes place at the oxidative stabilizing and carbonization of the materials. On the other hand, the basal planes aligned along the axes of the fiber establish at the carbonization stage. According to the findings by the wide-angle x-ray data, an increase in the stack size and basal plane alignments takes place in line with the corresponding rise in the heat treatment temperature. 

Alferjani et al. (48) argue that stabilized fiber displays differences between the core and sheath frameworks. Its skin has a high axial alignment and dense stacking of the crystals.  However, the core of a carbon fiber has a lower alignment and a lower size of the crystallite.

The Properties

From a general perspective, the determination of the graphite is entirely dependent on the precursor’s tensile durability. Both modulus and tensile durability are enhanced through the carbonization process. However, the process only takes place when the particles are under strain by stabilization. A research about x-ray and electron diffraction reveals that in great modulus fiber types, the crystallites get aligned along the longitudinal axes of the carbon fibers with plane layers highly focused in parallel lines to the axes. 

Colloquially, the kind of precursor used, existence of faults, manufacturing circumstances, and temperature ranges for heat treatment dictates the durability of any fiber. With PAN-centered fibers, the durability improves with rise in temperature up to highest 1300 ºC and then progressively falls. The modulus is believed to be increasing with the rise in temperature ranges. 

Such fibers typically buckle at high pressures to form kink banks at the inner parts. However, kind pitch-based materials with similar large modulus deform at the shear kink bank procedure established at 45° to the fiber axes (Huang 2371). Usually, the carbon compounds have very weak structures. However, they have strong covalent bonds, which align the layers in the compounds. Its sheet-like aggregations allow easy reproduction of breaks. When bent, carbon fibers fail at the slightest strain.

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The Process of Fabrication: PAN (Polyacrylonitrile) and Pitch Method

Pyrolysis involves inducing changes in substances by heat. An example of this process involves heating a yarn strand and making the content carbonize to turn dark in color. Alferjani et al. (49) argues that the temperatures appropriate for carbonizing and graphitizing are 1500°C and 3000°C, respectively. The following are the standard series of functions used in the production of carbon fiber materials from PAN (polyacrylonitrile):

Spinning

Spinning involves combining the acrylonitrile powder with another polymer and catalyst to form a reacting agent in a suspension or solution polymerization process. This mixture is used for the production of a certain component, polyacrylonitrile (PAN) polymer. After which, one of the previous techniques is selected for spinning the plastic into several fibers.  

In some cases, PAN is combined with other chemicals, prior to injecting it through small planes into the quench region used by the material for coagulation.  It then solidify into a set of fibers. This procedure is similar to the one used for generating polycyclic fabric particles. In an alternative techniques, the material is warmed prior to injecting through tiny planes planes into a region where other chemicals evaporate and leave residues of solid fiber. Spinning is vital to the formation of the inner core of the fibers. 

The next step involves cleaning and expanding the materials into the required fiber diameter. This helps arrange the elements within the fibers and provide a ground for the development of the tightly connected crystalline carbon after carbonization.

Stabilizing

Before carbonizing the fibers, they must be chemically changed to turn their atomic linear connection to a thermally constant ladder connection. This is achieved by warming the materials in oxygen to roughly 390-590° C for 40-120 minutes (Bakis et al. 78). This allows the fibers to gather oxygen elements and change their atomic connection design. The reactions of the stabilizing chemicals are complicated and include a series of steps, most happening at the same time. They also produce their heat, demanding to be managed to prevent overheating the materials. 

From the commercial perspective, the stabilization procedure uses various strategies and equipment. In other procedures, the compounds must be drawn via a sequence of warmed chambers. Alternatively, the materials can be passed over heated rollers and across layers of loose materials suspended by a stream of heating air. In some procedures, hot air combined with certain fumes that chemically speed up stability is used.  

Carbonizing

After stabilizing the fibers, they are warmed to approximately 1900° in a furnace loaded with a mixture of gasses minus oxygen. Absence of oxygen stops the materials from burning on the excessive temperature ranges. The pressure of gas inside the furnace must exceed the external pressure and the meeting point of the materials, while entering and exiting the heater is enclosed to prevent the entry of oxygen. 

While heating the fibers, they start losing their non-carbon atoms in the version of gases such as carbon dioxide, nitrogen, hydrogen, ammonia, water vapor and carbon monoxide. As they remove and expel non-carbon atoms, the remaining atoms create firmly bonded carbons arranged parallel to the elongated fiber axis (Huang 2374).  In some procedures, two heaters working at differing temperature ranges are handy in controlling the heating rate in the process of carbonizing.

Surface treatment

Since the fibers have been carbonized, they have an area that cannot withstand elements like epoxies, useful in forming composite materials. For the fibers to gain an improved bonding quality, their surface must be oxidized. The oxidation of the atoms around the outer lining area promotes improved chemical bonding qualities, while roughening the outer lining area to enhance the mechanical bonding qualities.

To achieve oxidation, components can be submerged in various gases notably carbon dioxide, oxygen or ozone, or in fluids like nitric acid or sodium chlorite. In addition, the components can also be covered electrolytic ally. This is acquired if the components are converted into a positive terminal in a pool of electronically conductive components (Bakis et al. 79). The process of treating the surface demands caution and control to deter developing minor surface defects, like pits, which can lead to the failure of the process.

Sizing

Now that the surface has been treated, the components are covered to ensure they are not damaged while weaving or winding. We refer to this process as sizing. Coating components must match the adhesive employed to create composite components. Typical coating components include urethane, nylon, polyester and epoxy. 

Coated fibers are wrapped into tubes known as bobbins. Then, they are loaded in a rotating machine, where the components are converted to yarns of different sizes.

Challenges of carbon fiber use in the Engineering Industry

Regardless of its benefits over traditional construction materials, FRP is slowly approved by the engineering sector. Three main issues leading to this slow usage are cost, structural performance and durability.

Code specifications: Expenses attracted in construction venture using FRP compounds are classified as short-term and long-term costs. Short-term price contains content price, manufacturing price, and construction price. Currently, content and manufacturing costs of FRP compounds for Manufacturing Engineering programs are still expensive compared to the traditional elements. Most manufacturing procedures are initially used in the airplane, marine, and motor vehicle sectors, in which mass manufacturing of one-style requirements is common. Manufacturing Engineering market, on the other hand, includes the development and designs of large-scale elements, in which style requirements usually differ from venture to venture. Some manufacturing techniques of FRP may not be financially appropriate for Manufacturing Engineering market. However, light-weighted and flip elements made from FRP can help reduce construction price. This contains easy construction or set up, transportation and the absence of heavy equipment mobilization. More saving, though challenging to evaluate, they can also be obtained through less construction time, less traffic interruption, or other factors commonly affected by construction ventures. These pros are regarded on a case-by-case basis. Compared to other sectors, in which FRP compounds have been efficiently presented, construction market is very cost-sensitive. It is challenging to rationalize the use of FRP compound over other less expensive materials, when a venture does not require a specific advantage of FRP compounds. The claim of a lower life-cycle price is also challenging to rationalize because a small number of appropriate projects have been built using FRP compounds.

Structural Performance: In general, ductile components are applied in bridge engineering to ensure ductile failing and apparent deformation and caution to customers. For example, metal is used for reinforcement because of its natural linear elastic. However, FRP compound is also very delicate to strength concentration. When pressure concentration happens at some point, pressure is not allocated over this area due to linear elastic nature of FRP compounds. Hence, if this is not considered, a framework designed from FRP compound can fail miserably. Another part of structural performance, which bridge technicians are still doubtful of, is the dependency of durability of FRP compounds on fibers alignment and positioning. Since the matrix offers minimal resistance to load, alternative load routes are almost nonexistent in FRP compounds. This situation is crucial in engineering because load routes are very difficult to project, even for a simple framework designed from concrete or metal (Goyal 143).  Therefore, it is considered far better to use the components that can offer load level of resistance from unforeseen guidelines.

Durability: The advocates of FRP compounds argue that mechanical, chemical and environmental durability is one of the advantages over traditional components. A number of component elements have a prospective resistance against moisture effect, ultra violet rays, substance attack, freeze periods, material aging and dynamic loading effects. Several tests performed in the past emphasize this prospective. However, this is not obvious in current engineering application of FRP compounds because all of them have been in service for a few months period. Therefore, long-term strength data are required to enhance such claim.

Composites of Fiber reinforced Polymer for Construction Process

The fiber-reinforced polymers are any of the mixtures or compositions that consist of two or more components at individual stages, at least one of which is a polymer. By mixing a polymer with content, such as carbon, glass or another polymer, it is often possible to acquire unique mixtures or levels of properties. Common illustrations of polymeric compounds consist of glass-, carbon-, or polymer-fiber-reinforced, polycarbonate or thermosetting resins, carbon-reinforced rubberized, polymer combinations, silica- or mica-reinforced resins, and polymer-bonded or -impregnated timber or concrete. Often, it is useful to consider such components as crystalline polymers coatings to be compounds. Natural occurring composites consist of bone and wood. On the other hand, polymeric compositions combined with a plasticizer or very low ratios of pigmentation or processing reinforcements are not normally regarded as composites (Huang 2378). The objective is to enhance durability, rigidity, sturdiness, or dimensional balance by embedding fibers or particles in a matrix or binding stage. A second objective is to use affordable, easily obtainable fillers to improve a more expensive or limited resin; this objective is progressively important as oil supplies become more expensive and less efficient. Applications consist of the use of some fillers like glass spheres to enhance process ability, the integration of dry-lubricant elements such as molybdenum sulfide to generate a self-lubricant and fillers to minimize permeability (Goyal 145).  

The most common composites of fiber-reinforced polymer are based on glass materials, fabric, mat, or roving included in a matrix of polyester resin or epoxy. Strengthened thermosetting resins containing boron, polyaramids, and especially carbon materials refer to high levels of durability and rigidity. Carbon-fiber compounds have a comparative rigidity five times that of metal (Huang 2385).  Because of these excellent qualities, most applications are exclusively suitable for polyester and epoxy compounds, such as elements in new jet airplane, parts for vehicles, rocket motor cases, boat hulls and chemical reaction vessels.

The Applications  

Strengthening reinforced concrete beam

Because of the economic hardships and shorter state budgets, it has become extremely costly to replace aging structures. Previously, innovative strategies were developed to reinforce structures in an effort geared towards reduced retrofitting costs of the structures. This is still applicable to buildings that are crucial for safety of the citizens. Facilities such as hospitals and main bridges are vital in the transport sector of the states. As time pass, these structures may need to be strengthened to withstand bad weather conditions. Carbon fiber reinforced polymers (CFRP) are among the many effective tactics employed to enhance structural performance of the constructions. It has proven to be an economical option because the costs of reinforcing structures using FRP is cheaper than the cost of replacing the whole construction.  

In reinforced concrete beam, the role of concrete under neutral axis is mainly to position reinforcing metals and to secure them from corrosion. However, concrete has little tensile durability in comparison with metal. So concrete hairline breaking is common in reinforced elements, leading to ecological strike of the reinforcing metals. Therefore, there have been investigations on a compound that has concrete in the compressive part of beam and FRP piece below the neutral axis. A study has been performed on the use of duplex long-span beams (Huang 2392).  From this perspective, the term "duplex" means the mixture of concrete and FRP that generates architectural components, which offer the best possible qualities based on the individual attributes of each compound. Several possible benefits of duplex program are recognized as:

Potential decrease of transportation costs for completed compounds, and the versatility to set up the elements in a distant area.

Cost of production can be much like traditional content for a huge number of components.

Light and great durability

Another possible multiple settings are a round cross-section, in which the core of concrete is covered by FRP. This program is known as hybrid tube system. Although the core of the concrete does not offer much of flexural rigidity and power to the cross-section, it operates as the framework for the FRP so that its strength is fully used. It also makes the FRP pipe more constant, avoiding early local attachment failure and allows plug anchorage. The objective of this idea is two-fold. First, it can be used as non-corrosive compressive participant in an offshore framework. Secondly, it can be used as high-ductility line and connect in seismic areas. This idea is used in the first all-FRP cable-stayed bridges in America. 

Bridge decks consisting of fiber reinforced plastics

It is common to see bridges with concrete decks that have cracked. This has been attributed to an increase in the demand on current structures whose loads were never considered during the initial design. We must accept that bridge decks can deteriorate, get damaged and might need replacement or service. Bridge decks are among the most worsened components in bridge framework. There may be a need to improve traffic lanes, road rating or to comply with a new rule. To overcome cracking of concrete or other corrosion issues, application of non-corrosive compounds during construction can be a viable alternative. Alternatively, non-corrosive strengthening includes FRP compounds.  Therefore, FRP composite bridge decks have been presented as a new remedy into bridge engineering field. It provides easy setup, light and portable, and prospective level of resistance against chemical and environmental damages. The style of FRP bridge decks relies more on rigidity, rather than durability. Therefore, it is vulnerable to have over-strength style, which can be as small as 10-15% of the greatest durability of FRP. One of the limitations is still (Mara, Haghani, and Harryson 190).

However, pre-made FRP bridge decks are more costly than traditional compound. FRP can also be used in cable-stayed bridges, post-tensioning and suspension bridges. In this case, wires consist of assembled protruded CFRP cables (Goyal 146). One illustration of its application is the Stork Bridge, two-lane Bridge across paths at Winterthur railways in Switzerland. Two 12 FRP wires were set up and being supervised along with traditional metal wires. So far, the wires are performing as predicted. Although the development prices of CFRP wires are still high, it is likely that this price will reduce of the long run.

Conclusion

Many fibers can be used to increase the desired properties and strength of materials. Out of which boron fibers are widely used, but economical perspective as well as low price are more important factors as compared to others. Polymers are used in big amounts, due to room temperature properties, ease of production and price. Carbon fibers are produced by many procedures by using Pitch or PAN as a precursor. Pyrolysis of PAN generates fibers of great stiffness and strength. Carbon fiber is now an engineering compound that must be engineered, designed and produced according to the same requirements of perfection and quality control as any other engineering compound. Thus, graphite has totally changed the field of lightweight components. This can be used instead for metal without the most of latter complications like lack of corrosion resistance. The remedy to the issue of corrosion might be adoption of non-corrosive substitutes like fiber reinforced polymer. This is thus one of the future construction components.

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