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Highway bridge decks are often overlaid to extend service life by reducing the rate of chloride ion ingress and the rate of corrosion of reinforcing steel in the sound chloride-contaminated concrete that is left in-place. Bridge deck overlays in Virginia are usually either latex-modified concrete or microsilica concrete, and both types of overlay are considered equivalent in terms of performance. However, the latex-modified concrete overlays are more expensive to construct than the microsilica concrete overlays. Thus, it is important to determine if these overlays do perform equivalently to ensure that short-term savings do not lead to higher long-term costs. Shrinkage is one of the overlay performance parameters. Shrinkage is a three-dimensional deformation of concrete that results in an overall reduction in volume. Total shrinkage may be measured under either restrained or unrestrained conditions. This research examines the shrinkage performances of Virginia Department of Transportation-approved latex-modified and microsilica concrete overlay mixtures and was conducted on both field-sampled and laboratory-fabricated restrained and unrestrained specimens. Based on crack and delamination surveys of sampled bridge decks and laboratory test results, a shrinkage performance-based specification for the Virginia Department of Transportation was developed. There was no significant difference between the unrestrained shrinkage values of latex-modified and microsilica concrete overlay mixtures for the specified time periods. Restrained microsilica concrete specimens generally cracked earlier and more frequently than restrained latex-modified concrete specimens. However, the bridge deck crack and delamination surveys show that construction conditions and quality and traffic type and frequency may have a greater effect on cracking than the overlay material. / Master of Science

Among the most impressive developments observed in the last 20 years, the improvement of the installation methods of monolithic refractories is certainly to be taken into account. However, this evolution, from vibratable castables to shotcrete and drycrete was not applied to materials based on magnesia, which are still mostly commercialized as ramming mixes, or as pouring castables with poor properties due to excessive water use. The major issues associated to this lack of technology is the scarcity of submicrometric powders compatible to magnesian systems, and the expansion followed by hydration of the magnesia, which is a disruptive reaction. By a thorough research on the literature, some potential additives were identified to be tested as anti-hydration additives. Hydration tests of powders in autoclave, complemented by pH and rheological measurements on magnesia pastes have identified five possible additives which can be used to inhibit the hydration: tartaric acid, citric acid, boric acid, magnesium fluoride and microsilica. Salts from the organic acids can also be successfully used. Of these, microsilica also presented the advantage of providing the submicrometric particles necessary to improve the flow of the castable, and to improve the bond of the castable. The three acids are very effective in inhibiting the formation of magnesium hydroxide, but affect negatively flow properties and mechanical resistance after cure. Microsilica prevented hydration cracks due to the reaction between the silicic acid generated under basic environment with the newly formed brucite, leading to the precipitation of a magnesium-silica-hydrated phase of poor crystallinity between the magnesia grains. This phase does not promote volumetric change, and also enable water release at a wider temperature range. Due to its nature close to serpentine minerals, it forms forsterite and enstatite at low temperatures, thus generating suitable strength between room temperature and at least 1400 °C. Magnesium fluoride changed the nature of this magnesium-silica-hydrated phase, by being incorporated to it and forming a phase more similar to the humite minerals. These minerals present higher MgO:SiO2 molar ratio than serpentine, and their formation requires a lower content of microsilica for a same effect against hydration, which is beneficial for the overall properties of the castable. The properties of the castable, as well as the influence of a number of other variables (for instance, refractoriness under load, creep, cold crushing strength, cold modulus of rupture, bulk density and apparent porosity) were also studied and hereby reported. It is believed that this technology can be further developed for industrial use, provided that some issues regarding the properties at high temperatures are solved. Not only had the study and comprehension of the nature of the bond between microsilica and magnesia, and the role of magnesium fluoride been pioneered by this work, but also the methodology used to evaluate the hydration after the drying process of castings, which was close to real refractory components.

Made available in DSpace on 2014-12-17T14:09:13Z (GMT). No. of bitstreams: 1 KleberCC_TESE.pdf: 2548288 bytes, checksum: f214aa096a5ffb2a48cfa0e23356dfc4 (MD5) Previous issue date: 2011-07-22 / The preparation of cement slurries for offshore well cementing involves mixing all solid components to be added to the mixing water on the platform. The aim of this work was to study the formulation of pre-prepared dry mixtures, or grouts, for offshore oilwell cementing. The addition of mineral fillers in the strength of lightweight grouts applied for depths down to 400 m under water depths of 500 m was investigated. Lightweight materials and fine aggregates were selected. For the choice of starting materials, a study of the pozzolanic activity of low-cost fillers such as porcelain tile residue, microsilica and diatomaceous earth was carried out by X-ray diffraction and mechanical strength tests. Hardened grouts containing porcelain tile residue and microsilica depicted high strength at early ages. Based on such preliminary investigation, a study of the mechanical strength of grouts with density 1.74 g/cm3 (14.5 lb/gal) cured initially at 27 ?C was performed using cement, microsilica, porcelain tile residue and an anti-foaming agent. The results showed that the mixture containing 7% of porcelain tile residue and 7% of microsilica was the one with the highest compressive strength after curing for 24 hours. This composition was chosen to be studied and adapted for offshore conditions based on testes performed at 4 ?C. The grout containing cement, 7% of porcelain tile residue, 7% of active silica and admixtures (CaCl2), anti-foaming and dispersant resulted satisfactory rheology and mechanical strength after curing for 24 hours of curing / A prepara??o de pastas de cimento para po?os offshore envolve a mistura de todos os componentes s?lidos da pasta e a prepara??o da ?gua de mistura feita na pr?pria plataforma. O objetivo desse trabalho ? apresentar um estudo de formula??o de misturas secas pr?preparadas, ou grautes, para a cimenta??o de po?os offshore. Foi avaliado o efeito da adi??o de cargas minerais leves na resist?ncia mec?nica de grautes para cimenta??o prim?ria inicial (at? 400 m) com l?minas d ?gua acima de 500 m. Foi realizada uma sele??o de materiais leves e finos, em substitui??o aos agregados utilizados nos grautes da constru??o civil. Para a escolha dos materiais de partida, primeiramente foi realizado um estudo da atividade pozol?nica de materiais de baixo custo, como res?duo cer?mico de porcelanato, s?lica ativa e diatomita, por meio de difratometria de raios X e resist?ncia mec?nica ? compress?o. Verificou-se que as misturas com adi??o de res?duo de porcelanato e s?lica ativa apresentaram maiores resist?ncias nas primeiras idades. Com isso, foi desenvolvido um estudo da resist?ncia mec?nica ? compress?o de grautes com massa espec?fica 1,74 g/cm3 (14,5 lb/gal), curadas, inicialmente, a 27?C e compostas por cimento, res?duo de porcelanato e s?lica ativa, aditivadas com anti-espumante. Os resultados revelaram que a mistura com 7% de res?duo de porcelanato e 7% de s?lica ativa foi a que apresentou a maior resist?ncia mec?nica ? compress?o em ensaio realizado com 24 horas de cura. Escolhida a composi??o a ser estudada, ela foi adaptada ?s condi??es de po?o offshore, cujos ensaios foram realizados a 4?C. A mistura composta por cimento, 7% de res?duo de porcelanato e 7% de s?lica ativa foi aditivada com acelerador de pega (CaCl2), anti-espumante e dispersante. Os ensaios revelaram que essa composi??o mostrou-se satisfat?ria quanto ? resist?ncia mec?nica ? compress?o com 24 horas de cura, reologia, tempo de pega e volume de ?gua livre

Among the most impressive developments observed in the last 20 years, the improvement of the installation methods of monolithic refractories is certainly to be taken into account. However, this evolution, from vibratable castables to shotcrete and drycrete was not applied to materials based on magnesia, which are still mostly commercialized as ramming mixes, or as pouring castables with poor properties due to excessive water use. The major issues associated to this lack of technology is the scarcity of submicrometric powders compatible to magnesian systems, and the expansion followed by hydration of the magnesia, which is a disruptive reaction. By a thorough research on the literature, some potential additives were identified to be tested as anti-hydration additives. Hydration tests of powders in autoclave, complemented by pH and rheological measurements on magnesia pastes have identified five possible additives which can be used to inhibit the hydration: tartaric acid, citric acid, boric acid, magnesium fluoride and microsilica. Salts from the organic acids can also be successfully used. Of these, microsilica also presented the advantage of providing the submicrometric particles necessary to improve the flow of the castable, and to improve the bond of the castable. The three acids are very effective in inhibiting the formation of magnesium hydroxide, but affect negatively flow properties and mechanical resistance after cure. Microsilica prevented hydration cracks due to the reaction between the silicic acid generated under basic environment with the newly formed brucite, leading to the precipitation of a magnesium-silica-hydrated phase of poor crystallinity between the magnesia grains. This phase does not promote volumetric change, and also enable water release at a wider temperature range. Due to its nature close to serpentine minerals, it forms forsterite and enstatite at low temperatures, thus generating suitable strength between room temperature and at least 1400 °C. Magnesium fluoride changed the nature of this magnesium-silica-hydrated phase, by being incorporated to it and forming a phase more similar to the humite minerals. These minerals present higher MgO:SiO2 molar ratio than serpentine, and their formation requires a lower content of microsilica for a same effect against hydration, which is beneficial for the overall properties of the castable. The properties of the castable, as well as the influence of a number of other variables (for instance, refractoriness under load, creep, cold crushing strength, cold modulus of rupture, bulk density and apparent porosity) were also studied and hereby reported. It is believed that this technology can be further developed for industrial use, provided that some issues regarding the properties at high temperatures are solved. Not only had the study and comprehension of the nature of the bond between microsilica and magnesia, and the role of magnesium fluoride been pioneered by this work, but also the methodology used to evaluate the hydration after the drying process of castings, which was close to real refractory components.

This diploma thesis deals with the technology of production of ultralight concretes using direct lighten cementing compound and at the same time indirect lighten using lightweight aggregate. Further work deals with the choice of suitable raw materials for these concretes. The practical part consists of a proposal of several different recipes, experimental verification and by comparing their properties in a fresh or hardened state.

The master thesis dealing with problematic about durability of concrete, with use of recycled concrete and addition of silica additions. Predominant for resistance of concrete constructions is surface layer, through which aggressive gasses and liquids penetrate from surrounding environment. The most important indicator of concrete durability is ability of surface layer transmissions of aggressive substants. In experimental part will be defined the actual state of surface layer by normal testing methods. The transmissions of surface layer will be tested on concrete cubes. Tests for transmissions of air (method TORRENT), of water (method ISAT), of acid gases (dept of carbonation by quick test in 98% CO2) will be carried out and also strength tests. Assessment of positive or negative influence of additions and amount of cement on durability and mechanical properties of concrete will be discussed in conclusion.