Les discontinuités sont préjudiciables à la pérennité des structures en béton. Les méthodes non-destructives sont bien développées pour l’étude des altérations en surface, mais peu de techniques sont adaptées à la caractérisation de défauts dans la masse. Dans cette thèse, des mesures de résistivité électrique sont réalisées pour l’étude des discontinuités (fissures, joints, interfaces) au sein des ouvrages massifs en béton par l’intermédiaire des forages préexistants. La technique utilisée est la diagraphie électrique de résistivité en dispositif normal. Une première approche numérique (éléments finis) permet d’appréhender les corrections à apporter sur les mesures. Puis l’étude des paramètres d'ouverture, de contraste entre la résistivité de la discontinuité et du béton, et d'extension permet de proposer une méthode d’inversion des mesures pour la caractérisation de l’endommagement. Des essais sur des ouvrages hydrauliques sont réalisés afin de définir la méthodologie de mesure sur site. Les mesures sont ensuite confrontées à la méthode d’inversion pour la valider. / Discontinuities are one of the most harmful damage to the durability of concrete structures. The non-destructive methods appear to be effective for the detection and the location of surface cracks but they might be unsuitable for investigation of massive concrete body. In this thesis, the electrical resistivity measurements are made for the study of cracks and discontinuities (concrete joints, interfaces ...) in massive concrete structures by preexisting boreholes. The study is based on a first numerical approach (finite elements) to understand the corrections on data. Then the study of the aperture, the resistivity contrast between the discontinuity and the concrete, and the extension provide a method for the inversion of measures to characterize the damage. The tests on hydraulic structures are carried out to define the methodology for on measurement site. The measurements are then compared to the inversion method to validate it.

The durability of reinforced concrete structures derives from the protective effect provided by the concrete cover over the steel rebars. When the passivation of the steel is compromised, the whole structure is liable to corrosion phenomena, whose rate of propagation is mainly controlled by the electrical resistivity of the concrete between the anode and cathode and by the availability of oxygen at the cathode. The electrical resistivity of concrete is highly dependent on its physical and chemical characteristics. This study aimed at to investigate the influence of the content of rice husk ash (RHA) on the electrical resistivity of concrete and identify any correlations between electrical resistivity and compressive strength properties and changes in pore solution and pore structure. The mixtures in this study were prepared with water/binder ratios (w/b) of 0.35, 0.50 and 0.65 with RHA substitutions of 10%, 20% and 30% for cement. Samples with 50% blast furnace slag, 35% fly ash and a reference sample with 100% cement were also investigated. Electrical resistivity was determined using the four electrode method (Wenner s Method adapted for concrete). Tests of compressive strength, pore solution composition, pH e electrical condutivity, and mercury porosimetry were also performed. These indicate that that the age of the sample, the w/b ratio used and the mineral additions have a expressive effect on the electrical resistivity of concrete because of changes in the concrete pore structure and in the composition and volume of pore solution. Results show there is a exponential increase in concrete resistivity as the content of RHA grows. This is confirmed by the smaller size of the pore network and the lower specific conductivity of the pore solution, which show a sound correlation. The best results in electrical resistivity were obtained with content of 30% of RHA. The best cost/benefit ratio for compressive strength values of 65MPa and electrical resistivity of 30kΩ.cm was obtained with the use of 10% RHA and for compressive strength values of 65MPa and electrical resistivity of 60kΩ.cm, the best results were obtained with 20% RHA. / A durabilidade das estruturas de concreto armado é resultado da ação protetora do concreto sobre o aço. Quando a passivação do aço deixa de existir, a estrutura torna-se vulnerável ao fenômeno da corrosão, cuja propagação, após iniciada, é essencialmente controlada pela resistividade elétrica do concreto entre o ânodo e o cátodo e pela disponibilidade de oxigênio no cátodo. A resistividade elétrica do concreto é uma propriedade extremamente sensível às características físicas e químicas do mesmo. O presente trabalho buscou investigar a influência do teor de cinza de casca de arroz (CCA) na resistividade elétrica do concreto, bem como correlacionar os resultados obtidos com a resistência à compressão axial e alterações na composição da solução aquosa e estrutura dos poros. Foram investigadas misturas com relações água/aglomerante (a/ag) 0,35 , 0,50 e 0,65 com teores de substituição em massa de 10%, 20% e 30% de CCA. Para comparar os resultados, misturas com 50% de escória de alto forno, 35% de cinza volante e uma mistura de referência com 100% de cimento foram simultaneamente investigadas. A resistividade elétrica foi determinada utilizando o método dos quatro eletrodos (método de Wenner, adaptado para uso em concreto). Paralelamente, foram realizados ensaios de resistência à compressão axial, composição, pH e condutividade elétrica específica da solução aquosa dos poros e porosimetria por intrusão de mercúrio. Verificou-se que a idade, a relação a/ag e as adições minerais mostraram uma influência expressiva na resistividade elétrica do concreto, em virtude principalmente das alterações na estrutura dos poros e na quantidade e composição da solução dos mesmos. Os resultados mostraram um crescimento exponencial na resistividade do concreto com o aumento do teor de CCA. Tal fato foi confirmado pelo maior refinamento dos poros e menor condutividade específica da solução dos mesmos, mostrando haver uma ótima correlação entre estes fatores. Assim, os melhores resultados na resistividade elétrica foram obtidos com o teor de 30% de CCA. A melhor relação CUSTO/BENEFÍCIO, para 65MPa de resistência à compressão e 30kΩ.cm de resistividade elétrica, foi obtida com 10% de CCA e, para 65MPa e 60kΩ.cm, os melhores resultados foram atingidos com 20% desta adição.

In the present work, there was analyzed thermal evolution of the phase transformation in the MgZnAl and MgZnAlCa alloys with different concentration of the Zn and Ca. The grains were occupied by the phase with quasicrystaline icosaedral structure in the as-cast alloys and after isochronal annealing up to 240 řC. The thermal measurements revealed two exothermic effects in the MgZnAl alloy and three exothermic effects in the MgZnAlCa alloy during linear heat treatment in the temperature range of 100 - 250 řC. In agreement to the thermal response, two and three stages of electrical resistivity decrease were observed in the same temperature range. The lower thermal changes, absolute resistivity changes and microhardness were observed in the alloy with Ca-addition and lower concentration of Zn.

Philosophiae Doctor - PhD / The increasing population in search for better social and economic development in coastal areas puts groundwater resources under pressure because of the high fresh water demand for domestic and agriculture use. Seawater intrusion is widely recognised as major concern in coastal aquifers across the globe and is influenced by multiple factors, being climate variation which is projected to adjust recharge of groundwater because of decreased precipitation patterns and to increase sea level variations and over-abstraction due to high freshwater demand as a result of increased population and agricultural practices, thereby inducing salinization in groundwater. The coastal aquifer in Heuningnes Catchment is not exempted from these issues and salinization is a major concern in the area affecting groundwater quality. In Heuningnes Catchment and South Africa in general there is limited knowledge on the application of integrated approach for assessing groundwater quality especially salinization mechanism in coastal aquifers. The main goal of this research is to test and demonstrate the viability of using joint interpretation approach of geophysics, geochemical and geological information to investigate groundwater quality in coastal aquifers thus improving on the understanding of using such approach. This work offers the initial thorough assessment of groundwater quality and understanding of the salinity sources and hydro-geochemical processes governing the chemical composition of groundwater in the region. Thus provide advice on the fitness of this water for consumption and irrigation purposes. Thirty-two groundwater samples were collected and analysed for (Mg2+), (Ca2+), (Na+), (K+), (Cl-), (SO42), (HCO3-), (pH, TDS and EC). To estimate fitness of groundwater quality for consumption purposes WHO (2011) and SANS241 guideline were used and for irrigation utilization the water quality indices (EC), (Na+%), (SAR), (RSC), (KR) and (MR) were used. Statistics approaches were employed to ascertain the primary geochemical processes governing the chemical composition of groundwater in the research region. Lastly, the spatial distribution maps were created by means of ArcGIS. Electrical resistivity method was used to map the extent of saline distribution within the subsurface. The findings of this study revealed that groundwater in the region is alkaline type and TDS, EC, Na+, Cl- exceeded WHO and SANS241 guidelines for consumption water. The geophysical investigation revealed that the sandy clay/clayey sand, fine sand and fractured sandstone units make up the coastal aquifer systems within the area. Further, revealed that these aquifers were saturated with fresh, saline or brackish water depending on the subsurface layer. The presence of saline and brackish was confirmed by the chemical results which indicated a Na+-Cl- type as a dominant water type. Also classifying groundwater based on EC and TDS supports these findings. The foremost hydro-geochemical processes that controls the salinity and quality of groundwater in the study region as indicated by Gibbs plot are water-rock interaction followed by evaporation process. Furthermore, analysis of hydrochemical data also proposes that weathering of silicate minerals, ion-exchange and dissolution of carbonate minerals amended ion concentration in groundwater thus influencing salinisation in certain parts of the study region. Also assessment of ionic-ratios displays influences of marine sprays as well as seawater, on the chemical structure of groundwater within the Heuningnes Catchment aquifer. Valuation of groundwater quality and its fitness for ingestion and irrigation purposes, the results indicated that shallow groundwater in the area is not suitable for any use; however, groundwater from deeper boreholes was found fresh and appropriate for irrigation and household purposes. Findings of this study indicated that salinity is the major groundwater quality issue for this area and that monitoring of groundwater quality in Heuningnes Catchment is limited. The absence of consistent monitoring program on groundwater quality makes it difficult to ascertain long term trends on groundwater quality parameters. Therefore, this study emphasizes the need for regular groundwater quality monitoring to assess the trends of these parameters in order to make an informed decision as to what can be done for mitigation purposes.

Determination of the subsurface geology is very important for the rock quarry industry. This is primarily done by drilling and mapping of the surface geology. However in Sweden the bedrock is often completely covered by Quaternary sediments making the prediction of subsurface geology quite difficult. Incorrect prediction of the rock-mass quality can lead to economic problems for the quarry. By performing geophysical measurements a more complete understanding of the subsurface geology can be determined. This study shows that by doing 2D-parallel data sampling a 3D inversion of the dataset is possible, which greatly enhances the visualization of the subsurface. Furthermore the electrical resistivity technique together with the induced polarization method proved to be very efficient in detecting fracture frequency, identification of major fracture zones, and variations in rock-mass quality all of which can affect the aggregate quality. With this technique not only the rock-mass quality is determined but also the thickness of the overburden. Implementation of geophysics can be a valuable tool for the quarry industry, resulting in substantial economic benefits. / QC 20101118

The objectives of this research were to investigate the sensitivity of two-prong and fourprong resistivity measurements to certain operator-controlled variables and to conduct a direct comparison of the sensitivity of two-prong and four-prong resistivity measurements to certain concrete material variables. Four full-factorial experiments were designed for this research. In the experimentation on operator-controlled variables with two-prong resistivity testing, main effects that are both statistically significant and practically important include hole depth and surface water. In the experimentation on operator-controlled variables with four-prong resistivity testing, probe position, surface water, and prong spacing are all neither statistically significant nor practically important. This high degree of unexplained variation may be of concern to practitioners. In the experimentation on concrete material variables with two-prong and four-prong resistivity testing, main effects that are both statistically significant and practically important include chloride concentration and temperature, both of which exhibit inverse relationships with resistivity. These research findings support several important recommendations for resistivity testing. Operators of the two-prong resistivity device should use an accurately positioned drill stop to ensure that the prepared holes are consistently the correct depth, and they should expect to obtain different values depending on the presence of surface water on the deck surface. Operators considering use of the four-prong resistivity device should not expect the measurements to be sensitive to probe position with respect to rebar, presence of surface water, or prong spacing for conditions similar to those investigated in this research. Operators interested in monitoring resistivity values over time to ascertain material changes in a bridge deck should develop protocols for measuring concrete temperature in the field and subsequently normalizing resistivity measurements to a standard temperature.

This study involved a comparative investigation of chloride-induced corrosion detection techniques on loaded reinforced concrete slabs which were exposed to deicing salts and wetting-drying cycles to simulate typical aggressive environments in cold climates. The studied techniques involved linear polarization technique, galvanostatic pulse technique, electrochemical impedance spectroscopy, half-cell potential and concrete electrical resistivity mapping. The results showed that concrete quality and moisture content have a direct effect on corrosion activity, and these properties are represented well with concrete electrical resistivity. The galvanostatic pulse technique was shown to correlate well with electrochemical impedance spectroscopy, which was used as a benchmark for corrosion rate measurements in this study; however, the galvanostatic pulse technique was not capable of detecting corrosion activity in saturated concrete accurately. The results of this research do not support the criteria provided by the ASTM C876-09 standard for using half-cell potentials to estimate the probability of reinforcing steel corrosion in reinforced concrete structures.

Gypsum rich soils are found in many parts of the world, particularly in arid and semi-arid regions. Most gypsum occurs in the form of evaporites, which are minerals that precipitate out of water due to a high rate of evaporation and a high mineral concentration. Gypsum rich soils make good foundation material under dry conditions but pose major engineering hazards when exposed to water. Gypsum acts as a weak cementing material and has a moderate solubility of about 2.5 g/liter. The dissolution of gypsum causes the soils to undergo unpredictable collapse settlement leading to severe structural damages. The damages incur heavy financial losses every year. The objective of this research was to use geophysical methods such as free-free resonant column testing and electrical resistivity testing to characterize gypsum rich soils based on the shear wave velocity and electrical resistivity values. The geophysical testing methods could provide quick, non-intrusive and cost-effective methodologies to screen sites known to contain gypsum deposits. Reconstituted specimens of ground gypsum and quartz sand were prepared in the laboratory with varying amounts of gypsum and tested. Additionally geotechnical tests such as direct shear strength tests and consolidation tests were conducted to estimate the shear strength parameters (drained friction angle and cohesion) and the collapse potential of the soils. The effect of gypsum content on the geophysical and geotechnical parameters of soil was of particular interest. It was found that gypsum content had an influence on the shear wave velocity but had minimal effect on electrical resistivity. The collapsibility and friction angle of the soil increased with increase in gypsum. The information derived from the geophysical and geotechnical tests was used to develop statistical design equations and correlations to estimate gypsum content and soil collapse potential.

A caracterização geológica e geotécnica dos locais de implantação de aterros sanitários é fundamental, tanto para fornecer subsídios adequados ao projeto de instalação das células de deposição dos resíduos sólidos urbanos (RSU), quanto para que se conheçam as características da área antes de ser modificada pela obra. Neste sentido, o presente trabalho visou mostrar a contribuição que a geofísica, com o uso da técnica da eletrorresistividade e do potencial espontâneo, associado a informações de investigação geotécnica direta pode dar para o estabelecimento de um background da área de instalação do aterro sanitário da cidade de São Carlos-SP. Foram realizados 7 caminhamentos elétricos (CE) com o arranjo dipolo-dipolo com eletrodos espaçados de 10 metros e três sondagens elétricas verticais (SEV), utilizando o arranjo Schlumberger, com profundidade de investigação de até 100 metros. Para processamento dos modelos bidimensionais dos CE utilizou-se o programa RES2DINV, e enquanto que para as SEV foi utilizado o modelo unidimensional. A interpretação dos modelos geoelétricos foi aperfeiçoada pela confrontação com informações geológico-geotécnicas prévias da área, obtidas nos estudos de impacto ambiental (EIA/RIMA) e resultados de sondagens de simples reconhecimento (SPT), realizadas na fase de estudo para implantação do aterro sanitário. Com isso foi possível definir com clareza a profundidade do topo rochoso e das zonas de maior umidade nos CE e SEV. O conjunto de seções de CE foi georeferenciada com o auxílio de GPS de precisão, o que permitiu o tratamento espacial das informações e o estabelecimento dos mapas da superfície do topo rochoso, das zonas de fluxo de água subterrânea e da espessura dos materiais inconsolidados. O conjunto de informações obtido permitiu identificar locais possíveis para a instalação futura de poços de monitoramento, assim como os dados geoelétricos das várias camadas servirá como padrão para identificar eventuais contaminações do solo ou da água subterrânea no futuro. A identificação da presença do topo rochoso em pequena profundidade, em algumas áreas do aterro, permite o melhor planejamento das escavações para instalação das células de deposição do RSU. / The geological and geotechnical characterization of landfill implantation areas is crucial; even to provide appropriate subsidies of urban solid residues (USR) installation project of deposition cells and for knowing the characteristics of the area before being modified by the work. In this sense, the present work aimed to show the contribution that the geophysics, with the use of electrical resistivity technique and the spontaneous potential, associated with direct geotechnical investigation information can give to the establishment of a background of landfill installation area from São Carlos-SP city. Were performed 7 electrical imaging (EI) with the dipole-dipole array with electrodes spaced by 10 meters and three vertical electrical sounding (VES), using the Schlumberger array with depth research up to 100 meters. For processing of two-dimensional models of the EI was used the RES2DINV program and while for the vertical electrical sounding (VES)-was used one-dimensional model. Interpretation of geoelectric models was enhanced by the confrontation with geological and geotechnical information of prior area, obtained in the environmental impact assessment (EIA) and results of a simple reconnaissance probes, performed in the study phase for the landfill implementation. It was possible to clearly define the depth of the bedrock and the higher humidity areas in the EI and VES. The set of sections electrical Imaging (EI) was georeferenced with the aid of GPS accuracy that allowed the spatial treatment of Information and the setting maps of the bedrock surface, the groundwater flow zones and the thickness of the unconsolidated materials. The obtained set of information enabling identification of possible locations for the wells future monitoring installation, as well as the geoelectrical data from several layers will be use as a standard to identify possible contamination of the soil or groundwater in the future. The identification of bedrock presence in small depth, in some areas of landfill, allows better planning of excavation for installation of MSW deposition cells.

A variabilidade das propriedades físicas do solo apresenta impacto sobre o desempenho das atividades de produção agrícola. Métodos indiretos para obtenção de informações sobre as propriedades do solo com interesse agronômico são utilizados com o intuito de favorecer o uso de insumos de modo mais adequado. A condutividade elétrica aparente do solo (CEa) é influenciada por diversas propriedades, muitas delas interrelacionadas e com variabilidade em curta distância, sendo difícil a separação dos diversos fatores. As medidas de CEa são usualmente tomadas em superfície com arranjos de eletrodos para prospecção de um volume de solo proporcional à distância entre eles. Neste trabalho foi utilizada uma metodologia que permitiu identificar algumas das propriedades com maior impacto sobre a CEa, merecendo destaque aquelas relacionadas ao espaço poroso do solo. A caracterização detalhada da variação da CEa ao longo do perfil do solo e sua comparação com aquela obtida a partir da sondagem elétrica vertical permitiram identificar algumas limitações desta técnica. A presença de camadas com variação de diversas propriedades físicas e de umidade no perfil do solo alterou os valores observados em superfície. A relação entre a distância de separação dos eletrodos no arranjo com quatro pontas igualmente espaçadas, e a profundidade de prospecção, coeficiente k, oscilou entre 0,35 e 0,70 para os solos LVd, LAd e PVe avaliados. A sondagem elétrica empregada na caracterização de variabilidade espacial na horizontal e em profundidade em uma área com teores de argila oscilando entre 150 e 379 g kg-1 na camada 0 a 0,2 m e entre 225 e 326 g kg-1 na camada 0,6 a 0,8 m apresentou resultado satisfatório. / The variability of soil physical properties has an impact on the performance of agricultural production activities. Indirect methods for obtaining information on the soil properties with agronomic interest are used to allow the use of inputs more appropriately. The apparent soil electrical conductivity ( ECa ) is influenced by several properties , many of them interrelated and presenting variability in short distances, being difficult to separate the various factors. ECa measures are usually taken in surface, using electrode arrangements for prospecting a soil volume proportional to the distance between them. In this work, a methodology was used that identified some of the properties with the greatest impact on the ECa, with emphasis to those related to soil porous space. The detailed characterization of the variation of ECw throughout the soil profile and its comparison with that obtained from the vertical electrical sounding was carried to identify certain limitations of this technique. The presence of several layers with varying physical properties and moisture in the soil profile changed values obtained from surface sounding. The relationship between the separation of the electrodes in the array with four points equally spaced, the Wenner array, and the depth of exploration, coefficient k, ranged between 0.35 and 0.70 for the soils LVd , LAd PVe and evaluated. A survey was done for the ECa characterization of spatial variability in the horizontal and along soil profile in an area with clay content ranging from 150 to 379 g kg - 1 in the layer from 0 to 0.2 m and between 225 and 326 g kg - 1 in layer 0, 6 to 0.8 m. The use of ECa for characterizing this variability showed satisfactory results.