Uporaba ultrazvoka za analizo vpliva naknadnega mehanskega poseganja v strukturo betona : diplomska naloga

Hribar, Matevž (author), Turk, Goran (mentor), Trtnik, Gregor (co-mentor)

Glavni namen diplomske naloge je na podlagi ultrazvočnih meritev formiranja strukture materialov s cementnim vezivom ugotoviti vpliv mehanskega poseganja v strukturo v smislu občutnega vplivanja na vezanje in zgodnji razvoj trdnostnih karakteristik materiala. Proučevali smo predvsem spremembe mehanskih lastnosti: elastični modul, tlačno trdnost, konsistenco in čas vezanja. Tematike vpliva mehanskih posegov v strukturo materialov s cementnim vezivom (t.j. cementnih past, malt, betonov) na kakovost in mehanske lastnosti v odvisnosti od časa smo se lotili z vidika potreb po kvalitetni vgradnji in zagotavljanju ustreznih mehanskih lastnosti. Zanimal nas je vpliv v primerih kadar materiala ne vgradimo takoj po pripravi (dolg transport ali morebitne druge okoliščine, ki ne omogočajo takojšnje vgradnje) in vpliv mehanskih posegov v strukturo pri določenih časih (ponovno mešanje, revibriranje). Čase v obdobju vezanja, pri katerih smo mehansko posegli v strukturo materialov s cementnim vezivom in čas vezanja posamezne mešanice smo določili z novo ultrazvočno metodo, ki temelji na razmerju največjih amplitud dveh prevladujočih frekvenc, ki se pojavita v frekvenčnem spektru vzdolžnega valovanja. Za potrebe dosega cilja diplomskega dela smo poleg ultrazvočne metode uporabili klasične preskusne metode za določitev tlačnih trdnosti in statičnega elastičnega modula. Za analizo razvoja dinamičnega elastičnega modula smo uporabili napravo GrindoSonic, ki temelji na principu indukcije valovanja v vzorcu. Konsistenco pa smo določevali vizualno. Na podlagi lastnih eksperimentalnih preiskav smo ugotovili, da naknadni mehanski poseg (ne glede na obdobje v fazi vezanja) v strukturo mešanic ne vpliva bistveno na končne mehanske lastnosti. Časi vezanja se v relativnem smislu ponekod celo skrajšajo. Vendar pa nam konsistenca v praksi ne omogoča kvalitetne vgradnje brez uporabe dodatkov (plastifikatorjev).

• Language: Slovenian
• Keywords: gradbeništvo, diplomska naloga, UNI, cementni materiali, hidratacija, formiranje strukture, ultrazvočne meritve, vezanje, tlačna trdnost, elastični modul, konsistenca
• Work type: Undergraduate thesis
• Typology: 2.11 - Undergraduate Thesis
• Organization: FGG - Faculty of Civil and Geodetic Engineering
• Place of publishing: Ljubljana
• Publisher: [M. Hribar]
• Year: 2014
• Number of pages: XIII, 60 str.
• PID: 20.500.12556/RUL-32285
• UDC: 534:691(497.4)(043.2)
• COBISS.SI-ID: 6659169
• Publication date in RUL: 10.07.2015

Secondary language

• Language: English
• Title: The use of ultrasonic measurements for analysis of the impact on the subsequent mechanical intervention into the structure of concrete

Abstract

The main purpose of the thesis, based on the ultrasonic measurements of the formation of the materials with cement binders, is to determine the impact of the mechanical intervention into the structure, in terms of the significant influence on the setting and early development of characteristic strength of material. During our research we mostly pursued changes in mechanical properties: elastic modulus, compressive strength, consistency and setting time. The issue of the impact (of the mechanical intervention into the structure of the cement paste, mortars and concrete) on the quality and on mechanical properties in relation to time was dealt with from the perspective of the demand for a better built quality as well as with the aim to provide adequate mechanical properties. As far as the impacts were concerned, we were particularly interested in cases, when material is not built in immediately after its preparation (long transport or any other circumstances which do not allow for immediate placing operation) as well as in the impact of the mechanical intervention into the structure at certain times (revibration, remixing). Setting times, when mechanical intervention into the structure of the material with binding agent took place, as well as setting time of a particular mixture, were determined by a new ultrasonic method, which is based on the highest ratio of the amplitudes of the two dominant frequencies, which appear in the frequency spectrum of longitudinal waves. In addition to the ultrasonic method, classical test methods were carried out as well in order to determine compressive strength and static elastic modulus and reach the objective of the thesis. For the purpose of analysis of the dynamic elastic modulus development we used GrindoSonic device, which is based on the principle of induction of the wave in the sample. Consistency was determined visually. On the basis of our experimental research, we found out that subsequent mechanical intervention (irrespective of the period at the stage of setting) into the structure of the mixtures, does not affect substantially the final mechanical properties. In some cases setting times are even shortened in relative terms. However, consistency in practice does not allow us to ensure high quality of placing operation without the use of additives (plastificators).

• Keywords: cement based materials, hydration, formation of structure, ultrasonic measurements, setting, compressive strength, elastic modulus, consistency