In this experimental thesis it is investigated the efficacy of two green inhibitors: L- proline and L-tryptophan and a commercial superplasticizer, Sikaviscocrete 20HE, against chloride-induced corrosion in reinforced concrete structures. Corrosion is one of the most relevant cause for the premature failure of reinforced concrete structure. Therefore, it is fundamental, especially in very aggressive environment, the use of additional protection measure. Among these, one of the most efficient practice is the use of inhibitors. To eval- uate their inhibition effect against corrosion, first different solutions are prepared with different concentration of inhibitors, superplasticizer and chloride ions. These solutions are tested through Linear Polarization Resistance, which allows to evaluate the corrosion rate. The results obtained for cells containing L-proline and L-tryptophan are then sum- marized and analysed by Linear Polarization curve. Through the Polarization curves, it is analysed the value of the pitting potential. In addition, to compare the possible passi- vating effect of these inhibitors, the curves are compared with Nitrite compound, one of the most effective inorganic inhibitor. From the results, it is evident that L-tryptophan does not show a behavior similar to the one of nitrite, and so a passivating effect, while the L-proline might present a passivating effect. For what concern the superplasticizers, graphs showing the corrosion potential and corrosion rate related to the exposure time are prepared. By analyzing the curves, it is noticed that even with inhibitors are active, so they are corroding. After the result obtained, it is chosen to test only the superplas- ticizer in mortar through destructive techniques: Bending, Compression test, where it is evaluated the resistance of materials in both conditions, Differential thermal analysis and thermogravimetric analysis (TGA). Trough the combination of DTA and TGA different information are acquired such as the percentage of cement hydration, water weight loss of C-S-H gel and portlandite and the CO2 weight loss of carbonates as a function of time. What emerge from the mechanical tests, it is an increase of resistance for mortar containing the superplasticizers. Anyway, this result can be associated to a lower W/C ratio. Finally, for what concern the DTA and TGA, the addition of the additive does not penalise the hydration properties of the mortar sample.
In questa tesi sperimentale, è stata studiata l’efficacia di due inibitori green, L-prolina e L-Triptofano e un superfluidificante, Sikaviscocrete 20HE, nel contrastare la corrosione indotta da cloruri nelle strutture di calcestruzzo armato. La corrosione è una delle prin- cipali cause che conducono alla prematura degradazione del calcestruzzo armato. Per questo motivo, è fondamentale, in particolare modo in ambienti aggressivi, l’utilizzo di misure protettive addizionali. Tra queste, une delle più efficienti è l’uso degli inibitori. Per valutare l’effetto di inibizione della corrosione, sono state preparate diverse soluzioni con diverso contenuto di inibitori, ioni cloruro e superfluidificante. Queste soluzioni sono state testate attraverso diversi metodi: Resistenza di polarizzazione e Impedenza. Per analizzare i risultati ottenuti delle celle contenenti L-prolina e L-Triptofano sono costruite delle curve di polarizzazione. È stato poi ricavato il potentiale di pitting per ogni curva. Inoltre, per analizzare il possibile effetto passivante degli inibitori green, le curve sono state confrontate con quella relativa al nitrito, uno degli inibitori inorganici riconosciuto tra i più efficaci. Dai risultati, si ricava che nessuna curva dell’inibitore L-Triptofano mostra un comportamento ricondicibile a quello dei nitriti e quindi il comportamento è attivo. Nel caso di L-prolina invece sono stati ottenuti alcuni risultati positivi da appro- fondire. Per analizzare il comportamento del superfluidificante sono stati preparati grafici che mostrano la velocità di corrosione e il potenziale rispetto al tempo. Analizzando le curve, anche in presenza del superfluidificante, il metallo si corrode a velocità elevate. Dopo le prove in soluzione, il superfluidificante è stato testato anche in malta tramite prove distruttive quali: Test di Flessione e Compressione, Analisi Termica Differenziale e Analisi Termogravimetrica. Grazie alle analisi termiche, sono state ricavate diverse infor- mazioni sull’idratazione del cemento. Quello che emerge dai test meccanici è un aumento della resistenza sia a compressione che a flessione per i provini contenenti il superplastifi- cante. Ad ogni modo, questo risultato può essere associato a un rapporto acqua cemento inferiore rispetto ai provini senza i superfluidificanti. Per quanto riguarda la DTA e TGA, l’aggiunta dell’additivo non influenza l’idrazione del cemento.
Study of green inhibitors for reinforced concrete structures
Pisoni, Maria Giulia
2021/2022
Abstract
In this experimental thesis it is investigated the efficacy of two green inhibitors: L- proline and L-tryptophan and a commercial superplasticizer, Sikaviscocrete 20HE, against chloride-induced corrosion in reinforced concrete structures. Corrosion is one of the most relevant cause for the premature failure of reinforced concrete structure. Therefore, it is fundamental, especially in very aggressive environment, the use of additional protection measure. Among these, one of the most efficient practice is the use of inhibitors. To eval- uate their inhibition effect against corrosion, first different solutions are prepared with different concentration of inhibitors, superplasticizer and chloride ions. These solutions are tested through Linear Polarization Resistance, which allows to evaluate the corrosion rate. The results obtained for cells containing L-proline and L-tryptophan are then sum- marized and analysed by Linear Polarization curve. Through the Polarization curves, it is analysed the value of the pitting potential. In addition, to compare the possible passi- vating effect of these inhibitors, the curves are compared with Nitrite compound, one of the most effective inorganic inhibitor. From the results, it is evident that L-tryptophan does not show a behavior similar to the one of nitrite, and so a passivating effect, while the L-proline might present a passivating effect. For what concern the superplasticizers, graphs showing the corrosion potential and corrosion rate related to the exposure time are prepared. By analyzing the curves, it is noticed that even with inhibitors are active, so they are corroding. After the result obtained, it is chosen to test only the superplas- ticizer in mortar through destructive techniques: Bending, Compression test, where it is evaluated the resistance of materials in both conditions, Differential thermal analysis and thermogravimetric analysis (TGA). Trough the combination of DTA and TGA different information are acquired such as the percentage of cement hydration, water weight loss of C-S-H gel and portlandite and the CO2 weight loss of carbonates as a function of time. What emerge from the mechanical tests, it is an increase of resistance for mortar containing the superplasticizers. Anyway, this result can be associated to a lower W/C ratio. Finally, for what concern the DTA and TGA, the addition of the additive does not penalise the hydration properties of the mortar sample.File | Dimensione | Formato | |
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2022_12 PISONI SUMMARY.pdf
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https://hdl.handle.net/10589/198046