As the construction industry moves towards greater sustainability, the application of more durable and environmentally friendly materials, capable of providing comfort in buildings and infrastructure, is a key element to consider. In this context, the use of alkali-activated binders (AAB) and geopolymers (GP), which have a lower carbon footprint than ordinary Portland cement (OPC), has emerged as an important alternative. Moreover, the addition of waste-based lightweight aggregates (LWA) to AAB and GP matrices produces lightweight composites that offer enhanced mechanical performance and improved comfort as building materials, while offering an alternative use to the increasing number of waste materials from diverse sources. This paper presents a comprehensive review of the literature on the above-mentioned topics (waste LWA in an AAB/GP matrix) published between 2012 and 2023, mainly indexed in the Scopus database. The waste-based LWA reported in the literature were categorized, and their properties and morphology presented. Then, the influence of the size, quantity, and nature of the LWA on the composite's properties and performance was analyzed. Fresh state performance, mechanical performance, density, and thermal and acoustic insulation were considered. This review is complemented by a bibliometric analysis, where keyword correlation and co-authorship networks on this field are established. The review highlights the potential of cementitious composites including waste-based LWA as a sustainable building material for structural and non-structural applications. However, more studies are required to further understand the behaviour of these composites under innovative manufacturing processes, such as extrusion and 3D printing.

Cellular structures, formed by periodic two- or three-dimensional cells, offer weight reduction without compromising mechanical performance and are commonly fabricated via additive manufacturing. This study investigates the compressive behaviour of three polymer lattice structures—gyroid, diamond, and octet truss—fabricated by fused filament fabrication (FFF). A Box–Behnken experimental design was used to systematically evaluate the influence of three key parameters: cell size, strut/wall thickness, and layer thickness. A total of 225 samples were produced using PLA and subjected to compression testing in accordance with ASTM D1621. Linear regression and response surface methodology were employed to determine the statistical significance and impact of each factor. The results indicate that cell size has the strongest influence on both maximum force and displacement, followed by strut/wall thickness and layer thickness. Among the configurations, gyroid structures had the highest strength-to-density ratio, while diamond structures had the highest deformation capacity. These findings provide design insights for optimising lattice structures in lightweight applications and highlight the importance of carefully balancing geometric and printing parameters in FFF-based polymer components.

Objectives: The main objective of this study was to promote the formation of White and Brown Etching Layers (WEL and BEL) on R260 pearlitic steel by means of a controlled laboratory grinding process, in order to analyze the microstructural and mechanical changes from the surface to the base material.Materials and methods: R260 pearlitic steel used for railway rail manufacturing was investigated. The transformed surface layers were generated through a controlled grinding process. Microstructural characterization was performed using light optical microscopy (LOM) and scanning electron microscopy (SEM). Mechanical characterization was carried out by microhardness testing and nanoindentation from the ground surface toward the bulk material. Subsequently, the WEL region was analyzed by transmission electron microscopy (TEM) to identify microstructural changes in the different zones affected by the grinding process.Results: The results showed that WEL and BEL can be distinguished not only by their morphological features observed by LOM and SEM, but also by their mechanical properties. Both layers exhibited significantly higher hardness and Young’s modulus values than the pearlitic base material.Conclusions: The microstructural transformations induced by the grinding process were visually identified as WEL and BEL through contrast and texture variations observed by LOM and SEM. These layers extended from the ground surface to depths of approximately 30 µm and exhibited distinct mechanical responses associated with intrinsic microstructural changes generated by the grinding process.