Zeolitic tuffs as raw materials for lightweight aggregates R. de’ Gennaro a , P. Cappelletti b , G. Cerri c , M. de’ Gennaro b , M. Dondi d, * , A. Langella e a Societa ` Italiana Zeoliti,Via Pescarolo 1, 41040 Pigneto, Italy b Dipartimento di Scienze della Terra, Universita ` Federico II, Via Mezzocannone 8, 80138 Naples, Italy c Istituto di Scienze Geologico-Mineralogiche, Universita ` di Sassari, Corso Angioj 10, 07100 Sassari, Italy d Istituto di Scienza e Tecnologia dei Materiali Ceramici, CNR-ISTEC, via Granarolo 64, 48018 Faenza, Italy e Dipartimento di Studi Geologici ed Ambientali, Universita ` del Sannio, Via Port’Arsa 11, 82100 Benevento, Italy Received 22 October 2002; received in revised form 3 July 2003; accepted 11 August 2003 Abstract The aim of this research is to assess the possible use of Italian zeolitic rocks for the production of lightweight aggregates. In particular, both the expansion at high temperature and the technological features of fired products were investigated. Fifteen zeolite-bearing volcanoclastites from Northern Sardinia and three zeolitized tuffs from Campania and Tuscany (Sorano and Campanian ignimbrites and Neapolitan Yellow Tuff) were taken into account. The firing expansion turned out to be mainly dependent on the chemical composition (especially SiO 2 and fluxing oxides such as Fe 2 O 3 , Na 2 O, K 2 O, MgO and CaO) and the water content (largely related to the zeolite amount) of the raw materials. Other relevant parameters were the temperature of maximum expansion (ranging between 1350 and 1500 jC, without additives) and soaking time (between 2 and 5 min). Some products are highly impervious to water (water absorption below 1%) and exhibit a considerable firing expansion (>100% in volume), 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. D 2003 Elsevier B.V. All rights reserved. Keywords: Zeolite; Lightweight aggregates; Campi Flegrei; Sardinia; Vulsini district; Italy 1. Introduction Aggregates are commonly defined as natural or artificial incoherent materials constituted by elements with different grain size. They are generally used in the production of concretes or as raw materials for the manufacture of ‘‘concrete bricks’’, through compac- tion, sometimes using binders. Lightweight aggregates are defined as materials lighter than water and dis- tinctly more porous than sand, gravel and ground rock, which are commonly referred to as ‘‘dense’’ aggre- gates (Klinefelter, 1960; Dower, 1987; Loughbrough, 1991). In fact, the unit weight of lightweight aggre- gates is 2/3 but sometimes also 1/3, than dense aggregates (Bates, 1969). This feature sensibly reduces the bulk density (i.e. the load transmitted to the soil) and makes easier to work and transport the lightweight products. An expanded aggregate is formed by quick heating at high temperature of materials which are able to 0169-1317/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2003.08.005 * Corresponding author. Fax: +39-0546-46381. E-mail address: dondi@istec.cnr.it (M. Dondi). www.elsevier.com/locate/clay Applied Clay Science 25 (2004) 71 – 81