My own personal theory is that there is nothing that members of this board cannot answer. Always been quite amazed to be honest.
So, this question has been bugging me. The roads around my Moo Baan got tore up pretty badly in the big flood a few years ago. They finally got around last month to fixing them (!!). The old road was standard tarmac. So, instead of re-doing that, they worked in about 50 meter strips, half the road at a time. On top of the old road they put down a sand base, laid iron mesh on that, another layer of sand, then poured an inch or so of concrete on top of that. Means that the new surface is about 10cm or so higher than the original road, but as they filled back right to the property wall, it all worked out somehow. And now looks a lot better.
After they had let the concrete set, a day or so later they cut a channel into the concrete across the width, about 1 cm wide and half a cm deep using some special grinding machine. The cuts were made every 10 meters or so. They then poured black gunk into the ditch, together with the bit where the two half of the road met, along the center line.
Onto the question: Why. Why cut the grooves into the concrete? What purpose does it serve?
A followup would be why the black gunk. The thing is, in many places there is no black gunk, probably mixed with dust or the like and has now gone. So its probably not vitally important, but what is the purpose of it?
Answers will be appreciated, cause it irks the hell out of me not knowing.
Cheers.