What is the reason for pollution on a building site?

Question

why don't building sites re-use the scrap material to make something more usefull?

Answer 1

the main reason for pollution is that re-using scrap takes time & effort (aka can't be bovvered).

some building sites, especially small independent ones, are models of good practice & are very succesful and profitable

Others just make a lot of money anyway without trying.

Answer 2

Building materials are recycled as much as possible, because it makes good economic sense to do so.

For instance, if you only use a small piece of a 2x4 and can use the rest somewhere else, the builder will do so.

Unless it costs him more money to look for the scrap piece than to go to order another one.

There is nothing stopping some young, wild eyed environmentalist from approaching the builder to purchase his scrap (as long as they can give him  a valid manifest of recycling - so the builder will not get a bill for disposal and cleanup because the guy purchasing it dumped it on the side of the road), then they may sell him the scrap.

You have to remember that the builder is responsible in the eyes of the law for the proper disposal of his scrap.  If it ends up in the Hudson River, you can believe that the authorities will send him a big $$$$ for cleanup.  Sometimes it is cheaper to make sure things are disposed of properly instead of giving it away.