Search

Fibres of various types can be added to cementitious composites to reduce their autogenous shrinkage and/or post-cracking. [1] The high strength and modulus of elasticity of fibres limit the propagation of cracks in a brittle cement matrix resulting in longer service life and lower maintenance costs for structures. However, fibre production has a significant negative environmental impact. To meet the EU's transition to a carbon-neutral, resource-efficient, circular and competitive economy, the use of secondary materials is strongly encouraged. For example, waste fibres such as recycled tyre polymer fibres (RTPF) [2] could be used to reinforce cement composites if found resistant enough to highly alkaline environment (pH > 12). To simulate cement matrix conditions and evaluate alkali resistance, RTPFs were exposed to a synthetic pore solution for 90 days. The solution was prepared by dissolving calcium, sodium and potassium hydroxides and calcium sulphate in water (2.2 g/L Ca(OH)2, 3.99 g/L NaOH, 16.83 g/L KOH, 0.34 g/L CaSO4×H2O) so that the pH, ionic composition and strength were adjusted to best simulate cement matrix. [3] The morphology of untreated and treated RTPF was studied by SEM, thermal properties by DSC and TGA and FTIR were used to determine the chemical changes. Partial and limited alkaline hydrolysis was observed in treated RTPF, so it can be suggested that it can be used at least to limit the volume deformation of the cement composite at early age. The reduction in cracking depends on the mechanical properties of the fibres, which could not be evaluated because the RTPFs are too short. This highlights the difficulty of establishing standardized testing protocols for different types of (waste) fibres that could potentially be used to reinforce cement composites.

Different types of fibers are used in a variety of cementitious materials to improve their properties. Uniformly distributed and aligned fibers are crucial to ensure the desired improvements. Experimental techniques for microstructural characterization of materials, such as micro-computed tomography, are critical to understanding the contribution of fibers to the behavior of composite materials. As a non- destructive method, micro-computed tomography (CT) has been used in medicine as a diagnostic imaging technique since the 1970s and is gradually finding application in other industries. The 3D view of the internal structure of the materials under investigation makes CT a valuable tool for the evaluation of fiber-reinforced composites. The actual fiber content, distribution and orientation of individual fibers can be easily determined and used to explain the behavior of composites. To date, research has focused mainly on steel fibers, whose high specific density facilitates the identification of fibers in the cement matrix. Synthetic fibers present a greater challenge to CT due to their low density and lack of conductivity. In this paper, the basic principles of X-ray computed tomography, its advantages and limitations are presented, focusing on the methods for detecting the distribution of synthetic fibers in cementitious composites.

Cementni materijali imaju nisku vlačnu i savojnu čvrstoću. Zahvaljujući dobrim karakteristikama bazaltnih vlakana moguće je unaprijediti svojstva cementnog kompozita. Cementni kompozit karakteriziran je svojom visokom lužnatošću, pH iznad 12, te je kao takav nepogodan za trajnosna svojstva bazaltnih vlakana. Trenutni fokus brojnih istraživanja je primjena bazaltnih vlakana u cementnim kompozitima i njihova trajnosna svojstva u alkalnom okolišu. U ovom radu dan je kratak pregled upotrebe bazaltnih vlakana u cementnim kompozitima s naglaskom na trajnosna svojstva bazaltnih vlakana. Pregledom literature ustanovljeno da ne postoje uniformirana ispitivanja te nije nemoguće usporediti pojedina istraživanja. Prikazani su uvjeti ispitivanja u različitim alkalnim otopinama, ovisno o vremenu izloženosti i temperaturi, opisani su mehanizmi degradacije bazaltnih vlakana ovisno o alkalnim otopinama. Ustanovljeno je da je neophodno je razviti metodu ispitivanja trajnosnih svojstava bazaltnih vlakana u alkalnom okolišu.

Pitanje održivosti se sve više nameće kao važan zahtjev u građevinskoj industriji, posebice u području građevinskih materijala. Zadovoljenje potrebnih uvjeta održivosti može se pronaći u betonu ultra visokih uporabnih svojstava (eng. UHPC). Rad daje sažet pregled njegovih osnovnih svojstava i primjena uz prikaz eksperimentalnog dijela u kojem je ispitan utjecaj primjene otpadnih materijala na svojstva u svježem te očvrsnulom stanju. Otpadne materijale su činili zamjenski cementni materijali (metakaolin i vapnenački filer) te reciklirana čelična vlakna iz otpaadnih guma (eng. RTSF). Dobiveni rezultati su pokazali pogodnost njihove primjene za dobivanje UHPC-a uz potrebna poboljšanja koja će se provesti u daljnjim ispitivanjima.

Reducing greenhouse gas emissions and dependence on fossil fuels is the cornerstone of all European climate and energy strategies. At the same time, waste reduction and recycling are at the top of the European waste hierarchy. Therefore, the European Union (EU) is turning to renewable energy and sustainable options that address complex local conditions and growing energy and material needs. Bioenergy is the most important renewable energy source in the EU, accounting for more than 2/3 of the renewable energy mix. As wood is a carbon neutral energy source, it is one of the predominant sources of biomass for energy production in the EU. However, the continuous expansion of wood biomass power plants leads to the formation of wood biomass ash (WBA), a solid by-product of wood combustion on a large scale. The disposal of WBA is a problem that requires long-term strategic and sustainable solutions. Therefore, WBA is the focus of this paper as an alternative material with pozzolanic and/or hydraulic properties needed for the production of waste-based artificial hydraulic lime (AHL). This type of a novel hybrid WBA-lime binder would serve as an end result for the production of a repair mortar for historical buildings. Two different sources of locally available WBA were considered for the preparation of binders as mixtures of WBA and natural hydraulic lime (NHL) in different ratios. Based on the chemico-mineralogical composition and physical properties, the potential of WBA as a component of an AHL is evaluated. The contribution of the individual binder mixtures to mortar properties was analyzed on the basis of the demonstrated water demand, the flow diameter and the compressive and flexural strength according to EN 459-1.

In cementitious composites, the hydration process is the most important feature. The conditions, rate, and general manner of this process affect the properties of composites both at early and later ages. The development and prediction of future properties can be studied using both destructive and non-destructive methods to predict the potential and behaviour at later ages. Due to the early occurrence of autogenous shrinkage and the large influence of chemical shrinkage, the hydration process and the formation of the microstructure play an important role in determining the time zero point for autogenous shrinkage and the overall determination of the shrinkage value.

Trajnost vlakana u cementnoj matrici definirana je njihovom otpornošću alkalnom okolišu. Kako bi utvrdili svojstva trajnosti otpadnih vlakana u cementnim kompozitima vlakna se podvrgavaju različitim ispitivanjima u cilju utvrđivanja njihove kemijske stabilnosti, ali i promjene geometrijskih i mehaničkih svojstava nakon izlaganja alkalnom okolišu. U radu je prikazan sustavan pregled literature iz područja trajnosti staklenih, bazaltnih, ugljičnih vlakana i polimernih vlakana iz recikliranih otpadnih guma. Dan je pregled najčešće korištenih alkalnih otopina, uvjeti i trajanje ispitivanja, definirani su mehanizmi korozije za svaku vrstu vlakana iz dostupne literature. Na osnovi danih istraživanja zaključeno je da postoji nedostatak normiranih ispitivanja u cilju definiranja otpornosti vlakana u alkalnom okolišu, ali i temeljem provedenih ispitivanja predviđanja uporabnog vijeka u cementnim kompozitima.

Volume deformations of cementitious composites are an unavoidable phenomenon. Depending on the cause, a distinction is made between those caused by changes in ambient temperature and those caused by the water motion. Deformations caused by water motion in the cementitious composites occur as shrinkage or swelling of the mixture, or sometimes by their combination. To avoid adverse effects on the durability of cementitious composites, it is important to understand the mechanisms and triggers of shrinkage deformation. Therefore, this paper briefly discusses the basic types of shrinkage in cementitious composites. The focus is on chemical, autogenous, and drying shrinkage, explaining the mechanisms of each type and how they interact.

Vijadukt Bukovo (sjeverni objekt, smjer Rijeka, Hrvatska) u km 64+050, 00 autoceste A6 Rijeka- Zagreb, dionica Kikovica – Oštrovica pušten je u promet 1982. godine. Smješten na tzv. snježnoj dionici u Gorskom kotaru, tijekom godina izložen je agresivnom okolišu (smrzavanje/odmrzavanje sa soli, snažni udari bure, morski okoliš). Temeljem provedenog specijalističkog pregleda i proračuna mehaničke otpornosti i stabilnosti utvrđena je nužnost hitne obnove vijadukta te je izrađen izvedbeni projekt sanacije i provedena obnova. Cilj ove studije slučaja jest prikazati postupak ocjene stanja, odabrana tehnička rješenja sanacije i pojačanja konstrukcije Vijadukta Bukovo.

Uvod: Traumatske ozljede zuba zahtijevaju hitan postupak i svaki gubitak vremena umanjuje vjerojatnost da će liječenje biti uspješno. Avulzija ili traumatsko izbijanje zuba (eksartikulacija) jedan je od najdramatičnijih oblika ozljeđivanja zuba pri kojem zbog fizikalne traume u području lica ili čeljusti dolazi do ispadanja zuba iz zubne alveole. Cilj istraživanja bio je istražiti razinu znanja i spremnost u sanaciji dentalne traume u studenata završne godine stomatoloških fakulteta u Srbiji i Hrvatskoj netom prije završetka studija. Materijali i metode: Online anketa provedena je među studentima završne godine stomatoloških fakulteta u Hrvatskoj i Srbiji - Stomatološki fakultet u Zagrebu, Medicinski fakultet u Splitu, Fakultet Dentalne medicine Rijeka, Fakultet za Dentalnu medicinu i Zdravstvo Osijek, Fakultet medicinskih nauka Kragujevac, Stomatološki fakultet Pančevo te Stomatološki fakultet Beograd. Anketa se sastojala od 3 dijela: opći podatci, pitanja znanja te pitanja o samoprocjeni. Statistička usporedba izvedena je Kruskal-Wallis testom. RezultatI: U istraživanje je bilo uključeno 189 studenata. Prosječna starost ispitivane skupine bila je 25 godine. Dokazana je statistički značajna razlika u znanju studenata sa navedenih fakulteta (p=0, 000). Najbolju riješenost ankete imali su studenti sa Fakulteta Dentalne medicine u Rijeci sa prosječnom riješenosti 85, 4% te se nisu statistički značajno razlikovali od znanja studenata iz Zagreba, Splita te Osijeka. Studenti iz Srbije samokritičniji su prema svojem znanju, međutim svi studenti smatraju kako su dodatne edukacije na ovu temu potrebne. Zaključak: Ovim prikazom i spoznajom da neki studenti, a budući doktori nebi znali promptno reagirati na ovu traumu, smatramo kako su dodatne edukacije potrebne.

Zahtjev održivosti u građevinskoj industriji može ispuniti beton ultra visokih uporabnih svojstava (eng. UHPC). U radu je dan opći pregled UHPC-a uz provedena ispitivanja utjecaja silicijske prašine, metakaolina, vapnenačkog filera te nano gline na reološka i mehanička svojstva UHPC-a. Rezultati su pokazali sporiji prirast te manje vrijednosti ranih čvrstoća u odnosu na referentnu mješavinu. Istaknut je utjecaj nano gline na obradivost te potreba pronalaska optimalnog postupka miješanja i udjela nano gline.

Želatinozni zooplankton se pokazao kao dobar indikator termohalinih promjena u Jadranu. Brojnost i pojavnost stranih ili nedavno uspostavljenih želatinoznih vrsta su direktno povezani s promjenama u obrascima cirkulacije, a potencijalno i s razinom zagrijavanja Jadrana. U posljednjih deset godina u Jadranu su otkrivene dvije nove želatinozne planktonske vrste za znanost: Brooksia lacromae (Thaliacea, Tunicata) i Aurelia pseudosolida (Ulmaridae, Cnidaria). Indopacifička vrsta Paracytaeis octona (Cytaeididae, Cnidaria) je zabilježena od 2015. godine pa nadalje, dok su mediteranske vrste Doliopsis rubescens i Pegea bicaudata (Thaliacea, Tunicata) zabilježene u Jadranu prvi put 2016. godine. Sporadično su se bilježile i relativno rijetke vrste Pyrosoma atlanticum (Thaliacea, Tunicata), Porpita porpita (Porpitidae, Cnidaria) i Flaccisagitta hexaptera (Chaetognatha). Naši podaci sugeriraju da se ubrzavaju promjene u sastavu zajednica želatinoznog planktona u Jadranskom moru što upućuje na potrebu provođenja sustavnih programa monitoringa na državnoj razini. Da bi se procijenila mogućnost korištenja metoda sekvenciranja sljedeće generacije u praćenju promjena u sastavu Jadranskog zooplanktona proveli smo istraživanje u Sjevernom i Južnom Jadranu u trajanju od godine dana. Naši preliminarni podaci pokazuju da se rijetke vrste zooplanktona i pelagički plaštenjaci ne bilježe konzistentno upotrebom fragmenta gena podjedinice I citokrom oksidaze (COI).

In recent years, environmental disasters have been the main topic worldwide. The increasing amounts of waste and landfills, as well as the depletion of natural resources, have an impact on the climate changes that cause these disasters. The construction industry has a significant impact in this regard, especially as it relates to the depletion of natural resources. In order to meet the necessary requirements for building structures and construction materials, while reducing the negative impact on nature, the solution may lie in the use of waste materials. The aim of this paper is to highlight the use of waste fibres as reinforcing materials in cementitious composites as one of the ways to meet environmental and construction requirements. In this context, fibres are divided into synthetic and natural fibres. The advantages of using waste fibres over industrial fibres are highlighted. The main focus is on 4 types of waste fibres: Carbon, Glass, Basalt and RTPF (recycled tyre polymer fibres) and their effects on the properties of cementitious composites. In this context, fibre length, distribution, volume content, origin, etc. are studied. Recommendations are given for the possible use of waste fibres in the construction industry and their contribution to certain properties is explained.

Sustavno upravljanje građevinama kroz redovite preglede omogućava predviđanje preostalog uporabnog vijeka, te planiranje proaktivnog održavanja. Jedna od nužnih informacija za proračun preostalog uporabnog vijeka postojećih armiranobetonskih građevina je količina i stanje armature unutar betona. Metoda koja se uglavnom koristi za određivanje položaja armature unutar betona bez razaranja, tzv. tragač armature, bazira se na vrtložnim strujama. Sama metoda, iako jednostavna, ima određena ograničenja, poput dubine mjerenja, vremena potrebnog za ispitivanje i sl. Istovremeno, za lokalizaciju armature je moguće koristiti georadar. Georadar kao nerazorna metoda ispitivanja omogućava prikupljanje velikog broja podataka o građevini u kratkom vremenskom periodu i lokalizaciju armature pri znatno većim debljinama zaštitnog sloja. Georadar radi na principu elektromagnetskih valova, a primjerenom analizom i interpretacijom rezultata omogućava prikupljanje podataka o položaju armature i mogućim nepravilnostima u konstrukciji. U radu je dan prikaz prednosti i nedostataka georadara kao metode za ocjenu stanja armiranobetonskih građevina. Na nizu primjera studija slučaja prikazane su mogućnosti rekonstrukcije radargrama i njihove analize.

Shrinkage of cementitious composites is an unavoidable phenomenon which occurs right after the contact of cement and water, and it continues until late age. It is a complex phenomenon consisting of various types of shrinkage that occur due to different mechanisms. In early age it causes microcracks that form inside the composite because stresses exceed the strength value. Formed microcracks have a potential to grow into macrocracks. The presence of short fibres can restrain formed cracks and improve the properties of concrete in terms of durability. The aim of this work is to show the influence of the waste fibres on early- age properties of cementitious composites with the emphasis on autogenous shrinkage. Used fibres are alkali resistant glass, basalt, and carbon fibres obtained from a local producer of technical textiles.

This paper focuses on reviewing relevant work on autonomous ground systems for concrete bridge inspection. The current inspection of bridges is still based on visual inspection by inspectors or by using semi-destructive techniques. Current inspection practices require a large amount of time for inspection. In addition, complex scaffolding or expensive equipment is required for inaccessible areas, which also poses a risk to the safety of inspectors. These drawbacks could be overcome by using robotic systems equipped with non-destructive techniques (NDT). This paper presents the ground robotic systems that have been used in the inspection of concrete bridges, mainly for the localization of reinforcement, corrosion assessment and crack detection.