Advanced Composite Materials An Alternative To Reinforcement

ADVANCED COMPOSITE MATERIALS : AN ALTERNATIVE TO REINFORCEMENT, TENDONS AND CABLES. Pradip S Lande Snr. Lecturer in Civil Engineering Department, College of Engineering and Technology, AKOLA – 444 001 ABSTRACT Steel in the form of bars, cables, tendons etc. as a reinforcing material in cement concrete is extremely popular and widely accepted construction material all over the world. One of the major drawback with it , is it’s vulnerability to the environmental attacks and subsequent electro chemical destruction leading to corrosion which in turn reduces strength and serviceability of concrete structures. Engineers and scientists are in constant search of an alternative material which will be corrosion resistant, withstand extreme environmental conditions, light weight, stronger and fatigue resistant, easy to handle as compared to steel. Recent developments in the field of ADVANCED COMPOSITE MATERIALS (ACMs) makes it possible to use them as an effective and efficient alternative reinforcing material in place of steel and cables. These ACMs are unaffected by electro-chemical destructions and resists any environmental attacks and has high strength, high impact resistance, less weight, good thermal insulation property which renders them superior alternative reinforcing material. This paper presents a comprehensive review of recent advances in composite materials, their characteristics properties and their applications in place of steel.

1.INTRODUCTION Steel is one of the most popular and widely accepted construction material in R.C.C. construction. With the help of this material only, it has become possible to span large distances, construct huge hydraulic & nuclear structures, building frames etc. Till today it is the prime material through which designer put forward his ideas in to practices. Not withstands its admirable qualities such as easy availability, low cost, high strength, formability, ease in handling, transporting and errection etc, it has one significant drawback i.e., it’s susceptibility to environmental attack reverting the steel to it’s natural oxide state i.e. corrosion of steel. Corrosion is a complex electro-chemical process which expands the steel several times of its original volume and thus leads to reduction in strength of steel, bond failure, slippage of steel, spalling of the concrete and deterioration of concrete structures. The most common reason for early degradation, deterioration and disintegration of a concrete structural member is the corrosion of reinforcing steel. Due to corrosion of steel large numbers of bridges and other R.C.C. concrete structures are becoming structurally defective or functionally obsolete requiring costly maintenance, repairs rehabilitation and retrofitting of structures. It is estimated than in India yearly the loss caused by the corrosion related damages amounted to several crores of rupees, about five to six percent of GNP. Though the Engineers try to tackle this problem by using noncorrosive reinforcement mostly by epoxy coated steel bars but the permanent solution still evades them.

Because of these problems with steel, engineers have often wished for an ideal material which will be stronger, corrosion resistant, withstand extreme environmental conditions, light weight, high fatigue strength, easy to handle than the conventional steel. Also the modern science and technology are advancing so fast and becoming so sophisticated that the materials have to be correspondingly efficient, effective, high performancable, reliable, with exceptional environmental requirements for specific use. The conventional material i.e. steel will not be capable of meeting these demands. The recent developments in the field of Advanced composite materials (ACMs) has enabled in development of very efficient and effective alternative to steel bars and cables. These ACMs are unaffected by electro chemical deterioration and resists corrosive actions due to environmental attacks. Moreover ACMs can be used in many forms (like bars, plates, cables, wraps etc ). ACMs plates can be used in concrete members at a face to increase the tension capacity of members ( i.e. for retrofitting ), whereas ACMs bars as a reinforcement in beams and slabs replacing the conventional steel bars. It can also be used as cables, tendons in bridges. ACMs Wraps can be used as retrofitting material around concrete members to improve their strength. This papers presents a comprehensive review of recent advances in ACMs, their characteristic properties and their application replacing the steel in Civil engineering structures.

2. ADVANCED COMPOSITE MATERIALS (ACMs) ACMs can be defined as combination of materials appropriately arranged using reinforcing fibers, carefully chosen matrixes, and some times auxiliary materials like adhesive core and other inserts. These combinations after proper manipulation and processing result in finished structure/item with synergistic properties i.e. properties achieved after fabrication cannot be obtained by individual components acting alone. The ACMs can be classified in different categories on the basis of micro structures, multiphases, reinforcements, manner of packing fibers layered compositions, method of composition, matrix system processing methods etc. Basic components of ACMs are (i) Reinforcement (fibers) (ii) Matrix (iii) Honey comb core/adhesives ( for sand witched structures ). The great variety of fibers materials in various forms, shapes and sizes have been recently developed for use in ACMs and in the construction industries. Steel, glass, carbon, Aramid (kevlar), boron, silicon carbide, silicon nitrates, alumina fibers are some of the commonly used high performance reinforcement fibers in ACMs. The reinforcements may be called by different names according to sizes such as Whisker ( < 0.025 mm ), fiber ( 0.025 – 0.8 mm ), Wire ( 0.8 – 6.4 mm ), rod ( 6.4 – 50 mm ) and bar ( > 50 mm ). In general the continuous filamentary type reinforcement is important from structural application point of view. It is the reinforcement which is primarily responsible for the mechanical properties of ACMs. Usually all the reinforcements (fibers) are stronger in tension than steel, but weak in shear ( i.e. brittle ) requiring the filler material (Matrix) relatively strong in shear which will protect reinforcement against abrasion or environmental corrosion. Matrix also helps in distributing the load from reinforcement, absorbing energy, reducing stress concentration and preventing cracks propagation. Thermosetting and thermo plastic types of organic polymers are used as Matrix ( e.g. epoxide, phenolic, polyamide resins etc.).

Some of the important fibers used as reinforcement in ACMs along with their characteristic properties are discussed briefly. i)

Carbon/Graphite Fibers

Carbon fibers are produced from petroleum pitches in large volumes. These are low cost, low modulus. The current technology for producing carbon fibers generally centers on the thermal decomposition of various organic precursors, Rayons polyacrylonitrile (PAN), pitch, polyesters, polyamide polyvinyl alcohol, polyvinyl chloride, poly-p-phenylene and phenolic resins have all been considered and investigated as potential precursor materials for producing carbon fibres. These are produced by heat treating the precursor to temperature upto 10000c in inert atmosphere. Carbon fibers are very small in diameter and also manufactured as continuous mats, brails, continuous straight fibers. These are high strength, high modulus, low density, light weight, and has significant cost and handling advantage, outstanding creep and fatigue resistance. Pultruted carbon reinforced composites are noted for their lubricity, wear resistance, capacity of heat dissipation, and resistance to alkaline and soil solutions. Carbon fibers in general are not affected by moisture, atmosphere, solvents, bases etc. The Table No 1 Shows carbon fiber properties. * Table No 1 Carbon Fiber properties

1 2 3 4 5 6

High strength XAS, 3k 1.80 3270

High modulus

Very High modulus

T300,3k M40 P555 M50 Gy 70 Density (g/cm3) 1.74 1.81 2.02 1.91 1.96 Tensile strength 3040 2452 2100 2450 1860 (MPa) Tensile modulus 235 226 392 380 490 517 (GPa) Elongation at break 1.44 1.30 0.6 0.50 0.5 0.38 (%) Filament diameter 9 7 6 10 8 (mm) Precursor PAN PAN PAN PITCH PAN PAN (The grades mentioned above are proprietary designation of manufacturing companies)

ii)

P 75 2.0 2070 517 0.4 PITCH

Glass fibers On a specific strength (i.e. strength to weight) basis, glass fiber is one of the strongest and most commonly used structural materials. Some Lab tested fibers has shown strength upto 6896 MPa and commercial grades range from 3448 – 4830 MPa. The continuous glass filament are manufacture by two basic process i.e. by marble melt process and direct melt process respectively. To minimise abrasion related degradation of glass fibers, surface treatments (sizings) are applied prior to gathering of fibers in to strands. Commonly glass fibers are round and straight and have diameters ranging from G (9-10.2 µm) to T (22.9 – 24.1 µm ) are used. The glass fibers are available in different forms like continuous form, woven roving, surfacing mats, three dimensional and multidimensional (such as 5-D, 7-D, 11-D ) etc. There are several glass fiber types with different chemical compositions providing the specific physical/chemical properties.

E-glass ( calcium aluminoborosilicate composition) is best for general purpose structural use. S-glass (magnesium aluminosilicate composition) is a special glass with higher tensile strength and modulus, good heat resistance, strong resistance to acids. These properties make S-glass fibers suitable choice in ACMs to be used in elevated temperature and humid environments. C-glass has good chemical stability in chemical corrosive environments. T-glass fiber exhibits improved performance over Eglass such as 36% increase in tensile strength, 16% increase in tensile modulus, increased heat resistance, improved impact, electrical, thermal and chemical resistance properties. R-glass (magnesium-lime-aluminosilicate ) has higher tensile strength and modulus compared to E-glass and gives higher resistance to fatigue, aging temperature and corrosion. A-glass, ECR-glass, AR-glass, D-glass are some types of glass fibers. Table No. 2 : Glass fiber properties. E-glass 2.60 3400 73 4.5 3-14

Density (g/cm3) Tensile strength (Mpa) Tensile modulus (Gpa) Elongation at break (%) Filament diameter

R-glass 2.55 4400 86 5.2 3-14

D-glass 2.16 2500 55 4.5 3-14

S-glass 2.49 4580 86.93 5.4 --

iii) Aramid Fibers Aramid fibers ( aromatic polyamide ) was introduced by Dupont under the name Kevlar. The aromatic polyamide are believed to be made by solution polycondensation of diamines and diacid halides at low temperature. The structure of aramid fiber is anisotropic gives higher strength and modulus in the fiber longitudinal direction. Aramid is resistant to fatigue, exhibits good toughness and general tolerance characteristics. Applications of aramid fiber in civil structures include ropes, cables, prestressing tendons, pipes, walls etc. Table No 3 shows properties of Aramid fibers. Table 3. Properties of Aramid fibers Density 9/cm3 Tensile Strength(MPa) Tensile Modulus(GPa) Elongation at break % Filament diameter

Polyester 1.38 900

MONEX 1.38 670

Kevlar29 1.44 2700

Kevlar49 1.45 3500

Teflon 2.15

18

60

135

133

--

10-15

20-30

4

2.5

20-30

10-12

--

--

--

20

iv) Linear organic Fibers This fiber may become one of the major reinforcement for civil and building structure in future. This high strength and high modulus organic fiber can be produced by arranging the molecular structure of simple polymero to become straight during manufacture. The properties of this fiber includes rigidity (240 GPa), lower density (0.97), tensile modulus (117 GPa) and tensile strength (2.9-3.3 GPa)

v) Other notable high performance fibers are boron and silicon carbide fibers (Sic). Ceramic fibers (including oxide and non oxide) are also developed. Other organic fibers available are acrylic, nylon, polybenzimidazole (PBI), polyester, polypropylene and teflon.

3. ACMs AS REINFORCEMENT, CABLES AND TENDONS 3.1. ACMs VERSES STEEL Technical properties of ACMs depends upon type of reinforcing fibers, their form, style, proportion, direction etc. The characteristic properties of ACMs bars when compared with that of a high strength steel (ref fig I) can be summarised as:

i) ii) iii)

All the ACMs are stronger than steel. ACMs with carbon fibers has same stiffness as steel. ACMs with carbon fibers are stiffer than ACMs with aramid fibers which inturns are stronger than steel. iv) Stress strain carves of all ACMs are linear up to failure. v) All ACMs have less ductility and unpredictable plastic behaviour. vi) Due to their higher strengths and lower stiffnesses ACMs component develop much larger strains within elastic limits as compared to steel. vii) The ACMs has low bond strength which can be overcomed by providing mechanical anchorages and surface treatment to ACM bars. The ACMs properties like corrosion resistant, light weight, high tensile strength, high fatigue strength, withstanding extreme environmental attacks, zero electrical conductivity, high impact resistance, smooth and fine finishing with various colours, easy fabrication, handling, errection, vibration damping characteristics makes it far superior, efficient and effective and reliable construction material in place of steel.

3.2 ACMs as cables and Tendons. The application of ACMs in bridges as cables and tendons have been reported from different countries. As ACMs cables are much lighter, stronger than the conventional steel cables much longer distances can be spanned by ACMs cable. In costal areas where corrosion of steel cables is a very big problem, ACMs cables proves efficient and effective alternative. The state of the art application is cable stayed bridges. The pultruded cables and tendons of ACMs supporting concrete decks and girders in bridges render the structures stronger and durable than steel. The following are some of the case studies reported on use of ACMs as cables and tendons. • Pultruded cables using several hundred parallel carbon fibers composite wires (6 mm dia. pultruded from 500000 carbon fibers) using epoxy resin system. Bundled wires are embedded in a polymer matrix, non carbon radicals are then burned off in an inert atmosphere and replaced by carbon. These pultruded cables can yield two to three times the specific strength of steel and could last more than 100 years, permit longer span cable stayed bridges ( upto 6 to 9 km ). The steel cables would snap under their own weight over such a distance. • The idea of joining Europe and Africa across the strait of Gibraltar is being under serious consideration by using carbon fiber composite cable stayed bridge ( ref fig.2 ). • The Ullenbergstrace bridge in DUSSEL-DORF and Marienfelde bridge both in Germany are the first kind of post tensioned bridges incorporating tendons using glass fiber ACMs. Both the bridges are two spans each ranging between 20 to 25 m. Difficulties were observed in attaching the anchorages to the tendons. Slipping out and breaking out of tendons prematurely was reported. As the modulus of elasticity of glass fiber ACM, tendon is low leading to a strain as high as 2% at working stress level during initial prestressing which produce very long elongation of prestressing tendons and should be accommodated by long anchorages and enough space behind anchorages.(refer fig 3, 4 ) • Pretensioned slab on girder bridges and posttensioned using aramid fiber ACM tendons and carbon fiber ACM tendons have been reported from Japan. • The Heavy Assault bridge made for the U.S. Army is to be carried in three jointed sections on a armored vehicle, unfolds hydraulically to create 106ft. span and supports 70 ton load. Twelve carbon-epoxy chords about 38 ft long and 4x5 inch in cross section supports the structure. • ARAPREE is a composite prestressing tendon consisting of aramid filaments and epoxy matrix. The mechanical properties of rectangular strip (20 mm x 1.5 mm) with 50% fiber volume are : tensile strength 2800 MPa, Young’s modulus 125-130 GPa, failure strain 2.4%, density 2.4, Relaxation is 15 to 20%. • AFRP ROD from Teijin is another concrete reinforcing tendon using Technora aramid fibers. Mechanical properties of a typical 6 mm diameter rod with 65% fiber volume are : tensile strength 1862 MPa, tensile modulus 52.9 GPa, failure strain 3.7%, relaxation 7-14%. • CFCC is the carbon fiber composite cable from Tokyo Rope Manufacturing Company. PAN based carbon fiber is impregnated with epoxy. The Mechanical

properties of typical cable (Seven strands, dia. 0.49 inch ) are : tensile strength 2118 MPa, tensile modulus 137 GPa , specific weight 1.5, elongation at break 1.57 %, relaxation loss upto 2.46%, creep 0.04%, bond stress 7.2 MPa. 3.3 ACMs as Reinforcement It has been reported that ACM reinforced bar behave in the same manner as that of steel bars in the slabs and beams1. Due to their less young’s modulus deflection was considered as a limiting criteria in case of ACM reinforced beams. In slabs ACM bars are used as reinforcement in the form of composite grids, when compared with steel grid, the maximum load supported by slab reinforced with ACM grid was observed to equal or more than slab reinforced with steel grid2. Slabs when reinforced with 3-D continuous carbon fiber and loaded exhibited non linear behavior and reduction in stiffness in post cracking stage3. Kajima-FRC reported a type of composite concrete called 3R-FRC in which 3-D fabric, made by weaving the fiber rovings in three direction is impregnated by epoxy and cured, and is employed as main reinforcement. The fiber is a hybrid of PAN based carbon, aramid and vinylon fibers. NEFMAC is also a kind of composite reinforcement for concrete. A hybrid of continuous carbon, glass and aramid fibers is impregnated with resin and formed into mesh enabling thinner section of concrete to be used.

4 COST ECONOMICS In general composite products for main reinforcement of concrete, cables and tendons are more expensive than steel on the basis of weight for weight thereby prohibiting use of ACMs extensively in structural applications. However weight is not logical basis for cost comparisons. A more rational basis should be strength. The corrosion resistance, nonmagnetic properties, low electrical conductivity, weather durability, light weight and other properties of ACM’s may play an important role for engineers to select ACM reinforcement instead of conventional steel. If the cost of corrosion rehabilitation and repairs of R.C.C. structures is to be considered, ACMs cost could be comparable with steel. With the increase amount of usage, adopting a good design scheme, increase opportunities for application, sophistication in technology the cost of ACMs will be decreased considerably in future.

5.CONCLUSION Considering ACMs properties it can be said that ACMs are very effective and efficient and attractive alternative to reinforcing steel bars, cables and tendons. ACMs are being considered in several developed countries as a potential construction material in place of steel. Some of ACMs have been successfully applied to bridges and other structures. It can be hoped that day is not very far when ACMs will become good substitute for steel, tendons and cables in respect of both performances and price.

6.REFERENCES: 1) Brown V.L and C.L. Batholomew (1993). Fibre reinforced bar in reinforced concrete members. ACI materials Journal 90( 1); 34-39 2) Banthia N.M. AL. Aslay and S.Ma (1995), Behavior of concrete slabs reinforced with fibers plastic grid ASCE Journal of materials in CIVIL Engg. 3) Ahmad S.H.P. zia, T.J. Yu and Y Xie (1994) punching shear test of slab reinforced with 3D carbon Fiber fabric . ACI concrete International design and construction . 4) KIM P and U.Meier (1991) CFRP cables for large structures , Advanced composite materials in civil engineering structures proceedings Las Vagus. 5) Abhijit Mukherjee (1997) Application of Fiber reinforced polymer composite in repair and strengthening of structures. International conference on maintenance and durability of concrete structures Hyderabad proceedings. 6) V.Ramakrishanan (1993) Recent Advancements in concrete Fiber composites. International symposium of innovative world of concrete (ICI-IWI-93) . 7) Baidar Bhakht, Leslie Jaeger, Aftab Mufti, Plastic bridges. Architectural journal . 8. D.H.Kim, composite structures for civil and Architectural Engineering. 9. Dr.P. Mitra, Advanced composites, plastic vision India 1992. 10. J.E. Sumevak, Pultrusion an Expanding Technology.

Date : To, Mr. P.C. Sharma Editor New Building Materials and Construction World, 165, Jullena, Adj. Escort Heart Institute NEW DELHI – 110 025 Reference :

(i) Your letter NBM/PERLET/0601 dated 14 sept.2001. (ii) My Fax No – dated 01-10-01.

Subject

:

Forwarding the technical article (i)‘Advanced composite materials : An Alternative to Reinforcement, Tendons and cables’ (ii) ‘Reinforced Earthwork Approach Embankment Using ‘KOLOGRID’ for R.O.B. At Murtizapur (M.S.) : A Case Study’.

Dear Sir, With reference to above I am sending re-polished article “Advanced composite materials : An alternative to Reinforcement, Tendons and cables”, and a new technical article titled “ Reinforced earthwork approach embankment using kologrid for R.O.B. at Murtizapur (M.S.) : A Case Study”. I am very much thankful to you for giving me opportunity to publish my articles in your prestigious and esteem journal. Hoping you will also find 2nd article useful for publishing. This article has been selected for National Seminar to be held at Bhubneshwar in month of Nov.2001. May I request you to send me copies of the journals in which articles will be published. I also request you to enroll me for subscription by adjusting amount of honorarium for three years. Kindly acknowledge the same. Thanking you. Address for correspondence is given below. Address : Pradip S. Lande Shree Apartment Chaitanyawadi, Near S.B.I. Colony No 5, Small

Yours sincerely, Pradip S. Lande Sr.Lecturer in Civil Engineering College of Engineering & Technology,

Umari, AKOLA (M.S.) 444 005 Fax : (0724-59024)

AKOLA