1. INTRODUCTION. Table 1 Mechanical Property of Strand-sheet High-tension CFRP Tensile Modulus (GPa) 245 Tensile strength (N/mm 2 )

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1 T1A2 Experimental Study on ening Eect o CFRP Strand Sheet on RC Beams Applied with Several Kinds o Adhesives Atsuya. Komori. And Kenshi. Taniguchi Inrastructural Use Div., Nippon steel materials Co., Ltd, Tokyo, Japan Satoru. Nakamura Civil engineering Sales Div., Sato-Benec Co.,Ltd, Oita, Japan Kouhei Yamaguchi. And Shinichi Hino Department o Civil Engineering, Kyusyu University, Fukuoka, Japan ABSTRACT When attaching continuous iber sheets on concrete members on site, bonding deection such as bubbles or mal-impregnated area o the continuous iber sheets sometimes happens. FRP (Fiber Reinorced Polymer) strip bonding method doesn t have this kind o problem because it is impregnated and cured at the actory, but it also has demerit o less adhesion property caused by small bonding area. To solve these problems, we have developed advanced FRP strand sheets which consist o bunch o individually hardened continuous iber thin strands aliened and composed uni-directionally. The FRP strand sheets can be easily attached on the surace o concrete members with putty like adhesive and no impregnation needed. Thus, the advanced strand sheet method can assure better construction quality and cut down the application time and costs. The purpose o this study is to clariy the inluence o the dierences o the adhesives on strengthening eect o strengthened RC (Reinorced Concrete) beams with FRP strand sheets. In this study, adhesives o Epoxy, MMA (Methyl methacrylate) resin, PCM (Polymer Cement Mortar) and JCM (Ultra rapid hardening Jet cement mortar) were tested and compared. As results, it is ound that t all adhesives were eective or improving lexural capacity o RC beams and the bonding strength was depend on the kind o adhesives. KEYWORD CFRP, FRP, Strand-sheet, RC-beam, Epoxy, PCM, MMA, Ultra rapid hardening-cement, Mortar, Flexural strength, CFS, CFSS,

2 1. INTRODUCTION The continuous iber sheet (CFS) bonding method has become very popular in Japan because o its high strengthening eects, its excellent durability, its lightness, it s easy applicability and its thinness. However, in order to execute this method perectly to the structures especially which has uneven concrete surace, it requires a lot o time and eort to prepare smooth enough surace using epoxy putty or applying CFS. Sometimes very skilled workers are needed. The newly developed continuous iber strand sheet (CFSS) consists o thin strands which are already impregnated and cured with resin and abricated as sheet material, which is attached to reinorce the structures using putty like adhesives. The adhesives are putty like materials and thick application is possible, so CFSS can be applied on rough surace. And the impregnation is already done at the actory, so the application o CFSS is much easier than that o CFS. The purpose o this study is to study the eects o types o adhesives on reinorcing eects o CFSS reinorced RC beams. In this study, our types o adhesives o epoxy, MMA, PCM, and JCM are used and evaluated. We have conducted both basic bonding tests o individual materials and RC beam bending tests reinorced with each adhesive. These tests results were compared and evaluated. 2. BOND PROPERTIES OF FRP STRAND-SHEET TO CONCRETE WITH USE OF VARIOUS ADHESIVES 2.1 Material Properties o FRP Strand Sheet and Adhesives In this study, high tensile strength carbon iber strand sheets are used. Table 1 shows the mechanical property o Strand-sheet. The Epoxy is the typical adhesive which has been used as a standard application adhesive. MMA is the rapid curing resin adhesive, which can also be used in low temperature conditions. MMA can be cured in about two hours ater installation. PCM is the abbreviation o Polymer Cement Mortar, which is or wet surace applications. PCM consists o polymer-emulsion, cement, and sands. In case o JCM, it is or used together with epoxy adhesive. This epoxy adhesive is applied to the concrete surace and CFSS surace in order to adhere between the concrete and JCM, and between CFSS and JCM. JCM is inorganic material which consists o ultra-rapid hardening cement and sands. Table 2 shows the mechanical property o each adhesive. Table 1 Mechanical Property o Strand-sheet Type High-tension CFRP Tensile Modulus (GPa) 245 Tensile strength (N/mm 2 ) 3,4 Unit Weight (g/m 2 ) 6 Design Thickness (mm).333 Table 2 Mechanical Property o Adhesives (N/mm 2 ) Type Epoxy MMA PCM JCM Compressive Compressive Modulus 3,97 2,5 4,8 26,2 Tensile Flexural Lap-share N/A N/A 2. 2 Outline o Experiments Properties o used concrete are shown in Table 3. The dimensions o the adhesion test specimens are shown in Fig. 1. The experiments were executed based on the standard o JSCE-E [1]. The name o the test methodology is a test method or bond properties o continuous iver sheets to concrete. The suraces o concrete specimens were treated by alumina powder blasting at blasting density o 3kg/m 2. The carbon iber sheet was rapped at right angle over CFSS in order not to peel beore the peeling o testing area. In cases o Epoxy and MMA applications, the adhesive were coated to the concrete specimens at 2.5kg/m 2 and the CFSS was applied beore the adhesive was hardened. The PCM was applied at 1mm thickness, and CFSS was buried into the PCM.

3 In case o JCM application, liquid epoxy adhesive was applied irstly at 1.4kg/m 2 to the specimen beore JCM was applied at 5mm thickness. And then the same epoxy adhesive was coated at 3.kg/m 2 and CFSS was buried in the adhesive layer. Ater that JCM was by 5mm in thickness. All the procedures had been completed beore each one o materials was hardened. When more than 2 layers o CFSS application were needed, the edge o the upper layer was applied 25mm shorter than the previous layer at the edge in order to avoid the stress concentration (see Fig. 1). Compressive strength o specimen concrete was 37.1N/mm 2 ater 28 days o curing. Ater days o cuing time, the bonding tests o CFSS were carried out. 2.3 Interacial Fracture Energy and Bond The test results are shown in Table 4. The specimens were racture at either side o concrete where CFSS were applied at both sides. Type layers Table 4 Bond test result maximum-load P max (kn) measured value Ave. interacial destruction energy G (N/mm) measured value Ave. bond strength τ u (N/mm 2 ) measured value Ave Epoxy MMA PCM JCM Interacial racture energy G and bond strength τ u were calculated by using equations (1) and (2) based on JSCE-E [2] G u P 2 max 8b 2 E Pmax 2b t (1) (2) Fig. 1 Schema o bond test specimens Fig. 2 Cross section o reinorcing material Table 3 Properties o used concrete Kind o cement Compressive Compressive Modulus Age Rapid hardening 37.1N/mm cement N/mm 2 days The interacial racture energy between concrete and one layer o carbon iber sheet is assumed to be more than.5n/mm 2 according to the research in the past. Most o the obtained G s were exceeded.5n/mm 2 except that o three layer application o MMA adhesive. The interacial racture energy o each adhesive was the order o JCM > Epoxy > MMA > PCM compared at 1 layer o Strand-sheet. And, the bond strengths are increased as the number o the layers is increased. 2.4 Bond Stress Transmission Length Fig. 3 shows the distribution o the strain o CFSS along with the iber direction or example. At the point o P=1kN loading where the peeling hasn t been occurred, the strain isn t observed

4 strain(μ) strain(μ) urther than 6mm rom the edge. In this area, the tensile stress o CFSS was transmitted to concrete. At the point o 5kN loading where the peeling starts to be occurred, the strain was even at - 6mm area where the peeling is occurred. In 6-12mm area, the strain is decreased rapidly as the distance rom the edge is increased and it is assumed that in this region the tensile stress o CFSS was transmitted to concrete. In 12-28mm area, the strain is decreased gradually as the distance rom the edge is increased. In this region, it is assumed that peeling isn t occurred. A F : Cross section o Strand-sheet (mm 2 ) S g : Interval o strain gauge (mm) b : Width o strand-sheet (mm) l e : Eective bond length (mm) : Maximum load (N) P max 6 Epoxy(single-layer) Epoxy(two-layars) 5 Epoxy(three-layers) MMA(single-layer) 4 MMA(two-layers) MMA(three-layers) 3 PCM(single-layer) PCM(two-layers) 2 JCM(single-layer) Peeling area Increasing area S g Δε F Distance rom center o test specimen(mm) 1kN 2kN 3kN 4kN 5kN distance rom center o specimen(mm) Fig. 4 Strain distribution (P 5kN) The eective bond length is increased as the number o layers o Strand sheet increases. For example, in case o one layer, the eective bond length is 13-19mm, but in case o two layers, the eective bond length is around 25mm. Fig. 3 Strain distribution (Epoxy 2-layeres) 2.5 Eective Bond Length It is well known that the average bond strength becomes lower as the bond length becomes longer. This is because the eective bond area is not the all the bond area but some limited area. In this paper, this limited area was deined as the eective bond length o Strand-sheet based on the report o the research committee on continuous iber reinorcement concrete (JCI) [4]. The maximum bond stress is obtained by equation (3). The strain inclination Δε F is obtained rom strain dierence between the measured strains at two points in strain increasing area. The eective bond length is calculated by using expression (4). F EF AF y (3) S b e g Pmax 2 b y τ y :Maximum bond stress (N/mm 2 ) Δε F :The dierence o strain o strain in cruse area at the maximum load E F : Tensile modulus o strand-sheet (N/mm 2 ) (4) In cases o three layers o CFSS applications using MMA and epoxy adhesives, the strains are decreased gradually to as the distance rom the edge is increased to 28mm and no saturation zone is observed. So in these cases, the eective bond lengths are thought to be longer than 28mm. The riction stress degree was calculated rom the strain dierence o each strain measurement point in accordance with the reports o the joint research on the repair and the reinorcement o concrete members (PWRI) [5]. The relation between riction stress and the load o three layers o epoxy application is shown in Fig. 6. The riction stress at -3mm area is increased as the load is increased until P=35kN. In this zone, the de-bonding between CFSS and concrete is thought to be partially progressing. And the riction stress is decreased gradually ater P=35kN. In this zone, the de-bonding is spread all over the area, and only the rictional orce is remained. In 3-6mm area, the similar mechanism is observed and the total de-bonding is observed ater P=48kN. In three layers experiments o Fig. 4, the

5 riction re-strain stress(n/mm) Eective length(mm) de-bondings were also observed at -6mm area as the loads were increased. The inal racture is thought to be occurred as the peeling ailure when the bond area is decreased to the limit as the load is increased. at the edge in cases o more than two layers applications. In joint test specimens, 2mm o lap joints were made at the center o RC-beams. Ater curing or more than one week, we conducted our-point lexural tests Load and Delection The results o beam bending tests are shown in Table-7 and Fig. 8. In Fig. 8, the data o E-J, M-J, J-J, and M-1 are omitted because these data are very similar to that o E-1 (one layer o epoxy application) Fig. 5 eective length (mm) The maximum load and the bending stiness are increased in each reinorced beam compared to non-reinorced beam "N". The initial bending stiness o "JCM" is higher than any other reinorced one. In this case, the total height o the beam was thickened by applying JCM at 5mm thick, the bending stiness o the beam itsel was increased. There is the tendency that the lexural stiness beyond the rebar yielding point (P=2kN) is increased as the number o the layers is increased except the cases E-3 and P-3 whose reinorcing CFSS were peeled o beore their yielding points LOAD(kN) -3mm 3-6mm 6-9mm 9-12mm 12-15mm 15-18mm 18-21mm 21-24mm 24-27mm Fig. 6 Relation between rictional stress and load (Epoxy three-layers) 3. REINFORCING EFFECTS OF FRP STRAND-SHEET ON RC-BEAM BENDING TESTS 3.1 Overview o Experiments The speciications o test specimens are shown in Table 5 and the properties o used re-bar and concrete are shown in Table 6. The schematic diagram o test specimen is shown in Fig. 7. The materials properties o CFSS are listed in Table 1. The number o the RC-beams was 14, and the adhesive were selected among PCM, MMA, and JCM (JCM is used together with liquid epoxy adhesive). All test specimens were reinorced by the same Strand-sheet. And in order to avoid the stress concentration at the sheet edges, the coming layer was applied 25mm shorter than the previous layer Table 5 RC-beams speciications Reinorcers Type adhesives remarks Lap-joint layer N unreinorced E-1 1 E-2 no 2 Epoxy E-3 3 E-J yes 1 M-1 1 M-2 no 2 MMA M-3 3 M-J yes 1 P-1 no 1 PCM P-2 no 2 J-1 no 1 J-2 JCM no 2 J-J yes 1 Table 6 Rebar and concrete properties as usually method method or wet suraces rapidhardening rapidhardening method (N/mm 2 ) D1 yield strength 376 (SD345) Tensile strength 548 D13 yield strength 395 (SD345) Tensile strength 551 Modulus D19 yield strength 47 (SD345) Tensile strength 559 Concrete Compressive strength Situation o Fracture The schematic diagrams crack distributions o RC-beams are shown in Fig. 1 and the photos o

6 cross section o ractured specimens are shown in Photo. 1. Ater yielding point, the no reinorced test specimen "N" was broken at the compression edge o the concrete beam. The cracks were introduced at about 3mm intervals. In other reinorced test specimens crack distributions were more requent than that o the no reinorcement test specimens "N", and the crack intervals were about 15mm. In one layer reinorced specimens, Strand-sheets were peeled o under the loading point only ater the re-bars were yield. In most o two layers reinorced specimens, the ailure modes were similar to those o one layer-reinorcement. But only in "P-2", Strand-sheet was peeled o almost at the same time with yield o the rebar. In three layers reinorced "M-3" specimen, the diagonal crack was introduced rom the edge o CFSS ater the yielding point, and the crack width was increased as the load was increased. And then the concrete cover was peeled o together with CFSS. In case o "E-3" specimen, CFSS was peeled o beore the rebar was yielded. The load o every reinorced specimens were decreased to the load level o the no reinorcement test specimen "N" ater Strand-sheet were peeled o. Ater that, the displacement was gained dramatically, and the specimen was ailed at the compression edge. In joint specimens "E-J", "M-J" and "J-J" where the installed Strand-sheets have lap joints at the center o the span, the ailure modes were the same as those o non-joint specimens, and the joints were never broken. Concrete covers were adhered to the back side o the sheet ater loading in all test specimens. The ultimate load P ucs in Table 7 were calculated by using equation (5) using interacial racture energy (G )s whose values were calculated based on the bond test results described in chapter 2.3 [3]. 2G E n t σ :Allowable stress o Strand-sheet in bend cracks generation displacement by maximum lexural moment (N/mm 2 ) G :Interacial detachable energy o Strand-sheet and concrete (N/mm) E :Tensile modulus o Strand-sheet. (N/mm 2 ) n :Number o laminating o Strand-sheet :Thickness o Strand-sheet. (mm) t In all the cases except P-2, the ratio o the experiment value and the designed values were between and considered to be the sae side. In P-2 the ratio was.94, 6% below the saety standard 1.. In cases, E-3(three layer/epoxy) and P-2(two layer/pcm), the diagonal cracks were introduced at the edges o the sheets and the sheets were peeled o together with cover concrete. In these cases, the stress concentration at the sheet edges thought to have some eect to the entire ailure modes. In this study, 25mm stepwise application o CFSS was adopted in order to avoid the edge stress concentration. But considering that some ailures were initiated by the edges stress, it should be necessary to study urther about the prevention o stress concentration at the edges. For example, it seems that longer step length is eective to reduce stress concentration at the sheet edges. (5) 3.4 Evaluations o Flexural Capacity The maximum loads o the reinorced test specimens were times higher than that o non-reinorced one. The lexural capacity was the order o Epoxy> JCM > MMA > PCM compared at 1 layer o Strand-sheet. Designed P ycs in Table 7 are the calculated values based on the assumptions that CFRP Strand-sheet is completely bonded to the RC beam, Bernoulli-Euler theory can be adopted, and that concrete tensile strength was disregarded. The ratio between experiments and calculations are scattered between and the calculation proved to be very accurate. Fig. 7 Over view o RC-beam specimen

7 load (kn) Table 7 RC-beams lexure test results detachment with covered concrete detachement o thin layer yields load ultimate load Type experimental desigined experimental desigined racture mode load P y (kn) load P yc (kn) P y /P yc load P u (kn) load P uc (kn) P y /P uc N Flexure racture Epoxy AdhesionPCM CoveredPCM E E E sheet detached rom under the loading point detached rom edge detachment with covered concrete detachement with covered concrete E-J M M M sheet detached rom under the loading point detached rom edge MMA inter layed Rpoxy JCM M-J P P sheet detached rom under the loading point detached rom edge Photo. 1 Cross section views o ailed specimens J J J-J Fig. 8 Load and displacement o the span sheet detached rom under the loading point displacement at center o eective span (mm) (a)n (b)e-1 (c)e-2 (d)e-3 (e)e-j ()P-1 (h)m-1 (i)m-2 (j)m-3 (k)m-j (l)j-1 (m)j-2 N E-1 E-2 E-3 M-2 M-3 P-1 P-2 J-1 J-2 4. CONCLUSIONS The results obtained by the present study are as ollows. (1) Most o interacial racture energy o Concrete surace and Strand-sheet were bigger than usual value o CFS (.5 N/mm), where various types o adhesives were used or applying CFSS except M-3(three layers o MMA application). And the interacial racture energy was decreased as the number o applied CFSS was increased. (2) The eective bond length becomes longer as the number o the layers is increased. And that o one layer is 13-19mm, that o two layers is about 25mm, and that o three layers is 35-58mm even when the adhesive is changed. (3) The lexural strength and lexural stiness o RC-beam was improved by times by bonding Strand-sheet using various types o adhesives, (4) The calculations and the experimental results o yielding loads were agreed well to ratio based on the Bernoulli-Euler theory. (5) The ratio o estimated racture loads calculated using interacial racture energy and the experimental values were between and considered to be the sae side in exception o P-2. But in order to prevent the sheet edge initiated ractures resulted in E-3 and P-2, urther studies on edge application should be needed. (g)p-2 (n)j-j REFERENCES Fig. 9 Schematic diagrams o crack distributions o each specimen [1] Japan Society o Civil Engineers. (JSCE): Standard Speciication or Concrete

8 Structures. Test Methods and Speciications, 27.5 [2] JSCE: Recommendations or upgrading o concrete structures with use o continuous iber sheets. The 41 st o concrete engineering series, 2.7 [3] Japan bridge engineering center: Earthquake-proo reinorcement industrial method case collection o existing bridges [4] Japan Concrete Institute. (JCI): JCI standards, ( ) pp , 24.4 [5] Pubic Works Research Institute (PWRI): The joint research report on repair and reinorcement o concrete members (3) pp ,