INFLUENCE OF POZZOLANA ON THE HYDRATION OF C4AF RICH CEMENT IN CHLORIDE ENVIRONMENT

This study investigated the influence of natural pozzolana - opoka additive on the hydration of C4AF rich cement and the effects of chloride ions on the hydrates formed. In the samples, 25 % (by weight) of the sintered C4AF rich cement and OPC was replaced with pozzolana. The mixtures were hardened for 28 days in water, soaked in a saturated NaCl solution for 3 months at 20°C. It was estimated that under normal conditions, pozzolana additive accelerates the hydration of calcium silicates and initiates the formation of CO32- - AFm in the Brownmillerite rich cement. However, the hydration of Brownmillerite cement with opoka additive is still slower to compare with hydration of Portland cement. Also, opoka decreases total porosity and threshold pore diameter of Brownmillerite cement paste after two days of hydration. After 28 days of hydration threshold pore diameter became smaller even to compare with threshold pore diameter of Portland cement. Opoka additive promotes the formation of Friedel’s salt in Brownmillerite samples treated in saturated NaCl solution, because CO32-–AFm affected by saturated NaCl solution become unstable and takes part in reactions producing Friedel’s salt

Optimum Mass Matrices for Short Wave Pulse Propagation Finite Element Models

The matrices of a substructure ensuring minimum modal errors of the whole structure are obtained by using optimization approach. The mass and stiffness matrices of a small component domain of selected dimension are obtained by applying the modal synthesis of a limited number of closeto-exact modes such that after assembling a larger joined domain model the modal convergence rate of the latter should be as high as possible. The goal is achieved by formulating the minimization problem for the penaltytype target function representing the cumulative relative modal error of the joined domain and by applying the gradient descent minimization method. After the optimum matrices of a component domain are obtained, they can be used in any structure as higher-order elements or super-elements. The “combined” mass matrices can be treated as a special case of the presented approach. The performance of the obtained dynamic models is demonstrated by solving short wave pulse propagation problems by using a only few nodal points per pulse length

Influence of pozzolana on C4AF hydratio n and the effects of chloride and sulfate io ns on the hydrates formed

This study investigated the influence of natural pozzolana additive on the hydration of C4AF (aluminoferrite) and the effects of chloride and sulfate ions on the hydrates formed. In the samples, 25% (by weight) of the C4AF was replaced with pozzolana. The mixture was then hardened for 28 days in water, soaked in a saturated NaCl solution for 3 months, and then soaked in a 5% Na2SO4 solution for 3 months at 20°C. It is estimated that under normal conditions, pozzolana additive accelerates the formation of CO32-–AFm (monocarboaluminate) and gibbsite, however, impede the formation of cubic aluminum hydrates. Also, part of the amorphous SiO2 penetrates into the structure of hydrates of C4AF and initiates the formation of hydrated alumino-silicate (gismondine). Monocarboaluminate affected by NaCl becomes unstable and takes part in reactions producing Ca2Al(OH)6Cl·2H2O (hydrocalumite-M). After samples were transferred from a saturated NaCl solution to a 5% Na2SO4 solution, hydrocalumite-M was the source of aluminates for the formation of ettringite. In samples with pozzolana additive, the hydrated alumino-silicate and gibbsite compounds that were formed remained stable in an environment containing chloride and sulfate ions and retarded the corrosion reaction of C4AF hydrates

Elastic wave simulation based on modal excitation in 3D medium

Paper describes a simulation of an elastic wave in homogenous isotropic waveguide with generic cross-section using semi-analytical finite element (SAFE) formulation. The wave is considered a travelling displacement field in the waveguide as a result to forcing excitation and is expressed via modes’ superposition. The solutions for modes are obtained solving SAFE governing eigen problem. Attenuation of the medium in SAFE framework differently from prior researchers is simulated via Rayleigh damping. It is shown, that severe damping is not properly supported by the SAFE formulation and revision for properly accepting linear viscosity is needed

Application of Google-based Data for Travel Time Analysis: Kaunas City Case Study

Recently, new traffic data sources have emerged raising new challenges and opportunities when applying novel methodologies. The purpose of this research is to analyse car travel time data collected from smartphones by Google Company. Geographic information system (GIS) tools and Python programming language were employed in this study to establish the initial framework as well as to automatically extract, analyse, and visualize data. The analysis resulted in the calculation of travel time fluctuation during the day, calculation of travel time variability and estimation of origin-destination (OD) skim matrices. Furthermore, we accomplished the accessibility analysis and provided recommendations for further research.</p

A finite element model in a form of structural dynamic equation for the transient analysis of pressure in pipelines

The finite element model of transient pressure pulse propagation in a pipeline is presented in the form of the standard structural dynamic equation, which combines steady flow analysis for obtaining the initial conditions of the flow in the form of pressures and flow rates and non-linear dynamic analysis by using explicit numerical integration techniques. Three options of simplification of governing equation set have been analyzed. At low values of steady flow speed many non-linear and convection terms could be omitted, while at the flow speeds comparable with the wave propagation speed the full equation system has been analyzed. The full equation system analysis involves the techniques ensuring corrections of the initial conditions and of the nodal flow rate balance. The investigated pipelines may contain large number of branches and loops. Parts of large pipelines are analyzed as separate sub-models by employing non-reflecting boundary conditions at the cut boundaries. Properties of pressure pulse front degradation as it propagates through branching points of the pipeline can be examined

Investigation of thermo-elastic damping of vibrations of rectangular and ring-shaped mems resonators

The paper deals with finite element analysis of damped modal vibrations Q-factor values determined by taking into account the thermally-elastic damping. Modal properties of square- and ring-shaped MEMS resonators have been investigated by taking into account the layered structure of MEMS and the influence of the geometry of the clamping zone. The calculations have been performed by employing the COMSOL Multiphysics finite element software. The solution method has been verified comparing numerically and analitically obtained damped modal properties of cantilever MEMS resonator. Experimental investigations of Q-factor values have been performed. The comparison of calculated and experimentally obtained resonant frequencies and Q-factor values indicated good agreement of tendencies of change of the quantities against temperatur

Assessment and modelling of urban bypasses’ influence on transport flows distribution in street network

Disertacijoje nagrinėjama aplinkkelių ir greito eismo gatvių vietos parinkimo mieste problema. Pagrindinis darbo objektas – aplinkkelių ir greito eismo gatvių padėties poveikis transporto srautams gatvių tinkle. Panaudojant transporto srautų modeliavimą sukurta aplinkkelio ir greito eismo gatvės vietos parinkimo metodika, nereikalaujanti sudėtingo, daug laiko ir lėšų atimančio viso miesto transporto srautų modeliavimo. Metodika yra pritaikyta dviem didžiausiams Lietuvos miestams – Vilniui ir Kaunui. Darbo tikslas – sudaryti aplinkkelių ir greito eismo gatvių vietos parinkimo metodiką, panaudojant transporto srautų modeliavimą, ją pritaikyti praktikoje, ir siekti sumažinti miesto gyventojų patiriamas laiko sąnaudas susisiekimui. Disertaciją sudaro įvadas, 3 skyriai, bendrosios išvados, literatūros sąrašas, publikacijų sąrašas ir 11 priedų. Įvade trumpai aptariama tiriamoji problema, darbo aktualumas, aprašomas tyrimo objektas, formuluojamas darbo tikslas ir uždaviniai, aprašoma mokslinis darbo naujumas, ginamieji teiginiai. Įvado pabaigoje pristatomos autoriaus paskelbtos publikacijos disertacijos tema, pranešimai konferencijose ir pateikiama disertacijos struktūra. Pirmame skyriuje pateikiama literatūros apžvalga nagrinėjama tematika. Atliekama mokslinių darbų analizė. Taip pat įvertinami Lietuvos Respublikos bei Europos Sąjungos dokumentai, formuojantys transporto politiką. Antrajame skyriuje pristatomas sukurtas idealizuoto miesto transporto modelis. Darbo metu yra sumodeliuota 90 skirtingų aplinkkelių ir (ar) greito eismo gatvių įrengimo padėties variantų. Apibendrinus gautus modeliavimo rezultatus ir atlikus jų analizę, sudaryta miesto aplinkkelių ir greito eismo gatvių vietos parinkimo metodika. Trečiajame skyriuje aptarti pagrindiniai transporto tyrimų būdai, – išsiskiriantys prieinamumu ir minimalia kaina bei užtikrinantys pakankamą aprėptį ir tikslumą. Išnagrinėtos dviejų didžiausių Lietuvos miestų, – Vilniaus ir Kauno, susisiekimo sistemos, nustatyti jų pagrindiniai parametrai bei pritaikyta aplinkkelių ir greito eismo gatvių vietos parinkimo metodika. Disertacijos tema paskelbtos penkios mokslinės publikacijos, iš kurių keturios referuojamuose duomenų bazės Clarivate Analytics (ISI Web of Science) recenzuojamuose mokslo žurnaluose. Atliktų tyrimų rezultatai paskelbti dvejose Lietuvos ir vienoje užsienio konferencijose.Disertacij