Alkali-activated systems (AAS) represent an ecologically and economically sustainable inorganic binder as an alternative to ordinary Portland cement (OPC). One of the main benefits of AAS is their durability in aggressive environments, which can be equal or even better than that of OPC. In this paper, the influence of the type of alkaline activator in alkali-activated blast furnace slag (AAS) in terms of resistance to sulfur dioxide corrosion was investigated. The durability testing process was based on the CSN EN ISO 3231 standard and simultaneously compared with mortar samples prepared by using Blastfurnace cement CEM III/A 32.5R. The degradation progress was evaluated by employing several different methods such as observing the compressive strength development, weight change evaluation, non-destructive testing methods like ultrasound or impact echo technique, or visual phenolphthalein technique. Subsequently, fundamental characterization of samples by the XRD method was performed during the degradation test. The obtained results indicate that none of the testing methods used could be prioritized over others to determine the resistance of AAS against the action of sulfur dioxide. For this reason, the durability testing of AAS remains an issue, and the development of specific standards considering the behavior of AAS seems necessary.
The aim of this paper is to evaluate the possibility of using the impact-echo method for monitoring extremely long-term frost resistance of ceramic tiles. Non-destructive testing methods make it possible to sensitively identify the occurrence and development of defects in materials. Impact-echo methods belong to the family of non-destructive testing methods and can be applied in many branches, among others also in civil engineering. To assess the ceramic-tile frost resistance, a new measurement method was developed based on using the acoustic properties of ceramic tiles. Sets of ceramic tiles of the Ia class were analyzed according to the EN 14 411 B standard. The ceramic tiles under investigation were subjected to degradation due to 500 freezethaw cycles in compliance with the relevant EN ISO 10545-12 standard. To verify the correctness of the impact-echo-method results, additional physical properties of the tested ceramic tiles were measured. To analyze the specimen-surface condition, we also used an Olympus LEXT 3100 confocal scanning microscope. It was proved that the impact-echo acoustic method is a sensitive indicator of a structure condition and can be applied to assess the frost resistance of a ceramic cladding element and predict its service life. Keywords: impact-echo, ceramic tiles, frost resistance, confocal microscopy, freeze-thaw cycles Namen tega~lanka je oceniti mo`nosti za uporabo metode Impact-echo za kontrolo ekstremno dolge odpornosti kerami~nih plo{~ic proti zmrzali. Neporu{ne preiskovalne metode omogo~ajo selektivno identifikacijo pojava in napredovanja napak v materialu. Metoda Impact-echo pripada skupini neporu{nih metod preiskav in je uporabna v mnogih bran`ah, med drugim tudi v gradbeni{tvu. Za oceno odpornosti kerami~nih plo{~ic je bila razvita nova merilna metoda, ki temelji na akusti~nih lastnostih kerami~nih plo{~ic. Analizirani so bili kompleti kerami~nih plo{~ic kvalitete Ia po standardu EN 14 411 B. Preiskovane kerami~ne plo{~ice so bile izpostavljene degradaciji pri 500 ciklih zamrznitve-odtaljevanja skladno z odgovarjajo~im standardom EN ISO 10545-12. Za preverjanje ustreznosti rezultatov metode Impact-echo so bile izmerjene dodatne fizikalne lastnosti kerami~nih plo{~ic. Za analizo stanja povr{ine vzorca je bil uporabljen konfokalni vrsti~ni mikroskop Olympus LEXT 3100. Dokazano je bilo, da je akusti~na metoda Impact-echo ob~utljiv pokazatelj stanja konstrukcije in je uporabna za ugotavljanje odpornosti proti zmrzovanju kerami~nih plo{~ic in za napovedovanje trajnostne dobe plo{~ic. Klju~ne besede: Impact-echo, kerami~ne plo{~ice, odpornost proti zmrzovanju, konfokalna mikroskopija, cikli zmrzovanje-odtaljevanje
This paper is focused on failure monitoring in lightweight concrete (special high-performance concrete that contains porous aggregate with a low bulk density) with high-strength polypropylene fibers under mechanical loading. The aim was to determine how the cracks' generation intensity in the tested concrete samples depends on the fibers' length and quantity. Our diagnostic method is based on a measurement of the acoustic and electromagnetic emission signals, which occur when solid dielectric materials are mechanically stressed. Several groups of lightweight concrete samples with various types and concentrations of high-strength polypropylene fibers were prepared for our experiment. We made two-channel measurements of the concrete samples from each group for defined loading conditions. The first channel was electromagnetic emission (EME) and the second was acoustic emission (AE). The electromagnetic emission and acoustic emission methods are promising methods to study the generation and behavior of cracks. The main advantage of EME and AE is their ability to be detected already in the stressed stage, which prevents macroscopic deterioration in solids. From the obtained results it can be concluded that the generated cracks' intensity is significantly affected by the presence of polypropylene fibers and by their length and dosage. Keywords: acoustic emission, electromagnetic emission, lightweight concrete, fiberŝ lanek je usmerjen na pregled po{kodb pri mehanskem obremenjevanju lahkega betona (poseben visoko zmogljiv beton, ki vsebuje porozne sestavine z majhno gostoto), z visokotrdnostnimi polipropilenskimi vlakni. Namen je bil ugotoviti, kako je intenziteta nastanka razpok odvisna od dol`ine in koli~ine vlaken. Diagnosti~na metoda je temeljila na merjenju akusti~nih signalov in signalov elektromagnetne emisije, ki se pojavijo kadar je trden dielektri~ni material mehansko obremenjen. Za eksperiment je bilo pripravljenih ve~vrst lahkih betonov z razli~no vrsto in koncentracijo visokotrdnostnih polipropilenskih vlaken. Pri dolo~enih pogojih obremenitve smo izvr{ili dvokanalne meritve vzorcev betona iz vsake skupine. Prvi kanal je bila elektromagnetna emisija (EME), drugi pa akusti~na emisija (AE). Metodi elektromagnetne emisije in akusti~ne emisije sta obetajo~i metodi za {tudij nastanka in obna{anja razpok. Glavna prednost EME in AE je, da ju je mogo~e odkriti`e med stanjem napetosti, kar prepre~i lokalne makroskopske po{kodbe v trdnem stanju. Iz dobljenih rezultatov je mogo~e zaklju~iti, da je intenzivnost nastajanja razpoke mo~no odvisna od prisotnosti polipropilenskih vlaken, od njihove dol`ine in odmerka. Klju~ne besede: akusti~na emisija, elektromagnetna emisija, lahki beton, vlakna
The aim of this paper is to evaluate the possibility of using the Impact-echo method for assessment of extremely long period of frost resistance of ceramic tiles. Sets of ceramic tiles of the Ia class to EN 14 411 B standard made by manufacture RACOs have been analyzed. The ceramic tiles under investigation have been subjected to 500 freeze-thaw-cycle based degradation in compliance with the relevant EN ISO 10545-12 standard. To verify the correctness of the Impact-echo method results, additional physical properties of the ceramic tiles under test have been measured. To analyze the specimen surface condition, we also used Olympus LEXT 3100 confocal scanning microscope. It has been proved that the acoustic method Impact-echo is a sensitive indicator of the structure condition and can be applied to the ceramic cladding element frost resistance and service life prediction assessment.
Acoustic emission is an experimental tool well suited for monitoring fracture processes. The paper presents experiment focused on analysing acoustic emission signals captured during three-point bending fracture test of specimens of concrete. Quantitative acoustic emission techniques were used to measure micro fracture properties. For three different concrete mixtures typical acoustic emission patterns were identified in the acoustic emission records to further describe the under-the-stress behaviour and failure development. If we have a better understanding of the relationships between micro structural events and macroscopic behaviour we can better formulate predictive models for large-scale structural performance and reliability. An understanding of microstructureperformance relationships is the key to true understanding of material behaviours. Three-point bending fracture tests were conducted on these specimens and load versus crack mouth opening displacement (Load-CMOD) diagrams were recorded during the testing.
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