Structural Concretes with Waste-Based Lightweight Aggregates: From Landfill to Engineered Materials

This research provides possible opportunities in the reuse of waste and particularly muds, coming from both ornamental stone (granite sludges from sawing and polishing operations) andceramic production (porcelain stoneware tile polishing sludge), for the manufacture of lightweight aggregates. Lab simulation of the manufacturing cycle was performed by pelletizingand firing the waste mixes in a rotative furnace up to 1300 °C, and determining composition and physicomechanicalproperties of lightweight aggregates. The best formulation was used to produce and test lightweight structural concretesaccording to standard procedures. Both granite and porcelain stoneware polishing sludges exhibit a suitable firing behavior due to the occurrence of SiC (an abrasive component) which, bydecomposing at high temperature with gas release, acts as a bloating promoter, resulting in aggregates with particle density <1 Mg/m3. However, slight variations of mixture composition produce aggregates with rather different properties, going from values close to those of typical commercialexpanded clays (particle density 0.68 Mg/m3; strength of particle 1.2 MPa) to products with high mechanical features (particledensity 1.25 Mg/m3; strength of particle 6.9 MPa). The bestformulation (50 wt.% porcelain stoneware polishing sludge +50wt.% granite sawing sludge) was used to successfullymanufacture lightweight structural concretes with suitable properties (compressive strength 28 days>20 MPa, bulk density 1.4-2.0 Mg/m3).