Experimental characterization of fiber-reinforced cementitious mortar under tension

This work focuses on the mechanical characterization of the inorganic matrix used for Fiber-Reinforced Cementitious Matrix (FRCM) composites, nowadays widely used to retrofit existing reinforced concrete and masonry structures. While several works in technical literature investigate the experimental behavior of the whole FRCM composite, few information are available on the mechanical characterization of the mortar, which contains polymers and synthetic fibers in its admixture. However, the knowledge of its behavior in tension, especially after crack formation, is an important feature for the calibration of constitutive models to be adopted in the study of structural elements strengthened with FRCM. To this aim, an experimental program was performed on mortar specimens characterized by different shapes and dimensions, tested under direct tension or three-point-bending. From the performed tests, it was possible to characterize inorganic matrix behavior both in the uncracked stage, through the determination of the elastic parameters (elastic modulus and Poisson’s coefficient), and in the cracked stage. The use of digital image correlation (DIC) technique also allowed the study of the evolution of crack propagation in the specimens. Lastly, a correlation factor between axial and flexural tensile strength is proposed, for both design and numerical modelling purposes

Experimental and numerical study on cement-based composites (FRCM) for the strengthening of RC structural members

Il presente elaborato di tesi verte sullo studio di sistemi di rinforzo a matrice cementizia addizionata con fibre inorganiche, conosciuti come FRCM (Fiber-Reinforced Cementitious Matrix). Il materiale investigato, impiegato per il rinforzo di elementi strutturali in cemento armato e muratura, è stato solo recentemente introdotto sul mercato, non è ancora normato in tutti i paesi ed è pertanto oggetto di numerosi studi e ricerche al fine di caratterizzarne in modo approfondito il comportamento meccanico e l’interazione col supporto. In relazione a ciò, la ricerca è stata condotta seguendo due filoni principali. Il primo filone è stato rivolto alla modellazione e simulazione numerica del comportamento meccanico del materiale e degli elementi rinforzati con questa tecnica, mentre il secondo ha riguardato l’esecuzione di una serie di prove sperimentali volte alla determinazione delle proprietà meccaniche del composito e dei suoi componenti, in particolare della malta cementizia. Dopo aver analizzato la letteratura tecnico-scientifica relativa sia ai sistemi di rinforzo più tradizionali che agli FRCM, si è proceduto allo sviluppo di un legame costitutivo per lo studio del materiale composito. In particolare, si è adottato un approccio continuo in cui, nei diversi stadi del materiale (prima e dopo la comparsa della fessurazione), i contributi irrigidenti legati alla matrice e alla rete sono valutati separatamente e poi combinati tra loro in modo da formare la matrice di rigidezza del materiale, implementata in un codice di calcolo ad elementi finiti. Nello stadio non fessurato si è assunta l’ipotesi di perfetta aderenza tra la malta e la rete di rinforzo, considerando un comportamento elastico-lineare per entrambi i materiali. Nella fase fessurata, la deformazione totale è assunta pari alla somma della deformazione del materiale tra le fessure e di quella della fessura. L’efficacia del modello è stata quindi verificata effettuando dei confronti con numerosi risultati sperimentali reperiti in letteratura scientifica, relativi sia a tiranti in FRCM, che a travi in c.a. rinforzate a flessione. Tali confronti hanno messo in luce un ottimo accordo tra i risultati numerici e sperimentali. Al fine di meglio indagare alcuni parametri utili per la messa a punto di idonei legami costitutivi presenti nel modello meccanico proposto, è stato deciso di effettuare una campagna di prove sperimentali rivolta alla caratterizzazione meccanica della malta, nonché dell’intero composito FRCM. Nello specifico, si sono eseguite prove a flessione su prismi di sola malta per la determinazione della resistenza a trazione per flessione e per ottenere l’energia specifica di frattura. Al fine di integrare i dati ottenuti e per avere una correlazione analitica tra la resistenza a trazione diretta e quella flessionale apposita per il materiale in questione, si è proceduto ad eseguire ulteriori prove di trazione diretta su provini a “osso di cane” di sola malta. Oltre a ciò, si è studiato il comportamento dell’intero composito, eseguendo delle prove a trazione diretta su provini prismatici in FRCM. Le prove sono state eseguite nel laboratorio di “Prove materiali e strutture” dell’Università di Parma e le rielaborazioni sono state eseguite anche mediante l’uso della DIC (Digital Image Correlation). Dalla campagna sperimentale si è ottenuta una serie di dati utili per una corretta calibrazione del legame costitutivo. Tra questi si annoverano, per la malta cementizia, il coefficiente di Poisson e il modulo di elasticità normale, nonché l’energia specifica di frattura. Per quanto concerne l’intero composito FRCM, si sono ottenute informazioni utili in termini di carico-spostamento e soprattutto una conoscenza della distanza e dell’apertura di fessura che sono dati difficilmente reperibili in letteratura.This work aims to study a new strengthening material, which is formed by a cement-based mortar enriched by inorganic fibers, known as FRCM (Fiber- Reinforced Cementitious Matrix). The investigated material, which is used to strengthen structural elements made of reinforced concrete and masonry, has been only recently launched on the market consequently, it is not yet regulated in all the countries and, it is still object of several studies and research works, in order to deeply characterize its mechanical behaviour and its interaction with the support. In relation to this, the research carried out in this work was structured into two main branches. The first one was the modeling and the numerical simulation of the material and of the elements strengthened with this technique, while the second one was relative to the execution of a series of experimental tests for the determination of the mechanical properties of both the composite and its components. After the analysis of the technical literature relative to both traditional reinforcing techniques and to FRCMs, a constitutive model was developed to study the nonlinear behavior of the composite material. In more detail, a continuous approach was adopted. Both in the uncracked and cracked stages, the stiffening contributions related to the mortar and to the fiber grid were separately evaluated, and then combined to each other in order to build the material stiffness matrix, implemented into a finite elements code. In the uncracked stage, perfect bond between the mortar and the fiber grid was assumed, hypothesizing a linear-elastic behavior for both the constituent materials. In the cracked stage, the total strain was assumed as the sum of the strain of the material between the cracks, and that in the crack. The effectiveness of the proposed model was then verified by carrying out several comparisons with experimental results from the technical literature, relative to both FRCM tension ties, and RC beams retrofitted in bending. These comparisons showed an excellent agreement between numerical and experimental results. However, in order to better investigate some parameters required for the calibration of the constitutive models adopted in the proposed mechanical model, it was decided to perform an experimental campaign, devoted to the mechanical characterization of the cement-based mortar and of the whole FRCM composite. In more detail, flexural tests on prismatic specimens of mortar were first made so as to determine the flexural strength and the material fracture energy. These latter allowed to complete the obtained data on the mortar and to find an analytical correlation between the tensile and the flexural strength of the material. Further tensile tests on “dog bone” specimen of mortar were also made. In addition to this, the behavior of the whole composite was studied, by performing tensile tests on prismatic FRCM specimens. All the tests were carried out at the “Testing Laboratory of Materials and Structures” of the University of Parma. The post-processing was made by also using the DIC technique (Digital Image Correlation). As already stated, the experimental campaign allowed to obtained several data required for the correct calibration of the constitutive model. Among these, the Poisson’s coefficient, the normal elastic modulus and the fracture energy for the mortar were calculated. As regards the entire FRCM composite, useful information in terms of load-displacement behavior and, above all, the knowledge of the cracking distances and openings, hardly available in the literature, were obtained

A non-linear constitutive relation for the analysis of FRCM elements

Nowadays, the strengthening of existing buildings represents one of the most innovative fields within current research in civil engineering. Among the developed techniques, a recent solution consists in the use of FRCM composites (Fabric Reinforced Cementitious Matrix), which are obtained by placing a dry grid of fibers inside a cement-based material (mortar). In comparison with traditional systems, the use of FRCM seems to provide some advantages; however, a full understanding of the mechanical properties of each component (mortar and fibers) and of their interaction, as well as their effect on the strengthened structure, still represents an open research topic. This work aims to be a first attempt to numerically simulate the global behavior of FRCM composites through the development of a macroscopic constitutive model subsequently implemented into a Non-Linear Finite Element (NLFE) procedure. The effectiveness of the proposed procedure is verified through comparisons with significant experimental results available in technical literature, relative to FRCM tension ties. The influence exerted by the adoption of different materials (such as Poliparafenilenbenzobisoxazolo (PBO) and carbon) for the internal fiber grid on the global behavior is also analyzed and discussed

Experimental characterization of fiber-reinforced cementitious mortar under tension

This work focuses on the mechanical characterization of the inorganic matrix used for Fiber-Reinforced Cementitious Matrix (FRCM) composites, nowadays widely used to retrofit existing reinforced concrete and masonry structures. While several works in technical literature investigate the experimental behavior of the whole FRCM composite, few information are available on the mechanical characterization of the mortar, which contains polymers and synthetic fibers in its admixture. However, the knowledge of its behavior in tension, especially after crack formation, is an important feature for the calibration of constitutive models to be adopted in the study of structural elements strengthened with FRCM. To this aim, an experimental program was performed on mortar specimens characterized by different shapes and dimensions, tested under direct tension or three-point-bending. From the performed tests, it was possible to characterize inorganic matrix behavior both in the uncracked stage, through the determination of the elastic parameters (elastic modulus and Poisson’s coefficient), and in the cracked stage. The use of digital image correlation (DIC) technique also allowed the study of the evolution of crack propagation in the specimens. Lastly, a correlation factor between axial and flexural tensile strenght is proposed, for both design and numerical modelling purposes

Italian registry of cardiac computed tomography

Cardiac CT (CCT) is an imaging modality that is becoming a standard in clinical cardiology. We evaluated indications, safety, and impact on patient management of routine CCT in a multicenter national registry. MATERIALS AND METHODS: During a period of 6 months, 47 centers in Italy enrolled 3,455 patients. RESULTS: CCT was performed mainly with 64-slice CT scanners (73.02 %). Contrast agents were administrated in 3,185 patients (92.5 %). Mean DLP changes with type of scanner and was lower in >64 row detector scanner. The most frequent indication for CCT was suspected CAD (44.8 %), followed by calcium scoring (9.6 %), post-angioplasty/stenting (8.3 %), post-CABGs (7.5 %), study of cardiac anatomy (4.22 %) and assessment in patients with known CAD (4.1 %) and acute chest pain (1.99 %). Most of the CCTs were performed in outpatient settings (2,549; 74 %) and a minority in inpatient settings (719, 20.8 %). Adverse clinical events (mild-moderate) occurred in 26 examinations (0.75 %). None of them was severe. In 45.3 % of the cases CCT findings impacted patient management. CONCLUSION: CCT is performed with different workloads in participating centers. It is a safe procedure and its results have a strong impact on patient management

Italian Registry of Cardiac Computed Tomography

Cardiac CT (CCT) is an imaging modality that is becoming a standard in clinical cardiology. We evaluated indications, safety, and impact on patient management of routine CCT in a multicenter national registry.During a period of 6 months, 47 centers in Italy enrolled 3,455 patients.CCT was performed mainly with 64-slice CT scanners (73.02 %). Contrast agents were administrated in 3,185 patients (92.5 %). Mean DLP changes with type of scanner and was lower in > 64 row detector scanner. The most frequent indication for CCT was suspected CAD (44.8 %), followed by calcium scoring (9.6 %), post-angioplasty/stenting (8.3 %), post-CABGs (7.5 %), study of cardiac anatomy (4.22 %) and assessment in patients with known CAD (4.1 %) and acute chest pain (1.99 %). Most of the CCTs were performed in outpatient settings (2,549; 74 %) and a minority in inpatient settings (719, 20.8 %). Adverse clinical events (mild-moderate) occurred in 26 examinations (0.75 %). None of them was severe. In 45.3 % of the cases CCT findings impacted patient management.CCT is performed with different workloads in participating centers. It is a safe procedure and its results have a strong impact on patient management

A multi-element psychosocial intervention for early psychosis (GET UP PIANO TRIAL) conducted in a catchment area of 10 million inhabitants: study protocol for a pragmatic cluster randomized controlled trial

Multi-element interventions for first-episode psychosis (FEP) are promising, but have mostly been conducted in non-epidemiologically representative samples, thereby raising the risk of underestimating the complexities involved in treating FEP in 'real-world' services