- Email: [email protected]
Assessing pavement interfacial bonding condition
Construction and Building Materials 124 (2016) 85–94
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Assessing pavement interfacial bonding condition Chengchao Guo ⇑, Fuming Wang, Yanhui Zhong Zhengzhou University, No. 100 of Science Road, Zhengzhou, Henan, China
h i g h l i g h t s The modulus and interfacial bonding condition is an order on the deflection, and the strength and bonding condition take same effect on the structure
deformation. With the interfacial friction coefficient decreasing, the deflection all increase, and the difference of interfacial radial stress gets larger. The interfacial friction coefficient has good relationship with the deflection basin index, and SCI/BCI and F1/F2 can be used to reflect the interfacial
bonding condition.
a r t i c l e
i n f o
Article history: Received 2 April 2016 Received in revised form 27 June 2016 Accepted 15 July 2016
Keywords: Deflection basin index Stress difference Interface Bonding condition Assessment
a b s t r a c t When analyzing the pavement structure, the interface condition is always supposed to be completely continuous, but it doesn’t correspond to the reality. To deal with this situation and provide suggestions on pavement construction, the asphalt pavement will be studied further. Taking a practical project as an example, the mechanical response of the structure layer of asphalt pavement has been analyzed by finite element software ABAQUS with different interlayer friction coefficients. It shows that the interlayer friction coefficient has great influence on the surface deflection, the tensile stress at the bottom layer and the stress differences among radial stresses of the interface bonding position. Moreover, the deflection basin index has a good relationship with the interlayer friction coefficient. The relation between deflection basin index and interlayer friction coefficients is established, and a method of assessing the pavement interfacial bonding condition is suggested. Ó 2016 Published by Elsevier Ltd.
1. Foreword As analyzing the pavement structure, the interfacial state of pavement structure is usually supposed to be completely continuous, i.e. ‘‘full friction” or ‘‘full bonding” between layers. However, the material characteristics and the construction qualities are difference, it will result in that the interfacial bonding condition, which is the contact state of the pavement structure layers, may vary from completely continuous to slip. In addition, for built roads, it is inevitable that its layer contact condition will change under the traffic load, temperature, moisture and other external environmental factors. It does not correspond to the assumed full bonding situation, and the result of theoretical analysis is not accurate [11]. In order to improve construction qualities, predict early defect and reduce maintenance and rehabilitation cost, the cohesive effect of interface in road construction should be ensured,
⇑ Corresponding author. E-mail addresses: [email protected], [email protected] (C. Guo). http://dx.doi.org/10.1016/j.conbuildmat.2016.07.064 0950-0618/Ó 2016 Published by Elsevier Ltd.
and the rational evaluation should be performed in road service process [7]. Many methods such as shear box test [12], shear strength [10], modified Leutner test, torque test, impulse hammer test, have been used to test and evaluate the bonding condition between layers. Based on the testing data and theoretical analysis, some factors were put forward to represent its interfacial bonding status of pavement [2]. Salman et al. [8] presented a new fracture-energy based on Interface Bond Test (IBT), which could be used to evaluate the bonding between pavement layers as a practical method. The results of laboratory and field are demonstrated to distinguish the ability between samples produced with different tack coat application rates and modified versus unmodified tack coat materials. Results from the IBT test were also compared with direct tension, and it was found that the trend was similar [8]. The Falling Weight Deflectometer (FWD) is widely used for the pavement defect detection and residual life assessment. A new back-analysis method was suggested to assess the bonding condition between bituminous layers with the structure stiffness from FWD test results [1]. Mehta’s studies showed that, surface
86
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
layer modulus calculated from FWD data could be used to identify the lack of interlayer bonding in pavement, and the effect of slip between two asphalt layers of similar properties would be reflected by the modulus of the top layer lower than that of the bottom layer [13]. In addition, based on the elongated reflections in ground-penetrating radar Lech and Jacek [4], put forward the assessment of the interlayer bonding condition of the bituminous pavement by an impulse high-frequency Ground Penetrating Radar (GPR) [4]. Three-dimensional finite element simulations of the deflection under a standard axle load were carried out, and the pavement layers were considered to be linear elastic and the interface condition complied with three different hypotheses: perfectly bonded, perfectly smooth and frictional, and the numerical result showed that the first derivative of the deflection curve and the curvature radius beneath the wheel load provided suitable indications of the flaw presence and extension [9]. The FWD had become the key technology and equipment in pavement structure evaluation and rehabilitation, and was used to simulate the loading and record the deflections by pavement managements and testing organization all over the world [7]. In fact, the presence of some defects, such as rutting, stripping, cracking or debonding in the layers of flexible pavements, will contribute to the changes in deflection data. The deflection basin index deriving from combination of the different place’s deflections had a good correlation with tensile stress at the bottom of surface layer and compressive stress at the top of the base, so it could be used to reflect pavement layer condition [3], and this avoids singularity and misconvergence of back-calculated modulus. The pavement interfacial bonding condition evaluation by FWD is studied in this paper. The mechanical response of the structure layers under different interlayer friction coefficients is analyzed with software ABAQUS, and the stress and deformation are simulated. Moreover, the deflection basin and deflection basin index under different interlayer friction coefficient are calculated. Therefore, the relation between deflection basin index and the interlayer friction coefficient is established. According to the measured deflection, the deflection basin index is calculated, and based on the relation between the deflection basin index and the interlayer friction coefficient, the interlayer friction coefficient is obtained. Furthermore, samples are cored at selected positions in the tested road, and then shear test by triaxial shearing rheometer is adopted to examine the results, and the assessing method of pavement interfacial bonding condition is developed.
Table 1 Calculated results of different model. Dimensions
The maximum deformation (lm)
The maximum compressive stress (kPa)
The maximum tensile stress (kPa)
5.5.3 5.5.5 8.8.8 10.10.10 12.12.12
278.4 294.5 298.6 300.3 300.4
692.3 685.0 682.5 679.9 679.4
69.6 67.5 64.2 62.1 62.1
2. Finite element analysis of pavement model ABAQUS is common software for calculation and analysis, and its application in road engineering is an important field [5]. This software provides a powerful tool for deeply understanding of road defect problems, and it is taken as a platform of mechanical analysis in this paper. 3. Modeling Based on the actual pavement structure, a 10 layers road structure model is established. In order to reduce the size effect, five models, whose length, width and height are separately 5.5.3, 5.5.5, 8.8.8, 10.10.10 and 12.12.12, are selected to check the structural response under the standard axle load. The results are shown in Table 1, in which the maximum deformation and the maximum compressive stress are acting at loading direction, and the maximum tensile stress is vertical to loading action direction. According to the calculated data in Table 1, when the model size is greater than 10.10.10, the result is almost the same, so considering the calculation cost, the 10.10.10 is adopted as the computed model. The cube model is chosen in this paper, and the thickness of pavement structure is 1.36 m, and so is 8.64 m for the subgrade, which is shown in Fig. 1. In the model, X is width direction, and Y is driving direction, and Z is depth direction. Assumed that the subgrade bottom is completely fixed, the whole model boundary has no displacement at Y direction, and also has no displacement at X direction. The subdivision technique of linear hexahedron element C3D8R is used to grid the model, and the mesh generation is shown in Fig. 1.
Fig. 1. Model and mesh.
87
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94 Table 2 Parameter of pavement structure. Layer number
Basic parameters
Elastic modulus (MPa)
Density (kg/m3)
Poisson’s ratio
1 2 3 4 5 6 7 8 9 10
4 cm fine-grained asphalt concrete (AC-13) 6 cm medium-grained asphalt concrete (AC-16) 8 cm coarse-grained asphalt concrete (AC-25) 19 cm cement stabilized gravel base (top) 19 cm cement stabilized gravel base (bottom) 20 cm 12% cement stabilized soil cushion 20 cm 6% cement stabilized soil subbase 20 cm 4% cement soil treatment layer (top) 20 cm 4% cement soil treatment layer (bottom) Subgrade
2000 1800 1400 2500 2500 400 150 90 90 40
2400 2400 2400 2390 2390 1840 1790 1790 1880 1740
0.25 0.25 0.25 0.25 0.25 0.3 0.3 0.35 0.35 0.35
Table 3 Sensors layout.
Distance from the load center (m)
D1
D2
D3
D4
D5
D6
D7
D8
D9
0.000
0.203
0.305
0.457
0.610
0.914
1.219
1.524
1.829
Table 4 Parameter of pavement layers. Modulus(MPa)
Maximum modulus and fully integrated Maximum modulus and completely slip Minimum modulus and fully integrated Minimum modulus and completely slip
Frictional coefficient
Top layer
Middle layer
Bottom layer
Cement stabilized base
2000 2000 1400 1400
1800 1800 1200 1200
1400 1400 800 800
2500 2500 1600 1600
The material parameters are selected from design value, which is shown in Table 2. In simulation, the layout of sensors is listed in Table 3, and the dynamic load from Dynatest 8000 FWD is applied. The pavement interfacial bonding condition is determined by the friction coefficient between the middle layer and the bottom layer, and the numerical value is from 0.05 to 1 which characterizes its different contact status. 4. Response under different contact conditions and structural strengths The structural strength is represented by layers modulus and contact condition is reflected by interfacial frictional coefficient. The modulus of top layer, middle layer, bottom layer, cement
1 0.05 1 0.05
stabilized base and frictional coefficient between middle layer and bottom layer are shown in Table 4, and Table 2 can be referred to about other parameter. The computed deflection basin is shown in Fig. 2, from which it can be seen that the interfacial bonding condition and structural strength have great effects on the central deflection and deflection basin. The central deflection is selected to compare and analyze, which is shown in Table 5. In the case of maximum modulus being fixed, the amplitude of variation of central deflection is 34.6 lm with friction coefficient from 0.05 to 1, and the change rate is 23.9%. In the case of minimum modulus being fixed, the amplitude of variation of central deflection is 43.0 lm with friction coefficient from 0.05 to 1, and the change rate is 24.6%.
Fig. 2. Deflection basin under different structural strength and contact condition.
88
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
Table 5 Central deflections under different strengths and contact conditions.
Fully integrated Completely slip
Maximum modulus
Minimum modulus
145.1 lm 179.7 lm
175.2 lm 218.2 lm
In the case of fully integrated being fixed, the amplitude of variation of central deflection is 30.1 lm with modulus from maximum to minimum, and the rate change is 20.8%. In the case of completely slip being fixed, the amplitude of variation of central deflection is 38.5 lm with modulus from maximum to minimum, and the change rate is 21.4%. It shows that the interfacial bonding condition and structural strength have similar effects on the deflection at an order of magnitude. In order to accurately determine the actual working condition before pavement is maintained and treated, not only should be the bearing capacity of each layer from back-calculated modulus, but also the bonding condition between pavement layers should be tested and evaluated.
Fig. 4. Comparison of the tensile stress at surface layer bottom.
5. Comparative analysis of different boning condition between layers Assumed that the other layers are completely continuous, and the friction coefficient between middle layer and the bottom layer of pavement is variable, the pavement structure response is analyzed. In the same way, assumed that the other layers are completely continuous, and the friction coefficient between bituminous layer and base is variable, the pavement structure response is analyzed. The central vertical elastic deflection, the bottom layer tensile stress, the maximum compressive stress and interlayer radial stress difference are calculated as shown in Figs. 3–6 respectively. Except that the maximum compressive stress curve is not regular, it can be seen that the central vertical elastic deflection, the bottom layer tensile stress and the interlayer radial stress all have good correlation with the friction coefficient. The same conclusion can be drawn between bituminous layer and base, the maximum compressive stress has nothing to do with the friction coefficient, but the central vertical elastic deflection, the bottom layer tensile stress and the interlayer radial stress difference all have good correlation with the friction coefficient. From Figs. 3–5, the interfacial bonding condition has effects on deflection and tensile stress. For central vertical elastic deflection
Fig. 5. Comparison of the interlaminar radial stress difference.
Fig. 6. Comparison of the maximum compressive stress.
Fig. 3. Comparison of the central vertical (z) elastic deflection.
and interlayer radial stress difference, the interfacial bonding condition between bituminous layer and base plays the major role, while fortensile stress, the condition between middle layer and bottom layer of pavement have major impact. With the increase of friction coefficient, the curve is gradually approaching, and it has small effects on the above parameters. Particularly, when the friction coefficient is above 0.7, the central deflection and interlayer radial stress difference are almost the same, so it has little influence on deformation. As the contact state between layers is close to fully continuous, the structural response is nearly the same and very small, so the bonding condition between middle and bottom layer of pavement or between bituminous layer and base does not have to be considered.
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
6. The relationship between deflection basin index and friction coefficient of surface layer The use of nondestructive deflection testing has become an integral part of the structural evaluation and rehabilitation process of pavements in recent years. When pavement experiences some forms of distress, pavement deflections and shape of deflection basins along a project will change because of the differences in the condition of pavement layers. Thus, researchers should identify and evaluate methods for assessing pavement layer condition based on deflection measurements and develop better methods to relate deflection data to layer and interlayer condition [13]. It is shown that the ratio of F1/F2 has a good correlation with the interlayer condition. From the above calculated result, assumed that the different friction coefficient between middle layer and bottom layer of pavement varies from 0.05 to 1, the corresponding deflection basin index can be calculated. The area indexes AI1 = (D1 + D2)/(2D1) and AI2 = (D2 + D3)/(2D1), shape factors F1 = (D1 D3)/D2 and F2 = (D2 D4)/D3, surface curvature index SCI = D1 D2, base curvature index BCI = D2 D3 and the ratio of AI1/AI2, F1/F2, SCI/
89
BCI are calculated. The curves of ratio of AI1/AI2, F1/F2 and SCI/ BCI versus friction coefficient are shown in Figs. 7–9, which show that the ratio of F1/F2 and SCI/BCI have good correlations with the friction coefficient between surface layers.
7. The relationship between deflection basin index and frictional coefficient between bituminous layer and base In the same way, the different friction coefficient between bituminous layer and base varying from 0.05 to 1 is supposed, and the corresponding deflection basin index AI1, AI2, F1, F2, SCI, BCI and the ratio of AI1/AI2, F1/F2, SCI/BCI are calculated, and the curves of ratio of AI1/AI2, F1/F2 and SCI/BCI versus friction coefficient was shown in Figs. 10–12, which show that the ratio of AI1/AI2, F1/F2 and SCI/BCI all have good correlations with the friction coefficient bituminous layer and base. Taken together, the F1/F2 and SCI/BCI have good correlations with the frictional coefficient, they can be used to represent interfacial contact condition. Further, they may indicate bonding condition. However, this needs to be studied further.
Fig. 7. Ratio of AI1/AI2 under different friction coefficient of the surface layer.
Fig. 8. Ratio of F1/F2 under different friction coefficient of the surface layer.
Fig. 9. Ratio of SCI/BCI under different friction coefficient of the surface layer.
90
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
Fig. 10. Ratio of AI1/AI2 under different friction coefficient between surface layer and base.
Fig. 11. Ratio of F1/F2 under different friction coefficient between surface layer and base.
Fig. 12. Ratio of SCI/BCI under different friction coefficient between surface layer and base.
8. Interface bonding condition evaluation experiment In order to verify the above mentioned method, a experiment about interfacial bonding condition between structure layers is carried out. For a new built project, whose structure is the same as the model in Table 2, after the surface layer is paved and compacted, the deflection test is conducted by FWD, which is listed in Table 6. Subsequently, all the asphalt layers are taken out, and the coring samples are carefully sent to the laboratory. The specimens are made to meet the test requirements, which are shown in Fig. 13. Then the samples are taken by the shear test to measure its shear strength with triaxial shearing rheometer, which is illustrated in Fig. 14. So compared with the friction coefficient, the matching between shearing strength and structural bonding degree is used to confirm. In the process of the test, the average shearing stress of the specimen interface increases with time, and decreases once reaching the peak. This reflects the shearing strength of the specimen interface, and the test result is shown in Table 7. Based on the measured deflection and the deflection basin index calculation method, the values of F1, F2 and F1/F2 are calculated respectively. According to the foregoing relationship between
Table 6 Measured deflection basin. Number
1 2 3 4 5 6 7 8 9 10 11 12
Deflection D1
D2
D3
D4
D5
D6
D7
D8
D9
149.4 123.3 144.8 107.3 134.8 149.0 139.3 120.1 140.3 133.4 117.3 151.7
120.1 92.6 112.8 88.9 111.8 110.4 98.1 94.0 101.3 102.2 93.8 103.6
104.5 84.3 97.6 83.4 103.6 93.0 90.8 86.6 89.8 88.0 88.9 85.3
102.7 76.5 95.8 79.3 99.9 89.8 78.8 79.8 81.6 84.3 82.0 80.7
99.0 70.1 89.8 76.5 94.9 86.6 68.8 72.0 67.4 75.2 73.8 76.5
98.1 67.4 84.3 67.4 89.8 83.0 66.9 60.5 59.6 69.7 68.8 69.7
90.8 62.3 80.7 66.9 79.8 78.8 62.3 55.0 55.5 61.0 60.5 61.4
84.3 59.6 77.0 66.5 71.0 75.6 60.0 52.3 51.3 57.3 55.5 56.8
77.0 58.7 69.2 51.8 61.4 64.6 41.7 46.8 39.0 52.7 50.0 51.3
F1/F2 and the friction coefficient, the interfacial friction coefficient between middle layer and bottom layer of the coring sample can be calculated, which is listed in Table 8. Based on the shearing strength in Table 7 and the interface friction coefficient in Table 8, the relationship between shearing
91
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
Fig. 13. Coring samples and the tested specimens.
Fig. 14. Tested triaxial shearing rheometer.
Table 7 Tested shearing strength. Number
1
2
3
4
5
6
7
8
9
10
11
12
Shearing strength (MPa)
0.222
0.216
0.373
0.266
0.408
0.403
0.279
0.145
0.229
0.187
0.293
0.355
strength and friction coefficient is established, which is shown in Fig. 15. It can be seen from the Fig. 15, there are two outliers, which measured shearing strength do not correspond to the calculated friction coefficient. The reasons are likely to be that the coring machine disturbs the specimen which can not represent the real interfacial bonding condition, or the shearing plane does not completely coincide with the actual interface. By weeding out the two abnormal data, the rest is shown in Fig. 16. The friction coefficient
Table 8 Calculated deflection basin index and friction coefficient. Number
F1
F2
F1/F2
Friction coefficient
1 2 3 4 5 6 7 8 9 10 11 12
0.374 0.421 0.419 0.268 0.279 0.528 0.495 0.336 0.498 0.444 0.300 0.642
0.167 0.190 0.174 0.115 0.115 0.172 0.212 0.228 0.219 0.203 0.144 0.269
2.244 2.212 2.410 2.323 2.422 2.291 2.335 2.171 2.269 2.186 2.282 2.387
0.544 0.443 0.885 0.728 0.904 0.661 0.752 0.232 0.609 0.329 0.641 0.846
between layers calculated from deflection basin index is consistent with the measured shearing strength, and with the increase of friction coefficient between layers, the shearing strength also enlarges, which means better bonding condition. Therefore, the ratio between F1 and F2 can be used to indicate the interfacial bonding status. 9. Field case study In order to verify the availability of the above mentioned method, a case study of FWD test on semi-rigid base pavement is discussed in Shenzhen, China. The defects, such as debonding or stripping between bitumen layer and base or between middle layer and bottom layer by FWD test in field, is detected mainly here. The tested highway is located in hilly and mountainous areas in south of China, which were open to traffic in May 1999. After years of service, there are some defects, such as rut, crack, pothole, sink, in pavement surface or interior, and it severely affects the driving comfortability and safety. Before the pavement is repaired and rebuilt, the FWD and GPR are used to evaluate its condition, including the type, scale, and degree of deep defect. The tested pavement structure is as following: (1) Fine-grained modified asphalt concrete (AC-13C): 4 cm. (2) Medium-grained modified asphalt concrete (AC-20C): 6 cm.
92
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
Fig. 15. Curve of measured shearing strength versus friction coefficient.
Fig. 16. Modified curve of measured shearing strength versus friction coefficient.
Table 9 Bonding state of pavement structural layers. Item
Top-middle
None defect in surface
Number Ratio (%) Number Ratio (%) Number Ratio (%)
Some defect in surface
Surface-base
Base-subbase
Poor
Good
Poor
Good
Poor
Good
Poor
40 90.9 32 48.5 72 65.5
4 9.1 34 51.5 38 34.5
37 84.1 25 37.9 62 56.4
7 15.9 41 62.1 48 43.6
24 54.5 6 9.1 30 27.3
20 45.5 60 90.9 80 72.7
9 20.5 2 3.0 11 10.0
35 79.5 64 97.0 99 90.0
Cumulative Frequency
Total
Middle-bottom
Good
F1/F2 Fig. 17. Cumulative distribution of F1/F2 in the surveyed road.
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
93
Table 10 Comparison of judgment and coring sample.
position
deflection basin index F1/F2 SCI/BCI
sample description
photo
K2903+120
4.4
1.8
There is unbonding between surface layer and base.
K2886+080
1.2
0.7
There is poor bonding between surface layer and base, and there is loose at interface.
K2886+240
3.7
0.9
The surface layer is completely broken, and the throughout crack exists in base,The poor bonding is in surface layer and base.
K2887+340
3.2
1.0
There is poor bonding between surface layer and base.
K2895+360
3.1
1.3
There is excellent bonding between surface layer and base.
K2898+780
6.4
2.4
The pavement structure is integral, and the better bonding state is between surface layer and base.
0.7
The top surface layer structure is integral, and the medium and bottom layer is loose, and the poor bonding state is between the layers.
K2886+680
(3) (4) (5) (6)
2.7
Coarse-grained asphalt concrete (ATB-30):10 cm. Emulsified asphalt seal coat: 1 cm. Cement stabilized gravel base: 36 cm. Low cement stabilized subbase: 18 cm.
pavement structures, the SCI/BCI or F1/F2 should not be a fixed value, but the interfacial bonding condition can be estimated from them, and the quantitative results will further be studied. 10. Conclusions
Based on the aforementioned discussion, the interfacial bonding condition can be evaluated by GPR or FWD, and the deflection basin index is used to reflect bonding state between the layers. In fact, for this road, it is found that the poor interfacial bonding from coring, which is listed in Table 9. It is seen that there is poor bonding in each interlayer, the top-middle is 34.5%, the middlebottom is 43.6%, the surface-base is 72.7%, and the base-subbase is 90.0%. From top to bottom, the pavement structural bonding gets increasingly poorer. From the further statistical analysis of this road, it is found that when the surface-base bonding is poor, the ratio is 72.7%, and the corresponding deflection basin parameters F1/F2 is 1.7. So the value 1.7 is taken as the criteria for judgement. If F1/F2 is more than 1.7, the interfacial bonding condition is regarded as being better, on the contrary, it is taken as worse, which is showed in Fig. 17. The deflection test result of the downlink carriageway of this road, the calculated deflection basin index, the sample description and photo are shown in Table 10. The coring also reveals that the value can be used to estimate bonding condition. Despite that the central deflection is not pretty larger, there are some defects in surface layer or base or poor bonding between the layers in some samples. If SCI/BCI or F1/F2 is relatively small, the poor bonding condition between the layers appears. For different
The deflection depends on the modulus and friction coefficient, and the strength and interlayer bonding have the similar effect on the structure deformation. As the friction coefficient between layers decreases, the central deflection and all the deflections of other position increase, and the difference of interfacial radial stress also gets large. The friction coefficient between layers calculated from deflection basin index is consistent with the measured shearing strength, and with the increase of friction coefficient between layers, the shearing strength also enlarges, which means better bonding condition. The friction coefficient between layers has a good relationship with the deflection basin index. Above all, the deflection basin index SCI/BCI and F1/F2 have good correlations with the friction coefficient. SCI/BCI and F1/F2 can be used to reflect the interfacial bonding condition. If SCI/BCI or F1/F2 is relatively smaller, there is poorer bonding condition between the layers. Acknowledgements This article is supported by Program for Innovative Research Team (in Science and Technology) in University of Henan Province
94
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
(No.: 14IRTSTHN027), and also is supported by Research of Fundamental and Frontier Technology of Henan Province (No.: 162300410210).
References [1] Bachar Al Hakim, Lam Wah Cheung, Robert J. Armitage, Use of FWD data for prediction of bonding between pavement layers, Int. J. Pavement Eng. 1 (1) (2000) 49–59, http://dx.doi.org/10.1080/10298439908901696. [2] De-cheng Feng, Song Yu, Study of test and evaluation method on interfacial combining state of asphalt pavement, J. Harbin Inst. Technol. 39 (4) (2007) (in Chinese). [3] Y.R. Kim, Assessing Pavement Layer Condition Using Deflection Data, TRB NCHRP Project, 2001, pp. 10–48. [4] Lech Krysin´ski, Jacek Sudyka, Typology of reflections in the assessment of the interlayer bonding condition of the bituminous pavement by the use of an impulse high-frequency ground-penetrating radar, Nondestr. Test. Eval. 27 (3) (2012) 219–227, http://dx.doi.org/10.1080/10589759.2012.674525. [5] Gong-yun Liao, Xiao-ming Huang, Application of Finite Element Software ABAQUS in Road Engineering, Dongnan University Press, Nanjing, 2008 (in Chinese).
[7] S. Nazarian, K.M. Boodapati, Pavement-falling weight deflectometer interaction using dynamic finite-element analysis, Transportation Research Record No.1482 (1995) 33–43. [8] Salman Hakimzadeh, Nathan Abay Kebede, William G. Buttlar, Sarfraz Ahmed, Marvin Exline, Development of fracture-energy based interface bond test for asphalt concrete, Road Mater. Pavement Des. 13 (Suppl. 1) (2012) 76–87. Special Issue: Papers from the 87th Association of Asphalt Paving Technologists’ Annual Meeting, April 1–4, 2012. [9] Savuth Chea, Juan Martinez, Using surface deflection for detection of interface damage between pavement layers, Road Mater. Pavement Des. 9 (Suppl. 1) (2008) 359–372, http://dx.doi.org/10.1080/14680629.2008.9690174. Special Issue: Special Issue on Asphalt Technology (EATA 2008). [10] G.A. Sholar, G.C. Page, J.A. Musselman, P.B. Upshaw, H.L. Moseley, Preliminary investigation of a test method to evaluate bond strength of bituminous tack coats, J. Assoc. Asphalt Pavement Technol. 73 (2004) 771–806. [11] Kai Su, Analysis of Cutting-slippage between the Base and Surface of Asphalt Pavement on Mountain Road (Master’s thesis), Changan University, Changan, China, 2004 (in Chinese). [12] J. Uzan, M. Livneh, Y. Eshed, Investigation of adhesion properties between asphaltic-concrete layers, J. Asphalt Paving Technol. 47 (1978) 495–521. [13] Yusuf A. Mehta, Nusrat Siraj, Evaluation of Interlayer Bonding In HMA Pavements, in: Wisconsin Highway Research Program # 0092- 02-13. Report No. WHRP 07-07, 2007.
Contents lists available at ScienceDirect
Construction and Building Materials journal homepage: www.elsevier.com/locate/conbuildmat
Assessing pavement interfacial bonding condition Chengchao Guo ⇑, Fuming Wang, Yanhui Zhong Zhengzhou University, No. 100 of Science Road, Zhengzhou, Henan, China
h i g h l i g h t s The modulus and interfacial bonding condition is an order on the deflection, and the strength and bonding condition take same effect on the structure
deformation. With the interfacial friction coefficient decreasing, the deflection all increase, and the difference of interfacial radial stress gets larger. The interfacial friction coefficient has good relationship with the deflection basin index, and SCI/BCI and F1/F2 can be used to reflect the interfacial
bonding condition.
a r t i c l e
i n f o
Article history: Received 2 April 2016 Received in revised form 27 June 2016 Accepted 15 July 2016
Keywords: Deflection basin index Stress difference Interface Bonding condition Assessment
a b s t r a c t When analyzing the pavement structure, the interface condition is always supposed to be completely continuous, but it doesn’t correspond to the reality. To deal with this situation and provide suggestions on pavement construction, the asphalt pavement will be studied further. Taking a practical project as an example, the mechanical response of the structure layer of asphalt pavement has been analyzed by finite element software ABAQUS with different interlayer friction coefficients. It shows that the interlayer friction coefficient has great influence on the surface deflection, the tensile stress at the bottom layer and the stress differences among radial stresses of the interface bonding position. Moreover, the deflection basin index has a good relationship with the interlayer friction coefficient. The relation between deflection basin index and interlayer friction coefficients is established, and a method of assessing the pavement interfacial bonding condition is suggested. Ó 2016 Published by Elsevier Ltd.
1. Foreword As analyzing the pavement structure, the interfacial state of pavement structure is usually supposed to be completely continuous, i.e. ‘‘full friction” or ‘‘full bonding” between layers. However, the material characteristics and the construction qualities are difference, it will result in that the interfacial bonding condition, which is the contact state of the pavement structure layers, may vary from completely continuous to slip. In addition, for built roads, it is inevitable that its layer contact condition will change under the traffic load, temperature, moisture and other external environmental factors. It does not correspond to the assumed full bonding situation, and the result of theoretical analysis is not accurate [11]. In order to improve construction qualities, predict early defect and reduce maintenance and rehabilitation cost, the cohesive effect of interface in road construction should be ensured,
⇑ Corresponding author. E-mail addresses: [email protected], [email protected] (C. Guo). http://dx.doi.org/10.1016/j.conbuildmat.2016.07.064 0950-0618/Ó 2016 Published by Elsevier Ltd.
and the rational evaluation should be performed in road service process [7]. Many methods such as shear box test [12], shear strength [10], modified Leutner test, torque test, impulse hammer test, have been used to test and evaluate the bonding condition between layers. Based on the testing data and theoretical analysis, some factors were put forward to represent its interfacial bonding status of pavement [2]. Salman et al. [8] presented a new fracture-energy based on Interface Bond Test (IBT), which could be used to evaluate the bonding between pavement layers as a practical method. The results of laboratory and field are demonstrated to distinguish the ability between samples produced with different tack coat application rates and modified versus unmodified tack coat materials. Results from the IBT test were also compared with direct tension, and it was found that the trend was similar [8]. The Falling Weight Deflectometer (FWD) is widely used for the pavement defect detection and residual life assessment. A new back-analysis method was suggested to assess the bonding condition between bituminous layers with the structure stiffness from FWD test results [1]. Mehta’s studies showed that, surface
86
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
layer modulus calculated from FWD data could be used to identify the lack of interlayer bonding in pavement, and the effect of slip between two asphalt layers of similar properties would be reflected by the modulus of the top layer lower than that of the bottom layer [13]. In addition, based on the elongated reflections in ground-penetrating radar Lech and Jacek [4], put forward the assessment of the interlayer bonding condition of the bituminous pavement by an impulse high-frequency Ground Penetrating Radar (GPR) [4]. Three-dimensional finite element simulations of the deflection under a standard axle load were carried out, and the pavement layers were considered to be linear elastic and the interface condition complied with three different hypotheses: perfectly bonded, perfectly smooth and frictional, and the numerical result showed that the first derivative of the deflection curve and the curvature radius beneath the wheel load provided suitable indications of the flaw presence and extension [9]. The FWD had become the key technology and equipment in pavement structure evaluation and rehabilitation, and was used to simulate the loading and record the deflections by pavement managements and testing organization all over the world [7]. In fact, the presence of some defects, such as rutting, stripping, cracking or debonding in the layers of flexible pavements, will contribute to the changes in deflection data. The deflection basin index deriving from combination of the different place’s deflections had a good correlation with tensile stress at the bottom of surface layer and compressive stress at the top of the base, so it could be used to reflect pavement layer condition [3], and this avoids singularity and misconvergence of back-calculated modulus. The pavement interfacial bonding condition evaluation by FWD is studied in this paper. The mechanical response of the structure layers under different interlayer friction coefficients is analyzed with software ABAQUS, and the stress and deformation are simulated. Moreover, the deflection basin and deflection basin index under different interlayer friction coefficient are calculated. Therefore, the relation between deflection basin index and the interlayer friction coefficient is established. According to the measured deflection, the deflection basin index is calculated, and based on the relation between the deflection basin index and the interlayer friction coefficient, the interlayer friction coefficient is obtained. Furthermore, samples are cored at selected positions in the tested road, and then shear test by triaxial shearing rheometer is adopted to examine the results, and the assessing method of pavement interfacial bonding condition is developed.
Table 1 Calculated results of different model. Dimensions
The maximum deformation (lm)
The maximum compressive stress (kPa)
The maximum tensile stress (kPa)
5.5.3 5.5.5 8.8.8 10.10.10 12.12.12
278.4 294.5 298.6 300.3 300.4
692.3 685.0 682.5 679.9 679.4
69.6 67.5 64.2 62.1 62.1
2. Finite element analysis of pavement model ABAQUS is common software for calculation and analysis, and its application in road engineering is an important field [5]. This software provides a powerful tool for deeply understanding of road defect problems, and it is taken as a platform of mechanical analysis in this paper. 3. Modeling Based on the actual pavement structure, a 10 layers road structure model is established. In order to reduce the size effect, five models, whose length, width and height are separately 5.5.3, 5.5.5, 8.8.8, 10.10.10 and 12.12.12, are selected to check the structural response under the standard axle load. The results are shown in Table 1, in which the maximum deformation and the maximum compressive stress are acting at loading direction, and the maximum tensile stress is vertical to loading action direction. According to the calculated data in Table 1, when the model size is greater than 10.10.10, the result is almost the same, so considering the calculation cost, the 10.10.10 is adopted as the computed model. The cube model is chosen in this paper, and the thickness of pavement structure is 1.36 m, and so is 8.64 m for the subgrade, which is shown in Fig. 1. In the model, X is width direction, and Y is driving direction, and Z is depth direction. Assumed that the subgrade bottom is completely fixed, the whole model boundary has no displacement at Y direction, and also has no displacement at X direction. The subdivision technique of linear hexahedron element C3D8R is used to grid the model, and the mesh generation is shown in Fig. 1.
Fig. 1. Model and mesh.
87
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94 Table 2 Parameter of pavement structure. Layer number
Basic parameters
Elastic modulus (MPa)
Density (kg/m3)
Poisson’s ratio
1 2 3 4 5 6 7 8 9 10
4 cm fine-grained asphalt concrete (AC-13) 6 cm medium-grained asphalt concrete (AC-16) 8 cm coarse-grained asphalt concrete (AC-25) 19 cm cement stabilized gravel base (top) 19 cm cement stabilized gravel base (bottom) 20 cm 12% cement stabilized soil cushion 20 cm 6% cement stabilized soil subbase 20 cm 4% cement soil treatment layer (top) 20 cm 4% cement soil treatment layer (bottom) Subgrade
2000 1800 1400 2500 2500 400 150 90 90 40
2400 2400 2400 2390 2390 1840 1790 1790 1880 1740
0.25 0.25 0.25 0.25 0.25 0.3 0.3 0.35 0.35 0.35
Table 3 Sensors layout.
Distance from the load center (m)
D1
D2
D3
D4
D5
D6
D7
D8
D9
0.000
0.203
0.305
0.457
0.610
0.914
1.219
1.524
1.829
Table 4 Parameter of pavement layers. Modulus(MPa)
Maximum modulus and fully integrated Maximum modulus and completely slip Minimum modulus and fully integrated Minimum modulus and completely slip
Frictional coefficient
Top layer
Middle layer
Bottom layer
Cement stabilized base
2000 2000 1400 1400
1800 1800 1200 1200
1400 1400 800 800
2500 2500 1600 1600
The material parameters are selected from design value, which is shown in Table 2. In simulation, the layout of sensors is listed in Table 3, and the dynamic load from Dynatest 8000 FWD is applied. The pavement interfacial bonding condition is determined by the friction coefficient between the middle layer and the bottom layer, and the numerical value is from 0.05 to 1 which characterizes its different contact status. 4. Response under different contact conditions and structural strengths The structural strength is represented by layers modulus and contact condition is reflected by interfacial frictional coefficient. The modulus of top layer, middle layer, bottom layer, cement
1 0.05 1 0.05
stabilized base and frictional coefficient between middle layer and bottom layer are shown in Table 4, and Table 2 can be referred to about other parameter. The computed deflection basin is shown in Fig. 2, from which it can be seen that the interfacial bonding condition and structural strength have great effects on the central deflection and deflection basin. The central deflection is selected to compare and analyze, which is shown in Table 5. In the case of maximum modulus being fixed, the amplitude of variation of central deflection is 34.6 lm with friction coefficient from 0.05 to 1, and the change rate is 23.9%. In the case of minimum modulus being fixed, the amplitude of variation of central deflection is 43.0 lm with friction coefficient from 0.05 to 1, and the change rate is 24.6%.
Fig. 2. Deflection basin under different structural strength and contact condition.
88
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
Table 5 Central deflections under different strengths and contact conditions.
Fully integrated Completely slip
Maximum modulus
Minimum modulus
145.1 lm 179.7 lm
175.2 lm 218.2 lm
In the case of fully integrated being fixed, the amplitude of variation of central deflection is 30.1 lm with modulus from maximum to minimum, and the rate change is 20.8%. In the case of completely slip being fixed, the amplitude of variation of central deflection is 38.5 lm with modulus from maximum to minimum, and the change rate is 21.4%. It shows that the interfacial bonding condition and structural strength have similar effects on the deflection at an order of magnitude. In order to accurately determine the actual working condition before pavement is maintained and treated, not only should be the bearing capacity of each layer from back-calculated modulus, but also the bonding condition between pavement layers should be tested and evaluated.
Fig. 4. Comparison of the tensile stress at surface layer bottom.
5. Comparative analysis of different boning condition between layers Assumed that the other layers are completely continuous, and the friction coefficient between middle layer and the bottom layer of pavement is variable, the pavement structure response is analyzed. In the same way, assumed that the other layers are completely continuous, and the friction coefficient between bituminous layer and base is variable, the pavement structure response is analyzed. The central vertical elastic deflection, the bottom layer tensile stress, the maximum compressive stress and interlayer radial stress difference are calculated as shown in Figs. 3–6 respectively. Except that the maximum compressive stress curve is not regular, it can be seen that the central vertical elastic deflection, the bottom layer tensile stress and the interlayer radial stress all have good correlation with the friction coefficient. The same conclusion can be drawn between bituminous layer and base, the maximum compressive stress has nothing to do with the friction coefficient, but the central vertical elastic deflection, the bottom layer tensile stress and the interlayer radial stress difference all have good correlation with the friction coefficient. From Figs. 3–5, the interfacial bonding condition has effects on deflection and tensile stress. For central vertical elastic deflection
Fig. 5. Comparison of the interlaminar radial stress difference.
Fig. 6. Comparison of the maximum compressive stress.
Fig. 3. Comparison of the central vertical (z) elastic deflection.
and interlayer radial stress difference, the interfacial bonding condition between bituminous layer and base plays the major role, while fortensile stress, the condition between middle layer and bottom layer of pavement have major impact. With the increase of friction coefficient, the curve is gradually approaching, and it has small effects on the above parameters. Particularly, when the friction coefficient is above 0.7, the central deflection and interlayer radial stress difference are almost the same, so it has little influence on deformation. As the contact state between layers is close to fully continuous, the structural response is nearly the same and very small, so the bonding condition between middle and bottom layer of pavement or between bituminous layer and base does not have to be considered.
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
6. The relationship between deflection basin index and friction coefficient of surface layer The use of nondestructive deflection testing has become an integral part of the structural evaluation and rehabilitation process of pavements in recent years. When pavement experiences some forms of distress, pavement deflections and shape of deflection basins along a project will change because of the differences in the condition of pavement layers. Thus, researchers should identify and evaluate methods for assessing pavement layer condition based on deflection measurements and develop better methods to relate deflection data to layer and interlayer condition [13]. It is shown that the ratio of F1/F2 has a good correlation with the interlayer condition. From the above calculated result, assumed that the different friction coefficient between middle layer and bottom layer of pavement varies from 0.05 to 1, the corresponding deflection basin index can be calculated. The area indexes AI1 = (D1 + D2)/(2D1) and AI2 = (D2 + D3)/(2D1), shape factors F1 = (D1 D3)/D2 and F2 = (D2 D4)/D3, surface curvature index SCI = D1 D2, base curvature index BCI = D2 D3 and the ratio of AI1/AI2, F1/F2, SCI/
89
BCI are calculated. The curves of ratio of AI1/AI2, F1/F2 and SCI/ BCI versus friction coefficient are shown in Figs. 7–9, which show that the ratio of F1/F2 and SCI/BCI have good correlations with the friction coefficient between surface layers.
7. The relationship between deflection basin index and frictional coefficient between bituminous layer and base In the same way, the different friction coefficient between bituminous layer and base varying from 0.05 to 1 is supposed, and the corresponding deflection basin index AI1, AI2, F1, F2, SCI, BCI and the ratio of AI1/AI2, F1/F2, SCI/BCI are calculated, and the curves of ratio of AI1/AI2, F1/F2 and SCI/BCI versus friction coefficient was shown in Figs. 10–12, which show that the ratio of AI1/AI2, F1/F2 and SCI/BCI all have good correlations with the friction coefficient bituminous layer and base. Taken together, the F1/F2 and SCI/BCI have good correlations with the frictional coefficient, they can be used to represent interfacial contact condition. Further, they may indicate bonding condition. However, this needs to be studied further.
Fig. 7. Ratio of AI1/AI2 under different friction coefficient of the surface layer.
Fig. 8. Ratio of F1/F2 under different friction coefficient of the surface layer.
Fig. 9. Ratio of SCI/BCI under different friction coefficient of the surface layer.
90
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
Fig. 10. Ratio of AI1/AI2 under different friction coefficient between surface layer and base.
Fig. 11. Ratio of F1/F2 under different friction coefficient between surface layer and base.
Fig. 12. Ratio of SCI/BCI under different friction coefficient between surface layer and base.
8. Interface bonding condition evaluation experiment In order to verify the above mentioned method, a experiment about interfacial bonding condition between structure layers is carried out. For a new built project, whose structure is the same as the model in Table 2, after the surface layer is paved and compacted, the deflection test is conducted by FWD, which is listed in Table 6. Subsequently, all the asphalt layers are taken out, and the coring samples are carefully sent to the laboratory. The specimens are made to meet the test requirements, which are shown in Fig. 13. Then the samples are taken by the shear test to measure its shear strength with triaxial shearing rheometer, which is illustrated in Fig. 14. So compared with the friction coefficient, the matching between shearing strength and structural bonding degree is used to confirm. In the process of the test, the average shearing stress of the specimen interface increases with time, and decreases once reaching the peak. This reflects the shearing strength of the specimen interface, and the test result is shown in Table 7. Based on the measured deflection and the deflection basin index calculation method, the values of F1, F2 and F1/F2 are calculated respectively. According to the foregoing relationship between
Table 6 Measured deflection basin. Number
1 2 3 4 5 6 7 8 9 10 11 12
Deflection D1
D2
D3
D4
D5
D6
D7
D8
D9
149.4 123.3 144.8 107.3 134.8 149.0 139.3 120.1 140.3 133.4 117.3 151.7
120.1 92.6 112.8 88.9 111.8 110.4 98.1 94.0 101.3 102.2 93.8 103.6
104.5 84.3 97.6 83.4 103.6 93.0 90.8 86.6 89.8 88.0 88.9 85.3
102.7 76.5 95.8 79.3 99.9 89.8 78.8 79.8 81.6 84.3 82.0 80.7
99.0 70.1 89.8 76.5 94.9 86.6 68.8 72.0 67.4 75.2 73.8 76.5
98.1 67.4 84.3 67.4 89.8 83.0 66.9 60.5 59.6 69.7 68.8 69.7
90.8 62.3 80.7 66.9 79.8 78.8 62.3 55.0 55.5 61.0 60.5 61.4
84.3 59.6 77.0 66.5 71.0 75.6 60.0 52.3 51.3 57.3 55.5 56.8
77.0 58.7 69.2 51.8 61.4 64.6 41.7 46.8 39.0 52.7 50.0 51.3
F1/F2 and the friction coefficient, the interfacial friction coefficient between middle layer and bottom layer of the coring sample can be calculated, which is listed in Table 8. Based on the shearing strength in Table 7 and the interface friction coefficient in Table 8, the relationship between shearing
91
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
Fig. 13. Coring samples and the tested specimens.
Fig. 14. Tested triaxial shearing rheometer.
Table 7 Tested shearing strength. Number
1
2
3
4
5
6
7
8
9
10
11
12
Shearing strength (MPa)
0.222
0.216
0.373
0.266
0.408
0.403
0.279
0.145
0.229
0.187
0.293
0.355
strength and friction coefficient is established, which is shown in Fig. 15. It can be seen from the Fig. 15, there are two outliers, which measured shearing strength do not correspond to the calculated friction coefficient. The reasons are likely to be that the coring machine disturbs the specimen which can not represent the real interfacial bonding condition, or the shearing plane does not completely coincide with the actual interface. By weeding out the two abnormal data, the rest is shown in Fig. 16. The friction coefficient
Table 8 Calculated deflection basin index and friction coefficient. Number
F1
F2
F1/F2
Friction coefficient
1 2 3 4 5 6 7 8 9 10 11 12
0.374 0.421 0.419 0.268 0.279 0.528 0.495 0.336 0.498 0.444 0.300 0.642
0.167 0.190 0.174 0.115 0.115 0.172 0.212 0.228 0.219 0.203 0.144 0.269
2.244 2.212 2.410 2.323 2.422 2.291 2.335 2.171 2.269 2.186 2.282 2.387
0.544 0.443 0.885 0.728 0.904 0.661 0.752 0.232 0.609 0.329 0.641 0.846
between layers calculated from deflection basin index is consistent with the measured shearing strength, and with the increase of friction coefficient between layers, the shearing strength also enlarges, which means better bonding condition. Therefore, the ratio between F1 and F2 can be used to indicate the interfacial bonding status. 9. Field case study In order to verify the availability of the above mentioned method, a case study of FWD test on semi-rigid base pavement is discussed in Shenzhen, China. The defects, such as debonding or stripping between bitumen layer and base or between middle layer and bottom layer by FWD test in field, is detected mainly here. The tested highway is located in hilly and mountainous areas in south of China, which were open to traffic in May 1999. After years of service, there are some defects, such as rut, crack, pothole, sink, in pavement surface or interior, and it severely affects the driving comfortability and safety. Before the pavement is repaired and rebuilt, the FWD and GPR are used to evaluate its condition, including the type, scale, and degree of deep defect. The tested pavement structure is as following: (1) Fine-grained modified asphalt concrete (AC-13C): 4 cm. (2) Medium-grained modified asphalt concrete (AC-20C): 6 cm.
92
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
Fig. 15. Curve of measured shearing strength versus friction coefficient.
Fig. 16. Modified curve of measured shearing strength versus friction coefficient.
Table 9 Bonding state of pavement structural layers. Item
Top-middle
None defect in surface
Number Ratio (%) Number Ratio (%) Number Ratio (%)
Some defect in surface
Surface-base
Base-subbase
Poor
Good
Poor
Good
Poor
Good
Poor
40 90.9 32 48.5 72 65.5
4 9.1 34 51.5 38 34.5
37 84.1 25 37.9 62 56.4
7 15.9 41 62.1 48 43.6
24 54.5 6 9.1 30 27.3
20 45.5 60 90.9 80 72.7
9 20.5 2 3.0 11 10.0
35 79.5 64 97.0 99 90.0
Cumulative Frequency
Total
Middle-bottom
Good
F1/F2 Fig. 17. Cumulative distribution of F1/F2 in the surveyed road.
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
93
Table 10 Comparison of judgment and coring sample.
position
deflection basin index F1/F2 SCI/BCI
sample description
photo
K2903+120
4.4
1.8
There is unbonding between surface layer and base.
K2886+080
1.2
0.7
There is poor bonding between surface layer and base, and there is loose at interface.
K2886+240
3.7
0.9
The surface layer is completely broken, and the throughout crack exists in base,The poor bonding is in surface layer and base.
K2887+340
3.2
1.0
There is poor bonding between surface layer and base.
K2895+360
3.1
1.3
There is excellent bonding between surface layer and base.
K2898+780
6.4
2.4
The pavement structure is integral, and the better bonding state is between surface layer and base.
0.7
The top surface layer structure is integral, and the medium and bottom layer is loose, and the poor bonding state is between the layers.
K2886+680
(3) (4) (5) (6)
2.7
Coarse-grained asphalt concrete (ATB-30):10 cm. Emulsified asphalt seal coat: 1 cm. Cement stabilized gravel base: 36 cm. Low cement stabilized subbase: 18 cm.
pavement structures, the SCI/BCI or F1/F2 should not be a fixed value, but the interfacial bonding condition can be estimated from them, and the quantitative results will further be studied. 10. Conclusions
Based on the aforementioned discussion, the interfacial bonding condition can be evaluated by GPR or FWD, and the deflection basin index is used to reflect bonding state between the layers. In fact, for this road, it is found that the poor interfacial bonding from coring, which is listed in Table 9. It is seen that there is poor bonding in each interlayer, the top-middle is 34.5%, the middlebottom is 43.6%, the surface-base is 72.7%, and the base-subbase is 90.0%. From top to bottom, the pavement structural bonding gets increasingly poorer. From the further statistical analysis of this road, it is found that when the surface-base bonding is poor, the ratio is 72.7%, and the corresponding deflection basin parameters F1/F2 is 1.7. So the value 1.7 is taken as the criteria for judgement. If F1/F2 is more than 1.7, the interfacial bonding condition is regarded as being better, on the contrary, it is taken as worse, which is showed in Fig. 17. The deflection test result of the downlink carriageway of this road, the calculated deflection basin index, the sample description and photo are shown in Table 10. The coring also reveals that the value can be used to estimate bonding condition. Despite that the central deflection is not pretty larger, there are some defects in surface layer or base or poor bonding between the layers in some samples. If SCI/BCI or F1/F2 is relatively small, the poor bonding condition between the layers appears. For different
The deflection depends on the modulus and friction coefficient, and the strength and interlayer bonding have the similar effect on the structure deformation. As the friction coefficient between layers decreases, the central deflection and all the deflections of other position increase, and the difference of interfacial radial stress also gets large. The friction coefficient between layers calculated from deflection basin index is consistent with the measured shearing strength, and with the increase of friction coefficient between layers, the shearing strength also enlarges, which means better bonding condition. The friction coefficient between layers has a good relationship with the deflection basin index. Above all, the deflection basin index SCI/BCI and F1/F2 have good correlations with the friction coefficient. SCI/BCI and F1/F2 can be used to reflect the interfacial bonding condition. If SCI/BCI or F1/F2 is relatively smaller, there is poorer bonding condition between the layers. Acknowledgements This article is supported by Program for Innovative Research Team (in Science and Technology) in University of Henan Province
94
C. Guo et al. / Construction and Building Materials 124 (2016) 85–94
(No.: 14IRTSTHN027), and also is supported by Research of Fundamental and Frontier Technology of Henan Province (No.: 162300410210).
References [1] Bachar Al Hakim, Lam Wah Cheung, Robert J. Armitage, Use of FWD data for prediction of bonding between pavement layers, Int. J. Pavement Eng. 1 (1) (2000) 49–59, http://dx.doi.org/10.1080/10298439908901696. [2] De-cheng Feng, Song Yu, Study of test and evaluation method on interfacial combining state of asphalt pavement, J. Harbin Inst. Technol. 39 (4) (2007) (in Chinese). [3] Y.R. Kim, Assessing Pavement Layer Condition Using Deflection Data, TRB NCHRP Project, 2001, pp. 10–48. [4] Lech Krysin´ski, Jacek Sudyka, Typology of reflections in the assessment of the interlayer bonding condition of the bituminous pavement by the use of an impulse high-frequency ground-penetrating radar, Nondestr. Test. Eval. 27 (3) (2012) 219–227, http://dx.doi.org/10.1080/10589759.2012.674525. [5] Gong-yun Liao, Xiao-ming Huang, Application of Finite Element Software ABAQUS in Road Engineering, Dongnan University Press, Nanjing, 2008 (in Chinese).
[7] S. Nazarian, K.M. Boodapati, Pavement-falling weight deflectometer interaction using dynamic finite-element analysis, Transportation Research Record No.1482 (1995) 33–43. [8] Salman Hakimzadeh, Nathan Abay Kebede, William G. Buttlar, Sarfraz Ahmed, Marvin Exline, Development of fracture-energy based interface bond test for asphalt concrete, Road Mater. Pavement Des. 13 (Suppl. 1) (2012) 76–87. Special Issue: Papers from the 87th Association of Asphalt Paving Technologists’ Annual Meeting, April 1–4, 2012. [9] Savuth Chea, Juan Martinez, Using surface deflection for detection of interface damage between pavement layers, Road Mater. Pavement Des. 9 (Suppl. 1) (2008) 359–372, http://dx.doi.org/10.1080/14680629.2008.9690174. Special Issue: Special Issue on Asphalt Technology (EATA 2008). [10] G.A. Sholar, G.C. Page, J.A. Musselman, P.B. Upshaw, H.L. Moseley, Preliminary investigation of a test method to evaluate bond strength of bituminous tack coats, J. Assoc. Asphalt Pavement Technol. 73 (2004) 771–806. [11] Kai Su, Analysis of Cutting-slippage between the Base and Surface of Asphalt Pavement on Mountain Road (Master’s thesis), Changan University, Changan, China, 2004 (in Chinese). [12] J. Uzan, M. Livneh, Y. Eshed, Investigation of adhesion properties between asphaltic-concrete layers, J. Asphalt Paving Technol. 47 (1978) 495–521. [13] Yusuf A. Mehta, Nusrat Siraj, Evaluation of Interlayer Bonding In HMA Pavements, in: Wisconsin Highway Research Program # 0092- 02-13. Report No. WHRP 07-07, 2007.