New Asphalt Driveway - How Soon to Drive Tractor over it?

[dragoneggs]

Shaking my head here... This whole discussion on tire pressure vs. ground force is faulty.

Look at it this way... say you had 'steel' tires. The pressure exerted on the ground would be a linear function based on the weight of the tractor. If the tractor weighs twice as much, the ground force (and pressure) at each tire is double. Now increase the pressure inside the rigid tire... the footprint of the steel tire does not change. The ground force and pressure does not change.

Now let's introduce a semi-compressible tire... the tire will indeed deform and create a larger footprint. But it will not deform so much that the contact pressure on the ground will remain constant based on the internal pressure of the tire. You must factor in the stiffness of the tire (pressure vessel).

 

[Peter 315]

What is road mix I hear that term and would love an explanation

Has anyone got out and looked at the road to see if it is still perfectly smooth no imperfections? Once that is done would you want your driveway to look like what you see

They have a lot of mix recipes the size of the stone the amount of sand etc . road top (mix) usually has bigger stone I get mix all the time state top or dense binder ........Half the time it all looks the same.......:confused3:

 

[Diggin It]

Road mix ....

Stuff that cracks, crumbles, sluffs off to marbles, succumbs to potholes and needs to be resurfaced every few years.

 

[dodge man]

Road mix is a generic term. It would be a high quality mix that would be the same as used on highways. Usually a state DOT mix. There are many different kinds of mixes also. Like already said asphalt on highways is put does in layers, you can only compact so deep. The lower layers are often called binder courses and tend to be a little coarse while the final layers are called surface.

Also the edges tend to not compact as well, there is nothing for it to squish against when rolling it. If you had a curb along the edge it would compact along the curb better than if it was not there.

 

[chim]

Shaking my head here... This whole discussion on tire pressure vs. ground force is faulty.

Look at it this way... say you had 'steel' tires. The pressure exerted on the ground would be a linear function based on the weight of the tractor. If the tractor weighs twice as much, the ground force (and pressure) at each tire is double. Now increase the pressure inside the rigid tire... the footprint of the steel tire does not change. The ground force and pressure does not change.

Now let's introduce a semi-compressible tire... the tire will indeed deform and create a larger footprint. But it will not deform so much that the contact pressure on the ground will remain constant based on the internal pressure of the tire. You must factor in the stiffness of the tire (pressure vessel).

Perfect brief explanation!

 

[Buppies]

Each state has different requirements for different mix designs. Interstates vs US highways. Primary Roads vs Secondary Roads, Subdivision Roads most are based on traffic counts as to which mix design will be specified. In my home state there is no such thing as road mix vs driveway mix. I will not get technical here as there are numerous mix designs varying between each plant but for VDOT work must meet their requirements.

The length of time a driveway lasts depends on numerous factors but the main one in my opinion is the base. Asphalt is a running surface only and will not support its own weight without proper support

The OPs driveway looks great he is happy. Asphalt generally cures in one year and will show scuff marks etc until it gets cold. They will reappear in the spring but will stop after that one year period. Would have no issues running on with tractor after 9 days but would not park it on it

 

[BigBlue1]

Mental note to self: Do not come back to tractor forum with physics questions...

 

[HKUSPnut]

Look at it this way... say you had 'steel' tires. The pressure exerted on the ground would be a linear function based on the weight of the tractor. If the tractor weighs twice as much, the ground force (and pressure) at each tire is double. Now increase the pressure inside the rigid tire... the footprint of the steel tire does not change. The ground force and pressure does not change.

I think this is the cleanest explanation so far. Much better than my attempt. I think when this problem is broken down too simply, it is assumed that the air in the tires is what is supporting the load. This is only partially true. The air pressure is also keeping the sidewalls rigid which helps transfer the load from the wheels to the contact patch. When the tire deforms (flat contact patch) and volume is displaced within the tire, this further reinforces the sidewall, keeping it rigid.

 

[s219]

Shaking my head here... This whole discussion on tire pressure vs. ground force is faulty.

Look at it this way... say you had 'steel' tires. The pressure exerted on the ground would be a linear function based on the weight of the tractor. If the tractor weighs twice as much, the ground force (and pressure) at each tire is double. Now increase the pressure inside the rigid tire... the footprint of the steel tire does not change. The ground force and pressure does not change.

Now let's introduce a semi-compressible tire... the tire will indeed deform and create a larger footprint. But it will not deform so much that the contact pressure on the ground will remain constant based on the internal pressure of the tire. You must factor in the stiffness of the tire (pressure vessel).

Unfortunately that is not the way it works unless you have a very stiff tire (like a runflat tire) that is able to support full load with zero pressure. For any tire that will go completely flat or become so flat that it cannot be safely driven on when deflated, then the air is what carries the load. This is very easy to see if you can do a simple statics analysis and draw a free body diagram. When doing the math, any structural contribution from the tire sidewalls come out to be peanuts compared to pressure*area on the contact patch, and they are so small they can be completely ignored.

A statics analysis involves looking at vertical and horizontal forces separately. The horizontal calculation is simple because pressure loads on opposite sidewalls cancel out, plus there is no external force applied horizontally. The vertical calculation is the big one, since it's the direction where we have an applied external force, in the form of the gravity load or weight carried by the tire. Work your way through the math and you end up with:

weight = (tire pressure) X (contact area) + (sidewall stiffness)

For non structural tires you can ignore the second sidewall stiffness term because its very small compared to the first pressure*area term.

This is extremely easy to verify on a car with smooth tires (I only suggest smooth because it makes the next part easier). Park on concrete with a pice of graph paper under the tires. Gently saw at the steering wheel slightly, to smudge the tread pattern of the contact patch onto the paper. Now remove the paper and count up the area of the contact patch on the graph paper, in square inches. Multiple that area by the tire PSI to get the weight on the tire. With even middling accuracy of your area calculation, the number you come up with will be within a few % of the actual weight carried by the tire. What's more, you can repeat the experiment with a range of tire pressures and you will see the contact patch area adjust accordingly. It really does work.

There are also inflatable structures used for things as simple as tents and pool floats, all the way up to complicated space structures. These follow a similar concept, where deflated they don't do a darn thing. Inflated, they become stiff semi-rigid structures. The outer membrane's job is to contain the air pressure and provide a template for the shape. But it's the pressurized air that carries the load and makes the structure.

 

[PILOON]

Well if tires are at 40 PSI and U let air out to 20 PSI then you should have 1/2 the PSI's on the asphalt.
Try it and let us know!