Campanian Ignimbrite as raw material for lightweight aggregates

Aimof this research is an evaluation of the zeolitized facies ofCampanian Ignimbrite as rawmaterial for the production of lightweightexpanded aggregates (LEA).Acommercial product (Cab70)was used as reference for this rock. Tests were carried out on “pure” samplesor mixed with an industrial waste mud (DPM—Dried Polishing Mud) deriving from a porcelain stoneware tile polishing process. Thismud contains SiC, a phase known to act as bloating enhancer. Rawmaterials were subjected tomineralogical (XRPD–RIR method) andchemical (XRF) analyses. Bloating upon heating was measured (Leitz heating microscope) on Cab70, DPM and on three mixtureshaving the following Cab70/DPMratios: 85/15 (Mix1); 70/30 (Mix2); 50/50 (Mix3). LEAproductionwas assessed both in static (mufflekiln) and in dynamic (rotating kiln) conditions by firing pellets, 3–8 mm in size, between 1220–1380 °C. The unit weight of the singleparticle was determined on fired and unfired products. All materials evidenced a decreasing density with temperature whereas the sameparameter decreases with DPM increasing content. Cab70 LEAs never dropped below 0.90 g/cm3, even at the highest temperature,whereas DPM LEAs range between 0.86 g/cm3 (at 1260 °C) and 0.46 g/cm3 (at 1380 °C). A direct but not linear relationship betweenDPMcontent and density was evidenced.Among the three mixtures,Mix2 showed the lowest DPMcontent able to produce the strongestdensity reduction. To get LEAs with the same density the rotating kiln required temperatures generally 60–80 °C higher than those of themuffle kiln. This difference should be related to the different thermal insulation of the two systems during firing. Two sets of LEAs weremassively produced in dynamic conditions from Cab70 (at 1380 °C) and Mix2 (at 1300 °C). These latter showed better technicalperformances in terms of unit weight of the single particle (0.81 vs. 0.98 g/cm3), bulk unit weight (460 vs. 565 kg/m3), water absorptioncoefficients (1.4 vs. 5.5% after 24 h) and compressive strength of the particles (2.9 vs. 0.6 MPa). Differences in pore shape, dimension,abundance and spatial distribution were observed by SEMbetween the two sets. The technical features of these LEAs were comparableto some expanded clays, with similar grain size, commercialised in Italy.These results are worth interesting as they reveal new perspectives of application both for a rock characterized by a low exploitationcost and widely available in central-southern Italy, as well as for an industrial waste produced in high amount but not recycled at all.