The increasing demand for durable and sustainable construction materials highlights the need for innovative solutions that combine structural performance with real-time monitoring. Ultra-High-Performance Concrete (UHPC) reinforced with conductive fillers offers a promising approach to extend service life and enable self-sensing functionality. This research investigates the mechanical and piezoresistive behavior of UHPC composites incorporating multi-scale reinforcement: steel or alloy fibers as macro-reinforcement, recycled carbon fibers at the microscale, and multiwalled carbon nanotubes at the nanoscale. An experimental campaign was carried out to evaluate compressive and flexural strength, electrical resistivity, and self-sensing response under cyclic compressive loading. The results confirm that the inclusion of conductive fillers increases up to 11% the compressive strength and up to 72% the flexural strength compared to the UHPC matrix with only steel fiber reinforcement. Steel fibers achieved values of fracture energy 85% greater than those of alloy fibers, which indicated greater energy absorption capacity. The addition of carbon nanotubes and recycled carbon fibers further improved flexural strength and energy absorption capacity, with hybrid mixes achieving up to 72% higher flexural strength and 21% higher energy absorption capacity when compared to the UHPC with steel fiber reinforcement. Electrical tests demonstrated that conductive fillers reduced resistivity by up to 97%, due to the created conductive pathways within the matrix. Self-sensing performance was significantly enhanced, with the best response obtained by the tri-phasic UHPC mix containing steel fibers, RCFs, and CNTs. This group achieved the highest fractional change in resistance (34%) and confirmed the synergistic effect of multi-scale reinforcement. However, poor repeatability was observed, highlighting the need for standardized testing protocols and further systematic studies on the topic. Overall, this study demonstrates that multi-scale reinforced UHPC can act as a smart material that couples superior mechanical performance with self-sensing properties, leading the way for more durable, sustainable, and intelligent infrastructures.
La crescente domanda di materiali da costruzione durevoli e sostenibili evidenzia la necessità di soluzioni innovative che combinino elevate prestazioni strutturali con il monitoraggio in tempo reale. Il calcestruzzo ad altissime prestazioni (UHPC), rinforzato con filler conduttivi, rappresenta un approccio promettente per prolungare la vita utile delle strutture e abilitare funzionalità di auto-sensing. Questa ricerca indaga il comportamento meccanico e piezoresistivo di compositi UHPC con rinforzo multi-scala: fibre d’acciaio o in lega come macro-rinforzo, fibre di carbonio riciclate alla scala microscopica e nanotubi di carbonio multi-parete alla scala nanometrica. È stata condotta una campagna sperimentale per valutare la resistenza a compressione e a flessione, la resistività elettrica e la risposta auto-sensibile sotto carichi ciclici di compressione. I risultati confermano che l’inclusione di filler conduttivi incrementa fino all’11% la resistenza a compressione e fino al 72% la resistenza a flessione rispetto alla matrice UHPC con il solo rinforzo in fibre d’acciaio. Le fibre d’acciaio hanno raggiunto valori di energia di frattura superiori dell’85% rispetto alle fibre in lega, indicando una maggiore capacità di assorbimento energetico. L’aggiunta di nanotubi di carbonio e fibre di carbonio riciclate ha ulteriormente migliorato la resistenza a flessione e la capacità di assorbimento energetico: le miscele ibride hanno mostrato incrementi fino al 72% della resistenza a flessione e fino al 21% della capacità di assorbimento energetico rispetto all’UHPC con rinforzo in fibre d’acciaio. Le prove elettriche hanno dimostrato che i filler conduttivi riducono la resistività fino al 97%, grazie alla formazione di percorsi conduttivi all’interno della matrice. Le prestazioni di auto-sensing sono risultate significativamente migliorate, con la risposta migliore ottenuta dalla miscela UHPC tri-fasica contenente fibre d’acciaio, fibre di carbonio riciclate e nanotubi di carbonio. Questo gruppo ha raggiunto la massima variazione frazionaria di resistenza (34%), confermando l’effetto sinergico del rinforzo multi-scala. Tuttavia, è stata osservata una scarsa ripetibilità, evidenziando la necessità di protocolli di prova standardizzati e di ulteriori studi sistematici sul tema. In conclusione, questo studio dimostra che l’UHPC con rinforzo multi-scala può agire come materiale “intelligente”, capace di unire prestazioni meccaniche superiori a proprietà di auto-sensing, aprendo la strada a infrastrutture più durevoli, sostenibili e intelligenti.
Development of smart ultra-high-performance concrete: an experimental approach
Rangel Orduz, Silvia Alejandra
2024/2025
Abstract
The increasing demand for durable and sustainable construction materials highlights the need for innovative solutions that combine structural performance with real-time monitoring. Ultra-High-Performance Concrete (UHPC) reinforced with conductive fillers offers a promising approach to extend service life and enable self-sensing functionality. This research investigates the mechanical and piezoresistive behavior of UHPC composites incorporating multi-scale reinforcement: steel or alloy fibers as macro-reinforcement, recycled carbon fibers at the microscale, and multiwalled carbon nanotubes at the nanoscale. An experimental campaign was carried out to evaluate compressive and flexural strength, electrical resistivity, and self-sensing response under cyclic compressive loading. The results confirm that the inclusion of conductive fillers increases up to 11% the compressive strength and up to 72% the flexural strength compared to the UHPC matrix with only steel fiber reinforcement. Steel fibers achieved values of fracture energy 85% greater than those of alloy fibers, which indicated greater energy absorption capacity. The addition of carbon nanotubes and recycled carbon fibers further improved flexural strength and energy absorption capacity, with hybrid mixes achieving up to 72% higher flexural strength and 21% higher energy absorption capacity when compared to the UHPC with steel fiber reinforcement. Electrical tests demonstrated that conductive fillers reduced resistivity by up to 97%, due to the created conductive pathways within the matrix. Self-sensing performance was significantly enhanced, with the best response obtained by the tri-phasic UHPC mix containing steel fibers, RCFs, and CNTs. This group achieved the highest fractional change in resistance (34%) and confirmed the synergistic effect of multi-scale reinforcement. However, poor repeatability was observed, highlighting the need for standardized testing protocols and further systematic studies on the topic. Overall, this study demonstrates that multi-scale reinforced UHPC can act as a smart material that couples superior mechanical performance with self-sensing properties, leading the way for more durable, sustainable, and intelligent infrastructures.| File | Dimensione | Formato | |
|---|---|---|---|
|
2025_10_Rangel_Orduz.pdf
non accessibile
Descrizione: Text of the thesis
Dimensione
7.18 MB
Formato
Adobe PDF
|
7.18 MB | Adobe PDF | Visualizza/Apri |
I documenti in POLITesi sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/10589/242841