I believe asphalt overlay on concrete can help in following way:

1. To reduce moisture damage in subgrade

2. To improve adhesion between the vehicle tire and the road surface (note that concrete surface has lower adhesion than asphalt surface)

3. To reduce noise 

4. To reduce deicing salt penetration and thereby to reduce to corrosion in rebar

Hope it helps Amjad!

Cheers

Kamal

The use of bituminous surfacing over concrete structures (e.g. existing

concrete roads) is widespread to improve the skid-resistance and the

general appearance of roads on one hand, and to avoid the pre-mature

failure of concrete surface by frost spalling in cold countries on the other

hand.

In designing the bituminous surfacing over concrete, there are several

areas to which engineers should pay attention. Firstly, the laying of thin

bituminous material over the joints or existing cracks of concrete structure

would lead to reflective cracking because the thermal movement of

concrete induces swift formation of cracks in bituminous surfacing. Past

research demonstrated that with the adoption of minimum thickness of

100mm bituminous surfacing the occurrence of reflective cracks would be

delayed when compared with the use of thinner surfacing. Secondly,

sufficient adhesion between concrete and bituminous surfacing has to be

achieved. Therefore, it is recommended to apply a layer of tack coat on the

concrete surface to promote bonding

Also if a concrete pavement is 400 mm thick and a heavier vehicle (eg. a new aircraft) requires it to be 500 mm thick, an asphalt overlay can provide the difference.  A rule of thumb is 2mm of asphalt is equivalent to 1mm of concrete for these designs.

Cheers, Greg

To improve concrete's impermeability property. Therefore it may reduce the risk of chemical ingress and water penetration that may harm the steel reinforcement inside the concrete and eventually weaken the concrete structure.

thanks all 

To seal the concrete against the elements, to increase skid resistance value and reduce noise

thanks John

I believe asphalt overlay on concrete can help in following way:

1. To reduce moisture damage in subgrade

2. To improve adhesion between the vehicle tire and the road surface (note that concrete surface has lower adhesion than asphalt surface)

3. To reduce noise 

4. To reduce deicing salt penetration and thereby to reduce to corrosion in rebar

Hope it helps Amjad!

Cheers

Kamal

thanks Kamal

Good answer Kamal