Inorganic polymers on the basis of alumina and silica units, often called geopolymers (Davidovits 1999; Hanzlicek and Steinerova 2002; Palomo and López de la Fuente 2003; Van Jaarsveld 2002), can be synthesized from a wide range of dehydroxylated aluminosilicate powders, including natural pozzolans (Davidovits 1991, 1994a). The preparation of geopolymer cement using natural pozzolanas from vitreous pyroclastic materials produced by violent volcanic eruptions reduces the environmental impact of cement manufacture, and if long-term durability can be achieved, materials similar to the ancient Roman cemented structures can be prepared