Mixed mode fracture behavior of concrete pavement containing RAP - 3D finite element analysis

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1 Available online at ScienceDirect Procedia Structural Integrity 5 (7) nd International Conference on Structural Integrity, ICSI 7, -7 September 7, Funchal, Madeira, Portugal Mixed mode fracture behavior of concrete pavement containing RAP - D finite element analysis M.A. Mubaraki a, A.A. Abd-Elhady a,b, *, S.A. Osman c, and H.E.M. Sallam a,d a Faculty of Engineering, Jazan University, Jazan 76, Kingdom of Saudi Arabia. b On sabbatical leave from Faculty of Engineering, Helwan University, Cairo, Egypt. c College of Engineering, University of Dammam, Dammam, KSA. d On sabbatical leave from Faculty of Engineering, Zagazig University, Zagazig, Egypt. Abstract Reclaimed asphalt pavement (RAP) is commonly used to improve the sustainability of asphalt concrete pavement. The main objective of the present work is to study the effect of RAP content on the mixed mode fracture behavior of concrete pavement numerically. An extended finite-element model was adopted to simulate crack growth under mixed mode loading. Semi-circular bending (SCB) specimen was used with three different crack geometries, namely inclined crack at the middle with different inclination angles (SCB-) and vertical crack subjected to asymmetric three point bending. The effect of specimen geometry on the mode I fracture toughness (KIC) has been studied. The relationships between both RAP content and specimen geometry and mixed mode fracture toughness have been correlated. It is found that, the present D finite element model is a good candidate to predict the fracture behavior of concrete pavement containing RAP. To examine the reliability of each type of specimen geometry for predicting KIC, the maximum undamaged defect size (d max) concept has been applied. It is found that, KIC predicted from the classical SCB (SCB-) is reliable compared the values predicted from the other specimen geometries. Where the ratio of d max to the maximum aggregate size (d max/maz) ranged between unity and in the case of SCB-, it ranged between 5 and in the other cases. Furthermore, the relationship between the present numerical values of KIC predicted from SCB- specimen and the flexural strength measured experimentally by Hossiney et al. () is strongly correlated. 7 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of ICSI 7 Keywords: Concrete pavement; RAP; mixed-mode fracture toughness; the maximum undamaged defect size concept. * Corresponding author. Tel.: ; fax: address: aelhady@jazanu.edu.sa, aaa_elhady@yahoo.com The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Scientific Committee of ICSI 7.6/j.prostr.7.7.5

2 A.A. Abd-Elhady et al. / Procedia Structural Integrity 5 (7) 9 6. Introduction The optimal usage of recycled materials in pavements and geotechnical applications is one of the main objectives of many researches. Reclaimed asphalt pavement (RAP) is commonly used for several purposes such as hot-mix asphalt (HMA), Ghabchi et al. (6), in concrete pavement, Su et al. (), and as base, subbase or general fill materials, Cosentino et al. (). Hossiney et al. () and Su et al. () studied the effect of RAP% and W/C ratio on the mechanical behavior of concrete pavement slab. Table shows their results. Table. Experimental results of Hossiney et al. () and Su et al. () RAP% W/C Ratio Modulus of Elasticity, E, Poisson's Tensile Strength Compressive Strength Flexural (GPa) Ratio, (MPa) (MPa) Strength (MPa) Braham et al. () analyzed fracture properties of three asphaltic concrete mixes in the laboratory by using singleedge notch beam test. Ozer et al. (6) used semi-circular bending (SCB) test geometry to measure the fracture toughness of HMA containing RAP. Their results showed a positive correlation between SCB test results and other independent fatigue tests. Many researchers use SCB specimen to investigate mixed mode I/II crack growth behavior, notably Yousheng et al. (7), Aliha et al. (, ), Sallam and Abd-Elhady (), Ayatollahi et al. (6, 8), and Lim et al. (99). Sallam and Abd-Elhady () concluded that, the site of crack initiation in SCB- specimen (see Fig..a) is found at the point of the highest vertical coordinate on the notch surface for different notch inclination angles. They also found that, the development of crack front shape is little affected by the value of mode of mixity and the shape of crack front is still more or less the thumbnail shape. Ameri et al. () obtained different modes of mixity by changing the position of supports and/or the site of pre crack, SCB- and SCB-, as shown in Fig..b & c. The main objective of the present work is to study the effect of RAP% on the fracture behavior of concrete pavement under pure mode I, pure mode II, and mixed mode using the three different geometries of SCB specimen shown in Fig.. The comparison between the mode I fracture toughness obtained from the different geometries of SCB specimen has been made based on the maximum undamaged defect size (dmax) concept suggested by Sallam and coworkers, Al Hazmi et al. (), Sallam et al. () and Abou El-Mal et al. (5). Y P P P X Z R b a R L a R L a S S S (a) SCB- (b) SCB- (c) SCB- S Fig.. Three types of SCB specimen to simulate mixed mode I/II crack growth

3 A.A. Abd-Elhady et al. / Procedia Structural Integrity 5 (7) 9 6. Numerical work.. Mechanical properties of the materials and specimen geometries The major advantages in using SCB are that it has a simple geometry, it has a simple loading configuration, and different modes of mixity can be obtained. Three types of SCB geometry are used in the present work, as shown in Fig.. The dimensions of the specimens used in the present work to get different modes of mixity are tabulated in Table. The modulus of elasticity, Poisson's ratio, tensile strength, and flexural strength measured by Hossiney et al. () and Su (), as shown in Table, were used in the present work to study the effect of the RAP% and W/C ratio on the fracture behavior of concrete pavement. Table. Specimen geometry to simulate mixed mode I/II crack growth Radius, R Crack S S S Specimen b (mm) Ratio, a/r (mm) (mm) (mm) o Pure Pure Mixed Mode L/R Mode I Mode II I/II SCB SCB SCB SCB Finite element analysis The fracture behavior of concrete pavement containing different RAP% and W/C ratio has been investigated by using Abaqus/Explicit and Abaqus/Standard finite element codes (6). The concrete was assumed as isotropic and homogeneous material and in elastic state. The meshes were constructed with hexagonal structural mesh, CD8 (8- node linear brick) elements; around elements are used in the present model. The size of element decreases gradually with decreasing the distance from the tip of the pre-crack. This means that FE meshes in the neighborhood of the pre-crack are much denser. X-FEM was used for simulating the crack propagation in various crack analysis problems such as in Abd-Elhady and Sallam (5), Mahmoud et al. (), and Mubaraki et al. (). In the present investigation, crack growth direction was chosen as that normal for the direction of maximum tensile stress.. Results and discussion. Crack path Figure shows typical crack paths in SCB specimens for cracks emanating from pre-crack with different SCB geometries. As shown in Fig..a, SCB- specimen, by changing the pre-crack inclined angle, b, the mode of mixity increases. When b = o, mode I occurs and cracks initiate and propagate parallel to the load and perpendicular to the tensile stress, as shown in Fig..a-. Furthermore by increasing the value of b, the mode of mixity increases to reach the maximum of b = 5 o as pure mode II. By increasing b, the fracture path deviates from the original inclination angle and grows along a curvilinear trajectory to extend toward the upper loading point as shown in Fig..a- and.a-. Figure.b shows the effects of the value of distance L on the crack path at different modes of mixity for SCB- specimen, i.e., S = S = S. At L =, the crack initiates at pure mode I, while, when L increases the mode of mixity increases and reaches pure mode II at L/R =.5. Figures.c and.d show the crack path for SBC- when S S. It is clear that pure mode I and pure mode II occurring at different values of L. It can be concluded that, when S = S the crack path at different modes of mixity can be changed by changing the value of b or L.

4 A.A. Abd-Elhady et al. / Procedia Structural Integrity 5 (7) 9 6 It is found that the crack path at different modes of mixity is independent of the mechanical properties of the materials, i.e., it is not affected by changes in the value of W/C ratio or RAP%. This finding is in agreement with the conclusions drawn by Sallam and Abd-Elhady (). (a-) SCB- & Pure Mode I (a-) SCB- & Mixed Mode I/II (a-) SCB- & Pure Mode II (b-) SCB- & Pure Mode I (b-) SCB- & Mixed Mode I/II sss (b-) SCB- & Pure Mode II (c-) SCB-- & Pure Mode I (c-) SCB-- & Mixed Mode I/II (c-) SCB-- & Pure Mode II (d-) SCB-- & Pure Mode I (d-) SCB-- & Mixed Mode I/II (d-) SCB-- & Pure Mode II Fig.. Progressive crack growth with SCB-, SCB- and SCB- specimens, using XFEM. The effect of the mode of mixity on the load-displacement relationship Figure illustrates the effect of mode of mixity and SCB specimen geometry on the load-displacement diagram for concrete pavement with W/C ratio =. and RAP% =. Firstly, the initial stiffness is not affected by the mode of mixity for either of the specimen geometries. By increasing the applied load, the effect of mode mixity on stiffness became clear. Where the pure mode II has the highest stiffness, pure mode I has the lowest stiffness for both specimen geometries. When the load reached about half of its maximum value, the linear relationship between the load and displacement converted to become nonlinear, i.e., it entered the crack initiation zone. When the load reached its maximum load, i.e. unstable crack growth (the commencement of the descending part), the applied load decreased gradually with increasing displacement. It is worth noting that the descending part of the curve can be obtained if the specimen is tested under displacement control. As is already known, for the same pre-cracked position, i.e., pure mode I in specimens SCB- and SCB-, the maximum load increases by decreasing the span (S), see Fig. and Table. The resistance of the material to fracturing increases by increasing the value of mode of mixity; hence, the maximum load increases by increasing the mode of mixity.

5 A.A. Abd-Elhady et al. / Procedia Structural Integrity 5 (7) % RAP & W/C =. & SCB % RAP & W/C =. & SCB- - Pure Mode I - Load (N) Mixed Mode I/II PureMode II Load (N) Pure Mode I Displacement (mm) - Mixed Mode I/II Pure Mode II Displacement (mm) Fig.. The load displacement diagram for different specimens and different mode of mixity (RAP% = and W/C =.). Figure shows the effect of RAP content on the load-displacement diagram for SCB- under pure mode I, Fig..a, and pure mode II, Fig..b. As the RAP content increased both stiffness and ultimate load decreased in the cases of pure mode I and pure mode II. This observation agrees with the experimental results in Hossiney et al. () and Su et al. (), in which they found that the compressive, tensile, and flexural strengths of concrete pavement containing RAP decreased by increasing the RAP content (see Table ). On the other hand, SCB- specimen under pure mode II has an ultimate load higher than that under pure mode I, regardless of the type of material, i.e., RAP% (a) W/C =. & Pure Mode I -7-6 (b) W/C =. & Pure Mode II -5-5 Load (N) RAP % & SCB- Load (N) & SCB Displacement (mm) & SCB Displacement (mm) -. Fig.. The effect of RAP% on load-displacement curve for SCB- specimen: (a) Pure mode I and (b) Pure mode II.. The effect of W/C ratio and RAP% on the fracture behavior of concrete pavement One of the main objectives of the present work is to study the effects of W/C ratio and RAP content on the fracture behavior of concrete. The values of mode I and mode II fracture toughness (K IC and K IIC) of concrete pavement with different W/C ratios and % of RAP predicted from different SCB specimen geometries are shown in Fig. 5. As expected both K IC and K IIC decreased by increasing W/C ratio. Hossiney et al. () and Su et al. () showed the negative effect of W/C ratio on the mechanical properties of concrete pavement containing RAP. All values predicted from SCB- specimen are much lower than those predicted from the other specimen geometries. It is worth noting that, Mahmoud et al. () stated that SCB- specimen has become a popular tool to determine the fracture toughness of HMA, and it is a very promising development. In the next section, the reliability of each type of specimen geometry for predicting K IC has been applied based on the concept of maximum undamaged defect size (d max).

6 A.A. Abd-Elhady et al. / Procedia Structural Integrity 5 (7) 9 6 Mode I Fracture Toughness, MPa m 6 5 (a) Effect of W/C on KIc SCB- SCB- SCB-- SCB-- Mode II Fracture Toughness, MPa m 6 5 (b) Effect of W/C on KIIc SCB- SCB- SCB W/C Ratio Fig. 5. The effect of W/C ratio on the fracture toughness of concrete pavement without RAP: (a) Mode I and (b) Mode II. Figure 6 shows the effect of RAP content on the fracture toughness of concrete pavement with W/C ratio =. predicted from several types of SCB specimen geometries. This figure reveals several points of interest; the values of fracture toughness decrease by increasing the RAP content. Mode I and mode II fracture toughness are dependent on the type of SCB specimen geometry. The same trend was also observed in this figure, i.e., all values predicted from SCB- specimen are much lower than those predicted from the other specimen geometries W/C Ratio Mode I Fracture Toughness, MPa m 6 5 (a) Effect of RAP% on KIc SCB- SCB- SCB-- SCB-- Mode II Fracture Toughness, MPa m 6 5 (b) Effect of RAP% on KIIc SCB- SCB- SCB-- RAP% RAP% Fig. 6. The effect of RAP content on the fracture toughness of concrete pavement: (a) Mode I (b) Mode II.. The reliability of the different geometries of SCB specimen for predicting KIC The objective of this section is to examine the values of K IC of concrete pavement containing RAP predicted from different geometries of SCB specimen. Sallam and co-workers Al Hazmi et al. (), Sallam et al. () and Abou El-Mal et al. (5) incorporated the materials' properties, i.e., flexural strength (f fl) or shear strength, instead of the critical applied stress, cr, along with the fracture toughness, i.e. K IC or K IIC respectively, of the material to predict the so-called "maximum undamaged defect size (d max)", instead of the crack length, as follows: K IC then K IC d max Y f fl where Y is the geometry correction factor. Y a Y f () cr fl d max ()

7 A.A. Abd-Elhady et al. / Procedia Structural Integrity 5 (7) To check the reliability of the present results, d max has been normalized by the maximum aggregate size (MAZ), i.e d max/maz. The values of d max/maz are calculated and presented in Fig. 7. Although all values of d max/maz are greater than unity, the values of SCB- are closest to it and these values range between unity and. The values of other geometries are greater than times the MAZ and that is unacceptable; hence, SCB- and SCB- specimens are unreliable to predict the fracture toughness of concrete pavement containing RAP. 6 (a) RAP% = SCB- SCB- SCB-- SCB-- (b) W/C Ratio =. dmax/maz W/C Ratio RAP% Fig. 7. The calculated d max/maz from mode I fracture toughness predicted from different geometries of SCB specimen. The correlation between KIC in the present research predicted from SCB- specimen and f fl measured experimentally by Hossiney et al. () of concrete pavement containing RAP with different values of W/C ratio has been made and is presented in Fig. 8. As is already known, the values of f fl and KIC are positive and the extrapolation of the relation between them must go through the origin. In the case of linear relation, correlation coefficient R =.885, while, R =.99 for a nd order polynomial. The inflection point of a nd order polynomial will occur out of the range of the logical relation, i.e., it will have a negative value. Therefore, it can be concluded that the relationship between the present numerical values of mode I fracture toughness predicted from SCB- specimen and the flexural strength measured experimentally by Hossiney et al. () is strongly correlated. Mode I Fracture Toughness, MPa m Y =.5x +.57x R =.99 y =.9x R² = Flexural Strength (MPa) Fig, 8. The relation between KIC predicted from SCB- specimen and flexural strength of concrete pavement.

8 6 A.A. Abd-Elhady et al. / Procedia Structural Integrity 5 (7) 9 6. Conclusions The present numerical results support the following conclusions: - Mode I, mode II, and mixed mode fracture toughness of concrete pavement decreased with increasing W/C ratio and/or RAP%. - Good prediction of crack path is not evidence for the reliability of the test results. - SCB- and SCB- specimens are unreliable to predict the fracture toughness of concrete pavement. - The relationship between the mode I fracture toughness predicted from SCB- specimen and the flexural strength is strongly correlated. Acknowledgements This work was funded by the Deanship of Scientific Research (DSR) at Jazan University, KSA. Project: DSR # JUP7/6/7. References ABAQUS, 6. analysis of the user s manual. Version 6. Dassault Systèmes; Abd-Elhady, A.A. Sallam, H.E.M., 5. Crack Sensitivity of Bolted Metallic and Polymeric. Engineering Fracture Mechanics Abou El-Mal, H.S., Sherbini, A.S., Sallam, H.E.M., 5. Mode II Fracture Toughness of Hybrid FRCs. International Journal of Concrete Structures and Materials Al Hazmi, H.S.J.,Al Hazmi, W.H., Shubaili, M.A., Sallam, H.E.M.,. Fracture Energy of Hybrid Polypropylene Steel Fiber High Strength Concrete, HPSM, High Performance Structure and Materials, VI, 9 8. Aliha, M.R.M., Ayatollahi, M.R., Smith, D.J., Pavier, M.J.,. Geometry and size effects on fracture trajectory in a limestone rock under mixed mode loading. Engineering Fracture Mechanics 77,. Aliha, M.R.M., Behbahani, H., Fazaeli, H., Rezaifar, M.H.,. Study of characteristic specification on mixed mode fracture toughness of asphalt mixtures. Construction and Building Materials 5, 6 65 Ayatollahi, M.R., Aliha, M.R.M., 8. On the use of Brazilian disc specimen for calculating mixed mode I II fracture toughness of rock materials. Engineering Fracture Mechanics. 75, 6 6. Ayatollahi, M.R., Aliha, M.R.M., Hassani, M.M., 6. Mixed mode brittle fracture in PMMA An experimental study using SCB specimens. Mat. Sci. and Eng. 7, 8 56 Ameri, M., Mansourian, A., Pirmohammad, S., Aliha, M.R.M., Ayatollahi, M.R.,. Mixed mode fracture resistance of asphalt concrete mixtures. Engineering Fracture Mechanics 9, Braham, A., Buttlar, W., Ni, F.,. Laboratory Mixed-Mode Cracking of Asphalt Concrete Using the Single-Edge Notch Beam. Road Materials and Pavement Design.,, Cosentino P.J., Kalajian E., Shieh C.S., Mathurin W.J., Cleary E. D., Treeratrakoon A.,. Developing Specification for Using Recycled Asphalt Pavement as Base, Subbase or General Fill Materials Phase, Final Report from Florida Institute of Technology, Florida USA, pp. 7. Ghabchi, R., Barman, M., Singh, D., Zaman, M., Mubaraki, M.A., 6. Comparison of laboratory performance of asphalt mixes containing different proportions of RAS and RAP. Construction and Building Materials, 5. Hossiney, N., Tia, M., Bergin M.,. Concrete Containing RAP for Use in Concrete Pavement. Int. J. Pavement Res. Technol. (5):5-58 Lim, I. L., Johnston, I. W., CHOI, S. K., 99. Stress intensity factors for semi-circular Specimens under three-point bending. Engineering Fracture Mechanics, 6-8. Mahmoud, E., Saadeh, S., Hakimelahi, H., Harvey, J.,. Extended finite element modelling of asphalt mixtures fracture properties using the semicircular bending test. Road Materials and Pavement Design. 5, Mubaraki, M., Abd-Elhady, A.A. Sallam, H.E.M.,. Mixed Mode Fracture Toughness of Recycled Tire Rubber-Filled Concrete for Airfield Rigid Pavements. Int J Pavement Res Technol Ozer, H., Al-Qadi, I.L., Lambros, J., El-Khatib, A., Singhvi, P., Doll, B., 6. Development of the fracture-based flexibility index for asphalt concrete cracking potential using modified semi-circle bending test parameters. Construction and Building Materials, 5, 9 Sallam, H.E.M., Abd-Elhady, A.A.. Mixed mode crack initiation and growth in notched semi-circular specimens-three dimensional finite element analysis. Asian J Mater Sci. -. Sallam, H.E.M., Mubaraki, M., Yusoff, N.I.Md.,. Application of the Maximum Undamaged Defect Size (dmax) Concept in Fiber-Reinforced Concrete Pavements. Arab J Sci Eng Su, Y., Hossiney, N., Tia, M., Bergin M.,. Mechanical Properties Assessment of Concrete Containing Reclaimed Asphalt Pavement Using the Superpave Indirect Tensile Strength Test. Journal of Testing and Evaluation., 9-9. Yousheng, X., Cao, P., Jin, J., Wang, M., 7. Mixed mode fracture analysis of semi-circular bend (SCB) specimen: A numerical study based on extended finite element method. Computers and Geotechnics. 8, 57 7