Self compacting concrete (SCC) is a valuable alternative to conventional vibrated concrete (NVC), indeed its hight fluidity and the low segregation tendency allow a higher filling capacity of the formwork and a better expulsion of the exceeding entrapped air, without the requirement of any mechanical operation of consolidation. For these reasons the cast operations are less time demanding, independent from workmen skills and less cost demanding in comparison to the conventional vibrated concrete. Even if the SCC seems to constitute a better alternative to the NVC, existing differences in their composition suggest performing further studies to gain insight into the viscoelastic and the mechanical properties which characterize the SCC. Specifically, an experimental analysis is needed in order to determine the entity and the evolution of the deformations that the concrete analyzed in the study undergoes over time. The analysis is performed not only on SCC, but also on an ordinary concrete of analogous compressive strength, that is used as a benchmark in order to evaluate the performance of the SCC. Two sets of specimens (8 made with SCC and 8 made with ordinary concrete) were made and subjected to the same curing and environment conditions. Among these, 4 specimens of both SCC and ordinary concrete sets were coated with plastic material, the other 4 were left free to exchange humidity with the air. For each set two coated and two free specimens were loaded to determine the stress dependent component of the strains. The remaining specimens of each set were instead used to determine the shrinkage. The measurements, appropriately re-elaborated, provide the evolution of the total deformation over time for both type of concrete. Since the comparative analysis shows a similarity in the deformational behaviour of the two concrete, the SCC could be use in substitution of the ordinary concrete. Based on the experimental measurements a parametrical analysis has been conduct in order to test the predictive capacity of some codes and models (ACI 209R-92, Bazant-B3, CEB MC90, fib MC 2010 e Eurocode 2).
I calcestruzzi autocompattanti (SCC) sono una valida alternativa ai tradizionali calcestruzzi vibrati (NVC). La loro alta fluidità e la bassa tendenza alla segregazione con cui riescono a fluire in spazi ridotti, riempiendo le casseforme e avvolgendo i ferri di armatura, hanno come naturale conseguenza la velocizzazione e la semplificazione delle operazioni di posa, rispetto a quelle conseguibili con calcestruzzi ordinari. Le differenze che sussistono tra gli SCC e i calcestruzzi ordinari (maggiore volume di pasta cementizia, largo uso di aggiunte minerali e alti dosaggi di fluidificanti spesso in combinazione con agenti modificatori della viscosità) invitano a porsi degli interrogativi a proposito delle proprietà viscoelastiche che caratterizzano gli SCC. Sulla base di tali presupposti, è nata l’esigenza di uno studio sperimentale, al fine di valutare l’entità e l’evoluzione delle deformazioni subite da un calcestruzzo autocompattante nel tempo. Lo studio non riguarda il solo SCC, ma anche un calcestruzzo ordinario di analoga resistenza a compressione, utilizzato come riferimento per valutare il comportamento dell’SCC. Sono stati realizzati 16 campioni cilindrici (8 in calcestruzzo ordinario, 8 in calcestruzzo autocompattante) di cui quattro provini per ciascun mix sono stati sigillati con materiale plastico. Per ciascuna tipologia di calcestruzzo, due provini sigillati e due provini non sigillati sono stati caricati a 28 giorni dalla data di getto per eseguire misure di creep, mentre gli altri quattro corrispondenti non sono stati caricati e sono stati oggetto di misure di solo ritiro. I dati delle misurazioni, appropriatamente rielaborate, forniscono l’evoluzione della deformazione totale nel tempo per entrambi i calcestruzzi. L’analisi comparativa mostra che i due calcestruzzi subiscono deformazioni nel tempo comparabili, l’SCC può essere quindi utilizzato in sostituzione di quello ordinario. Sulla base delle misurazioni sperimentali, è stato poi condotto uno studio parametrico per valutare la capacità delle principali normative e modelli (tra cui ACI 209R-92, Bazant-B3, CEB MC90, fib MC 2010 e Eurocode 2) di riprodurne l’andamento. ACI 209R-92, nella sua forma base, è il modello che meglio riproduce l’evoluzione delle deformazioni nel tempo.
Analisi sperimentale del comportamento reologico di un calcestruzzo autocompattante e confronto con le normative
CAZZOLA, PAOLO
2016/2017
Abstract
Self compacting concrete (SCC) is a valuable alternative to conventional vibrated concrete (NVC), indeed its hight fluidity and the low segregation tendency allow a higher filling capacity of the formwork and a better expulsion of the exceeding entrapped air, without the requirement of any mechanical operation of consolidation. For these reasons the cast operations are less time demanding, independent from workmen skills and less cost demanding in comparison to the conventional vibrated concrete. Even if the SCC seems to constitute a better alternative to the NVC, existing differences in their composition suggest performing further studies to gain insight into the viscoelastic and the mechanical properties which characterize the SCC. Specifically, an experimental analysis is needed in order to determine the entity and the evolution of the deformations that the concrete analyzed in the study undergoes over time. The analysis is performed not only on SCC, but also on an ordinary concrete of analogous compressive strength, that is used as a benchmark in order to evaluate the performance of the SCC. Two sets of specimens (8 made with SCC and 8 made with ordinary concrete) were made and subjected to the same curing and environment conditions. Among these, 4 specimens of both SCC and ordinary concrete sets were coated with plastic material, the other 4 were left free to exchange humidity with the air. For each set two coated and two free specimens were loaded to determine the stress dependent component of the strains. The remaining specimens of each set were instead used to determine the shrinkage. The measurements, appropriately re-elaborated, provide the evolution of the total deformation over time for both type of concrete. Since the comparative analysis shows a similarity in the deformational behaviour of the two concrete, the SCC could be use in substitution of the ordinary concrete. Based on the experimental measurements a parametrical analysis has been conduct in order to test the predictive capacity of some codes and models (ACI 209R-92, Bazant-B3, CEB MC90, fib MC 2010 e Eurocode 2).| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/138188