http://repositorio.lnec.pt:8080/jspui/handle/123456789/31 2026-07-20T12:20:04Z http://repositorio.lnec.pt:8080/jspui/handle/123456789/1019297 Title: Pozzolanic potential of recycled aggregates for 3D printed concrete Authors: Santos, K.; Pacheco, J.; Vieira, M.; Silva, A.; Santos, S.; Lopes, R.; Monteiro, M. Abstract: The emerging technology of 3D concrete printing enables faster construction, complex geometries, and reduced on-site injury risks. Despite its benefits, it still relies heavily on cement. Incorporating recycled aggregate powder offers a promising strategy to lower environmental impact, though it poses challenges. Assessing the pozzolanic reactivity of these materials is essential, as they may contribute to mechanical and durability properties or act as inert fillers that enhance rheology and setting. This study investigates the pozzolanic activity and hydration behavior of recycled aggregate powder used to replace 50% of the binder and cement by mass in 3D-printed concrete. The experimental program included X-ray diffraction (XRD), thermogravimetric analysis (TGA), Frattini and Chapelle tests, setting time measurements, and the Strength Activity Index (SAI). Results show that the recycled material lacks significant pozzolanic activity. However, its influence on hydration and setting provides insights into its role as a filler in sustainable printable cementitious formulations. These findings underscore the importance of evaluating recycled materials before their application in additive manufacturing. 2025-09-01T00:00:00Z http://repositorio.lnec.pt:8080/jspui/handle/123456789/1019284 Title: Betão com a incorporação de agregado reciclado ARG 6,3/12,5: sustentabilidade, viabilidade técnica e inovação Authors: Pereira, J.; Henriques, G.; Vieira, M. Abstract: A incorporação de agregados reciclados (AR) em betões estruturais é uma via concreta para operacionalizar a economia circular na construção, reduzindo a extração de recursos naturais e o envio de resíduos de construção e demolição (RCD) para aterro. Este artigo sintetiza e discute a evidência técnica disponível para o agregado reciclado ARG 6,3/12,5 da Eco Impact (Pragosa) – com marcação CE e apto a substituir a fração 6,3/12,5 do agregado natural em betões simples e armados – com base no Documento de Aplicação LNEC DA‑143 (2024) e no Relatório LNEC 415/2023. Mostra‑se que o ARG 6,3/12,5 cumpre os requisitos da NP EN 12620 e da Especificação LNEC E471 (classe ARB1), apresentando propriedades físicas, químicas e mecânicas compatíveis com o uso estrutural. Em composições estudadas pelo LNEC, a substituição do agregado natural grosso 6,3/12,5 por ARG 6,3/12,5 pode reduzir a resistência à compressão de 1 até 2 classes consoante a classe do betão e a remessa do AR; a resistência à difusão de cloretos manteve‑se globalmente equivalente para classes XS, ao passo que a resistência à carbonatação justificou, em classes XC2–XC4, aumentos de recobrimento de 5/10/15 mm para garantir 50 anos de vida útil..pdf).pdf) Do ponto de vista ambiental, a literatura europeia indica que o provisionamento de AR tende a ter menor pegada de carbono do que o de agregados naturais, e que incorporações moderadas (≈20–30%) viabilizam reduções líquidas de CO₂ sempre que a distância de transporte do AR seja menor do que a do agregado natural e que o desenho de mistura evite aumentos relevantes de cimento. A produção industrial do ARG 6,3/12,5 é certificada (ISO 9001/14001 e CPR), assegurando rastreabilidade, controlo e escalabilidade. 2025-10-01T00:00:00Z http://repositorio.lnec.pt:8080/jspui/handle/123456789/1019282 Title: Thermal properties of recycled cement compressed stabilised earth blocks Authors: Real, S.; Bogas, J. 2025-01-01T00:00:00Z http://repositorio.lnec.pt:8080/jspui/handle/123456789/1019280 Title: A novel method for assessing time zero of cementitious pastes using ultrasonic pulse in corrugated tubes (UPCT) Authors: Silva, A.; Santos, K.; Capuzzo, V.; Ribeiro, A. C.; Custódio, J. Abstract: The Time Zero in cementitious mixtures marks the transition from a fluid suspension to a rigid structure, a critical phase for shrinkage analysis. This paper proposes a novel technique to measure Time Zero in cementitious materials through Ultrasonic Pulse in Corrugated Tubes (UPCT), originally used for autogenous shrinkage measurements. The corrugated tube design enables ultrasonic wave transmission while accommodating material deformation, preventing loss of contact due to volumetric changes. Cement pastes with a 0.35 water-to-binder ratio were tested, including a reference mixture with Portland cement and a second mixture incorporating 0.3% of a superabsorbent polymer (SAP). Time Zero was determined through ultrasonic pulse propagation time, VICAT needle penetration, and autogenous shrinkage tests using corrugated tubes. Results indicate that, for the reference mix, time-zero measurements were consistent across all methods, validating the ultrasonic approach proposed. However, in the SAP-modified mix, discrepancies arose, particularly in Vicat results, suggesting a delayed mechanical stiffening process. In cement paste with SAP, the reserve of water that the polymer allows, which is then released as hydration continues, may explain the observed delay in the kinetics of solid formation and is responsible for the reduction in autogenous shrinkage. These findings highlight the effectiveness of ultrasonic techniques in measuring the global structural evolution of cementitious materials. Nevertheless, variations in mixture composition and hydration mechanisms may compromise the reliability of certain methods, such as Vicat needle penetration, for accurately determining the transition to the hardening stage in cementitious materials. 2025-06-13T00:00:00Z