Concrete is the most employed material all over the world after water. In the last decades its performance has been progressively enhanced through the introduction of macro-, micro-, and nanoscale components able to counterbalance the deficiencies of the traditional material, thus providing new properties. Nowadays, the most performing cementitious materials are Ultra-High-Performance Concretes (UHPC), characterised by high cement and supplementary cementitious materials content, low water-to-binder ratio, superplasticizer admixture, fine aggregates, and short fibres inside the mix. It is also possible to introduce crystalline admixtures, to enhance the autogenous self-healing, and nanomaterials. UHPC can reduce the required volume of concrete for infrastructures and also foster their durability. This work provides a methodology to analyse UHPC with both destructive and non-destructive tests, addressing mechanical properties and their evolution over time, influenced by autogenous self-healing, sustained flexural load, and aggressive environments. An extended experimental campaign was conducted to validate the proposed methodology. Three different materials were tested, with steel fibres, crystalline admixture, and various nanomaterials. Specifically, the first batch included alumina nano-fibres, while the second one cellulose nano-crystals. The third one was used as a reference, without nanomaterials. Thin beam specimens, 500x100x30 mm, were pre-cracked and put inside three different exposures, under four-point bending sustained load. The specimens were cured for 1, 2, 3, and 6 months respectively, being exposed to chloride solution, geothermal water, and tap water as a reference. Test results allowed to point out the effects of each parameter – type of material and exposure – on the mechanical behaviour and its evolution over time. An already available simplified five-points inverse analysis was adjusted for beams with different slenderness. The inverse analysis provided a quadrilinear constitutive law derived from the structural flexural behaviour of four-point bending tests.
Il calcestruzzo, il materiale più impiegato al mondo, ha attraversato diverse fasi di miglioramento delle prestazioni, ottenute con l’introduzione di componenti su scala macro-, micro- e nanoscopica in grado di compensare specifiche carenze del materiale tradizionale e conferire proprietà altrimenti assenti. Ad oggi, i materiali più performanti sono i calcestruzzi ad altissime prestazioni (UHPC), caratterizzati da alto contenuto di cemento e materiali cementizi supplementari, basso rapporto acqua/legante, additivo superfluidificante, aggregati fini e fibre corte disperse, oltre alla possibile introduzione di additivi cristallizzanti, per promuovere l’autoriparazione autogena, e nanomateriali. L’impiego di UHPC consente di ridurre i volumi di materiale necessari e di assicurare elevata durabilità. Il presente elaborato propone una metodologia di indagine degli UHPC che coniuga prove distruttive e non, finalizzate alla determinazione delle prestazioni meccaniche del materiale e della loro evoluzione nel tempo, condizionata dalla concomitante influenza di autoriparazione autogena, azione flettente costante ed esposizione ad ambienti aggressivi. La campagna sperimentale condotta per validare la metodologia ha previsto l’impiego di tre miscele, contenenti fibre metalliche e additivo cristallizzante e distinte in funzione dei nanomateriali utilizzati: nano-fibre di allumina, nano-cristalli di cellulosa e impasto di riferimento privo di nanomateriali. Travetti sottili di dimensioni 500x100x30 mm sono stati fessurati e sottoposti a carico costante, con flessione a quattro punti, poi inseriti in tre ambienti di esposizione, contenenti rispettivamente acqua dolce, soluzione con cloruri e acqua di centrale geotermica, in cui sono stati mantenuti per periodi di tempo pari a 1, 2, 3 e 6 mesi. L’analisi dei risultati ha consentito di individuare l’influenza dei differenti parametri sulle caratteristiche meccaniche e sulla loro evoluzione temporale. È infine proposto l’adattamento di una analisi inversa semplificata a cinque punti per provini di differente snellezza per definire un comportamento costitutivo quadrilineare a partire da prove di flessione, di natura strutturale.
Calcestruzzi ad altissime prestazioni. Una metodologia sperimentale per la valutazione della capacità di autoriparazione sotto azioni combinate meccaniche e ambientali
Davolio, Marco
2021/2022
Abstract
Concrete is the most employed material all over the world after water. In the last decades its performance has been progressively enhanced through the introduction of macro-, micro-, and nanoscale components able to counterbalance the deficiencies of the traditional material, thus providing new properties. Nowadays, the most performing cementitious materials are Ultra-High-Performance Concretes (UHPC), characterised by high cement and supplementary cementitious materials content, low water-to-binder ratio, superplasticizer admixture, fine aggregates, and short fibres inside the mix. It is also possible to introduce crystalline admixtures, to enhance the autogenous self-healing, and nanomaterials. UHPC can reduce the required volume of concrete for infrastructures and also foster their durability. This work provides a methodology to analyse UHPC with both destructive and non-destructive tests, addressing mechanical properties and their evolution over time, influenced by autogenous self-healing, sustained flexural load, and aggressive environments. An extended experimental campaign was conducted to validate the proposed methodology. Three different materials were tested, with steel fibres, crystalline admixture, and various nanomaterials. Specifically, the first batch included alumina nano-fibres, while the second one cellulose nano-crystals. The third one was used as a reference, without nanomaterials. Thin beam specimens, 500x100x30 mm, were pre-cracked and put inside three different exposures, under four-point bending sustained load. The specimens were cured for 1, 2, 3, and 6 months respectively, being exposed to chloride solution, geothermal water, and tap water as a reference. Test results allowed to point out the effects of each parameter – type of material and exposure – on the mechanical behaviour and its evolution over time. An already available simplified five-points inverse analysis was adjusted for beams with different slenderness. The inverse analysis provided a quadrilinear constitutive law derived from the structural flexural behaviour of four-point bending tests.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/187057