Asphalt Concrete Mix Placement

1. Work organization plan

Asphalt concrete paving is applied in one or two layers.  The technological steps are as follows:
1. Preparation works
2. Placement of asphalt concrete mix by paving machine
3. Compaction of applied layer with rollers.

2. Order of works for preparing the base
- Asphalt concrete mix is layered on dry, clean and not frozen base, when the air temperature is not less than 5 degrees by C in spring and 10 degrees by C – in autumn.
- To ensure high-quality adhesion of the cover and the base, before application of asphalt concrete cover the base should be cleaned of dust and dirt with the help of mechanical broom, air blowing by a portable compressor or by other means.
The wet base can be dried with the help of heated up to 250-300 degrees of C sand or finer gravel, as well as with the help of special heating devices.

- To ensure best adhesion with the base, as well as between asphalt concrete layers, before asphalt concrete application the preliminary processing of the surface with the help of viscous or liquid bitumen, as well as with bitumen emulsion is needed.

In this case:
The spending of viscous bitumen should be 0.2-0.3 l/m2.
- Preliminary sprinkling of binding substances can be skipped, if the base is newly made and one of these binding substances was used in it, or the asphalt concrete inner layer was applied no more than two days before and there was no traffic over it.


3. Preparation of Equipment

- Before paver exploitation the operator checks the feeder and the stacker, the augers, the hopper, and makes sure that there are no chunks of asphalt sticking or other shortcomings, then regulates the screed  controls locating in the rear of the paver, which adjust the thickness of the supplied layer. Then turns on the heaters and the smoothing vibroplate, makes sure that the machine is in proper working condition.
- The screed is brought to working position by placing beneath it the rod which adjusts the placement layer thickness to correspond to project.
That size should be 15-20% more than the project, which will be compacted after the rollers are applied to get project thickness.


4.  Placement of Asphalt Concrete Mix

- Hot I grade A type asphalt concrete mix should correspond to the state standard GOST 9128-97 requirements.
- Placement of the mix on a base or a/c underlayment is not allowed without the permission of inspecting engineer.
- Inspecting engineers should check the base and the a/c sub-layer cleanness, smoothness, treatment of cracks, surface dryness, lateral slope, air temperature, and other defects which can hamper the placement of the asphalt concrete mix or affect its quality.
- The asphalt concrete mix temperature during the placement should be no less than 130° C for A type hot mix, where are used surface-active substances at 115° C.
A/c mix should be homogeneous, loose, should not cling to the truck body.  When in doubt, check in the laboratory.

- During placement a/c mix minimal temperature should correspond to ShN&K 3.06.03-85, page 52, table 14.

- Placement of a/c mix is carried out by paving machines.  It is optimal to lay the pavement across the entire roadway, as in this case the longitudinal joints are eliminated.  In exceptional cases, when constructing the underlayment, it is allowed to place the mix by motor graders.

5. Asphalt Concrete Mix Compaction
- Compaction of a/c mix should be started immediately after its placement, while maintaining the required temperature conditions for it.
- For a/c mix of A and B types, where the content of gravel is over 40%, compaction is performed by smooth rollers weighing 10-13 tons, and then – with rubber rollers weighing 16 tons and the final rolling – by smooth drum weighing 11-13 tons.  In all cases 4-6 passes should be made.

- For V, G and D type a/c mixes, where the content of gravel is over 40%, first the compaction is performed by smooth rollers  weighing 6-8 tons in 2-3 passes, then by smooth rollers  weighing 10-13 tons in 6-8 passes, and then – with rubber wheel  rollers weighing 16 tons in 4-6 passes.  The final compaction is performed with smooth rollers weighing 11-18 tons making 4 passes. 
The speed should not exceed for smooth rollers 5 km/hr, for rubber wheel rollers – 10 km/hr and for vibratory rollers – 5 km/hr.
-    During the initial passes the leading wheels of smooth rollers should be in front.
- If the a/c mix is placed in adjacent strips, when placing the second strip, the connecting edge of the first strip should be heated up to a width of 10-20 cm.
- When a/c mix is laid across the entire width of the roadway with two pavers, then along the entire length of the first strip near the center line on the width of 10 cm is not pressed:  it should be compacted when laying the second strip.  The seams of strips should be compacted and smooth.
- Transverse seams of strips should be vertical to the center-line of the road.
- When asphalt concrete is placed on top of a pre- existing layer, it must be first repaired, and the compaction of this cover should be performed in compliance with all the requirements presented above. 


6. Requirements for pavement quality assurance

- When constructing a/c pavements should be guided by the requirements of ShNK 3.06.03-85 “Motor Roads”
- The completed a/c pavement should comply with the acting procedures of “Acceptance of Works during Motor Roads Construction”.
- The pavement width and lateral slope is checked every 100 meters.
- Evenness of pavement by its longitude and cross-section is checked every 20-30 meters with a template (rod).
-    The clearance between the rod and the pavement should not exceed 5 mm.
-    The road allowances of the project  should be:
1)  For pavement length – no more than 5 mm
2)  For pavement thickness - ± 10% of projected
3)  For lateral slope - ± 0.5% of projected.