Spun concrete poles have been in use for over 100 years. Increases in the strength of concrete and, to a lesser extent, steel for prestressing strand, have made possible innovations in the poles themselves. These include high-capacity poles, reverse tapered poles, and hybrid poles. The use of high-strength concrete results in more economical poles that can compete successfully with wood- and steel poles. The low porosity and low permeability of high-strength spun concrete make it durable even in harsh environments. Concrete poles can generally be embedded direcdy in the ground, without the need for a separate foundation. Centrifugal casting removes water from the concrete and compacts it for greater strength and durability.