Cement production accounts for nearly half of the total CO2 emissions related to industrial processes. Concrete, with cement as its main constituent, is the most used man-made material worldwide. Concrete is widely used in most infrastructure projects, either big or small scale, from dams to sidewalks; however, it has inherited cracking vulnerability, which is unavoidable. Even small cracks (<0.3 mm) allow the ingress of water or harmful substances that deteriorate the concrete matrix, corrode the reinforcement, and thus reduce concrete structures' service life, leading to costly maintenance operations and inspections. Hence, any improvement in the life cycle of concrete materials will hugely benefit the environment and society. Autogenous self-healing concrete is a material that can self-seal/heal cracks, which recovers concrete's permeability and mechanical properties. This research aims to devise a methodology to evaluate the autogenous self-healing capacity of ultra-high performance fiber reinforced concrete (UHPFRC) under cyclic load. The experimental campaign had two stages; in the first stage, preliminary tests were performed to characterize the material's mechanical properties under flexure, including monotonic and cyclic tests. In the second stage, cyclic loading induced fatigue damage on pre-cracked UHPFRC beam specimens. Finally, the damaged specimens were immersed in water to activate the self-healing; immersion periods were 1 and 3 months. After the healing period, the specimens were brought to failure by cyclic loading. Ultrasonic pulse velocity (UPV) tests and microscopic imaging were employed to evaluate the healing occurrence, from which recovery indices by UPV and crack sealing were determined. The results obtained were used to evaluate the fatigue life of the specimens before and after the healing process, comparing changes in variables such as the number of cycles to failure, stiffness, critical crack opening displacement (COD), and rate of COD. The results suggest that the water immersion process favors healing in cracks of less than 100 µm. Moreover, there seems to be an improvement in the fatigue life after healing, observed by stiffness recovery of the specimens.
La produzione di cemento rappresenta quasi la metà delle emissioni totali di CO2 legate ai processi industriali. Il calcestruzzo, con il cemento come componente principale, è il materiale artificiale più utilizzato al mondo. Il calcestruzzo è ampiamente utilizzato nella maggior parte dei progetti infrastrutturali, sia di piccola che grande scala, dalle dighe ai marciapiedi, tuttavia questi ereditano la vulnerabilità del materiale alla formazione di fessure che sono inevitabili. Anche piccole fessure (<0,3 mm) permettono l'ingresso di acqua o sostanze dannose che deteriorano la matrice del calcestruzzo, corrodono i rinforzi, e di conseguenza riducono la vita utile delle strutture portando ad alti costi per le operazioni di ispezione e di manutenzione. Di conseguenza qualsiasi miglioramento del ciclo di vita del calcestruzzo avrà notevoli benefici per l'ambiente e per la società. Il calcestruzzo intrinsecamente autoriparante è un materiale in grado di riparare le fessure, recuperando le proprietà meccaniche e di permeabilità. Questa ricerca ha lo scopo di sviluppare un metodo per la valutazione della capacità di autoriparazione autogena di calcestruzzi fibrorinforzati ad alte o altissime prestazioni (Ultra High Performance Fiber Reinforced Concretes – UHPFRC) sottoposto a carico ciclico. La campagna sperimentale è organizzata in due fasi: nella prima sono stati eseguiti test preliminari per caratterizzare le proprietà meccaniche del materiale sottoposto a flessione, inclusi test ciclici e monotoni. Nella seconda fase sono stati indotti danni da fatica in campioni UHPFRC pre-fessurati (pre-cracked) attraverso carichi ciclici. Infine i campioni danneggiati sono stati immersi in acqua per attivare l'autoriparazione con periodi di immersione di 1 e 3 mesi. Dopo il periodo di autoriparazione i campioni sono stati portati a cedimento attraverso carichi monotoni o ciclici. Test UPV e tecniche per immagini microscopiche sono stati utilizzati per valutare il processo di autoriparazione. I risultati ottenuti sono stati usati per valutare la vita a fatica dei campioni prima e dopo il processo di autoriparazione, confrontando cambiamenti nel numero di cicli per indurre cedimento, rigidità, COD critico e tasso di COD. I risultati indicano che l’immersione in acqua favorisce la rigenerazione delle fessure minori di 100 µm. In più vi è un miglioramento della vita a fatica a seguito dell’autoriparazione misurato come recupero della rigidità dei campioni.
Stimulated autogenous self healing capacity of high performance concrete under cyclic loads
Ocampo Pacheco, Yanira Ginori;CLERQUE VELA, DAVID ALEJANDRO
2020/2021
Abstract
Cement production accounts for nearly half of the total CO2 emissions related to industrial processes. Concrete, with cement as its main constituent, is the most used man-made material worldwide. Concrete is widely used in most infrastructure projects, either big or small scale, from dams to sidewalks; however, it has inherited cracking vulnerability, which is unavoidable. Even small cracks (<0.3 mm) allow the ingress of water or harmful substances that deteriorate the concrete matrix, corrode the reinforcement, and thus reduce concrete structures' service life, leading to costly maintenance operations and inspections. Hence, any improvement in the life cycle of concrete materials will hugely benefit the environment and society. Autogenous self-healing concrete is a material that can self-seal/heal cracks, which recovers concrete's permeability and mechanical properties. This research aims to devise a methodology to evaluate the autogenous self-healing capacity of ultra-high performance fiber reinforced concrete (UHPFRC) under cyclic load. The experimental campaign had two stages; in the first stage, preliminary tests were performed to characterize the material's mechanical properties under flexure, including monotonic and cyclic tests. In the second stage, cyclic loading induced fatigue damage on pre-cracked UHPFRC beam specimens. Finally, the damaged specimens were immersed in water to activate the self-healing; immersion periods were 1 and 3 months. After the healing period, the specimens were brought to failure by cyclic loading. Ultrasonic pulse velocity (UPV) tests and microscopic imaging were employed to evaluate the healing occurrence, from which recovery indices by UPV and crack sealing were determined. The results obtained were used to evaluate the fatigue life of the specimens before and after the healing process, comparing changes in variables such as the number of cycles to failure, stiffness, critical crack opening displacement (COD), and rate of COD. The results suggest that the water immersion process favors healing in cracks of less than 100 µm. Moreover, there seems to be an improvement in the fatigue life after healing, observed by stiffness recovery of the specimens.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/181516