^^^

anyone know why? i know not all of em are like that but there are some... anyone know if its a scientific reason or just financial or what?

*shrug*


its for school if u're wondering why i'm asking

 

Cost - Asphalt is cheap and quicker to build.

 

Purely financial. In my economics class, the prof related how the original deal for building the majority of freeways in certain cities was calculated using incorrect values (or not taking maintenance costs or something like that into account) and so concrete came out as the "best choice" for the material. Later it was shown that an error(s) had been made and that asphalt was/is actually cheaper. So, now asphalt is used where possible.

Physical reasons do exist, as concrete is harder and should last longer, but also cracks more easily (asphalt is more ductile, allowing it to bend and mold better) and therefore will tend to require repairs if the ground shifts or there is a lot of impact on it. We could never use concrete here in Canada in most places, as frost and ground heaves would rapidly destroy it.

 

The way most roads are built now are concrete sub layer and asphalt top. It makes the best economical sense.

The concrete lasts but is expensive.
Asphalt is cheap but erodes easier.
Asphalt is recyclable and can be scrapped up and reused.

Therefore, use less concrete by only using it as the foundation and place reusable asphalt as the top layer.

Konrad

 

I should point out that the word "concrete" basically describes a mixture of cement/water/aggregate. its the CEMENT being used that makes for the two different paving materials.

Portland Concrete Cement (commonly referred to as PCC) is the lighter colored stuff that you are all referring to as "concrete"

Asphalt Cement (commonly referred to as AC) is the black stuff you are all calling "asphalt"

AC is used in the construction of traffic lanes, auxiliary lanes, ramps, parking areas, frontage roads, and shoulders. AC pavement adjusts to limited amounts of differential settlement. It's easily repaired, and add'l thicknesses can be placed at any time to withstand increased usage and loading. Over time, its nonskid properties do not significantly deteriorate. However, as the asphalt oxidizes, it loses some of its flexibility and cohesion, often requiring resurfacing sooner than would be needed with PCC. Asphalt concrete is not normally chosen where water is expected to permeate the surface layer.

PCC is the most common form of rigid pavement because of its excellent durability and long service life. Its raw materials are readily available and reasonably inexpensive, it is easily formed, it withstands expposure to water w/o deterioration, and is recyclable. The primary disadvantages of PCC pavement are that it can lose its original nonskid surface over time, it must be used with an even subgrade and only where uniform settling is expected, and it may rise and fall at transverse joints.

 

Either you work with this stuff a lot or else you copied that out of a book or website!

Good correction on "cement", though - you are quite right.

 

yeah, I'm a Civil Engineer here in CA and that text I wrote actually came ouf of the Civil Engineering reference manual I keep on my desk. And no I didn't get copyright permission..he he he

 

Ah ha. No wonder it was spot on and well-worded. That said, I don't doubt that you could rattle that stuff off the top of your head awfully well.

 

if I had to do it in my own words, it would probably sound something like this:

we pave with asphalt because it is cool. I like it.