Integrated Experimental, Environmental, and Statistical Performance Assessment of Sustainable Lightweight Aggregates from Smectite Clays and Porcelain Polishing Residue

The growing demand for sustainable construction materials has intensified research on eco-efficient lightweight artificial aggregates (LWAs). This study evaluates the feasibility of producing LWAs with potential structural applicability from smectite (bentonite) clays from Paraíba, Brazil, combined with porcelain polishing residue (PPR). Raw materials were comprehensively characterized by XRD, XRF, and TGA, confirming montmorillonite as the dominant mineral phase in the clays and revealing the high silica and alumina content of the residue. The incorporation of PPR proved essential, as the clays alone could not be effectively sintered. An experimental matrix comprising ten formulations across four clay types was tested at five sintering temperatures (1100–1250 °C), resulting in 50 formulation–temperature experimental conditions. Approximately 66% of the 50 formulation–temperature experimental conditions met key physical and mechanical criteria typically associated with structural lightweight aggregates, demonstrating strong potential for use in structural lightweight concrete, although concrete-scale validation is still required to confirm their performance within cementitious mixtures. Mechanical performance was strongly influenced by thermal processing and residue incorporation, with peak strengths observed within a narrow sintering window around 1150 °C, where conditions were consistent with enhanced vitrification and pore evolution. The lightweight behavior was directly associated with the formation and expansion of internal pores during sintering, which are essential for density reduction. In this context, an optimal balance between mechanical strength and internal porosity must be achieved, since excessive densification may limit pore development. Water absorption was used as an indirect indicator of pore connectivity and internal structure evolution. An environmental assessment based on modeled production scenarios demonstrated that increasing residue content and reducing firing temperature generally reduced the calculated cumulative energy demand and global warming potential under the adopted inventory assumptions. Because thermal-energy requirements were estimated rather than directly measured in industrial kilns, the environmental results are interpreted as comparative scenario-based estimates rather than direct measurements of industrial-scale performance. Overall, the developed aggregates show strong potential for structural lightweight concrete applications, although concrete-scale validation remains necessary to confirm their performance in cementitious mixtures. This approach establishes a quantitatively grounded framework for designing low-carbon LWAs, contributing to decarbonization strategies in the ceramic and construction sectors.