Numerical and experimental study of failure mode of CFRP strengthened concrete under tension and shear loading

Document Type : Research Article


1 Department of Civil Engineering, Engineering Faculty, International Imam Khomeini University, Qazvin, Iran

2 Department of civil engineering, Faculty of engineering, International Imam Khomeini university, Qazvin, Iran


Today, the use of carbon fiber reinforced polymers (CFRP) is used as an efficient method for the reinforcement of concrete structures. Concrete structures strengthened with CFRP sheets may have a failure due to debonding mechanisms. In this study, the bond strength and failure mode of CFRP strengthened concrete in tensile and shear stresses are investigated using nonlinear finite element and experimental methods. Because in the study of mechanical behavior of concrete strengthened with CFRP sheet, the assumption of homogeneity of concrete leads to unrealistic results, so in this study, a mesoscale model is used to model concrete. The mesoscopic model of concrete includes three-phase inhomogeneous material consisting of aggregate, mortar, and Interfacial Transition Zone (ITZ). Tests performed include "pull-off" and "twist-off" to determine tension and shear bond strength. The results show that the tension and shear strength of the finite element model is 18% and 13% higher than the results of the "pull-off" and "twist-off" tests, respectively, which are due to laboratory influencing factors and ignoring They are acceptable in numerical modeling of this difference. Also, the tensile strength of the numerical and experimental models is 34% and 33% lower than the shear strength, respectively. According to the obtained results, the debonding in the CFRP strengthened concrete sample was from the substrate concrete. The results show that the micro-cracks, followed by debonding in the mortar and ITZ phases of concrete, due to high porosity and lower strength than the aggregate phase, spread easily.


Main Subjects

[1] A. Di Tommaso, U. Neubauer, A. Pantuso, F.S. Rostasy, Behavior of adhesively bonded concrete-CFRP joints at low and high temperatures, Mechanics of Composite Materials, 37(4) (2001) 327-338 %@ 0191-5665.
[2] J. Yao, J.G. Teng, J.F. Chen, Experimental study on FRP-to-concrete bonded joints, Composites Part B: Engineering, 36(2) (2005) 99-113 %@ 1359-8368.
[3] J.G. Teng, J.-F. Chen, S.T. Smith, L. Lam, FRP: strengthened RC structures, 2002.
[4] B. Mohammadi, K.S. Asl, A. Farrokhabadi, Matrix cracking and induced delamination in symmetrically laminated composites subjected to static loading by using multi scale damage mechanics,  (2017).
[5] V. Palmieri, L. De Lorenzis, Multiscale modeling of concrete and of the FRP–concrete interface, Engineering Fracture Mechanics, 131 (2014) 150-175 %@ 0013-7944.
[6] Y.B. Zaitsev, F.H. Wittmann, Simulation of crack propagation and failure of concrete, Matériaux et Construction, 14(5) (1981) 357-365 %@ 0025-5432.
[7] G.I. Barenblatt, The mathematical theory of equilibrium cracks in brittle fracture, Advances in applied mechanics, 7(1) (1962) 55-129.
[8] J. Wang, Cohesive-bridging zone model of FRP–concrete interface debonding, Engineering fracture mechanics, 74(17) (2007) 2643-2658 %@ 0013-7944.
[9] F. Chen, P. Qiao, Debonding analysis of FRP–concrete interface between two balanced adjacent flexural cracks in plated beams, International journal of solids and structures, 46(13) (2009) 2618-2628 %@ 0020-7683.
[10] R. Xu, C. Liu, CZM-based debonding simulation of cracked beams strengthened by FRP sheets, Journal of engineering mechanics, 138(2) (2012) 210-220 %@ 0733-9399.
[11] C. Carloni, T. D’Antino, L.H. Sneed, C. Pellegrino, Three-dimensional numerical modeling of single-lap direct shear tests of FRCM-concrete joints using a cohesive damaged contact approach, Journal of Composites for Construction, 22(1) (2018) 04017048 %@ 04011090-04010268.
[12] B.S. En, 480-11. Admixtures for concrete, mortar and grout-test methods-part 11: determination of air void characteristics in hardened concrete, London: British Standards Institution,  (2005).
[13] A.I. Astm, D7522, D7522M,“Standard Test Method for Pull-Off Strength for FRP Laminate Systems Bonded to Concrete Substrate,  (2015).
[14] D. Astm, 4541, Standard Test Method for Pull-Off Strength of Coatings Using Portable Adhesion Testers, Annual Book of ASTM Standards,  (2002) 1-13.
[15] M. Naderi, New twist-off method for the evaluation of in-situ strength of concrete, Journal of Testing and Evaluation, 35(6) (2007) 602-608 %@ 0090-3973.
[16] A.J. Wagner, A practical introduction to the lattice Boltzmann method, Adt. notes for Statistical Mechanics, 463 (2008) 663.
[17] Q. Xiong, X. Wang, A.P. Jivkov, A 3D multi-phase meso-scale model for modelling coupling of damage and transport properties in concrete, Cement and Concrete Composites, 109 (2020) 103545 %@ 100958-109465.
[18] F. Javidrad, M. Mashayekhy, A Cohesive zone model for crack growth simulation in AISI 304 Steel, Journal of Solid Mechanics, 6(4) (2014) 378-388 %@ 2008-3505.
[19] X.Z. Lu, J.G. Teng, L.P. Ye, J.J. Jiang, Bond–slip models for FRP sheets/plates bonded to concrete, Engineering structures, 27(6) (2005) 920-937 %@ 0141-0296.
[20] M.L. Benzeggagh, M. Kenane, Measurement of mixed-mode delamination fracture toughness of unidirectional glass/epoxy composites with mixed-mode bending apparatus, Composites science and technology, 56(4) (1996) 439-449 %@ 0266-3538.
[21] X. Liu, J. Jiang, G. Wang, J. Wang, R. Xu, Debonding analysis of curved RC beams externally bonded with FRP plates using CZM, Engineering Structures, 205 (2020) 110103 %@ 110141-110296.
[22] L.N. Lowes, Finite element modeling of reinforced concrete beam-column bridge connections, University of California, Berkeley, 1999.
[23] I.M. Nikbin, M.H.A. Beygi, M.T. Kazemi, J.V. Amiri, E. Rahmani, S. Rabbanifar, M. Eslami, A comprehensive investigation into the effect of aging and coarse aggregate size and volume on mechanical properties of self-compacting concrete, Materials & Design, 59 (2014) 199-210 %@ 0261-3069.
[24] O. Buyukozturk, O. Gunes, E. Karaca, Progress on understanding debonding problems in reinforced concrete and steel members strengthened using FRP composites, Construction and Building Materials, 18(1) (2004) 9-19 %@ 0950-0618.
[25] R. Chendes, S. Dan, L. Courard, Comparison of shear and pull-off tests for testing adhesion of different content limestone fillers mortars used as repair system, Construction sustainability: efficient solution for design, execution and rehabilitation of the building %@ 6065546623, (2013).