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A pothole patching material for epoxy asphalt pavement on steel bridges: Fatigue test and numerical analysis
Construction and Building Materials 94 (2015) 299–305
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
A pothole patching material for epoxy asphalt pavement on steel bridges: Fatigue test and numerical analysis Yuming Yang, Zhendong Qian ⇑, Xin Song Intelligent Transport System Research Center, Southeast University, PR China
h i g h l i g h t s A fine gradation patching material is developed for epoxy asphalt pavement. The generalized Maxwell model is used to analyze the viscoelastic response. The patching interfaces are vulnerable to cyclic load due to stress concentration. The increase of viscoelastic difference causes worse stress state on patching interface.
a r t i c l e
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Article history: Received 9 February 2015 Received in revised form 7 July 2015 Accepted 9 July 2015
Keywords: Pothole patching Epoxy asphalt pavement Fatigue test Composite beam Generalized Maxwell model Prony series Viscoelastic difference
a b s t r a c t Various patching materials and field procedures have been studied for pothole repairing on highway asphalt pavements. However, only a few publications have focused on patching materials for epoxy asphalt pavement 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 structure, 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 used to analyze the viscoelastic response of different patched beams and the effect of viscoelastic difference. The results showed that the fatigue test 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 growth of viscoelastic difference between patching material and original material, the stress state on vertical patching interface becomes worse, and the interface becomes easier to fracture under cyclic load. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Epoxy asphalt concrete (EAC) has been proved as a better pavement material for steel bridge pavement than other conventional asphalt mixtures [1]. 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 [2], 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 [3]. Because of the poor field construction quality, fatigue failure or falling objects from vehicles, ⇑ Corresponding author at: Intelligent Transport System Research Center, Southeast University, 35 Jinxianghe Road, Nanjing 210096, PR China. E-mail addresses: [email protected] (Y. Yang), [email protected] (Z. Qian), [email protected] (X. Song). http://dx.doi.org/10.1016/j.conbuildmat.2015.07.017 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.
part of the EAC pavement surface would break into pieces and be pulled up by travelling wheels, thus a pothole could form on the pavement surface. In addition, the water inside the potholes would cause more damage under the vehicle load and accelerate the pothole development. Pothole significantly reduces pavement performance level and service life, and is one of the most aggravating pavement distresses for traffic safety. Pothole has been a common distress on highway asphalt pavements. Various materials and field procedures for pothole repair have been studied and used by researchers and highway agencies. The Strategic Highway Research Program (SHRP) [4,5] evaluated the performance of different patching materials and various repair techniques by field experiment and investigations. It was found that bituminous hot mixtures have higher quality but limited applicability under different weather conditions while cold-mixed mixtures have lower quality but are workable under most weather conditions. New Jersey Department of
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Transportation [6] tried the blade resistance test and rolling sieve test to evaluate the workability and the cohesion of patching materials. Fragachan [7] proposed an accelerated testing procedure for evaluating pavement patching materials under the simulation of traffic loading and environmental conditions. Dong et al. [8] investigated and modified special laboratory procedures to evaluate the bonding, freeze-thaw resistance and rutting potential of the patching materials. Yuan et al. [9] identified a polymeric material, dicyclopentadiene (DCPD) resin to become an ultra-tough material for pothole repair. Li et al. [10] evaluated the performance of a rapid patching material which combines magnesium phosphate cement and emulsified asphalt. For pothole repair on steel bridge pavements, only a few studies have been published. Luo et al. [11] investigated the performance of EAC pavement on the Second Nanjing Yangtze River Bridge and pointed out that the dynamic water pressure in the early cracks would decrease the fatigue life of EAC and contribute to the development of potholes. Huang et al. [12] 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 field tests. They suggested the EAC to be used for the pavement overhaul on the bridge. To determine the semi-permanent patching material and field procedure on EAC pavement, the differences from highway pavements in pavement structure, pavement materials and work conditions should be considered. The thickness of EAC pavement on steel bridges usually ranges from 50 to 60 mm which is much thinner than highway pavements, and the aggregate gradation with a 9.5 mm nominal maximum size is also finer 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, a fine gradation epoxy asphalt pavement patching material (EAPP) is proposed in this research. This patching material was prepared using a fast cure thermosetting binder, limestone filler and basalt aggregates. In order to evaluate the fatigue performance of EAPP, three types of composite beams were fabricated and tested in three-point bending fatigue test. In addition, the Prony series presentations of the generalized Maxwell model for different materials were obtained and used to analyze the viscoelastic response of patched beams.
2. Experimental program
With considerations on workability, water resistance and adhesion performance, the patching material should have low air-void content, easy handling, and a strong interface bonding with the original pavement. Therefore, a fine aggregate gradation was selected for the patch material as shown in Fig. 1. The asphalt content was determined as 9.8% by conducting the Marshall test on specimens. The EAC has been widely used on the pavements of steel bridges such as the 2nd Yangtze River Bridge, the Runyang Cable Stay and the Sutong Bridge. In this study, the asphalt binder of EAC was 2910-type local epoxy asphalt and the asphalt content is 6.5%. The details about the binder and the mix design of EAC can be found from [14].
2.2. Fatigue test method 2.2.1. Specimen fabrication Composite beams were fabricated to evaluate the performance of EAPP in patched EAC pavement structure. Firstly, a 50 mm-thick EAC layer was filled and compacted in a 300 mm 300 mm mold. After curing, a groove (25 mm deep 100 mm wide) 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 poured into the groove and compacted manually. After curing for 24 h at 25 h, the specimen was cut into three types of composite beams sized 300 mm 40 mm 50 mm as shown in Fig. 2. Beam I consists of two 25 mm-thick EAC layers. Beama is made up of an upper EAPP layer and a lower EAC layer. In Beamb, the middle part of the upper layer is EAPP while the other parts are EAC.
2.2.2. Test condition The fatigue test was conducted on a three-point bending fatigue test system as shown in Fig. 3. The test temperature was set at 15 h according to local conditions. The test was carried out in load control using a sinusoidal load with a 10 Hz frequency, and the stress ratios (the ratio of applied peak load to the bending failure load) were selected as 0.3, 0.4, 0.5 and 0.6. The load was applied in the middle of the beam and the span of the beam was 250 mm. The stiffness modulus (tensile stress divided by tensile strain at middle transverse section) was recorded at every load cycle until the beams were completely destroyed. Fatigue failure is defined at 50% reduction with respect to the initial stiffness of the composite beams and the corresponding number of load cycle is defined as fatigue life.
2.1. Raw materials
Table 1 Technical index of epoxy asphalt binder. Technical indexes
Criteria
Test method
Mass ratio (TAF-EPOXY:70# asphalt) Tensile strength (MPa, 23 °C) Fracture elongation (%, 23 °C) Viscosity 170 °C 1 h (mPa s)
1:1 P2.0 P100 62000
ASTM D638 ASTM D638 ASTM D4402
100 90 80
Percent Passing (%)
The EAPP is composed of epoxy asphalt binder, limestone filler and basalt fine graded aggregates. The epoxy asphalt binder is composed of TAF-EPOXY and 70# 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 70# asphalt is a type of asphalt binder usually used for heavy traffic in China with a penetration value from 60 to 80 (25 °C, 5 s, 100 g) [13]. The basic information of the epoxy asphalt binder is provided in Table 1.
70 60 50 40 30
Upper limite
20
Lower limite
10
Desgined gradation
0 0.075 0.15 0.3
0.6
1.18
Sieve Size (mm) Fig. 1. Aggregates gradation of EAPP.
2.36
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Fig. 2. Composite beams for fatigue test.
Fig. 3. Fatigue test of composite beam.
Once obtained from Eq. (2), the data curve of E0 can be smoothed using a log-sigmoidal function [16] defined as:
3. Numerical analysis 3.1. Complex modulus and pre-smoothing 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 [15]. The sinusoidal load was applied at nine frequencies 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10, 20, 25 Hz, and four temperatures 10, 20, 40, 60 °C. Then the complex modulus E⁄ and phase angle / at certain loading frequency and temperature can be determined. The complex modulus is composed of the storage modulus and loss modulus:
0
E ¼ E þ iE
00
E0 ðxr Þ ¼ f ðxr Þ ¼ a1 þ
a2 a3 þ exp½a5 þaa64 log ðxr Þ
ð4Þ
where a1,2,. . .,6 are the fitting coefficients; xr represents the reduced frequency at reference temperature. Based on the time–temperature superposition principle, the reduced frequency xr can be determined by the second-order polynomial [17], as shown in Eq. (5):
log xr ¼ log x þ k1 ðT r TÞ þ k2 ðT r TÞ2
ð5Þ
ð1Þ
jE0 j ¼ jE j cos f
ð2Þ
jE00 j ¼ jE j sin /
ð3Þ
where E0 is the storage modulus, E00 is the loss modulus, and i is (1)1/2.
where x is the loading frequency at the test temperature, Hz; k1, k2 are the fitting coefficients; Tr is the reference temperature, and T is the test temperature. The smoothed data curve of E0 can be obtained based on the frequency sweep test result by combing Eqs. (4) and (5). Fig. 4 shows the shifted experimental results and pre-smoothed curves of EAPP and EAC at the reference temperature of 15 °C.
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radian frequencies xr. Thus, the Prony series presentation of GMM can be determined and used to describe the viscoelasticity of materials. 3.3. Numerical simulation
Fig. 4. Storage modulus of EAPP and EAC at 15 °C.
3.2. Viscoelastic model and Prony series The generalized Maxwell model (GMM) was used in the numerical analysis to describe the time dependency property. The schematic of GMM is given in Fig. 5. The model consists of two basic units, the linear elastic spring and the linear viscous dash-pot. The combination of spring units and dashpot units defines the viscoelastic behavior. In a time-domain, the relaxation modulus E(t) of GMM in the form of Prony series can be expressed as follows:
EðtÞ ¼ E1 þ
M X Em exp ðt=qm Þ
ð6Þ
m¼1
where E1, Em and qm are infinite relaxation modulus, Prony coefficients, and relaxation time, respectively; M is the number of spring and dashpot combination units in GMM. In a frequency-domain, the complex modulus E⁄(xn) of GMM can be obtained from the constitutive equation [18] given as follows: M X ixn qm Em E ðxn Þ ¼ E1 þ ; i x n qm þ 1 m¼1
n ¼ 1; :::; N
ð7Þ
where xn, n = 1, 2. . ., N is the reduced frequency. Then the storage modulus in frequency-domain can be determined by taking the real parts of the complex modulus:
E0 ðxn Þ ¼ E1 þ
M X x2n q2m Em ; 2 q2 þ 1 x n m m¼1
n ¼ 1; :::; N
ð8Þ
To determine the Prony series function in Eqs. (6) and (7), the equivalent E1, qm, and Em shown in Eq. (8) must be obtained first. Combining Eq. (8) and the smoothed curve shown in Fig. 4, E1 can be found by the limit of E0 (xr)|0 < xr 1. The Prony series coefficients Em were obtained based on selected relaxation times qm and
To analysis the LVE response of the composite beams, viscoelastic finite element (FE) simulation was conducted in the software ABAQUS. As the numerical beams are at LVE stage, the bond layer between patching material and original material is considered in a good working condition. Therefore, for the simplification of modeling, the two parts of different materials were modeled to be tied together without a bond layer. That also means the displacements are continuous across the patching interface. Though, using this method, the failure and cracks were unable to be simulated, the development of tensile stress concentration and the viscoelastic response of patched beams can still be modeled and analyzed effectively. To utilize the GMM in FE modeling, the parameters presented by Prony series were imported into the model. Table 2 shows the Prony series of EAPP as an example. A sinusoidal load ranges from 0.5 to 3.5 kN were applied on the meshed numerical beams for 500 load cycles, and the load frequency was also 10 Hz. The loading cycle was selected as 500 times because the stress concentration develops relatively slowly after that as observed in the simulation. At first, three numerical composite beams (Beams I, II and III) was modeled to analyze the viscoelastic response of EAPP patched beams. Then, to investigate the effect of viscoelasticity difference on stress distribution, two more types of patched beams using different patching materials (Materials A and B) were modeled and analyzed. 4. Results and discussion 4.1. Experiment results The stiffness modulus of the composite beams was recorded during the fatigue test. As an example, Fig. 6 shows the stiffness modulus variation of the composite beams under the stress ratio of 0.4. In spite of the tight range fluctuation over the load cycle, all the recorded data show a clear and consistent decreasing trend which indicates the process of fatigue failure. At the early stage, 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 indicates the complete failure of the beams. It can be also found that the stiffness modulus varies considerably between different patched beams. The initial stiffness modulus of Beam I is about 2800 MPa which is larger than 650 MPa of Beam II and 1300 MPa of 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 beams. Fig. 7 illustrates the fatigue performance of all the three structures under different stress ratios. The fatigue life of the three
Table 2 Prony series of EAPP at 15 °C.
Fig. 5. Schematic of the generalized Maxwell model.
Item
qm (s)
Em (MPa)
Item
qm (s)
Em (MPa)
1 2 3 4 5 6 E1/MPa
105 104 103 102 101 1
8889.5 5654.9 7134.3 6120.3 5024.1 3486.3
7 8 9 10 11 12 244.6
10 102 103 104 105 106
2165.4 1213.6 645.2 338.6 176.0 111.2
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Fig. 6. Stiffness modulus of composite beams at stress ratio 0.4.
structures decreases with the increase of the stress ratio. Beam II shows the best performance in fatigue resistance followed by Beam I. The result indicates that the EAPP has a better fatigue resistance than EAC. However, the fatigue life of Beam III is considerably smaller than that of Beams I and II under all loading conditions in the test. This result shows that even though the EAPP has a good fatigue performance, the vertical patching interface has an adverse effect on the fatigue resistance of the patched structure. Fig. 8 shows the fatigue failure forms of the three structures. Beam III fractured at the middle transverse section or the vertical patching interface, while Beams I and II only fracture at the middle transverse section. This suggests that the vertical patching interface between EAPP and EAC is vulnerable and could be the potential fracture section under sinusoidal load. The mechanism of this effect will be studied subsequently by numerical analysis.
4.2. Numerical analysis of experiment As observed above, fracture could occur at the vertical patching interface between EAPP and EAC, which implies that the viscoelastic response in the patching interface is different from the homogeneous transverse sections. Therefore, the patching interface which is also the transverse section at 1/4 length of the beams, needs further viscoelastic analysis. Fig. 9 shows the distribution of tensile stress in two directions on beam III after 500 load cycles. It can be found that the transverse tensile stress S11 and vertical tensile stress S22 increase rapidly near the patching interface, and a high contrast of the stress value can be observed. The results indicate that the patching interfaces between EAPP and EAC can cause tensile stress concentration in both transverse direction and vertical direction, which could contribute to its failure under cyclic load.
Fig. 7. Fatigue life of composite beams at different stress ratios.
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Fig. 10 compares the maximum principal stress of a certain point on the patching interface of different composite beams. It can be found that the peak value of maximum principal stress increase at first few load cycles and then become stable gradually. It is obvious that the patching interface of beam III is subjected to much greater sinusoidal tensile stress, and the peak value is approximately 3 times larger than that on other beams. This means that patched EAC pavement structures are more likely to fracture at the interface than original 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 interface is a potential failure section even though the adhesion performs well. 4.3. Effect of viscoelastic difference Based on the LVE assumption of GMM, it is supposable that the stress concentration is caused by the different viscoelasticity between patching material and original material. To evaluate the effect of viscoelasticity difference, more types of patching materials need to be compared. Therefore, Materials A and B were also molded as patching material in the numerical bending test on patched beams. The dynamic modulus of different materials at 15 °C is compared in Fig. 11. It shows that within the load frequency range from 0.01 to 100 Hz, the dynamic modulus of patching materials are all smaller than that of EAC. EAPP shows the largest dynamic modulus among the patching materials including Material A and Material B. To indicate the viscoelasticity difference between the materials and the variation of viscoelastic response in different patched beams, two indexes was utilized. The dynamic modulus difference (DMD) was used to show the viscoelasticity difference between patching material and original material as shown in Eq. (9)
DMD ¼ DMðEACÞ DMðPMÞ =DMðEACÞ
ð9Þ
where DMD is the dynamic modulus difference between EAC and a patching material (EAPP, Material A or Material B), DM(EAC) is the dynamic modulus of EAC, DM(PM) is the dynamic modulus of the patching material. The ratio of stress in original beam to stress in patched beams (SR) was adopted to show the viscoelastic response variation in different patched beams, as shown in Eq. (10)
SR ¼ SðPÞ =SðOÞ
ð10Þ
where S(P) is the stress value of patched beams, S(O) is the stress value of original beam (beam I). All the stress values was collected form a certain point on patching interface (transverse section at 1/4 length for original beam) after 500 load cycles. Using the index DMD and SR, the effect of viscoelasticity difference on stress response can be described. As shown in Fig. 12(a), the tensile stress in transverse direction (S11) and vertical direction (S22) increase rapidly as the DDM grows, while the longitudinal tensile stress (S33) is not susceptible to the change of DMD. Fig. 12(b) shows the variation of max principle stress and shear stress on patching interface. It can be found that the horizontal shear stress (S31) is also susceptible to the viscoelasticity difference, it grows 8 times when the DMD increase to 87%. By contrast, the SR of vertical shear stress (S32) decrease from 1.00 to 0.37, which indicates it decreases and then changes to the opposite direction with the growth of DMD. As a comprehensive reflection of tensile stress and shear stress, the max principle stress shows a modest growth with the increase of DMD. Based on the above numerical results, it can be concluded that the transverse tensile stress, vertical tensile stress and the shear
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Fig. 8. Fatigue failure forms of composite beams.
Fig. 9. Transverse and vertical tensile stress on beam III (Pa). (a) Transverse tensile stress S11, (b) vertical tensile stress S22.
Fig. 10. Maximum principal stress of patching interface.
Fig. 11. Dynamic modulus of different materials.
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material cause tensile stress concentration near the interface. With the increase of the viscoelastic difference, the patching interface is subjected to worse stress state. 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. The viscoelastic difference should be considered to choose suitable patching material. Moreover, attention should be paid to the patched areas during pavement evaluation in case of second time failure. Acknowledgements The authors are grateful to the sponsorship of contribution by the National Natural Science Foundation of China (NSFC, No. 51378122). References
Fig. 12. SR at different DMD (a) tensile stress in three directions (b) shear stress and maximum principal stress.
stress on the patching interface are all susceptible to the difference of viscoelasticity. With the increase of the viscoelastic difference, the patching interface is subjected to worse stress state and tends to fracture earlier under cyclic load. 5. 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: (1) 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. (2) 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. (3) 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 104 Hz. (4) The numerical analysis results indicate that the different viscoelastic properties of patching material and original
[1] R. Gaul, A long life pavement for orthotropic bridge decks in China, Proceedings of the 2009 GeoHunan international conference, Geotechnical Special Publication No. 196, American Society of Civil Engineers, Reston, USA, 2009, pp. 1–8. [2] X.H. Chen, Z.D. Qian, X.Y. Liu, L. Zhang, State of art of asphalt surfacings on long-spanned orthotropic steel decks in China, J. Test Eval. 40 (7) (2012). [3] J.S. Miller, W.Y. Bellinger, Distress identification manual for the long-term pavement performance program. Report No. FHWA-RD-03-031, Federal Highway Administration, Washington, D.C., USA, 2003. [4] T.P. Wilson, A.R. Romine, Innovative materials development and testing volume 2: pothole repair. Report No. SHRP-H-353, Strategic Highway Research Program, National Research Council, Washington, D.C., USA, 1993. [5] T.P. Wilson, A.R. Romine, Materials and procedures for repair of potholes in asphalt surfaced pavements–manual of practice. Report No. FHWA-RD-99-168, Federal Highway Administration, Washington, D.C., USA, 2000. [6] A. Maher, N. Gucunski, W. Yanko, F. Petsi, Evaluation of pothole patching materials. Report No. FHWA 2001–02, Federal Highway Administration, Washington, D.C., USA, 2001. [7] Fragachan JM. Accelerated testing methodology for evaluating pavement patching materials. Master Thesis. Worcester Polytechnic Institute; 2008. [8] Q. Dong, B.S. Huang, S. Zhao, Field and laboratory evaluation of winter season pavement pothole patching materials, Int. J. Pavement Eng. 15 (4) (2014) 279– 289. [9] W. Yuan, K.Y. Yuan, L.H. Zou, J.M. Yang, J.W. Ju, W. Kao, DCPD resin catalyzed with Grubbs catalysts for reinforcing pothole patching materials, Proceedings of SPIE – The International Society for Optical Engineering, SPIE, Bellingham (USA), 2012. [10] J. Li, G. Xu, Y. Chen, G. Liu, Multiple scaling investigation of magnesium phosphate cement modified by emulsified asphalt for rapid repair of asphalt mixture pavement, Constr. Build. Mater. 69 (2014) 350–364. [11] S. Luo, Z.D. Qian, H. Wang, Condition survey and analysis of epoxy asphalt concrete pavement on second Nanjing Yangtze River Bridge: a ten-year review, J. Southeast Univ. (English Ed.) 27 (4) (2011) 417–422. [12] W. Huang, Z.D. Qian, L. Zhang, Experimental study on partly patching scheme of steel bridge deck paving, Chin. Civ. Eng. J. 39 (8) (2006) 87–90 (in Chinese). [13] ASTM D5/D5M-13, Standard test method for penetration of bituminous materials, American Society for Testing and Materials, West Conshohocken (PA), USA, 2013. [14] L.L. Chen, Z.D. Qian, L. Zhang, Evaluation of epoxy asphalt concrete damping parameters using impact resonance test, J. Test Eval. 40 (5) (2012). [15] R.F. Bonaquist, D.W. Christensen, Simple performance tester for superpave mix design: first-article development and evaluation. NCHRP Report 513, National Cooperative Highway Research Program, Transportation Research Board, Washington, D.C., USA, 2003. [16] S. Mun, G.C. Chehab, Y.R. Kim, Determination of time-domain viscoelastic functions using optimized interconversion techniques, Road Mater. Pavement Des. 8 (2) (2007) 351–365. [17] AASHTO PP 62, Standard practice for developing dynamic modulus master curves for hot mix asphalt (HMA), American Association of State Highway and Transportation Officials, Washington, D.C., USA, 2009. [18] S.W. Park, R.A. Schapery, Methods of interconversion between linear viscoelastic material functions. Part I – a numerical method based on Prony series, Int. J. Solids Struct. 36 (11) (1999) 1653–1675.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
A pothole patching material for epoxy asphalt pavement on steel bridges: Fatigue test and numerical analysis Yuming Yang, Zhendong Qian ⇑, Xin Song Intelligent Transport System Research Center, Southeast University, PR China
h i g h l i g h t s A fine gradation patching material is developed for epoxy asphalt pavement. The generalized Maxwell model is used to analyze the viscoelastic response. The patching interfaces are vulnerable to cyclic load due to stress concentration. The increase of viscoelastic difference causes worse stress state on patching interface.
a r t i c l e
i n f o
Article history: Received 9 February 2015 Received in revised form 7 July 2015 Accepted 9 July 2015
Keywords: Pothole patching Epoxy asphalt pavement Fatigue test Composite beam Generalized Maxwell model Prony series Viscoelastic difference
a b s t r a c t Various patching materials and field procedures have been studied for pothole repairing on highway asphalt pavements. However, only a few publications have focused on patching materials for epoxy asphalt pavement 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 structure, 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 used to analyze the viscoelastic response of different patched beams and the effect of viscoelastic difference. The results showed that the fatigue test 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 growth of viscoelastic difference between patching material and original material, the stress state on vertical patching interface becomes worse, and the interface becomes easier to fracture under cyclic load. Ó 2015 Elsevier Ltd. All rights reserved.
1. Introduction Epoxy asphalt concrete (EAC) has been proved as a better pavement material for steel bridge pavement than other conventional asphalt mixtures [1]. 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 [2], 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 [3]. Because of the poor field construction quality, fatigue failure or falling objects from vehicles, ⇑ Corresponding author at: Intelligent Transport System Research Center, Southeast University, 35 Jinxianghe Road, Nanjing 210096, PR China. E-mail addresses: [email protected] (Y. Yang), [email protected] (Z. Qian), [email protected] (X. Song). http://dx.doi.org/10.1016/j.conbuildmat.2015.07.017 0950-0618/Ó 2015 Elsevier Ltd. All rights reserved.
part of the EAC pavement surface would break into pieces and be pulled up by travelling wheels, thus a pothole could form on the pavement surface. In addition, the water inside the potholes would cause more damage under the vehicle load and accelerate the pothole development. Pothole significantly reduces pavement performance level and service life, and is one of the most aggravating pavement distresses for traffic safety. Pothole has been a common distress on highway asphalt pavements. Various materials and field procedures for pothole repair have been studied and used by researchers and highway agencies. The Strategic Highway Research Program (SHRP) [4,5] evaluated the performance of different patching materials and various repair techniques by field experiment and investigations. It was found that bituminous hot mixtures have higher quality but limited applicability under different weather conditions while cold-mixed mixtures have lower quality but are workable under most weather conditions. New Jersey Department of
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Transportation [6] tried the blade resistance test and rolling sieve test to evaluate the workability and the cohesion of patching materials. Fragachan [7] proposed an accelerated testing procedure for evaluating pavement patching materials under the simulation of traffic loading and environmental conditions. Dong et al. [8] investigated and modified special laboratory procedures to evaluate the bonding, freeze-thaw resistance and rutting potential of the patching materials. Yuan et al. [9] identified a polymeric material, dicyclopentadiene (DCPD) resin to become an ultra-tough material for pothole repair. Li et al. [10] evaluated the performance of a rapid patching material which combines magnesium phosphate cement and emulsified asphalt. For pothole repair on steel bridge pavements, only a few studies have been published. Luo et al. [11] investigated the performance of EAC pavement on the Second Nanjing Yangtze River Bridge and pointed out that the dynamic water pressure in the early cracks would decrease the fatigue life of EAC and contribute to the development of potholes. Huang et al. [12] 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 field tests. They suggested the EAC to be used for the pavement overhaul on the bridge. To determine the semi-permanent patching material and field procedure on EAC pavement, the differences from highway pavements in pavement structure, pavement materials and work conditions should be considered. The thickness of EAC pavement on steel bridges usually ranges from 50 to 60 mm which is much thinner than highway pavements, and the aggregate gradation with a 9.5 mm nominal maximum size is also finer 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, a fine gradation epoxy asphalt pavement patching material (EAPP) is proposed in this research. This patching material was prepared using a fast cure thermosetting binder, limestone filler and basalt aggregates. In order to evaluate the fatigue performance of EAPP, three types of composite beams were fabricated and tested in three-point bending fatigue test. In addition, the Prony series presentations of the generalized Maxwell model for different materials were obtained and used to analyze the viscoelastic response of patched beams.
2. Experimental program
With considerations on workability, water resistance and adhesion performance, the patching material should have low air-void content, easy handling, and a strong interface bonding with the original pavement. Therefore, a fine aggregate gradation was selected for the patch material as shown in Fig. 1. The asphalt content was determined as 9.8% by conducting the Marshall test on specimens. The EAC has been widely used on the pavements of steel bridges such as the 2nd Yangtze River Bridge, the Runyang Cable Stay and the Sutong Bridge. In this study, the asphalt binder of EAC was 2910-type local epoxy asphalt and the asphalt content is 6.5%. The details about the binder and the mix design of EAC can be found from [14].
2.2. Fatigue test method 2.2.1. Specimen fabrication Composite beams were fabricated to evaluate the performance of EAPP in patched EAC pavement structure. Firstly, a 50 mm-thick EAC layer was filled and compacted in a 300 mm 300 mm mold. After curing, a groove (25 mm deep 100 mm wide) 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 poured into the groove and compacted manually. After curing for 24 h at 25 h, the specimen was cut into three types of composite beams sized 300 mm 40 mm 50 mm as shown in Fig. 2. Beam I consists of two 25 mm-thick EAC layers. Beama is made up of an upper EAPP layer and a lower EAC layer. In Beamb, the middle part of the upper layer is EAPP while the other parts are EAC.
2.2.2. Test condition The fatigue test was conducted on a three-point bending fatigue test system as shown in Fig. 3. The test temperature was set at 15 h according to local conditions. The test was carried out in load control using a sinusoidal load with a 10 Hz frequency, and the stress ratios (the ratio of applied peak load to the bending failure load) were selected as 0.3, 0.4, 0.5 and 0.6. The load was applied in the middle of the beam and the span of the beam was 250 mm. The stiffness modulus (tensile stress divided by tensile strain at middle transverse section) was recorded at every load cycle until the beams were completely destroyed. Fatigue failure is defined at 50% reduction with respect to the initial stiffness of the composite beams and the corresponding number of load cycle is defined as fatigue life.
2.1. Raw materials
Table 1 Technical index of epoxy asphalt binder. Technical indexes
Criteria
Test method
Mass ratio (TAF-EPOXY:70# asphalt) Tensile strength (MPa, 23 °C) Fracture elongation (%, 23 °C) Viscosity 170 °C 1 h (mPa s)
1:1 P2.0 P100 62000
ASTM D638 ASTM D638 ASTM D4402
100 90 80
Percent Passing (%)
The EAPP is composed of epoxy asphalt binder, limestone filler and basalt fine graded aggregates. The epoxy asphalt binder is composed of TAF-EPOXY and 70# 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 70# asphalt is a type of asphalt binder usually used for heavy traffic in China with a penetration value from 60 to 80 (25 °C, 5 s, 100 g) [13]. The basic information of the epoxy asphalt binder is provided in Table 1.
70 60 50 40 30
Upper limite
20
Lower limite
10
Desgined gradation
0 0.075 0.15 0.3
0.6
1.18
Sieve Size (mm) Fig. 1. Aggregates gradation of EAPP.
2.36
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Fig. 2. Composite beams for fatigue test.
Fig. 3. Fatigue test of composite beam.
Once obtained from Eq. (2), the data curve of E0 can be smoothed using a log-sigmoidal function [16] defined as:
3. Numerical analysis 3.1. Complex modulus and pre-smoothing 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 [15]. The sinusoidal load was applied at nine frequencies 0.1, 0.2, 0.5, 1.0, 2.0, 5.0, 10, 20, 25 Hz, and four temperatures 10, 20, 40, 60 °C. Then the complex modulus E⁄ and phase angle / at certain loading frequency and temperature can be determined. The complex modulus is composed of the storage modulus and loss modulus:
0
E ¼ E þ iE
00
E0 ðxr Þ ¼ f ðxr Þ ¼ a1 þ
a2 a3 þ exp½a5 þaa64 log ðxr Þ
ð4Þ
where a1,2,. . .,6 are the fitting coefficients; xr represents the reduced frequency at reference temperature. Based on the time–temperature superposition principle, the reduced frequency xr can be determined by the second-order polynomial [17], as shown in Eq. (5):
log xr ¼ log x þ k1 ðT r TÞ þ k2 ðT r TÞ2
ð5Þ
ð1Þ
jE0 j ¼ jE j cos f
ð2Þ
jE00 j ¼ jE j sin /
ð3Þ
where E0 is the storage modulus, E00 is the loss modulus, and i is (1)1/2.
where x is the loading frequency at the test temperature, Hz; k1, k2 are the fitting coefficients; Tr is the reference temperature, and T is the test temperature. The smoothed data curve of E0 can be obtained based on the frequency sweep test result by combing Eqs. (4) and (5). Fig. 4 shows the shifted experimental results and pre-smoothed curves of EAPP and EAC at the reference temperature of 15 °C.
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radian frequencies xr. Thus, the Prony series presentation of GMM can be determined and used to describe the viscoelasticity of materials. 3.3. Numerical simulation
Fig. 4. Storage modulus of EAPP and EAC at 15 °C.
3.2. Viscoelastic model and Prony series The generalized Maxwell model (GMM) was used in the numerical analysis to describe the time dependency property. The schematic of GMM is given in Fig. 5. The model consists of two basic units, the linear elastic spring and the linear viscous dash-pot. The combination of spring units and dashpot units defines the viscoelastic behavior. In a time-domain, the relaxation modulus E(t) of GMM in the form of Prony series can be expressed as follows:
EðtÞ ¼ E1 þ
M X Em exp ðt=qm Þ
ð6Þ
m¼1
where E1, Em and qm are infinite relaxation modulus, Prony coefficients, and relaxation time, respectively; M is the number of spring and dashpot combination units in GMM. In a frequency-domain, the complex modulus E⁄(xn) of GMM can be obtained from the constitutive equation [18] given as follows: M X ixn qm Em E ðxn Þ ¼ E1 þ ; i x n qm þ 1 m¼1
n ¼ 1; :::; N
ð7Þ
where xn, n = 1, 2. . ., N is the reduced frequency. Then the storage modulus in frequency-domain can be determined by taking the real parts of the complex modulus:
E0 ðxn Þ ¼ E1 þ
M X x2n q2m Em ; 2 q2 þ 1 x n m m¼1
n ¼ 1; :::; N
ð8Þ
To determine the Prony series function in Eqs. (6) and (7), the equivalent E1, qm, and Em shown in Eq. (8) must be obtained first. Combining Eq. (8) and the smoothed curve shown in Fig. 4, E1 can be found by the limit of E0 (xr)|0 < xr 1. The Prony series coefficients Em were obtained based on selected relaxation times qm and
To analysis the LVE response of the composite beams, viscoelastic finite element (FE) simulation was conducted in the software ABAQUS. As the numerical beams are at LVE stage, the bond layer between patching material and original material is considered in a good working condition. Therefore, for the simplification of modeling, the two parts of different materials were modeled to be tied together without a bond layer. That also means the displacements are continuous across the patching interface. Though, using this method, the failure and cracks were unable to be simulated, the development of tensile stress concentration and the viscoelastic response of patched beams can still be modeled and analyzed effectively. To utilize the GMM in FE modeling, the parameters presented by Prony series were imported into the model. Table 2 shows the Prony series of EAPP as an example. A sinusoidal load ranges from 0.5 to 3.5 kN were applied on the meshed numerical beams for 500 load cycles, and the load frequency was also 10 Hz. The loading cycle was selected as 500 times because the stress concentration develops relatively slowly after that as observed in the simulation. At first, three numerical composite beams (Beams I, II and III) was modeled to analyze the viscoelastic response of EAPP patched beams. Then, to investigate the effect of viscoelasticity difference on stress distribution, two more types of patched beams using different patching materials (Materials A and B) were modeled and analyzed. 4. Results and discussion 4.1. Experiment results The stiffness modulus of the composite beams was recorded during the fatigue test. As an example, Fig. 6 shows the stiffness modulus variation of the composite beams under the stress ratio of 0.4. In spite of the tight range fluctuation over the load cycle, all the recorded data show a clear and consistent decreasing trend which indicates the process of fatigue failure. At the early stage, 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 indicates the complete failure of the beams. It can be also found that the stiffness modulus varies considerably between different patched beams. The initial stiffness modulus of Beam I is about 2800 MPa which is larger than 650 MPa of Beam II and 1300 MPa of 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 beams. Fig. 7 illustrates the fatigue performance of all the three structures under different stress ratios. The fatigue life of the three
Table 2 Prony series of EAPP at 15 °C.
Fig. 5. Schematic of the generalized Maxwell model.
Item
qm (s)
Em (MPa)
Item
qm (s)
Em (MPa)
1 2 3 4 5 6 E1/MPa
105 104 103 102 101 1
8889.5 5654.9 7134.3 6120.3 5024.1 3486.3
7 8 9 10 11 12 244.6
10 102 103 104 105 106
2165.4 1213.6 645.2 338.6 176.0 111.2
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Fig. 6. Stiffness modulus of composite beams at stress ratio 0.4.
structures decreases with the increase of the stress ratio. Beam II shows the best performance in fatigue resistance followed by Beam I. The result indicates that the EAPP has a better fatigue resistance than EAC. However, the fatigue life of Beam III is considerably smaller than that of Beams I and II under all loading conditions in the test. This result shows that even though the EAPP has a good fatigue performance, the vertical patching interface has an adverse effect on the fatigue resistance of the patched structure. Fig. 8 shows the fatigue failure forms of the three structures. Beam III fractured at the middle transverse section or the vertical patching interface, while Beams I and II only fracture at the middle transverse section. This suggests that the vertical patching interface between EAPP and EAC is vulnerable and could be the potential fracture section under sinusoidal load. The mechanism of this effect will be studied subsequently by numerical analysis.
4.2. Numerical analysis of experiment As observed above, fracture could occur at the vertical patching interface between EAPP and EAC, which implies that the viscoelastic response in the patching interface is different from the homogeneous transverse sections. Therefore, the patching interface which is also the transverse section at 1/4 length of the beams, needs further viscoelastic analysis. Fig. 9 shows the distribution of tensile stress in two directions on beam III after 500 load cycles. It can be found that the transverse tensile stress S11 and vertical tensile stress S22 increase rapidly near the patching interface, and a high contrast of the stress value can be observed. The results indicate that the patching interfaces between EAPP and EAC can cause tensile stress concentration in both transverse direction and vertical direction, which could contribute to its failure under cyclic load.
Fig. 7. Fatigue life of composite beams at different stress ratios.
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Fig. 10 compares the maximum principal stress of a certain point on the patching interface of different composite beams. It can be found that the peak value of maximum principal stress increase at first few load cycles and then become stable gradually. It is obvious that the patching interface of beam III is subjected to much greater sinusoidal tensile stress, and the peak value is approximately 3 times larger than that on other beams. This means that patched EAC pavement structures are more likely to fracture at the interface than original 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 interface is a potential failure section even though the adhesion performs well. 4.3. Effect of viscoelastic difference Based on the LVE assumption of GMM, it is supposable that the stress concentration is caused by the different viscoelasticity between patching material and original material. To evaluate the effect of viscoelasticity difference, more types of patching materials need to be compared. Therefore, Materials A and B were also molded as patching material in the numerical bending test on patched beams. The dynamic modulus of different materials at 15 °C is compared in Fig. 11. It shows that within the load frequency range from 0.01 to 100 Hz, the dynamic modulus of patching materials are all smaller than that of EAC. EAPP shows the largest dynamic modulus among the patching materials including Material A and Material B. To indicate the viscoelasticity difference between the materials and the variation of viscoelastic response in different patched beams, two indexes was utilized. The dynamic modulus difference (DMD) was used to show the viscoelasticity difference between patching material and original material as shown in Eq. (9)
DMD ¼ DMðEACÞ DMðPMÞ =DMðEACÞ
ð9Þ
where DMD is the dynamic modulus difference between EAC and a patching material (EAPP, Material A or Material B), DM(EAC) is the dynamic modulus of EAC, DM(PM) is the dynamic modulus of the patching material. The ratio of stress in original beam to stress in patched beams (SR) was adopted to show the viscoelastic response variation in different patched beams, as shown in Eq. (10)
SR ¼ SðPÞ =SðOÞ
ð10Þ
where S(P) is the stress value of patched beams, S(O) is the stress value of original beam (beam I). All the stress values was collected form a certain point on patching interface (transverse section at 1/4 length for original beam) after 500 load cycles. Using the index DMD and SR, the effect of viscoelasticity difference on stress response can be described. As shown in Fig. 12(a), the tensile stress in transverse direction (S11) and vertical direction (S22) increase rapidly as the DDM grows, while the longitudinal tensile stress (S33) is not susceptible to the change of DMD. Fig. 12(b) shows the variation of max principle stress and shear stress on patching interface. It can be found that the horizontal shear stress (S31) is also susceptible to the viscoelasticity difference, it grows 8 times when the DMD increase to 87%. By contrast, the SR of vertical shear stress (S32) decrease from 1.00 to 0.37, which indicates it decreases and then changes to the opposite direction with the growth of DMD. As a comprehensive reflection of tensile stress and shear stress, the max principle stress shows a modest growth with the increase of DMD. Based on the above numerical results, it can be concluded that the transverse tensile stress, vertical tensile stress and the shear
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Fig. 8. Fatigue failure forms of composite beams.
Fig. 9. Transverse and vertical tensile stress on beam III (Pa). (a) Transverse tensile stress S11, (b) vertical tensile stress S22.
Fig. 10. Maximum principal stress of patching interface.
Fig. 11. Dynamic modulus of different materials.
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material cause tensile stress concentration near the interface. With the increase of the viscoelastic difference, the patching interface is subjected to worse stress state. 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. The viscoelastic difference should be considered to choose suitable patching material. Moreover, attention should be paid to the patched areas during pavement evaluation in case of second time failure. Acknowledgements The authors are grateful to the sponsorship of contribution by the National Natural Science Foundation of China (NSFC, No. 51378122). References
Fig. 12. SR at different DMD (a) tensile stress in three directions (b) shear stress and maximum principal stress.
stress on the patching interface are all susceptible to the difference of viscoelasticity. With the increase of the viscoelastic difference, the patching interface is subjected to worse stress state and tends to fracture earlier under cyclic load. 5. 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: (1) 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. (2) 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. (3) 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 104 Hz. (4) The numerical analysis results indicate that the different viscoelastic properties of patching material and original
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