Use of Zeolitized Rock Wastes for Lightweight Expanded Aggregates Production

This paper represents a review of a ten-years research aimed at testing zeolitized rocks for the production of Expanded Lightweight Aggregates (ELAs). These are generally obtained by firing raw materials like clay, shale and slate at high temperatures.

Raw materials used for these researches are industrial wastes of phillipsite and chabazite bearing tuffs of central-southern Italy (Campanian Ignimbrite – Cab70, Neapolitan Yellow Tuff - NYT, Sorano Ignimbrite - IS) and clinoptilolite epiclastites from Sardinia (LacBen) and Turkey (IZclino). Zeolite content is always higher than 50 wt. %. An industrial waste (SiC bearing mud deriving from polishing of porcelain tiles – FLG) and some expanding additives (fuel oil, SiC, CaCO3) were also used. FLG is constituted by glass, feldspar, quartz, zircon, and minor amounts (2%) of SiC.

Zeolitized materials were ground and powders (without or with additive) were pressed to get pellets fired in static or rotative kilns at temperatures between 1200-1450 °C.

Firing of additive-free zeolitized materials at temperatures of 1400 °C or higher gave lightweight aggregates with bulk density lower than 1 g/cm3, but these temperatures are non-economic when compared with those required by clays in ELAs production (1300 °C). A 0.5-1.0 % of SiC addition allows to get aggregates with densities of 0.6-0.8 g/cm3 yet at 1250 °C. These aggregates show a good mechanical strength with respect to those prepared without additive. The high costs of SiC drove to test FLG. The annual production of this waste in Italy is 50.000 tons. Mixtures of FLG with Cab70 and IZclino were fired at 1300 °C. Results were similar, regardless the zeolitized material used, and evidenced that bloating grows with FLG content. The technical features of ELAs are close to those of commercial expanded clays.

Two concretes prepared with this ELAs satisfy the requirements of lightweight structural concretes.