Design Code agrees on setting the service life of an ordinary concrete structure to 50 years. However, in all cases involving highly aggressive environments (e.g. marine environments), in which premature degradation is most likely to occur, this prescription may be difficult to fulfill. To avoid costly repair activities in all these situations, some protective system should be adopted. Better understanding and engineering of the complex structure of cement-based materials at the nano-level can help to develop a new generation of materials with an improved microstructure that are not only stronger but, more importantly, tougher and more durable, with desired stress-strain behavior and with a whole range of newly introduced “smart” functionalities. The application of nanotechnology and nanoadditions such as cellulose (nanocrystals and nanofibrils) and alumina nanofibers is considered a new and very promising direction to engineering the performance of cement-based materials. The main aim of this work is to obtain Ultra High Durable Concretes (UHDC) with improved specific features due to the addition of different nanoadditions to obtain more durable concretes with better shrinkage characteristics and strength recovery behavior. As a matter of fact, five different mixes including steel fibers, slag and different nanoadditions have been analyzed. The steel fibers have been used to improve cracking behavior. Slag to improve the efficiency of concrete as well as make it economical by reducing the cement usage, crystalline admixtures to obtain a more durable concrete permanently sealed against the water penetration and resistant to harsh environmental exposures, the ultrafine particles of nanoadditives have been used to act as a filler agent that reduces the formation of micropores, producing a very dense concrete and automatically reducing the growth of micropores in the UHDC structures. Tests have been performed with specimens cured in climate room (Ta =20o C, RH=95% ) or completely submerged in geothermal water since this formulated UHDC will be used to construct the cooling basins of a geothermal power plant. The enhancement due to the addition of nanoadditives in terms of shrinkage, compressive and flexural strength, self-healing of cracks and porosity was observed in these aggressive environments for concrete structures
Il Codice di progettazione si impegna a stabilire a 50 la vita utile di una normale struttura in calcestruzzoanni. Tuttavia, in tutti i casi che coinvolgono ambienti altamente aggressivi (ad esempio ambienti marini), in cui è più probabile che si verifichi una degradazione prematura, questa prescrizione potrebbeessere difficile da soddisfare. Per evitare costose attività di riparazione in tutte queste situazioni, alcune protettivesistema dovrebbe essere adottato.Una migliore comprensione e ingegnerizzazione della complessa struttura dei materiali a base di cemento a livello nanometrico può aiutare a sviluppare una nuova generazione di materiali con unmicrostruttura migliorata che non solo è più forte ma, soprattutto, più resistente epiù durevole, con il comportamento desiderato di sollecitazione-sollecitazione e con un'intera gamma di funzionalità "intelligenti" di recente introduzione. L'applicazione delle nanotecnologie e delle nanoaddizionicome la cellulosa (nanocristalli e nanofibrille) e le nanofibre di allumina sono considerate adirezione nuova e molto promettente per progettare le prestazioni dei materiali a base di cemento.Lo scopo principale di questo lavoro è quello di ottenere calcoli Ultra High Durable (UHDC) miglioraticaratteristiche specifiche grazie all'aggiunta di diverse nanoaddizioni per ottenere una maggiore duratacalcestruzzi con migliori caratteristiche di ritiro e comportamento di recupero della forza. Come unDi fatto, cinque diversi mix tra cui fibre di acciaio, scorie e diverse nanoaddizionisono stati analizzatiLe fibre d'acciaio sono state utilizzate per migliorare il comportamento di cracking. Scorie per migliorare l'efficienza del calcestruzzo e renderlo economico riducendo l'utilizzo di cemento, gli additivi cristallini per ottenere un cemento più duraturo sigillato permanentemente contro ilpenetrazione dell'acqua e resistente alle esposizioni ambientali difficili, le particelle ultrafinidi nanoadditiv sono stati usati per agire come un agente di riempimento che riduce la formazione dimicropori, producendo un calcestruzzo molto denso e riducendo automaticamente la crescitadi micropori nelle strutture UHDC.I test sono stati eseguiti con campioni induriti in camera climatica (Ta = 20 ° C, UR = 95%)o completamente immersi nell'acqua geotermica poiché verrà utilizzata questa UHDC formulatacostruire i bacini di raffreddamento di una centrale geotermica. Il miglioramento a causa dil'aggiunta di nanoadditiv in termini di contrazione, resistenza alla compressione e alla flessione,in questi ambienti aggressivi è stata osservata l'auto-riparazione di crepe e porositàstrutture concrete
Effect of nanoadditions on the performance of fiber reinforced cementitious composites in aggressive environments
AWAIS, MUHAMMAD;AHMED, WAQAR
2018/2019
Abstract
Design Code agrees on setting the service life of an ordinary concrete structure to 50 years. However, in all cases involving highly aggressive environments (e.g. marine environments), in which premature degradation is most likely to occur, this prescription may be difficult to fulfill. To avoid costly repair activities in all these situations, some protective system should be adopted. Better understanding and engineering of the complex structure of cement-based materials at the nano-level can help to develop a new generation of materials with an improved microstructure that are not only stronger but, more importantly, tougher and more durable, with desired stress-strain behavior and with a whole range of newly introduced “smart” functionalities. The application of nanotechnology and nanoadditions such as cellulose (nanocrystals and nanofibrils) and alumina nanofibers is considered a new and very promising direction to engineering the performance of cement-based materials. The main aim of this work is to obtain Ultra High Durable Concretes (UHDC) with improved specific features due to the addition of different nanoadditions to obtain more durable concretes with better shrinkage characteristics and strength recovery behavior. As a matter of fact, five different mixes including steel fibers, slag and different nanoadditions have been analyzed. The steel fibers have been used to improve cracking behavior. Slag to improve the efficiency of concrete as well as make it economical by reducing the cement usage, crystalline admixtures to obtain a more durable concrete permanently sealed against the water penetration and resistant to harsh environmental exposures, the ultrafine particles of nanoadditives have been used to act as a filler agent that reduces the formation of micropores, producing a very dense concrete and automatically reducing the growth of micropores in the UHDC structures. Tests have been performed with specimens cured in climate room (Ta =20o C, RH=95% ) or completely submerged in geothermal water since this formulated UHDC will be used to construct the cooling basins of a geothermal power plant. The enhancement due to the addition of nanoadditives in terms of shrinkage, compressive and flexural strength, self-healing of cracks and porosity was observed in these aggressive environments for concrete structures| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/146431