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In UK standard, the joint filling can use materials mixed on site or premixed material。 The material is placed in layers and each layer is compacted。 Preheating the vertical surface of block-out may be an effective way to insure perfect adhesion along the inter- face [30]。 Hot-air fans are recommended to use for preheating the interface and to remove weak zones by the strong hot-air wind。 The application of bonding agents (primers and tack coats) with or- ganic solvents was found to be not necessary [28]。 Adhesion test can be used to examine the effect of various bonding agents。
To avoid stress concentrations and cracks, friction between the steel plate and the joint material should be reduced to a minimum。 The weak interface bonding is helpful for the joint moments, but it will reduce the resistance to traffic loadings。 The joint binders are usually applied in hot and in fluid condition, with temperatures up to 180–190 °C [7,8,10]。 However, installation practice indicates that the full control of installation temperature becomes difficult。
Over-heating of the binder results in polymer decomposition and thus influences the binder’s performance。 Low installation temper- ature may lead to high binder viscosity, poor fluidity, and thus in- crease the air voids in the joint。 Infrared thermometers and digital thermometers could be used for temperature control purpose。 However, these thermometers should be carefully calibrated [14,20]。
In order to avoid an extensive deformation, APJs should be in- stalled in an ambient air temperature of 5–10 °C。 The joint should be protected from traffic until the material was cooled to 52 °C or after broadcast stone placement is complete。 Compaction of the joint filling material will allow opening the joint to traffic within a few hours [10]。
5。 Structural improvements
Tension failures control the joint design and performance。 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 [17,18]。 It indicates that the joint geometry can be optimized to reduce the interface stresses or the tensile stresses within the joint filling materials。 Table 5 lists some results ob- tained from finite element analysis that aims for improved joint geometry。
Reid performed a study to investigate the effect of joint geom- etry on the interface stress between pavement and joint [18]。 Stan- dard joint, trapezoidal joint and sinusoidal joint were compared。 Simulation results showed that high stress concentration occurred at the top of the joint-pavement interface of standard joint under bridge movements or traffic loading。 Trapezoidal joint design was useful to reduce the stress at the top surface of the joint-pavement interface when subjected to bridge movements, but it may lead to high stresses under traffic loads。 Sinusoidal joint showed a wider distribution of stresses under bridge movements, however, it has a positive effect to reduce the interface stress during tire passage。 It indicated that the application of trapezoidal joint and sinusoidal joint may lead to improved performance。 But for a complex joint geometry, in practice they are not easy to install。
Finite element analysis showed that the joint-pavement inter- face was subjected to stress reversal when wheel tire passed from one side to the other。 This may lead to the possibility of fatigue fail- ure of interface bonding。 This possibility increases when trucks axles on the joint accelerate or brake sharply。 The subjected inter- facial stresses can be relaxed or increased depending on the visco- elastice response of joint material [15,16]。 It implies that binder optimization based on relaxation behavior and adhesion is also important to prevent interface debonding under repeated traffic loads。 It also showed that the magnitude of the interface stress de- creased as the joint angle between the plug-pavement interface and the vertical was increased from 0° to 45°。