D. Gopalakrishnan
Sardar Vallabhbhai Patel institute of Textile Management,
1483, Avinashi Road, Coimbatore � 64 1004,
E-mail: dgk.textiles@gmail.com

ABSTRACT:

This article presents an overview of fiber applications in cementitious composites. The socio-economic considerations surrounding materials development in civil engineering in general, and fiber reinforced cementitious materials in particular, are described. Current FRC applications are summarized, and the where, how, and why fibers are used in these applications, are documented. An attempt is made to extract common denominators among the widely varied applications. The R&D and industrial trends of applying fibers in enhancing structural performance are depicted. An actual case study involving a tunnel lining constructed in Japan is given to illustrate how a newly proposed structural design guideline takes into account the load carrying contribution of fibers. Composite properties related to structural performance are described for a number of FRCs targeted for use in load carrying structural members. Structural applications of FRCs are currently under rapid development. In coming years, it is envisioned that the ultra-high performance FRC, with ductility matching that of metals, will be commercially exploited in various applications. Highlights of such a material are presented in this article. Finally, conclusions on market trends are drawn, and favorable fiber characteristics for structural applications are provided.

INTRODUCTION:

CIVIL ENGINEERING

Civil engineering
is a broad field of engineering that deals with the planning, construction, and maintenance of fixed structures, or public works, as they are related to earth, water, or civilization and their processes. Most civil engineering today deals with power plants, bridges, roads, railways, structures, water supply, irrigation, environmental, sewer, flood control, transportation, telecommunications and traffic. Civil engineering is the broadest of the engineering fields, partly because it is the oldest of all engineering fields. In fact, engineering was once divided into only two fields - military and civil. Civil engineering is still an umbrella term, comprised of many related specialities.

General engineering

General civil engineering is concerned with the overall interface of human created fixed projects with the greater world. General civil engineers work closely with surveyors and specialized civil engineers to fit and serve fixed projects within their given site, community and terrain by designing grading, drainage (flood control), pavement, water supply, sewer service, electric and communications supply and land (real property) divisions.

Structural engineering

In the field of civil engineering, structural engineering is concerned with structural design and structural analysis of structural components of buildings and nonbuilding structures. This involves calculating the stresses and forces that affect or arise within a structure. Major design concerns are building structures resistant to wind and seismic forces and seismically retrofitting existing structures.


HIGH PERFORMANCE FIBERS

High-performance fibers are those that are engineered for specific uses that require exceptional strength, stiffness, heat resistance, or chemical resistance. These fibers have generally higher tenacity and higher modulus than typical fibers. High performance fibers are used increasingly for a wide range of applications including geotextiles and geomembranes for construction and civil engineering. High Performance Fibers provides comprehensive coverage of the design and manufacture of high performance fibers and covers their capabilities and applications.

The fiber is an important constituent in composites. A great deal of research and development has been done with the fibers on the effects in the types, volume fraction, architecture, and orientations. The fiber generally occupies 30% - 70% of the matrix volume in the composites. The fibers can be chopped, woven, stitched, and/or braided. They are usually treated with sizings such as starch, gelatin, oil or wax to improve the bond as well as binders to improve the handling. The most common types of fibers used in advanced composites for structural applications are the fiberglass, aramid, and carbon. The fiberglass is the least expensive and carbon being the most expensive. The cost of aramid fibers is about the same as the lower grades of the carbon fiber. "Other high-strength high-modulus fibers such as boron are at the present time considered to be economically prohibitive"

TYPES OF HIGH PERFORMANCE FIBERS:

The high performance fibers range from

� Carbon fiber / Graphite fiber
� Kevlar fiber
� Polymeric fibers such as aramid and extended-chain polyethylene
� Fiber glass
� Boron fiber.

General fiber properties are described below:

� Carbon/graphite fibers are high-strength, high-modulus, lightweight fibers, used as reinforcement for high-performance applications.
� Kevlar fibers are organic fibers which have high strength and stiffness which is possible in fully aligned polymers. Kevlar fibers have a very low resistance to failure under axial compression.
� Glass fibers (fiberglass) have excellent electrical insulating properties, good chemical and moisture resistance, and low cost. Glass fibers come in several grades (higher performance S-glass with greater tensile strength and higher use temperatures versus lower performance E-glass) and are widely used in industrial composites.
� Mixed fiber structures use a combination of Kevlar, glass, carbon, or other fibers to fabricate hybrid composites to optimize composite properties and cost.

There are a number of unique characteristics of civil/building engineering materials which set them apart from those used in other industries. These characteristics include:

� Low cost�for example, concrete costs $0.1/kg (in contrast to eye contact lens which cost $100,000/kg).
� Large volume application�e.g., on a worldwide basis, 6 billion tons of concrete and a half billion tons of steel are used in infrastructure construction annually.
� Durability requirement�our infrastructures generally are designed for much longer life than consumer goods, e.g., most bridges are designed with a 75-year service life, compared with an automobile with a typical design life of 10�20 years.
� Public Safety�it goes without saying that the general public will not tolerate failure of infrastructures. The experiences from the recent Northridge earthquake in the United States and the Kobe earthquake in Japan serve important lessons.
� Construction labor�materials have to be processed into infrastructures. Construction workers generally do not have the same kind of training ceramics engineers have. This implies that the material, if processed at a construction site, must be tolerant of low-precision processing.


CARBON FIBER:

Carbon fiber is one of the most important high-performance fibers for military and aerospace applications. Carbon fiber is engineered for strength and stiffness, but variations differ in electrical conductivity, thermal, and chemical properties. The primary factors governing the physical properties are the degree of carbonization, the orientation of the layered carbon planes, and the degree of crystallization. They have lower thermal expansion coefficients than both the glass and aramid fibers and the material has a very high fatigue and creep resistance.

Carbon fiber is most notably used to reinforce composite materials, particularly the class of materials known as carbon fiber reinforced plastics. Carbon fiber reinforced plastic or (CFRP or CRP), is a strong, light and very expensive composite material or fiber reinforced plastic. Similar to glass-reinforced plastic, which is sometimes simply called fiberglass, the composite material is commonly referred to by the name of its reinforcing fibers (carbon fiber). The plastic is most often epoxy, but other plastics, such as polyester, vinylester or nylon, are also sometimes used. Some composites contain both carbon fiber and fiberglass reinforcement. Less commonly, the term graphite-reinforced plastic is also used

Civil engineering applications:

CFRP has recently become somewhat of a hot topic in the field of Structural Engineering, surprisingly enough, due to cost-effectiveness. For example, many old bridges in the world were designed to tolerate far lower service loads than they are subject to today, and compared with the cost of replacing the bridge, reinforcing it with CFRP is quite cheap. Due to the incredible stiffness of CFRP, it can be used underneath spans to help prevent excessive deflections, or wrapped around beams to limit shear stresses. As of 2005, the Westgate Bridge in Melbourne, is the largest bridge in the world to be reinforced with carbon fiber laminates.

Much research is also now being done using CFRP as internal reinforcement in concrete structures, such as beams and bridge decks. The material has many advantages over conventional steel, mainly that it is much stiffer and corrosion resistant.

GRAPHITE FIBER

Graphite fiber is one of the allotropes of carbon. carbon fiber graphite is an extremely strong, heat-resistant (to 3000 �C) material. Carbon nanotubes are also used in graphite reinforced plastics, and in heat-resistant composites such as reinforced carbon-carbon (RCC)).

KEVLAR FIBER:

Kevlar
is DuPont Company's brand name for a particular light but very strong aramid fibre.

The following properties characterize Kevlar:

� High tensile strength at low weight
� Flame resistant, self-extinguishing
� Low electrical conductivity
� High chemical resistance
� Excellent dimensional stability
� Low thermal shrinkage
� Low elongation to break
� High toughness (work-to-break)
� High cut resistance
� High modulus (structural rigidity)


It can be spun into ropes or sheets of fabric that can either be used as-is, or used in the construction of composite components as

� Ropes and Cables
� Antennae Guide Wires
� Fish Line
� Industrial and Marine Utility Ropes
� Lifting Slings
� Emergency Tow Lines
� Netting and Webbing
� Pull Tabs

ARAMID FIBER:

Aramid
fibre is a fire-resistant and strong synthetic fiber. It is used in aerospace and military applications, for "bullet-proof" body armor fabric, and as an asbestos substitute. The term is a shortened form of "aromatic polyamide". A well-known type of aramid fiber (a para-aramid nylon) is Kevlar, or Twaron from the Teijin company. An especially fireproof variant is Nomex.

Aramid fiber characteristics

� sensitive to degradation from ultraviolet radiation
� good resistance to abrasion, organic solvents, and thermal degradation
� sensitive to moisture and salts
� nonconductive
� no melting point
� low flammability
� good fabric integrity at elevated temperatures
� para-aramid fibers such as Kevlar and Twaron, which have a slightly different molecular    structure, also provide outstanding strength-to-weight properties, and have high tenacity, and    high Young's modulus.
� difficult to dye - usually solution dyed [1]
� prone to static build-up unless finished

Major industrial uses:

� composite materials
� asbestos replacement
� ropes and cables

GLASS FIBER:

Glass is the oldest high-performance fiber, one that has been manufactured since the 1930s. Today's glass fibers can be found in such end uses as insulation, fire-resistant fabrics, and reinforcement for fiberglass composites such as bathtub enclosures and boats. In addition, continuous filaments of optical-quality glass have revolutionized the communications industry in recent years. Fiberglass or glassfibre is material made from extremely fine fibers of glass. It is used as a reinforcing agent for many polymer products; the resulting composite material, properly known as fiber-reinforced polymers (FRP), is called "fiberglass" in popular usage.

The glass fibers are divided into three classes -- E-glass, S-glass and C-glass. The E-glass is designated for electrical use and the S-glass for high strength. The C-glass is for high corrosion resistance, and it is uncommon for civil engineering application. Of the three fibers, the E-glass is the most common reinforcement material used in civil structures. Basalt fiber or fibre is a material made from extremely fine fibers of basalt, which is composed of the minerals plagioclase, pyroxene, and olivine. It is similar to carbon fibre and fiberglass, having better physicomechanical properties than fiberglass, but being significantly cheaper than carbon fibre.


Construction

� Fire protective wall, floor & ceiling panels. Fire proof curtains and partitions for indoors and outdoors
� Heat insulation in heating systems, power generation, incinerators
� Roofing: rigid and flexible roof covers with raised fire resistance
� Fire protective clothing
� Fire resistant floor coverings: backing, reinforcement
� Fire resistant interior decoration

Building insulation:

The goal of thermal insulation used in building construction is to slow down heat transfer. To keep buildings cooler in hot climates, and warmer in cold climates, requires the same materials. Different methods may be used because of the necessity to manage humidity buildup differently, as occupied buildings always need to evacuate humidity. Operational costs are lower in a well insulated building, as less energy is required to heat and to cool; this advantage also applies to wider environmental concerns. The three means of Heat-transfer resistance reduce radiation, conductive and convective losses and gains.

Indications that a house is poorly insulated and poorly ventilated include the attic being oppressively, almost unbearably hot in the summer, and dew and frost forming on cold surfaces in the attic, such as on the underside of the roof sheathing, during the winter. In some climates, large thermal mass can be used to damp daily swings in temperature. Adobe, earth, stone, and concrete are poor insulators but serve the purpose of regulating indoor temperature by damping.

Methods of insulation in buildings

� Planning the proper placement of building elements (e.g. windows, doors, heaters) is a significant part of insulating and lowering energy consumption for heating and cooling
� Execution of insulation is an important part of ensuring that the insulation performs as expected. Insulated glass can be also used as curtain wall

Glass

By far the most common glazing type, glass can be of an almost infinite combination of color, thickness, and opacity. For commercial construction, the two most common thicknesses are 1/4 inch (6 mm) monolithic and 1 inch (25 mm) insulating glass. Presently, 1/4 inch glass is typically used only in spandrel areas, while insulating glass is used for the rest of the building (sometimes spandrel glass is specified as insulating glass as well). The 1 inch insulation glass is typically made up of two 1/4-inch lites of glass with a 1/2 inch (12 mm) airspace. The air inside is usually atmospheric air, but some inert gases, such as argon, may be used to offer better thermal transmittance values. In residential construction, thicknesses commonly used are 1/8 inch (3 mm) monolithic and 5/8 inch (16 mm) insulating glass. Larger thicknesses are typically employed for buildings or areas with higher thermal, relative humidity, or sound transmission requirements, such as laboratory areas or recording studios.

Glass may be used which is transparent, translucent, or opaque, or in varying degrees thereof. Transparent glass usually refers to vision glass in a curtain wall. Spandrel or vision glass may also contain translucent glass, which could be for security or aesthetic purposes. Opaque glass is used in areas to hide a column or spandrel beam or shear wall behind the curtain wall. Another method of hiding spandrel areas is through shadow box construction (providing a dark enclosed space behind the transparent or translucent glass). Shadow box construction creates a perception of depth behind the glass that is sometimes desired.


BORON FIBER

Boron Fiber
�The original high performance composite reinforcement�

Boron Fibers, when combined with organic or metal matrices, create high-performance composite structures that offer lightweight, high-strength and high-stiffness properties.It is somewhat lighter than carbon fiber, but considerably stiffer. Boron fiber is produced by chemical vapour deposition at high temperatures from the reaction between boron trichloride and hydrogen gas. The rigidity of the fibers defeats weaving, so boron fiber is generally used only in unidirectional tapes and patches, although some simple woven materials are available on a small scale.

COMPOSITES IN CIVIL ENGINEERING

Today high performance fibre reinforced plastics (FRP) are starting to challenge that most ubiquitous material, steel, in everyday applications as diverse as automobile bodies and civil infrastructure .Composite materials are formed by the combination of two or more materials that retain their respective characteristics when combined together to achieve properties (physical, chemical, etc.) that are superior to those of individual constituents. The main components of composites are reinforcing agents and matrix. Fibre reinforced composites can be further divided into those containing discontinuous or continuous fibres. Another commonly practiced classification is by the matrix used: polymer, metallic and ceramic.

Glass fibre is by far the most widely used fibre reinforcement and hence the terms "GRP" (glass reinforced plastic), "Fibreglass" and "FRP" (fibre reinforced plastic) are often used to describe articles fabricated from composites particularly for application in civil engineering.Composites are able to meet diverse design requirements with significant weight savings as well as high strength-to-weight ratio as compared to conventional materials. Some advantages of composite materials over conventional one are mentioned below:

� Tensile strength of composites is four to six times greater than that of steel or aluminium.
� Improved torsional stiffness and impact properties
� Composites have higher fatigue endurance limit (up to 60% of the ultimate tensile strength).
� Composite materials are 30-45% lighter than aluminium structures designed to the same functional requirements
� Lower embedded energy compared to other structural materials like steel, aluminium etc.
� Composites are less noisy while in operation and provide lower vibration transmission than metals
� Composites are more versatile than metals and can be tailored to meet performance needs and complex design requirements
� Long life offers excellent fatigue, impact, environmental resistance and reduced maintenance
� Composites enjoy reduced life cycle cost compared to metals
� Composites exhibit excellent corrosion resistance and fire retardancy
� Improved appearance with smooth surfaces and readily incorporable integral decorative melamine are other characteristics of composites
� Composite parts can eliminate joints/fasteners, providing part simplification and integrated design compared to conventional metallic parts

Composites for Structural Applications

Composites have long been used in the construction industry. Applications range from non-structural gratings and claddings to full structural systems for industrial supports, buildings, long span roof structures, tanks, bridge components and complete bridge systems. Their benefits of corrosion resistance and low weight have proven attractive in many low stress applications. An extension to the use of high performance FRP in primary structural applications, however, has been slower to gain acceptance although there is much development activity. Composites present immense opportunities to play increasing role as an alternate material to replace timber, steel, aluminium and concrete in buildings.



Road Bridges

Bridges account for a major sector of the construction industry and have attracted strong interest for the utilization of high performance FRP. FRP has been found quite suitable for repair, seismic retrofitting and upgrading of concrete bridges as a way to extend the service life of existing structures. FRP is also being considered as an economic solution for new bridge structures. Decks for both pedestrian and vehicle bridges across waterways, railways and roadways are bridges being built entirely from composites. The lightweight of composites is especially valuable for the construction of waterway bridges incorporating a lift-up section to permit the passage of boats, and for ease of transportation and erection in remote areas without access to heavy lifting equipment. The composite deck has six to seven times the load capacity of a reinforced concrete deck with only 20 percent of the weight.

The composite bridge decks are quite suitable for replacing conventional/old bridge decks having super structure intact. The replacement can be carried out in a short time with minimal disturbance to the traffic. Composites can significantly reduce maintenance and replacement costs because of the material's excellent resistance to corrosion and fatigue. The composite bridge decks are modular in design and can be produced in continuous lengths because of the inherent process adopted (pultrusion technique) and these lengths can be cut to size depending on the user�s requirement. Composite bridge decks are being used for both permanent bridges for state/national highways.

Composite as Building Materials

The composite is an ideal material for the manufacture of prefabricated, portable and modular buildings as well as for exterior cladding panels which can simulate masonry or stone. The all too familiar translucent roof sheeting is now supplied in a variety of colors and profiles to suit both commercial and domestic building needs. In interior applications, composites are used in the manufacture of shower enclosures and trays, baths, sinks, troughs and spas. Cast composite products are widely used for the production of vanity units, bench tops and basins. The availability of highly fire resistant phenolic composites opens up the opportunity for new, safer and cost effective building techniques to be developed.

With the growing population pressure and increasing labour & material costs, composite usage in construction may provide cheaper solutions to a large extent. A growth rate of 10-11% p.a. in the usage of composites is expected after 2000 AD in the building & construction sector. The key restricting factors in the application of composites are initial costs due to raw materials and also inefficient conventional moulding processes. The key restricting factors in the application of composites are initial costs due to raw materials and also inefficient conventional moulding processes.

FRP Doors & Door Frames

With the scarcity of wood for building products, the alternative, which merits attention is to promote the manufacturing of low cost FRP building materials to meet the demands of the housing & building sectors In addition, usage of composite material for the doors makes them totally water & termite resistant. FRP doors are much cheaper than the wooden ones. The FRP doorframes can also be fabricated by contact moulding.


Plumbing Components

Lightweight fibre glass composite components for toilet are easy to instal and they are corrosion resistant. Due to poor thermal conductivity, the composite surface is warm to the touch unlike porcelain and steel. Ease in moulding technique for composite allows more aesthetic shapes and excellent surface finishes.

Ceiling Panel

The fibre glass veil facing used while moulding the panels for suspended ceilings increases panel stiffness and resists puncturing. Due to their easy printability, the veil imparts good panel aesthetics. The suspended ceilings are used to cover up electrical wiring, ducting, piping and fittings. The veil with an optimum porosity contributes to improved acoustical quality of the working or living space.

Natural Fibre Composites in Building Materials

Natural fibres, as a substitute for glass fibres in composite components, have gained interest in the housing sector. The moderate mechanical properties of natural fibres prevent them from being used in high-performance applications (e.g. where carbon reinforced composites would be utilized), but for many reasons they can compete with glass fibres. Advantages and disadvantages determine the choice. Low specific weight, which results in a higher specific strength and stiffness than glass is a benefit especially in parts designed for bending stiffness. The tensile strength and Young�s modulus of natural fibre like jute are lower than those of glass fibers, the specific modulus of jute fiber is superior to that of glass and on a modulus per cost basis, jute is far superior. The specific strength per unit cost of jute, too, approaches that of glass. The need for using jute fibers in place of the traditional glass fibre partly or fully as reinforcing agents in composites stems from its lower specific gravity (1.29) and higher specific modulus (40 GPa) of jute compared with those of glass (2.5 & 30 GPa respectively). Apart from much lower cost and renewable nature of jute, much lower energy requirement for the production of jute (only 2% of that for glass) makes it attractive as a reinforcing fibre in composites.

SIMCON: Slurry Infiltrated Mat Concrete

The Need


The cost of civil infrastructure constitutes a major portion of the national wealth. Its rapid deterioration has thus created an urgent need for the development of novel, long-lasting and cost-effective methods for repair, retrofit and new construction. A promising new way of resolving this problem is to selectively use advanced composites, such as High-Performance Fiber Reinforced Cementitious Composites (HPFRCCs). With such materials, novel repair, retrofit and new-construction approaches can be developed that would lead to substantially higher strengths, seismic resistance, ductility, durability, while also being faster and more cost-effective to construct than conventional methods.

SIMCON: Continuous fiber-mat High-Performance Fiber Reinforced Cementitious Composites



The Technology

The investigations conducted in North Carolina University have demonstrated that a special type of continuous fiber-mat HPFRCC, called SIMCON which stands for Slurry Infiltrated Mat Concrete, is well suited for the development of novel repair, retrofit and new-construction solutions that lead to economical and improved structural performance. The use of continuous mats, typically made with stainless steel to control corrosion in very thin members, permits development of high flexural strengths and very high ductility with a reduced volume of fibers.

Furthermore, since fiber-mats are pre-packed in the plant, distribution and orientation of fibers can be more accurately controlled, than is the case with short discontinuous fiber HPFRCs. These characteristics allow for the manufacturing of a unique cement-based fiber composite that can have different yet easily controllable properties in the longitudinal and transversal directions. The investigations also demonstrate that SIMCON has considerable potential for both seismic repair/retrofit, as well as the development of novel, high-performance composite structural systems. SIMCON is well suited for manufacturing high strength, high ductility, and thin stay-in-place formwork elements that eliminate the need for secondary and most of the primary reinforcement

CONCLUSION:

The building and construction industry has very sensitivity to material cost. Introduction of fibers into concrete must therefore bring out significant improvements in structural performance. Synthetic material optimization � using minimal amount of expensive material for maximum structures enhancement, rather than empirical trial and error approach, should provide the most direct path to satisfying the required benefit/cost ratio in this industry.

REFERENCES:

www.new-technologies.org
www.specmaterials.com
www.nap.edu/books/0309096146/html
www.netcompostes.com
http://www.tifac.org.in/news/civil.htm
http://www.engineeredcomposites.com/publications/li_APS02.pdf
http://en.wikipedia.org/wiki/Graphite-reinforced_plastic

About the author:

Gopalkrishnan is pursuing his PG Diploma in Home Textile Management. He completed his Diploma in Textile Technology from PSG College of Technology and joined Cambodia Mills in Coimbatore as a Production and Maintenance supervisor. After working there for three years, he did his B.Tech from Polytechnic College.

Gopalkrishanan has presented 17 papers in various technical symposiums and many national & international conferences. He has participated in various technical workshops and innovative project works. He has several articles published in journals and magazines to his credit. His areas of interest include Innovative and Technical Textiles.

You can contact him on: dgk_psgtech@yahoo.co.in


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