The first object they were securing to the steel cage was the baseplate. This is the "top" of the piling, as the piling will be sunk into the ground. The steel building will be bolted and possibly also welded to these baseplates. The steaming helps the concrete cure faster. It hardens better, faster this way. Nobody will ever see those pilings when they are in use but it is nice to know what the roots of your high-rise look like. I have a degree in materials engineering, and have worked in concrete prestressed bridge beam construction. The steam aids in curing the concrete. The base plates are used to tension the steel rebar core. These both help speed the process and make for a much stronger end product. Steel is very strong in tension and concrete is very strong in compression. When you combine the two strengths of each you get an even stronger more flexible end result. The steam curing is probably needed for strength. Concrete always cracks as it cures - there's no way to completely stop all cracking. If it develops large cracks, the concrete will be weak, but if it only develops micro cracks that you can't even see, it will be much stronger. One of the ways you can minimize cracking is by keeping the concrete wet while it cures. That's why when they pour concrete driveways, it's best to keep misting water on them for a day or two. It will increase the strength of the concrete tremendously. Another way to minimize cracking is to keep it the same temperature all over the concrete. And since the center will get quite hot (concrete makes its own heat as it cures), they use heat to keep the outside from cooling off too quickly.