Određivanje svojstava cementnog gela transverzalnim ultrazvučnim valovima

doctoral thesis

• Author: Rudi Čop; VIAF: 305635598
• Mentor: Mladen Maletić (mentor)
• Committee member: Hrvoje Domitrović (predsjednik povjerenstva)
• Committee member: Mladen Maletić (član povjerenstva)
• Committee member: Dunja Mikulić (član povjerenstva)
• Committee member: Stanko Tonković (član povjerenstva)
• Committee member: Siniša Fajt (član povjerenstva)
• Granter: University of Zagreb; Faculty of Electrical Engineering and Computing; (Department of Electroacoustics); Zagreb
• Defense date and country: 2004-06-07, Croatia
• Scientific / art field, discipline and subdiscipline: TECHNICAL SCIENCES; Electrical Engineering; Electronics
• Universal decimal classification (UDC): 621.3 - Electrical engineering ; 53 - Physics ; 666 - Glass industry. Ceramics. Cement and concrete

Abstract

Sve ne-destruktivne metode za ispitivanje svježog betona posebno su zanimljive, jer omogućavaju predviđanje svojstava betona u njegovoj konačnoj fazi (faza zrelog betona) i to prije njegovog polaganja. Zato je takvim metodama posvećena najveća pažnja. Jedna od uspješnih metoda za određivanje mehaničkih svojstava cementnog gela u trenutku njegovog prelaska u čvrsto stanje, jeste metoda koja koristi refleksiju ultrazvuka pri njegovom prelasku kroz ispitivani uzorak. Metoda se bazira na mjerenju refleksije transverzalnih ultrazvučnih valova od gornjeg sloja cementnog gela u trenutku njegovog stvrdnjavanja korištenjem linije kašnjenja. Moduli elastičnosti i viskoznosti odrede se na osnovi odnosa između prvog i drugog reflektiranog vala. Za mjerenje kinetike hidratacije konstruiran je mjerni sustav u koji su unesene određene popravke za postizanje točnijih rezultata. Pri tom se naročito vodilo računa da se izradi odgovarajuća ispitivačka komora u koju se postavlja uzorak cementnog gela kod ultrazvučnog mjerenja. Uzajamno djelovanje cementnog gela i ultrazvučnih valova može se primijeniti kod ispitivanja kakvoće samog mjerenja kinetike hidratacije uz primjenu mjernih standarda. Pored toga primjena mjernih standarda omogućava još brže određivanje svojstava uzorka, jer se u tom slučaju može iskoristiti podatak o ubrzanju hidratacije. Opisane su i prednosti koje donosi spektralna analiza demoduliranog signala refleksija i spektralna analiza samog signala visoke frekvencije ispred demodulatora.

Abstract (english)

All non-destructive testing methods in civil engineering for fresh concrete are of special interest because they allow predictions to be made about the concrete's properties prior to its placement. That is why the special attention is devoted to such types of the testing method. The Determination of Elastic Properties of Fresh Special Concrete Using Ultrasonic Shear Waves Ultrasonic waves have been used successfully for the determination of the mechanical properties of hardened cement paste and concrete. For this purpose researchers are measuring the ultrasonic shear wave reflections from the upper layer of the hardening cement paste using the buffer rod. The modulus of elasticity and viscosity are determined as a rate between the first and second reflected waves. For measuring of the cement mortar hydration kinetics there has been constructed the measuring setup, which was improved to achieve the more accurate results. The greatest importance is given to the appropriate measuring chamber were the cement gel sample should be inserted, for the ultrasound testing measurements. The interaction between the cement gel and the ultrasonic waves, together with application of the measuring standards, could be used to obtain information on the quality of the cement mortar hydration kinetics measuring process. Besides, usage of the measuring standards enables the earlier determination of the sample properties, because the data on the hydration acceleration is available. There are also described the advantages of the demodulated-reflection-signal spectrum analysis and the spectrum analysis of the high-frequency-signal on the demodulator input.

• Keywords: transverzalni ultrazvučni valovi; refleksija; kinetika hidratacije; cementni gel; mjerni sustav
• Keywords (english): ultrasonic shear waves; reflection; kinetics of hydration; cement gel; measuring setup
• Language: croatian
• URN:NBN: urn:nbn:hr:168:846247
• Promotion: 2020
• Study programme: Title: Doctoral study programme "Electrical Engineering and Computing"; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, po-dručje tehničkih znanosti (doktor/doktorica znanosti, po-dručje tehničkih znanosti)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Closed access
• Created on: 2020-06-24 07:38:59