Development of lightweight aggregates from coffee grounds and rice husk ash

ABSTRACT Coffee grounds (SCG) and rice husk ash (RHA) are used in this study as raw materials to obtain lightweight aggregates (LWAs), replacing clay. The waste generated during the processing of coffee and rice is commonly disposed of in landfills and rubbish dumps, aggravating environmental impacts. Combined with the scarcity of natural resources and the sustainable management of this waste, its properties favour the development of LWAs. However, research into their use is scarce and superficial. The aim of this research is to evaluate the application of SCG and RHA as raw materials in the production of a new sustainable LWA. The starting materials were benefited and then characterized by laser granulometry, X-ray fluorescence and diffraction, and scanning electron microscopy. The mixtures were then formulated according to the Riley diagram. The specimens developed were then dried and sintered at temperatures of 1100 to 1250 °C. A total of 20 different specimens were produced, with clay substitution ranging from 15% to 62%, 12 of which have at least one engineering application. The manufactured aggregates had a bloating index (BI ) of –79.90% to –7.80%, loss of mass (LOI ) of 15% to 53%, particle density ( ρd ) of 0.88 to 2.23 g/cm3, water absorption (WA24H) of 0.1% to 61.7% and crushing strength (S ) of 0.81 to 29.32 MPa, as well as being assessed for mineralogy and microstructure. In general, the main properties of LWAs were affected by the firing method and the proportions of starting materials. The results show that the production of sustainable LWAs from SCG and RHA is feasible, with the appropriate indices being achieved for application in engineering works and services.