1,721,023 research outputs found
Applicazione delle nanotecnologie alla realizzazione di sensori a base cementizia per il monitoraggio delle strutture
No full textLo sviluppo delle nanotecnologie ha permesso la realizzazione di nuovi materiali multifunzionali. In particolare, l'aggiunta di nanoparticelle di carbonio ad una matrice cementizia conferisce al materiale una sensibilità al proprio stato di tensione e deformazione. La funzione di autodiagnosi viene ottenuta correlando la variazione delle sollecitazioni applicate con la variazione di adeguati parametri del materiale, come la resistenza elettrica. Rispetto ai sensori tradizionali utilizzati per il monitoraggio strutturale, questi sensori innovativi presentano dei vantaggi dovuti alla maggiore durabilità, alla facilità di applicazione e alla possibilità di essere applicati in maniera estesa. Per le caratteristiche del materiale con cui sono realizzati, essi sono particolarmente adatti per il monitoraggio delle strutture in c.a.
Il presente articolo riguarda l’analisi delle caratteristiche elettromeccaniche di sensori a base cementizia con aggiunta di nanotubi di carbonio multi parete (MWCNT) e la loro applicazione al monitoraggio di un elemento in c.a. di dimensioni reali. I risultati delle prove sperimentali di caratterizzazione dinamica evidenziano che il comportamento dei sensori innovativi nanoadditivati è paragonabile a quello di sensori tradizionali, come estensimetri e accelerometri, anche ad alte frequenze di vibrazione
Carbon nanotube cement-based sensors for dynamic monitoring of concrete structures
No full textStructural Health Monitoring (SHM) is one of the most significant topics of civil engineering. It allows to examine the actual conditions of a structure during its service life. The main purpose of SHM is finding any deficiency before it can reach a worrying damage level able to compromise structural safety. The recent development of nanotechnology allows the creation and the development of new types of sensors made by adding carbon nanotubes to the cement paste.
In this paper, tests on cement-based sensors for monitoring the dynamic behavior of concrete elements subjected to time-varying loads, are presented
L'esemplare e il suo valore per l'esperienza: tradizione e attualità di un concetto
No full textLa categoria dell’ ‘esemplare’ viene considerata nella sua logica specifica, in quanto distinta dalla logica dell’ ‘esempio’ rispetto alla funzione di categoria-ponte tra universale e particolare e in un senso sia linguistico ed epistemologico che storico, tra tradizione e modernità. Il radicamento nel contingente e la sua vicinanza in particolare alla prassi umana concernente la regola e la sua applicazione suggeriscono, sulla scorta di alcune riflessioni di Emilio Garroni dedicate a questo tema, di collegare la ‘necessità esemplare’ teorizzata dal Kant della Terza Critica alle difficoltà e alle soluzioni possibili dell’applicare una regola in vista del suo potenziale creativo
Smart Cement Paste with Carbon Nanotubes
No full textCarbon nanotubes can be added to cementitious materials to create a multifunctional nanocomposite with excellent piezoresistive and strain-sensing properties. The use of carbon nanotubes provides high strain sensitivity and signal-to-noise ratio, which are ideal for fabricating self-sensing nanocomposite cement paste for applications to structural health monitoring of concrete structures. The authors have recently developed an innovative sensor, the carbon nanotube cement-based sensor (CNTCS), made from a nanocomposite cement paste. This CNTCS is durable because it is fabricated with a material that has a life expectancy similar to the one of the monitored structure, and provides a natural strong mechanical bond with structural concrete. These characteristics enable embedded and spatially distributed sensing. The CNTCS was conceived to conduct vibration-based structural health monitoring.This chapter presents an overview of the sensing properties of cement pastes doped with multiwalled carbon nanotubes. After introducing the topic, including a brief state of the art on multifunctional cement-based materials, the fabrication process of the CNTCSs is discussed. Then, unstrained and strained electrical responses of the nanocomposite sensors are discussed and interpreted in light of a lumped electromechanical circuit model used to characterize both the polarization effects and the sensing capability of the CNTCSs. Finally, a proof-of-concept laboratory application consisting of vibration monitoring and modal identification of a full-scale concrete beam is presented, where outputs of CNTCSs are benchmarked against mature off-the-shelf sensing technologies
Comportamento al fuoco di solai per edifici di cemento armato: confronto tra metodo tabellare, sperimentale ed analitico.
No full textFire performance assessment of HPLWC hollow core slabs through full-scale furnace testing
No full textHigh-Performance Light-Weight Concrete has been recently used for many structural
applications when it is required superior strength and low self-weight of the structural components.
This can be the case of slender floor structures, like hollow core slabs, that require characteristics of
lightness, relatively high resistance and superior durability. Although the fire performance of normal
strength concrete hollow core slabs has been extensively studied, the behavior of high performance
light-weight concrete hollow core slabs has not been suitably investigated.
In this paper are reported the results of experimental investigations on the behavior of high
performance light-weight concrete hollow core slabs under fire conditions. Full-scale furnace tests
were performed to assess the slabs' load bearing capacity under fire conditions along with the
characteristics of the thermal field. Tests were carried out on both loaded and unloaded slabs. The
latter were subsequently used to assess the residual strength after fire. The numerical evaluation of the
thermal field and the fire resistance was also carried out. The experimental and the numerical
investigations gave insight into the fire performance of HPLWC hollow core slabs and highlighted the
influence of dry curing conditions in reducing the spalling and increasing their fire resistanc
Self-powered Sensors Through Harvester Beams: Application to Weigh-in-Motion and Dynamic Sensing
No full textNatural frequencies identification of a reinforced concrete beam using carbon nanotube cement-based sensors
No full textCementitious materials doped with carbon nanoparticles are robust materials capable of transducing
strain into changes in electrical resistance. These properties encourage the development of spatially distributed
sensors for structural health monitoring of concrete structures. Yet, very few applications of
transducers made of cement-based nanocomposites to structural elements have been documented.
The majority of applications are limited to measurement of static responses.
The authors have recently proposed the novel application of cement-based nanocomposite technologies
for vibration-based structural health monitoring of concrete structures. To this aim, prismatic sensors
made of cement paste doped with carbon nanotubes have been proposed as embedded sensors
for concrete structures. Prior results have shown the promise of these sensors at vibration measurements.
In this paper, the authors further the understanding of the dynamic behavior of cement-based carbon
nanotube sensors by conducting experiments on a full-scale reinforced concrete beam for output-only
identification of natural frequencies. The performance of the novel sensor is benchmarked against offthe-
shelf strain gauges and accelerometers. Results show that the proposed sensor compares well against
existing technologies at vibration monitoring. Also, the nanocomposite sensor is capable of detecting high
frequencies, which is made possible by a very low level of noise and an excellent signal-to-noise ratio
obtained from shielded wire connections and proper tailoring of the fabrication process
Automated crack detection in conductive smart-concrete structures using a resistor mesh model
No full textVarious nondestructive evaluation techniques are currently used to automatically detect and
monitor cracks in concrete infrastructure. However, these methods often lack the scalability
and cost-effectiveness over large geometries. A solution is the use of self-sensing carbondoped
cementitious materials. These self-sensing materials are capable of providing a
measurable change in electrical output that can be related to their damage state. Previous work
by the authors showed that a resistor mesh model could be used to track damage in structural
components fabricated from electrically conductive concrete, where damage was located
through the identification of high resistance value resistors in a resistor mesh model. In this
work, an automated damage detection strategy that works through placing high value resistors
into the previously developed resistor mesh model using a sequential Monte Carlo method is
introduced. Here, high value resistors are used to mimic the internal condition of damaged
cementitious specimens. The proposed automated damage detection method is experimentally
validated using a 500 × 500 × 50 mm3 reinforced cement paste plate doped with multi-walled
carbon nanotubes exposed to 100 identical impact tests. Results demonstrate that the proposed
Monte Carlo method is capable of detecting and localizing the most prominent damage in a
structure, demonstrating that automated damage detection in smart-concrete structures is a
promising strategy for real-time structural health monitoring of civil infrastructure
Improved understanding of grouted mixture fatigue behavior under indirect tensile test configuration
No full textThis paper focuses on the long-term performance of a grouted mixture, a relatively new pavement material which consists of an open grade asphalt concrete whose voids are filled with cement mortar. Its peculiar characteristics, depending on mix design and level of filling, induce a variability of its mechanical behavior. The purpose of this paper is understanding how such variability affects the fatigue properties of the material, under indirect tensile test configuration. Experimental results have revealed a remarkable influence of stiffness properties on fatigue life. Following this observation, the fatigue behavior of grouted mixture is described through a new analytical model, which explicitly introduces the dependence of the fatigue life on the stiffness modulus. Comparative analysis demonstrates that the proposed analytical model significantly outperforms traditional fatigue modeling for the peculiar type of investigated composite pavement system
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