Tesis sobre el tema "Concrete electrical resistivity"

The purpose of this research project was to identify the extent that concrete resistivity measurements (bulk and/or surface) can be used as a performance based lab test to improve the quality of concrete in Utah bridge decks. By allowing UDOT to specify a required resistivity, concrete bridge deck quality will increase and future maintenance costs will decrease. This research consisted of two phases: the field phase and the lab phase. In the field phase, concrete samples were gathered from local concrete producers in Utah. These concrete samples were made with common concrete mixes used in bridge decks across the state of Utah. Testing multiple mix designs allowed the research team to investigate several variations of concrete constituents, for instance, water to cement ratio, common Utah supplementary cementitious materials, curing type, and aggregate type. Mechanical and durability testing was performed on concrete of different ages. These tests included strength, surface resistivity, bulk resistivity, rapid chloride permeability, and freeze and thaw tests. In the lab phase, one of the field mixes was selected as the control mix. This mix was then duplicated in the lab in order to see the performance differences of each mix in the controlled and field experiments. In addition, changes were made to the lab control mix, to see the effect of different materials on the resistivity and durability of concrete.

Concrete repair materials are being widely used to restore and extend the service life of structures. While most cement-based repair materials are compatible with concrete structures, their durability properties do not attract much attention which it deserves from researchers. Since repair materials can deteriorate like conventional concrete, the search for reliable, long-lasting concrete repair materials is becoming more intensive. Amongst other factors, concrete permeability and chloride diffusivity within concrete are believed to play a major role in determining the durability and success of the repair. These two parameters determine the penetration rate of aggressive substances into concrete and how fast degradation could take place. A number of test methods have been proposed to study these two factors, and the commonly used test methods are water penetration, surface/bulk electrical resistivity, rapid chloride permeability (RCP), and half-cell potential. However, the relationship between each durability test method and their correlation with compressive strength measurement have not been fully understood. So, in this study, we aim for using multiple testing techniques, destructive and non-destructive, to evaluate the durability of concrete repair materials as well as correlating different test methods. Three types of commercially available cement-based materials are tested and evaluated, and results have indicated that cementitious concrete mortar (termed as Mix M) amongst others has the best durability performance which means low water permeability, high resistivity, and compressive strength. Whereas, the flexural performance of Mix M still needs some improvement in terms of flexural strength and flexural toughness. For various durability testing methods, surface resistivity is found to have a strong linear relation and a polynomial relation to bulk resistivity and water permeability respectively. No relationship is established between concrete resistivity and compressive strength, though high-strength concrete tends to have a high resistivity in our study. RCP test results do not correlate well with resistivity measurements, which requires further study to overcome its heating and binding effect when measurements are being taken. Half-cell potential method is used for validating test results but it reveals no difference for materials with different permeability and resistivity. A model is proposed to counteract temperature’s effect while calculating the coefficient of diffusion, which indicates the concrete to resist chloride diffusion. It is found that this model can shift the RCP measurement slightly closer to its theoretical prediction but the difference between them is still large. Therefore, further research is required for acquiring more raw data from RCP measurements as the regression analysis input. In addition, a more comprehensive model that involves more correction factors for binding effects, etc., is also needed.
Graduate
2020-04-30

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.

In regions where chloride-based deicing salts are applied to bridge decks, corrosion of the interior steel reinforcement is a major problem. Vertical electrical impedance (VEI) is an effective measurement technique to quantitatively assess the cover protection on bridges against aggressive chemical penetration of reinforced concrete. In its current form, traditional vertical electrical impedance is time-consuming and destructive because a direct connection to the reinforcing steel is required to provide a ground reference. A new method using a large-area electrode (LAE) permits VEI measurement without a direct electrical connection to the steel reinforcement. The LAE creates a nondestructive, semi-direct, low impedance connection between the measurement electronics and the reinforcing steel. In this work, numerical simulations are performed on common electrode arrangements to demonstrate the effectiveness of the LAE when significant variations in concrete conductivity exist. Physical experiments of a large-area electrode are carried out in the laboratory and field to validate the numerical simulations and to provide additional comparisons with the traditional tapped steel reinforcement method. The results of this study are a set of important design considerations for VEI utilizing a LAE to connect to the underlying rebar. Using these design considerations, the large-area electrode method was validated using both an analytical and a finite-element model, laboratory experiments, and field experiments on two bridges in Utah. The validation results indicate the LAE can replace the direct connection to the reinforcing steel. As a result of this work, a multichannel VEI scanner which uses the LAE method was built which can provide VEI information for bridge engineers and managers to better rehabilitate deteriorating reinforced concrete.

Concrete has been used in a number of civil engineering applications due to its interesting fresh, hardened, and durability-related properties. 28-day compressive strength is the most important hardened state property and is frequently used as an indicator of the material’s quality. However, early-age mechanical properties are a key factor nowadays to enhance construction planning. Several advanced techniques have been proposed to appraise concrete microstructure and quality, and among those electrical resistivity (ER) is one of the most commonly used since it is a non-destructive and low-cost technique. Although recent literature data have shown that ER may be significantly influenced by a variety of parameters such as the test setup, material porosity and moisture content, binder type/amount and presence of supplementary cementing materials (SCMs) along with the nature of the aggregates used in the mix, further research must be performed to clarify the influence of the raw materials (i.e. SCMs and aggregate nature) on ER using distinct setups. Therefore, this work aims to appraise the influence of the coarse aggregate nature and binder replacement/amount on the concrete ER and compressive strength predictions models through ER. Twenty-four concrete mixtures were developed with two different coarse aggregate natures (i.e. granite and limestone), two different water-to-binder ratios (w/b; i.e. 0.6 and 0.4) and incorporating two different SCMs (i.e. slag and fly-ash class F) with different replacement levels. Moreover, three distinct ER techniques (e.g. bulk, surface, and internal) and compressive strength tests were performed at different ages (i.e. 3, 7, 14, and 28 days). Results indicate that the binder type and replacement amount significantly affect ER and compressive strength. Otherwise, the coarse aggregate nature presented only trivial influence for 0.6 w/b mixes, except for 50% fly-ash replacement samples; whereas for concrete specimens with enhanced microstructure (i.e. 0.4 w/b), the aggregate nature influence was statically significant especially for the binary mixtures with high SCMs replacement levels (i.e. 70% GGBS and 50% fly-ash). Finally, all ER test setups were considered to be quite suitable and reliable NDT techniques correlating themselves very well. Yet the internal resistivity setup demonstrated to be the device which yields the lowest variability amongst them.

The integrity of the rebars in reinforced concrete structures is related to the chemical and physical protection provided by the concrete layer that covers the steel. The destruction of the passivation layer precedes the onset of corrosion. Once the corrosion process starts, its rate of propagation will depend on the electrical resistivity between cathode and anode and the amount of oxygen available on the cathode. Concrete resistivity is a property linked both to the chemical and physical properties of the concrete. This study investigated the effect of the addition of blast furnace slag (BFS) on the electrical resistivity of concrete and correlated the effects of this addition on the concrete compressive strength as well as on changes in the chemical composition of aqueous phase and pore structure. Test specimens were prepared using different water/binder ratios (0.35, 0.50 and 0.65) and substitutions of 50 and 70% of BFS for cement by weight. A control sample (no BFS) was also prepared. Additionally, the effect of 4% sodium sulfate (Na2SO4) in samples with 50% BFS was also investigated. The electrical resistivity of concrete was determined using the fourelectrode method (Wenner s method adapted for use in concrete). Tests of compressive strength, porosimetry, electrical conductivity in the pore solution and the concentration of ions in the aqueous phase were performed. The tests showed there is an increase in the electrical resistivity of concrete as the degree of hydration and the concentration of BFS increase. This is related to the lower specific conductivity of the pore solution and the reduction in concrete pore size, which is shown by the good correlation between these two factors. The binary mixture with 50% BFS (50E) showed the best cost/benefit ratio for strength levels of 30MPa and 50MPa at 28 days and also for the strength level of 50MPa at 91 days.
A manutenção da integridade das armaduras nas estruturas de concreto é uma conseqüência da proteção física e química do concreto sobre o aço. A destruição da camada passivadora antecede o processo corrosivo. Uma vez iniciada a corrosão, a velocidade desta dependerá da resistividade elétrica existente entre o ânodo e o cátodo e também pela quantia de oxigênio presentes junto ao cátodo. A resistividade do concreto caracteriza-se por ser uma propriedade ligada tanto a características físicas como químicas do mesmo. Neste trabalho objetivou-se estudar o comportamento da adição de escória de alto forno na resistividade elétrica aparente dos concretos, assim como correlacionar com a resistência à compressão e as alterações químicas na fase aquosa bem como na estrutura dos poros. Foram realizadas investigações em misturas com relação a/agl 0,35, 0,50 e 0,65 com teores de substituição em massa de 0, 50 e 70% de EAF. Investigou-se também os efeitos produzidos pela incorporação de 4% de sulfato de sódio (Na2SO4) em misturas contendo 50% de EAF. A resistividade elétrica do concreto foi determinada utilizando o método dos quatro eletrodos (método de Wenner adaptado para uso em concreto). Foram também realizados ensaios de resistência à compressão axial, porosimetria, concentração de íons da fase aquosa e determinada a condutividade elétrica específica da solução dos poros. Constatou-se aumento na resistividade elétrica do concreto com o aumento no grau de hidratação e do teor de escória. Este comportamento está relacionado a menor condutividade elétrica específica da solução dos poros e ao refinamento dos poros comprovado pela boa correlação entre esses dois fatores. A mistura binária composta por 50% de escória (50E) apresentou a melhor relação custo/benefício para os níveis de resistência de 30MPa e 50MPa aos 28 dias e também para o nível de resistência de 50MPa aos 91 dias.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
The durability of concrete structures is the result of protective action of concrete over the rebar. When the passivation of steel ceases to exist the structure becomes vulnerable to the phenomenon of corrosion, which spread after start is largely controlled by the electrical resistivity of concrete. Another important factor in the durability of concrete structures is the absorption, which is one of the properties governing the transport of ions inside the concrete. This study aimed to evaluate the electrical resistivity and capillary absorption of concrete that have undergone surface treatment: a monolithic polymeric mortar applied in a layer of 4mm, and a pore blocker with a single coat and a pore blocker with a double coat. The concrete surface subjected to treatment were made with three types of cement,CP IV-32, CP II-F 32 and CP V and levels of compressive strength of 15MPa, 20MPa and 25MPa. The electrical resistivity was measured by the method of four electrodes and capillary absorption by the method NBR 9779. Treatment with the pore blocker with a double coat was more effective in reducing capillary absorption than a pore blocker with a single coat for the three types of cement, but the best results were obtained using the polymer mortar. In this work the pozzolanic effect present on cement CP IV became more clear in the result of electrical resistivity for all treatment studied. The different behavior of the electrical resistivity of concrete with cement CP IV in relation to others, CPII F and CP V, is justified by changes in the microstructure of the paste, pore refinement and composition of pore solution. In addition to this, when compared to concrete made with CP V, the lower relations/binder of CP IV to obtain the compressive strengh levels investigated, fck = 15 Mpa , 20Mpa and 25Mpa. Even the reference concrete without surface treatment showed values of resistivity well above the actual reference compounds with CP II-F and CP V and also subjected to surface treatment.
A durabilidade das estruturas de concreto armado é resultado da ação protetora do concreto sobre a armadura. 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. Outro fator importante na durabilidade das estruturas do concreto é a absorção capilar, a qual é uma das propriedades que regem o transporte de íons no interior do concreto. O presente estudo teve por objetivo avaliar a resistividade elétrica e a absorção capilar em concretos que foram submetidos a tratamento superficial: uma argamassa polimérica monocomponente aplicada em camada de 4mm, e um produto obturador dos poros aplicado em uma e duas demãos. Os concretos submetidos ao tratamento superficial foram produzidos com três tipos de cimento, CP IV 32, CP II F 32 e CP V, e para os níveis de resistência à compressão de 15MPa, 20MPa e 25MPa. A resistividade elétrica foi medida pelo método dos quatros eletrodos e a absorção capilar segundo o método NBR 9779. O tratamento com o produto obturador dos poros em dupla demão mostrou-se mais efetivo na redução da absorção capilar do que o tratamento com uma demão para os três tipos de cimento, contudo, os melhores resultados foram obtidos com o uso da argamassa polimérica. Neste trabalho o efeito pozolânico presente no cimento CP IV ficou claro nos resultados de resistividade elétrica para todos os tratamentos estudados. Este comportamento diferenciado do CP IV em relação aos demais, CP II F e CP V, se justifica pelas alterações na microestrutura da pasta, refinamento dos poros e composição da solução dos poros. Acresce a isto, quando comparado aos concretos produzidos com CP V, as menores relações a/agl do CP IV para obtenção dos níveis de resistência à compressão investigados. Mesmo o concreto de referência sem tratamento superficial apresentou valores de resistividade elétrica muito superiores aos concretos de referência compostos com CP II F e CP V e também submetidos a tratamento superficial.

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CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
PROSUP - Programa de Suporte à Pós-Gradução de Instituições de Ensino Particulares
Durante a execução de elementos de concreto no canteiro de obras, procedimentos de controle de qualidade do concreto são adotados com o objetivo de verificar se o material atende às características de projeto. Esta verificação também visa evitar falhas durante as etapas subsequentes da construção, que podem levar até à inviabilização do empreendimento. Estudos sobre métodos que têm como objetivo estimar a relação água/cimento (a/c) do concreto no estado fresco vêm recebendo maior atenção nos últimos tempos, devido à importância deste parâmetro sobre a resistência e durabilidade das estruturas de concreto, e por não existirem métodos práticos e precisos disponíveis até o momento, que permitam a sua determinação após a realização da mistura. Estudos sobre o método da resistividade elétrica apontam para uma forte correlação entre os valores de resistividade e a relação água/cimento do concreto no estado fresco, possibilitando a utilização do método como uma interessante alternativa para determinação da relação a/c. O presente estudo tem como objetivo apresentar uma análise do método da resistividade elétrica, aplicado à estimativa de valores de relação água/cimento de concretos no estado fresco, confeccionados com cimentos nacionais, além da estimativa de valores de resistência à compressão axial do concreto no estado endurecido. Foram realizados ensaios com concretos dosados a partir do método IPT/EPUSP para seis cimentos nacionais (CPV-ARI, CPIV-32, CPIII-40, CPII-Z-32, CPII-F-32 e CPII-E-40), variando-se a relação a/c (0,35, 0,45, 0,55 e 0,65), utilizando uma sonda aprimorada para realização dos testes, a qual foi desenvolvida neste estudo com base num protótipo já desenvolvido anteriormente. Os resultados obtidos apontam para uma forte correlação existente entre a resistividade elétrica do concreto no estado fresco e a relação a/c, com valores médios das estimativas para relação a/c dentro do intervalo de ±0,02, com relação aos valores efetivos das misturas testadas. A margem de erro média para as estimativas de relação a/c, considerando-se todos os cimentos testados, ficou no intervalo entre 2,25% e 9,38%. Foram obtidos coeficientes de determinação na ordem de 85,7% a 95,2% para as estimativas de resistência à compressão, mostrando que é possível determinar tanto a relação a/c quanto a resistência à compressão do concreto através do método da resistividade elétrica, quando o material encontra-se ainda no estado fresco.
During construction of concrete elements in the building site, quality control proceedings are adopted in order to verify if the concrete reaches its design specifications, which also avoids failures during the subsequent stages of the construction. Test methods used for the determination of the water-cement (w/c) ratio have received increased attention, due to the importance of this ratio for the concrete resistance and durability, and also because there isn’t any practical and sufficiently precise method available at the moment, which could be used for determining water-cement ration after mixing. Studies about the electrical resistivity method have shown a strong relationship between the measured resistivity values and water-cement ratio, for the fresh concrete, making this method an interesting alternative for determining w/c ratio. This study presents an analysis of the electrical resistivity method, applied to determine the water-cement ratio of several fresh concrete mixtures made with different types of Brazilian cements, in addition to estimates of compressive strength values of the hardened concretes. Concrete mixtures were made out of six cement types (CPV-ARI, CPIV-32, CPIII-40, CPII-Z-32, CPII-F-32 and CPII-E-40), dosed by the IPT/EPUSP method, and four water-cement ratios (0.35, 0.45, 0.55 and 0.65). Tests were performed using an improved probe, developed in this study, based in one prototype developed previously. Results shown a strong relationship between the electrical resistivity of fresh concrete and its water-cement ratio, with average estimated values within ±0,02 of the actual water-cement ratio values for the mixtures tested. The average error for the w/c ratio estimated values, considering all of the cements tested, was between 2,25% and 9,38%. The compressive strength estimates reached coefficients of determination between 85,7% and 95,2%, showing that it is possible to estimate both w/c ratio and compressive strength of concrete while still in the fresh state with the electrical resistivity method presented here.

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.

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.

The electrical resistivity is an important concrete property that allows evaluating the access facility of aggressive agents before the corrosion process begins and estimates the velocity of the same process after it begun. The electrical resistivity and the oxygen availability are the characteristics that control the corrosion velocity. This work aimed to evaluate the performance of white Portland cement concretes with high blast furnace slag content and chemical activation on the electrical resistivity. Other properties were measured, as axial compressive strength, porosity and specific electrical conductivity of pore solution. Four mixtures were tested, a reference one, only with white Portland cement as binder, a second one, with 50% of blast furnace slag in substitution of cement, other with 70% slag content, and the last one, with 50% of slag and alkaline activation, 4% of Na2SO4. The water/binder ratios were fixed at 0,30, 0,42 and 0,55 for all samples. The electrical resistivity was measured using the four electrode method (Wenner method). The sample age, water/binder ratio and the slag content have an expressive effect over the electrical resistivity, especially because it results in changes of the pore structure. The electrical resistivity grows as the amount of slag increases. The increase of slag amount also results in smaller specific electrical conductivity of pore solution and pore structure refinement. On the other hand, the axial compressive strength decreases as the slag amount increases. The biggest resistivity results were obtained for the mixture with 70% of slag. This mixture showed the best cost/benefit ratio as compressive strength were fixed at 35 and 55 MPa, at 28 days, and 60 MPa, at 91 days.
A resistividade elétrica é uma importante propriedade do concreto por permitir avaliar a facilidade de acesso de agentes agressivos antes de instalado o processo corrosivo e estimar a velocidade do mesmo depois de instalado, sendo conjuntamente com a disponibilidade de oxigênio um dos parâmetros determinantes para a velocidade da corrosão. Este trabalho teve como objetivo avaliar o desempenho de concretos de cimento Portland branco com elevados teores de escória de alto forno e ativação química quanto à resistividade elétrica aparente. Foram avaliadas além da resistividade outras grandezas como resistência à compressão, porosidade e condutividade específica da solução dos poros. Foram investigadas quatro misturas, uma de referência contendo apenas cimento, uma segunda com teor de substituição de cimento por escória de 50%, outra com teor de substituição de 70% e uma última contendo 50% de escória e ativador alcalino, Na2SO4, em um teor de 4%. As relações água/aglomerante foram fixadas em 0,30, 0,42 e 0,55 para todas as misturas. A medida da resistividade elétrica foi realizada através do método dos quatro eletrodos (Wenner). A resistividade elétrica se mostrou dependente da idade, relação a/ag e teor de escória, principalmente, em função das alterações que estas proporcionam na estrutura de poros da pasta. A resistividade cresceu proporcionalmente ao aumento do teor de escória. O aumento do teor de escória resultou também em menor condutividade da solução aquosa e refinamento da estrutura de poros da pasta. Por outro lado, a resistência à compressão diminuiu com o crescimento do teor de escória. Os maiores valores de resistividade elétrica foram apresentados pela mistura contendo 70% de escória. Esta mistura se mostrou a de melhor relação custo/benefício quando se fixaram valores de resistência à compressão de 35 e 55 MPa, aos 28 dias, e 60 MPa, aos 91 dias.

Résumé : Le vieillissement des ouvrages en béton est une préoccupation majeure affectant la pérennité et l’efficacité des structures. Le maître d’ouvrage se doit de maintenir les fonctions d’usage de la structure tout en gardant une gestion économique efficace. L’objectif final de ces travaux de recherche est, donc de pouvoir renseigner sur l’état global de fissuration de la structure afin d’aider le maître d’ouvrage à respecter ses engagements. Dans cette optique, cette thèse développe une nouvelle technique aidant à la quantification de l’état des ouvrages massifs en béton. Elle s’appuie, pour cela, sur la méthode non-destructive de résistivité électrique en surface, connue pour sa sensibilité face à des facteurs révélateurs d’une altération. Toutefois, à cause de sa dépendance entre la profondeur d’investigation et la résolution, la méthode ne peut pas garantir de l’état global d’un ouvrage. De ce fait, il a été décidé d’utiliser la résistivité électrique via des forages préexistants dans la structure (diagraphie électrique). L’outil utilisé est une sonde en dispositif normal réservée jusqu’à présent pour la prospection pétrolière et hydrogéologique. En plus d’une prospection en profondeur via le forage, cette sonde peut acquérir des informations sur un rayon de 3.2m autour du forage. Cependant, à mesure que le volume de béton sondé augmente, la résolution décroit. La difficulté est donc de pouvoir exploiter les capacités de prospection de la sonde tout en sachant que la résolution faillit. Il s’agit de contourner le problème en maîtrisant les concepts de la diagraphie et son nouveau milieu d’application. Cette thèse est basée sur une première approche numérique permettant d’apporter des corrections sur les données de terrain et de déterminer la sensibilité de l’outil face à de l’endommagement d’ouverture plurimillimétrique à centimétrique. Ceci est validé par des mesures réalisées sur une écluse de la Voie Maritime du Saint-Laurent. Une étude numérique de la réponse de l’outil en fonction des paramètres de fissure tels que l’ouverture, le contraste entre la résistivité de la discontinuité et du béton, et l’extension est réalisée. Elle permet de construire une base de données afin de développer une méthode pour la caractérisation de l’endommagement. Cette méthode s’appuie sur ces réponses diagraphiques pour retrouver les paramètres de fissure recherchés (problème inverse). Nous procédons tout d’abord par une analyse préliminaire se basant sur un croisement des informations apportées par les différentes électrodes de la sonde puis nous optimisons les résultats par la méthode de recuit simulé. La méthode, ainsi développée est ensuite appliquée à un deuxième ouvrage pour en déterminer l’état interne. Ces travaux détectent plusieurs zones endommagées et caractérisent l’une d’elles par une ouverture centimétrique et une extension comprise entre 1.6m et 3.2m. Ces travaux prometteurs, attestent d’un premier diagnostic interne des ouvrages massifs en béton, un enjeu qui restait sans réponses satisfaisantes jusqu’à maintenant. // Abstract : The aging of concrete structures is a major problem affecting their sustainability and their efficiency. The owner must maintain the structure serviceability and provide cost-effective management. The goal of this work is to provide detailed information about the state of cracking inside the structure in order to assist the owner to meet its commitments. In this context, this thesis develops a new technology to assess the condition of mass concrete structures. It relies on a non-destructive method based on electrical resistivity measured from surface, known for its sensitivity to factors associated with concrete deterioration. However, because of its dependence between the investigation depth and the resolution, the method cannot assess the overall state of a structure. Therefore, it was decided to use the electrical resistivity through preexisting boreholes in the structure (electrical logging). The tool used is a normal probe, which has been traditionally used for oil and hydrogeological exploration. In addition to the investigation in depth via boreholes, this probe can get information over a radius of 3.2m around the borehole. However, as the probing volume of concrete increases, the resolution decreases. Difficulty is to use the exploration abilities of the tool, knowing that the resolution is limited. This is to get around the problem by mastering logging concepts and its new application environment. This thesis is based on a first numerical approach to make corrections on field data and to determine the tool sensitivity with regard to the multi-millimeter and centimeter crack size damage. This was validated with measurements made on a full-size lock located on the St. Lawrence Seaway. A numerical study of the tool response versus the discontinuities parameters such as the crack aperture, the resistivity contrast between the discontinuity and the concrete, and the extension was done. It allowed building a database used to develop a method for the characterization of the damage. This method is based on the tool responses to find the crack parameters (inverse problem). First, we proceed with a preliminary analysis based on a cross of information provided by the different electrodes of the probe then we optimize the results by the method of simulated annealing. The characterization method is applied to another structure to quantify its internal state. These studies detect several damaged areas and characterize one of them by a centimeter aperture and an extension between 1.6m and 3.2m. This work attest to a first internal diagnosis of massive concrete structures, an issue that remained without satisfactory answers so far.

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O trabalho apresenta um estudo exploratório sobre o uso de cinzas de casca de arroz como finos em argamassas autoadensáveis. Para tanto foram realizadas composições de argamassas vibradas e autoadensáveis variando-se os parâmetros tais como a relação água/cimento, superplastificante/cimento, e volume de agregado miúdo/volume de argamassa, mantendo-se constante a relação finos/cimento, e as relações água/materiais secos, bastante próximas. Foram realizados ensaios no estado fresco e no estado endurecido. Para o estado fresco foram realizados de modo a poder nortear as composições, a saber: ensaio Flow- table para os casos de argamassas vibradas e de espalhamento Slump-flow para os casos de argamassas autoadensáveis, ensaio Slump-test para os casos de argamassas vibradas e de escoamento confinado V-funnel para os casos de argamassas autoadensáveis, e avaliação da massa específica aparente. No estado endurecido foram realizados os ensaios de resistência à compressão simples e diametral, e os de absorção d’água. Os resultados foram então comparados uns com os outros ou analisados dentro do seu contexto. Encontraram-se valores que puderam corroborar para as vantagens do uso das cinzas de casca de arroz nas argamassas autoadensáveis, sobretudo nos resultados relativos aos valores das resistências mecânicas alcançadas e dos níveis de absorção d’água. Observou-se também aparente rigidez para os casos das argamassas autoadensáveis. Observou-se que as argamassas autoadensáveis podem alcançar um comportamento diferenciado na diminuição dos valores de absorção d’água com o tempo, de modo a se antecipar estas reduções dentro de seus níveis máximos permitidos.
The paper presents an exploratory study on the use of rice husk ash as fine in self-compacting mortars. Therefore, we conducted compositions vibrated and self-compacting mortars varying parameters such as the water/cement superplasticizer/cement ratio and the volume of fine aggregate/volume of mortar, keeping constant the fines/cement ratio, and the relationship water/dry materials very close. Assays were performed in fresh and hardened state. For fresh state were conducted in order to guide the compositions as follows: Flow-test table for cases of vibrated mortar Slump-flow and spread in cases of self-compacting mortar, Slump-test assay for the cases of mortars vibrated and V-funnel flow confined to cases self-compacting mortars, and evaluation of the bulk density. In the hardened state were performed strength tests to simple and diametrical compression, and the water absorption. The results were then compared with each other or analyzed in context. They met values that might corroborate the advantages of the use of rice husk ash in self-compacting mortars, particularly in the results for the values of mechanical strength and achieved the levels of water absorption. There was also apparent rigidity for cases of self-compacting mortars. It was observed that the mortar self-compacting can achieve a differentiated behavior in decreasing the water absorption values over time in order to anticipate these reductions within their maximum permitted levels.

Orientador: Maria da Consolação Fonseca de Albuquerque
Resumo: O trabalho apresenta um estudo exploratório sobre o uso de cinzas de casca de arroz como finos em argamassas autoadensáveis. Para tanto foram realizadas composições de argamassas vibradas e autoadensáveis variando-se os parâmetros tais como a relação água/cimento, superplastificante/cimento, e volume de agregado miúdo/volume de argamassa, mantendo-se constante a relação finos/cimento, e as relações água/materiais secos, bastante próximas. Foram realizados ensaios no estado fresco e no estado endurecido. Para o estado fresco foram realizados de modo a poder nortear as composições, a saber: ensaio Flow- table para os casos de argamassas vibradas e de espalhamento Slump-flow para os casos de argamassas autoadensáveis, ensaio Slump-test para os casos de argamassas vibradas e de escoamento confinado V-funnel para os casos de argamassas autoadensáveis, e avaliação da massa específica aparente. No estado endurecido foram realizados os ensaios de resistência à compressão simples e diametral, e os de absorção d’água. Os resultados foram então comparados uns com os outros ou analisados dentro do seu contexto. Encontraram-se valores que puderam corroborar para as vantagens do uso das cinzas de casca de arroz nas argamassas autoadensáveis, sobretudo nos resultados relativos aos valores das resistências mecânicas alcançadas e dos níveis de absorção d’água. Observou-se também aparente rigidez para os casos das argamassas autoadensáveis. Observou-se que as argamassas autoadensáveis podem al... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The paper presents an exploratory study on the use of rice husk ash as fine in self-compacting mortars. Therefore, we conducted compositions vibrated and self-compacting mortars varying parameters such as the water/cement superplasticizer/cement ratio and the volume of fine aggregate/volume of mortar, keeping constant the fines/cement ratio, and the relationship water/dry materials very close. Assays were performed in fresh and hardened state. For fresh state were conducted in order to guide the compositions as follows: Flow-test table for cases of vibrated mortar Slump-flow and spread in cases of self-compacting mortar, Slump-test assay for the cases of mortars vibrated and V-funnel flow confined to cases self-compacting mortars, and evaluation of the bulk density. In the hardened state were performed strength tests to simple and diametrical compression, and the water absorption. The results were then compared with each other or analyzed in context. They met values that might corroborate the advantages of the use of rice husk ash in self-compacting mortars, particularly in the results for the values of mechanical strength and achieved the levels of water absorption. There was also apparent rigidity for cases of self-compacting mortars. It was observed that the mortar self-compacting can achieve a differentiated behavior in decreasing the water absorption values over time in order to anticipate these reductions within their maximum permitted levels.
Mestre

There are constant searches for alternatives to reduce the environmental impact in the production of in consumables, like concrete, that is actually a pollutant. Mineral additions have been investigated as partial substitutions for cement in concrete because other than taking advantage of industrial residues, that many times don t have a specific distinction and are degrading in the ambiental view, they can offer better material durability characteristics, as proved in previous studies. In Brazil, a big rice producer, millions of tons of rice husk are produced, where part is utilized for energy production in thermoelectric plants. The rice husk ash, result of the burning of the husk, has been the font of studies as a partial substitution of cement in concrete. There are still very few studies that make a comparison of the viability influence of the utilization of rice husk ash with different levels of carbon graphitic (light and dark grey), obtained by controlled burnings, a durable characteristic in concretes. In this work, mixtures containing different levels of light and dark RHA were investigated in concrete structural performance through water capillary absorption, following the NBR 9779:1995 and apparent electrical resistivity, conforming to the four electrode method (Wenner). Additionally, an analysis was made of the axial compressive strength in accordance with the NBR 5739:2007. For this, eight compound mixtures were tested and investigated in relation to their w/wc 0,35, 0,50 e 0,65: one composited of 100% Portland cement, REF, three with substitution of cement by light RHA in levels of 10%, 20% and 30%, namely 10 LRHA, 20 LRHA, 30 LRHA, respectively, and another three with the same levels of dark RHA replace cement, identified as 10 DRHA, 20 DRHA and 30 DRHA, respectively, and a mixture with 10% of silica fume, 10 SF, to compare results. The increase in cure time and in the purport of the substitution of cement by RHA resulted in better performance as to the investigated properties. In equality of w/wc relations, the compressive strength values were, in general, similar, indifferent to the level of carbon graphitic of the RHA. The composite mixture with DRHA presented better performance with regards to capillary absorption, even though it was overcome by the mixture with SF. In relation to electrical resistivity, the composed mixture of 30% LRHA presented better performance in all analysis times.
Há, cada vez mais, uma busca de alternativas para reduzir o impacto ambiental na produção de insumos, como o cimento, que é altamente poluente. Adições minerais têm sido investigadas como substituições parciais ao cimento no concreto, pois, além de propiciar o aproveitamento de resíduos industriais, os quais muitas vezes não possuem destinação específica e são degradantes do ponto de vista ambiental, podem oferecer melhora nas características de durabilidade do material, conforme verificado em estudos anteriores. No Brasil, que é um grande produtor de arroz, são geradas anualmente milhões de toneladas da casca deste cereal, sendo parte dessa utilizada para produção de energia, em usinas termoelétricas. A cinza da casca de arroz, resultante da queima da casca, tem sido fonte de pesquisas visando a sua utilização como substituição parcial ao cimento do concreto. Ainda são poucos os estudos que fazem um comparativo da influência da viabilidade da utilização da cinza de casca de arroz com diferentes teores de carbono grafítico (cinza clara e escura), obtidas por queima controlada, frente a características de durabilidade em concretos. Neste trabalho, misturas contendo diferentes teores de CCA clara e escura foram investigadas quanto ao desempenho em concreto estrutural, através dos ensaios de absorção de água por capilaridade, segundo a NBR 9779:1995 e resistividade elétrica aparente, conforme o método dos quatro eletrodos (Wenner). Adicionalmente, realizou-se o ensaio de resistência à compressão axial, de acordo com a NBR 5739:2007. Para isso, foram testadas oito misturas aglomerantes, investigadas nas relações a/ag 0,35, 0,50 e 0,65: uma composta por 100% de cimento Portland, REF, três com substituição de cimento por CCA clara, em teores de 10%, 20% e 30%, denominadas 10 CCAC, 20 CCAC e 30 CCAC, respectivamente, outras três com os mesmos teores de troca de cimento por CCA escura, identificadas por 10 CCAE, 20 CCAE e 30 CCAE, respectivamente, e uma mistura com 10% de sílica ativa, 10 SA, para comparação de resultados. O aumento no prazo de cura e no teor de substituição de cimento por CCA resultou em melhor desempenho para as propriedades investigadas. Em igualdade de relação a/ag, no geral, os valores de resistência à compressão foram semelhantes, indiferentemente do teor de carbono grafítico da CCA. As misturas compostas com CCAE apresentaram melhor desempenho quanto à absorção capilar, embora superadas pela mistura com SA. Com relação à resistividade elétrica, a mistura composta com 30% de CCAC apresentou melhor desempenho em todas as idades de ensaio.

O aterramento elétrico cumpre uma função essencial em um sistema de distribuição de energia elétrica, devendo atender, dentre vários requisitos, aqueles estabelecidos quanto aos valores de tensão de passo e de toque. Entretanto, em locais onde o solo apresenta valores elevados de resistividade, surgem dificuldades que nem sempre são superadas no sentido de obedecer às exigências citadas nas normas técnicas e especificações. Dentro deste contexto, este trabalho tem por objetivo avaliar a utilização de condutores e hastes envolvidos em concreto em sistemas de aterramento, visando à redução dos valores de resistência de terra. Inicialmente é abordada uma configuração convencional de malha de aterramento adotada por uma concessionária de energia elétrica, sendo realizados estudos de modo a verificar a influência do espaçamento e da quantidade das hastes nos valores de resistência de terra. São também consideradas modificações nas dimensões da malha e a utilização de hastes profundas e, na seqüência, são analisados os resultados de outras configurações. De modo a verificar a efetividade do uso do concreto, foram realizadas várias simulações computacionais considerando o sistema de aterramento com a utilização de condutores e hastes envolvidos em concreto. Diversas situações foram investigadas, sendo possível concluir que o uso do concreto resulta em menores valores de resistência de terra em relação às malhas convencionais. Esse resultado, de certo modo, vem ao encontro das expectativas, porém deve ser ressaltada a contribuição do trabalho, a qual possibilita a análise, através de cálculos teóricos, do comportamento das malhas de aterramento com o uso do concreto. A literatura pesquisada apresenta poucos resultados teóricos, sendo encontradas algumas investigações nesse tema onde são consideradas somente medições realizadas no campo.
The electrical grounding plays an essential role in a system of electric power distribution, and must follow, among many requirements, those ones established as step voltage values and touch voltage values. However, in those places where the soil has high resistivity values, some difficulties arise and may not always be overcomed in order to follow the requirements set forth in technical standards and specifications. In this context, the aim of this study is to evaluate the use of electrical conductors and rods encased in concrete inside grounding systems, in order to reduce the ground resistance values. Initially it was observed a conventional configuration of grounding grid that is used by an electric utility, and studies were made in order to verify the influence of the number of rods and the distance between them in the values of grounding resistance. There are also been taken into consideration the changes in the grounding grid dimensions and the use of deep rods and, right after, the results of other configurations are analyzed. In order to verify the effectiveness of the use of concrete, several computer simulations were performed considering the grounding system that used conductors and rods encased in concrete. Several situations were investigated, and it was possible to conclude that the use of concrete results in lower values of ground resistance compared to conventional grounding grid. This result, in a certain way, matches with the expectations, but it should be emphasized the contribution of the study which enables, through theoretical calculations, the analysis of the grounding grid behavior with the use of concrete. The literature shows few theoretical results and presents only some researches on this issue in which ones only measurements made in the field are considered.

L'homogénéité des caractéristiques est garantie par une présence en fibres constante en tout point du matériau. La dispersion d'une espèce dans une autre est régie par des mécanismes de convection et/ou de diffusion. Pour des objets de la taille d'une fibre métallique, ces deux phénomènes trouvent leur origine dans le cisaillement appliqué au matériau, une donnée souvent inconnue et difficile à mesurer dans des malaxeurs à béton. Dans un premier temps, nous proposons une méthode permettant d'estimer l'efficacité d'un malaxeur. Elle est basée sur la mesure du diamètre moyen de granules de ciment fabriqués dans ce malaxeur. Nous montrons que la mesure de ce diamètre moyen permet de quantifier le cisaillement moyen. Dans un second temps, nous présentons un moyen de mesurer la dispersion des fibres pendant le malaxage des bétons à base de mesures de résistivité électrique. Puis, dans un troisième temps, nous mesurons la présence en fibres pendant le malaxage et relions le temps nécessaire à l'obtention d'une répartition homogène à la capacité de cisaillement du malaxeur
Fibers are added to the concrete to give it news properties. The homogeneity of these characteristics is assured by a constant presence of fiber as the whole material. The dispersion of one species within another is governed by convection and/or diffusion mechanisms. Concerning objects having the size of steel fiber, these two phenomena are caused by the shearing applied to the material, an unknown and difficult to measure datum in the case of concrete mixer. To begin, a method allowing to estimate the mixer's shearing is suggested. This method is based on the measurement of the medium diameter of cement aggregates produced in the mixer. The link between the medium diameter and the mean shearing is established. In a second time, a mean to measure fiber dispersion from electrical resistivity measurements during the concrete mixing is presented. Then, in a third time, fiber dispersion are measured during mixing. The link between necessary time to obtain an homogeneous distribution and the mixer's shearing ability is established

Les méthodes d’évaluation non destructives donnant accès à la mesure de la résistivité électrique et de la permittivité diélectrique sont très sensibles au degré de saturation du béton. Inversées et calibrées indépendamment, ces mesures permettent d’obtenir des profils de gradients de degré de saturation en fonction de la profondeur. Dans cette thèse, nous développons une méthode d’inversion conjointe des mesures de résistivité et de permittivité pour améliorer la fiabilité et la précision des profils de degré de saturation estimés. Nous modélisons les mesures sur une dalle de béton en 3D par la méthode des éléments finis, le béton étant considéré comme un milieu homogène vis-à-vis des granulats mais présentant un profil de saturation avec la profondeur, représenté par un modèle continu prenant la forme d'une distribution de Weibull à quatre paramètres. Pour inverser les mesures pour estimer le profil de S, nous avons développé un algorithme de moindres carrés non linéaires de type LevenbergMarquardt. La prise en compte des incertitudes associées à chaque jeu de mesures fait partie intégrante de la méthode développée afin d’affiner sa fiabilité, permettant en outre de propager ces incertitudes sur les paramètres estimés. Deux campagnes expérimentales, l’une de séchage, l’autre d’imbibition, sur des dalles de béton, sont organisées pour tester l’algorithme de l’inversion conjointe. Des avancées notables sont constatées avec l’estimation des profils par la nouvelle approche d’inversion conjointe. Ces profils, par ailleurs comparés à plusieurs autres méthodes indépendantes, se montrent plus stables et plus cohérents avec l’évolution due au séchage et à l’imbibition du béton que ceux estimés par inversion séparée des observables
Non-destructive assessment methods providing access to the measurement of electrical resistivity and dielectric permittivity are very sensitive to the degree of saturation of concrete. When inverted and calibrated independently, these measurements provide profiles of saturation degree gradients as a function of depth. In this thesis, we develop a joint inversion approach for resistivity and permittivity measurements to improve the reliability and accuracy of the estimated saturation degree profiles. We model the measurements on a concrete slab in 3D by the finite element method, the concrete being considered as a homogeneous medium with respect to aggregates but having a saturation profile with depth, represented by a continuous model taking the form of a Weibull distribution with four parameters. For the inversion of measurements to estimate the profile of S, we have developed a non-linear least-squares algorithm of the Levenberg-Marquardt type. Taking into account the uncertainties associated with each set of measurements is an integral part of the method developed in order to refine its reliability, which also makes it possible to propagate these uncertainties over the estimated parameters. Two experimental campaigns, one of drying, the other of imbibition, on concrete slabs, are organized to test the algorithm of joint inversion. Significant progress has been made with the estimation of profiles by the new joint inversion approach. These profiles, also compared to other independent methods, appear to be more stable and more consistent with the evolution due to the drying and the imbibition of concrete than those estimated by separate inversion of the observables

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Electrical grounding is part of the Atmospheric Discharge Protection System (ADPS), whose functions are to provide a path for the circulation of electric current in the ground and to enable the detection of a possible fault between the energized conductors and the earth. For grounding to be efficient, some characteristics must be taken into account, such as soil type and resistivity. In this sense, measurements of resistivity and soil stratification are important for a correct sizing of the grounding system. Soils with high water concentration (low resistivity) are better current conductors than dry soils, for example. Soils with high resistivity can cause a return current. Thus, some decisions aimed at strengthening the grounding system should be taken when there are soils with inadequate grounding characteristics. Therefore, this work aims to evaluate the influence of soil electrical resistivity and enveloping types using concrete types in the substation electrical grounding system through software simulations, taking into account soil resistivity characteristics. In the analysis of types of envelopment, it was possible to observe that the concretes with greater amount of water in their composition have a lower electrical resistivity. The use of concrete enveloping is feasible for soils with high resistivity, as in the case of the land located in the city of Campinas, and it was possible to verify that for soils with low resistivity its use may be impractical since other options such as inclusion of more cables and installation of the rods in the layers with less resistivity are sufficient and more economical.
O aterramento el?trico faz parte do Sistema de Prote??o Contra Descargas Atmosf?ricas (SPDA), cujas fun??es s?o fornecer um caminho para a circula??o de corrente el?trica na terra, escoamento para a terra de cargas induzidas nas carca?as dos equipamentos el?tricos e, em conjunto com os dispositivos diferenciais-residuais, possibilitar a detec??o de uma poss?vel falha entre os condutores energizados e a terra. Para que o aterramento seja eficiente, algumas caracter?sticas devem ser levadas em considera??o, tais como o tipo e a resistividade do solo. Neste sentido, medi??es da resistividade e a estratifica??o do solo s?o importantes para um dimensionamento correto do sistema de aterramento. Solos com alta concentra??o de ?gua (baixa resistividade) s?o melhores condutores de corrente do que um solo seco, por exemplo. Solos com alta resistividade podem ocasionar uma corrente de retorno. Assim, algumas decis?es visando o refor?o do sistema de aterramento devem ser tomadas quando se tem solos com caracter?sticas inadequadas ao aterramento. Portanto, esse trabalho teve como objetivo avaliar a influ?ncia da resistividade el?trica do solo e de tipos de envelopamento utilizando tipos de concreto no sistema de aterramento el?trico de subesta??es atrav?s de simula??es em software, levando em conta as caracter?sticas de resistividade do solo. Nas an?lises de tipos de envelopamento, foi poss?vel observar que os concretos com maior quantidade de ?gua em sua composi??o possuem uma resistividade el?trica mais baixa. A utiliza??o do envelopamento de concreto ? vi?vel para solos com alta resistividade, como ? o caso do terreno localizado na cidade de Campinas, e foi poss?vel verificar que para solos com resistividade baixa sua utiliza??o pode ser invi?vel j? que outras op??es como inclus?o de mais cabos e instala??o das hastes nas camadas com menor resistividade s?o suficientes e mais econ?micas.

Les méthodes d’évaluation non destructives donnant accès à la mesure de la résistivité électrique et de la permittivité diélectrique sont très sensibles au degré de saturation du béton. Inversées et calibrées indépendamment, ces mesures permettent d’obtenir des profils de gradients de degré de saturation en fonction de la profondeur. Dans cette thèse, nous développons une méthode d’inversion conjointe des mesures de résistivité et de permittivité pour améliorer la fiabilité et la précision des profils de degré de saturation estimés. Nous modélisons les mesures sur une dalle de béton en 3D par la méthode des éléments finis, le béton étant considéré comme un milieu homogène vis-à-vis des granulats mais présentant un profil de saturation avec la profondeur, représenté par un modèle continu prenant la forme d'une distribution de Weibull à quatre paramètres. Pour inverser les mesures pour estimer le profil de S, nous avons développé un algorithme de moindres carrés non linéaires de type Levenberg Marquardt. La prise en compte des incertitudes associées à chaque jeu de mesures fait partie intégrante de la méthode développée afin d’affiner sa fiabilité, permettant en outre de propager ces incertitudes sur les paramètres estimés. Deux campagnes expérimentales, l’une de séchage, l’autre d’imbibition, sur des dalles de béton, sont organisées pour tester l’algorithme de l’inversion conjointe. Des avancées notables sont constatées avec l’estimation des profils par la nouvelle approche d’inversion conjointe. Ces profils, par ailleurs comparés à plusieurs autres méthodes indépendantes, se montrent plus stables et plus cohérents avec l’évolution due au séchage et à l’imbibition du béton que ceux estimés par inversion séparée des observables
Non-destructive assessment methods providing access to the measurement of electrical resistivity and dielectric permittivity are very sensitive to the degree of saturation of concrete. When inverted and calibrated independently, these measurements provide profiles of saturation degree gradients as a function of depth. In this thesis, we develop a joint inversion approach for resistivity and permittivity measurements to improve the reliability and accuracy of the estimated saturation degree profiles. We model the measurements on a concrete slab in 3D by the finite element method, the concrete being considered as a homogeneous medium with respect to aggregates but having a saturation profile with depth, represented by a continuous model taking the form of a Weibull distribution with four parameters. For the inversion of measurements to estimate the profile of S, we have developed a non-linear least-squares algorithm of the Levenberg-Marquardt type. Taking into account the uncertainties associated with each set of measurements is an integral part of the method developed in order to refine its reliability, which also makes it possible to propagate these uncertainties over the estimated parameters. Two experimental campaigns, one of drying, the other of imbibition, on concrete slabs, are organized to test the algorithm of joint inversion. Significant progress has been made with the estimation of profiles by the new joint inversion approach. These profiles, also compared to other independent methods, appear to be more stable and more consistent with the evolution due to the drying and the imbibition of concrete than those estimated by separate inversion of the observables

La résistivité électrique est un paramètre sensible à différentes propriétés du béton, dont la teneur en eau qui est l'un des principaux indicateurs gouvernant sa durabilité. Dans cette étude, la problématique du suivi du profil de teneur en eau du béton sur toute son épaisseur est abordée en utilisant une méthode électrique à courant continu comme méthode de mesure. Cette problématique revêt une grande importance pour les structures de stockage en béton utilisées pour les déchets radioactifs et pour les applications nécessitant une résolution spatiale centimétrique de la mesure du profil de teneur en eau sur une grande épaisseur. L'objectif de cette thèse est de concevoir et de réaliser des capteurs multi-électrodes noyés dans des structures en béton pour évaluer le profil de résistivité dans leur épaisseur afin de remonter au profil de teneur en eau. L'étude porte sur la conception de deux capteurs (Echelle et Anneau) sous la forme de circuits imprimés, ce qui présente plusieurs avantages, en particulier la précision géométrique et la limitation de l'encombrement des câblages afin d'une part d'augmenter la durabilité des capteurs et d'autre part de réduire leur caractère invasif. Différentes configurations de mesure sont analysées et comparées. Une modélisation numérique de la réponse électrique des capteurs et de leur capacité à évaluer un profil de résistivité imposé est réalisée ainsi que l'influence des armatures métalliques sur la réponse des capteurs placés au centre de la maille d'armature. Des validations expérimentales à la fois dans des solutions salines de conductivité connue et sur des échantillons de béton soumis au séchage sont également mises en œuvre. Les résultats démontrent la capacité des capteurs à évaluer les profils de résistivité dans le béton avec une résolution centimétrique. Pour changer d'échelle et s'approcher des conditions de mesure sur des structures réelles, les capteurs sont intégrés dans deux dalles de béton armé de 30 cm d'épaisseur instrumentées par d'autres capteurs afin de comparer les résultats. Enfin, une calibration des mesures est réalisée pour remonter au profil de teneur en eau en tenant compte de la température. Les profils de degré de saturation obtenus avec les capteurs innovants développés dans cette thèse sont encadrés par les profils obtenus par des mesures de référence (capteurs thermohygrométriques THR et gammadensimétrie) et donnent des résultats cohérents avec l'évolution due au séchage du béton
Electrical resistivity is a parameter sensitive to various properties of concrete, including water content, which is one of the key parameters governing concrete long-term durability. In this study, the problem of monitoring the concrete water content profile throughout the concrete structure thickness is addressed using a method based on DC- electrical resistivity measurements. This is of great importance for concrete repository structures used for radioactive waste and for applications requiring centimetric resolution of the water content profile over a thick structure. The aim of this thesis is to design and produce a novel multi-electrode embedded sensor for monitoring the resistivity profile over depth in order to estimate the water content profile. The study focuses on the design of two sensors based on printed circuit board (PCB), which brings several advantages, including geometric accuracy and mitigation of wiring issues, in order to increase the durability of the sensors and to reduce invasiveness. Different measurement configurations are analyzed and compared. In addition, numerical modeling of the sensor response and its ability to assess an imposed resistivity profile is carried out, as well as the influence of the steel reinforcement on the response of the sensors placed in the center of the reinforcement mesh. Experimental validations using saline solutions of known conductivity and concrete specimens subjected to drying are studied. The results demonstrate the capability of the sensor to evaluate resistivity profiles in concrete with centimetric resolution. To enlarge our scale and approach real structures, the sensors are embedded in two 30 cm thick concrete slabs instrumented by other sensors to compare the results. Calibration of the measurements is carried out to determine the water content profile taking the temperature into account. The saturation degree profiles obtained with the innovative sensors developed in this thesis are compared to the profiles obtained from reference measurements (thermohygrometric sensors and gammadensimetry) and give consistent results with the evolution of the concrete due to drying

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.

碩士
國立成功大學
土木工程學系碩博士班
100
In this study, the influences of coarse aggregate to the electrical resistivities of concrete were investigated. Specifically, types and sizes of the aggregates were targeted as the studied parameters. Commercially available granites and marbles with various sizes of 4.75, 9.5, 12.5, and 19mm were used in the concrete mixtures, and the resistivities at the age of 28 days were investigated. Polarization induced resistivity growth during the electrical measurement were considered and experimentally nullified, such that the real bulk resistivities of concrete specimens can be obtained for comparison. Concrete specimens were made by cement mortars and several degrees (amounts) of coarse aggregates; with a fixed size of coarse aggregates used in a single specimen. Cement mortars were mixed with the water/cement ratio of 0.4, and the cement/sand ratio was held constantly at 1:1. The microstructures of certain specimen samples were obtained by Scanning Electron Microscopy so as to estimate the porosity of cement pastes, which is the primary conductive portion of cementitious materials. This was done to validate the resistivity observation. The results show that the electrical resistivities of concrete made with crushed granites were quite close to those that made with crushed marbles. Moreover, the particle size of aggregates seems to have no significant influences to concrete resistivities while it is to concrete strengths. As a partial study of nondestructive testing technologies to the performance estimations of concrete, further studies were required and we have drew a few comments.

碩士
國立海洋大學
河海工程學系
86
In this thesis，the effect of fly ash on the chloride diffusion coefficient and electrical resistivity of concrete is studied. The two-cell accelerated ion migration test has been adopted for measuring the chloride diffusion coefficient of concrete，and the four-eletrode resistivity measurement is used for evlaluating the surface and cross-sectional resistance of concrete. Test variables include various water/binder rations and various cement weight replacement percentanges by fly ash.It is found that the chloride diffusion coefficient apparantly increase as the water/binder ratio increase，and under the same water/binder ratio condition it decrease as the cement replacement by fly ash increase. Also the resistivity decreases as the water/binder ratio increase，and under the same water/ binder ratio condition it increase as the cement replacement by fly ash increase. There exists a unifield relation between the chloride diffusion coefficient and resistivity. Due to the lack of aggregate effect，the surface resistance is not appropriate to be an index of the compacthess of concrete.

碩士
國立臺北科技大學
土木工程系土木與防災碩士班
104
Concrete has been widely used in various fields of civil engineering in many decades, and the health monitoring of the concrete structures has become more important in recent years. The high-performance sensing materials continue to be adopted in the monitoring and sensing of civil engineering structures, such as the piezoelectric material and carbon fiber material, etc., the suitable materials for applying to the civil engineering should have the features of low cost, well durability and stability, and high sensitivity. Carbon fiber material is one of the sensing materials that can be applied to the monitoring and sensing of civil engineering structures. When the carbon fiber concrete specimen subjected to the applied loads, the stretch or squeeze of the carbon fiber itself will cause the change of resistivity of the specimen, therefore, this properties can be applied to measure the deformation of the concrete specimen by measuring the change of the resistivity. In this research, the main purpose is to discuss the influence of the loading rate and cycles of loading to the fractional change of resistivity of the carbon fiber concrete. The test results show that the change of resistivity decreased as the loading rate increased under the same loading, and the influence from the cycles of loading is not very obviously.

Many Ministry of Transportation of Ontario (MTO) projects consist of construction and maintenance of reinforced concrete structures. Where appropriate test methods exist, MTO has been moving towards use of performance-based specifications for durability control of concrete. MTO currently uses ASTM C1202 (RCPT) coulomb values to assess concrete durability. This test requires taking cores, so replacing this test with a faster non-destructive technique is important. The main focus of this program was to study the Wenner probe surface resistivity as a non-destructive test device and evaluate the potential for replacement of RCPT with the Wenner resistivity. This research program consists of the determination of RCPT values, water sorptivity coefficients and electrical resistivities (bulk and surface) of nine concrete mixtures. In addition, the development of the Wenner probe instrument was studied. As well, correlations between resistivity and ASTM C1202 and C1585 are provided followed by technical recommendations for improving the Wenner test.

It is well-known that concrete permeability is a good indicator of its expected durability until it remains uncracked. However, in various stages of its service life, different types of cracking in concrete can be developed due to exposure to different deterioration processes such as early plastic shrinkage or chloride-induced reinforcement corrosion. Although these cracks may not endanger concrete’s structural performance from the mechanical point of view, they create a pathway for aggressive ions that can initiate degradation processes, lead to increase in concrete permeability and thus reduce its durability. Cracking in concrete might not be preventable, but its capability to naturally seal small cracks, named autogenous self-healing (SH), provides an additional feature to manufacture more durable concrete structures. However, natural self-healing capability of concrete is limited and therefore it is typically omitted in the design of concrete structures. Hence, more attention has been recently paid to Engineered Self-healing Concrete (EShC) which is associated with artificially triggered healing mechanisms into the cementitious matrix by incorporating various substances such as crystalline products. EShC helps in reducing concrete permeability; thus, increasing its service-life and durability. Due to formation of needle-shaped pore-blocking crystals, Crystalline Admixtures (CA), as a candidate from the Permeability-Reducing Admixtures (PRA) category, can be implemented into concrete mixtures to fabricate EShC concretes. Crystalline waterproofing technology is not new, but still is unknown to many researchers, engineers, and construction industry professionals. The lack of knowledge of its microstructure and self-healing properties limits CA’s proper usage in the construction industry. The techniques to assess the self-healing capability of mortar and concrete are not well-standardized yet. No research work has been done to address certain durability characteristics of this material (i.e. electrical resistivity (ER) or chloride diffusivity) especially when combined with Supplementary Cementitious Materials (SCM) and Portland Limestone Cement (PLC). Since the resistance of concrete against ions’ penetration is a function of its permeability, it might be a straightforward and reliable parameter to rapidly evaluate concrete’s durability during its intended service life. Hence, electrical resistivity measurement is considered as an indirect and alternative tool for other time-consuming permeability testing techniques to examine the CA’s efficiency as it modifies the concrete’s microstructure by crystals’ deposition; thus, leads to permeability improvement. In comparison to previous studies, on a larger scale, this thesis aims to systematically study the effects of CA on the microstructural features, self-healing properties and long-term durability and resistivity of cement-based materials and in addition, draw some comprehensive conclusions on the use of CA in new and repair applications. This study is divided into three major phases to propose all-inclusive work on using CA in construction industry. To satisfy the goals of each individual phase, a test matrix consisting of a series of four mixes with variables such as use of PLC or presence of CA in powder form is considered. In order to address to the lack of research and industry knowledge discussed above, this PhD thesis includes the following phases: Phase (I) In this phase, the main focus is on the microstructural properties and the changes in the pore structure and chemical compositions of the cement phase of mortar mixes when treated with CA. These microstructural features are studied using Scanning Electron Microscope (SEM) and Scanning Transmission Electron Holography Microscope (STEHM). Moreover, physical and chemical characteristics of the hydration products are determined using image analysis and Energy Dispersive X-ray (EDX) Spectroscopy, respectively. Phase (II) This phase is allocated to macro-level investigation of durability characteristics such as chloride/water permeability and electrical resistivity of concrete structures containing CA and PLC cement. To non-destructively measure the chloride ion concentration in the field conditions, both changes in corrosion potential of rebars and concrete electrical resistivity in treated circular hollow-section steel reinforced columns exposed to simulated marine environment is monitored and compared over a 2-year period with control samples. In addition, laboratory-size concrete samples are studied to investigate the effects of CA presence on long-term resistivity, rapid chloride permeability, water permeability and chloride diffusivity of concrete. Later, a resistivity-based model is developed to predict long-term performance of concretes incorporating slag or metakaolin, studied in various environmental conditions. The long-term goal of this phase is to develop a standard design guideline and durability-based model. Phase (III) Using an innovative self-healing testing method [1], quantitative analysis of crack closure ability and self-healing potential of CA treated and control concretes with OPC or PLC cement is accomplished during this phase. The obtained results from first phase showed that hydrated CA particle revealed fine, compact, homogenous morphology examined by STEHM and its diffraction pattern after water-activation indicated nearly amorphous structure, however, diffuse rings, an evidence for short-range structural order and sub-crystalline region, were observed which requires further investigation. The SEM micrographs taken from specimen’s fractured surface showed formation of pore-blocking crystals for all treated mixes while similar spots in un-treated sections were left uncovered. Although needle-shaped crystals were observed in the treated mortar specimens, but not all of them had shapes and chemical compositions other than ettringite (well-known to form needle-like crystals). Using backscatter SEM images and EDX spectrums, examination of polished mortar sections with and without CA also showed typical hydration phases, forming in the control system. Results from phase II showed that concretes treated with CA had almost 50% lower water penetration depth and thus smaller permeability coefficient when compared with the virgin OPC or PLC concretes. According to salt ponding test results, the use of CA helped in enhancing the resistance to chloride penetration compared to control concrete. This improvement increases with increasing in concrete age. Strong linear relationship between Surface Resistivity (SR) and Bulk Resistivity (BR) data was observed which indicates that these test methods can be used interchangeably. The presence of SCM in concrete indicated considerable increase in both SR and BR compared to control concrete. Concretes incorporating slag or metakaolin have tendency to react more slowly (or rapidly in MK case), consume calcium hydroxide over time, form more Calcium Silicate Hydrate (C-S-H) gel, densify internal matrix, and also reduce OH- in the pores’ solution; thus, increase concrete electrical resistivity. For laboratory specimens, environmental conditions such as temperature variation and degree of water saturation indicated considerable effects on electrical resistivity measurements. As temperature or water content of concrete decreases, its electrical resistivity greatly increases by more than 2-3 times from reference environmental condition. This is mostly because of variation or accessibility in electron mobility. Experimental results from field investigation showed that electrical resistivity readings were highly influenced by the presence of rebar and concrete moisture conditions. In addition, concrete cover thickness and CA addition into cementitious matrix had a negligible effect on its resistivity. In the last phase, an optical microscope was used to measure the average crack width. OPC samples had an average measured crack width of 0.244 mm as compared to 0.245 mm for OPC-CA, 0.251 mm for PLC, and 0.247 mm for PLC-CA. Self-healing test results also showed 90% self-healing ratio for CA modified mix within few days after starting experiment. Addition of CA into the mix led to higher rates of healing and full crack closure (width up to 250 µm) when compared to reference concrete. An empirical equation that relates water initial flow rate to the crack width (Q∝〖CW〗^3) was also proposed in this phase. Presence of PLC and CA in the mixture resulted in positive improvement in crack-closing capability and self-healing ratio.
Graduate
2019-09-11