Concrete is widely used in residential construction for footings, stem walls, and exposed basement flooring, as a subfloor for slab-on — grade construction, and as a finished floor material. Concrete consists of cement (usually Portland cement), water, and sand and other aggregates.
Once cured, concrete becomes an inert product and is not usually associated with toxic exposure, although there may be some more subtle health effects. (Refer to the essay by George Swanson to learn more about these effects and about products that can be substituted for Portland cement.) Certain common construction practices can make concrete harmful to human health and should be avoided. These practices are discussed in the following sections.
Cement is the “glue” that holds the various components of concrete together and comprises approximately 18 percent of the concrete by volume. Concrete is high in embodied energy because of the tremendous heat required to make cement. Cements are often advertised as “green” because they substitute a waste product for Portland cement. The replacement of Portland cement with fly ash has become a common practice. However, fly ash can be a byproduct of the incineration of toxic or hazardous waste. We therefore believe that cement products containing fly ash should be used only if it can be determined that it is derived from a nonhazardous source.
Although it is difficult to build a home today without the use of some concrete, there are many strategies, discussed throughout the book, that we can employ to reduce our use of Portland cement.
Clean, potable water should be specified for mixing concrete:
• Water shall be of potable quality, free of taste, color, and odor, and should not foam or fizzle.
The aggregate component accounts for 60 to 80 percent of concrete volume. The size and characteristics of the aggregate will affect the quantities of cement and water required and
the compressive strength, weight, and surface character of the finished concrete. Aggregate materials range in size from fine sand to crushed rock pieces. Sometimes recycled materials are used as aggregate and these may be a source of contamination. Recycled industrial waste products may contain hydrocarbons and sulfur. If the source is an industrial process with residual heavy metals or toxic compounds, it can result in a product with toxic properties.
