Asphalt over existing concrete sidewalk

[pats1003]

Project calls for widening a 1.5 m (5') concrete sidewalk to a 3 m (10') wide asphalt multi-use trail (pedestrians and cyclists). Owner wants to keep existing concrete sidewalk in-tact and black top over it. We are thinking of using 100 mm (4") of compacted granulars over the existing concrete and then 50 mm (2") of asphalt. The new 1.5 m (5') wide section that abuts the existing will be excavated to solid bearing and filled with compacted gravel. The entire 3 m wide trail will then be paved uniformly. Location is in climate that experiences all four seasons. Thoughts on structiral integrity and potential for cracking would be appreciated.

 

[bridgebuster]

The existing sidewalk will create a hard point, but since it's only pedestrians and bikes there shouldn't be much settlement; make sure everything is properly compacted.

 

[Ron]

I would fracture the existing concrete sidewalk as much as possible (crack and seat process). Then you'll be less likely to get a corresponding crack in the asphalt at the linear edge of the concrete. As bridgebuster noted, you'll have a hard spot in the concrete as compared to the adjacent soil, even with the separation layer.

There's nothing to be gained by leaving it in place and its removal will not be expensive...I'd take it out.

 

[cvg]

take it out, crush and reuse as your gravel base material

 

[AAEC]

Since the owner wants existing concrete, I'd say honor the client wished except that you need to make it clear to the owner about the hardpoints to cover yourself. The hardpoints issue should not be a problem since there are no heavy loads and that you will have 4" think granular gravel over the existing concrete. As bridgebuster said, just make sure to compact the structural fill really good.

Good luck on your project.