The Materials Used in Precast Concrete Walls

Cement

• Like any concrete, precast concrete includes Portland cement, a mixture of calcium silicates, calcium sulfate and other ingredients. The silicates react with water to form a nice, thick gel that gradually hardens and becomes rock-solid, gluing the other particles in the concrete mixture together. The final product will be stronger and tougher if it's allowed to harden under the right conditions, a process known as curing.

Aggregate

• Another key ingredient is the aggregate -- the crushed rock, sand and/or gravel that constitutes a large portion of the total volume. The mineral composition of the aggregate varies depending on where it was quarried. Concretes usually incorporate a mixture of both fine and coarse aggregates, although the precise ratios of the ingredients may vary depending on the manufacturer and the kind of precast concrete you buy.

Water and Air

• Water is another vital ingredient; cement won't begin to harden until water is added. Water quality is not so important for concrete mixing as it is for drinking, of course, but excessive impurities in the water can damage the quality of the final product, so manufacturers generally use water that meets at least some minimum standard of purity. A small fraction of the total volume also consists of air spaces -- tiny capillaries and pores that remain unfilled as the concrete hardens.

Other Ingredients

• Cement, water and aggregate are the basic ingredients in all precast concretes. Depending on the product, however, precast concretes may also contain other additives such as air entraining agents, which create microscopic air bubbles in the concrete to improve its resistance to certain kinds of wear. Precast concretes may also contain fly ash as an optional addition to the aggregate. Steel or carbon fiber reinforcement lends precast concrete extra strength, while water reducing admixtures can help to make the concrete more workable.