The growing demand for lightweight aggregates (LWAs) in the construction industry is driving the development of sustainable alternatives based on the reuse of solid industrial waste. The aim of this study was to assess the technical feasibility of using red ceramic waste (RCW) as a partial or total substitute for red clay (RC) to produce lightweight expandable aggregates. Six formulations were made with different proportions of RCW and RC and sintered at four temperatures (1100, 1150, 1200 and 1250 °C). They were characterised using physical, thermal, morphological, chemical and mechanical analyses, according to standard protocols. The results showed that almost all the formulations sintered at 1200 and 1250 °C had a positive bloating index (BI > 0), particle density of less than 2.0 g/cm³, low water absorption of less than 2% and mechanical strength of more than 5.4 MPa, revealing strong potential for use in lightweight structural and non-structural concrete. The main conclusion is that RCW, even used in isolation, has physicochemical and mineralogical properties suitable for the production of lightweight aggregates under optimised thermal conditions, contributing to the development of sustainable materials with a competitive technical performance compared to commercial LWAs.

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 (WA_24H) 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.

This study assessed the feasibility of producing lightweight aggregates (LWAs) using diatomite waste (DW) as a clay substitute. The research aimed to reduce the consumption of natural resources and minimise the environmental impacts caused by the disorderly disposal of DW. Chemical, physical, and mechanical tests were carried out on six formulations of mixtures containing 50% to 100% DW, sintered between 1100 and 1250 °C, resulting in 24 samples. The aggregates had a particle density between 1.14 and 2.13 g/cm³, a maximum bloating index of 5.7%, a crushing strength of up to 11.14 MPa, and a mass loss of up to 8.7%. Minimum porosity of 2.8 percent and water absorption of 2.0 percent were observed. Sixteen samples met the criteria required for commercial applications, demonstrating that replacing clay with DW is technically feasible. The high porosity of DW was found to influence the density of the LWAs. The findings of this study highlight the environmental sustainability of using DW as an alternative raw material, contributing to circular economy strategies in the construction sector.