Use of stainless steel as concrete reinforcement

Polazeći od štetnosti korozije armature na trajnost i troškove održavanja armiranobetonskih konstrukcija, u radu se kao način sprečavanja korozije armature opisuje primjena armature od određenih vrsta nehrđajućih čelika koji su otporni na koroziju. Prikazani su rezultati ispitivanja korozijske otpornosti nehrđajućih čelika i ugljičnog čelika te su dane preporuke za upotrebu nehrđajućih čelika kao armature ovisno o razredu izloženosti projektirane armiranobetonske konstrukcije.Starting from the impact the steel corrosion has on the durability and maintenance costs of reinforced- concrete structures, the authors describe how steel corrosion can be prevented by using reinforcement made of certain types of stainless steel that are resistant to corrosion. Results obtained by testing corrosion resistance of stainless steel and carbon steel are presented, and recommendations are given for the use of stainless steel as reinforcement depending on exposure category of a particular reinforced structure

Use of sludge generated at WWTP in the production of cement mortar and concrete

U radu je opisana problematika vezana uz generiranje i zbrinjavanje mulja s UPOV-a (uređaja za pročišćavanje otpadnih voda) u Hrvatskoj. Poseban osvrt je dan na mogućnost i opravdanost korištenja pepela dobivenog spaljivanjem mulja. Naglasak je stavljen na ugradnju pepela u betonskoj industriji, pri proizvodnji cementnog morta i betona. U radu su opisani rezultati dosada provedenih istraživanja u okviru svjetske prakse, s primarnim osvrtom na utjecaj ugradnje pepela na karakteristike cementnog morta i betona.Problems relating to disposal of sludge accumulating at waste-water treatment plants (WWTP) in Croatia are described in the paper. The possibility and adequacy of using ash obtained through incineration of sludge is considered. A special emphasis is placed on the significance of ash in concrete industry during production of cement mortar and concrete. Results of worldwide research conducted so far are described, with indications about the ways in which ash use influences properties of cement mortar and concrete

ČELIČANSKA ZGURA KAO KORISTAN MATERIJAL ZA PROIZVODNJU BETONA

This paper aims to investigate the possibility of utilizing steel slags locally produced in Croatian plants as a concrete aggregate. Therefore, eight concrete mixtures were prepared with coarse slag fractions and different binders whose hardened state properties (compressive strength, static modulus of elasticity, volume changes and corrosion susceptibility) were then compared with the properties of reference concrete made of commonly used natural aggregate materials, dolomite. According to the obtained test results it can be concluded that concrete containing slag possesses acceptable mechanical properties and volume changes for its structural use but could represent a risk in terms of corrosion of reinforcement in case of slag with higher amount of sulphur in its chemical composition.U radu se istražuje mogućnost uporabe čeličanske zgure nastale u hrvatskim željezarama kao agregata u betonu. Pripremljeno je osam mješavina betona sa zgurom kao krupnom frakcijom i različitim vezivima te ispitana svojstva takvog betona u očvrslom stanju (tlačna čvrstoća, statički modul elastičnosti, volumne promjene i sklonost ka koroziji) i uspoređena sa svojstvima referentnog betona pripremljenog sa uobičajeno korištenim agregatom, dolomitom. Prema ostvarenim rezultatima ispitivanja može se zaključiti da beton sa zgurom u sastavu svojim mehaničkim svojstvima i volumnim promjenama zadovoljava uvjete za primjenu u konstrukciji ali može djelovati korozivno na armaturni čelik ukoliko zgura sadrži veći udio sumpora u kemijskom sastavu

Micro-Mechanical Analysis of Corrosion Products Formed During Long-Term Carbonation Induced Corrosion of Steel

During corrosion distinct types of corrosion products form, composed of different ratios of ferrous ions and oxide, hydroxides. Corrosion products have different physical and mechanical properties, mainly density, resistivity, volume and modulus of elasticity compared to iron. Knowing properties of corrosion products is indispensable for service life modelling of structures and can give valuable insight into the long-term corrosion propagation process. In this study micro-indentation method was used to evaluate mechanical properties of different layers formed during long-term carbonation induced corrosion of steel in concrete. Investigation was performed on three sets of reinforced concrete samples, that underwent corrosion during 50, 60 and 70 years. Raman microspectroscopy was performed locally to determine and locate the constitutive phases of the corrosion system and to correlate them to the results of micro-indentation. Using grid technique, spatial distribution of phases with different mechanical properties was obtained for samples of different age. Comparison of values of mechanical properties for the same phases obtained on different samples, allowed hypothesis on their long-term behaviour

UTJECAJ OPLATA KONTROLIRANE PROPUSNOSTI NA MEHANIČKA I TRAJNOSNA SVOJSTVA ZAŠTITNOG SLOJA BETONA

Oplate kontrolirane propusnosti (engl. Controlled Permeability Formwork, CPF) sastoje se od vlaknaste membrane koja upija višak vode i zraka iz površinskog sloja betona. Samim time, vodocementni omjer površinskog, zaštitnog sloja betona ostaje manji u odnosu na preostali presjek betonskog elementa. Cilj ispitivanja je odrediti utjecaj dvije različite vrste CPF oplate na mehanička i trajnosna svojstva zaštitnog sloja betona. Tijekom ispitivanja varirana je debljina zaštitnog sloja betona (3 i 5 cm) te se oplata ponovno koristila nakon što je pripremljena prva grupa uzoraka, kako bi se razmotrila mogućnost višestrukog korištenja CPF oplata. Tijekom rada ispitivana su sljedeća mehanička i trajnosna svojstva: brzina ultrazvuka, indeks sklerometra, čvrstoća prianjanja, plinopropusnost i kapilarno upijanje. Svojstva zaštitnog sloja betonskih elemenata pripremljenih u CPF oplatama uspoređena su sa svojstvima zaštitnog sloja betonskog elementa pripremljenog u običnoj oplati

Corrosion and stray currents at urban track infrastructure

Tračnice su dio kolosiječne konstrukcije na kojima će se korozija neizbježno pojaviti, osim ako su u potpunosti izolirane te nemaju kontakt s bilo kojim drugim dijelom kolosijeka (prag, pričvrsni pribor) ili elektrolitom poput vlažnog tla ili vode u kolosiječnoj konstrukciji. Korozija će biti znatno brža u prisutnosti lutajućih struja, što će kroz vrlo kratko vrijeme rezultirati gubitkom materijala na nožici tračnice. U radu je dan pregled i opis parametara koji utječu na razinu lutajućih struja, poput električnog potencijala u tračnici i uzdužne provodljivosti tračnice, električnog otpora između tračnice i tla, kao i električne provodljivosti nosivih betonskih slojeva kolosiječne konstrukcije i električne provodljivosti tla.Rails are a part of track structure where corrosion process inevitably occurs, except if they are fully insulated and devoid of contact with any other part of the structure (sleepers, fastening accessories) or electrolyte like moist soil or water in track structure. Corrosion occurs much faster in the presence of stray currents, which very soon results in the loss of material at the rail foot. The paper presents an overview and description of parameters influencing stray current levels, such as electrical potential in rail and longitudinal rail conductivity, rail-to-earth electrical resistance, electrical conductivity of load-bearing concrete layers of truck structure, and electrical conductivity of soil

UTJECAJ OPLATA KONTROLIRANE PROPUSNOSTI NA MEHANIČKA I TRAJNOSNA SVOJSTVA ZAŠTITNOG SLOJA BETONA

Oplate kontrolirane propusnosti (engl. Controlled Permeability Formwork, CPF) sastoje se od vlaknaste membrane koja upija višak vode i zraka iz površinskog sloja betona. Samim time, vodocementni omjer površinskog, zaštitnog sloja betona ostaje manji u odnosu na preostali presjek betonskog elementa. Cilj ispitivanja je odrediti utjecaj dvije različite vrste CPF oplate na mehanička i trajnosna svojstva zaštitnog sloja betona. Tijekom ispitivanja varirana je debljina zaštitnog sloja betona (3 i 5 cm) te se oplata ponovno koristila nakon što je pripremljena prva grupa uzoraka, kako bi se razmotrila mogućnost višestrukog korištenja CPF oplata. Tijekom rada ispitivana su sljedeća mehanička i trajnosna svojstva: brzina ultrazvuka, indeks sklerometra, čvrstoća prianjanja, plinopropusnost i kapilarno upijanje. Svojstva zaštitnog sloja betonskih elemenata pripremljenih u CPF oplatama uspoređena su sa svojstvima zaštitnog sloja betonskog elementa pripremljenog u običnoj oplati

Use of incinerated sewage sludge ash in cement mortars: case study in Croatia

U ovom radu je provedeno istraživanje mogućnosti i opravdanosti uporabe mulja s uređaja za pročišćavanje otpadnih voda na način da se pepeo dobiven spaljivanjem mulja ugrađuje u cementni mort kao sirovina (zamjena dijela cementa). U radu su provedena ispitivanja na cementnom mortu, pri čemu su razmatrane usporedbe osnovnih svojstava mješavina morta bez dodatka pepela i s dodatkom određenih udjela pepela dobivenog spaljivanjem mulja na temperaturi 800 °C. Dodatno je ispitivan i utjecaj dodatka aditiva (metakaolina i silicijske prašine), s ciljem poboljšanja fizikalnih karakteristika morta. Ukupno je proizvedeno i ispitano 177 uzoraka cementnog morta s 9 različitih mješavina. Za potrebe ovog istraživanja rabljen je mulj dobiven na uređaju za pročišćavanje otpadnih voda u Zagrebu. Dobiveni rezultati s dodatkom pepela pokazali su zadovoljavajuća svojstva što navodi na zaključak da je u pogledu ispitivanih svojstava (obradljivost, vrijeme vezivanja, čvrstoća na savijanje i tlačna čvrstoća) moguća i opravdana uporaba mulja u proizvodnji cementnog morta.In the paper an experimental research has been carried out regarding the possibility for the use of incinerated sewage sludge ash (ISSA) in the production of cement mortars with partial cement replacement. Different mixtures of cement mortar have been investigated, with comparison of its basic characteristics with and without certain amounts of added ISSA that was incinerated at the temperature of 800 °C. Additionally, the influence of the additives (metakaolin and silicon dust) was also investigated with the purpose to improve the physical characteristics of mortars. Altogether 177 specimens of cement mortar were investigated, with 9 different mixtures. In this research the sewage sludge from the Zagreb wastewater treatment plant was used. Results have shown satisfying physical and mechanical characteristics of mortars with added ISSA (workability, setting time, flexural and compressive strength) which brings to conclusion that use of ISSA in production of cement mortars seems possible and justified

Extended Round Robin Testing program of COST Action TU1404 – lessons learned from the initial experimental phase

The extended round robin testing program (RRT + ) is used in the Working Group 1 of the COST Action TU1404 as a fundamental mechanism: i) to validate advanced, non- standardised experimental techniques for testing cement-based materials and structures, ii) to benchmark different sustainable variations of concrete mixes prepared with mineral admixtures, recycled materials and/or by-products, and iii) to obtain input data for a range of concrete properties which could serve designers and engineers to better predict lifespan, durability, and serviceability of concrete struct ures. With a total of 45 laboratories from Europe, Japan and Canada, performing over 50 test methods on the same concrete mix, it presents one of the most extensive initiatives for joint testing of cement-based materials. The RRT + is divided into two phases: the initial and main experimental phases. During the initial phase, an ordinary concrete mix is prepared using the same constituting materials and following identical preconditioning, preparation, conditioning and test procedures. Even though the framework is identical and potential external causes of deviations are limited, concrete is prepared in different laboratories and some scatter in results can be expected. This paper describes the observations during the initial experimental phase and discusses methods including statistical analysis performed to understand the scatter and results obtainedEDF, France, CEVA Logistics, Austria and Germany, OeBB Infra, Austria, Staten Vegvesen, Norway and Schleibinger Gerate, German