POZZOLANS AND BY-PRODUCTS Eighteen million tons of concrete block are created each year in the United States; 170 pounds per person. Because block is 80 percent air by volume, it has low embodied energy and is composed of 90% plentiful inert material; it is already an ecologically sound building component. Its chief environmental deficiency is reliance on portland cement, a material whose ingredients have changed little since 1900. Cement requires 1.6 tons of raw material for each ton produced and releases 1 ton of emissions in production due to fossil fuel use and carbon dioxide release. This is due primarily to the persistent use of limestone which requires high processing temperatures to become a pozzolan. Cement manufacturers use limestone because they have always used limestone. Limestone is a pozzolan, a material when finely ground and combined with water, reacts with calcium hydroxide to form a cement. Existing research has identified more than a dozen naturally occurring or by-product pozzolans that can perform equal to or better than limestone and would not require high-temperature processing. Our research identified three pozzolans that could be implemented immediately as more ecologically sound substitutes if several industries joined together in collaboration. Concrete block is inherently a regional material. Production must occur in the vicinity of resources to be efficient, typically a radius of fifty miles. Our research revealed the potential to create greater regional diversity in concrete block by utilizing limestone alternatives and aggregate alternatives available in the vicinity of each production facility. In addition to more efficient use of resources, these alternatives will lend a unique color and texture to block produced and utilized in each locale. Rather than cling to forced uniformity, block manufacturers could embrace natural diversity to distinguish and promote their product in a competitive market while increasing their economic margins. |