Experimental research Fullpaper Experimental Study on the Concrete Surface Preparation Influence

Han Ay Lie Procedia Engineering 00 2017 000–000 3

3. Experimental research

3.1. Shear-bond behavior Shear-bond test methods for FRP are limited; research work on FRP in shear is mostly applied to FRP plates having a much higher rigidity as compared to sheets or wraps [4, 5, 6, 7, 8, 9]. Since the FRP sheets have significantly less stiffness as compared to FRP plates, the typical one-face-tensile, and the one-face and double-face- push tests as introduced by the majority of researchers, was not applicable. The effect of misalignment would heavily influence the outcome [10]. Considering all aspect, a modification of the test method based the fib-CEB technical specifications [2, 11] was chosen Fig 2. Fig. 2. Shear test set up and specimen preparation. Instead of using steel clamps as was advised by the fib-CEB, a smaller bond area measuring only 50 by 50 mm was designed to localize bond failure. The opposite contact areas were made larger, measuring 50 by 150 mm. An un-bonded zone 50 mm in width was designated to prevent premature spalling due to high stress concentrations in the concrete corner. This un-bonded area was bridged by a two-ply FRP composite attached by an epoxy layer at the interface. The epoxy resin was also applied the exposed face of the FRP. The D22 steel bar dimension; its development length and the concrete reinforcements were carefully designed to ensure failure in the bond. Six specimens were prepared for each surface treatment, and standardized cylinders sized 150 by 300 mm were produced to monitor the 28 th day’s concrete compression strength. The strength was recorded as 55.60 MPa. At the age of 28 days, the groves were applied to the concrete surface using a circular diamond saw, and sandblasted to clean the groves of small particles. The FRP sheet was applied using the epoxy-resin and cured for seven days. Upon testing, the specimen was placed in a wooden frame to prevent secondary strains in the bonded and un-bonded FRP area. The specimen was further placed within the gripping jaws of the Universal Testing Machine, and the D22 steel bars clamed. A direct tensile force with a loading rate of 1.5 kNsec was applied to these steel bars. The load increment, the failure load, and the strain response in the strain gauge, were recorded. Additionally, the strain in the un-bonded FRP was measured using strain gauges attached to the FRP surface prior to the application of the epoxy resin Fig. 2. The specimens were designated S T , S D , S C , S L and S N based on the surface preparation type. All specimens S T , S D , S C and S L failed due to concrete-shear failure; the S N specimen failed in de- bonding between the epoxy-resin and the concrete Figures 3a and 3b 3.2. A bond the c and t T The This 55.6 bond prod A gaug un-b had doub from 4 t and a two a Shear bond str All specimens S d mode betwee concrete at the the concrete, a The S N specime shear-bond str s concrete-shea 0 MPa concre d using the ex duced between A closer observ ges showed tha bonded FRP se a material stiff ble play genera m single-ply FR to the initial sti a 0.50 mm thic bond faces. a Fig. 3. Shear-b rength S T , S D . S C and en the FRP and un-bounded ar and the stress-fl en failing in sh rength was calc ar strength clos te strength is 7 act same mate the FRP and c vation to the s at the bonded F ction had a ma fness of 90 kN ally resulted in RP-resin specim iffness of the m ckness of the e Sri Tudjono ond and concrete- S L failed due to d the concrete. rea. This was d flow propagatio Fig. 4. Concrete hear-bond had culated to be 5 sely approache 7.46 Nmm 2 . T erial resulted in oncrete, conse strain response FRP had a mu aterial stiffness Nmm in combin n a higher elast mens [12]. The material. The Y poxy resin laye Procedia Enginee b shear failure; a D o concrete shea Except for the due to the high on in the direct spalling due to hig a significantly 5.24 Nmm 2 , co es the concrete- The report on t n average shea quently the fai e in the un-bo uch higher stiff s of 63 kNmm nation with a Y tic modulus as e double layere Young’s modul ers. The tensile ering 00 2017 00 De-bonding failure ar-cracking, wh predicted patte h stresses in th tion outward of gh shear-stress con y lower failure ompared to the -shear capacity the single-lap s ar-bond streng ilure mode shou nded and bon fness as compa m with a Young Young’s modu compared to t ed FRP and the lus was determ e load was also 00–000 e; b Concrete-sh hile the S N spe ern as seen in F e vicinity of th f the maximum ncentrations. stress as comp e concrete-shea y as predicted shear test perf gth of 16.6 MP uld be due to c nded FRP secti ared to the un- g’s modulus of ulus of 67 GPa the Young’s m e additional ep mined based on o assumed to b hear failure. ecimens failed Fig. 3, spalling he border betw m shear stresses pared to S T , S D ar strength of 8 by the ACI co formed on the Pa [12]. If a g concrete-shear. ion recorded b -bonded FRP f 57 GPa. The . The composit modulus of 55 G poxy-resin trea a 0.13 mm FR be distributed e in the shear- g occurred in ween the FRP s Fig. 4. D . S C and S L . 8.12 Nmm 2 . ode that for a FRP-to-FRP good bond is . by the strain Fig. 5. The bonded FRP te FRP-resin GPa resulted atment added RP thickness, equally to the 3.3. D To betwe and a Th T N . T Upon the sl draw failur 3.4. T Al failur streng calcu test r surfa Direct tensile b o test the resp een the FRP an an accuracy lev he concrete sur The synthetic s n testing, a cyl lab. The alumin -bolt. This dra re, and the load Tensile bond st ll but one of t re due to tensio gth measured t ulated from the results. The cra ce showed a cl F behavior onse in direct nd concrete. T vel of less than rface was prep heet was attach inder with a d num test disc w aw bolt had a d recorded Fig trength he T N specime on. The tensile to be 3.20 MP e fib-CEB mod acking pattern lear breaking m Han Ay Lie Fig. 5. Stress-strain tension, an ex he Dyna Proce 2 with a stro ared in the sam hed to the con diameter of 50 was attached to conical head g 6. Fig ens failed in te e-bond failure r a. This value w del code 2010 was easily dis mode in the inte Procedia Engine n behavior of bond xperimental m eq haftprufer p oke of 3.5 mm, me manner as t crete surface a mm was core- o the FRP with to ensure a co . 6. Direct tensile t ensile-bond mo resulted in a st was taken as av predicted a ten tinguishable fr erface between eering 00 2017 00 ded and un-bonded model was cons pull-off tester Z , was used. the shear specim and the specim -drilled in the h resin, and con oncentric tensi testing method. ode. All other tress of 1.29 N verage of all th nsile strength o rom the tensile n the aggregate 00–000 d FRP wraps structed that ta Z16 having a p mens, and den mens were teste concrete surfa nnected to the ion force. The surface treatm Nmm 2 , compar he data. The co of 3.84 MPa, w e-bond failure, e and the morta argets only the pull-out capaci noted as T T , T D ed after seven d ace, creating a pull-off tester e specimen wa ments resulted red to the conc oncrete tensile which is very since the conc ar Fig 7. 5 e bond area ity of 16 kN D . T C , T L and days curing. cone inside through the as tested till in concrete crete-tensile e strength as close to the crete failure Sri Tudjono Procedia Engineering 00 2017 000–000 a. b. Fig. 7. a De-bonding in tension; b Mortar tension failure.

4. Analysis and discussion