Mix four basic ingredients - water, cement, sand, and aggregate - and you have concrete. However, if you want concrete that is stronger, more durable, and wards off the attacks of chemicals and the weather, then you need to go beyond the basics and consider using a specialty concrete. Included here are just a few of the more than 65 types of specialty concretes. There's one for just about every application. If not, it is said that necessity is the mother of invention: Silica fume or microsilica, slag, fly ash, polymer or latex-modified, lightweight or insulating, high-strength, heavyweight, preplaced aggregate, roller-compacted, porous or permeable, cyclopean (rubble), foamed, no-slump, sawdust, spun, and vacuum concrete.