What is the public works concession contract?
Ok, let's go to the grain and bluntly: the famous public works concession contract is basically when the government, either because it does not want or cannot, the ball passes to a private company to build and take care of a work (bridges, highways, whatever) for a while. It is not that they give you the work, eye, the private one plays it: he builds it, maintains it and, if everything goes well, it does its money charging tolls, selling services or what it touches.
The grace of this contract is that the State gets rid of the brown of the initial expenditure and the risks, especially when the thing costs an eye of the face or neither the experience to do so alone. That is, it's like saying "do it that I leave you, but if you screw it, it's your problem." Win-Win ... in theory.
Now, what makes it different from other public contracts? Well, to start, here the private does not charge only for putting bricks, but they let the work explode a good time to get juice. If there are tolls, he charges them. If you sell water, then. But of course, if the work does not give even pipas, the one who loses is the concessionaire, not the State. So there is more risk for the private than in a normal contract, where you pay and forget.
The legal roll varies according to the country, but there are normally rules so that finger concessions are not distributed between friends. There must be public tender, transparency, and some type of control so that the concessionaire does not do what they want. Come on, it is not the distant west.
If you are a company and want to get into this eggplant, you better know well what you get. You have to read the small print, have muscle to endure the fluctuations, and be ready to deal with politicians, bureaucracy and pissed off users. And be careful, as these contracts are usually in the long term, prepare for changes of government, economic crises and other surprises. It is not for lazy, really.