Joint filling materials are bitumen-rich mixtures and thus APJs show strongly temperature and time dependence。 In summer, they are vulnerable to rutting and shoving under traffic load while they become stiff and brittle in winter and thus result in loss of relaxa- tion and flexibility to bear with joint movements。 Rutting test that is commonly used for traditional asphalt mixtures can be used to investigate permanent deformation resistance。 Test results ob- tained from model mobile load simulator as well as full-scale accelerated pavement tests indicated that APJs can have a good rutting resistance comparable with traditional asphalt mixtures。 Three-point bending tests indicated that bending strains at failure ranged from 0。5% to 3% at low temperatures。 However, low-tem- perature joint movement simulation testing showed that the ten- sile strains of joint materials could be in a range from 5% to 10% at a joint movement of 25 mm。 Minimum material tensile failure strain should be established by considering joint movement and extremely low temperature。 Furthermore, relaxation behavior, for example, the time to relax to 75% of initial load, should be tested to avoid thermal stress  accumulation。文献综述

The interface between the pavement and joint and the edges of the steel gap plates are two critical locations within an APJ that are especially vulnerable to cracking as a result of bridge movement or traffic loads。 Finite element modeling has been demonstrated to be a useful tool for geometry optimization as well as material perfor- mance evaluation。 Insight into improved joint structure and mate- rials can be obtained。 The simulation results can be well validated by using joint movement simulation test。 The embedment of springs within the joint filling material allows obtaining a homoge- neous longitudinal strain distribution。 This increases the effective length of the joint and leads to the development of APJs with larger moments。

Apart from material quality, workmanship in installing the joint has been frequently reported to be the most important to ensure the good performance of the joint。 APJs require careful construc-

tion, installation and quality control。 For this reason, comprehen- sive staff training is needed to properly handle materials, equipments and test apparatus。

Acknowledgements

Thanks Dr。 Rien Huurman for the discussions on modeling work and material testing。 Mr。 Jan Voskuilen at DVS, Rijkswaterstaat, is appreciated for sending the Dutch project reports of Silent and Durable Road Expansion Joints。 Thanks also go to Prof。 M。N。 Partl and Mr。 S。 Hean at EMPA for providing their publications and re- ports on APJs。 The work was supported by the Fundamental Re- search Funds for the Central Universities (2012-IV-024), Doctoral Fund of Ministry of Education of  China  (20110143120013)  and the Scientific Research Foundation for the Returned Overseas Chi- nese Scholars, State Education Ministry。 Financial support by Pro- ject on the Integration of Industry, Education and Research of Guangdong Province and Ministry of Education (No。 2012B091000162) is also  acknowledged。

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