Asphalt storage pad

[TheGumpster]

I'm extending my driveway (12' wide) by 17 feet so I can park my 33' Forest River 5th wheel on it for a few days before and after our trips. We have an offsite storage facility for long-term storage. The dry weight is 10,000 pounds, axle dry weight is 8,000 pounds, hitch weight 2,000 pounds. It is a dual axle. When parked, we will have 2x12's (2' long) under the rear stabilizers and under the front jacks. I'm getting quotes for the asphalt. One contractor says 4" crush run and 2-1/2" hot mix will do the job. The other contractor says 6" crush run and 3" hot mix and is using the "better safe than sorry" argument. Where can I get an objective opinion on how thick the asphalt needs to be?

[manualman]

Fun aside: In regards to why highways don't hold up like they seemed to in the past? It's controversial, but almost certainly is not lack of rebar, much less lack of wire mesh. In the past, total traffic volume was much lower, which probably is the biggest factor.

In my opinion, the next biggest factor is that we've used 28 day old compressive strength as the largest quality control factor in Portland cement concrete for many decades. The problem with that is that in the 1960's factory economics were such that cement granules left the factory coarser than they do today. That meant you needed more of it to hit your 28 day strength because coarse granules gained strength slowly. Today, ultra fine cement results in very fast strength gain, so they use less of it to get the same 28 day strength. The downside is that the 90 day strength today is much lower than the 90 day strength of 1960's concrete. But nobody checks that. Our admixtures have gotten better, but we've become stupidly short-sighted about ultimate strength and it's effects on longevity. Others in the industry see it differently, but that's my opinion.

This is why you sometimes see "1890" stamped on concrete railroad bridges that are in fine shape next to interstate concrete bridges built in 1990 that are dropping chunks off as you watch traffic go over...

[Grit_dog]

To add to it, qc of mesh placement is very difficult and typically not in the right spot in the slab. Not rigid enough to chair up like rebar so sometimes it gets pulled up into the slab during the pour. Most of the time it is sitting on dirt with little to no concrete cover.
In a 1 way reinforced slab on grade, you're looking to increase the flexural strength of the tension side of the slab (the bottom). So you want the reinf as far down from the neutral bending axis with enough conc cover to protect from corrosion. Mesh is better than nothing but sucks for achieving this due to what I wrote above.
Much better solution if needing some reinforcing in a thin slab on grade is fiber mesh reinforcement.
Again none of it is a replacement for good sub prep.

[manualman]

Sam Spade wrote:

Grit dog wrote:

Typical concrete pavement design for highways or runways is unreinforced save for tie bars at the longitudinal jts and dowel bars at the cjs.

Wow, I'm amazed. If universally true, that might explain why the pavement needs to be re-done so often (job security).

I can't imagine this being a good thing up north where it freezes hard. Maybe what I have seen was prep for a bridge pour or similar.

You may have seen the approach slab on the land side of a bridge abutment. Those are often reinforced with bars (not mesh) because the abutment is relatively fixed in place at one end while the ground moves slightly with changes in moisture and temperature on the other end. Dowel rods at the land end of the approach slab keep it in vertical alignment with the plain slab next in line.

On topic, it's mostly architects and old guys still putting wire mesh in slab on grade details. Engineers have long concluded that money spent on steel and labor would yield better returns making the concrete a little thicker, properly preparing the base and assuring good contraction joint layout. Some contractors still like the mesh because it's good enough to get a sloppy job through the warranty period (typically a year). Cracking after that due to a poor base is the owner's problem, not his.

[Grit_dog]

Sam Spade wrote:

Grit dog wrote:

Typical concrete pavement design for highways or runways is unreinforced save for tie bars at the longitudinal jts and dowel bars at the cjs.

Wow, I'm amazed. If universally true, that might explain why the pavement needs to be re-done so often (job security).

I can't imagine this being a good thing up north where it freezes hard. Maybe what I have seen was prep for a bridge pour or similar.

It's akin to what manualman said above. Roadway concrete theoretically is strictly in direct compression and just like AC paving is really just a wear surface for the dirt (to oversimplify it). Does help bridge the load as well.
Think about asphalt (AC) pavement. No reinforcing, and it's compressive,flexural and tensile strength is considerably less than even modest structural concrete.
Even typical airport runways and Tarmac are unreinforced concrete. Albeit a much deep section than roadway PCCP. But, in runway construction, the subgrade prep specs are much more involved. Typically 3-4' deep of compaction requirements or even complete replacement with structural type fill to those same depths.
Like I said, there are reinforced concrete roadways in areas, but they are typically very limited as usually the design considers the cost of stabilizing subgrade (which is 100% necessary) is much cheaper than miles of rebar mats.
Back to the simple rv storage pad. If proper subgrade stability is achieved, a 2" mat of asphalt is sufficient. Now asphalt "creeps" much more than concrete and over time, a static applied load (parked trailer tires or Jack stand) will cause the asphalt to slowly creep. It will depress if the subgrade is soft or "shove" if the ground is unyielding. Think about the ruts you see in asphalt at an intersection in the wheel paths, particularly in the truck lane. Depending on the type of oil and binder, temperature, subgrade stability etc, this will be more or less pronounced. Hence the reason it's a good idea to park a long term applied load on something that will spread and lessen the pressure, like some stout boards.

[Sam_Spade]

Grit dog wrote:

Typical concrete pavement design for highways or runways is unreinforced save for tie bars at the longitudinal jts and dowel bars at the cjs.

Wow, I'm amazed. If universally true, that might explain why the pavement needs to be re-done so often (job security).

I can't imagine this being a good thing up north where it freezes hard. Maybe what I have seen was prep for a bridge pour or similar.

[Cummins12V98]

I thought we were talking about a pad for a RV????????

[Grit_dog]

manualman wrote:
Fun stuff, these old habits have long life. 22 years in the biz of happy and repeat clients. Wire mesh is a band aid for poor base prep and drainage. Good base = no need. Bad base and it's not enough steel to help. There's no point to it.

Which is why you won't find the stuff in any highway pavement anymore. They use prepositioned dowel rods located where contraction joints will go and ZERO wire mesh. The stuff is junk.

This is generally correct. And the reason I suggested the op get some real opinions and quotes AT his house, in person. We have no idea what the subgrade is like. 1" of asphalt (not feasible) may hold up for 20 years or may need to be sub exc'd and stabilized to park a geo on it.

[Grit_dog]

Sam Spade wrote:

manualman wrote:
They use prepositioned dowel rods located where contraction joints will go and ZERO wire mesh. The stuff is junk.

Just to clarify a bit, a modern highway has 1/2 inch (I think) rebar about 12 inches or less apart in the WHOLE length of the pour. Isn't that right ?

I don't think anyone here was suggesting that the commonly used fence wire mesh would be appropriate for a real highway. And most of us are suggesting that it really isn't appropriate for anything except maybe a sidewalk.

I've seen some reinforced PCCP, but can't remember where.
Typical concrete pavement design for highways or runways is unreinforced save for tie bars at the longitudinal jts and dowel bars at the cjs.

[Sam_Spade]

manualman wrote:
They use prepositioned dowel rods located where contraction joints will go and ZERO wire mesh. The stuff is junk.

Just to clarify a bit, a modern highway has 1/2 inch (I think) rebar about 12 inches or less apart in the WHOLE length of the pour. Isn't that right ?

I don't think anyone here was suggesting that the commonly used fence wire mesh would be appropriate for a real highway. And most of us are suggesting that it really isn't appropriate for anything except maybe a sidewalk.

[manualman]

Fun stuff, these old habits have long life. 22 years in the biz of happy and repeat clients. Wire mesh is a band aid for poor base prep and drainage. Good base = no need. Bad base and it's not enough steel to help. There's no point to it.

Which is why you won't find the stuff in any highway pavement anymore. They use prepositioned dowel rods located where contraction joints will go and ZERO wire mesh. The stuff is junk.

[Grit_dog]

I'd suggest getting some professional opinions AT your house where the insitu conditions can be considered.
Every retired dot inspector and ex construction guy on here could be right......or wrong based on subgrade conditions, drainage, application of load,etc.
And you've received some super false info here as well.

[Cummins12V98]

korbe wrote:

Cummins12V98 wrote:

Aron wrote:
I'm an engineer with some experience designing highway pavements. In general, 10,000 lbs is fairly light for a pavement design, so pretty much any of the suggestions in this thread would work (including either of the OP's original pavement and gravel thicknesses), especially if its only carrying that weight occasionally. Its possible that parking a static load in one spot for a few hot days could create a bit of a divot (asphalt is basically a mix of tar and gravel, and tar flows in heat), but I wouldn't think it would be bad. It's really the gravel that provides the load carrying support, so don't skimp there. There's probably not a huge cost difference between the 2.5"/4" design and the 3"/6" design, so I would probably go with the slightly thicker one just for added assurance.

Speaking of gravel, the only suggestion in this thread that I wouldn't follow is the use of pea gravel. It's the angular interlocking characteristics of compacted gravel that provide the weight bearing support; over time, rounded pea gravel would tend to flow away from the concentrated weight points under the tires. I suppose it could work under concrete if the concrete is thick enough, but under asphalt it would probably provide poor support.

If you are referring to me I never suggested using pea gravel for substrate under asphalt. Yes it works VERY well for backfill in ditches and under concrete slabs.

We once filled an old 5'x 5'access well within a sidewalk with pea gravel. We required the contractor to compact with a vibra-plate and he thought we were kidding. The vibra-plate lessened the voids tremendously and more pea gravel was needed to fill in. Don't know if you call that compaction, but it sure wasn't ready for the concrete.

There needs to be a bit of common sense, walking it in layers if very deep is smart especially if it's full of fines. You certainly don't need to use a compactor in that condition unless you really feel the need.

[korbe]

Cummins12V98 wrote:

Aron wrote:
I'm an engineer with some experience designing highway pavements. In general, 10,000 lbs is fairly light for a pavement design, so pretty much any of the suggestions in this thread would work (including either of the OP's original pavement and gravel thicknesses), especially if its only carrying that weight occasionally. Its possible that parking a static load in one spot for a few hot days could create a bit of a divot (asphalt is basically a mix of tar and gravel, and tar flows in heat), but I wouldn't think it would be bad. It's really the gravel that provides the load carrying support, so don't skimp there. There's probably not a huge cost difference between the 2.5"/4" design and the 3"/6" design, so I would probably go with the slightly thicker one just for added assurance.

Speaking of gravel, the only suggestion in this thread that I wouldn't follow is the use of pea gravel. It's the angular interlocking characteristics of compacted gravel that provide the weight bearing support; over time, rounded pea gravel would tend to flow away from the concentrated weight points under the tires. I suppose it could work under concrete if the concrete is thick enough, but under asphalt it would probably provide poor support.

If you are referring to me I never suggested using pea gravel for substrate under asphalt. Yes it works VERY well for backfill in ditches and under concrete slabs.

We once filled an old 5'x 5'access well within a sidewalk with pea gravel. We required the contractor to compact with a vibra-plate and he thought we were kidding. The vibra-plate lessened the voids tremendously and more pea gravel was needed to fill in. Don't know if you call that compaction, but it sure wasn't ready for the concrete.

[spoon059]

Good point CavemanCharlie... I poured raised concrete pads for my tires, and used gravel under the rest of the trailer. Cost me a couple hundred bucks, with the money I saved doing it myself, I bought a Carolina Carport and store my camper out of the elements.

If I had it to do all over again, I would do the EXACT same thing.