"Professionals" always say that concrete will crack, but it ain't so. If its mixed on the dry side, compacted well, and allowed to dry slow it can last many lifetimes without cracks, as long as the design and re-enforcement is done properly. My brother runs a concrete constuction company and also says that all concrete will crack. He is still waiting for my 22-year old projects to crack, including a bridge and a backyard pond. The bridge has had heavy equipment over it many times (including concrete trucks), but it has proper footings, was mixed on the dry side (in wheelbarrows, compacted well (with a 4x4), has plenty of rebar, and dried slowly under plastic.
