Eliane Khoury

Constitués de plusieurs composants (granulats naturels et pâte de ciment adhérente), les GBR ne sont à l’heure actuelle pas utilisés largement dans la formulation de nouveaux bétons. Les propriétés médiocres des GBR compliquent considérablement la détermination de la quantité d’eau efficace dans le béton frais. Tout d’abord, une étude bibliographique va mettre en évidence la grande dispersion des résultats des essais de caractérisation des GBR et des propriétés des bétons recyclés à l’état frais et durci. Ensuite, une étude vise à analyser l’hétérogénéité des GBR et des granulats de béton concassé (GBC) par rapport à différents paramètres : aux impuretés granulaires, à la densité et à la teneur en pâte de ciment, au malaxage du béton parent, et au niveau de la capacité d’absorption d’eau des GBC en fonction de leur état de pré-humidification. Enfin, une dernière partie est destinée à améliorer la maîtrise de l’eau efficace réelle dans la fabrication du béton recyclé. La cinétique d’absorption des GBC dans une pâte de ciment est tout d’abord étudiée. Ensuite, l’évolution de l’eau efficace durant le malaxage de bétons à base de GBC est investiguée au moyen d’une méthode originale basée sur le suivi des courbes de puissance du malaxeur. Finalement, l’effet d’un malaxage sous vide relatif sur les propriétés des bétons à base de granulats naturels et des bétons à base de GBC est étudié.

This study investigates the use of recycled concrete aggregates as a replacement for natural sand in printable mortars, comparing the properties of both fresh and hardened states. Two types of mortars were considered, natural mortar and recycled mortar, with further variations based on mixing methods under ordinary atmospheric pressure and vacuum pressure. The experimental approach included air content, mini-slump, printability, and various hardened state tests such as compressive strength and porosity measurements using both water absorption and mercury intrusion porosimetry (MIP). The results showed that mortars made with recycled sand exhibited higher fluidity, as evidenced by an increase in slump of approximately 50 to 70 mm across 30 min, compared to those made with natural sand. This difference was attributed to the pre-saturation of recycled sand, which, as a hypothesis, may increase with the amount of free water available while mixing under vacuum. Additionally, mortars containing recycled sand exhibited higher water-accessible porosity (approximately +7% compared to natural mortars) and lower compressive strength, with a reduction of about 5 to 10% for printed and cast samples, with the decrease being more pronounced in printed specimens. However, vacuum mixing was found to significantly reduce entrapped air content, by about 53% in natural mortars and 62% in recycled ones, and to enhance the workability of both types. The pore size distribution indicated that recycled mortars had a more complex pore network, with pores in the ranges of [0.01–0.1] mm and [0.1–1] mm, contributing to increased porosity and reduced mechanical strength. Overall, this study demonstrates the potential of using recycled sand in mortar formulations, with proper control of pre-saturation and mixing conditions to optimize performance in both fresh and hardened states.

This comprehensive literature review investigates the impact of stabilization and reinforcement techniques on the mechanical, hygrothermal properties, and durability of adobe and compressed earth blocks (CEBs). Recent advancements in understanding these properties have spurred a burgeoning body of research, prompting a meticulous analysis of 70 journal articles and conference proceedings. The selection criteria focused on key parameters including construction method (block type), incorporation of natural fibers or powders, partial or complete cement replacement, pressing techniques, and block preparation methods (adobe or CEB). The findings unearth several significant trends. Foremost, there is a prevailing interest in utilizing waste materials, such as plant matter, construction and demolition waste, and mining by-products, to fortify or stabilize earth blocks. Additionally, the incorporation of natural fibers manifests in a discernible reduction in crack size attributable to shrinkage, accompanied by enhancements in durability, mechanical strength, and thermal resistance. Moreover, this review underscores the imperative of methodological coherence among researchers to facilitate scalable and transposable results. Challenges emerge from the variability in base soil granulometry and disparate research standards, necessitating concerted efforts to harness findings effectively. Furthermore, this review illuminates a gap in complete lifecycle analyses of earthen structures, underscoring the critical necessity for further research to address this shortfall. It emphasizes the urgent need for deeper exploration of properties and sustainability indicators, recognizing the inherent potential and enduring relevance of earthen materials in fostering sustainable development. This synthesis significantly contributes to the advancement of knowledge in the field and underscores the continued importance of earth-based construction methodologies in contemporary sustainable practices.