Web interface for execution of computational tasks in a high - throughput computing environment

The main purpose of the research work in framework of this thesis was the development or modification of CEM ("concrete equivalent method") for the design of equivalent mortar composition from concrete composition. The optimal formulation method should be determined based on the flow table test and rheological characteristics obtained by ConTec Viscometer 5. Based on the composition of concretes designed and tested in the framework of other diploma works we designed five reference mortar mixtures, which were later modified. We wanted to find out whether the reference mortar mixture is the best mixture to estimate the rheological properties of concrete or one of modified mixtures could be a better choice. All mixtures were composed of water, aggregate, cement and additives. The type of water and aggregate were the same for all mortars and we used two types of cement. In four mixtures we substituted part of the cement with mineral additive, microsilica or slag. As chemical admixtures we selected superplasticizer and air entraining agent. We focused on the results of flow table test, which represented the basis for the estimation of rheological characteristics of the equivalent mortar mixtures; these were later compared with the results obtained on concretes and correlations were made. Finally, based on the similar flow values we also compared rheological parameters of mortars and concretes acquired with the rheometer ConTec Viscometer 5

Electrochemical corrosion tests on steel in alkali-activated materials

One of the potential alternatives to Ordinary Portland Cement (OPC) are Alkali-Activated Materials (AAMs). The service life of reinforced concrete structures greatly depends on the corrosion resistance of embedded steel reinforcement. Due to the wide range of AAMs and their diverse properties, corrosion processes of steel in these materials are relatively unknown. Corrosion monitoring methods or their interpretations in certain cases cannot be directly transferred from the ones for OPC materials. The chemical compositions of pore solution in different AAMs influence the results of electrochemical measurements and their interpretations. Within this research, three different alkali-activated mortar mixes were prepared, based on fly ash, slag or metakaolin. Pore solutions were extracted from each mortar andchemical analysis was acquired. Different electrochemical corrosion measurements were performed on steel submerged to synthetic pore solutions. In parallel, ordinary carbon steel reinforcing bar was installed in the same types of alkali-activated mortar mixes. Specimens were exposed to wet/dry cycles with saline solution and periodic measurements of electrochemical impedance spectroscopy (EIS) were performed. Measured parameters in both systems were analysedand compared. It was concluded that electrochemical measurements in pore solutions can provide basic overview on corrosion behaviour in different AAMs environments. Periodic EIS measurements enabled monitoring of corrosion initiation and propagation on steel reinforcement in AAMs, although the information on the corrosion type is missing. Interpretation of results depends on visual analysis of corrosion damages after the end of exposure, providing information on corrosion type and intensity. The continuation of research on corrosion monitoring techniques will be performed by using Electrical Resistance (ER) sensors and Coupled Multi-Electrode Array (CMEA) sensors

Sensor development for corrosion monitoring of stainless steels in H₂SO₄ solutions

Equipment made of different stainless steels is often used in the hydrometallurgical processing industry. In this study, an electrical resistance sensor was developed for monitoring corrosion in acidic solutions at high temperature. Two types of stainless steel were used as the electrode materials, namely grade 316L stainless steel (EN 1.4404) and grade 2507 duplex stainless steel (EN 1.4410). The materials and sensors were exposed to a 10% H2SO4 solution containing 5000 mg/L of NaCl at various temperatures. Results from the sensors were verified using electrochemical techniques and postexposure examination. Results showed that the microstructure played an important role in the interpretation of corrosion rates, highlighting the importance of using an appropriate stainless steel for the production of sensors. Electrochemical tests and postexposure examination both showed that the grade 2507 had a significantly lower corrosion rate compared to the grade 316L. Under industrial‑process conditions, the results for the grade 2507 sensor were promising with respect to sensor durability and performance, despite the extremely harsh operating environment

Steel corrosion in different alkali-activated mortars

One of the potential alternatives to Ordinary Portland Cement (OPC) are Alkali-Activated Materials (AAMs) [1]. The service life of reinforced concrete structures greatly depends on the corrosion resistance of embedded steel reinforcement. Due to the wide range of AAMs with their diverse properties, corrosion processes of steel in these materials are relatively unknown. Corrosion monitoring methods or their interpretations in certain cases cannot be directly transferred from the ones for OPC materials, and therefore results of different corrosion studies are sometimes contradictory [2]. The chemical composition of pore solution in different AAMs are influencing the results of electrochemical measurements and their interpretation, e.g. the presence of sulphides reduces the redox potential of the pore solution, but enables the steel to remain in an apparently passive state [3]. The aim of this paper is to compare electrochemical parameters measured on steel reinforcement in different alkali-activated and OPC mortars. Ordinary carbon steel reinforcing bar was installed in three different alkali-activated mortar mixtures, based on fly ash, slag or metakaolin. Specimens were exposed to wet/dry cycles with saline solution and periodic measurements of electrochemical impedance spectroscopy (EIS). Measured parameters were analyzed and compared to the ones measured in reference OPC mortar. The propagation of corrosion damages on embedded steel bars was also followed using x-ray computed microtomography (MicroCT). In addition to corrosion tests, information on pore water chemistry was obtained, as well as general mechanical and physical properties of tested AAMs. In certain specimens also Electrical Resistance (ER) probes were implemented, which can successfully detect corrosion initiation and monitor general corrosion rate [4]. It was concluded that EIS method can follow the evolution of corrosion processes on steel reinforcement in AAMs, although the caution is needed when interpreting the results. The additional use of the MicroCT can provide verification of ongoing results obtained by electrochemical methods, and deeper insight in corrosion processes in AAMs. [1] J.L. Provis, Cem. Concr. Res. (2017). [2] M. Criado, C. Monticelli, S. Fajardo, D. Gelli, V. Grassi, J.M. Bastidas, Constr. Build. Mater. 35 (2012) 30–37. [3] M. Criado, S.A. Bernal, P. Garcia-Triñanes, J.L. Provis, J. Mater. Sci. (2017) 1–20. [4] A. Česen, T. Kosec, A. Legat, Corros. Sci. 75 (2013) 47–57

Characterization of chloride induced steel corrosion processes in blended cements

Doktorska disertacija obravnava področje karakterizacije korozijskih procesov jekla v betonih iz mešanih cementov, kjer je cementni klinker delno nadomeščen z mineralnimi dodatki žlindre, filtrskega pepela, naravnega pucolana ali apnenca. V okviru preiskav na preizkusnem polju v Luki Koper smo 4,5 let spremljali korozijske procese jekla v betonskih stebrih iz portlandskega cementa in cementa z dodatkom žlindre. Stebri so bili ves čas izpostavljeni naravnemu plimovanju, pršenju morske vode in zunanjim spremembam temperature. Za spremljanje korozije smo uporabili uporovne senzorje in sklopljene elektrode, razporejene po višini stebra. V okviru laboratorijskih preiskav smo izdelali večje število maltnih vzorcev iz portlandskega cementa in treh mešanih cementov z dodatkom filtrskega pepela, naravnega pucolana, žlindre ali apnenca. Polovico vzorcev iz vsakega cementa smo pospešeno karbonatizirali in na vseh kombinacijah malte in karbonatizacijskega stanja smo ob različnih časih izpostavitve ugotovili nekatere lastnosti malt. Vzorce smo za 1 leto izpostavili cikličnemu močenju s 3,5 % raztopino NaCl in med izpostavitvijo analizirali sestavo pornih vod posameznih cementov. Za spremljanje korozijskih procesov v maltah smo uporabili tehniko galvanostatskega pulza, uporovnih senzorjev in sklopljeno mrežo elektrod. Za določitev korozijskih lastnosti jekla v pornih vodah smo merili potencial odprtega kroga, linearno polarizacijo in potenciodinamsko ciklično polarizacijo. Z uporabo večjega števila komplementarnih in inovativnih merilnih tehnik smo uspešno spremljali razvoj in napredovanje korozijskih procesov v maltah iz mešanih cementov in te rezultate povezali z izmerjenimi fizikalnimi in kemijskimi lastnostmi malt. Pri cementih z večjo vsebnostjo cementnega klinkerja se je izkazalo, da imajo daljši čas iniciacije kot cementi z manjšo vsebnostjo klinkerja, saj do iniciacije korozije lahko pride pred zadostno reakcijo mineralnih dodatkov. Po iniciaciji korozije so bile korozijske hitrosti v portlandskem cementu manjše od nekaterih mešanih cementov, kasneje pa so cementi z mineralnimi dodatki bolje zavirali korozijske procese. Izkazalo se je tudi, da imajo lahko jekla v mešanih cementih in v karbonatiziranem stanju korozijske poškodbe z manjšimi globinami od tistih, ki v enakem času nastanejo v portlandskem cementu.Doctoral dissertation discusses the topic of chloride induced steel corrosion processes in blended cements, where cement clinker is partially replaced with slag, fly ash, natural pozzolan and limestone mineral admixtures. During the on-field investigation in Port of Koper for 4.5 years, corrosion processes in concrete columns made of ordinary portland cement and portland slag cement were monitored. The columns were exposed to natural tiding, salt-water spray and environmental temperature changes throughout the exposure period. Electrical resistance sensors and coupled multi-electrodes were used as corrosion monitoring techniques. As part of the laboratory experiments, multiple mortar specimens were made of portland cement and three blended cements using fly ash, natural pozzolan, slag and limestone as partial clinker replacement. Half the specimens were subjected to accelerated carbonation and some properties of mortars in both carbonation states were characterised at different exposure periods. The specimens were exposed to 3.5 % NaCl solution for 1 year and during the exposure, pore solutions were extracted for each cement. Galvanostatic pulse, electrical resistance sensors and coupled multi-electrode array were used to monitor corrosion processes in mortar. In order to determine corrosion properties of steel in pore solutions, cyclic potentiodynamic polarization, linear polarization and open circuit potential were measured. Using multiple complementary and innovative monitoring techniques we were able to successfully monitor initiation and propagation of steel corrosion in mortars made of blended cements and link those results to physical and chemical mortar properties. Using cements with higher clinker content, it was shown that the initiation time is longer than cements with mineral admixtures. After initiation, corrosion rates in portland cement can initially be slightly lower than specific blended cements, but later blended cements offer reduced corrosion rates compared to portland cement. It was also shown that mortars made of cements with mineral admixtures and in carbonated state can have corrosion damage with lower maximum depth than those that appear in portland cement mortars in the same timeframe

Corrosion behavior of steel in pore solutions extracted from different blended cements

Mortar specimens made from four different types of cement, CEM I, CEM II, CEM III, and CEM IV, were prepared and pore solutions extracted. Three different types of exposure were studied: noncarbonated without chlorides, noncarbonated with chlorides, and carbonated with chlorides. Various electrochemical methods (linear polarization, potentiodynamic polarization measurements) were implemented to characterize the processes of corrosion on steel in these solutions. The type and extent of corrosion products were evaluated by means of various spectroscopic techniques. Specific differences in the type and extent of corrosion damage were determined and compared for each of the extracted pore solutions from the different blended cements. An attempt was made to classify these differences in comparison with the reference cement (CEM I) and in relation to the different types of exposure

Characterization of steel corrosion processes in various blended cements by means of coupled multi-electrode arrays

Supplementary cementitious materials can affect the porosity of concrete, pore solution pH and chloride binding, all of which influence the type and magnitude of corrosion damage. Advanced corrosion monitoring techniques are needed to follow the development of corrosion on steel embedded in concrete across space and over time. In this study, coupled multi-electrode arrays (CMEAs) were used to characterise corrosion processes in OPC and three blended cements. Cyclic wetting with chlorides was undertaken to initiate corrosion. The results showed three distinct types of corrosion: localised corrosion (CEM I), localised corrosion that expanded over time (CEM II), and a combination of localised and general corrosion (CEM III and CEM IV). Cathodic locations were also monitored successfully, and the corrosion behaviour was related to total porosity and pH of the pore solution. MicroCT was used to quantify the volume of corroded material, which agreed well with results calculated from the CMEA measurements

The microstructure, mechanical and electrochemical properties of 3D printed alloys with reusing powders

CoCrMo and Ti6Al4V are widely used in medical, dental and 3D printing technology, allowing the accurate fabrication of geometrically complicated structures. In order to reduce the costs of printed objects, the reuse of powder is common daily practice. AQ1 When using 3D printing technology, the direct impact of elevated temperatures and the influence of the laser beam may change the properties of the powder when it is reused, thus affecting the final properties of the printed object. The main aim of the present study was to investigate the impact of reused powder on the mechanical, microstructural and electrochemical properties of 3D printed objects. 3D printed objects fabricated from virgin and reused powder of both alloys were analyzed by metallographic observation, computed tomography, XRD and electrochemical methods. The main finding of the study was that the use of reused powder (recycled 3 times) does not detrimentally affect the mechanical and corrosion integrity of 3D printed CoCr and Ti6Al4V alloys, especially for the purpose of applications in dentistry

Korozijska odpornost jekla v pornih vodah iz mešanih cementov

Blended cements might change the chemistry of the pore solution and subsequently affect the corrosion of steel in concrete. Pore solutions were extracted, analyzed and compared from mortars made of CEM I, CEM II, CEM III and CEM IV cements. Three combinations of carbonation and chloride states were studied, i.e., non-carbonated without chlorides, non-carbonated with chlorides and carbonated with chlorides. Different electrochemical and spectroscopic techniques were used to study the electrochemical properties, the type and the extent of the corrosion products, as well as the type and the extent of the corrosion damage. It was confirmed that the most corrosive environments were pore solutions extracted from the carbonated mortars with chlorides. In this environment the highest corrosion rate was observed for the CEM III pore solution, and the lowest for the CEM I. The extent and the type of corrosion products and the corrosion damage varied according to the environment.Cementi z mineralnimi dodatki lahko spremenijo strukturo porne vode in posledično vplivajo na korozijske lastnosti jekla. Porne vode so bile iztisnjene in analizirane iz malt, narejenih iz CEM I, CEM II, CEM III in CEM IV cementov. Malte so bile predhodno izpostavljene kloridom ali pospešeni karbonatizaciji v treh kombinacijah: brez karbonatizacije in brez kloridov, brez karbonatizacije s kloridi in v karbonatizaciji s kloridi. Za ugotavljanje korozijskih lastnosti jekla v pornih vodah so bile uporabljene različne elektrokemijske in spektroskopske metode. Analizirane so bile elektrokemijske lastnosti, tip in obseg korozijskih produktov ter tip in obseg korozijskih poškodb. Ugotovljeno je bilo, da najbolj korozivno okolje pripada pornim vodam v karbonatizirani malti s kloridi, kjer je bila najvišja korozijska hitrost izmerjena v pornih vodah iz CEM III cementa, najmanj{a pa iz CEM I cementa. Obseg in tip korozijskih produktov ter poškodb se je razlikoval skladno s korozivnostjo okolja

Effects of blended cements and carbonation on chloride-induced corrosion propagation

Supplementary cementitious materials are known to refine the pore structure of concrete and accelerate the carbonation progress. The combination of the two processes can have both beneficial and disadvantageous effects on corrosion, especially when chlorides are also involved. In this study the corrosion properties of multiple blended cements were evaluated in carbonated and non%carbonated states, with chlorides introduced through cyclic ponding. The examination involved monitoring the propagation phase, determining the microstructural properties of cements, and assessing the final corrosion damage. The results showed that the steel in the blended cements initially had a relatively high corrosion activity, which later decreased compared to the OPC. This stabilisation was presumably due to the beneficial changes to the pore structure. Carbonation had a significant impact on the corrosion, with carbonated mortars revealing shallower damage over a larger surface area. This effect was more pronounced for blended cements that exhibited greater susceptibility to carbonation