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Introduction An asphalt plug joint APJ is a type of bridge expansion joint that is becoming popular with some state departments of trans-portation in the United States Transportation Research Board 2003. It is made of flexible asphalt concrete usually comprising 20% asphalt and 80% aggregates by weight. As shown in Fig. 1,the APJ material is placed into a prepared space between pave-ments permitting a smooth ride across the joint while accommo-dating thermal movements of the bridge deck at the same time.The Bridge Joint Association 2003 indicated that the typical size of an APJ is 500 mm wide and 100 mm deep and its allowable movement without cracking at the lowest operating design tem-perature is 20 mm. ASTM D6297-01 ASTM 2007 specifies that the standard minimum blockout dimensions for an APJ are 50500 mm, and the maximum allowable movement is 25 mm.By providing a smooth transition across an expansion joint, an APJ offers better bridge surface flatness than other types of joints.Simplicity and low cost of its installation are additional important advantages of APJs Qian et al. 2000. On the other hand, APJs frequently suffer from premature failure, sometimes as early as 6 months after installation, even though they are generally expected to have a life of about 6–7 years. Barnard and Cuninghame1998 pointed out the overall cost of replacing a damaged APJ 23566
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can exceed the cost of a new APJ installation in the United King-
dom. According to a survey by Bramel et al. 1999, 41 states in
the United States have installed APJs. Of those, 23 states still use
APJs for either new construction or retrofit, without geographic
preference. Bramel et al. 1999 reported that premature failure
was one of the important problems hindering the widespread use
of APJs in the United States.
The various failure modes in APJs can be categorized into two
classes: cracking related failures and rutting. According to Bramel
et al. 1999, two locations within an APJ are especially vulner-
able to cracking as a result of bridge movement: 1 the interface
between the pavement and joint; and 2 the edges of the steel gap
plates. Based on the assumption that APJ failures occur as a result
of traffic-related fatigue, Reid et al. 1998 suggested two alter-
native geometries that are less prone to fatigue than the standard
configuration. Subsequently, Qian et al. 2000 proposed an opti-
mum shape for one of the alternative designs suggested by Reid
et al. 1998. These two studies provided good insight into the
reasons for early failure in APJs. However, both studies made
assumptions that limit their generality: 1 only traffic loading
was considered in the analysis, i.e., loading due to bridge thermal
movement was not considered; 2 the effects of viscosity and
temperature dependency of the APJ were not considered in the
material model; and 3 the stress concentration at the end of the
gap plate was not considered. Through detailed finite-element
analysis, Park et al. 2010 showed that stress and strain demands
under traffic loading are higher at the interface between the pave-
ment and joint than at the edges of the steel gap plates, while
demands due to thermal movement are higher at the latter than the
former. The study also showed that: 1 the effect of temperature
on traffic-related stress demands is small; 2 thermal movement
causes stress demands that are most critical when tensile move-
ment occurs corresponding to the coldest temperature, but are
negligible when compressive movement occurs corresponding to
rising temperature; and 3 intentionally debonding the interfacebetween the gap plate and asphalt can significantly reduce stress
and strain demands.
The goal of the study reported in this paper is to utilize the
models developed in Park et al. 2010 to develop an improved