remove/replace existing AC road 2

[CrazyHorse81]

there is an existing subdivision road (undeveloped yet) that has settled alot due to lack of compaction of the sewer main backfill. this has called for its replacement prior to any homes being built. so the existing road should have been 6" ac over 6" limestone, however it was constructed nonuniform like 3 over 9, 9 over 3, 2 over 10.

is there anyway to reuse what is there? would it be wise to reclaim and reuse the existing? is there anyway to salvage the pavement and let the public works department have it for future patch jobs? like by milling?

we have to overexcavate 18" and lay a geogrid down, backfill with well graded subbase then apply the HMA - that is the design we have.

I am having problems realizing how this could be done efficiently, and without the need for high expertise during construction for QA/QC purposes - being that I am a W/WW guy...

 

[Ron]

First of all, your pavement section is way out of whack for a subdivision. 6"ac over 6" limestone base? Unless you have some very bad soil conditions, that's an absurd light pavement section. Further, if the designer was compensating for poor soil conditions, he didn't consider constructibility....difficult pavement section to build properly.

Yes, you can reclaim what is there. In fact, that would be my recommendation. Do a mix-in-place recycling program whereby you mix the upper 8 to 12 inches of material together using a reclaimer. You can then inject asphalt emulsion into the mix at the time of mixing and follow immediately with compaction. If you have any unstable areas, you can add a small amount of portland cement into the mixture. This will create a very stable base material upon which you can place a structural course of asphaltic concrete surfacing. I doubt that you need 6" of asphalt...more like 2".

 

[CrazyHorse81]

Thank you for your response it only makes for more questions...heh heh

The soils are fat clays so are unsuitable. Blow counts 4-8.

So let me regurgitate your recommendation and see if it makes sense in steps of construction:

1. Remove existing asphalt/limestone thickness and perform overexcavation for preparing the subbase - stockpile onsite the asphalt/limestone separated from the unsuitable materials

2. Prepare the road way site, lay geogrid, place and compact engineered fill to required grade

3. mix-in-place stockpiled material with asphalt emulsion, place and compact

If this is correct can these be done simultaneously? or would it be phased?

So the mix-in-place is considered Recycled Asphalt Pavement correct? Is there another term for asphalt emulsion? Like asphalt binder? I don't have specifications for this kind of work - any recommendations there?

 

[Ron]

Ch...difficult soil conditions. Probably can't use mix-in-place recycling, but you can salvage the materials for future/other use by the county.

Mill the existing pavement to use for recycling into other mixes.

Once you have done this, you can consider mixing the existing limestone base into the clayey subgrade, but you might have to mix either lime or portland cement into the process to achieve adequate strength.

Geotextile/grid not necessary. If you prepare the subgrade as noted, provide a flexible base (compacted limestone) and a reasonable surface structural course, you'll be fine.

 

[francesca]

We always used to have them build the houses first, then fix the road after all the heavy vehicles and grading equipment (from digging basements, etc.) was done tearing the road up.

 

[CrazyHorse81]

Ron - why would the soils cease the ability to do the mix-in-place? is it because of the bearing capacity of the soil couldn't bear the equipment required to do the work?


francesca - that makes sense to stage it that way.

 

[Ron]

Ch...mix in place recycling is difficult to do with plastic clays. The mixing process literally gets "gummed up".

If the clays are unstable, then putting heavy equipment on top can be a problem as well.

 

[Drumchaser]

CH81

I would reclaim the existing base and ACP together and stockpile off roadway. Perform corrective backfill on the utility cuts. Lime treat the subgrade (12"), replace, regrade existing ACP and base to density. Then place 2-3' of new ACP surface.

 

[apmssoriano01]

This is supplementary information regarding Full-Depth Reclamation (FDR) with a stabilizing agent (i.e. - asphalt emulsion, Class C or F fly ash, Portland Cement, kiln dust, etc.). If there is the potential to get into the fatty clay while reclaiming, then mineral admixtures should be used in-lieu of emulsions. Successive passes with a reclaimer (i.e. - 3 to 8) will break up the clay balls that form at first, as mentioned by Ron. The much higher surface area of the mineral admixtures alone will help dry out the material and reduce its plastic behavior, in addition to any cementing behavior.

We have used FDR and/or soil cementing since 2007 and have tested all ten (10) of our projects with a Falling Weight Deflectometer (FWD). We used the deflection-based structural assessment methodology outlined in the 1993 AASHTO Pavement Design Guide to back out a structural coefficient for the reclaimed material that ranged from 0.16 to 0.43 for Portland Cement additions of about 3- to 4-percent by moist unit weight. The 0.16 value was for reclaimed material with about 90-percent clay/10-percent asphalt mix. The 0.43 was reversed - about 10-percent clay/90-percent asphalt/aggregate base mix. The reclaimed depth ranged from 6- to 12-inches.