“…This meta-state is widely addressed as being reactive as pozzolana (Ambroise et al, 1985(Ambroise et al, , 1987Applied Clay Science xxx (2015) xxx-xxx He et al, 1995aHe et al, , 1995bHe et al, , 2000Baronio and Binda, 1997;Liebig and Althaus, 1997;Kakali et al, 2001;Sabir et al, 2001). Nevertheless, firing to higher temperatures results in the formation of new unreactive phases such as spinel and mullite (Mendelovici, 1997;Bondar et al, 2011a). Anyway, a careful calcination can activate the material leading to an increase of its geopolymeric reactivity (Xu and Van Deventer, 2002) and a consequent increase in terms of compression strength of the final product obtained.…”