High-Performance Concrete is an advanced cementitious material characterized by high strength and stiffness, and by low porosity and permeability; these advantages generally allow to improve bearing capacity, stiffness and durability of R/C structures. The increasing use of High-Performance Concrete in many structures exposed to extreme environmental conditions (tunnels, off-shore platforms, Liquefied Natural Gas terminals, containment shells), and the need to repair/strengthen many existing structures in order to meet the most recent code provisions or to increase their service life (e.g. nuclear power plants), bring in new problems, which go beyond the excellent knowledge we have on the behaviour of ordinary concrete in extreme conditions. At high temperature, in fact, High-Performance Concrete shows to be more heat sensitive than ordinary concrete in terms of mechanical behaviour, mainly due to its denser matrix that leads to a more brittle response and to the development of higher values of pore pressure during heating. A great number of studies have been conducted on concrete in order to highlight the role played by both material factors (fibre content, aggregate type, moisture content, porosity, concrete grade, etc.) and external factors (heating rate, loads and constrains). These studies proved that mix design optimization in terms of aggregate type, fibre type and content can ensure a better mechanical response of High-Performance Concrete subjected to fire. In the present research project, the influence of the mix design on concrete mechanical behaviour under uniaxial compression at high temperatures (T ≥ 500°C) is investigated. Eleven concrete mixes were studied, considering three different grades (cubic compressive strength Rc = 45, 70, 95 MPa), three aggregate types (silico-calcareous/calcareous/basaltic aggregate), as well as three fibre types (monofilament or fibrillated polypropylene fibres, and steel fibres). Results are compared with the mechanical properties in virgin and residual conditions. Numerical models are built up aimed at focusing on the influence of heating rate and thermal stress, via the finite element method. This investigation, however, will be part of an ongoing work.
Il calcestruzzo ad alte prestazioni (HPC) è un materiale cementizio avanzato caratterizzato da elevata resistenza e rigidezza, e bassa porosità e permeabilità; tali peculiarità consentono generalmente di migliorare la capacità portante, la rigidezza e la durabilità delle strutture in calcestruzzo armato. Il crescente utilizzo di HPC in molte strutture esposte a condizioni ambientali estreme (gallerie, piattaforme off-shore, terminali di gas naturale liquefatto, gusci di contenimento), e la necessità di riparare/rinforzare molte strutture esistenti al fine di soddisfare le più recenti disposizioni normative o di aumentarne la vita utile (ad esempio, le centrali nucleari), porta nuove problematiche, che vanno al di là della pur ottima conoscenza raggiunta sul comportamento del calcestruzzo ordinario in condizioni estreme. Alle temperature elevate, infatti, l’HPC mostra una maggiore sensibilità al danneggiamento termico rispetto al calcestruzzo ordinario in termini di comportamento meccanico, a causa principalmente della sua matrice più densa; quest’ultimo aspetto, infatti, porta ad una risposta più fragile del materiale e allo sviluppo di valori più elevati di pressione nei pori durante il riscaldamento. Un gran numero di studi è stato condotto sul calcestruzzo soggetto ad alte temperature, per indagare il ruolo giocato da diversi fattori sia a livello del materiale (contenuto di fibre, tipologia degli aggregati, contenuto di umidità, porosità, classe di resistenza, ecc) che esterni (velocità di riscaldamento, carichi e vincoli). Tali studi hanno dimostrato come l'ottimizzazione della miscela cementizia in termini di tipologia degli aggregati, tipologia e contenuto delle fibre, permetta di ottenere una migliore risposta meccanica dell’HPC in condizioni di incendio. Nel presente Progetto di Ricerca si studia l'influenza delle principali componenti della miscela,sulla risposta meccanica del calcestruzzo in compressione uniassiale ad alte temperature (T ≥ 500°C). Sono state confezionate undici miscele di calcestruzzo considerando: tre diverse classi di resistenza (resistenza cubica a compressione Rc = 45, 70, 95 MPa), tre tipologie di aggregati (silico-calcarea, calcarea e basaltica), e tre tipologie di fibre (fibre di polipropilene monofilamento o fibrillate, e fibre in acciaio). I risultati ottenuti sono stati confrontati con le proprietà meccaniche in condizioni vergini e residuali. Sono stati realizzati, inoltre, modelli ad elementi finiti per analizzare il ruolo della velocità di riscaldamento e delle auto-tensioni termiche.
Mix design effect on the compressive behaviour of concrete at high temperature
LI, YUHANG;XU, ZHIJIN
2013/2014
Abstract
High-Performance Concrete is an advanced cementitious material characterized by high strength and stiffness, and by low porosity and permeability; these advantages generally allow to improve bearing capacity, stiffness and durability of R/C structures. The increasing use of High-Performance Concrete in many structures exposed to extreme environmental conditions (tunnels, off-shore platforms, Liquefied Natural Gas terminals, containment shells), and the need to repair/strengthen many existing structures in order to meet the most recent code provisions or to increase their service life (e.g. nuclear power plants), bring in new problems, which go beyond the excellent knowledge we have on the behaviour of ordinary concrete in extreme conditions. At high temperature, in fact, High-Performance Concrete shows to be more heat sensitive than ordinary concrete in terms of mechanical behaviour, mainly due to its denser matrix that leads to a more brittle response and to the development of higher values of pore pressure during heating. A great number of studies have been conducted on concrete in order to highlight the role played by both material factors (fibre content, aggregate type, moisture content, porosity, concrete grade, etc.) and external factors (heating rate, loads and constrains). These studies proved that mix design optimization in terms of aggregate type, fibre type and content can ensure a better mechanical response of High-Performance Concrete subjected to fire. In the present research project, the influence of the mix design on concrete mechanical behaviour under uniaxial compression at high temperatures (T ≥ 500°C) is investigated. Eleven concrete mixes were studied, considering three different grades (cubic compressive strength Rc = 45, 70, 95 MPa), three aggregate types (silico-calcareous/calcareous/basaltic aggregate), as well as three fibre types (monofilament or fibrillated polypropylene fibres, and steel fibres). Results are compared with the mechanical properties in virgin and residual conditions. Numerical models are built up aimed at focusing on the influence of heating rate and thermal stress, via the finite element method. This investigation, however, will be part of an ongoing work.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/101921