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Trtnik G.,IGMAT Building Materials Institute | Gams M.,Slovenian National Building And Civil Engineering Institute
Cement and Concrete Research | Year: 2015

In this paper, a possibility of using frequency spectrum of ultrasonic P-waves to determine very early age compressive strength (fc) of cement based materials (CBMs) is analyzed. TG parameter, representing the ratio between maximum amplitudes of high and low frequency ranges that appear in the frequency spectrum of the transmitted signal, is used to observe the changes in the spectrum. Both fc and TG start to increase simultaneously and later develop according to similar trend. Thus, strong correlation between fc and TG is established, regardless of the CBM's composition. By comparing stress-strain curves and time derivatives of TG-t curves, the stage when the material is clearly plastic and stage when material exhibits solid behavior, can be distinguished. These results explain physical meaning of TG parameter in more detail and expand the range of practical applications of methods based on spectral analysis of transmitted P-waves. © 2014 Elsevier Ltd. All rights reserved. Source

Hiti M.,Slovenian National Building And Civil Engineering Institute
Measurement Science and Technology | Year: 2015

This article describes a resistor network for linearity verification of voltage ratio-indicating instruments. The network is based on a resistive divider with low variation of input and output resistance. To compensate for the output resistance change due to a selection of various output ratios, a switched variable compensating resistor network is added to the output leads of the voltage divider. It limits the variation of output resistance to <5% at a ratio of 1:10 and <0.5% for ratios 1:100 or higher. The application of the circuit is shown in the example of an output voltage ratio simulation of a strain gauge bridge transducer, typical in the measurement of mechanical quantities such as force, torque, and pressure. The circuit is suitable for verifying the linearity of voltage ratio measuring instruments by using a combinatorial calibration technique without the need to calibrate the resistor network. Results are shown for the linearity check of a high-precision strain gauge amplifier. © 2015 IOP Publishing Ltd. Source

Trtnik G.,IGMAT Building Materials Institute | Gams M.,Slovenian National Building And Civil Engineering Institute
Ultrasonics | Year: 2014

To summarize some of the most important findings in the field of ultrasonic (US) testing of early age hydration and formation of structure of different cement based materials (CBMs), a review of literature with focus on US P-wave transmission and S-wave reflection methods is presented in this paper. The review shows a great ability of both US techniques to observe setting phenomena and to determine different milestones during the early age formation of CBM's microstructure. Clear physical basis, high accuracy, and non-destructive nature of the method indicate that US methods could become standardized in the near future. © 2013 Elsevier B.V. All rights reserved. Source

Tomazevic M.,Slovenian National Building And Civil Engineering Institute
International Journal of Architectural Heritage | Year: 2011

In the past three decades, significant research has been conducted on seismic behavior of masonry buildings in historic urban and rural nuclei. On the basis of the earthquake damage observations and subsequent experimental simulations of the observed mechanisms, technical measures for the improvement of the seismic resistance have been proposed and methods for seismic resistance verification developed. By in situ and laboratory testing, the basic mechanical properties of the existing and strengthened masonry have been determined. The research results have been used to analyze the requirements of Eurocode regarding the design methods and parameters for structural assessment and retrofitting of buildings. Modifications have been proposed that would lead to more realistic assessment of seismic resistance in the case of historic masonry buildings. For this purpose, the seismic behavior of buildings, subjected to design-level earthquakes for the second time in just a few decades, has been analyzed and correlated with the actually observed earthquake damage. Copyright © Taylor & Francis Group, LLC. Source

Gams M.,Slovenian National Building And Civil Engineering Institute | Trtnik G.,IGMAT Building Materials Institute
Cement and Concrete Research | Year: 2013

The paper presents a new method to determine the transition of different cementitious materials from liquid to solid state, usually defined as a setting period. The method is based on a ratio between maximum amplitudes of two dominant frequency ranges that appear in the frequency spectrum of ultrasonic (US) P-waves, called a TG parameter. Clear and unambiguous correlation between characteristic points in the evolution of TG parameter and penetration resistance in time is established on samples with different material composition during the early hydration process. The correlation indicates that TG parameter detects the development of rigid bonds between hydrating cement particles. The ability and accuracy of the method to determine setting period is unaffected by the material composition. Non-destructive nature and insensitivity of the method to aggregate size gives it an advantage over penetration methods and other US methods in determining the setting period of cement pastes, mortars, and concretes. © 2013 Elsevier Ltd. Source

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