Asphalt alligatored: Crush & Shape or Mill & Cap?

[square1]

I have two "experts" giving conflicting advice on repair of a badly alligatored asphalt parking lot. The original installation was, in both experts opinion, very well (overly) done in regards to the base and surface. This is evidenced by the fact the lot isn't heaving or settling. The surface has merely gotten to the point that repairing a section this year and a different section next year, etc... has become more costly than doing the entire lot. Previous repairs have always been cut out a section down to the dirt and install new asphalt. These repairs have held up well.

One adviser says the best solution will be to grind up all the asphalt (down to the dirt base), remix it and put it back down. The other is recommending milling off 3 inches (the asphalt is 6" thick ) and putting down 3 inches of new asphalt.

It's a parking lot, not a highway, it does see axle loadings in excess of 10,000 pounds on a regular basis.

With cost out of the picture, which would be the better solution?

With cost in the picture, how much more (or less) percentage wise would you pay for the solution you suggest over the other option?

Are there other repair methods that should be considered?

 

[Egon]

Consider professional design help.

 

[vtsnowedin]

A picture would help. Six inches of asphalt is way over built for a parking lot if the base under it is sound. At today's oil and asphalt prices any full depth replacement will cost an arm and a leg.
If cost is out of the picture mill off three inches and replace with new half inch aggregate mix applied in two lifts.
With cost considered spray a heavy tack coat on it so it runs down into all the alligator cracks and top it with a one inch overlay. In ten years or so do it again. ten years after that it will be somebody else s problem most likely.

 

[square1]

Consider professional design help.

Those are the professionals' opinions.

ten years after that it will be somebody else s problem most likely.

:yes: actually (hopefully) after the first ten it will be somebody else dealing with it

 

[vtsnowedin]

Well if that is your time line consider just having it sand sealed. A coat of hot emulsion sprayed on either from a distributor truck or tack buggy and clean sand spread on top and rolled in with a rubber tired roller. let cure a couple of days then sweep up any excess sand and your done. Repeat in three to five years. Do it early in the summer and it will look perfect all that season. Its silly to do it late in the fall and have the plows start on it two weeks later.

 

[Gary Fowler]

If you have 6" of asphalt, I would just mill off 3" and put a top wear coat of 1.5" thick after compaction of a fine crushed rock/asphalt mix. You have too much asphalt which might be the source of your problem. Most highways have no more than 4" (compacted) over a good solid base.
The milled product could be recycled to make more asphalt by just adding a bit more asphalt and heating. This could be sold to the asphalt supplier for a good offset of your cost.

I once saw a road repair "train" working up a mountain road repair. It consisted of a milling machine removing the old asphalt that then went into a portable kiln for heating and mixing of additional asphalt (just a small amount needed). Next came a huge burner box that was heating the fresh milled road bed followed closely behind by a machine taking the recycled asphalt and laying it back down on the road. Following was a couple of compacting rollers. The operation moved along at a slow walk pace completing the road repair in one operation. I have never seen this done anywhere else. It was repairing one full width lane of the road.

 

[Jim Nelson]

I have a 680' long driveway that is in pretty bad shape so I talked to 3 different contractors.Two of them said a 1.5" overlay would be fine,the other guy said I will take out a section and replace it then overlay a short section and you watch it for a year and you will see that the overlay will mirror the old surface.Sure as the world the patch looks like new and the overlay looks just like the old alligator. Now all I have to do is come up with a spare $25000 to have it pulverized and re-done.

 

[paulharvey]

Do you have 6" of asphalt on top of dirt or 6" of asphalt on top of road base/rock? If it's all asphalt, they did what we call "black base" were you use additional lifts/layers of asphalt in place of base. The guide line is 2" of base=1" of asphalt base (10" rock can be replaced with 5" of asphalt). The catch is that you would never want to place 5" of asphalt in one lift, because you would never get compaction. SP-9.5 (old S3; 3/8" rock) shouldn't be placed more than 2" thick in one lift; SP-12.5 (old S-1; 1/2" rock) no more than 2.5"; and I'll about guarantee you don't have SP-19.0 (19mm rock; 3/4") I thick can be placed upto 3.5", but I wouldn't recommend it. All of those numbers are assuming a 8 ton roller at least. Most driveway paving crews only use 2-5 ton rollers.

If it's 6" of asphalt on top of dirt there are two concerns:
1: I wonder is the subgrade was either not compacted well, or was wet
2: if they did 6" in one lift, there is no possible way they really got good compaction on the asphalt.

That covers some of the why; now to the fix.

One option is to reclaim the existing asphalt and some of the subgrade. They use a reclaimer (similar to a mixer with milling machine teeth; 300hp rototiller with carbide teeth) to grind the asphalt and subgrade in place, and reshape and re compact the mix as a new base. It does not fix any problems with unsuitable materials, but it does basically allow you to start from scratch.

Another option is to crack seal the existing asphalt with a special melted rubber-asphalt and then overlay it. This might be the cheapest, but it doesn't fix the underlying problem; failed base. But it is probably the cheapest option, and as long as any settling is done it will work fine.

Mill and overlay will do nothing for base problems either, as alligator cracking is a sign of base problems, not failed asphalt. Milling off all or some of your asphalt and laying more on top of the same problem won't help.

 

[paulharvey]

I once saw a road repair "train" working up a mountain road repair. It consisted of a milling machine removing the old asphalt that then went into a portable kiln for heating and mixing of additional asphalt (just a small amount needed). Next came a huge burner box that was heating the fresh milled road bed followed closely behind by a machine taking the recycled asphalt and laying it back down on the road. Following was a couple of compacting rollers. The operation moved along at a slow walk pace completing the road repair in one operation. I have never seen this done anywhere else. It was repairing one full width lane of the road.

They tried that a few years ago (probably more like 10 years ago) on a few roads around here, and it didn't hold up well. We had the best luck; on projects I personally worked on; with crack seal; 110#(1") of leveling, 220#(2") of SP-12.5 structural; and 110#(1") of FC-9.5 wearing coarse.

One problem we had rebuilding roads was the county started getting cheap. They would take the leveliing out, do 1.5" of structural and 1" of friction.

 

[madmax12]

If you have 6" of asphalt, I would just mill off 3" and put a top wear coat of 1.5" thick after compaction of a fine crushed rock/asphalt mix. You have too much asphalt which might be the source of your problem. Most highways have no more than 4" (compacted) over a good solid base.
The milled product could be recycled to make more asphalt by just adding a bit more asphalt and heating. This could be sold to the asphalt supplier for a good offset of your cost.

I once saw a road repair "train" working up a mountain road repair. It consisted of a milling machine removing the old asphalt that then went into a portable kiln for heating and mixing of additional asphalt (just a small amount needed). Next came a huge burner box that was heating the fresh milled road bed followed closely behind by a machine taking the recycled asphalt and laying it back down on the road. Following was a couple of compacting rollers. The operation moved along at a slow walk pace completing the road repair in one operation. I have never seen this done anywhere else. It was repairing one full width lane of the road.

I saw something like that being done on a road yesterday, just west of sanford, Maine.