The use of cementitious composites with adapted rheology has been rapidly increasing in the last years, the material performance in the fresh state and hence its “processability” being recognized as part of the whole set of performances governing the successful building of the engineering feat as well as its structural performance. A further development of these concepts has been recently become popular with widespread diffusion of digital fabrication technologies with cementitious composites. 3D printing, which is an automated production process with layer-by-layer control, has been gaining rapid development in recent years. The technology has been adopted in the manufacturing industry for several years and has recently been introduced in the construction industry. The 3D printing technologies, compared to traditional techniques of building construction, could be considered as environmental friendly giving almost unlimited possibilities for geometric complexity realizations. Moreover, additive manufacturing can bring significant benefits to the construction industry in terms of increased customization, reduced construction time, reduced manpower and construction cost, decreased injuries and casualties on construction sites and minimization of the pollution. Despite many advantages ad hopes, this technology still has many limitations. In particular, further studies are necessary to develop cementitious composites which have the proper characteristics to be printed. The use of fiber reinforced concrete for future applications to 3D printing could bring several benefits, with the reduction or even the elimination of the traditional reinforcement and the increment of the mechanical properties of the cementitious composites. In the first part of this thesis, fiber reinforced concrete is described with its mechanical characteristics and its advantages. Subsequently, the main 3D printing systems are described with the illustration of the principal benefits and limits. The properties of the cementitious composites for the 3D printing are illustrated and some examples of the achievements of companies in the field of 3D printing are presented. In the second part, the experimental work on high performance fiber reinforced concrete is illustrated and critically analyzed. This thesis wants to develop a methodology that could give significant indications on the rupture mechanisms and properties of the cementitious composites that could be used for future applications in the 3D printing. Tensile, shear and slump flow tests has been carried out on different high performance fiber reinforced cementitious composites with adapted rheology in order to study the properties for very short curing times. Four types of mixes have been employed varying the amount of fibers introduced. For each type of mix different “curing” times have been studied, ranging between 60 and 180 minutes. The experimental data have been analyzed developing charts which show the tensile and shear stresses as a function of time, the fracture energy and the slump flow diameter in time. The latter, gives information on the workability retention of the fresh concrete, which is a very important parameter for the successful use of this category of materials. Finally, the tensile and shear tests have been compared to each other and also with the loss of slump flow in time. The comparison of the all mixes used in this experimental thesis could give very important information for future studies and applications of cementitious composites with adapted rheology.
L’uso di composti cementizi con reologia adattata è cresciuto rapidamente negli ultimi anni, le prestazioni dei materiali allo stato fresco e quindi la loro “processabilità” sono state riconosciute come parte dell'intera serie di prestazioni che governano il successo di una realizzazione. Un ulteriore sviluppo di questi concetti è diventato recentemente popolare con la diffusione delle tecnologie di fabbricazione digitale con compositi cementizi. La stampa 3D, che è un processo di produzione automatizzato con deposizione controllata del materiale in strati successivi, ha ottenuto un rapido sviluppo negli ultimi anni. La tecnologia è stata adottata nel settore manifatturiero da alcuni anni ed è stata recentemente introdotta nel settore delle costruzioni. Le tecnologie di stampa 3D, rispetto alle tecniche tradizionali di costruzione degli edifici, potrebbero essere considerate come rispettose dell'ambiente, altresì offrendo possibilità quasi illimitate per realizzazioni di complessità geometrica. Inoltre, la produzione automatizzata può apportare vantaggi significativi all'industria delle costruzioni in termini di maggiore personalizzazione dei prodotti, riduzione dei tempi di costruzione, riduzione della manodopera e dei costi di costruzione, riduzione degli infortuni nei cantieri e riduzione dell'inquinamento. Nonostante molti vantaggi e speranze, questa tecnologia ha ancora molti limiti. In particolare, sono necessari ulteriori studi per sviluppare compositi cementizi che abbiano le caratteristiche appropriate per essere stampati. L'uso del calcestruzzo fibrorinforzato per future applicazioni alla stampa 3D potrebbe portare numerosi vantaggi, con la riduzione o addirittura l'eliminazione dell’armatura tradizionale e l'incremento delle proprietà meccaniche dei compositi cementizi. Nella prima parte di questa tesi, il calcestruzzo fibrorinforzato è descritto con le sue caratteristiche meccaniche e i suoi vantaggi. Successivamente, i principali sistemi di stampa 3D sono descritti con l'illustrazione dei principali vantaggi e limiti. Vengono analizzate le proprietà dei compositi cementizi per la stampa 3D e vengono presentati alcuni esempi dei risultati raggiunti dalle aziende nel campo della stampa 3D. Nella seconda parte, il lavoro sperimentale sul calcestruzzo fibrorinforzato ad alte prestazioni è illustrato e analizzato criticamente. Questa tesi vuole sviluppare una metodologia che possa fornire indicazioni significative sui meccanismi di rottura e sulle proprietà dei compositi cementizi che potrebbero essere utilizzati per future applicazioni nella stampa 3D. Sono state realizzate prove di trazione, taglio e di spandimento su diverse miscele fibrorinforzate a elevate prestazioni con il fine di studiare le proprietà alle brevissime stagionature. Sono stati impiegati quattro tipi di miscele variando le quantità di fibre introdotte. Per ogni tipo di miscela sono stati studiati tempi di stagionatura diversi, in particolare tra 60 e 180 minuti. I dati sperimentali sono stati analizzati sviluppando grafici che mostrano gli sforzi di trazione e taglio in funzione del tempo, l'energia di frattura e il diametro della prova di spandimento nel tempo. Quest'ultimo fornisce informazioni sulla lavorabilità del calcestruzzo fresco, che è un parametro molto importante per un uso efficace di questa categoria di materiali. Infine, le prove di trazione e di taglio sono state confrontate tra loro e anche con la perdita di spandimento nel tempo. Il confronto di tutte le miscele utilizzate in questa tesi sperimentale potrebbe fornire informazioni molto importanti per futuri studi e applicazioni di compositi cementizi con prestazioni reologiche funzionalizzate.
An experimental methodology to measure the evolution of very early age mechanical performance of high performance fibre reinforced concrete
GATTI, MARIO
2018/2019
Abstract
The use of cementitious composites with adapted rheology has been rapidly increasing in the last years, the material performance in the fresh state and hence its “processability” being recognized as part of the whole set of performances governing the successful building of the engineering feat as well as its structural performance. A further development of these concepts has been recently become popular with widespread diffusion of digital fabrication technologies with cementitious composites. 3D printing, which is an automated production process with layer-by-layer control, has been gaining rapid development in recent years. The technology has been adopted in the manufacturing industry for several years and has recently been introduced in the construction industry. The 3D printing technologies, compared to traditional techniques of building construction, could be considered as environmental friendly giving almost unlimited possibilities for geometric complexity realizations. Moreover, additive manufacturing can bring significant benefits to the construction industry in terms of increased customization, reduced construction time, reduced manpower and construction cost, decreased injuries and casualties on construction sites and minimization of the pollution. Despite many advantages ad hopes, this technology still has many limitations. In particular, further studies are necessary to develop cementitious composites which have the proper characteristics to be printed. The use of fiber reinforced concrete for future applications to 3D printing could bring several benefits, with the reduction or even the elimination of the traditional reinforcement and the increment of the mechanical properties of the cementitious composites. In the first part of this thesis, fiber reinforced concrete is described with its mechanical characteristics and its advantages. Subsequently, the main 3D printing systems are described with the illustration of the principal benefits and limits. The properties of the cementitious composites for the 3D printing are illustrated and some examples of the achievements of companies in the field of 3D printing are presented. In the second part, the experimental work on high performance fiber reinforced concrete is illustrated and critically analyzed. This thesis wants to develop a methodology that could give significant indications on the rupture mechanisms and properties of the cementitious composites that could be used for future applications in the 3D printing. Tensile, shear and slump flow tests has been carried out on different high performance fiber reinforced cementitious composites with adapted rheology in order to study the properties for very short curing times. Four types of mixes have been employed varying the amount of fibers introduced. For each type of mix different “curing” times have been studied, ranging between 60 and 180 minutes. The experimental data have been analyzed developing charts which show the tensile and shear stresses as a function of time, the fracture energy and the slump flow diameter in time. The latter, gives information on the workability retention of the fresh concrete, which is a very important parameter for the successful use of this category of materials. Finally, the tensile and shear tests have been compared to each other and also with the loss of slump flow in time. The comparison of the all mixes used in this experimental thesis could give very important information for future studies and applications of cementitious composites with adapted rheology.| File | Dimensione | Formato | |
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2019_12_Gatti.pdf
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https://hdl.handle.net/10589/150780