Zeolitic tuffs as raw materials for lightweight aggregates

The possible use of zeolitic rocks for the production of lightweight aggregates was assessed, investigating both the expansion at high temperature and the technological features of fired products. Eighteen zeolite-bearing rocks from Sardinia, Campania and Tuscany (Italy) were taken into account. The firing expansion depends mainly on the chemical composition (especially silica and fluxing oxides) and the water content (largely related to the zeolite amount). Other relevant parameters are the temperature of maximum expansion (1350-1500°C, without additives) and soaking time (2-5 minutes). Some products are highly impervious (water absorption <1%) and exhibit a considerable firing expansion (>100% vol.), a low bulk density (0.5-0.7 g×cm-3) and fair technical properties (loose weight and strength of particles). These encouraging results make some of the investigated tuffs interesting raw materials for the production of lightweight aggregates.