Fiber Reinforced Polymer (FRP) and Fiber Reinforced Cementitious Matrix (FRCM) have been increasingly adopted to repair and strengthen structural members in the last years. However, there is limited information available on their durability. The current research consists of two main parts aiming to investigate the performance of these two composites under hygrothermal and wet-dry conditions. The first part was dedicated to studying the effect of the hygrothermal and wet-dry conditions on the CFRP-concrete joint and constituent materials (i.e., epoxy resin and CFRP strip). The hygrothermal condition was composed of continuous immersion in water at 38 2 oC; however, the wet-dry condition comprised of 50 cycles with 6 hours of immersion in water followed by 18 hours of drying at 50 oC for each cycle. In total, eighty-two specimens were tested in this part of the research. Digital image correlation technique was also utilized to determine strain profile, cohesive material law, and subsequently, fracture energy of the CFRP-concrete interface. A two-dimensional finite element model was also utilized to calibrate the obtained cohesive material laws so they could be implemented in any numerical model aimed to evaluate the durability of the reinforced concrete structures externally bonded with CFRP. The results of this part of the research indicated some visible and mechanical changes in the performance of the epoxy resin. Furthermore, the failure mode of the CFRP-concrete joints exposed to wet-dry cycles was changed from a cohesive debonding in the concrete substrate to an adhesive debonding in the interface. However, the load-carrying capacity of the joint was not significantly influenced. The second part of the research focused on investigating the effect of the wet-dry condition on the FRCM-masonry joints. Forty specimens were tested in this part of the dissertation. The specimens were prepared of three types of FRCM composites, which are made of carbon, PBO, and AR-glass textiles, and one type of Steel Reinforced Grout (SRG) composite. Both FRCM and SRG composites were externally bonded to masonry blocks. The specimens were exposed to 50 wet-dry cycles. Subsequently, the performance of the joints was evaluated using single-lap shear tests. The result of this part of the research implied some changes in the failure mode where it was changed for some specimens from a debonding failure within the matrix-fiber interface to a debonding within the matrix-substrate interface. Furthermore, the average bond capacity of all composites was affected in different ranges. The last section of this part of the research was dedicated to analytically simulate the behavior of the FRCM-masonry joints using a trilinear cohesive material law. The model has accurately simulated the behavior of the carbon and PBO FRCM-masonry joints that developed a debonding failure in the matrix-fiber interface.
Negli ultimi anni, i materiali compositi a matrice organica (FRP) ed inorganica (FRCM) sono stati adottati sempre più spesso per il consolidamento di strutture esistenti. Tuttavia, le informazioni disponibili sulla loro durabilità sono attualmente limitate. Allo stato attuale, la ricerca inerente questo tema è articolata in due filoni principali, mirati allo studio delle prestazioni di questi materiali in ambiente umido ed in condizioni cicliche umido-secco. La prima parte di questa tesi si è concentrata sullo studio dell'effetto dei condizionamenti in ambiente umido e di cicli umido-secco sulle prestazioni di polimeri fibrorinforzati in carbonio (CFRP) e sull’aderenza tra CFRP e supporti in calcestruzzo. A tal fine sono stati sottoposti a condizionamento in ambiente umido campioni in calcestruzzo rinforzati con materiale composito, immergendoli in acqua a 38 ± 2 °C. Il trattamento in condizioni cicliche umido-secco invece comprendeva 50 cicli da 24 ore ciascuno, suddivisi in 6 ore di immersione in acqua seguite da 18 ore di essiccazione a 50 °C. Successivamente al condizionamento i campioni sono stati testati secondo la modalità di prova single-lap shear test. In totale, i campioni testati in questa parte della ricerca sono stati 82. La tecnica digital image correlation è stata utilizzata per determinare la deformazione del campione, la legge del materiale coesivo e, successivamente, l'energia di frattura dell'interfaccia CFRP-calcestruzzo. È stato inoltre utilizzato un modello bidimensionale agli elementi finiti per calibrare le leggi coesive dei materiali ottenute, in modo che potessero essere implementate in modelli numerici volti a valutare la durabilità di applicazioni di tipo CFRP su elementi strutturali in cemento armato. I risultati di questa parte della ricerca hanno indicato effetti dei condizionamenti sulle prestazioni della resina epossidica. Inoltre, è stata riscontrata un’alterazione nella modalità di crisi dei giunti CFRP-calcestruzzo esposti a cicli umido-secco, passata da una crisi per distacco distacco coesivo nel substrato di calcestruzzo a un distacco all'interfaccia composito-substrato. Tuttavia, la capacità aderente del giunto non è stata influenzata in modo significativo. La seconda parte della ricerca si è concentrata sullo studio dell'effetto di cicli umido-secco sull’aderenza di compositi a matrice inorganica, applicati a supporti in muratura. Quaranta campioni sono stati testati in questa parte della tesi. Campioni in muratura di mattoni laterizi sono stati rinforzati esternamente con tre diversi compositi FRCM ed un composito di tipo Steel Reinforced Grout (SRG). I compositi FRCM includevano rispettivamente un tessuto in fibra di carbonio, uno in fibra PBO ed uno in fibra di vetro resistente agli alcali (AR). I campioni sono stati esposti a 50 cicli umido-secco. Successivamente, le prestazioni dei giunti composito-muratura sono state valutate mediante prove di distacco single-lap shear test. L’evidenza sperimentale ha mostrato un’alterazione della modalità di crisi del rinforzo a seguito del condizionamento. In particolare, per alcuni campioni si è passati da una crisi di aderenza all’interfaccia matrice-tessuto, esibita da campioni non condizionati, a un distacco all'interfaccia tra matrice e substrato. Inoltre, la capacità media di aderenza di tutti i compositi analizzati è stata influenzata significativamente dal condizionamento. Infine, il comportamento dei giunti FRCM-muratura testati sperimentalmente è stato simulato analiticamente, utilizzando una legge materiale coesiva trilineare. Il modello sviluppato ha dimostrato di approssimare accuratamente il reale comportamento dei giunti in fibra di carbonio e PBO FRCM caratterizzati da una crisi di aderenza all'interfaccia matrice-tessuto.
Bond durability of FRP-concrete and FRCM-masonry joints under the effect of environmental conditions
AL-LAMI, KARRAR ALI FEZEA
2020/2021
Abstract
Fiber Reinforced Polymer (FRP) and Fiber Reinforced Cementitious Matrix (FRCM) have been increasingly adopted to repair and strengthen structural members in the last years. However, there is limited information available on their durability. The current research consists of two main parts aiming to investigate the performance of these two composites under hygrothermal and wet-dry conditions. The first part was dedicated to studying the effect of the hygrothermal and wet-dry conditions on the CFRP-concrete joint and constituent materials (i.e., epoxy resin and CFRP strip). The hygrothermal condition was composed of continuous immersion in water at 38 2 oC; however, the wet-dry condition comprised of 50 cycles with 6 hours of immersion in water followed by 18 hours of drying at 50 oC for each cycle. In total, eighty-two specimens were tested in this part of the research. Digital image correlation technique was also utilized to determine strain profile, cohesive material law, and subsequently, fracture energy of the CFRP-concrete interface. A two-dimensional finite element model was also utilized to calibrate the obtained cohesive material laws so they could be implemented in any numerical model aimed to evaluate the durability of the reinforced concrete structures externally bonded with CFRP. The results of this part of the research indicated some visible and mechanical changes in the performance of the epoxy resin. Furthermore, the failure mode of the CFRP-concrete joints exposed to wet-dry cycles was changed from a cohesive debonding in the concrete substrate to an adhesive debonding in the interface. However, the load-carrying capacity of the joint was not significantly influenced. The second part of the research focused on investigating the effect of the wet-dry condition on the FRCM-masonry joints. Forty specimens were tested in this part of the dissertation. The specimens were prepared of three types of FRCM composites, which are made of carbon, PBO, and AR-glass textiles, and one type of Steel Reinforced Grout (SRG) composite. Both FRCM and SRG composites were externally bonded to masonry blocks. The specimens were exposed to 50 wet-dry cycles. Subsequently, the performance of the joints was evaluated using single-lap shear tests. The result of this part of the research implied some changes in the failure mode where it was changed for some specimens from a debonding failure within the matrix-fiber interface to a debonding within the matrix-substrate interface. Furthermore, the average bond capacity of all composites was affected in different ranges. The last section of this part of the research was dedicated to analytically simulate the behavior of the FRCM-masonry joints using a trilinear cohesive material law. The model has accurately simulated the behavior of the carbon and PBO FRCM-masonry joints that developed a debonding failure in the matrix-fiber interface.| File | Dimensione | Formato | |
|---|---|---|---|
|
Karrar Al-Lami. Doctoral dissertation.pdf
Open Access dal 30/06/2022
Dimensione
6.31 MB
Formato
Adobe PDF
|
6.31 MB | Adobe PDF | Visualizza/Apri |
I documenti in POLITesi sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
https://hdl.handle.net/10589/177112