50 mm motion on a bridge located in Cheyenne, Wyoming。 Cyclic joint movement

than  75 mm  [8]。  In  the UK,  the aggregate  used  for  APJs  shall be  graded,  washed

and drained crushed rock from the trade group basalt, dolerite, gabbro or granite。

simulation tests were done at 25 °C, 4。4 °C   and

—7 °C to correspond to  seasonal

The aggregate grading shall give a controllable void content when placed in the joint。 For this reason, the aggregate gradation is specified [7]。 In Switzerland, gap- graded aggregate with a maximum size of 22 mm is used [14]。 Mogawer performed a gradation analysis of the aggregates received from the APJ producers。 The test re- sults indicated that the mineral filler passing 0。075 mm sieve was less than 1。0%。Two gradations were determined: one is a maximum size of 12。5 mm, 92% passing 9。5 mm and 7。5% passing 4。75 mm; The other gradation is a maximum size of 25 mm, 96。6% passing 19 mm, 24。9% passing 12。5 mm and 4。2% passing 9。5 mm。 APJ cores were drilled to determine the mixture composition including asphalt con- tent and aggregate gradation。 Asphalt content was found in two levels: 20% and 40%。 The content of mineral filler, that is, material passing 0。075 mm was also in two levels: 5% and 10% dependent on asphalt content。 More information on the aggregate gradation obtained from drilled cores can be found in [33]。

3。3。 Joint mixtures

In many countries, what is being specified and subjected to quality control tests are the constituent materials including the binder and aggregates, but not the final joint mixture。 In most cases, APJs are being used and installed following the man- ufacturers’ recommendations。 These recommendations were developed through application experience and incorporate little engineering assessment。 An APJ usu- ally consists of two or more layers of different mixtures。 The mixture used for the bottom layer is a more binder-rich mixture compared to the one used for the top layer [30]。 APJs shows strongly temperature and time dependence。 It becomes soft at high temperatures in summer and thus is vulnerable to rutting  and  shoving un- der traffic load。 However, it becomes stiff and brittle at low temperatures in winter and thus results in loss of relaxation and flexibility to deal with joint movements。 Rapid temperature changes are more likely to accumulate thermal stress that leads to joint cracking。 In order to evaluate the performance of joint mixture, common laboratory  testing  includes rutting, relaxation,  direct  tensile  and  bending tests。

3。3。1。 Low temperature properties

Yu and Li conducted a research on improving performance of polymer modified APJs by optimum combination of polymer, binder and aggregates [30]。 Mixtures prepared using three different binders with a binder to aggregate ratio 1:4 showed a bending strain at failure ranging from 0。48% to 0。63% at —10 °C。 Indirect tensile test indicated the failure strain was in the order of 0。8%。 Reducing temperature re- sulted in lower values of bending strain at failure。 Increasing the binder content, for example a binder to aggregate ratio of 1:3。5, only led to a slight improvement in low-temperature property。

Mo reported that APJs containing high content of crumb rubber powder and granules exhibited a bending strain at failure ranging from 0。7% to 2。6% at —10 °C depending on the amount of rubber granules。 The replacement of part of mineral aggregates by rubber granules can form a new stone–rubber skeleton, which allows large deformations occur compared to simple traditional stone skeleton [34]。 Mix- ture (binder:aggregate = 1:3) prepared by BJ200-green binder, Prismo, UK, showed a bending strain at failure of 2–3% [44]。 It was reported that BEJs worked well when the joint materials had a yield strain above 1%。 As the yield strain was between 0。1% and 0。3%, the joints were susceptible to cold weather failure [9,11]。 From bending test  results  on  transitional  asphalt  mixtures,  the  flexural  strain  at  failure     at