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Experimental Study of Mechanical Wave Propagation in Solidifying Cement-Based Composites
(MDPI, 2024-12-06) Jakubka, Luboš; Topolář, Libor; Nekorancová, Anna; Dvořák, Richard; Hrabová, Kristýna; Černý, Felix; Skibicky, Szymon; Pazdera, Luboš
In this paper, a new measurement procedure is presented as an experimental study. In this experimental study, a measurement system using the pass-through pulsed ultrasonic method was used. The pilot application of the measurement setup was to monitor mechanical wave changes during the solidification and hardening of fine-grained cement-based composites. The fine-grained composites had different water–cement ratios. The measured results show apparent differences in the recorded mechanical wave parameters. Significant differences were observed in the waveforms of the amplitude increase in the passing mechanical waves. At the same time, the frequency spectra of the five most dominant frequencies are presented, where the frequency lines are clear, indicating the quality of the hydration process. Based on the results, it can be concluded that the new method is usable for fine-grained cement-based materials but is not limited to that. The advantages of this method are its high variability and non-destructive character. The experimental study also outlines the possible future applications of the pulsed passage ultrasonic method.
Non-destructive Testing of CIPP Defects Using Machine Learning Approach
(Institute of Metals and Technology, 2024-09-15) Dvořák, Richard; Pazdera, Luboš; Topolář, Libor; Jakubka, Luboš; Puchýř, Jan
In civil engineering, retrofitting actions involving repairs to pipes inside buildings and in extravehicular locations present complex and challenging tasks. Traditional repair procedures typically involve disassembling the surrounding structure, leading to technological pauses and potential work environment disruptions. An alternative approach to these procedures uses the cured-in-place-pipe (CIPP) technology for repairs. Unlike standard repairs, CIPP repairs do not require a disassembly of the surrounding structures; only the access points at the beginning and end of the pipe need to be accessible. However, this method introduces the possibility of different types of defects.1 1 This research aims to observe the defects between the host and newly cured pipes. The presence of holes, cracks, or obstacles prevents achieving a desired close-fit state, ultimately reducing the life expectancy of the retrofitting. This paper focuses on the non-destructive observation of these defects using the non-destructive testing (NDT) impact-echo (IE) method. The study explicitly applies this method to the composite segments inside concrete host pipes, forming a testing polygon. Previous results have indicated that the mechanical behaviour of cured composite pipes can vary in stiffness depending on factors such as the curing procedure and environmental conditions.2 2 The change in acoustic parameters such as resonance frequency, attenuation and other features of typical IE signals can describe the stiffness evolution. This study compares different sensors used for the proposed IE testing, namely piezoceramic and microphone sensors. It evaluates their ability to distinguish between the defects present in the body of a CIPP via a machine-learning approach using random tree classifiers.
Impedance Spectroscopy – comparison of experimental ceramic results with model parameters
(IOP Publishing, 2024-08-25) Kusák, Ivo; Luňák, Miroslav; Dvořák, Richard; Nekorancová, Anna; Mizerová, Cecílie; Rovnaník, Pavel
Impedance spectroscopy is a non-destructive test method belonging to the group of electrical engineering measurements. The method is suitable for monitoring the quality of building materials even with low conductivity. Although the method focuses on the intrinsic conductivity of systems, most IS techniques, including data analysis methods, conceive of the material in terms of a lossy dielectric. In selecting the material for testing with the IS method, an attempt was made to bring the IS capabilities as close as possible to practical, real-world materials. This paper is devoted to a comparison of the impedance characteristics of ceramics with three types of dielectric models that are described in theory or referenced in the literature. The ceramic samples were fabricated using different material additions, such as bentonite, phosphoric acid, or sodium water glass. Experimental curves of the loss factor versus frequency for all samples are described and then approximations of selected samples are shown successively for all three models considered. Experimental results were obtained from more than 50 points in each characterization. Measurements were performed for frequencies from 40 Hz to 1 MHz.
Fractal Analysis of Rock Joint Profiles
(IOP Publishing, 2017-11-28) Audy, Ondřej; Ficker, Tomáš
Surface reliefs of rock joints are analyzed in geotechnics when shear strength of rocky slopes is estimated. The rock joint profiles actually are self-affine fractal curves and computations of their fractal dimensions require special methods. Many papers devoted to the fractal properties of these profiles were published in the past but only a few of those papers employed a convenient computational method that would have guaranteed a sound value of that dimension. As a consequence, anomalously low dimensions were presented. This contribution deals with two computational modifications that lead to sound fractal dimensions of the self-affine rock joint profiles. These are the modified box-counting method and the modified yard-stick method sometimes called the compass method. Both these methods are frequently applied to self-similar fractal curves but the self-affine profile curves due to their self-affine nature require modified computational procedures implemented in computer programs.
Efect of Chemical Aggressive Media on the Flexural Properties of Cured-In-Place Pipes Supported by Microstructure Observation and Acoustic Emission
(MDPI, 2020-07-08) Hodul, Jakub; Majerová, Jana; Drochytka, Rostislav; Dvořák, Richard; Topolář, Libor; Pazdera, Luboš
The cured-in-place pipe (CIPP) method is currently the most frequently used approach for the renovation of piping without digging; this technology is suitable for pipes made from all types of material. The authors of this paper examined how chemical substances and increased temperature change samples of CIPP with vinyl-ester resin taken from a simulated installation. Changes were observed at several levels: visually via a digital optical microscope, through changes of short-term bending properties and by observation of the activity of the sample structure by means of acoustic emission (AE). Interdependencies among the observed parameters were examined, specifically, the cumulative number of hits (cnt)/deflection and flexural properties/mechanic wave velocity. The test results prove that after three weeks of immersion in a simulated aggressive environment that mirrors what may happen to CIPP in real conditions, short-term mechanical properties change. This is also proven by the results of the AE measurements. For clarity, the results include images from a digital optical microscope. In addition, this paper proves that CIPP samples have good resistance to the action of organic and inorganic acids and to increased temperatures. After three weeks of exposure to a temperature of 100 °C the CIPP flexural properties of the samples had even improved.

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