Construction Technology Of Asphalt Mixture Surface Layer

Construction preparation

permeable layer and sticky layer

(1) paving asphalt mixture surface layer before, should be sprayed in the grass-roots surface permeable layer of oil, in the permeable layer of oil completely penetrate into the grass-roots level before paving surface layer. Construction should be based on the type of grass-roots selection of good permeability of liquid asphalt, emulsified asphalt for permeable oil.

(2) double or multi-layer type hot mix hot paving asphalt mixture layer should be sprayed between the sticky layer of oil, or in cement concrete pavement, asphalt stabilized gravel base, the old asphalt pavement paving asphalt mixture, should also be in the existing structure, curbs and inspection wells and other structures and asphalt mixture layer connection surface spraying sticky layer of oil.

(3) “Urban Road Construction and Quality Acceptance Specification” CJJ1-2008 stipulates that the asphalt mixture surface layer shall not be constructed in rain, snow and the maximum ambient temperature below 5 ℃.

Transport and fabric

(1) in order to prevent the asphalt mixture bonded carriage plate, loading materials should be sprayed before a thin layer of isolating agent or anti-bonding agent. Asphalt mixture in transport should be covered with tarpaulin insulation, rain and pollution prevention.

(2) The tyres of the truck shall not be contaminated with soil and other dirt that may pollute the road, and the asphalt mixture found during construction shall not be used if it does not meet the construction temperature requirements or if it is lumped together and has been rained on.

(3) Transport and fabric should be arranged according to the construction programme, and there should be enough trucks waiting in front of the paver; for high-grade roads, it is advisable to wait for more than 5 trucks before starting paving.

(4) The material truck should wait in neutral at 100-300mm in front of the paver, be slowly pushed forward by the paver and gradually unload the material to avoid hitting the paver. Each discharge must be poured clean, such as residual material should be removed in a timely manner to prevent hard caking.

Paving operations

Mechanical construction

(1) Hot mix asphalt mixture should be paved with asphalt pavers. The receiving hopper of the paver should be coated with a thin layer of isolating agent or anti-binder.

(2) paving high-grade road asphalt mixture, 1 paver paving width should not exceed 6m, usually using 2 or more pavers staggered 10 ~ 20m before and after the echelon way synchronous paving, between the two widths should be 30 ~ 60mm width of the lap, and should avoid the lane wheel track belt, the upper and lower lap position should be staggered 200mm above.

(3) The paver should be preheated in advance 0.5 to 1h before work so that the screed is not less than 100°C. Paving should choose a suitable screed vibrating or tamping device vibration frequency and amplitude, in order to improve the initial compaction of the pavement.

(4) The paver must pave slowly, evenly and continuously without interruption, without changing speed or stopping in the middle to improve the leveling and reduce the segregation of the asphalt mixture. Paving speed should be controlled in the range of 2-6m/min. When the asphalt mixture is found to appear obvious segregation, waves, cracks, drag marks, should analyse the causes, to be eliminated in a timely manner.

(5) The paver should adopt automatic levelling. The lower layer should be guided by wire rope for elevation control. The upper layer should be paved with a balance beam or sliding shoe and supplemented by a thickness control method.

(6) The minimum paving temperature of the hot mix asphalt mixture is determined by testing according to the temperature, the surface temperature of the lower layer, the paving thickness and the type of asphalt mixture.

(7) The loose paving factor of the asphalt mixture shall be determined according to test paving and test pressing. The thickness of the paving layer, the road arch and the cross slope should be checked at any time, and supplemented by the total amount of asphalt mix used and the area to check the average thickness

Manual construction

(1) Without mechanical paving situation, manual paving operations can be used.

(2) half of the construction, the side of the road should be pre-set baffle; paving should be buckled shovel fabric, not shovel far throw.

Compaction and jointing

Compaction forming

(1) according to the temperature of the completed asphalt mixture paving strict control of the initial pressure, re-compacting, final pressure (including forming) timing. The maximum thickness of the compacted layer should not be greater than 100mm, and each layer should meet the requirements of compaction and flatness.

(2) The speed of rolling should be slow and even, and the speed of rolling by the roller should be in accordance with the specification (see Table 2K311041-2)

(3) The rolling temperature of the roller should be determined by test pressing according to the type of asphalt and asphalt mixture, roller, temperature, layer thickness and other factors.

(4) The initial pressure should be done with a steel wheel roller for 1 to 2 times. Rolling should be done with the driving wheel of the roller facing the paver, from the outside to the centre, and from the low to the high on super high sections and ramps. The recompacting should start immediately after the initial rolling and should not be stopped at will. The total length of the rolled section should not exceed 80m.

(5) dense graded asphalt mixture recompression should be preferred to the use of heavy tyre roller for rolling, in order to increase the impermeability of the pavement, its total mass should not be less than 25t. adjacent rolling belt should overlap 1/3 ~ 1/2 wheel width.

For coarse aggregate-based mixture, it is appropriate to give priority to the use of vibratory rollers to recompact (thickness should be greater than 30mm), the layer thickness is larger when it is appropriate to use high-frequency large amplitude, the thickness is thin when it is appropriate to use low amplitude, in order to prevent aggregate fragmentation.

When using a three-wheeled steel cylinder roller, the total mass should not be less than 12t, and the adjacent rolling belt should overlap the 1/2 wheel width of the rear wheel and should not be less than 200mm.

(6) The final pressure should be carried out immediately after the recompression. The final compaction should be carried out with a two-wheeled steel cylinder roller or a vibratory roller with the vibrations turned off, and should not be rolled less than 2 times until there are no visible wheel marks.

(7) To prevent the asphalt mixture from sticking to the wheel, the roller wheel can be painted with isolating agent or anti-bonding agent, it is strictly forbidden to brush diesel oil; it can also be sprayed with a small amount of surfactant mist water to the roller wheel.

(8) The roller must not turn, turn around, add water or stay on the unrolled and formed section. In the day forming the road surface, shall not park all kinds of mechanical equipment or vehicles, shall not scatter minerals, oil and debris.

Joints

(1) The construction joints of the asphalt mixture surface layer should be tight and smooth. The upper and lower layers of the longitudinal joints should be staggered 150mm (hot joints) or 300-400mm (cold joints) or more. The transverse joints of two adjacent and upper and lower layers should be staggered by more than 1m. A 3m straightedge should be used to check to ensure that the flatness meets the requirements.

(2) When paving with echelon operation, hot joints should be used, leaving the paved part 100-200mm wide for the time being, as the subsequent part of the reference surface, and then compacting across the joints. If cold joints are used for half-width construction, it is advisable to add a baffle plate or to plan out the hewn asphalt mixture, paint the sticky layer of oil and then lay new material, overlap the new material on the paved layer by 50-100mm, soften the lower layer and then shovel away, and then compact and squeeze across the joints.

Longitudinal joints: remove the baffle (planing hew) → brush sticky layer oil → lay new material to soften the lower layer after shovelling away → cross-joint crushing

(3) high grade road surface layer transverse joints should be used vertical flat joints, the following layers and other levels of road layers can be used can be used oblique joints or stepped joints

The lap length of the oblique joints is related to the thickness and should be 0.4-0.8m; the steps of the stepped joints are formed by mirror planing and sprinkled with sticky layer of asphalt, and the lap length should not be less than 3m.

Flat joints should be mechanically cut or manually planed to remove the insufficient layer thickness, so that the working joints are connected at right angles. Remove the mud and water left when cutting, paint the sticky layer oil after drying, pave the new mixture joint should make the joint soften, roller first for horizontal rolling, then longitudinal full compaction, smooth connection.

Transverse joints: thickness flatness check and plan out the layer thickness shortage part → remove mud and water dry → brush sticky layer oil → preheat → paving material first transverse then longitudinal rolling