Different types of asphalt on different type roads

[roadman65]

I noticed in Central Florida that the texture of asphalt is different on roads with curbs as those without.  For example, I have seen that on FL 423 from north of FL 50 to I-4 in and around Orlando where it changes at the place the curbs end.

Last year there was a project to resurface FL 423 from FL 50 to I-4 and just north of FL 50 where the curbing is the stones are well held together and it was applied without removing the existing pavement.  Then at the place the curb ends the stones have crevices between them and stand out after the workers recycled the original pavement and reapplied two coats of blacktop. Basically the stones are not glued together on curbless sections and are loose on top.

I was wondering why it is done that way?  Also, why Florida does not use a bed of stones to lay new roadways down like New Jersey, New York, Pennsylvania, etc?  I asked that to an FDOT employee and he never heard of that procedure of laying a bed of stones underneath the roadway before.  Then I asked my cousin in New Jersey  who is in construction about why Florida engineers do not place stones before paving the roads and he thought that Florida is nuts!  Do engineers not communicate among each other?  It seems that Florida just compresses the soil and lays the road down while other places (I do not know who practices like FDOT) lay down a bed first and both are doing it from their own knowledge.

[Beltway]

That is called Aggregate Base Course, the layer of crushed stone mixed with fines like sand.  That is a standard road construction process nearly everywhere, to place from 4 to 10 inches of that (depending on the roadway type and traffic volume and types) on the subgrade (soil base), and then the asphalt or concrete pavement is placed on top of the Aggregate Base Course.

Aggregate Base Course is permeous in that water can drain out of it.  Building a road without Aggregate Base Course seems odd, but if the asphalt is made commensuratly thicker, at least the load bearing issues can be satisfied.  I wouldn't recommend that unless the subgrade was of a sandy permeous nature and could fulfill part of what the Aggregate Base Course is intended for.

I think I can say with confidence that in Virginia that no roadway is built without Aggregate Base Course included.

[hbelkins]

I have noticed that on several recent projects, Kentucky puts down a layer of thick black plastic sheeting between the dirt and the rock.

[Brian556]

Concerning subgrade:
The purpose of the subgrade is to support the road so that it does not sink into the ground.
Here in Texas, many TxDot asphalt roads have "flex base" under them. it is a mix of sand and gravel.
Newly constructed concrete state roads have mixed, packed subgrade, with asphalt on top, them concrete on top of that.
When I worked for the city, when they reconstructed a street, they would mix concrete power into the dirt, spray it with water, and pack it back down. This doesn't seen very permiable. It is very hard when cured.

Concerning asphalt surfaces:
Here in Texas, TxDOT uses "seal coating" to preserve asphalt roadway surfaces. It involves spraying a thick layer of tar, and covering it with gravel. The gravel is rolled then swept. LOOSE GRAVEL signs have to be posted for a period of time because stones often come loose from this type of surface.

[roadman65]

Concerning subgrade:
The purpose of the subgrade is to support the road so that it does not sink into the ground.
Here in Texas, many TxDot asphalt roads have "flex base" under them. it is a mix of sand and gravel.
Newly constructed concrete state roads have mixed, packed subgrade, with asphalt on top, them concrete on top of that.
When I worked for the city, when they reconstructed a street, they would mix concrete power into the dirt, spray it with water, and pack it back down. This doesn't seen very permiable. It is very hard when cured.

Concerning asphalt surfaces:
Here in Texas, TxDOT uses "seal coating" to preserve asphalt roadway surfaces. It involves spraying a thick layer of tar, and covering it with gravel. The gravel is rolled then swept. LOOSE GRAVEL signs have to be posted for a period of time because stones often come loose from this type of surface.

The fact is that Florida does not have the subgrade and just packs the soil down hard with a steam roller and then puts the grade on.  My cousin told me that a subgrade is needed to drain out the water and found it odd that the Sunshine State does not grade roads and parking lots this way.

[realjd]

Concerning subgrade:
The purpose of the subgrade is to support the road so that it does not sink into the ground.
Here in Texas, many TxDot asphalt roads have "flex base" under them. it is a mix of sand and gravel.
Newly constructed concrete state roads have mixed, packed subgrade, with asphalt on top, them concrete on top of that.
When I worked for the city, when they reconstructed a street, they would mix concrete power into the dirt, spray it with water, and pack it back down. This doesn't seen very permiable. It is very hard when cured.

Concerning asphalt surfaces:
Here in Texas, TxDOT uses "seal coating" to preserve asphalt roadway surfaces. It involves spraying a thick layer of tar, and covering it with gravel. The gravel is rolled then swept. LOOSE GRAVEL signs have to be posted for a period of time because stones often come loose from this type of surface.

The fact is that Florida does not have the subgrade and just packs the soil down hard with a steam roller and then puts the grade on.  My cousin told me that a subgrade is needed to drain out the water and found it odd that the Sunshine State does not grade roads and parking lots this way.

What do you mean by draining the water? Doesn't it all flow off into the swales or storm sewers along the road?

[roadman65]

I don't see my cousin that often.  In fact, I have not talked to him in years.  It was 05 when we got into this discussion. 

[Scott5114]

Concerning asphalt surfaces:
Here in Texas, TxDOT uses "seal coating" to preserve asphalt roadway surfaces. It involves spraying a thick layer of tar, and covering it with gravel. The gravel is rolled then swept. LOOSE GRAVEL signs have to be posted for a period of time because stones often come loose from this type of surface.

Also called "chip seal". You will find this sort of surface extensively on Oklahoma county roads, and even some minor state roads. It's cheap, but it doesn't hold up very well.

[hbelkins]

Chip sealing is considered a quick and easy way to pave a gravel road, or keep the dust down.

My memory is a little fuzzy, but it seems like a number of major routes out in the southwest were chip-sealed when I was out there, including former US 666 in New Mexico.

[roadfro]

Concerning subgrade:
The purpose of the subgrade is to support the road so that it does not sink into the ground.
Here in Texas, many TxDot asphalt roads have "flex base" under them. it is a mix of sand and gravel.
Newly constructed concrete state roads have mixed, packed subgrade, with asphalt on top, them concrete on top of that.
When I worked for the city, when they reconstructed a street, they would mix concrete power into the dirt, spray it with water, and pack it back down. This doesn't seen very permiable. It is very hard when cured.

Concerning asphalt surfaces:
Here in Texas, TxDOT uses "seal coating" to preserve asphalt roadway surfaces. It involves spraying a thick layer of tar, and covering it with gravel. The gravel is rolled then swept. LOOSE GRAVEL signs have to be posted for a period of time because stones often come loose from this type of surface.

The fact is that Florida does not have the subgrade and just packs the soil down hard with a steam roller and then puts the grade on.  My cousin told me that a subgrade is needed to drain out the water and found it odd that the Sunshine State does not grade roads and parking lots this way.

What do you mean by draining the water? Doesn't it all flow off into the swales or storm sewers along the road?

You assume the road is so improved to have a storm sewer, swale, ditch or other such improvement...not necessarily the case.

However, from what I recall of pavement design classes, the subgrade is the native soil on which a pavement section is constructed. It's the sub-base that is the main structural support section and also helps with drainage--that is, drainage of any water that has permeated below the upper layer of pavement.

[roadman65]

Another thing that is interesting is the fact the motor road to Pikes Peak in Colorado is gravel after a certain altitude and not paved up to the summit.  There was a reason told to me years ago, but it slipped my mind.  Obviously, the road there is better off as gravel than to pave it and it must be a good one as it would be harder to plow a dirt road than a asphalt one.  Then again, is the Pikes Peak Summit open in Winter?