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.

Contexto: Se realizó una búsqueda local de tejidos de fibras vegetales para determinar la composición de los grupos funcionales y morfología de su superficie antes y después de un tratamiento alcalino con miras a su empleo como refuerzo en compuestos de matriz polimérica.Método: La búsqueda se desarrolló dentro del área metropolitana del Valle de Aburrá, Colombia. Las fibras se trataron por inmersión en NaOH disuelto al 6 % w/v por 48 horas, seguida por una neutralización en ácido acético al 1 % v/v por una hora. Posteriormente fueron secadas a 60 °C por 24 horas. Las técnicas empleadas para los análisis fueron la espectroscopía infrarroja por transformada de Fourier (FTIR) y la microscopía electrónica de barrido (SEM).Resultados: Se seleccionaron tejidos de fique, yute, corteza de coco, lino y algodón. Los análisis FTIR muestran una tendencia a la disminución de ácidos grasos, hemicelulosas, ligninas y enlaces β en la superficie de las fibras, mientras que las imágenes SEM demuestran la remoción de impurezas, la exposición de rugosidades y la creación de espacios interfibrales.Conclusiones: El tratamiento alcalino podría favorecer el mecanismo de anclaje del polímero termofijo a la superficie de las fibras y la creación de enlaces entre las moléculas polares de las fibras y el polímero termofijo, disminuyendo el deslizamiento relativo entre matriz y refuerzo durante la aplicación de cargas.

In the context of the circular economy and the adoption of one of its business models, namely ”resource recovery”, this study presents an opportunity to valorize industrial and urban wastes using alkaline activation technology to produce hybrid binders. Several alkali-activated binders were produced using response surface methodology based on a mixture of 45/45/10 clay brick waste, fly ash, and Portland cement. The compressive strength and setting time of each were evaluated. The hybrid cementitious pastes achieved up to 45 MPa after 28 days of setting. Based on the experimental data, two binders were selected as the cementitious matrix for composites, with paper sludge as the lightweight aggregate. Incorporating up to 45% volume of paper sludge allowed extrusion of the materials. The addition of paper sludge reduced the compressive and flexural strength. These results were explained by the decrease in density and the increase in porosity. However, there was an improvement in the thermal properties of the composites; in particular, the thermal conductivity range between 0.35 and 0.49 W/mK. Finally, it was found that the composites with 25% volume of paper sludge had the best combination of properties, positioning them as potential construction materials.

The largest proportion of solid waste comes from the construction industry. Construction and demolition waste (CDW) include among others, petrous waste like those derived from concretes and masonry, ceramic rips, and excavation products, being the latter, the ones with the largest generation percentage. Petrous waste reuse is well studied in literature, however, the reincorporation of excavated soils with poorly geotechnical features represents a major challenge than traditional type of reuse. In this paper, experimental results are shown for the design of compacted blends composed of excavated soils, CDW and cement, which are selected as the main supply of prefabricated hydraulic elements. Technical feasibility was established from Proctor test and unconfined compressive strength results, both as a criterion for workability and maximum densification and use of waste. A life cycle assessment (LCA) was performed for the compacted blends with the best technical feasibility results to evaluate its environmental impact. The results showed that compacted blends with at least 90% of waste meet the technical criteria for being reused.

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.