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Ocena mehanskih lastnosti betona predhodno izpostavljenega visokim temperaturam z uporabo neporušnih metod : magistrsko delo
Novak, Katja (Author), Hozjan, Tomaž (Mentor) More about this mentor... This link opens in a new window, Trtnik, Gregor (Co-mentor)

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Abstract
Magistrsko delo obravnava možnost ocene osnovnih mehanskih lastnosti apnenčevega betona, izpostavljenega različnim visokim temperaturam (200 °C, 400 °C, 600 °C ali 800 °C) z uporabo neporušnih in porušnih metod. Eksperimentalna študija je bila izvedena na dveh betonskih mešanicah M1 in M2, ki sta se razlikovali v vodo-cementnem (v/c) razmerju. Z vsako mešanico smo pripravili 15 kock dimenzij 10 × 10 × 10 cm3 in 15 prizem dimenzij 4 × 4 × 16 cm3, za vsako temperaturno raven po tri kocke in tri prizme. Preiskovali smo osnovne mehanske lastnosti betona, to so tlačna trdnost, upogibna natezna trdnost, površinska trdnost, dinamični elastični modul in dinamični strižni modul. Začetne oz. referenčne vrednosti pri sobni temperaturi 20 °C smo izmerili na betonskih preskušancih, ki so bili negovani skladno s standardom SIST EN 12390-2:2009. Posamezno skupino preskušancev smo nato postavili v električno peč ter preko vgrajenih visoko temperaturno odpornih termočlenov spremljali razvoj temperature s časom znotraj preskušancev. Po izpostavitvi določeni visoki temperaturi smo preskušance kontrolirano ohladili na sobno temperaturo. Izvedli smo vizualni pregled in podali grobo oceno poškodovanosti betonske površine. Nadalje so bili izvedeni različni neporušni testi: ultrazvočna (UZ) metoda, sklerometrična metoda in metoda resonančne frekvence. Za določitev preostalih mehanskih lastnosti betona po izpostavitvi visokim temperaturam smo na koncu izvedli standardni porušni preiskavi tlačne in upogibne trdnosti betona. Ugotovili smo, da imajo visoke temperature največji vpliv na padec dinamičnih elastičnih lastnosti betona (Edyn in G), sledita upogibna natezna trdnost (fcf) in tlačna trdnost (fc) betona, medtem ko najmanjši padec vrednosti zaznamo pri površinski trdnosti betona (fc,surf). Analiza variance (ANOVA) pa je pokazala, da je vpliv temperature na eksperimentalne rezultate za obe mešanici M1 in M2 statistično značilen.

Language:Slovenian
Keywords:apnenčev agregat, visoke temperature, mehanske lastnosti, neporušne metode, porušne metode, ultrazvočna metoda, sklerometrična metoda, metoda resonančne frekvence, tlačni preizkus, upogibni preizkus, analiza variance
Work type:Master's thesis/paper (mb22)
Tipology:2.09 - Master's Thesis
Organization:FGG - Faculty of Civil and Geodetic Engineering
Year:2021
Publisher:[K. Novak]
Place:Ljubljana
UDC:539.411:691.32(497.4)(043.3)
COBISS.SI-ID:68508163 This link opens in a new window
Views:277
Downloads:104
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Secondary language

Language:English
Title:Estimation of mechanical properties of concrete after exposure to high temperatures using nondestructive methods : master thesis
Abstract:
Master thesis introduces evaluation of the mechanical properties of limestone concrete after exposure to various high temperatures, i.e. 200 °C, 400 °C, 600 °C or 800 °C, using nondestructive and destructive tests. Experimental study was carried out on two concrete mixtures M1 and M2. The only difference between them was in water to cement (w/c) ratio. With each mixture we prepared 15 cubic samples dimension 10 × 10 × 10 cm3 and 15 prismatic samples dimension 4 × 4 × 16 cm3, for each temperature level three cubic and three prismatic samples. The basic mechanical properties of concrete samples were investigated in the research, i.e. compressive strength, flexural strength, surface strength, dynamic elastic, and shear modulus. Initial or reference values at room temperature 20 °C were measured on concrete samples after standard curing time proposed by standard SIST EN 12390-2:2009. Each group of samples was then placed in an electric furnace and exposed to a certain high temperature level. The development of the temperature inside the samples was monitored via built-in thermocouples. After exposure to a certain high temperature level, the samples were slowly cooled down to a room temperature. Afterwards, the specimens were initialy visually inspected to assess the damage of the concrete surface. Further on, various nondestructive tests including ultrasonic (US) method, determination of rebound number, and resonant frequency method were performed. Finally, to determine the residual mechanical properties of specimens after exposure to high temperature destructive tests were carried out, i.e. the compressive and bending test. It was found out that high temperatures have the greatest impact on the reduction of dynamic elastic properties (Edyn and G), followed by flexural strength (fcf) and compressive strength (fc). While the impact of high temepratures on surface strength (fc,surf) is the lowest. Additionaly, analysis of variance (ANOVA) showed that the influence of temperature on experimental results is highly statistically significant for both mixtures M1 and M2.

Keywords:limestone aggregate, high temperatures, mechanical properties, nondestructive methods, destructive methods, ultrasonic method, rebond hammer method, resonant frequency method, compressive test, bending test, analysis of variance

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