Microstructure and mineralogy of lightweight aggregates manufactured from mining and industrial wastes

► We have studied the microstructure and mineralogy of LWA produced by wastes. ► The microstructure is controlled by the raw materials and heating conditions. ► There are several relations between the microstructure and the physical properties. The microstructure and mineralogy of lightweight aggregates manufactured with washing aggregate sludge, sewage sludge and a clay-rich sediment have been studied. The mineralogical analysis revealed the neo-formation of plagioclase and pyroxene group minerals and a minor presence of gehlenite. Some relationships may be established: (i) heating temperature and dwell time affect the formation of new porosity; (ii) the disappearance of pyroxenes could produce changes in the density of the solid material in the lightweight aggregates; (iii) when an external glassy film is not present, water absorption values depend on the size and number of each type of pore.