Pozzolans are made up of siliceous or siliceous and alumi-nous materials that, in finely divided form, will react with calcium hydroxide to form cementitious materials. The term “pozzolan” evolved from the name given to a deposit of volcanic material located near Pozzuoli, Italy. This deposit, originally referred to as pozzolana, consisted of pumice ash, or tuff, comprised of trachyte found near Naples and Segni, Italy. Trachyte is a volcanic rock comprised primarily of feldspar crystals in a matrix of siliceous glass. Pozzolana was formed from an explosive volcanic eruption in 79 AD at Mount Vesuvius, which engulfed Herculaneum, Pompeii, and other towns along the bay of Naples. Chapter 3 provides historical information about the use of pozzolans.
The term “natural pozzolan” encompasses a broad range of materials. A few of these materials are pozzolanic in their natural state. However, most of the materials considered natural pozzolans require some type of processing to render the material pozzolanic. Some may require only drying and grinding/classifying, while others may require heat treat-ment and grinding to adequately activate the pozzolanic nature of the material. Chapter 4 provides a brief descrip-tion of the various materials classified as natural pozzolans, which are the focus of this report.
This report contains information and recommendations concerning the selection and use of natural pozzolans generally conforming to the requirements of ASTM C618-08. Topics covered include the effect of natural pozzolans on concrete properties, a discussion of quality control and quality assurance practices, and guidance regarding handling and use of natural pozzolans in specific applications.