This is an excellent question, and many homeowners and business owners are asking it. When it comes down to it we recommend asphalt driveways over concrete for three main reasons:
- It has faster installation
- It has better resistance to weather
- It is more cost-effective
However, if there’s an existing concrete driveway, this presents new challenges.
If the question is “CAN I lay asphalt over concrete?” then the answer is “Yes.” This is absolutely possible if elevations allow for it, and we’re happy to lay asphalt driveways over concrete if that’s what you want. It’s also the cheaper option since heavy equipment is required to dig up an existing concrete slab.
Nevertheless, there are significant downsides to this. Generally speaking, we recommend removing the existing concrete first, for two big reasons.
1. A Concrete Driveway Sub Base Is Different Than an Asphalt Driveway Sub Base
The big problem with laying asphalt driveways over concrete has to do with the initial preparation of the site.
With concrete, if you’re concerned about strength and stability, the solution is to simply lay a thicker slab. Because of this, contractors laying concrete rarely worry about preparing the base. The ground underneath a concrete driveway may be prone to shifting or sinking, and there’s really no way of knowing what’s down there until it’s dug up.
Laying asphalt over concrete creates two layers to worry about:
- The unprepared sub base
- The concrete itself
If something is wrong with either of these layers, it will show through the asphalt. Unfortunately, when asphalt driveways are poured over concrete resting on an unstable base, the resulting asphalt pour is prone to instability. Expansion joints in the concrete will quickly turn into cracks in the asphalt, which will require costly ongoing repair jobs. In extreme cases, shifts in the ground could crack the entire surface, just as a house’s foundation may crack if improperly laid.
2. Pouring Asphalt Over Concrete Is Bad for the Longevity of Your Driveway
So yes, pouring asphalt over concrete may look good at first, but there are bound to be troubles over time. It just doesn’t make fiscal sense to do it, as that driveway will need a lot more work in the near future.
Asphalt driveways last longer and look better when they are built from the ground up. Your new asphalt driveway will have a proper, stable base, and therefore will require less maintenance as time goes on, saving money in the long run.
There are some instances where concrete and asphalt work well together, such as curbs and edges. But generally, they work better side by side rather than one on top of the other.
Concrete Stability is Important for Paving
Concrete is not usually a compacted surface because it hardens no matter what it is poured over. Asphalt, on the other hand, has to be compacted to get longevity and strength. Concrete pavement is occasionally poured over the top of unstable soils because concrete has the ability to “bridge” the instability. If the concrete has been poured over an unstable base, the slabs, once they crack at the expansion joints, can pivot slightly with traffic.
Think of a time when you have driven down a bumpy concrete road where the bumps are rhythmic. Those slabs have pivoted slightly from where they were originally poured. Chances are these slabs weren’t poured over an unstable base, but rather, frost heaving moved them.
Each individual slab can move at the expansion joints, and if you have an unstable base, the condition can occur more often. A concrete pavement that moves will damage any asphalt overlay over time. If you are looking to add asphalt over concrete, you will need to make sure you have a stable concrete surface below, with no expansion joint shifting, to make a proper base for overlay.
Concrete Expansion Over Time May Cause Reflective Cracks
Concrete has expansion joints where asphalt does not. Over time, the expansion joints will shift the concrete surface and wherever your concrete has a crack, the asphalt will eventually crack there as well. The expansion joint in the concrete is a designed area to allow for a crack, and while there are special reinforcing fabric strips that can be applied prior to overlay, over time, there is a very good chance that the cracks will eventually crack in the same spot on the asphalt. This is not considered pavement failure, but it is just a result of ongoing heat and cold expanding and contracting. Regular maintenance of your asphalt driveway or parking lot, and crackfilling these reflective cracks to prevent water intrusion will leave you with pavement that will last a long time.