Road Building

[woodchip]

Calling TC et. al. Watching a section of the expressway being tore out and replaced leaves me with a few questions google doesn't supply. Like what happened to road mesh? As I watch the new pavement go in I see a black fabric go over the compacted base and then a layer of coarse concrete over that. Next part is what I don't get. Instead of a mat of road mesh, a steel ladder with legs is placed every couple of feet and then the main concrete bed is poured. So why no mesh? I thought that gave the concrete flexibility? The steel ladders do that better? Any explanation would appreciated.

[Krom]

Once the concrete has hardened they saw cut it over where the metal ladders are so the concrete cracks predictably over that point, the metal ladder keeps it from moving around excessively. Rebar (the mesh you are talking about) is only used to strengthen concrete from tensile loads as concrete is very weak when you pull on it. Roads don't need it because for the most part they are only subject to compression loads which concrete is very strong for.

[Tunnelcat]

Yeah, it's better to have predictable places for cracks to form when pouring concrete structures. Nothing like an undesirable crack in the wrong location to make things fall apart quicker, especially a road surface. Also probably makes it easier to control water infiltration and allow for better maintenance in the future. Maybe they plan on putting in flexible sealing joints since they know the concrete is going to crack in known locations. Because concrete shrinks as it hardens, cracks will form, no matter what, so a builder might as well design in some predictability.

You should see my basement floor. The birdbrain contractor didn't trowel in any control joints and I now have random wandering cracks all over the place in the floor. He claimed that this new fiberglass concrete additive would prevent that, NOT! But I've never seen this new way to pour a concrete road base. All I've ever seen is the old rebar mesh method. Got any pics?

[AlphaDoG]

Here is HOW they should be constructed in the U.S., but, alas.

http://en.wikipedia.org/wiki/Road#Construction

[Krom]

http://en.wikipedia.org/wiki/Pavement_( ... )#Concrete
The type of surface he is talking about is jointed plain.

[woodchip]

Once the concrete has hardened they saw cut it over where the metal ladders are so the concrete cracks predictably over that point, the metal ladder keeps it from moving around excessively.

They are not saw cutting every couple of feet as that is ladder spacing.

[woodchip]

http://en.wikipedia.org/wiki/Pavement_( ... )#Concrete
The type of surface he is talking about is jointed plain.

Nope, not what I'm seeing:

Jointed Plain Concrete Pavements (JPCP) contain enough joints to control the location of all the expected natural cracks. The concrete cracks at the joints and not elsewhere in the slabs. Jointed plain pavements do not contain any steel reinforcement. However, there may be smooth steel bars at transverse joints and deformed steel bars at longitudinal joints. The spacing between transverse joints is typically about 15 feet for slabs 7–12 inches thick. Today, a majority of the U.S. state agencies build jointed plain pavements.

[woodchip]

Finally talked to someone knowledgeable about what I was trying to figure out. The ladders are called \"low transfer baskets\". Black fabric is a geo tectonic or geo-grid fabric that combined with the coarse sub aggregate, spreads wheel load over a wide area. Anyway a link to what I'm trying to descibe:

http://www.cptechcenter.org/publication ... te_000.pdf