Asphalt resurfacing

[SCEngr1]

I have a project with an existing asphaltic concrete parking lot. The parking lot has several cracks in it as well as a recently cut trench for a water line installation. The trench has some soil fill material that was placed in it to cover it up, but it has not been covered with asphalt or concrete.

What would be the best approach to determining the repair/patch on the trench and the repairs of the cracks? Also, how would you determine how thick the new asphalt overlay should be?





("You're only as old as you want to feel." - Satchel Paige)

 

[epongra2]

If there is no documentation that the trench backfill was observed, tested and documented by a soils company, watch out.

 

[SCEngr1]

What about the surface repairs and new topping layer thickness?





("You're only as old as you want to feel." - Satchel Paige)

 

[SCEngr1]

Is this on the wrong forum?





("You're only as old as you want to feel." - Satchel Paige)

 

[bpattengale]

All bituminous pavement will have cracks. Simply putting an overlay on the pavement will not fix that. Cracks can mean a lot of things, such as the subgrade has failed, the pavement section has reached the end of its design life, or any number of things.

First to fix the trench cut it is common to simply match the existing pavement section or to specify a minimum pavement section and use the thicker of the two.

The cracks are more of a problem. If they are just thermal cracks that is normal, but if you just place a overlay reflective cracking will appear in the overlay within a year of two. Those cracks will then need to be sealed to prevent premature failure of the pavement.

The overlay thickness depends on the condition of the existin pavement and the purpose of the overlay. AASHTO has a design procedure for overlays on light duty roads and streets, but that is probably overkill for a parking lot, plus it is not the same type of loading.

If the existing pavement has failed an overlay is not going to fix that.

 

[SCEngr1]

Would you have to run some non-destructive tests on the parking lot to determine the condition of the existing pavement?

What if the client's budget is real tight? Are there some reasonable assumptions that could be made to develop a recommendation for repairs and overlay?





("You're only as old as you want to feel." - Satchel Paige)

 

[ACtrafficengr]

The only non-destructive test methods I'm aware of require some sort of specialized equipment, such as a falling weight deflectometer.

It would be probably cheaper to just take a conventional core sample of the pavement and then use the hole to get a sample of your subbase and subgrade. Just remember that if you use a water-cooled core drill, it will wash away the fines in the subbase and throw off your gradation.

"...students of traffic are beginning to realize the false economy of mechanically controlled traffic, and hand work by trained officers will again prevail." - Wm. Phelps Eno, ca. 1928

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[civilman72]

"What if the client's budget is real tight? Are there some reasonable assumptions that could be made to develop a recommendation for repairs and overlay?"


You, and the Owner's first discussion should be about liability. If he wants to take on all the liability for future failures of these new repairs, then state that in your contract and give the owner a design that in your professional opinion is addressing the site conditions while optimizing the money he spends. If he says something like "you're the engineer, I'm paying you to design this right. It better work." Then you reply, "without information such as trench compaction, existing depth of asphalt, etc., I cannot determine the "right" design." The Owner needs to realize that it costs money to get someone to take on the liability for this kind of project. But if the Owner didn't have the knowledge to get the trench compaction tested during construction, it might be hard to get him to listen.

Cracks in the surface indicate a potential problem with the subgrade, which is why you want a core sample (as mentioned above). This core sample and proposed asphalt design from a geotech engineer should be less than $1,000. If the Owner doesn't want to pay this, then he needs to be prepared to take on the liability on his own, as discussed above. The Owner also needs to be prepared to find out that the pavement design from the geotech might require that he places more asphalt than he was prepared to pay for. Lastly, he needs to pay the geotech to be on-site during construction to test materials as they are placed.

If the Owner is reasonable, and will not hold you liable, then for design purposes, go with a 1-1/2" asphalt overlay as a minimum thickness. If the Owner wants to go cheap, you could also talk to contractors about other surfacing options like chip-seal. Make sure you seal the cracks and compact the trench prior to overlaying. If the water line is not very deep, the trench compaction efforts should be done carefully.

Good luck.

 

[SCEngr1]

Great information! Thanks for the feedback!!





("You're only as old as you want to feel." - Satchel Paige)

 

[BigH]

My question is what kind of parking lot? Is it like at a mall - or strip mall? What kind of cracking? Alligator or just a few longitudinal or transverse cracking? Evidence of existing pavement breakup? How long has the existing pavement been down. Any details on the pavement structure of the existing pavement? These questions need to be raised in addition to the above noted comments about the owner's and your relationship, etc.
For the trench - normally, I have seen people put in the fill and "raise" it up above the existing surface and let the traffic "pound it down" along with "settlement" under self weight and precipitation. This is the non-engineered way - and may be okay for you. After several months, then you can excavate down 300 or so and replace with well-graded crushed road base - then surface.
For the parking lot itself, the loads will be quite small (cars/SUVs/Vans/pickups) except in delivery lanes for semis (presuming this is a mall or strip mall) and fire fighting equipment. I know that the conventional way in USA and Canada is to use HMA. This is expensive - say what is the cost of even 1.5"? If the existing pavement is not broken up (alligator cracking) it might be a thought to surface the parking lot with a chip seal - using 9.5mm first layer followed by 6mm second layer. This gives a nice smooth surface and is a lot cheaper than HMA. Treat the cracking, then prime coat - allow to cure, then overlay with the chip seal and I think that you will get a nice surface. If the pavement is broken up badly (alligator cracking, etc), then you may have subgrade problems (frost, dry-swell, etc.) that might have to be addressed - but would be expensive to fix. Depending on the what the client is willing to accept - tri-yearly chip seal overlays may be sufficient in the parking areas. of course, in the delivery and fire lanes, you might wish to beef it up with HMA - and perhaps a 6mm chip seal for continuity of appearance.
Just some thoughts.

 

[msucog]

i hate seeing these kind of projects...the kind where there's "no money" to adequately evaluate the problems but the owner insists on real recommendations. for a seemingly simple issue, this would probably be one of the most complicated things to discuss on an online forum.

there are some real good points in the other posts. my advice: if it's a sizeable area where a significant amount of money is about to be spent, hire a geotech to assist. if it's a small area, i'd weigh the options with the owner to see if they want to spend the money to hire a geotech to really look at the area. just keep in mind that it's the owner's pavement (not yours) so let them make all the real choices and as noted above, make sure your contract clearly states what you are doing and who is responsible for what. if you handle getting the thing repaired and it doesn't work (in the eyes of the owner based on their expectations--which may be anything but "reasonable"), you might get hung out to dry.

if there's no money for a condition assessment and pavement evaluation, then the owner can roll the dice and let it ride. if it's an old pavement without severe damage, minimal effort/remediation may do just fine for what the owner wants...but maybe not. this particular topic can be very wishy washy if that makes sense. it's all very subjective and depends on several factors (most of which need to be addressed by the owner).

sorry if this doesn't help answer your question.