A POTHOLE PATCHING MATERIAL FOR EPOXY ASPHALT PAVEMENT ON STEEL BRIDGES:FATIGUE TEST AND NUMERICAL ANALYSIS

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1 Yang, Qian and Song A POTHOLE PATCHING MATERIAL FOR EPOXY ASPHALT PAVEMENT ON STEEL BRIDGES:FATIGUE TEST AND NUMERICAL ANALYSIS Yuming Yang, Ph.D. Candidate Intelligent Transportation System Research Center Southeast University No. Jinxianghe Road Nanjing, 00, P.R. China Tel: ()0- Fax: ()0- ymyang@seu.edu.cn Zhendong Qian, Ph.D. (Corresponding Author) Professor Intelligent Transportation System Research Center Southeast University No. Jinxianghe Road Nanjing, 00, P.R. China Tel: ()0- Fax: ()0- qianzd@seu.edu.cn Xin Song Graduate Research Assistant Intelligent Transportation System Research Center Southeast University No. Jinxianghe Road Nanjing, 00, P.R. China Tel: ()0- Fax: ()0- songxin0@.com Total Words (,): Abstract (0) + Text (,) + Figures/Tables ( 0=,000) Paper submission for the th Transportation Research Board Annual Meeting.

2 Yang, Qian and Song 0 ABSTRACT Various patching materials and field procedures have been studied in order to repair potholes on highway asphalt pavements. However, only a few publications have focused on patching materials for epoxy asphalt pavement which has been widely used on steel bridge decks. Considering the requirements of steel deck pavements, a patching material was developed using a fast cure thermosetting binder and a fine gradation. Then, to evaluate the fatigue performance of patched structures, a three-point bending fatigue test was conducted on three types of composite beams under four different stress ratios. After that, the Prony series presentation of the generalized Maxwell model was obtained and used to analyze the viscoelastic response of patched structures. The results showed that the fatigue test on composite beams performed well on exposing the vulnerable parts of patched structures. The developed patching material had a smaller dynamic modulus and performed better in fatigue resistance than commonly used epoxy asphalt mixture. Nevertheless, with the tensile stress concentration on it, the vertical patching interface became a potential fracture section and reduced the fatigue life of the patched structure.

3 Yang, Qian and Song INTRODUCTION Epoxy asphalt concrete (EAC) has been proved as a better pavement material for steel bridge pavement than other conventional asphalt mixtures. Due to its good performance in durability, high temperature stability and waterproofness, EAC has been widely used on the steel bridges in China recently. However, according to the investigations (), distresses caused by various factors still appear in the EAC layers of some steel bridge pavements. Among all the distresses, potholes are bowl-shaped holes existing on the surface of EAC layers (). Because of the poor field construction quality, fatigue failure or falling objects from vehicles, part of the EAC pavement surface break into pieces and then pulled up by travelling wheels thus forms a pothole. In addition, the water inside the potholes would cause more damage under the vehicle load and accelerate the formation of greater potholes. Potholes significantly reduce pavement performance level and service life, and are the most aggravating pavement distresses for traffic safety. Pothole has been a common distress on highway asphalt pavements and various materials and field procedures have been studied and used by researchers and highway agencies. Anderson et al. () evaluated more than 0 experimental binders and adopted a mix design procedure for cold-mix, stockpiled patching materials. The field trials results showed that mixtures employing certain high-float medium-set emulsion binders performed demonstrably better than companion control mixtures. The Strategic Highway Research Program (SHRP) (-) evaluated the performance of different patching materials and various repair techniques by field experiment and investigations. It was found that bituminous hot mixes have the highest quality but limited applicability in different weather conditions while cold-mixed mixtures have lower quality but are workable under most weather conditions. The study proposed a method to calculate the cost-effectiveness. New Jersey DOT used blade resistance test to evaluate the workability and rolling sieve test to evaluate the cohesion of patching materials(). The results showed that Blade resistance testing provided very little insight into material properties and the rolling sieve test provided a low variance, highly repeatable result. However, no distress correlated with the rolling sieve values. Fragachan () proposed an accelerated testing procedure for evaluating pavement patching materials under the simulation of traffic loading and environmental conditions. The test results showed that the method was successful in differentiating the performance of good and poor quality mixes. Yuan et al. () identified a polymeric material, dicyclopentadiene (DCPD) resin to become an ultra-tough material for pothole repair. It was found that DCPD increased the indirect tensile strength of mixes and improved the bonding strength between the mixes with the well-compacted part. Dong et al. () investigated and modified special laboratory procedures tests to evaluate the bonding, freeze thaw resistance and rutting potentials of the patching materials. It was found that testing temperatures, laboratory sample compaction efforts as well as wheel loading in loaded wheel test significantly affected the testing results of pothole patching materials. For pothole repair on steel bridge pavements, only a few studies have been published. Zong (0) pointed out that because of the difficulties in production and construction of epoxy asphalt mixtures, some distresses could occur at an early stage and then become potholes. Huang et al. () analyzed the pavement damages of the Jiangyin Bridge and then evaluated the performance of EAC pavement and gussasphalt mixture+ epoxy asphalt mixture structure by laboratory tests as well as

4 Yang, Qian and Song 0 0 field tests. They pointed out that EAC performs as well as a permanent patching material for steel bridges in China. To determine the semi-permanent patching material and field procedure on EAC bridge pavement, the differences to highway pavements in pavement structure, pavement materials and work conditions should be considered. The thickness of EAC pavement on steel bridges usually ranges from 0mm to 0mm which is much thinner than highway pavements, and the aggregate gradation with a.mm nominal maximum size is also smaller than that for highways. Moreover, the work conditions of steel bridges require the EAC pavement patching materials to perform well in workability, rutting resistance, waterproofness, adhesion and durability. On the basis of above considerations, the research team from Southeast University in China has developed an epoxy asphalt pavement patching (EAPP) material for EAC pavement on steel bridge decks. The EAPP has been used in the patching works on Tianxingzhou Bridge and Baishazhou Bridge in China and showed a good workability and high temperature stability (). However, the fatigue performance of EAPP and the viscoelastic response should be further studied. The objective of this study was to evaluate the fatigue performance of EAPP on patched structure and to analyze the influence of vertical patching interface on viscoelastic response. For this objective, the patching material was prepared using a fast cure thermosetting binder and a fine gradation. Three types of composite beams were fabricated and tested under four stress ratios to evaluate the fatigue performance of the patched structure. In addition, the Prony series presentations of the generalized Maxwell model for the materials were obtained and used to analyze the viscoelastic response of patched structure. MATERIALS AND METHODS 0 Raw materials Based on the study of Qian et al. (), the EAPP is composed of epoxy asphalt binder, limestone fillers and basalt fine graded aggregates. The epoxy asphalt binder is composed of TAF-EPOXY and 0# asphalt. TAF-EPOXY is a mixture of epoxy resin and curing agent. It cures fast thus can reduce the traffic control time after patching. The 0# asphalt is a type of asphalt binder usually used for heavy traffic in China with a penetration value from 0 to 0 (). The basic information of the epoxy asphalt binder is provided in Table. TABLE Technical Index of Epoxy Asphalt Binder Technical Indexes Criteria Test Method Mass ratio(taf-epoxy 0 # asphalt) : Tensile strength(mpa, ).0 ASTM D Fracture elongation(%, ) 00 ASTM D Viscosity 0 hr(mpa s) 000 ASTM D 0

5 Yang, Qian and Song With considerations on workability, water resistance and adhesion performance, the patching material should have low air void, be easy handling, shoveling, and compacting, and needs a strong interface bonding with the original pavement. Therefore a fine aggregate gradation should be selected for the patch material as shown in Table. The asphalt content was determined as.% by conducting the Marshall test on specimens with asphalt content from.0%-0%. TABLE Aggregates Gradation of EAPP TYPE The percentage of the passing following sieve ( mm ), % EAPP The EAC has been widely used on the pavements of steel bridges such as the nd Yangtze River Bridge, Runyang Cable Stay and Sutong Bridge. In this study, the asphalt binder of EAC was 0-type local epoxy asphalt with a content of.%. The details about the binder and the mix design of EAC can be found from (). Fatigue test 0 Specimen Fabrication To simulate the patched pavement structure with EAPP and EAC, composite beams were fabricated for the fatigue test. Firstly, a 0mm thick EAC layer was filled and compacted in a 00mm 00mm mold. After curing, a mm deep and 00mm wide groove was cut in the middle of the specimen. The surface of the groove was cleaned and brushed with epoxy asphalt adhesive layer. After that the EAPP was filled into the groove and compacted manually. After curing for h at, the specimen was cut into three types of composite beams sized 00mm 0mm 0mm as shown in Figure. Beam I consists of two mm thick EAC layers. BeamⅡis made up of an upper EAPP layer and a lower EAC layer. In beam Ⅲ, the EAPP is in the middle of the upper layer while the other parts are EAC. Load Fulcrum Fulcrum FIGURE Composite beams for fatigue test.

6 Yang, Qian and Song Test condition The fatigue test was conducted on a three-point bending fatigue test system at the temperature of (), as shown in Figure. The test was carried out in load control using a sinusoidal load with a 0 Hz frequency and the stress ratios were selected as 0., 0., 0. and 0.. The load was applied in the middle of the beam and the span of the beam was 0mm. The stiffness modulus was recorded at every load cycle until the beams were completely destroyed. Fatigue failure is defined at 0% reduction with respect to the initial stiffness of the composite beams and the corresponding number of load cycle is defined as fatigue life. 0 (a) Asphalt mixture fatigue test system (b) Fatigue test on composite beam FIGURE Fatigue test of composite beam. 0 Numerical analysis Complex modulus and pre-smoothing In this study, the time-domain Prony series representation of a viscoelastic model was used in the numerical analysis of linear viscoelastic (LVE) response. The Prony series was determined from the complex modulus in frequency-domain which was obtained by the frequency sweep test. The test was performed as discussed by Bonaquist and Christensen (). The sinusoidal load was applied at nine frequencies 0.Hz, 0.Hz, 0.Hz,.0Hz,.0Hz,.0Hz, 0Hz, 0Hz, Hz, and four temperatures 0, 0, 0, 0. Then the complex modulus E* and phase angle ϕ at certain loading frequency and temperature can be determined. The complex modulus is composed of the storage modulus and loss modulus as follows: () * E E ie E E * cos () E E * sin () Where E is the storage modulus, E is the loss modulus, and i is (-) /. Once obtained from Equation (), the data curve of E can be smoothed using a log-sigmoidal function () defined as:

7 E' (MPa) Yang, Qian and Song 0 E ( r) f ( r) a a a a exp[ a a log( )] Where a, are the fitting coefficients; ω r represents a reduced frequency at the temperature of interest. Based on the time temperature superposition principle, the reduced frequency ω r can be determined by the Second-Order Polynomial (), as shown in Equation (): log log ( ) ( ) r r k Tr T k Tr T () Where ω is the loading frequency at the test temperature, Hz; k, k are the fitting coefficients; T r is the reference temperature, and T is the test temperature. The smoothed data curve of E can be obtained based on the frequency sweep test result by combing Equation () and (). Figure shows the shifted experimental results and pre-smoothed curves of EAPP and EAC at reference temperature of. () EAPP experimental result EAC-0 experimental result EAPP smoothed curve EAC-0 smoothed curve log(ω r ) FIGURE Storage modulus of EAPP and EAC at. Viscoelastic model and Prony series The generalized Maxwell model (GMM) was used in the numerical analysis to simulate the time dependency property. The schematic of GMM is given in Figure. FIGURE Schematic of the generalized Maxwell model.

8 Yang, Qian and Song 0 0 The model consists of two basic units, a linear elastic spring and a linear viscous dash-pot. Various combinations of these spring and dashpot units define the type of viscoelastic behavior. In a time-domain, the relaxation modulus E(t) of GMM in the form of Prony series can be expressed as follows: M E( t) E Emexp( t / m) () m Where E, E m and ρ m are infinite relaxation modulus, Prony coefficients, and relaxation time respectively;m is the number of spring and dashpot units in GMM. In a frequency-domain, the complex modulus E*(ω n) of GMM can be obtained from the constitutive equation () given as follows: i E () M * n m m E ( n) E, n,..., N m i n m Where ω n, n=, N is the reduced frequency Then the storage modulus in frequency-domain can be determined by taking the real parts of the complex modulus: E E ( n) E, n,..., N () M n m m m n m To determine the Prony series function in Equation () and (), the equivalent E, ρ m, and E m shown in Equation () must be obtained first. Combining Equation () and the smoothed curve shown in Figure, E can be found by the limit of E (ω r) 0<ω r <<. The Prony series coefficients E m were obtained based on selected relaxation times ρ m and radian frequencies ω r. Thus, the Prony series presentation of GMM can be determined and imported into the property definition section in the software ABAQUS to simulate the viscoelasticity of EAPP and EAC. Finite element model To simulate the viscoelastic response of the composite beams, viscoelastic FE simulation was conducted in software ABAQUS. Viscoelastic model parameters presented by Prony series were imported into the FE model as given in Table. A sinusoidal load ranges from 0.kN to.kn were applied on the meshed D numerical samples, and the load frequencies was also 0Hz. There were also three numerical samples corresponding with three kind composite beams in the fatigue test.

9 Yang, Qian and Song TABLE Prony Series Parameters for EAPP and EAC i EAPP EAC ρ i E i ρ i E i.00e-0.00e-0.00e-0.00e-0.00e-0.00e-0.00e E-0.00E E-0.00E+00.00E+00.00E+0.00E+0..00E+0.00E+0.00E+0.00E E+0.00E E+0.00E+0.00E+0.00E+0 RESULTS AND DISCUSSION 0 0 Fatigue test The stiffness modulus of the composite beams was recorded during the fatigue test. As an example, Figure shows the change process of the stiffness modulus of the composite beams under the stress ratio of 0.. In spite of the tight range fluctuation over each load cycles, all the recorded data show a clear and consistent decreasing trend which indicates the process of fatigue failure. It can be seen that at first, the stiffness modulus of composite beams decreases smoothly with the increase of load cycle. Then, when the load cycle reaches a critical number, the moduli decrease rapidly to zero which means the complete failure of the beams. It can be also found that the stiffness modulus varies considerably between different structures. The initial stiffness modulus of beamⅠis about 00 MPa which is. times larger than beamⅡand times larger than beam Ⅲ. This is because the fine gradation leads to the low stiffness modulus of EAPP and thus reduce the stiffness modulus of the patched structure. Figure illustrates the fatigue performance of all the three structures under different stress ratios. The fatigue life of the three structures decreases with the increase of the stress ratio. Comparing the test results of the structures, beamⅡshows the best performance in fatigue resistance followed by beamⅠ. The result indicates that the EAPP has a better fatigue resistance than EAC and can meet the requirements of EAC pavement as a patching layer on EAC. However, the fatigue life of beam Ⅲis considerably smaller than that of structureⅠandⅡunder all the loading conditions in the test. This result shows that even though the EAPP has a good fatigue property, the vertical patching interface has an adverse effect on the fatigue resistance of the patched structure. Figure shows the fatigue failure forms of the three structures. Beam Ⅲ fracture in the middle cross section or in the vertical patching interface, while beamⅠandⅡonly fracture in the middle cross section of the beam. This suggests that the vertical patching interface between EAPP and EAC is also vulnerable under sinusoidal load and it can reduce fatigue resistance as discussed above. The mechanism of this effect will be studied subsequently by numerical analysis.

10 Fatigue life Stiffness modulus (MPa) Yang, Qian and Song BeamⅠ BeamⅡ BeamⅢ E+00.0E+0.0E+0.0E+0.0E+0.0E+0.0E+0 Load Cycle FIGURE Stiffness modulus of composite beams at stress ratio BeamⅠ BeamⅡ BeamⅢ Stress ratio FIGURE Fatigue life of composite beams at different stress ratios. FIGURE Fatigue failure forms of composite beams.

11 Yang, Qian and Song 0 0 Numerical analysis As observed above, fracture could occur in the vertical patching interface between EAPP and EAC, which implies that the viscoelastic response in the patching interface is different from the homogeneous cross sections. To study the viscoelastic response and influence of vertical patching interfaces, loading on composite beams in the viscoelastic stage was simulated and analyzed. The loading cycle was selected as 00 times because the stress concentration develops relatively slowly after that as observed in the simulation. Though the failure and cracks were unable to be simulated using the GMM in this research, the simulation results can show the development of stress concentration and the mechanic response of patched beams. The transverse section at / length of beams are called section A and selected to be analyzed and compared in this study. Figure shows the distribution of tensile stress in two directions on beam Ⅲ after 00 load cycles. It can be found that the tensile stress S (in the direction of X axis) and S (in the direction of Y axis) increase rapidly near the interface, and a high contrast of the stress value can be observed on the interface. The results indicates that the patching interfaces between EAPP and EAC can cause tensile stress concentration in the directions of X axis and Y axis, which could contribute to its failure under cyclic load. Figure compares the max principle stress of a certain point on section A of different composite beams. It can be found that the peak value of max principle stress increase at first few load cycles and then become stable. It is obvious that section A of beam Ⅲ is subjected to much greater sinusoidal tensile stress, and the peak tensile stress is approximately times larger than that on other beams. This means that patched EAC pavement structures are more likely to fracture in the interface than other homogeneous structures. The above analysis results show that the patching interface can change the stress distribution of the pavement structures and cause stress concentration nearby. Accordingly, the patching interfaces are potential failure faces even though the adhesion performs well, and the fracture could happen there after a number of load cycles as shown in figure. Section A Section A (a) Tensile stress in the direction of X axis (S) (b) Tensile stress in the direction of Y axis (S) FIGURE Distribution of tensile stress in the direction of X axis and Y axis

12 Max principle stress (MPa) Yang, Qian and Song BeamⅠ BeamⅡ BeamⅢ Load cycle FIGURE Max principle stress at patching interface. 0 0 CONCLUSIONS AND RECOMMENDATIONS This study proposes a pothole patching material for epoxy asphalt pavement on steel bridges. The fatigue property of the patched pavement was evaluated using three-point bending fatigue test on composite beams. The viscoelastic response of the patching interface was also studied using numerical analysis. Based on the results, conclusions can be drawn as follows: The TAF epoxy asphalt binder and fine gradation enable EAPP to perform well in fatigue resistance as a patching layer on EAC. At the same time, EAPP reduces the stiffness modulus of the patched structure due to its fine gradation. The vertical patching interface between EAPP and EAC reduces the fatigue life of the patched structure substantially. The fracture forms also show that the interface is a potential fracture section of the patched structure. The Prony series presentation of generalized Maxwell model was obtained by conducting frequency sweep test and pre-smoothing the storage modulus data. The results show that the storage modulus of EAPP is smaller than EAC under reduced frequency less than 0 Hz. The numerical analysis results indicate that the different viscoelastic properties of EAPP and EAC influence the stress distribution on the composite beam and cause tensile stress concentration near the interface. Thus, the fatigue failure is more likely to occur in the patching interface. Since the patching interface is subjected to greater tensile stress and could be potential fatigue failure section, it is recommended that high quality adhesive materials and reasonable field procedures be selected for the pothole patching on EAC pavement. Moreover, more attention should be paid to patched areas during pavement evaluation in case of second time failure.

13 Yang, Qian and Song ACKNOWLEDGEMENTS The authors are grateful to the sponsorship of contribution by National Natural Science Foundation of China (NSFC, No. ) REFERENCE. Chen, X. H., Z. D. Qian, X. Y. Liu, and L. Zhang. State of Art of Asphalt Surfacings on Long-spanned Orthotropic Steel Decks in China. Journal of Testing and Evaluation, Vol. 0, No., 0.. Miller, J.S. and W.Y. Bellinger. Distress Identification Manual for the Long-term Pavement Performance Program. Report No. FHWA-RD-0-0. Federal Highway Administration, Office of Infrastructure Research and Development, Mclean, Virginia, 00.. Anderson, D.A., H. R. Thomas, Z. Siddiqui, et al. More Effective Cold, Wet-Weather Patching Materials for Asphalt Pavements. Report No. FHWA-RD--00. Federal Highway Administration, U.S. Department of transportation, Washington, D.C.,.. Wilson, T.P. and A.R. Romine. Innovative materials development and testing volume : pothole repair. Report No. SHRP-H-. Strategic Highway Research Program, National Research Council, Washington, D.C.,.. Wilson, T.P. and A.R. Romine. Materials and procedures for repair of potholes in asphalt surfaced pavements manual of practice. Report No. FHWA-RD--. Federal Highway Administration, Office of Infrastructure Research and Development, Mclean, Virginia, Maher, A., N. Gucunski, W. Yanko, and F. Petsi. Evaluation of Pothole Patching Materials. Report No. FHWA Federal Highway Administration, U.S. Department of Transportation, Washington, D.C., 00.. Fragachan, J.M. Accelerated Testing Methodology for Evaluating Pavement Patching Materials. M. S. Dissertation, Worcester Polytechnic Institute, 00.. Yuan, W., K. Y. Yuan, L. H. Zou, et al. DCPD Resin Catalyzed with Grubbs Catalysts for Reinforcing Pothole Patching Materials. Proceedings of SPIE - The International Society for Optical Engineering, San Diego, United States, Volume, 0.. Dong, Q., B. S. Huang and S. Zhao. Field and laboratory evaluation of winter season pavement pothole patching materials. International Journal of Pavement Engineering, Vol., No., 0, pp Zong, H. Technique Research on Diseases Restoration for Epoxy Asphalt Concrete Paved on Steel Deck Bridge. M.S. Dissertation, Southeast University, 00. (in Chinese). Huang, W., Z. D. Qian, L. Zhang. Experimental Study on Partly Patching Scheme of Steel Bridge Deck Paving. China Civil Engineering Journal, Vol., No., 00, pp.-0. (in Chinese). Qian, Z. D., X. D. Wang, S. Liu, et al. Research on Maintenance and Rehabilitation for Asphalt Pavement on Steel Deck Bridge. Western Transportation Construction Technical Program, Ministry of Transport of the People s Republic of China, Beijing, 0. (in Chinese). Research Institute of Highway Ministry of Transport. Technical Specification for Construction of Highway Asphalt Pavements JTG F0-00. China Communication Press, Beijing, 00. (in

14 Yang, Qian and Song 0 Chinese). Chen, L. L., Z. D. Qian and L. Zhang. Evaluation of epoxy asphalt concrete damping parameters using impact resonance test. Journal of Testing and Evaluation, Vol. 0, No., 0.. Research Institute of Highway Ministry of Transport. Standard Test Methods of Bitumen and Bituminous Mixtures for Highway Engineering JTG E0-0. China Communication Press, Beijing, 0. (in Chinese). Bonaquist, R. F., D. W. Christensen. Simple Performance Tester for Superpave Mix Design: First-Article Development and Evaluation. NCHRP Report. National Cooperative Highway Research Program, Transportation Research Board, Washington, D. C., 00.. Mun, S., G. C. Chehab and Y. R. Kim. Determination of Time-domain Viscoelastic Functions using Optimized Interconversion Techniques. Road and Pavement Design, Vol., No., 00, pp. -.. AASHTO PP -0. Standard Practice for Developing Dynamic Modulus Master Curves for Hot Mix Asphalt (HMA). American Association of State Highway and Transportation Officials, Washington, D. C., 00.. Park, S. W., R. A. Schapery. Methods of interconversion between linear viscoelastic material functions. Part I - a numerical method based on Prony series. International Journal of Solids and Structures. Vol., No.,, pp. -.