Preparation before asphalt concrete pavement construction
(I) Materials and requirements
Coarse and fine aggregates used in ssphalt concrete, fillers and asphalt should meet the contract technical specification requirements, and the detailed description of the recommended mixture ratio includes: aggregate gradation, asphalt content, stability (including residual stability) , Saturation, flow value, density and porosity of the Marshall test specimen, etc., should be submitted to the supervision engineer for approval at least one month before the start of the project.
(II) Equipments
Asphalt mixing equipment ,transport equipment and paving equipment shall comply with the contract technical specification requirements.
(III) Coating of sphalt
The contact surfaces of kerbs, road trenches, inspection wells and other structures should be evenly coated with a thin layer of bitumen.
(IV) Inspection
To check the curbstone on both sides is in intact situation or not, location elevation does not meet the requirements should be corrected, if any disturbance or damage must be promptly replaced, pay particular attention to the back compaction, to ensure not being squeezed, moving during the paving and rolling.
(V) construction measurement and setting out sample
Restore the center line: Set a reinforced concrete pile every 10m in the straight line, and set a pile every 5m in the flat curve. The position of the pile is 20cm outside the width of the paving structure layer of the central isolation belt.
Horizontal measurement: do level measurement of the well-set reinforced concrete pile, and mark the design elevation of paving layer, hang steel bar, as automatically leveling baseline of the paver.
(VI) asphalt material preparation
Preparation of asphalt material, the asphalt material should be heated firstly to avoid local overheating, and to ensure convey the asphalt material from the storage tank to the mixing equipment at uniform temperature , foaming or be heated to more than 160⁰C asphalt rubber structure should not be used.
(VII) Preparation of aggregates
Preparation of aggregate, aggregate should be heated to no more than 170 ⁰ C, water content of aggregates sent into the mixing equipment should not exceed 1%, the drying flame should be properly adjusted to avoid over-baking and over-fumigation aggregate to damaged and blackened circumstances, the moisture content of mixture output by the drying drum mixing equipment should not exceed 0.5%.
Asphalt concrete pavement construction process
(I) Mixing and transportation
1. Mixing
Using asphalt mixing equipment (150t/h) to mix centrally . Amount of aggregate and asphalt materials according to the site ratio formula requirements and delivered into the mixing equipment, Temperature of the aggregate delivered into the mixing equipment should comply with the provisions , temperature of mixture in the mixing equipment and outside the factory should not exceed 1600C. After putting the specified amount of aggregates and asphalt material into the mixing equipment, the two materials are thoroughly mixed until all the aggregates have been fully coated by the asphalt binder and the asphalt material has been completely distributed throughout the mixture. Asphalt mixture mixed by the mixing plant should be uniform, no white material, no clumps.
If mixed-well hot asphalt mixture is not paved immediately, it can be stored in thermal finished product storage bin, storage time shall not exceed 72h, if use storage bin without insulation equipment, the allowable storage time should be consistent with the paving temperature requirement.
Asphalt mixture produced by mixing shall comply with the approved requirements of the construction site mix ratio, and should be within the allowable deviation of the target value, the deviation of aggregate target value should meet the contract technical specifications.
2. Asphalt mixture transportation
Transportation of asphalt mixture uses 15t dump track, in order to reduce the segregation of coarse and fine aggregates, when releasing the mixture from the mixing equipment to the dump truck, move the location of truck after dumping a bucket of mixture, cover the dump truck with tarpaulin when transporting the material.
(II) paving and rolling
1. Paving
(1) Use an automatically flattened asphalt paver (maximum paving width 12.5m) to flatten mixture for full width paving and leveling. When automatically leveling by paver, the elevation of paving layer is controlled by the reference line formed by hanging wire on the metal edge, cross slope is controlled by the slope controller, accuracy is in the rolling ± 0.1% range.
(2) When paving, the asphalt mixture must be spread slowly, evenly and continuously. Do not change speed or pause in the middle casually. The height of the mixture in the pave screw feeder should be kept at least 2/3 of the height of the feeder. And ensure no segregation happens on the full width of the paver section.
(3) The paving of the mixture is carried out by a paving machine, and use the reference line to control the elevation of the paving layer.
(4) The horizontal seam between the upper and lower layers should be staggered by 50cm or more.
(5) Where machinery can not pave and renovate, artificial paving and renovation shall be carried out only with the consent of supervision engineer.
(6) In the arrangement of construction, when the temperature is below 10⁰C, the asphalt mixture paving operation is not arranged.
2. Rolling
(1) Once the asphalt mixture has been laid flat and the irregular surface has been trimmed, it needs to be fully and uniformly compacted immediately.
(2) Initial pressure is carried out after paving the mixture and at a higher temperature, the asphalt mixture temperature should not be lower than 120⁰C, no moving or cracking should occur. When using double drum vibratory roller (wheel width is 2.16m) to roll, driven wheel need to face the paver, rolling line and rolling direction shall not be suddenly changed, initial rolls twice.
(3) Re-compaction should be carried out immediately after the initial press. The asphalt mixture temperature shall not be lower than 90⁰C and use the triple-roller with a width of 2.79m together. Re-compact 4 to 6 times till its stable and not significant wheel tracks..
(4) The final pressure should be carried out immediately after re-compaction. The temperature of asphalt mixture shall not be lower than 70 ℃. The tire roller rolls 2 to 4 times to no wheel tracks. The final temperature of road surface compaction meets the specifications.
(5) Rolling start from the outside and longitudinal parallel to the center line of the road, double tires roller rolls overlap 30cm every time, three tires rolls overlap half width of the rear wheel, and gradually rolls to the inside, when paving by using the echelon method or followed the well-shopped driveway, firstly rolls longitudinal seam, and then rolls conventionally, in the ultra-high detours, use longitudinal parallel to the center line overlap method to roll from low to high edge. When rolling, compactors should be traveling at a constant speed, shall not stay ,turn or brake in the new shop mixture or unrolled and not cooling road section. In the rolling process, construction inspectors use nuclear density meter to detect solidity to ensure the required minimum degree of compaction, the temperature at the beginning of rolling should be controlled at not less than 120 ℃, end rolling temperature is controlled at not less than 70 ⁰ C, three different section compact seems of the initial pressure, re-compaction, the final pressure should be in different sections, staggered lateral 1m above.
(6) In order to prevent the sticky wheel phenomenon of asphalt mixture occurs during rolling , roller can be sprinkled with a small amount of water , water mixed with a very small amount of detergent or other approved materials to keep proper moisturize of the roller.
(III) Maintenance
1. Seams, repair and clearance
Paving of asphalt mixture should be done continuously as far as practicable. The road roller must not pass over the unprotected end of the new paving mixture. The transverse joint should be cut at the end of the previous run to expose the full surface of the layers. When joining the new mixture, apply an appropriate amount of sticky asphalt at the end of the last run, then press mixture against the previously pressed material, and note the height adjustment of the flat plate should be sufficient to reserve adequate compaction for rolling. The adjacent two and the upper and lower horizontal joints should be more than 1m dislocation. Lateral seems should be rolled horizontally and then rolled conventionally. The trimmed material and other waste asphalt mixtures should be cleaned from the road.
(Sourcing: Baidu)
