Using Recycled Concrete/Asphalt

[ohengineer]

Due to the increased push for contractors and others to use recycled products, we are seeing more and more people wanting to use recycled concrete and asphalt as construction materials. I have done some research and have seen in other localities that those materials are being used in base materials and concrete, but I am not seeing any technical literature on the matter. What I am seeing most is a client wanting to use recycled concrete for sub-base material under pavement or under a building slab. I think that initially it would perform satisfactorily, but I am concerned about long term performance especially under a pavement where conditions change and the effect of wheel loads. Appreciate any comments or the location/title of any literature that is available.

Thanks

 

[cvg]

one reason you don't see much literature is that the properties of this material vary from one source to another. There are no standards that I am aware of for recycled material. Lack of standards requires the engineer to evaluate the specific material source on a case by case basis and establish your own opinion on it's suitability. If the recycler does a good job with crushing, screening, washing and blending, then it can perform as well as typical aggregate materials. Locate your proposed stockpile and do your own tests to pre-qualify the material.

 

[msucog]

your concerns about long term performance are appropriate for pavements. under buildings, i'd be more worried about the "proper" placement of these materials for foundation support. there's a few threads around discussing reclaimed materials.

also see (most of these deal more with pavements):

http://www.cement.org/pavements/

http://www.arra.org/faqfulldepth.html

http://www.millergroup.ca/

https://www.fhwa.dot.gov/pavement/recycling/98042/16.cfm

http://www.wbdg.org/ccb/browse_cat.php?o=29&c=4

(see links around 3-250)

http://www.usace.army.mil/publications/eng-manuals/

reclaimed ac and base course material make jam up new base course material when used in a soil cement/stabilization type of application. depending on the site specific conditions, a bona fide soil cement design could easily replace a portion of the base course aggregate. the cost savings to the owner would depend greatly on the onsite material properties, pavement design considerations/expectations, quantity/area of pavement, etc. as always, be careful with using reclaimed materials. make considerations for quantities, costs, performance, secondary effects, etc. for the secondary effects comment, i'm implying that you should be careful to not create additional problems by doing something like specifying too much cement (ie. "more is better" mentality) and removing all the base course material which may cause cracking to show up in the asphalt surface.

 

[Mickney]

We have been involved with projects where recycled concrete was used beneath the pavement structure as the subbase. The recyling process tried to obtain the same gradation as the subbase stone. We ran numerous grain size tests to confirm and the pavements are performing well. Good quality control and observations during construction were key elements to its success.

 

[ohengineer]

cvg- In performing tests, I would assume possibly several sieve tests and Proctors. Are there any other tests that would be beneficial?

 

[cvg]

I think visual inspection is also useful to help determine how uniform the stockpile is, how well graded it is, how well the concrete is crushed, presence of any rebar or other materials etc. Also, talk with the recycler to find out what they are actively doing for quality control

 

[iandig]

If you can source the Specification for Highway works from the UK, it deals with the specification, testing and acceptance of a number of re-cycled aggregates and materials from everything from pipe bedding, general fill and sub-base materials. This is now backed up by a european standard EN 13242 [BS EN 13242 in UK] which covers the 'specification for hydraulically bound and unbound materials for use in civil engineering'. Over the last 6 years, a number of tests have been removed from the standards and replaced with 'new' tests to account for the widespread use of recycled materials - i.e. no longer do the 10% fines but replaced with Los Angeles Abrasion [LAV], Micro-deval etc...
In addition to this, if you go to the WRAP website at

http://www.wrap.org.uk,

then there are numerous case studies, and information on this. Also the BRE [Building Research Establishment] and TRL [Transport Research Laboratory] have a number of published documents, some going back several years on the use of recycled materials, including road plannings [asphalt] recycled concrete aggregate [RCA] and many other materials.