Volcanic ash

Volcanic ash (VA) is a natural resource whose use in cementitious materials has been extensively studied in the last thirty years. The pozzolanic activity makes the volcanic product suitable for use as supplementary cementitious material in concrete. However not all ashes possess this reactivity in their natural state. Low-reactive VAs can instead effectively be used as aggregates in lightweight composites. In the chapter, the physical and chemical properties of ash erupted by volcanoes located in various geographic areas are compared. The chemical composition and morphological and mineralogical features are examined. Particular attention is devoted to the reactivity of ashes and other volcanic products and to the standard test methods to assess their pozzolanic activity. The properties of concrete with VA as partial substitution of ordinary Portland cement are then widely treated. The effects of VA on fresh properties, mechanical strength and durability of concrete are analysed, including blended cement concrete containing other volcanic materials. Properties of concrete incorporating VA as aggregate are treated too. Next, two outstanding issues are discussed. The lack of standard test methods specifically conceived for this class of supplementary cementitious materials and the environmental benefit that results from the use of VA as replacement of Portland cement. Proposals for the recycling of waste VAs are presented at the end of the chapter.