In construction for the cause of renovation ofdeteriorating structures different retrofittingmaterials and techniques were adopted across theworld around last 20 years. General retrofittingmethods that use steel and cementitious materials arenot able to provide appropriate solution whereasretrofitting method with the help of FRP gives moreeconomical and best result compare to generalretrofitting method in many situations. Countlesspapers, reports and articles have been publisheddemonstrating how we could and should effectivelyapply FRP in concrete structure. The type andproperties of fibres, resins, orientation of fibres andthe interface bond strength determine the strength ofFRP confined structural members. Even thoughdifferent type of fibre reinforced polymers are at handfor strengthening and retrofitting works, carbon andglass fibre reinforced polymers are commonlypreferred. This study makes an effort to assess a safe
and economic use of aramid FRP as a strengtheningmaterial. Compressive, split tensile and flexuralbehaviour of FRP confined concrete specimens werestudied. Various experimental works are carried outto investigate the strengthening of structures usingfibre reinforced polymers as strengthening material.Japan (sheet wrapping) and Europe (laminatebonding) are the two countries which develop theretrofitting techniques in earlier stage. The externallybonded FRP repair materials are generally used inthe form of sheets, plates and prefabricated shells.The performance and properties of the final productis based on the preparation along with the curingcondition hence more care and correct procedureshould be followed. In last few years, a lot of researchworks are carried out by using FRP as an externallybonded reinforced material for strengthening ofconcrete structures. (Attari et al. 2012) was done anexperiment using FRP fabric (Glass‒Carbon) as astrengthening material in RC beam. In thisexperiments failure analysis of RC beam was
Abstract: Fibre Reinforced Polymer is a new type of reinforced material that can be produced by using fibresand resins. It is an effective and economical material used for repair of new and existing structures inconstruction. This type of composite materials also have good mechanical properties such as impact resistance,strength, stiffness, flexibility and load carrying ability. Use of FRP for confinement has proved to be effectivewhich is classified into two types retrofitting and strengthening. This study is determining the potential ofaramid FRP composites in strengthening of RC beams. Mechanical characteristics of Aramid Fibre ReinforcedPolymer (AFRP) confined concrete specimens can be analysed by conducting compression, split tension andflexural tests. Shear strength of AFRP wrapped RC beam was also taken into account. From the experimentalresults it is evidenced that the beams wrapped with AFRP possess better strength than the unconfined beamsin both wrapping of single and double plies.
The Effect of Aramid Fibre Reinforced PolymerComposites for Strengthening RC BeamsJ. Sahaya Ruben＊1,#, M. Murugan＊2, and J. Prakash Arul Jose＊3
＊1Assistant Professor, Department of Civil Engineering, Rohini College of Engineering and Technology,Kanyakumari-629 401, Tamil Nadu, India
＊2Assistant Professor, Department of Civil Engineering, Government College of Engineering,Tirunelveli -627 007, Tamil Nadu, India
＊3Professor, Department of Civil EngineeringAshoka Institute of Engineering and Technology, Hyderabad-508252, India
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examined using 4-point bending device underrepeated loading sequence. He also studies thestrength, stiffness, ductility and failure modes [2].(Ayman Abu-Obaida et al. 2018) investigated thebehaviour of short Span RC members reinforced withGFRP. They found that the shift in the mode of failureis the reason for the decrease in the strength of shortspan RC members with increase in the longitudinalGFRP reinforcement ratio [3]. (Beschi et al. 2011)explore the performance of beam-column jointretrofitted by high performance fibre reinforcedconcrete jacketing in both static and dynamic loading.It is concluded that the bearing capacity along withthe ductility of the column increases for the HPFRCjacketing column and hence increases the capabilityof the beam column joint [4]. (Brena et al. 2003) testeda series of R.C beams strengthened for flexure usingCFRP strips. They conducted an experiment to studystrengthening and also to analyse the failure due todetaching of the FRP strips. It was suggested thatfurnishing end anchorages reduced the break downdue to detaching and also improved the ductilebehaviour of beams [5]. (Fei Yan et al. 2016) hascontinued his old research with Glass fiber- reinforcedpolymer (GFRP) used as a reinforcement in RC beamto improve the bond strength. He also suggested analternative solution for the deteriorating structuresstructure by focusing more on the failure mode andbond strength [6]. (Hawelih et al. 2014) experimentallyinvestigated the behaviour of RC beams confinedusing association of various CFRP and GFRPs. Theyconducted series of tests on RC beams under fourpoint bending to investigate the flexural behaviour ofhybrid FRP sheets. They concluded that the ductilityat failure is higher in normal FRP sheets whencompared to hybrid sheets. They also developed ananalytical model to predict load-deflection response [7].(Hawelih et al. 2018) experimentally studied theflexural behaviour of RC beams confined with hardwire steel fibre sheets using epoxy adhesives. Fourpoint bending tests were carried out and the loaddeflection and strain reponse data at the mid-sectionof the beam were analysed. They concluded that theload carrying capacity of confined specimens showsincreased results from 29% to 62% as compared tounconfined specimens. Upon review, it is observedthat the experimental studies on strengthening/retrofitting of RC beams are conducted more onmodels constitutes 50% and on the prototypeconstitutes 20%, analytical studies constitutes 25%
and 5% of the studies are on the review of differentstudies conducted. When looking at the methods used,Cement grout constitutes 55%, Ferro-cement coverconstitutes 15%, Section enlargement constitutes 13%,External plate bonding constitutes 12% and FRPcomposites constitutes 5%. Grouting is the mostpreferred strengthening technique which takes about55% and the FRP composites used is the lease whichis 5%. While strengthening the beams using FRPcomposites, it has been proved that it gives anincrease in strength but the % of increase varies from25% to 75% which depends on parameters consideredby authors like type of FRP material, thickness ofFRP material, number of FRP layers, availablereinforcement, size of specimen considered for testing,grade of concrete and the grade of reinforcementsteel used in the structural member [8]. (Hawileh et al.2015) studied the effect of flexural CRP sheets overshear resistance of RC beams by attaching it to thebeam’s soffit. Thirteen beams were tested aftercasting with different longitudinal shearreinforcement ratio. The specimens failed because ofdiagonal tension crack. They concluded that theflexural longitudinal reinforcement ratio influencesthe shear strength of RC beams [9]. (JafarAli andGayathri 2017) carried out an investigation on CFRPand GFRP Sheets retrofitted in RC beam column joint.They analyse the performance of RC beam byvarying the thickness of CFRP and GFRP Sheets.From the result it is observed that the GFRP provide50% more strength than CFRP [14]. (Lamanna et al.2004) conducted an experiment on reinforcedconcrete specimens which are strengthened bymechanically fixing fibre-reinforced polymer strips.From the experimental investigation it is noted thatmechanically attached FRP strips provide higherductility than bonded FRP strip [15]. (Riyadh Al-Amery and Riyadh Al-Mahaidi 2006) studied thecoupling of shear-flexural strengthening of RC beams.The use of shear straps enhances the shear strengthby twice than that of using only CFRP sheets forflexural strengthening. Different proportions of CFRPsheets and straps were tested in RC beams. Theyconcluded that there is a considerable increase in thebeam strength because of coupling of CFRP strapsand sheets. Also the ductility behaviour in failure isprevented [17]. (Sangeetha and Sumathi 2010)performed an experimental investigation on concretecolumns wrapped by glass fibre under uniaxialcompression. It is summarized that the strength of
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concrete column wrapped with glass fibre increasedwhen loaded axially [18]. (Saxena et al. 2008)performed an exploration to study the failure analysisof reinforced concrete beams strengthened with FRP.Their complaint was that there was not enoughresearch done in predicting the limits at which FRPde-bonds. About 163 beams tested database wascollected from the literature and were studied toprovide details about the de -bonding [ 20 ] .(Vinodkumar and Muthukannan 2014) made aliterature survey to strengthen the ReinforcedConcrete beams with CFRP/GFRP laminates withdifferent thickness scheme. From that literaturereview it is evident that both the flexural and shearstrength of a beam laminate with CFRP/GFRP getincreased [21].
This review shows that still no comprehensiveresearch has been done on strengthened andretrofitted RC beams for shear subjected to staticvertical loads. Hence, the aim of the present researchwork is to redress this deficiency by carrying outstudies on FRP strengthened RC beams for shearsubjected to static vertical loads. The objectives of thework are given below;� To study the mechanical behaviour of FRP
confined concrete specimens� To study the behaviour of FRP strengthened
RC solid beams in shear zone subjected tostatic vertical loads
� To study the behaviour of FRP strengthenedRC hollow beams in shear zone subjected tostatic vertical loads
2. Materials and Methods
The method and used in this research work weretested as per the guidelines of the relevant IndianStandard (IS) codes.2.1 Materials and Properties
The concrete specimens were casted by ordinaryPortland cement with 31% standard consistency,initial setting time as 60 minutes and final setting timeas 320 minutes. The specific gravity of cement was3.14. According to IS: 383-1970, the fine aggregateused was the river sand and coarse aggregate usedwas the crushed granite stone. The specific gravity offine and coarse aggregate was 2.68 and 2.72respectively. The values of fineness modulus andabsorption of fine aggregate was 2.95 and 0.65%.
Similarly for coarse aggregate it was found to be 6.80and 0.45%. The size and diameter of reinforcementwere selected with references to IS: 1786 ‒ 1985. The8, 10 and 12 mm diameter rebars were used and theyhave been tested for their tensile stress in a universaltesting machine. The yield strength of steel was415 N/mm2. The quality of water also influence theproperties of concrete and hence the concretemembers. The M25 grade concrete used in thisinvestigation with the mixed ratio of 1: 1.42: 2.75 withwater-cement ratio of 0.48. From the preliminaryinvestigation the strength of concrete cubes found tobe 34.52 N/mm2.2.2 Methods of casting
Standard steel moulds were used for casting thespecimen, after one day of casting the moulds wereremoved and kept in water for 28 days. Now theconcrete specimen was make ready for FRPwrapping. The subsequent steps were adopted forFRP wrapping. Initially the exterior of the concretespecimens were scrubbed with a silicon carbidewater-proof paper sheet to smoothen the surface. Theprepared and cleaned surface was coated by a mixedmaterial of Nitowrap 30 primer. Afterwards it waspermitted to dry for one day. The density of primerwas 1.14 g/cm3. After the application of primercoating the Nitowrap 410 was done. The Nitowrap 410saturant coating system consist resin and hardener.Before applying the coating the saturant was mixedperfectly by using hand. The density of the saturantwas 1.25 ‒ 1.28 g/ cm3 and the applicationtemperature should be maintained as 15 ̊C ‒ 40 ̊C.Aramid fibre reinforced polymer was used inconjunction with an epoxy sealer cum primer,Nitowrap 30, and a high build epoxy saturantNitowrap 410. Nitowrap 30 primer and Nitowrap 410saturant are the epoxy products of FOSROC. It wasused for wrapping Aramid fibre reinforced polymerwith concrete surface. Fosroc is a Britishmanufacturer of specialized construction chemicalsthat cater to a range of sectors including commercial,industrial, residential, marine and infrastructure. ThePFRP sheet was confined straight over the surfaceafter the first coat of saturant was applied on theprimer coat. To avoid the glide or debonding of fibresin the time of test PFRP layer was confined all overthe concrete specimens with an overlap of (1/4)th ofthe perimeter and to conform the improvement oftotal strength. The specifications of the PFRPmaterial were tabulated in Table 1.
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Aramid, in full aromatic polyamide, any of a seriesof synthetic polymers (substances made of longchainlike multiple-unit molecules) in which repeatingunits containing large phenyl rings are linkedtogether by amide groups. The best known aramidKevlar, a high-strength fibre made into bulletproofvests was used in this work. The chemical structureof Kevlar is shown in Fig. 1. The melting point ofKevlar is above 500 ̊C (930 ̊F). The higher meltingpoint of Kevlar, as well as its greater stiffness andtensile strength, partly results from the regular para-orientation of its molecules. In solution the polymerassumes a liquid-crystal arrangement, which orientsthe molecules so that they can be spun and drawninto highly ordered fibres of ultrahigh stiffness andstrength.
3. Experimental Investigation
In this experimental investigation thecompression, split tensile and flexural test wereconducted to analysis the mechanical behaviour ofAFRP confined concrete specimens. In addition tothat of mechanical behaviour of AFRP confined RCbeams Shear strength of AFRP wrapped RC beamswere also studied.3.1 Compression test on concrete cubes
The standard sizes of 150×150×150 mm simpleplain concrete cubes were used for this study. Theexperimental analysis has been performed on 9 cubes.Out of the 9 cubes, three reference cubes were testedwithout any wrapping and the left 6 cubes wereconfined with AFRP mat with single and double plies.Three cubes were examined for each type trail andthe median of the values was recorded for futurework. Table 2 presents the compressive strength of
specimens. These tests were performed in accordancewith IS: 516 ‒ 1959(Reaffirmed 1999). From theexperimental results it is observed that the concretecubes which are confined with AFRP compositeshave high compressive strength than the unconfinedconcrete cubes. The increase in compressive strengthof concrete cubes confined by bidirectional AFRP matfor single and double plies was 37.78% and 73.93%respectively. Results also show that the concretecubes confined by double plies have high compressivestrength than the single ply concrete cubes.3.2 Split tensile test on concrete specimen
A standard test concrete cylinders were used forthis study. The experimental investigation has beenconducted on 9 cylinders. Out of the 9 cylinders, threereference cylinders were tested without anywrapping and the left 6 cylinders were confined withAFRP mat with single and double plies. Threecylinders were examined for each type trail and themedian of the values was recorded for future work.This test was also performed in accordance with IS:5816 ‒ 1999. Table 3 presents the type of concretecylinders along with their split tensile strength. Theseexperimental results shows that the concretecylinders confined with AFRP composites possesshigh split tensile strength than the unconfinedspecimens and also shows that the concrete cylindersconfined with double plies have high split tensilestrength than the single ply concrete cylinders. Theincrease in split tensile strength of concrete cylindersconfined by bidirectional AFRP mat for single anddouble plies was 54.87% and 100.95% respectively.
3.3 Flexure test on concrete prismsA simple plain concrete prism with a standard
size of 100×100×500 mm was used for this study.The experimental investigations have beenconducted on 9 prisms. Out of the 9 prisms, three
Properties Aramid fibre(Bi-directional)
Weight of fibre (g/m2) 227.5Fibre thickness (mm) 0.33Nominal thickness per layer (mm) 1.0Fibre tensile strength (N/mm2) 3900Tensile modulus (N/mm2) 131000
Number of plies Compressive strength(N/mm2)
Unconfined 34.52Confined with single ply 47.56Confined with double plies 60.04
Number of plies Split tensile strength(N/mm2)
Unconfined 4.21Confined with single ply 6.52Confined with double plies 8.46
Table 1 Specifications of AFRP material Table 2 Compressive strength of specimens
Fig. 1 Chemical structure of Kevlar
Table 3 Split tensile strength of concrete specimens
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reference prisms were tested without any wrappingand the left 6 prisms were confined with AFRP matwith single and double plies. Three prisms wereexamined for each type trail and the median of thevalues was taken out for future work. The test wascarried out as mention in IS: 516 ‒ 1959 (Reaffirmed1999). Table 4 contains the flexural strength of variousconcrete prisms. The experimental results shows thatthe concrete prisms confined with AFRP compositeshave high flexural strength than the unconfinedconcrete prisms and also show that the concreteprisms confined with double plies have high flexuralstrength than the single ply. The increase in flexuralstrength of concrete prisms confined by bidirectionalAFRP mat for single and double plies was 56.02% and99.53% respectively. Compressive, split tensile andflexural behaviour of AFRP confined concretespecimens were studied. The experimental resultsshowed that the specimens were confined with AFRPhave higher strength when compared to unconfinedspecimens and double plies have higher strength thanthe single ply.
3.4 Shear strength of AFRP wrapped RC beamsBoth of the RC hollow and solid beams were cast
with the help of wooden moulds of the innerdimensions 1200 mm×150 mm×250 mm. In hollowbeam, a core of dia. 76.2 mm was introduced andremains empty throughout the length of the beamjust below the neutral axis of beam to find the effectof hollow beam in shear strength. Three numbers of12 mm dia. bars at bottom and two numbers of 10 mmdia. bars at top were used as longitudinalreinforcement and 8 mm dia. bars were adopted asstirrups with a spacing of 150 mm. The failure ofbeam can attain due to shear but not by flexure andthe reinforcement of beam was designed in such away. Theoretical design strength of the beam by limitstate method was presented in Table 5. The rawmaterials were batched as per the mix design andwere mixed well by using hand mixing technique.The concrete was placed in the mould in three layersand properly compacted. Proper care must be givenfor uniform compaction and proper surface finishingthroughout the beam. The RC beams need to bedemoulded after the next day of it’s casting and cured.After 28 days curing, RC beams were ready for AFRPwrapping. By using the U-Jacketing technique theAFRP composites were wrapped in the shear zone ofthe beams. The RC beams were subjected to twopoint loading over an effective span of 900 mm. TheUTM was used for the testing of RC beams. The load
Condition Bending Moment (kNm) Shear strength (kN)Limit state of collapse : Shear － 53Limit state of collapse: Bending (based onthe tension reinforcement) 22 73
Limit state of collapse: Bending (based onthe compressive strength of concrete) 25 83
Number of plies Flexural strength(N/mm2)
Unconfined 4.32Confined with single ply 6.74Confined with double plies 8.62
Table 4 Flexural strength of concrete specimens
Table 5 Theoretical design strength of beam
Fig. 2 Experimental setup of AFRP wrapped RC beam
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was increased in the order of 10 kN. The deflectionreadings were noted accordingly. Typicalarrangement of testing of AFRP wrapped RC beamsis presented in Fig. 2. Conventional hollow and solidRC beams and AFRP strengthened hollow and solidRC beams are presented in Fig. 3 and Fig. 5respectively. Table 5 presents the shear strength ofconventional hollow & solid RC beams and AFRPstrengthened hollow& solid RC beams. Theexperimental finding show that the RC beamswrapped with AFRP composites have high shear
strength than the unwrapped RC beams for both solidand hollow RC beams. Results also show that the RCbeams wrapped with double plies have better shearstrength than the single ply. Fig. 7 shows thevariation in shear strength of RC beams wrappedwith AFRP composites.� The increase in shear strength of solid RC
beams wrapped with bidirectional AFRPmat were 18.91 % and 36 % for single anddouble plies respectively.
a) Solid RC beam b) Hollow RC beamFig. 3 Solid and hollow RC beams (Before loading)
a) Shear crack in solid RC beam b) Shear crack in hollow RC beamFig. 4 Solid and hollow RC beams (after loading)
Table 6 Shear strength of RC beams
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beams wrapped with bidirectional AFRPmat were 19.53 % and 37.89% for single anddouble plies respectively.
4. Conclusion
The capacity of AFRP for strengthening of RCstructures were studied by conducting compression,split tensile and flexural strength tests on concretespecimens with and without AFRP confinement andshear strength of RC beams were also studied on RC
beams with and without AFRP wrapping in the shearzone.� The feasibility of using AFRP in
strengthening of beam is strongly linked tothe capability of these materials to maintaintheir mechanical properties during service.
� The experimental results showed that thespecimens confined with AFRP have higherstrength when compared to unconfinedspecimens. The specimen wrapped withdouble plies have better strength than single
a) AFRP strengthened solid RC beam b) AFRPstrengthened hollow RC beamFig. 5 AFRP strengthened RC beams (Before loading)
Fig. 6 AFRP strengthened RC beams (After loading)
Fig. 7 Effect of AFRP wrapping on the shear strength of solid RC beams
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ply.� The experimental results indicated that the
beams wrapped with AFRP have betterstrength than the unwrapped beams.
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