Get Ready......
Why do we grind........
Allow me to elucidate.
rofessor
:notworthyAtlasRob:notworthy, I know you have experience with a concrete paving train from the Air Force runway pictures you posted.
What happens after that is a normal process of concrete curing and wear and tear from usage. The paving train covers the reinforcement and joints are cut in over the load transfer baskets to allow for controlled cracking. There can be expansion joints involved as well, however, you don't put many in an interstate highway. Because you have cut a joint in the slab surface, you have created a location for differential cooling of the concrete during the curing process. The area around the joint will cool faster than the rest of the top of the slab unless you go to extreme measures with a full blown water cure that usually is not possible when building miles of road. Water evaporates quicker at the joint during hydration as well. It's like a cake falling when you take it out of the oven, sort of.... Anyway, you get "slab curl." The arch enemy of all concrete pavers! Slab curl allows a hump to form at the joints. The joints are then subjected to massive impact loading under traffic. Especially todays traffic loads which are probably double or more of what the design loads were in the fifties when the interstates were designed. So the concrete at the joint fails.....
There are other reasons to grind. Subgrade failure, frost heave/settlement, poor drainage under the pavement, and even rutting (yes even in concrete) in the case of insufficient aggregate strength.
Point is, nothing is designed perfect from the start. There are too many variables out in the world. I'd like to think that observant and consciencious contractors and engineers would make adjustments in the field during construction. There are probably too many variables to build a concrete road that's perfect. Asphalt roads will have their own issues as well.
The upside is that concrete pavement can give you an extremely long and productive life cycle cost benefit. Usually the first 20 years of a concrete interstate require no maintenance whatsoever. Secondary roads may go as much as 30 years. Pretty good.
Grinding is one of your maintenance options early on. It eliminates slab curl. All a grinder does is act as a large straight edge that eats off the high points that pass under it. By eliminating the bumps, the road becomes smooth again and there is no more impact loading. This extends the life of the pavement. A few years later, you go in and repair cracked and damaged pavement and possibly grind again (usually not). Then in a few more years, you do a rehab. Remove bad concrete, grind everything, and reseal all the joints. You can do this for quite a while. Eventually, slab thickness will dictate a reconstruction. By then you should have in the neighborhood of fifty years of service from the pavement. The key is to stay on top of the impact loads and drainage issues. Most times those issues are tied together to cause the problems you are seeing.
Or..... You can do like a lot of Highway Departments and just pave over it with asphalt. :Banghead
Thus, we grind. :cool2
rofessor
