Acoustic and electromagnetic emission of lightweight concrete with polypropylene fibers

Abstract

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

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