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    T_Nowicki
    Asphalt recycling under a building
    Topic posted February 7, 2012 by T_NowickiMember, last edited February 9, 2012
    664 Views, 11 Comments
    Title:
    Asphalt recycling under a building
    Content:

    A contractor at a colleague's project site want to reuse the asphalt from the site by crushing it and using it as fill. The crushed asphalt would then be covered by 2 ft of crushed rock to provide the foundation for a building.  We're leaning towards saying this is a really bad idea but don't have any basis for that statement. Does anyone have any references on whether this is good or bad? The recycling people refer me to the solid waste people who refer me back.

    Asphalt gets recycled into road base and new asphalt all the time but has to be disposed of as solid waste. Crushed concrete gets reused as fill for building foundations.

    Comment

     

    • Tom Speight
      posted February 7, 2012 by Tom SpeightElite Contributor

      I doubt it would be a vapor intrusion issue, and not likely to produce other enviro issues unless the water table is really shallow, but I suspect that any structural or geotech engineer would veto the idea.  Unlike brick and concrete, asphalt is malleable and deforms under pressure rather than just cracking or crushing.... so that may not be the sort of thing you want to build a building on.  Most of the geotech guys I know are leery about building on fill, period, without a lot of major safety margins.

    • Vini
      posted February 8, 2012 by ViniMember

      Hi there! I found someone from one of our other social channels that wanted to lend a hand in the matter.

      Steve Collins(Health, Safety and Regulatory Compliance Manager at Cliff Berry Inc.) had this to say:


      There appear to be several questions to be answered: 
      1) Is this method allowed by regulation? Building codes differ by location. 
      2) Does the method provide the level of compaction and other geological considerations necessary to uphold the structure? This appears to have already been determined, but may be worth establishing for the record. 
      3) Is the crushed asphalt considered “clean” fill? Presumably the asphalt is weathered and has been exposed to road use contamination that may include chemicals of concern (breakdown products, deposits from on-road spills). 
      4) Will there be any environmental issues for the owner from leachate or other future characteristics from using crushed asphalt? Environmental impacts from surface applications of asphalt may be tolerable but the environmental impact of applications at depth with respect to aquifers or fractured formations may complicate estimating future environmental impacts. I hope this helps.

    • Vini
      posted February 8, 2012 by ViniMember

      Sorry, One more reply.

       

      Jeremy Squire (Senior Engineer at Murex Environmental) said:

      It's a common practice, and from an engineering standpoint, it makes a great road base and engineered fill. However, there are two potential problems. First, bituminous asphalt contains some small amounts of PAHs and heavy-chain TPH. Also, because of cars being parked on it for many years, it picks up drips of motor oil and gasoline. In most cases, this doesn't matter, but if you were building a school where import fill is tested or if there is a risk assessment being performed, that could have an impact on your project. This gets to the second problem: is the material a solid waste or a usable building material? I could argue both. Now - what to do? Document your decision based the fact that you are selecting to use recycled materials for construction, calculate the savings in carbon footprint as compared to excavating and importing non-native fill, and pat yourself on the back for adding LEED credits to the overall project.

    • kevin
      posted February 8, 2012 by kevinSuper Contributor

       Contractors are not engineers.  Crushed asphalt is a horrible foundation material. 

    • Scott
      posted February 8, 2012 by ScottSuper Contributor

       I don't think there'd be a significant environmental concern. Although there could be a multitude of petroleum and PAH compounds associated with the asphalt, they're going to be in relatively low volumes and pretty immobile within the tar.  That's irrelevant if you have shallow groundwater though.

      Beyond the environmental issue is the engineering problem, and the project geotech and local building official will both likely have to approve this.  I can tell you that none of the geotech PEs that I've worked with/for would accept recycled asphalt as fill beneath a building.  It's too difficult to re-crush uniformly, it doesn't have the necessary fine particles to fill void spaces, and it's too pliable to reliably compact.  I've only ever seen it approved as a fill beneath parking areas and sidewalks, and even then not in high traffic areas, and only in small quantities.

      I don't know what kind of building you're looking at or the soil conditions, but the fact that the contractor wants to put the asphalt beneath 2 feet of crushed rock makes me think that they just want an easy way to get rid of it - like maybe they are a little skinny on their bid and don't want to pay the disposal fees.  That quantity of crushed gravel will provide a fair bearing capacity on its own, the asphalt will do little to enhance it.

    • manno
      posted February 8, 2012 by mannoSuper Contributor

       

      I think more info is needed here.

      How much asphalt are we talking about?

      What is the size of the building?

      Is the building for industrial uses or something very sensitive like a school?

      Some districts allow small amounts of undesirables in the fill, e.g. 2% organics.

    • John Dougherty
      posted February 8, 2012 by John DoughertyMember

       The contractor should be able to find someone that will recycle the asphalt for a low cost. The cost of oil has made this a viable option these days.

    • Ronald Wolters
      posted February 8, 2012 by Ronald WoltersMember

      When crushing tar asphalt granulate (TAG; in the Netherlands defined as asphalt with PAH exceeding 70 mg/kg) the contractor may expose him self to intolerable levels of PAH in case no stringent HSE measures are taken. In comparison: soil exceeding 40 mg PAH/kg already results in the highest safety standard in Dutch equivalent of HAZWOPER, i.e. working with independent air supply. This in addition to being a potential source for groundwater contamination as mentioned by Scott. Suggestion is to take a core sample, being crushed in the lab and get it analyzed for PAH.

      There is a TAG recycling plant in port of Rotterdam, The Netherlands, that receives and treats TAG from all over Europe: http://www.bentumrecycling.nl/uk/brc_tagreiniging.htm

    • PanTerra
      posted February 8, 2012 by PanTerraMember

       Project in 1993

      During an investigation of reported TPH levels in soil on a parcel of land, potentially being considered for development as a Dart Station at Kiest and Southerland, we discovered that the fill brought in to raise the land out of Trinity River floodplain contained copious amounts of ashalt. The ashalt came from construction activities of the Dallas City Hall. After confirming the source of the TPH detected in soil and GW samples as asphalt, the TNRCC issued a NFA letterto the land owner. Note again that this was in 1993 and no other contaminants were suspected from the prior usage of the asphalt.

      Stephen J. Krogh

      The PanTerra Group
    • Show/Hide Replies
      T_Nowicki
      posted February 9, 2012 by T_NowickiMember

      We ended up saying this shouldn't happen but I guess it's up to the owner to make the final decision.

      The site is in an area with a high water table and so the asphalt would come in contact with groundwater.

      Additionally, geotechnically, it wasn't a good solution.  The original bid called for imported crushed rock. The low bid contractor who got the job is known as one who never saw a corner they can't cut.

      I did find out that asphalt isn't a regulated solid waste so there's no environmental regulations stopping it. The state would regulate it if it was "fresh" asphalt that could have leaching to groundwater. Since there's no testing required, I don't know how you could prevent it from getting emplaced to begin with if you had a shortcut crew.

      • Scott
        posted February 9, 2012 by ScottSuper Contributor
         It's a poor material geotechnically, so even if the owner won't stand in the way the engineer may not approve it. If their report included recommendations regarding the grading of the fill material, it's virtually impossible for recycled asphalt to meet them.