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L。 Mo et al。 / Construction and Building Materials 45 (2013) 106–114 111
Flat stamp penetration field test was applied to evaluate permanent deformation of APJs after installation in field。 The static penetration test with a 500 mm2 flat stamp under a static load of 400 N according to Swiss guidelines was carried out。 Two tests were reported with stamp penetrations of 5。0 mm at 14 °C and 8。4 mm at 18 °C after a loading time of 40 min [14]。 The test results indicated that vibration compaction was useful to increase penetration resistance。 Furthermore, the Model Mobile Load Sim-
ulator (MMLS) was also used。 The tire pressure was 0。6 MPa and test temperature was 35 °C controlled by a temperature chamber。 The test results indicated that joint mate- rials had a comparable permanent resistance with the adjacent Guss asphalt。 Four rutting tests done by MMLS showed that three of them had rut depths of about
3。5 mm after 15,000 passes at 30 °C; the remained test had a rut depth of 6。5 mm [14]。 Bramel used Georgia loaded wheel test to evaluate the rutting resistance of three different APJ materials at a temperature of 36 °C and a loading pressure of 0。69 MPa。 The obtained results indicated that the total rut depths were 8–14 mm after 4000 cy- cles。 This did not meet the acceptable rutting performance of a total rutting depth of less than 7 mm after 8000 cycles for traditional asphalt mixtures [9,11]。 Rutting test (60 °C and 0。69 MPa tire pressure) on BJ-200 green joint mixture showed a total rut depth of 13。4 mm after 10,000 cycles [44]。 It can be concluded that APJs are softer than asphalt pavements and rutting test that is the commonly used for asphalt mix- ture would be useful as a comparative test。
Huurman and Moraal executed full-scale accelerated pavement tests to evalu- ate the performance of five APJ systems by means of LINTRACK test facility [23,24]。 The joint systems were subjected to repeated loads by a wide base tire in- flated to 0。85 MPa at a speed of 18 Km/h。 The test section was heated by using infra- red heating system so that the surface temperature of the joint filling materials was controlled at a range of 30–40 °C。 After 100,000 repetitions, the traditional standard APJ showed an absolute rut depth of 39。9 mm, while the tested four innovative joint systems had a rut depth ranging from 8。1 mm to 34。4 mm。 The simulated service life indicated by LINTRACK testing showed that the innovative joint systems had an expected rutting life not less than 10 years [23,24]。
4。 Construction issues
The typical installation procedures of an APJ include block-out preparation, cleaning and drying, sealing and bridging the joint gap, coating the joint block-out, and filling joint by asphalt mix- tures。 This joint mixture can be mixed in three different ways [14]:
(1) Hot non-coated aggregate is placed into the joint and the APJ binder is then added。 This is most practical and widely used。 The hot aggregates can be spread easily in the mold and pro- vide a good aggregate skeleton in the APJ filling。 Dusty aggregates are avoided because of the poor coating with the binder。
(2) Hot aggregate is pre-coated with the APJ binder in a mixer and then spread into the joint and then the APJ binder is added。 This ensures good coating of the aggregate with the binder, however it is more difficult to spread and will require compacting to promote the aggregate interlock。
(3) Hot non-coated aggregates are dumped into the joint and mixed in-place with APJ binder。 The APJ filling is mixed in small batches, thus promoting quick temperature decreasing and producing difficulties in spreading the material。 This may result in cavities and over time in blistering。