Water is one of the fundamental components of concrete, not only for its role on the hydration of Portland cement, but also because of the physical functions it develops, which are associated with the main phases of concrete life: fresh state, hardened state and the useful life of the structures. The objective of this PhD Thesis is to study in detail the physical role of water in Portland cement mixtures: the aggregate absorption, the wetting and the fluidization of the granular skeletons that compose the cement pastes. The study covers the mathematical modelling of the mentioned physical functions in a way that it is possible to calculate the volume of water necessary to perform such functions, facilitating the mix-design process. The calculated volume is considered to be the total volume of water needed for production. Moreover, the calculation must take into account the conditions and constraints associated with the production and casting, as well as the technical requirements of the material to be designed. The modelling of the water physical functions allowed the development of a calculation method to quantify the approximate volume of water needed for concrete production. The developed method was used to calculate the volume of water of three different special concretes: a lightweight self-compacting concrete reinforced with fibres, an ultra-high performance concrete reinforced with steel fibres and a concrete with recycled aggregates. What is more, the volume of water for two conventional concretes, with compressive strengths of 25 and 30 MPa, was calculated. Since the calculation was based on granular skeletons for real mixtures, produced in laboratory or/and industrially, the results obtained through the use of the developed method were compared to the experimental results of each concrete. At last, the method was used to quantify the volume of paste necessary for the production of a porous concrete. The results show that the mathematical models used to describe the physical phenomena of absorption, wetting and fluidization fit well to the experimental reproduction of these phenomena. Corrections are needed in some situations due to the ideal boundary conditions adopted during modelling, which facilitate calculation. Anyhow, the errors are corrected through the use of adjusting coefficients. Therefore, the calculation method developed has proven itself effective and applicable in the mix-design of different types of conventional and special concretes, showing the potential to be used for the development of new materials. / El agua es uno de los componentes fundamentales del hormigón, no sólo por ser necesaria a la hidratación del cemento Portland, sino que también por las diferentes funciones físicas que desarrolla, las cuales están asociadas a las principales fases de la vida del hormigón: estado fresco, estado endurecido y vida útil de la estructura. El objetivo de la presente Tesis Doctoral es realizar un estudio detallado de las funciones físicas del agua en las mezclas de cemento Portland: la absorción de esta por los áridos, el mojado y la fluidificación de los conjuntos granulares que componen las pastas de cemento. Dicho estudio se traduce en la modelización matemática de las funciones físicas presentadas, en el sentido de dar una respuesta numérica que facilite el diseño de mezclas, acotando el volumen de agua necesario al desarrollo de las funciones especificadas, siendo éste el volumen de agua total necesario a la producción. Asimismo, el cálculo del referido volumen debe tener en cuenta los condicionantes de producción, puesta en obra, así como los requerimientos técnicos del material que se va diseñar. A través de la modelización de las funciones físicas del agua consideradas, se ha desarrollado un método de cálculo para acotar el volumen de agua total necesario a la producción de hormigones. Se ha utilizado el método desarrollado para el cálculo del volumen de agua de tres hormigones especiales distintos: hormigón ligero autocompactante con fibras, hormigón de ultra-alta resistencia reforzado con fibras de acero y hormigón con áridos reciclados. Asimismo, se ha calculado el volumen de agua para dos hormigones convencionales, de resistencias à compresión 25 y 30 MPa. Se han contrastado los resultados obtenidos por el uso del método desarrollado con los resultados experimentales de cada hormigón, ya que el cálculo se hizo con base en conjuntos granulares de mezclas reales, producidas en laboratorio y/o industrialmente. Por último, se ha utilizado el modelo desarrollado para la cuantificación del volumen de pasta necesario a la producción de un hormigón poroso. Los resultados demuestran que los modelos matemáticos utilizados para describir los fenómenos físicos de absorción, mojado y fluidificación se adecuan bien a la reproducción experimental de dichos fenómenos, en que correcciones son necesarias en algunas situaciones, debido a la adopción de condiciones de contorno ideales en la modelización, que facilitan los cálculos. De cualquier modo, los errores se corrigen a través de coeficientes de ajuste. Así, el método de cálculo desarrollado para acotar el volumen de agua se ha demostrado eficiente en el diseño de diferentes tipos de hormigones convencionales y especiales, pudiendo ser utilizado en el desarrollo de nuevos materiales.

No description available.

No description available.

This work aimed to elucidate basic aspects of the influence of chemical structure and surface topography on the surface properties of a polymer material in order to minimize the work of adhesion. End-functionalised aromatic perfluorinated oligo/polyesters have been chosen to clarify effect of chemical structure. Here, the comprehensive investigation of the influence of molecular architecture on processes of fluorine segregation in the topmost surface layer and surface properties of the end-functionalised aromatic perfluorinated linear and branched oligo-and polyesters were performed. It has been shown, that the character of the surface segregation of fluorinated moieties can be influenced by different factors i.e. conditions of preparation of polymer layers (by means of spin-coated and melt films), chemical structure of fluorinated tail and polymer backbone and slightly by molecular weight. Analysis of obtained results allows distinguishing contribution of each factor. Experimentally obtained results showed a good correlation with Scheutjens-Fleer self-consistent mean-field theory extended by Kumar and Koberstein, which corresponds to the surface segregation of various chemical functional moieties located on functional polymers of different architectures. In correlation with a self-consistent field approach, observed results confirmed that polymers with end fluorinated groups are promising for producing of low-energy surfaces.The effect of surface topography has been studied on the example of regular and irregular structured surfaces fabricated from core-shell particles. A simple and effective approach for designing regularly patterned surfaces with specifically designed surface roughness and chemistry using core-shell colloidal particles was demonstrated. The chemistry was varied by covalent grafting of polymer brushes onto silica particles or by chemisorption of fluorosilane. The modified colloidal spheres were organized into closely packed hemispherical hexagonal arrays either by a vertical deposition technique or by sedimentation on slightly inclined coated silicon wafers. In this way, an increase in the vertical roughness was achieved with increasing particle radius, but without changing the Wenzel roughness factor. Controllable variations in the surface chemistry and morphology were used for a systematic study of the wetting phenomenon on regular structured arrays. The regularity and periodicity of particle structures allowed modelling of wetting. The wetting was modelled according to WENZEL, CASSIE-BAXTER, EXTRAND theories as well as minimal and maximal possible contact angles introduced by SHUTTLEWORTH and BAILEY.It has been found that none of these theories completely describe the experimental results for all particle sizes except for the surfaces made from 0.2 Mikrometer large particles. It was revealed that wetting behaviour on fluorosilane modified particles with the diameter of 0.2 Mikrometer is close to the equilibrium contact angle described by WENZEL and CASSIE-BAXTER theories. It has been shown that the deviations contact angle from equilibrium state increase with increasing particle size, decreasing intrinsic contact angle, and increasing solid free energy of the particle ´shell´. This provides the experimental evidence for the theory proposed by JOHNSON and DETTRE. It was revealed that ultrahydrophobic surfaces couldn´t be observed on layers made from regularly packed core-shell particles. Design of fractal irregular surfaces is an appropriate way for preparation of ultrahydrophobic self-cleaning surfaces. It was demonstrated that fluorination is not an obligatory factor for design of water repellent coatings. The obtained results are of essential interest for industrial application.

No description available.

<p>The aim of this thesis work was to investigate theadsorption of surfactants to different nonpolar interfaces.Particularly, the effects of the polar group and the nature ofthe hydrophobic interface were elucidated. The interfacialbehavior of the liquid-vapor interface was investigated bymeans of surface tension measurements. Here the effect of thepolar group and the hydrocarbon chain length was investigatedin a systematic manner. It was found that the shorter of thetwo chains examined, decyl, generated a larger surface pressurecontribution than the longer, dodecyl. Furthermore, the sugarbased surfactants behaved differently as compared to theethylene oxide based ones. The former could be modelled byassuming a hard disc behavior of the head group while thelatter displayed polymeric behavior. The influence of saltconcentration on the surface tension behavior of an ionicsurfactant, sodium dodecyl sulphate, was investigated. Theresult could be rationalized by employing the Gouy- Chapmanmodel to the polar region. Furthermore, mixtures of two sugarbased surfactants were investigated by surface tensionmeasurements and the adsorbed amount of the two components atthe interface atdifferent concentrations and fractions in thebulk were obtained by applying the Gibbs surface tensionequation. It was found that the molecule with the smaller headgroup adsorbed preferentially, and more so as the totalsurfactant concentration was increased. These findings could beexplained by considering the interactions generated by thedifferent head groups. The adsorption of sugar surfactants toan isolated hydrophobic surface was studied by means of wettingmeasurements and the behavior was similar to that at theliquid-vapor interface. Wetting isotherms were measured on twodifferent hydrophobic surfaces where the covalently attachedhydrophobic layers were in a crystalline and fluid state,respectively. The wetting results revealed that the sugarsurfactants anchored in the fluid hydrophobic layer. This had asignificant influence on the force profile. For example, at thecrystalline surface the surfactant monolayers were easilyremoved as the surface came into contact at relatively lowapplied loads. This was not the case when the hydrophobic layerwas in a fluid state. Here a significant fraction of thesurfactants remained between the surfaces. Disjoining pressureisotherms were measured using a sugar based surfactant thatwere thoroughly purified and compared to the as receivedsample. Even the purified sample showed a double-layer forcealthough lower as compared to the as received, one. Asignificant difference in foam stability was also observed.</p>

Thesis (Ph. D.)--Institute of Paper Chemistry, 1976. / Bibliography: leaves 110-114.

For any crankcase scavenged two-stroke engine, the fuel dynamics is not easily predicted. This is due to the fact that the fuel has to pass the crankcase volume before it enters the combustion chamber. This thesis is about the development of a model for fuel dynamics in the crankcase of a small crankcase scavenged two-stroke engine that gives realistic dynamic behavior. The crankcase model developed in this thesis has two parts. One part is a model for wall wetting and the other part is a model for concentration of evaporated fuel in the crankcase. Wall wetting is a phenomenon where fuel is accumulated in fuel films on the crankcase walls. The wall wetting model has two parameters that have to be tuned. One is for the fraction of fuel from the carburetor that is not directly evaporated and one parameter is for the evaporation time of the fuel film. The thesis treats tuning of these parameters by running the model with input data from measurements. Since not all input data are possible to measure, models for these inputs are also needed. Hence, development of simple models for air flows, fuel flow, gas mixing in the exhaust and the behavior of the λ-probe used for measurements are also treated in this thesis. The parameter estimation for the crankcase model made in this thesis results in parameters that corresponds to constant fraction of fuel from the carburetor that evaporates directly and a wall wetting evaporation rate that increases with increasing engine speed. The parameter estimation is made with measurements at normal operation and three specific engine speeds. The validity of the model is limited to these speeds and does not apply during engine heat-up. The model is run and compared to validation data at some different operation conditions. The model predicts dynamic behavior well, but has a bias in terms of mean level of the output λ. Since this mean value depends on the relation between input air and fuel flow, this bias is probably an effect of inaccuracy in the simple models developed for these flows. / För alla tvåtaktsmotorer med bränslematning genom vevhuset är bränsledynamiken svårpredikterad. Detta beror på att bränslet måste passera vevhusvolymen innan det når förbränningskammaren. Denna uppsats handlar om utveckling av en modell som ger realistisk dynamik för bränslet i tvåtaktsmotorers vevhus. Vevhusmodellen i denna uppsats har två delar. Den ena delen är en modell för bränslefilm på motorväggar och den andra delen är en modell för koncentration av förångat bränsle i vevhusvolymen. Bränslefilmsmodellen har två parametrar som måste trimmas. Den ena är andelen bränsle från förgasaren som inte förångas direkt och den andra är tidsåtgången för förångning av bränslefilmen. Uppsatsen behandlar trimning av dessa parametrar genom körning av modellen med indata från mätningar. Eftersom inte all indata kan mätas behövs även modeller för dessa. Därför behandlar uppsatsen även utveckling av enkla modeller för luftflöde, bränsleflöde, gasblandning i avgasvolymen och beteende hos den för mätningar använda λ-sonden. Parameterestimeringen för vevhusmodellen som är gjord i denna uppsats resulterar i parametrar som svarar mot konstant andel av bränslet från förgasaren som förångas direkt och en förångningshastighet för bränslefilmen som ökar med ökande motorhastighet. Parameterestimeringen är gjord med mätdata från normal körning vid tre olika motorhastigheter. Giltigheten för modellen är begränsad till dessa hastigheter och kan inte appliceras på körning av motorn vid kallstart. Modellen är körd och jämförd med valideringsdata från olika körfall. Modellen förutser dynamiska beteenden väl, men har ett systematiskt fel gällande medelvärdet på λ. Eftersom detta medelvärde beror på förhållandet mellan luftflöde och bränsleflöde in i vevhuset är sannolikt detta systematiska fel en effekt av osäkerhet i de enkla modeller som utvecklats för dessa flöden.

Estimating the quantity of water that reaches the water table following an infiltration event is vital for modeling and management of water resources. Estimating the time scale of groundwater recharge after a rainfall event is difficult because of the dependence on nonlinear soil characteristics and variability in antecedent conditions. Modeling the flow of water through the variably saturated zone is computationally intensive since it requires simulation of Richards' equation, a nonlinear partial differential equation without a closed-form analytical solution, with parametric relationships that are difficult to approximate. Hence, regional scale coupled (surface water - groundwater) hydrological models make simplistic assumptions about the quantity and timing of recharge following infiltration. For simplicity, such models assume the quantity of recharge to be a fraction of the total rainfall and the time to recharge the saturated groundwater is scaled proportionally to the depth to water table, in lieu of simulating computationally intensive flow in the variably saturated zone. In integrated or coupled (surface water - groundwater) regional scale hydrological models, better representation of the timing and quantity of groundwater recharge is required and important for water resources management. This dissertation presents a practical groundwater recharge estimation method and relationships that predict the timing and volume accumulation of groundwater recharge to moderate to deep water table settings. This study combines theoretical, empirical, and simulation techniques to develop a relatively simple model to estimate the propagation of the soil moisture wetting front through variably saturated soil. This model estimates the time scale and progression of recharge following infiltration for a specified depth to water table, saturated hydraulic conductivity and equilibrium moisture condition. High-resolution soil moisture data from a set of experiments conducted in a laboratory soil column were used to calibrate the HYDRUS-1D model. The calibrated model was used to analyze the time scale of recharge by varying soil hydraulic properties and simulating the application of rainfall pulses of varying volume and intensities. Modeling results were used to develop an equation that relates the non-dimensional travel time of the wetting front to excess moisture moisture content above equilibrium. This research indicates that for a soil with a known retention curve, the wetting front arrival time at a given depth can be described by a power law, where the power is a function of the saturated hydraulic conductivity. This equation relates the non-dimensional travel time of the wetting front to excess moisture content above the equilibrium moisture content. Since the equilibrium moisture content is dependent on the water retention curve, the powers in the equation governing the timing of recharge depend on the saturated hydraulic conductivity for a large variation in water retention curve. Also, the power law relates recharge (normalized by applied pulse volume) to time (normalized by the time of arrival of wetting front at that depth). The resulting equations predicted the model simulated normalized (relative) recharge with root mean square errors of less than 14 percent for the tested cases.

Not available