Clays to lightweight aggregates: Thermochemical modeling and industrial validation

The creation of thermochemical models to forecast the dependent variables governing the bloatability of lightweight aggregates (LWAs) is the goal of this work. Laser particle size analysis, XRD, XRF, IR, TGA-DTA, SEM-EDX, Laser imaging system, µ-CT, hot-stage microscope and Factsage (8.3) thermodynamic software were used for clays and LWAs characterization in the temperature range 900–1250°C. It was found that the LWAs bloating zone occurs at 1050–1250°C with a minimum bulk density (BD) of (0.74 g/cm3) at 1250°C. During the LWAs pyroplastic state, the crystallization of anorthite from the silicate melt lowers its viscosity due mainly to the alkalis’ uptake into the anorthite lattice. However, the silicate melt is still viscous enough to trigger the reduction of hematite and consequently guarantees the evolution of bloating gases. The simultaneous association of higher evolved gas with less melt content of higher viscosity would promote the LWAs bloatability. The higher the gas that accompanied with low melt of lower viscosity would loosen the LWAs their consistency and sphericity upon their sudden cooling. Based on the LWAs bulk density and lab experimental observations, the production window limits of successful LWAs are ≥40 wt% silicate melt of 103-107 Pa.s viscosity that accompanied with (0.50–4.00 wt%) gas content. This production window has been verified by Liapor industrial kiln feed. The LWAs pyroplastic and post-quenching characteristics are all statistically significant variables (<0.05) for prediction modeling. The forecasting models are statistically verified by the multi-collinearity testing that shows VIF values <10 indicating the absence of any multi-collinearity among the models’ explanatory variables.