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Installing concrete over asphalt

  • 1.  Installing concrete over asphalt

    Posted 03-06-2020 10:33 AM
    ​​A client wants to install a 3 inch concrete floor over existing asphalt in a warehouse setting. Would you recommend an epoxy between the new concrete and old asphalt layer? or can the concrete just be put down over the asphalt?

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    Christopher Hanna P.E., M.ASCE

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  • 2.  RE: Installing concrete over asphalt

    Posted 03-07-2020 07:51 AM
    I would recommend a paving fabric (Petromat, Amopave) over the asphalt and 4" concrete.

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    Hans H. Coucheron-Aamot
    [Retired]
    Albuquerque NM
    [Phone]
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  • 3.  RE: Installing concrete over asphalt

    Posted 03-07-2020 12:48 PM
    Christopher,

    I'm not really qualified to speak on that specific subject, as more of a water resources civil engineer with a smattering of geotechnical experience.

    However, my first thought would be on the unstated questions about this situation that perhaps you have already considered but not stated.

    1. I would be more worried about the foundation layers below the existing asphalt, and how they and the AC layer might perform under the concrete.

    2.  Along the lines of 1) above, have you considered differential settlement? Concrete performs and behaves pretty different from AC. You might get lots of cracking.

    Perhaps it is just my fear of dealing with something I'm not qualified to deal with, but this sounds problematic.

    Good luck.

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    David Hook P.E., M.ASCE
    CIVIL ENGINEER
    San Jose CA
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  • 4.  RE: Installing concrete over asphalt

    Posted 03-07-2020 11:20 PM
    3 inches of concrete is very thin. Sidewalks are a minimum of 4 inches. Does the client plan on putting any rebar or wire mesh in the concrete? What is the current condition of the existing asphalt? A concrete layer that thin would have reflective cracking. If the epoxy is meant to be a bond breaker it sounds like a good idea.

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    Dustin Leduc A.M.ASCE
    Field Engineer
    Sambatek
    Shakopee MN
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  • 5.  RE: Installing concrete over asphalt

    Posted 03-07-2020 11:20 PM
    What drives the need for the new concrete floor?  The problem statement implies that it might be of a cosmetic nature only.  If it is not driven by simple appearance then who has determined the required slab thickness?  I can understand the Client providing the design loading for their intended use but not the slab thickness.

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    Mohsen Khani P.E., M.ASCE
    Sr. Civil Engineering Manager
    Bentonville AR
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  • 6.  RE: Installing concrete over asphalt

    Posted 03-08-2020 09:44 AM
    Saving the asphalt may well cause trouble and end up costing him more than just taking it out and installing a proper concrete slab by the book.

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    Hans H. Coucheron-Aamot
    Retired
    Albuquerque NM
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  • 7.  RE: Installing concrete over asphalt

    Posted 03-10-2020 01:12 PM
    This is not a new topic.  The concrete paving industry has been promoting this for over 25 years.

    Thickness procedure is well documented and can be found on the www.pavementdesigner.org.

    There are experts in every state on this to assist you.  www.acpa.org.  If you are in WI give me a call.

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    Kevin Mc Mullen P.E., M.ASCE
    President
    Wisconsin Concrete Pavement Association
    Janesville WI
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  • 8.  RE: Installing concrete over asphalt

    Posted 03-09-2020 07:51 AM
    Placing a rigid pavement over a flexible pavement is very common on airfields. Consider the asphalt, base and sub-base as flexible support for the concrete, Warehouses often have high point loads, so if this is the reason the client is looking at concrete, they are spot on. I would suggest designing the system with no adhesion between the asphalt and concrete. As the engineer, you will need to consider what the clients loading is expected to be in determining the thickness. If he has high frequency areas, look at the expected life the high frequency areas.  Thicken the slab at these locations. There are some surface treatments often use in the Warehouse industry, look into them. Remember, in determining the concrete mix design, the distance between the rebar and surface or forms must always be two and one-half times the largest aggregate.  This is the most common overlooked detail in the concrete industry.

    Good luck.

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    Robert Hinton, P.E- Life Member ASCE
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  • 9.  RE: Installing concrete over asphalt

    Posted 03-08-2020 09:44 AM
    I agree. This is a peculiar requirement and poses some interesting questions. Asphalt is a flexible paving while concrete is a rigid pavement, each with different loading considerations. My recommendation would be to design the concrete (thickness+reinforcement) as though the asphalt were simply a compacted subgrade and not give any structural consideration to the asphalt itself.

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    Joseph Dyches M.ASCE
    Clinton SC
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