Preparation and characterization of glass fibers polymers (epoxy) bars (GFRP) reinforced concrete for structural applications

Transcription

1 SSP - JOURNAL OF CIVIL ENGINEERING Vol. 11, Issue 1, 2016 DOI: /sspjce Preparation and characterization of glass fibers polymers (epoxy) bars (GFRP) reinforced concrete for structural applications Saeed Alkjk 1, Rafee Jabra 1, Salem Alkhater 2 1 Applied Physics Department Higher institute for applied sciences and technology (HIAST), 2 Faculty of civil engineering Damascus University. Damascus, Syria radsezer@gmail.com Abstract The paper presents some of the results from a large experimental program undertaken at the Department of Civil Engineering of Damascus University. The project aims to study the ability to reinforce and strengthen the concrete by bars from Epoxy polymer reinforced with glass fibers (GFRP) and compared with reinforce concrete by steel bars in terms of mechanical properties. Five diameters of GFRP bars, and steel bars (4mm, 6mm, 8mm, 10mm, 12mm) tested on tensile strength tests. The test shown that GFRP bars need tensile strength more than steel bars. The concrete beams measuring (15cm wide x 15cm deep x and 70cm long) reinforced by GFRP with 0.5 vol.% ratio, then the concrete beams reinforced by steel with 0.89 vol.% ratio. The concrete beams tested on deflection test. The test shown that beams which reinforced by GFRP has higher deflection resistance, than beams which reinforced by steel. Which give more advantage to reinforced concrete by GFRP. Key words: GFRP bars, steel bars, tensile strength, deflection 1 Introduction Since human had known concrete material and was able to combine it with steel, buildings and civil structures were expanded in a manner that hasn t been seen in previous era. Still, despite the weight of steel, its susceptibility to rust and large energy required to manufacture and transport it, reinforcing cement by steel represents the most prevalent traditional and worldwide way. Composite materials of polymers reinforced by fibers have shown remarkable performance and wide range of applications in many areas of construction. This is due to their distinctive characteristics of light weight, chemical stability and corrosion resistance against environment and harsh conditions, in addition to ease of fabrication, use and implementation in comparison to traditional materials used in construction areas. Over the last few decades, the use of Fibers-Reinforced Polymer (FRP) bars as reinforcement for concrete structures has been spread and particularly encouraged in the international 15

2 Saeed Alkjk, Rafee Jabra and Salem Alkhater technical and research community. On the other hand, specific technical instructions, guidelines and codes governing the use of this new reinforcement have been published. Japan was one of the forerunners and drew up in 1996the first design guidelines which were subsequently translated into English 1 year later [1]. Further guidelines were published in Canada in 1996 [2], followed by those published by ACI in 2000 and revised in 2006 [3]. More recently, technical documents dealing with the design and execution of FRP reinforced concrete construction have been published in Italy [4] and in Europe [5]. Kemp and Blowes studied the advantages offered by glass fibers reinforced polymer (GFRP) over steel especially when used in marine and other salt rich environments [6]. Achillides and Pilakoutas studied also bonding behavior of FRP bars (Glass, Carbon, Aramid and Hybrid) in concrete under direct pullout conditions [7]. Muruts and Nadcarried out the preparation of GFRP bars for structural concrete (beams) in the shape of rectangular bars with unidirectional laminates. They studied those bars with regards to tensile strength, elasticity module and bond strength of GFRP bars in concrete [8]. 2 Materials and methods 2.1 Materials The present work used glass fibers reinforced polymer (epoxy) rebars ACK from KomAR company Republic of Russian Federation as received from the manufacturer, grade 75 high yield steel rebars from Hmesho distribution company Syria, ordinary Portland cement of Syrian fabrication and local sand and gravels. Table 1 gives GFRP and steel rebars characteristics. Table 1: GFRP and steel bars characteristics GFRP rebars Steel rebars Density (g.cm -3 ) Tensile strength (MPa) Elastic modulus (GPa) Strain at break % Both rebars were tensile tested using samples of 300 mm length according to ASTMA Concrete formulation Table 2 gives concrete formulation according to local Syrian code and practice. Table 2: Concrete formulation constituent % cement 11.0 sand 47.0 gravel 31.0 water

3 SSP - JOURNAL OF CIVIL ENGINEERING Vol. 11, Issue 1, Reinforced concrete samples preparation Reinforced concrete samples for bending testing have been prepared using the above mentioned concrete formulation with either GFRP or steel rebars. Samples dimensions were 700x150x150 mm 3. In each case, every sample was reinforced by 4 rebars (6mm for GFRP rebars, 8mm for steel rebars) in 140mmsquare distribution. Reinforcement ratio was 0.5 vol. % and 0.89 vol.vol % for GFRP and steel reinforced samples respectively. These samples were cast in wooden molds. 2.4 Tensile and bending tests Tensile test Both rebars were tensile tested using 3 samples of 300 mm length and (CONTROLS, S.p.a 6/8,v) universal testing machine according to ASTM A 370. Tensile tests were made on GFRP ribbed bars samples with 4mm, 6mm, 8mm, 10mm, 12 mm diameters. The same has been done on ribbed steel bars except that 4mm diameter steel bars were of non ribbed type. Tensile mechanical properties were deduced as follows: - Young's modulus: (1) E: Young's modulus, σ:stress differentialbetween 2 points of the σ- ε linear region curve, ε: Strain differential between the same 2 points. - Tensile strength: F: load at break, S: cross section area of bars. - Strain at break: (2) L 0 : initial length of sample, L: length at break of sample. (3) Bending test For each reinforcement rebar type, three concrete reinforced beams were bending tested using (TONINDUSTRIE) machine according to ASTM C-78. Bending mechanical properties were deduced as follows: 17

4 Saeed Alkjk, Rafee Jabra and Salem Alkhater - Bending strength: R: bending strength, P: fracture load of the sample, L: span distance, B: sample width, H: sample thickness. (4) Epoxy content in GFRP- Ignition test To determine epoxy content in GFRP rebars, ignition test has been done on GFRP rebar sample at 600 C for 2 hour. For this purpose, ceramic crucible of m 0 weight was used. The weight of the crucible and GFRP rebar sample before ignition was m 1, this weight becamem 2 after ignition. The following relation gives glass fibers weight percent: (5) 3 Results and discussion 3.1 Tensile test results The tensile test results of GFRP bars are presented in Figure 1 and Table 3. Figure 1: Tensile curves of GFRP rebars 18

5 SSP - JOURNAL OF CIVIL ENGINEERING Vol. 11, Issue 1, 2016 Table 3: Tensile test results of GFRP rebars Diameter (mm) Tensile load(kn) Tensile stress (MPa) Strain (%) Young's modulus (GPa) The tensile test results of steel rebars are presented in Figure 2 and Table 4. Figure 2: Tensile test curves of steel rebars Table 4: Tensile test results of steel rebars Tensile Tensile stress Young's Diameter (mm) Strain (%) strength (KN) (MPa) modulus (GPa) Tensile test results show the main differences between GFRP and steel rebars. Steel rebars show, as expected, plastic behavior, while GFRP rebars are rather of brittle character. GFRP rebars are less ductile and more tensile resistant than steel rebars which are more stiff and 19

6 Saeed Alkjk, Rafee Jabra and Salem Alkhater deformation tolerant. This behavior of GFRP rebars is related to the behavior of their constituting components, i. e. glass fibres and epoxy, which are both rather of brittle nature. Tensile properties of GFRP rebars are not dependent of rebar diameter, this confirms their homogeneity and good fabrication regularity. The same observation could be made for steel rebars except of 4mm diameter steel un- ribbed rebar. Tensile test results show that tensile properties of both rebars are in good agreement with suppliers data sheets, published literatures and standards. 3.2 Bending test results Figure 3 shows one bending test on concrete beams reinforced by GFRP rebars. Figure 3:Bending test on GFRP bars reinforced concrete beam The bending test results of GFRP rebars reinforced concrete beams are presented in Table 5. Sample No: Table 5: Bending test results of GFRP rebars reinforced concrete beams Deep Wide Long Span Fracture load (N) Bending strength (MPa) The bending test results of steel rebars reinforced concrete beams are presented in Table 6. Sample No: Table 6: Bending test results of steel rebars reinforced concrete beams Deep Wide Long Span Fracture load (N) Bending strength (MPa)

7 SSP - JOURNAL OF CIVIL ENGINEERING Vol. 11, Issue 1, 2016 Bending test results show that bending bearing capacity of GFRP rebars reinforced concrete beams is higher than that of steel rebars reinforced concrete beams. Considering that bending strength of unreinforced concrete is around 2-4MPa, it could be concluded that GFRP rebars of 6 mm diameter and 0.5 vol.% increases concrete beam bending strength by around %. 3.3 Ignition test result - Epoxy content in GFRP Table 7 gives ignition test result. Table 7: Ignition test result Crucible Weight m 0 (g) Sample weight (g) Crucible & Sample Weight m 1 (g) Crucible & Sample Weight after ignition m 2 (g) Ignition test result leads to an epoxy content of 30 wt % and glass fiber content of 70 wt %. 4 Conclusions The present work allowed the determination of tensile properties of GFRP and steel rebars, the comparison of their properties and relative mechanical behavior. The reinforcement performance of both rebars has been evaluated through static 3 point bending test of concrete beams. It has been shown that smaller diameter GFRP rebars provide concrete beams with more bearing capacity than greater diameter steel rebars. This preliminary positive result together with international published reports and data open the perspective of designing and realizing a prototype structure with GFRP reinforcement and looking after for the design and realization of full scale structure. It is a matter of fact that until present days, Syrian civil engineering codes and practices are not familiar with GFRP rebars both on research and development and field applications levels. After 5 years of political and military crisis, Syria is expected to enter a great phase of infrastructure reconstruction. Building materials in general and reinforced concrete in particular constitute indispensable stuff for vaste and costly reparation, maintenance and reconstruction programs. Introducing new building materials is of utmost importance both technically and economically. The acceptance and spread-off of new building materials require determination, control and information of their intrinsic properties, distinguished characteristics and service performances. The present work constitutes a first step in introducing GFRP rebars within the Syrian civil engineering academic and industrial community. 21

8 Saeed Alkjk, Rafee Jabra and Salem Alkhater References [1] JSCE (Japan Society of Civil Engineers). (1997). Recommendation for Design and Construction of Concrete Structures Using Continuous Fiber Reinforcing Materials, Concrete Engineering Series, N. 23, Tokyo. [2] CSA (Canadian Standard Association) S (2002). Design and Construction of Buildings Components With Fiber-Reinforced Polymers. CSA, Toronto. [3] ACI Committee 440.1R.06. (2006). Guide for the Design and Construction of Concrete Reinforced With FRP Bars. American Concrete Institute, Farmington Hills. [4] FIB. (2005), FRP Reinforcement for RC Structures, Task Group 9.3 (Fiber Reinforced Polymer), Reinforcement for ConcreteStructures. FIB, Lausanne. [5] CNR-DT.(2/03/2006). Guide for the Design and Construction of Concrete Structures Reinforced With Fiber-Reinforced Polymer Bars. Website: [6] Kemp, B. (2011). Concrete reinforcement and glass fiber reinforced polymer. Queensland roads edition no ii September [7] Achillides, P. (2004). Bond behavior of fiber reinforced polymer bars under direct pullout conditions. Journal of Composites for Construction. 8(2), [8] Muruts, N. (1998). Laminated glass fiber reinforced plastic (GFRP) bars in concrete structures. 22