Acoustically assessed influence of air pore structure on failure of self-compacting concretes under compression / Akustiškai įvertinta oro porų struktūros įtaka susitankinančio betono susilpnėjimui veikiant gniuždymui

The paper presents the results of investigations into the influence of pore structure on the failure of self-compacting concretes modified with superplasticizers commonly used in construction. Pore structure examinations were carried out in practically the whole range of pore diameters by means of an image analyzer and a mercury porosimeter. The failure of the self-compacting concretes under compression, was investigated by the acoustic emission technique and other methods. The levels of cracking initiating stress σiand critical stress σcr, demarcating the different stages in the failure process, were determined. It has been shown that there is a relationship between the pore structure parameters and the levels. The fatigue strength of the self-compacting concretes was calculated from the experimental results and on this basis the suitability of the concretes for structures subject to cyclic loads was determined. Santrauka Straipsnyje pateikiami porų struktūros įtakos susitankinančio betono su superplastikliais susilpnėjimui tyrimų rezultatai. Buvo atlikti praktiškai visų skersmenų porų struktūros tyrimai naudojant vaizdo analizatorių ir gyvsidabrio porosimetrą. Susitankinančio betono susilpnėjimas esant gniuždymui buvo tiriamas akustinės emisijos ir kitais metodais. Nustatyti pleišėjimo lygiai ir įtampos, žymintys skirtingus susilpnėjimo lygius. Parodyta, kad yra ryšys tarp porų struktūros parametrų ir susilpnėjimo lygių. Pagal eksperimentinius rezultatus suskaičiuotas betono atsparumas ir nustatytas betono tinkamumas konstrukcijoms, atsižvelgiant į ciklines apkrovas. Reikšminiai žodžiai: susitankinantis betonas, porų struktūra, susilpnėjimas, gniuždymas, akustinė emisija, ultragarsa

Effect of Freeze–Thaw Cycling on the Failure of Fibre-Cement Boards, Assessed Using Acoustic Emission Method and Artificial Neural Network

This paper presents the results of investigations into the effect of freeze–thaw cycling on the failure of fibre-cement boards and on the changes taking place in their structure. Fibre-cement board specimens were subjected to one and ten freeze–thaw cycles and then investigated under three-point bending by means of the acoustic emission method. An artificial neural network was employed to analyse the results yielded by the acoustic emission method. The investigations conclusively proved that freeze–thaw cycling had an effect on the failure of fibre-cement boards, as indicated mainly by the fall in the number of acoustic emission (AE) events recognized as accompanying the breaking of fibres during the three-point bending of the specimens. SEM examinations were carried out to gain better insight into the changes taking place in the structure of the tested boards. Interesting results with significance for building practice were obtained

Review of modern non-destructive methods used to test fiber-cement boardsmethod system

W artykule przedstawiono i omówiono wybrane nowoczesne metody nieniszczące wykorzystywane do badania materiałów kompozytowych jakim są płyty włóknisto-cementowe. Omówiono metodę ultradźwiękową, w tym również z wykorzystaniem fal Lamba, metodę emisji akustycznej, metodę terahercową i metodę optyczną z wykorzystaniem elektronowego mikroskopu skaningowego SEM. Wszystkie te metody zostały z powodzeniem wykorzystane w badaniach, w tym również w badaniach własnych autorów, co jednoznacznie potwierdza ich przydatność w badaniu płyt włóknisto-cementowych.The article presents and discusses selected modern non-destructive methods used to test composite materials such as fiber-cement boards. The ultrasonic method, including the Lamb wave method, the acoustic emission method, the terahertz method and the optical method using the scanning electron microscope (SEM) are discussed. All these methods have been successfully used in research, including the authors' own research, which clearly confirms their usefulness in the study of fiber-cement boards

Identification of the Degree of Degradation of Fibre-Cement Boards Exposed to Fire by Means of the Acoustic Emission Method and Artificial Neural Networks

This paper presents the results of research aimed at identifying the degree of degradation of fibre-cement boards exposed to fire. The fibre-cement board samples were initially exposed to fire at various durations in the range of 1⁻15 min. The samples were then subjected to three-point bending and were investigated using the acoustic emission method. Artificial neural networks (ANNs) were employed to analyse the results yielded by the acoustic emission method. Fire was found to have a degrading effect on the fibres contained in the boards. As the length of exposure to fire increased, the fibres underwent gradual degradation, which was reflected in a decrease in the number of acoustic emission (AE) events recognised by the artificial neural networks as accompanying the breaking of the fibres during the three-point bending of the sample. It was shown that it is not sufficient to determine the degree of degradation of fibre-cement boards solely on the basis of bending strength (MOR)

Application of the Acoustic Emission Method and Artificial Neural Networks to Assess the Damaging Effect of High Temperature on the Structure of Fibre-Cement Boards

This article shows the results of research into the damaging effect of high temperature on the structure of fibre-cement boards. Samples of fibre-cement boards were exposed to high temperatures over various lengths of time and then they were investigated under the three-point bending and acoustic emission methods. In this way, the critical temperature and the duration of its influence on the structure of a fibre-cement board were determined. An artificial neural network was used to analyse the results obtained using the acoustic emission method. The investigations showed a marked fall in the number of registered AE events for the tested series of boards exposed to high temperature in comparison with the reference boards. Moreover, in the boards exposed to high temperature, a marked increase in the energy of AE events occurs during the bending test, whereby the registered events, by and large, come down to a single pulse induced by a brittle fracture. It is also demonstrated that the determination of the damaging effect of high temperature on the structure of fibre-cement boards solely on the basis of bending strength (MOR) is inadequate

Investigation of Structural Degradation of Fiber Cement Boards Due to Thermal Impact

The aim of the present study was to investigate the degradation of the microstructure and mechanical properties of fiber cement board (FCB), which was exposed to environmental hazards, resulting in thermal impact on the microstructure of the board. The process of structural degradation was conducted under laboratory conditions by storing the FCB specimens in a dry, electric oven for 3 h at a temperature of 230 °C. Five sets of specimens, that differed in cement and fiber content, were tested. Due to the applied heating procedure, the process of carbonization and resulting embrittlement of the fibers was observed. The fiber reinforcement morphology and the mechanical properties of the investigated compositions were identified both before, and after, their carbonization. Visual light and scanning electron microscopy, X-ray micro tomography, flexural strength, and work of flexural test Wf measurements were used. A dedicated instrumentation set was prepared to determine the ultrasound testing (UT) longitudinal wave velocity cL in all tested sets of specimens. The UT wave velocity cL loss was observed in all cases of thermal treatment; however, that loss varied from 2% to 20%, depending on the FCB composition. The results obtained suggest a possible application of the UT method for an on-site assessment of the degradation processes occurring in fiber cement boards

Multi-Scale Structural Assessment of Cellulose Fibres Cement Boards Subjected to High Temperature Treatment

The methodology of multi-scale structural assessment of the different cellulose fibre cement boards subjected to high temperature treatment was proposed. Two specimens were investigated: Board A (air-dry reference specimen) and Board B (exposed to a temperature of 230 °C for 3 h). At macroscale all considered samples were subjected to the three-point bending test. Next, two methodologically different microscopic techniques were used to identify evolution (caused by temperature treatment) of geometrical and mechanical morphology of boards. For that purpose, SEM imaging with EDS analysis and nanoindentation tests were utilized. High temperature was found to have a degrading effect on the fibres contained in the boards. Most of the fibres in the board were burnt-out, or melted into the matrix, leaving cavities and grooves which were visible in all of the tested boards. Nanoindentation tests revealed significant changes of mechanical properties caused by high temperature treatment: “global” decrease of the stiffness (characterized by nanoindentation modulus) and “local” decrease of hardness. The results observed at microscale are in a very good agreement with macroscale behaviour of considered composite. It was shown that it is not sufficient to determine the degree of degradation of fibre-cement boards solely on the basis of bending strength; advanced, microscale laboratory techniques can reveal intrinsic structural changes

Methodology of nondestructive identification of defective concrete zones in unilaterally accessible massive members

The paper deals with the nondestructive identification of defective concrete zones in unilaterally accessible massive members, for example, access galleries in hydroelectric power plants. The concrete in such zones is, for various reasons, excessively porous. The authors propose to use state-of-the-art acoustic testing techniques, including ultrasonic tomography, integratively to detect and identify defective zones. An original methodology for such tests has been developed. The methodology is illustrated with an example of its practical application to a real civil engineering structure. First published online: 24 Oct 201

Analiza business administration wykorzystania Pilskiej Karty Miejskiej w środkach komunikacji miejskiej w Pile

W artykule przedstawiono wykorzystanie Pilskiej Karty Miejskiej (PKM), która służy jako bilet w komunikacji miejskiej w Pile (MZK). W kolejnym etapie badań zostaną zaprezentowane inne możliwości jego wykorzystania. Celem pracy była analiza istniejącego systemu PKM oraz poznanie opinii publicznej na temat jego funkcjonowania i możliwości szerszego wykorzystania. Badania przeprowadzono na terenie miasta Piła za pomocą kwestionariusza składającego się z 12 pytań zamkniętych jednokrotnego wyboru i 2 pytań otwartych. Mieszkańcy Piły byli zadowoleni z usług świadczonych przez MZK oraz wprowadzenia biletu elektronicznego zakodowanego w PKM. Funkcjonowanie tej karty znacznie ułatwia podróżowanie. Respondenci przekazali również wiele ciekawych sugestii dotyczących innych zastosowań PKM niż tylko w komunikacji. Część propozycji, po konsultacjach z władzami miasta i MZK, jest obecnie wdrażana