ASSESSMENT OF CRACK SEALING MATERIALS AND TECHNIQUES FOR EPOXY ASPHALT PAVEMENT ON STEEL BRIDGE DECKS

Transcription

1 Chen, Qian and Luo ASSESSMENT OF CRACK SEALING MATERIALS AND TECHNIQUES FOR EPOXY ASPHALT PAVEMENT ON STEEL BRIDGE DECKS Leilei Chen, Ph.D.Candidate Intelligent Transportation System Research Center Southeast University No. Jinxianghe Road Nanjing, 00, P.R. China Tel: ()0- Fax: ()0- leilei@.com Zhendong Qian, Ph.D. (Corresponding Author) Professor Intelligent Transportation System Research Center Southeast University No. Jinxianghe Road Nanjing, 00, P.R. China Tel: ()0- Fax: ()0- qianzd@seu.edu.cn Sang Luo, Ph.D Intelligent Transportation System Research Center Southeast University No. Jinxianghe Road Nanjing, 00, P.R. China Tel: ()0- Fax: ()0- luosangseu@gmail.com Total Words (): Abstract () + Text () + Figures/Tables (0 0=,00) Paper submission for the 0 th Transportation Research Board Annual Meeting. TRB 0 Annual Meeting

2 Chen, Qian and Luo 0 ABSTRACT Cracking is the main distress mechanism for epoxy asphalt concrete pavements on bridge steel decks. It reduces the serviceability and service life of a pavement, and may even reduce the service life of a bridge if it cannot be treated properly. Crack treatments for highway pavement are often copied to treat bridge steel deck pavements for the lack of sealing materials and techniques. This has been found to lead to certain failure. To solve this problem, a chemically cured sealant for epoxy asphalt pavement on bridge steel deck has been developed and evaluated. Viscosity test, tensile test, pull-out test, tensile bond behavior test and shear bond behavior test were conducted in the laboratory, and the newly developed sealant proved to have rather good workability, bulk performance, interfacial performance and cooperative behavior with epoxy asphalt concrete. Monotonic and fatigue beam bending tests were also employed to assess the effect of different sealing techniques. The tests results showed that the bending strengths of sealed beams are approximately the same as undamaged beams while their fatigue lives are significantly shorter than those of the undamaged ones. On the other hand, the completely-fractural beams showed better sealing effect than the partly-fractured beams, and the 0mm 0mm, 0mm 0mm types of sealant configurations led to better sealing effect. Fatigue equations of undamaged beams and sealed beams were developed and they provide ways for the predicting fatigue life of the epoxy asphalt steel deck pavements both before and after sealing. TRB 0 Annual Meeting

3 Chen, Qian and Luo INTRODUCTION Epoxy asphalt concrete has been proved to be an excellent material for steel deck pavement, and it has been widely used in the steel bridge pavements all over the world, especially in China (). However, investigations show that cracking is the major distress of epoxy asphalt pavements (). Once cracks appear on a pavement surface, the pavement structure will become discontinuous. This may lead to further deteriorations like potholes, debonding of the bonding layer and even the rusting of the steel deck, if no appropriate treatments are taken. These secondary distresses may significantly reduce the serviceability and the service life of the bridges. So it is quite necessary to take measures soon after these cracks appearing in the steel deck pavement. Many research studies have conducted treatment on the asphalt pavement crack (-). The problem of cracks is handled in many ways, ranging from pavement maintenance activities, such as surface treatments and crack sealing, to full-scale pavement rehabilitation projects, like overlay and resurfacing. The cost-effectiveness analyses have also been conducted in the Strategic Highway Research Program (SHRP) and the maintenance treatments such as crack sealing were found to be most cost-effective (). However, there is no cure-all sealing material and technique that can meet the requirements of all asphalt pavements, the sealing material and technique are still being researched all over the world. ASTM standard D defines a sealant as a material that has both the adhesive and cohesive properties to form a seal which works as a barrier to prevent liquid and solid penetration into the pavement system. Over the past two decades, a new generation of highly modified crack sealants has been introduced to the market (). These products essentially fall into three families based on their chemical composition and manufacturing process: cold-applied thermoplastic materials, hot-applied thermoplastic materials and chemically cured thermosetting materials (). However, for the lack of effective evaluation, in many cases, the exact cause for sealant failure remains unknown and conversely, successful sealant installation can t be repeated (0). In addition, the sealants mainly aim at treating the cracks in highway pavement. Sealant products for steel deck pavement can rarely be found. As to sealing technique, according to the researches and the practical experiences, sealants can be placed in cracks in numerous configurations, and these configurations can be grouped into four categories: flush-fill, reservoir, over band and combination (reservoir and overband) (). However, few studies about the sealing techniques for crack in steel deck asphalt pavement could be found. The following questions remain to be solved: (a). whether the configurations can fit the crack in steel bridge pavement or not, and (b). which sealant configuration is most effective when using on steel deck. Cracks appear frequently in the steel deck pavement in China due to heavy overloads and severe environment conditions. However, only since recent years has the importance of maintenance of steel deck pavements been recognized, most crack treatments are copies of the highway pavement as mentioned above. The differences between structural condition and the stress mode of the highway pavement and the steel deck pavement lead this copy to certain failure. In this case, the sealant product for cracks in steel deck pavement is urgently needed, and suitable techniques should also be investigated to find out an effective way to install the crack sealants. TRB 0 Annual Meeting

4 Chen, Qian and Luo OBJECTIVE This paper presents a development and assessment of a crack sealant for epoxy asphalt pavement on steel bridge deck. The effect of different crack sealing techniques used on steel deck epoxy asphalt pavement is also evaluated. 0 MATERIALS AND METHODS Sealant Development As mentioned above, cold-applied thermoplastic materials, hot-applied thermoplastic materials and chemically cured thermosetting materials are three main types of crack sealant. The chemically cured thermosetting materials have been widely used in recent years for their good performances. Epoxy asphalt concrete is also a thermosetting material which is mixed with epoxy asphalt and high quality aggregates. Considering the similar performances and the good compatibility with epoxy asphalt mixture, the epoxy resin was selected to develop a chemically cured thermosetting sealant. 0 Selection of Raw Material The primary adhesive and curing agent are two main compositions of a chemically cured sealant. Based on the requirement of the raw material and the results of market investigations, liquid bisphenol-a type epoxy resin was selected as the primary adhesive due to its low initial viscosity. Meanwhile, mixed amines were selected as the cure agent, since no single amine could lead to a good effect. A chemical analysis was conducted to the selected primary adhesive and curing agent, the results showed the epoxy value of the primary adhesive was 0., which means a small initial viscosity. The active hydrogen equivalent of the cure agent was ranging from 0 to 0, which will be used to calculate the mixing percentage of the epoxy resin and the amines as presented below. 0 Mixing percentage The mixing percentage of the primary adhesive and the cure agent can be estimated by equation (): M ca = AHE EV () Where M ca is the mass portion of the cure agent in 00g primary adhesive, AHE is the hydrogen equivalent of the cure agent and EV is the epoxy value of the primary adhesive. So the M ca was calculated to be. to. according to equation (). To determine the accurate mixing percentage of the cure agent and the primary adhesive, the tensile test was employed following ASTM D-0. Tensile specimens with M ca ranging from 0 to 0 were prepared and tested after curing at, as shown in Figure. The test results were listed in Table. It can be found from Table that the tensile strength reached the peak when the mass portion of the cure agent was. However, the fracture elongation of the specimens decreased with the mass portion of the cure agent rising. On the other hand, the tensile strength and the fracture elongation didn t vary a lot when the mass portion of the cure agent changing from 0 to 0. So taking a comprehensive consideration of the tensile strength, the fracture elongation and the operation convenience, the mass portion of the cure agent was determined as 0. It means that the mass ratio of the primary adhesive and the cure agent is :. TRB 0 Annual Meeting

5 Chen, Qian and Luo (a) The tensile test specimens (b) The tensile test equipment FIGURE The tensile test of the developed sealant TABLE Tensile Test Results of the Sealant with Different Mixing Percentages Technical Indexes M ca / mass portion Tensile strength/mpa Fracture elongation /% Epoxy Asphalt Mixture Specimens Materials Preparation Two main materials were involved in the test. The details of preparing for both materials and specimen are introduced below. The binder used in the test was 0-type local epoxy asphalt, which was composed of two components marked as A and B. Component A was the epoxy resin while component B consisted of petroleum asphalt and curing agent. The basic information of the material is given in Table. 0 TABLE Technical Index of 0-Type Local Epoxy Asphalt Technical Indexes Measured Value Criteria Test Method Mass ratio(a B) 00:0 00:0 Tensile strength(mpa, )..0 ASTM D Fracture elongation(%, ) 00 ASTM D Viscosity from 0 to Pa s(min) 0 0 JTJ0-000 Aggregates take about to percentage of the weight in the total mixture. Therefore, careful considerations should be given to the selection of the aggregates. The basalt aggregate and the limestone powder for steel bridge pavement were selected based on the practical engineering. The max aggregate diameter was.mm. The basic information of the aggregate is shown in Table, the gradation curve for the aggregate is shown in Figure. TRB 0 Annual Meeting

6 Chen, Qian and Luo TABLE Technical Index of the Aggregate Material Technical Indexes Measured Criteria Test Method Compressive strength (MPa) 0 0 JTG E-00(T0-00) Los Angeles abrasion value (%)..0 JTG E-00(T0-00) Crushing value (%). JTG E-00(T0-00) #. #. Basalt Apparent density #. Aggregate. JTG E-00(T00-00) (g/cm ) #.00 #. #.0 Water absorption # 0. (%) #.. JTG E-00(T00-00) Limestone Powder Density (g/cm ).0.00 JTG E-00(T0-00) Hydrophilic coefficient (%) 0. JTG E-00(T0-00) Plasticity index (%)..0 JTG E-00(T0-00) FIGURE Designed gradations in the test 0 Specimen Preparation Based on the Marshall mixture design procedure, a.% binder content was determined as the optimum asphalt content. The asphalt mixtures were shaped to slabs and cut to the beams and cubes for the tests. Firstly, the binder and the aggregate were mixed at. After reserved for 0min at 0, a slab specimen was shaped using a wheel rolling machine. Then, after curing for h at 0, the plate was ready to be sawed. Three replicates were prepared for each test. TRB 0 Annual Meeting

7 Chen, Qian and Luo Evaluation Criteria and Method of Material Working Mechanism The working mechanism of the crack sealant should be studied before assessment. The structural condition and the stress mode of the highway pavement vary a lot from those of steel deck pavement (), as shown in Figure. FIGURE Comparison between typical highway pavement and steel deck pavement 0 For the different structural conditions, the maximum tensile stress and strain often appear at the bottom of the surface layer in highway asphalt pavement, while the tensile stress and strain peaks often appear at the top of the surface layer. Therefore, most of the cracks in highway asphalt pavement are down-to-top cracks due to the tensile stress and top-down cracks due to the shearing stress (), while in the steel deck pavement, most of the initial cracks are top-down cracks due to the tensile stress or strain (). So the working mechanisms of the sealant for highway and steel bridge pavement are different, and the evaluation criteria of sealant for steel bridge pavements are thus different from those for highway pavements. 0 Criteria The existing crack sealant often failed either cohesively or adhesively. Cohesive failure, characterized by the fracture of the sealant in the bulk, but still adhered to the crack walls; while on the other hand, the adhesive failure, a debonding near the sealant/asphalt concrete (AC) interface, is much more common. So both the bulk properties and the interfacial properties of the sealant should be evaluated to make sure of its cohesion and adhesion. In addition, the workability is also an important index to the sealant, especially to the chemically cured sealant, it may affect the effect of the crack sealing significantly. So the assessment of the sealant referred to three main items: bulk property, interfacial property and workability. Criteria of crack sealants for steel deck pavement were proposed, as presented in Table, through a comprehensive consideration on the characteristics of steel deck pavement and the performance requirements in some standards listed below: TRB 0 Annual Meeting

8 Chen, Qian and Luo One-component silicone resin sealing material for concrete pavement joints (ASTM D-0), Classification and requirements for building sealants (ISO/DIS ), Sealants for building joint of concrete construction (JC/T-00), Jointing sealants for concrete bridge and other concrete trafficable by vehicles (JC/T -00), Epoxy grouting for concrete crack (JC/T 0-00). TABLE Criteria of Crack Sealants for Steel Deck Pavement Item Content Criteria Test Method workability initial viscosity /mpa s <00 ASTM D operable time /min >0 ASTM D bulk property tensile strength /MPa ASTM D fracture elongation /% 0 ASTM D interfacial property adhesive strength /MPa GB/T 0 Other Method Besides the criteria above, there were two more tests employed here to evaluate the cooperative behavior of the sealant and the AC: tensile bond behavior test and shear bond behavior test, as shown in Figure. 0 Sealant 0 0 P 0 0 AC AC 0 0 P P 0 0 AC AC P Sealant (a) Tensile bond behavior test (b) Shear bond behavior test (c) Bond behavior test machine 0 FIGURE The cooperative behavior test of the sealant and AC 0 As shown in Figure, the sealant was filled into two epoxy asphalt mixture cubes at and then cured. The tensile strength and the shear strength of the specimens would be tested respectively following the test method GB/T. Evaluation Methods of Sealing Technique The beam bending strength test and beam bending fatigue test were adopted to compare the sealing effect of different configurations and to assess the sealing effect of the seal treatment. Firstly, some.mm 0mm mm epoxy asphalt mixture beams were prepared and divided into two subsets: one subset will be keep as is it and the other subset will be cracked artificially later and then sealed with the newly developed sealant. The undamaged beams and sealed beams will be test respectively for comparison. According to the crack conditions, the sealed beams could be divided into two groups: the completely-fractural beams and the partly-fractural beams. The completely-fractural beams are those beams which fracture to two halves while the partly-fractural beams are the beams with TRB 0 Annual Meeting

9 Chen, Qian and Luo 0 a crack that developed to half-depth of beam section. After the beams were shaped, the subset for sealing would be sawed at the midpoint. Six types of the crack channel configurations were prepared for the effect comparison, which were mm mm, 0mm mm, 0mm mm, mm 0mm, 0mm 0mm, 0mm 0mm along longitudinal and vertical directions. Then the cracks were sealed with the developed sealant above. At last, after the sealant was cured, the beam bending strength test was conducted at to determine the maximum bending strength of the beams. The Four point bending fatigue test was then conducted using the Universal Testing Machine at. Controlled-stress loading mode was selected in the fatigue test, the semi-sinusoidal wave was used, and were determined as the stress ratio according to the relative researches (). The control stress could be calculated through multiplying the maximum bending strength of the beams by the stress ratio. Three replicates were prepared for each testing. RESULTS AND DISCUSSION Sealants Workabilities The viscosity test was employed to evaluate the work abilities of the sealant. The viscosity of the sealant was tested using a Brookfield rotational dial viscometer with a rotating speed of 00 rpm ( # ), and the results were recorded in the Figure. 0 FIGURE The viscosity-time curve of the sealant It can be found easily that viscosity of the sealant increasing with the curing time growing. The initial viscosity of the sealant is mpa s, and the viscosity after curing for 0 minutes is 0mPa s. Both of them can meet the criteria of the sealant for steel deck pavement well as listed in Table. TRB 0 Annual Meeting

10 Chen, Qian and Luo 0 Bulk Performance Studies on crack sealants have mostly focused on their bulk properties (). Manufacturers have done much to improve the bulk properties of the sealant over the years. This has resulted to sealants with good cohesion. It also can be found in this study that the sealant has a rather good bulk performance, as listed in Table, the tensile strength and the fracture elongation are 0.MPa and.% respectively, which could satisfy the criteria in Table well. 0 Adhesive Performance The interfacial property of the sealant and the epoxy asphalt mixture was examined through the pull-out test, two groups of total six replicates were examined and the average adhesive strength is.mpa. The test result is much greater than the adhesive requirement of the bonding layer material, which is.mpa (), and it also meet the requirement in Table well. However, on the other hand, the fractural sections in the test are all at the interface between the sealant and the epoxy asphalt mixture, indicating that the interfacial performance is still a weak point of the sealant, so efforts should be made continuously on improving the interfacial performance of the sealant. 0 Cooperative performance The tensile bond behavior test and the shear bond behavior test have been conducted. The average results of the tensile and shear bond behavior are.mpa and.mpa respectively, the fractural sections are both at the interface between the sealant and the epoxy asphalt mixture. It is proved again that the bulk performance of the sealant is much better than the interfacial performance, so more efforts should be taken to improve the interfacial performance of the sealant in the future. Sealing Techniques 0 Beam Bending Strength Test The beam bending strength test was conducted to the undamaged beams and the sealed beams. The average bending strength of the undamaged beams is.mpa. The bending strength of the sealed beams with different channel configurations don t vary a lot, the results are ranging from.mpa to.0mpa, and the average bending strength is.mpa, not much smaller than that of the undamaged beams. A special phenomenon was observed in the tests that the fracture sections were neither at the bulk of the sealant nor at the interface of the sealant and the AC, but at the epoxy asphalt mixture near the formal crack. The reason is might be that the bulk performance and the interfacial performance are larger than the bending strength of the epoxy asphalt mixture at. So it also explained that why the bending strength of the sealed beams are not different from that of the undamaged beams. Beam Bending Fatigue Test The fatigue tests have been conducted at and the results are presented in Figure. Figure (a) shows the test results of sealed beams with different sealing configurations. The tests have been conducted to the completely-fractural beams and partly-fractural beams, with a control stress of.0mpa. It can be indicated from Figure (a) that the completely-fractural beams have a better sealing effect than TRB 0 Annual Meeting

11 Chen, Qian and Luo the partly-fractural beams. The reason is that the completely-fractural beams can be sealed more completely and easily. Though the crack channel may make the sealant fill into the crack deeper, but it s difficult to make sure the sealant filling into the full depth of the crack. In addition, it also can be found from Figure (a) that the 0mm 0mm and 0mm 0mm sealant configurations have better sealing effects. The reason might be the 0mm cut in depth can make the sealant filling deeper into the crack and so bring a better sealing effect than the mm cut. Meanwhile, the 0mm and 0mm cut in width may add the flexibilities of the epoxy asphalt mixture beams, and then leading to a longer fatigue life. 0 (a) Fatigue life of sealed beams with different sealant configurations (b) Comparison between fatigue lives of undamaged beams and sealed beams FIGURE Fatigue test results of different beams under Figure (b) presents the test results of the sealed beams and the undamaged beams under different stress ratios. The sealed beams with 0mm 0mm sealant configuration were selected in the test for its good sealing effect. Figure (b) shows that the fatigue lives of sealed beams are significantly smaller than that of the undamaged beams. It also can be indicated from Figure (b) that the fatigue lives of both two kinds of beams appeared linear law in the logarithmic coordinate system. So Equation () is adopted to determine the relationship between the fatigue life N f and the control stress σ (): TRB 0 Annual Meeting

12 Chen, Qian and Luo N c f K( ) () σ = Assuming K = lg K, and taking logarithm to the both sides of Equation (), it may transfer to lg N = K c lgσ () f Where N f is the fatigue life of the beams, σ is the control stress in the fatigue test, K and c are regression coefficients. After a regressive analysis to the results in Figure (b), the fatigue equations of undamaged beams and the sealed beams can be determined respectively, as Equation () and Equation () lg N =.0lgσ +. f () 0 lg N =.lgσ +. f Equation () and Equation () have provided ways for the life prediction of the epoxy asphalt steel deck pavements before cracking and after sealing. () 0 0 SUMMARIES AND CONCLUSIONS This paper presents an assessment to a newly developed crack sealant for steel deck epoxy asphalt concrete pavement, the effect of different sealing techniques have also been evaluated. The results are listed below: A chemically cured crack sealant for epoxy asphalt steel deck pavement was developed, and the evaluation criteria for the sealant were also determined with reference to the requirement of the steel bridge pavement and other relative standards. The workability, bulk performance, interfacial performance and cooperative performance of the developed sealant were assessed through viscosity test, tensile test, pull-out test, tensile bond behavior test and shear bond behavior test. The test shows that the developed sealant can satisfy the requirements and criteria of the steel deck pavement crack sealant well. The beam bending strength test was employed to evaluate the ultimate bearing capacity of the undamaged epoxy asphalt mixture beams and the sealed beams. The results show that both of the bending fractures occurred at the epoxy asphalt mixture sections, and the bending strength of the sealed beams do not vary a lot from that of undamaged ones at. The fatigue test results of sealed completely-fractural beams and sealed partly-fractural beams show that the sealing effect of completely-fractural beams is better than that of partly-fractural beams. The 0mm 0mm and 0mm 0mm sealant configurations were proved to have better sealing effects than other sealant configurations. The fatigue results of undamaged beams and sealed beams under different control modes show that the fatigue lives of sealed beams are significantly smaller than that of undamaged beams. The fatigue equations of undamaged beams and sealed beams at were regressed, and they have provided ways for the life prediction of the epoxy asphalt steel deck pavements before cracking and after sealing. TRB 0 Annual Meeting

13 Chen, Qian and Luo The pull-off test, cooperative performance test and the fatigue test results all presented that the fracture section were at the interfacial between the sealant and the epoxy asphalt mixture. It can be indicated that the interface between the sealant and the epoxy asphalt mixture are the most possible position of sealing failure. So efforts should still be made to improve the interfacial behavior of the sealant and the epoxy asphalt mixtures. 0 ACKNOWLEDGMENT AND DISCLAIMER This work was undertaken with funding from the Western Transportation Construction Technical Program for Chinese Ministry of Transport (No ). This funding is greatly appreciated. The opinions and conclusions expressed in this paper are those of the authors and do not necessarily represent those of Chinese Ministry of Transport. 0 0 REFERENCES. Gaul. R. A Long Life Pavement for Orthotropic Bridge Decks in China. Proceedings of Selected Papers from the 00 GeoHunan International Conference, 00.. Qian Z.D., G.Y. Han W. Huang, et al. A study on crack fatigue propagation of steel deck pavement based on BOTDA. CHINA CIVIL ENGINEERING JOURNAL. Vol., No. 0, 00, PP. -. Smith, K.L. et al. Innovative Materials and Equipment for Pavement Surface Repairs-Final Report. Volumes I and II. Publication SHRP-M/UFR--0. SHRP, National Research Council, Washington DC:.. Bullard, D. J., R. E. Smith, and T. J. Freeman. Development of a Procedure to Rate the Application of Maintenance Treatments. Publication. SHRP-H-, SHRP, National Research Council, Washington DC:.. Jordan W. and I. Howard. Applicability of Modified Vialit Adhesion Test for Seal Treatment Specifications. Presented at th Annual Meeting of the Transportation Research Board, Washington, D.C., 00. Lee J. and Y. R. Kim. Evaluation of Performance and Cost-Effectiveness of Polymer-Modified Chip Seals. Presented at th Annual Meeting of the Transportation Research Board, Washington, D.C., 00. Smith R., T. Freeman and O. Pendleton. Pavement Maintenance Effectiveness. Publication SHRP-H-, SHRP, National Research Council, Washington DC:.. Al-Qadi, I. L., S.-H. Yang, S. Dessouky, J.-F. Masson, and K. M. McGhee. Low Temperature Characterization of Hot-Poured Crack Sealant Using Modified SHRP Direct Tensile Tester. Presented at th Annual Meeting of the Transportation Research Board, Washington, D.C., 00.. Kelly L. A. Smith. Russell Romine. Manuals of Practice: Materials and Procedures for Sealing and Filling Cracks in Asphalt-Surfaced Pavements. Publication. SHRP-H-, SHRP, National Research Council, Washington DC: 0. Masson, J-F., and M.A Lacasse. A review of adhesion mechanisms at the crack sealant asphalt concrete interface. Durability of Building and Construction Sealants, A. Wolf Ed., RILEM, Paris, TRB 0 Annual Meeting

14 Chen, Qian and Luo 0 000, pp. -.. Chen T.J. Research on the cracking behavior of epoxy asphalt pavement on long span steel bridge. Southeast university, Nanjing R.P. China Zhang Q.S., J.L. Zheng. Y.H. Liu. Cracking mechanism for the semi-rigid based asphalt pavement structure. CHINA CIVIL ENGINEERING JOURNAL. Vol., No.,, PP. -. Liu Z.Q. Research on Key Technology of Long-span Steel Bridges Deck Surfacing Design. Southeast university, Nanjing R.P. China Ghuzlan K, S.H. Carpenter. Energy-derived/damage-based failure criteria for fatigue testing. Transportation research record, vol.. Washington DC: National Research Council; 000. pp. -.. Zanzotto, L. Laboratory Testing of Crack Sealing Materials for Flexible Pavements. Transportation Association of Canada, Ottawa, Canada,.. Huang W. Theory and method of deck paving design for long-span bridges. Beijing: China Construction Industrial Press, 00.. Lin G.P. Research on the Fatigue Life of the Steel Bridge Deck Pavement based on the Fracture Mechanics. Southeast university, Nanjing R.P. China. 00. TRB 0 Annual Meeting