Topping Existing Asphalt Pavement 3

[Trackfiend]

Has anyone ever specified compacting an existing cracked up asphalt pavement and topping with a new surface course?

The situation involves an existing asphalt parking lot that has been in use for some years (not sure how old exactly). The owner would like to merely mill, clean, and top the existing asphalt surface with a new 1" asphalt wearing course.

Due to various heavy machinery finding its way onto the existing asphalt surface, some of it has cracked up, forming chunks of aspahlt. Is it common to merely compact the cracked up areas and resurface the asphalt? I was thinking that any torn up areas needed to be removed and replaced with the existing subgrade (soil) recompacted and then a new layer of stone (8") and asphalt (1.5" wearing, 1.5" binding), and geotextile fabric be put into place. I have never heard of just compacting what is there (existing asphalt) and then retopping.

The parking lot will be used for only light duty traffic and sadly, no, there is no soil information what so ever. Requests for soil borings are being met with high resistance. I understand the importance of having the soil characteristics to be able to design a pavement section, but this is the situation in which I find myself.

Any suggestions or helpful past experience with this matter is much obliged.

 

[msucog]

doesn't sound promising to me. essentially, it appears that you'll end up with a base course (consisting of the old base course and asphalt) topped with 1" new asphalt. if the subgrade is busted up, the new asphalt will likely not do well. HOWEVER, if the pavement is very old with a few minor areas, maybe it's possible that minimal remediation will last another several years. i'd probably stay away from attempting to recompact the existing asphalt. (to go barebones on the money) i'd just mill the top, leave the rest alone so that you don't break it any further, and top it...this based on the owner not wanting to pay for doing it right (as a matter of fact, i'd save them more money and back myself out of the project--no sense in him paying me to sit there and tell him he's doing it completely wrong). otherwise (to fix it a little better), i'd try to pick and choose the "worst" spots for remediation. or to do it completely right, i'd go full blown in to a pavement evaluation/design/etc...i seldom see light duty pavements (especially old ones) go to this extent. i usually see a pick and choose mentality and hope it holds (sometimes full depth reclamation for very large areas). be sure to explain the risks of what might happen to the owner and thoroughly explain/document what your function is and what the owner's expectations are. give the owner lots of options and make them choose what they want.

 

[fattdad]

Cracking likely means the subgrade has failed. Milling and a new lift of surface mix will hold up for a little while, but the cracks will resurface with returning moisture and subgrade failure. There may be a geotextile that you could use to help minimize reflective cracking - check out the Amoco product line. I have no experience with this, but seem to recall there's something out there.

Reconstruction is what the project needs and the client should be told his/her risks.

f-d

¡papá gordo ain’t no madre flaca!

 

[LCruiser]

Reflective cracking will rapidly occur if you try to pave over existing cracking with 1" of HMA. Sounds like the owner is trying to cover up a problem and sell it quickly.

 

[Trackfiend]

I figured reflective cracking would be the biggest issue if the existing surface would be left in place.

I've had to make several assumptions (yes, I realize where assumptions can lead) in order to give the owner a suitable pavement design. My recommendation is to remove and replace with a conservative section design (subbase and surface) in order to account for any deficiencies in the soil. This of course would cause the owner to spend more than he should if say a soil's report was generated and the existing subgrade was found to be in good shape.

The situation is not a nice one, being that I've been thrust into the middle of an ongoing job that I'm not familiar with, the previous engineer who called for only topping, is not around anymore, and the asphalt paving crew is set to roll (mill and top existing pavement) in a few days. The owner is definitely not going to like my new change orders since it nearly doubles the cost of the original estimate. Oh well, such is life....

Thanks guys for all the input. Much appreciated.

 

[LCruiser]

What are the milling specs? What is the parking lot used for? You mentioned various "heavy machinery" - what kind of loadings are they? You are at a definite disadvantage without knowing what the existing pavement section and subgrade material are like. Instead of a partial mill, you might consider milling to double the depth of the existing HMA and using that as a base material, depending on what's underneath. Is there not a backhoe on the job to dig a little trench?

 

[Trackfiend]

The milling specs orginally called for 1" to be milled. It was then discovered that some of the existing asphaltic sections are less than 1" thick so it was determined that milling was not an option. And doubling the milling depth is not possible.

The parking lot will be used for only light duty traffic (cars, no heavy trucks or machinery). The heavy machinery mentioned was due to other construction in the area and the contractor should not have had their machinery going back and forth over this existing pavement.

I have just visited the site and recommended to the owner that he needs to remove and replace any of the areas of existing asphalt that are cracking or seem damaged in any way. Any existing asphalt that looks ok could be milled and retopped with 3" of new HMA. If the milling shows the existing section to be too thin, then it also will be called to be removed and replaced with a new section consisting of a stone subbase (or sand) and 3" of new HMA. I also went on the record with the owner in telling him/her that even though the existing asphalt may not look damaged to the naked eye, it could have some damage due to the machinery driving over it that could cause failure in time.


The owner was not happy about the recommendation, since the previous engineer called for only retopping, but realizes that the milling has uncovered a previously unknown condition (unfavorable depth of exisiting asphalt) that calls for a change order.

 

[bpattengale]

Have you looked at Full Depth Reclemation? I don't have any experience with it personally, but some of the information about it sounds interesting. Based on the material I've read it sounds like it may be an option.

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

The link I posted is using FDR with cement, but that's not a requirement. It can also be done without cement as I understand it.

 

[Trackfiend]

Since my last post, the owner had asked for several options concerning a pavement section design. Upon designing four different sections (with different subbase materials), it seems that an asphalt surface with a soil cement subbase would be the cheapest option (as opposed to either an equivalent stone or asphaltic subbase).

The contractor that is scheduled to do this job is extremely well versed in asphalt paving and just recently completed another project utilizing soil cement under a low volume roadway. I was actually quite amazed at the resilient modulus of soil cement (first time utilizing it in a design).

bpattengale "Full Depth Reclamation" –

That is interesting. I was initially calling for all existing asphalt to be removed and replaced with the new section, but if I can save on any fill brought in for the soil cement by using what is already there (old asphalt), then I’ll really make the developer smile. Thanks for the link.

 

[ACtrafficengr]

FDR with cement, CaCl, emulsion, foamed asphalt, etc. can be cost effective. Invest in some geotech work - which stabilizer to use and how much of it depends on the % fines in your subbase.

For example, using the right amount of PCC will give you a long-lasting base for the new pavement. Too much, and you'll get cracks as the cement-modified soil shrinks.

"...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

"I'm searching for the questions, so my answers will make sense." - Stephen Brust