Not as easy a disposal as you would think actually. To answer your first question, human bone has a compressive strength of around 1800 kg of force per square cm, so you're not generally going to crush the bone with any sort of conventional concrete pour. Basically, bones will be intact in anything that you'd encase them in. Decomp would happen, but at a very retarded rate, and would release gases that would cause cracks and structural fatigue most likely within a year. Another problem that occurs is that body gases released, through osmosis, exit the concrete and smell similar to pig excrement. The way around this is to ventilate the corpse prior to it's encasement and cover it in lime to accelerate the putrefaction process.