This thesis aims to experimentally investigate the self-healing capacity of cracks produced by torsion in fibre-reinforced cementitious materials UHPC (Ultra-High Performance Concrete). This type of cracks has a three-dimensionality which differs from the cracks produced by bending, whose self-healing has been more commonly studied. Additionally, the application fields of UHPC materials include uses in structural members where torsional load can play an important role. For this purpose, cylindrical specimens (diameter of 6cm and length of 50cm) were studied, made with a reference UHPC mix widely tested in the framework of the Horizon2020 ReSHEALience project. Two mixes were used, one containing a crystalline admixture and one without, in order to study the ability of the same admixture as a self-healing promoter. The specimens were torsionally pre-cracked in order to obtain cracks with a maximum width of about 300µm. Subsequently, a part of the specimens underwent wet and dry cycles, for 28 days, in two different curing environments (fresh and salt water), while the remaining part was left exposed to the air. The cracks were measured and photographed 5 times during the curing period, in order to describe the trend of their self-heling and the images were post-processed on Photoshop, in order to obtain the progress of the cracks widths. At the end of the curing period, the specimens were tested in torsion again until failure, in order to understand the effectiveness of crack self-healing. Finally, a finite element model of the torsion test performed on the specimens was produced on the software Abaqus, in order to post-validate the laboratory tests. The analyses were carried out considering both an elastic-perfectly plastic and a softening behaviour of the material, to have an upper and a lower bound to compare with the experimental results. The results obtained led to the conclusion that the best self-healing capacity can be attributed to the specimens casted with the mix containing crystalline admixture and which underwent w/d cycles in fresh water. Furthermore, the finite element analyses have shown a good comparison with the experimental results and the ultimate torsional moment values of the specimens containing crystalline admixture match with the results of the analysis performed using a material with softening behaviour.
Questa tesi si propone come obiettivo di indagare sperimentalmente la capacità di autoriparazione di fessure prodotte da torsione in materiali cementizi fibro-rinforzati UHPC (Ultra-High Performance Concrete). Tale tipologia di fessura presenta una tridimensionalità che differisce dalle fessure prodotte da flessione, la cui autoriparazione è più comunemente studiata. Inoltre, i campi di applicazione dei materiali UHPC comprendono utilizzi in elementi strutturali in cui la sollecitazione di torsione può giocare un ruolo importante. A tale scopo sono stati studiati provini cilindrici (diametro di 6cm e lunghezza di 50cm), realizzati con un UHPC mix ampiamente sperimentato nel progetto Horizon2020 ReSHEALience. Sono stati utilizzati un mix contenente additivo cristallino ed uno senza, al fine di studiarne la capacità di promuovere l’autoriparazione del materiale. I provini sono stati pre-fessurati a torsione per pttenere delle fessure con ampiezza massima di circa 300µm. In seguito, una parte dei provini è stata sottoposta a cicli di asciutto bagnato per 28 giorni in due ambienti di cura (acqua dolce e salata), mentre la restante parte è stata lasciata esposta all’aria. Le fessure sono state misurate e fotografate durante il periodo di cura per poter descrivere l’andamento nel tempo della loro autoriparazione e le immagini sono state post-processate sul software Photoshop per ottenere il progredire delle ampiezze delle fessure. Dopo il periodo di cura i provini sono stati ritestati a torsione fino a rottura per comprendere l’efficacia dell’autoriparazione delle fessure. Infine, è stato prodotto sul software Abaqus un modello ad elementi finiti della prova di torsione svolta sui provini per post-validare i test di laboratorio. Le analisi sono state effettuate considerando sia un comportamento elastico-perfettamente plastico del materiale, che uno di softening, per avere due curve limite con cui confrontare i risultati sperimentali. Dai risultati ottenuti si può concludere che la migliore capacità di autoriparazione è da attribuirsi ai provini realizzati con mix contenente additivo cristallino e sottoposti a cicli di asciutto/bagnato in acqua dolce. Le analisi sul software Abaqus hanno evidenziato una comparabilità con i risultati sperimentali ed i risultati di momento torsionale ultimo dei provini contenenti additivo cristallino trovano un riscontro nei risultati della analisi svolta utilizzando un materiale con comportamento softening.
Experimental investigation on the self-healing capacity of UHPC torsional cracks
Lo Gatto, Virginia
2021/2022
Abstract
This thesis aims to experimentally investigate the self-healing capacity of cracks produced by torsion in fibre-reinforced cementitious materials UHPC (Ultra-High Performance Concrete). This type of cracks has a three-dimensionality which differs from the cracks produced by bending, whose self-healing has been more commonly studied. Additionally, the application fields of UHPC materials include uses in structural members where torsional load can play an important role. For this purpose, cylindrical specimens (diameter of 6cm and length of 50cm) were studied, made with a reference UHPC mix widely tested in the framework of the Horizon2020 ReSHEALience project. Two mixes were used, one containing a crystalline admixture and one without, in order to study the ability of the same admixture as a self-healing promoter. The specimens were torsionally pre-cracked in order to obtain cracks with a maximum width of about 300µm. Subsequently, a part of the specimens underwent wet and dry cycles, for 28 days, in two different curing environments (fresh and salt water), while the remaining part was left exposed to the air. The cracks were measured and photographed 5 times during the curing period, in order to describe the trend of their self-heling and the images were post-processed on Photoshop, in order to obtain the progress of the cracks widths. At the end of the curing period, the specimens were tested in torsion again until failure, in order to understand the effectiveness of crack self-healing. Finally, a finite element model of the torsion test performed on the specimens was produced on the software Abaqus, in order to post-validate the laboratory tests. The analyses were carried out considering both an elastic-perfectly plastic and a softening behaviour of the material, to have an upper and a lower bound to compare with the experimental results. The results obtained led to the conclusion that the best self-healing capacity can be attributed to the specimens casted with the mix containing crystalline admixture and which underwent w/d cycles in fresh water. Furthermore, the finite element analyses have shown a good comparison with the experimental results and the ultimate torsional moment values of the specimens containing crystalline admixture match with the results of the analysis performed using a material with softening behaviour.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/201335