Dissertations / Theses on the topic 'Concrete admixture'

Alkali silica reaction (ASR), a reaction which occurs between reactive siliceous mineral components in the aggregate and the alkaline pore solution in concrete, is responsible for substantial damage to concrete structures in the U. S. and across the world. Lithium admixtures, including lithium nitrate (LiNO3), have been demonstrated to mitigate ASR damage, and are of particular interest for use in concrete airfield pavement construction, where ASR damage has been recently linked to the use of certain de-icing chemicals. Although the effectiveness of lithium admixtures at ASR-mitigation is well-researched, relatively less is known regarding the potential effects, including negative effects, on overall concrete behavior. The goal of this research is to better understand the influence of LiNO3 admixture on early age concrete behavior, and to determine if a maximum dosage rate for its use exists. Isothermal calorimetry, rheology and bleed water testing, time of setting, chemical shrinkage, autogenous shrinkage, free and restrained concrete shrinkage, and compressive and flexural strength were measured for pastes and concretes prepared with a range of LiNO3 dosages (i.e., 0, 50, 100, 200, and 400% of the recommended dosage). In addition, the interaction of LiNO3 with cement was evaluated by comparing results obtained with six cements of varying alkali and tricalcium aluminate (C3A) contents. Additionally, one of these cements, was examined alone and with 20% by weight Class F fly ash replacement. Results indicate that the hydration of the tricalcium silicate and tricalcium aluminate components of cement are accelerated by the use of LiNO3, and that low alkali cements (typically specified to avoid damage by ASR) may be particularly susceptible to this acceleration. However, inclusion of Class F fly ash at 20% by weight replacement of cement (also common in applications where ASR is a concern) appears to diminish these possibly negative effects of LiNO3 on early age hydration acceleration and heat generation. Dosages higher than the current standard dosage of LiNO3 may have minor effects on fresh concrete workability, causing slight decreases in Bingham yield stress, corresponding to slightly higher slump. Fresh concrete viscosity may also be affected, though more research is necessary to confirm this effect. LiNO3 had no effect on quantity of bleed water in the mixes tested. Generally, LiNO3 had no effect on initial and final setting times, although increasing dosages caused faster set times in the lowest alkali (Na2Oeq = 0.295%) cement examined. In shrinkage testing, higher LiNO3 dosages appeared to cause initial expansion in some sealed paste specimens, but in all cases the highest dosage led to greater autogenous shrinkage after 40 days. In concrete specimens, however, the restraining effect of aggregates diminished shrinkage, and no effect of the LiNO3 was apparent. In no cases, with any dosage of lithium tested, with or without fly ash replacement, did restrained shrinkage specimens show any cracking. Strength testing produced mixed results, with laboratory specimens increasing in 28-day compressive strength, but companion specimens cast in the field and tested by an outside laboratory, exhibited lower 28-day compressive strength, with increasing lithium dosages. Flexural specimens, also cast in the field and tested by an outside laboratory, appeared to show an increase in 28-day flexural strength with increasing lithium dosages. However, because of the conflicting results when comparing the various strength data, further research is necessary for conclusive evidence of LiNO3 effects on concrete strength.

Freezing and thawing cycles is one of the most damaging factors that affect the durability of concrete. The damages caused by the cyclic freeze-thaw action can be divided into two factors. The first factor is an increase in internal crack, which causes the loss in relative dynamic modulus (RDM) of the concrete and the second factor is surface scaling, which leads to weight loss of the concrete. In this study, the durability of concrete made by replacing natural coarse aggregates (NCA) with various percentages of recycled concrete aggregates (RCA). Also some tests have been conducted with the addition of air entraining admixture (AEA). Prior to mixing the concrete, both NCA and RCA were characterized to determine their suitability as a construction material. Concrete mixes consisting of 0, 20, 40, 60, 80, and 100% replacement (by weight) of NCA with RCA were prepared. The same concrete mixes were prepared again but with the addition of an air entraining admixtures (AEA). All specimens were tested for compressive strength after a curing period of 7, 14, and 28 days. The compressive strength of the concrete made with different percentage of RCA decreases as the percentage of RCA increases. After 28 days of curing, samples with 0, 40, and 100% replacement of NCA with RCA were placed in the freeze-thaw chamber along with 0, 20, 40, 60, 80, and 100% NCA replacement containing AEA. After several cycles of freezing and thawing; the RDM, change in weight and change in length were measured. In this study loss of RDM and weight loss were noticed, as the cyclic freeze-thaw increases. It has also been observed that concrete mixes containing AEA were still durable after 300 cycles of freezing and thawing; however, the specimens without AEA failed before 150 cycles.

This thesis work aims the ionic liquid pretreatment of peanut shells for co-production of glucose as fermentable sugar and lignin, considering a multi product perspective. The effects of ionic liquid type and pretreatment time period on the sugar and lignin yields were investigated, as the particle size and temperature parameters were determined in the preliminary studies. Peanut shells were pretreated at constant temperature, 150 oC, for 5, 15 and 30 minutes with 1-ethyl-3-methylimidazolium acetate and for 15, 30 and 60 minutes with 1-ethyl-3-methylimidazolium chloride. The pretreated peanut shells were then subjected to enzymatic hydrolysis in order to produce fermentable sugars, mostly, glucose. The solid residue obtained upon enzymatic hydrolysis was analyzed in terms of lignin quantity. 1-ethyl-3-methylimidazolium acetate pretreatment for 15 minutes resulted in the maximum reducing sugar and lignin yields
28 g of reducing sugar and 20 g of solid residue with 70% lignin were obtained per 100 g of peanut shells. Higher pretreatment time resulted in lower yields. Moreover, no optimal time period for 1-ethyl-3- methylimidazolium chloride pretreatment was obtained, since reducing sugar and lignin yields increased as the time period increased. Also all reducing sugar and lignin yields were lower than that obtained with 1-ethyl-3-methylimidazolium acetate. Lignin obtained upon enzymatic hydrolysis of 1-ethyl-3-methylimidazolium acetate pretreated peanut shells were characterized by SEM, FTIR, TGA and XRD analyses, which also showed the morphological and structural effects of pretreatment and enzymatic hydrolysis on peanut shells
and used as concrete admixture, which increased the flow of the concrete by 6%.

In recent years, there has been a growing interest in the use of supplementary cementing materials and polymers to produce high-performance concrete. Utilizing a mineral substance as cement replacement in concrete has less environmental pollution and greatly increases the service life of the concrete structures due to improve the most of concrete properties in compared with conventional concrete. The aim of this project is an experimental study of high-performance concrete using metakaolin (MK) additive as partial replacement of cement and addition of the Styrene-Butadiene rubber (SBR) and Polyvinyl acetate (PVA), to conduct a novel research to investigate the effectiveness of the additives materials on the performance of concrete. It also investigates the effect of additional recycled plastic and glass fibre as reinforcements used in the modified concrete. Firstly, trial mixes of 460 cubes, 24 cylinders and 30 prisms were made to study the setting time, workability, mechanical properties and water absorption of the concrete to find the optimum metakaolin to cement ratio (MK/C), polymer to cement ratio (P/C), water to cement ratio (W/C), and the best curing method among the wet, dry and moist, respectively. The designed concrete mixes have a certain cement/sand/gravel proportion of 1:1.5:3. The trial mixtures were tested for setting time, slump of fresh concrete mix, mechanical properties, including compressive, splitting and flexural strength, and water absorption capacity at age up to 28 days. Three polymers to cement ratios, which are 2.5, 5 and 7.5%, and five metakaolin replacement ratio for the cement, which are 10, 15, 20, 30 and 40%, were studied, respectively. For these mixtures, five W/C ratios, which are 0.35, 0.38, 0.40, 0.45, and 0.50, respectively, were compared. The use of recycled plastic and glass fibre reinforcements took 5% of the total cement weight and tested for splitting and flexural strength testes. The first phase work has shown clear improvement of the performance of concrete modified by partial replacement of cement by metakaolin and adding polymers admixture together. The optimised mix was identified to be that of 5% added polymers included 80% SBR and 20% PVA, 15% metakaolin replacement for cement, 0.45 W/C ratio, and using limestone aggregate as a coarse aggregates and using moist curing method as a curing condition for the concrete. Secondly, the optimum mixture identified in the trial study was further investigated for its mechanical including compressive, flexural, and deformable proprieties at prolonged ages up to 545 days. In addition, a specific durability properties of concrete including water and gas permeability, carbonation penetration, chloride penetration, chemical attack resistance, water absorption, rate of water absorption and the corrosion rate of the steel reinforcement in the concrete. The results show that significant improvement in mechanical properties including compressive, splitting, flexural strength and deformation properties. Also, the results show improvement in durability properties including chemical resistance, water absorption, rate of water absorption, carbonation depth of penetration, chloride ion penetration, water penetration under pressure, water permeability, gas penetration and steel corrosion resistance. The optimum mix of 15% partial replacement of cement by metakaolin, 5% polymer, 0.45 W/C ratio and moist curing condition of the modified concrete produced high-performance concrete more environmental friendly due to improved overall of the mechanical and durability properties of the concrete. Finally, microscopic composition of the hydration products and the corresponding pores structure have been investigated for the optimised mixes based on the material composition analysis and microscopic images obtained using scanning electronic microscope (SEM) and the computed tomography scanner (CT) technologies. Correlation between the mechanical, durability properties and the microscopic phases has been investigated and discussed for a deep understanding of the mechanism of the optimum mixture. SEM and CT scanner technologies provide qualitative and quantitative description of the concrete properties. It’s also, proved that the concrete modified by both of metakaolin and two types of polymers have a significant change in the pores structure of concrete compared with other mixes. Scanning electron microscopy and computed tomography scanner results show that the approach can be effectively applied in high-performance concrete related studies and provide further evidence on mechanical and durability properties of concrete.

Concrete which is manufactured in a mixing plant to be delivered to construction site in unhardened and plastic stage is called ready-mixed concrete. Because of technical and economical reasons, many mineral and chemical admixtures are used in ready-mixed concrete production. As a result of extra mixing and delayed placing of ready-mixed concrete (especially at hot weather conditions), there can be many problems about concrete, like slump loss. Addition of water for retempering concrete is the usual procedure, but addition of water without proper adjustment in mixture proportions, adversely affects compressive strength. During this study, effects of prolonged mixing and retempering with superplasticizer on properties of fresh and hardened concrete at hot weather conditions are observed. Some of the properties of concrete inspected are compressive strength, splitting tensile strength, slump and air content. All mixes contain air entrainer and water reducer at a standard amount. The difference between mixes comes from kind and amount of mineral admixture which cement is replaced by. During the study, fly ash, blast furnace slag, ground clay brick and natural pozzolan are used at amounts, 25% and 50% of cement. Also, a mixture of pure cement is prepared as control concrete. 15 cm initial slump is planned in the experimental work. After five minutes and at the end of first, second, third and fourth hours of mixing process, if needed retempering process is proceeded with superplasticizer and samples are taken. As a result of retempering with superplasticizer, the aimed slump values are obtained. The effects are than, observed. As a result of this study, it has been observed that replacing Portland cement with certain mineral admixtures, especially fly ash at certain amounts, can be a solution for slump loss problem, by retarding the slump loss effect of prolonged mixing. Also it has been seen that ground clay brick causes better performance for slump values at lateral stages of mixing with respect to pure Portland cement. Another important observation has been about the increase in the amount of air caused by air entraining admixtures in fresh concrete based on prolonged mixing at hot weather conditions.

Two metakaolins were evaluated for use as supplementary cementitious materials in cement-based systems. The metakaolins varied in their surface area (11.1 v. 25.4 m2/g), but were quite similar in mineralogical composition. Performance of metakaolin mixtures was compared to control mixtures and to mixtures incorporating silica fume as partial replacement for cement at water-to-cementitious materials ratios of 0.40, 0.50, and 0.60. In this study, the early age properties of fresh concrete and the mechanical and durability properties of hardened concrete were examined. Early age evaluations aimed to determine the reactivity of metakaolin (heat of hydration) and its effect on mixture workability (slump, setting time, unit weight). In addition, three types of shrinkage were monitored in metakaolin-cement systems: chemical, autogenous, and free. Compressive, tensile, and flexural strength and elastic modulus were measured at various concrete ages. The influence of metakaolin addition on durability was assessed through accelerated testing for sulfate resistance, expansion due to alkali-silica reaction, and through rapid chloride permeability measurements. To further quantify the underlying mechanisms of metakaolin's action, the microstructure of pastes was examined. Calcium hydroxide (CH) content was determined using thermogravimetric analysis and verified using differential thermal analysis. Surface area and pore size distribution were evaluated via nitrogen adsorption. These analyses yielded information about the pozzolanic reactivity of metakaolin, associated CH consumption and pore structure refinement, and resulting improvements in mechanical performance and durability of metakaolin-concretes.

L'emploi de certaines additions minérales et organiques dans la confection du mortier et du béton contribue à une modification du processus d'hydratation du ciment. L'incorporation de ces additions minérales entraîne également une modification de la distribution granulaire, l'apparition de nouveaux sites de nucléation et une nouvelle activité des surfaces des grains. Ceci nécessite le malaxage avec des superplastifiants qui viennent défloculer les grains, libérer l'eau piégée dans les interstices et améliorer l'ouvrabilité du béton. Ces modifications des propriétés physicochimiques des composants du béton affectent directement les propriétés rhéologiques du mortier et du béton à l'état frais ainsi que ses composantes finales.L'objectif principal de ce travail est focalisé sur la prédiction des modifications rhéologiques apportées par les additions minérales aux mortiers afin de trouver les meilleures compositions d'une mise en œuvre convenable. Une étude expérimentale est entamée sur des mortiers normalisés où le ciment ordinaire est substitué partiellement par différentes additions minérales telles que la fumée de silice, le laitier des hauts fourneaux, la pouzzolane naturelle et le calcaire. Avec l'eau de gâchage, on a ajouté plusieurs types de superplastifiants avec différents dosages où les paramètres rhéologiques du mortier ont été mesurés respectivement par un mini cône et un rhéomètre.Les paramètre rhéologiques obtenus varient sensiblement avec chaque type d'addition minérale et dépendent de ses propriétés et son interaction avec le superplastifiant et les grains de ciment. Le superplastifiant à base de polycarboxylates est plus efficace en présence du ciment contenant du calcaire ou du laitier conduisant à une amélioration des propriétés rhéologiques. Par contre, le mortier devient plus visqueux s'il contient un fort pourcentage de pouzzolane naturelle. Une relation mathématique est proposée qui exprime la variation de chaque paramètre rhéologique selon le taux de substitution du ciment et le dosage en superplastifiant. Cette relation est exprimée par le produit de trois paramètres; l'effet de l'addition minérale, l'effet du superplastifiant et l'effet de leur interaction. Les coefficients de corrélation trouvés sont proches de l'unité et justifient bien la convenance de ce choix. L'application de cette nouvelle relation à d'autres résultats trouvés par d'autres chercheurs présente une grande satisfaction avec des résultats satisfaisant et des coefficients de corrélation allant 0,9 à 0,98
The use of some organic and inorganic admixtures in the production of mortar and concrete contributes to a change in the cement hydration process. The incorporation of these mineral additions also causes a change in the grain distribution, the appearance of new nucleation sites and a new activity of the grain surfaces. This requires mixing with superplasticizers which deflocculates grains, releases the trapped water in the interstices and improves the workability of concrete. These changes in the physicochemical properties of the cement paste directly affect the rheological properties of mortar and concrete in the fresh state and its final components.The main objective of this work is focused on the prediction of rheological changes of mineral additions mortars and finds the best composition for a suitable casting. An experimental study is underway on standardized mortars where ordinary cement is partially substituted by different mineral additions such as silica fume, blast furnace slag, natural pouzzolan and limestone powder. With the mixing water, was added several types with different dosages of superplasticizers where the rheological parameters of the mortar were measured respectively by a rheometer apparatus and a mini cone test.The Theological parameters obtained vary with each type of mineral addition and depend on its properties and its interaction with the superplasticizer and cement grains. The polycarboxylate superplasticizer is more effective in the presence of limestone powder or cement containing slag resulting in improved rheological properties. However, the mortar becomes more viscous if it contains a high percentage of natural pozzolan. A mathematical relationship is provided which expresses the variation of each rheological parameter according the substitution rate of the cement and superplasticizer dosage. This relationship is expressed by the product of three parameters; the effect of the mineral addition, the effect of the superplasticizer and the effect of their interaction. The correlation coefficients found are close to unity and well justify the appropriateness of this choice. The application of this new relationship to other results found by other researchers has high satisfaction with satisfactory results and correlation coefficients ranging from 0.9 to 0.98

This thesis describes research carried out to investigate techniques for (i) rapidly assessing the reactivity of fly ash; and (ii) evaluating its interaction with air-entraining admixtures (AEAs), both with regard to use in concrete. The materials considered for the project included, 54 fly ashes from 8 UK sources, and an additional three materials from Bangladesh, covering a range of fineness, loss-on-ignition (LOI) and production conditions (run-of-station, carbon removed, air-classified, co-combustion, oxy-fuel technology); Portland Cements (PCs) from five UK sources with various properties (strength classes 32.5 R, 42.5 N and 52.5 N); laboratory grade hydrated and quick limes; and three commercial AEAs and a standard laboratory grade reagent (surfactant). The research examining fly ash reactivity considered activity index tests to BS EN 450 (BSI, 2005c) as the reference and investigated tests covering fly ash properties/providing measures of fly ash behaviour to rapidly assess this. These included (i) fly ash fineness (45 µm sieve residue, or LASER particle size distribution (PSD) parameters), LOI and flow properties; (ii) accelerated curing of PC and lime-based mortars (iii) lime consumption by fly ash when combined with PC in paste or suspension (Frattini) or from a saturated lime solution; (iv) various measures of fly ash chemical composition (based on oxide/mineralogical analysis); and (v) a quicklime slaking test. The test results were validated by strength tests with 100 mm concrete cube. Results of the above indicated good correlations between fly ash fineness, mortar flow/water requirement and (pozzolanic) activity index (standard or accelerated curing). However, fly ash reactivity and fresh properties appeared to be influenced by the properties of the test PC (e.g. chemical composition and fineness) and there is a need to take this into account during assessment. Generally, finer fly ashes gave better flow; however, there is an optimum fineness (d90 ~40 µm) for best performance, and which is similar to the fineness of the test PC. Strong correlations between the accelerated and standard cured PC-based mortar indicate the latter can be used to estimate the former taking account of the fly ash properties. In view of eliminating the effect of PC properties on reactivity, mortar tests with laboratory grade hydrated lime suggested potential for this. However, for better assessment, this approach requires further work to address issues relating to slower rates of strength gain and increased time requirements, although high temperature conditions were used for curing. Measuring Ca(OH)2 consumption from fly ash/PC paste or suspension agreed with the behaviour in mortar, but needs special instruments (e.g. TGA or XRF). A similar approach with saturated lime did not work well, despite several measures being taken to try and improve this. The oxide and mineralogical analysis results of fly ash did not give good correlations with activity index, but improved when a factor combining them with fineness was considered. The test results were validated in concrete and with air-classified fly ashes from single sources which gave clear trend/behaviour. The lime slaking test was found to be ineffective for identifying fly ash reactivity. The reactivity assessment results were validated by carrying out concrete strength tests. In general, more consistent trends were obtained for fly ash from single source as noted with mortar earlier. Methods adopted/developed to assess the interaction of fly ash with AEA included (i) the foam index test; (ii) acid blue 80 (AB80) dye adsorption test (spectroscopic method); and (iii) methylene blue test. High variability in foam index test results between different operators were noted, which reflected differences in the degree of shaking applied and difficulties in identification of the test end point. Adoption of an automatic shaker and determination of suitable test conditions reduced this by more than 50%. Reliable test procedures were also established for the AB80 dye adsorption method. The results obtained from these tests gave very good correlations with fly ash specific surface area and the AEA dose required (both with commercial AEAs and standard reagent) for achieving target air contents in mortar and concrete. The methylene blue dye test also gave good correlations with these parameters, but was less effective for low LOI fly ashes. Between laboratory tests were carried out at three UKQAA members and considered, LOI, fineness (45 µm sieve and LASER PSD), and activity index. The results gave good agreement with those obtained at the Concrete Technology Unit for this work and again emphasized the role of fly ash fineness on its reactivity. Overall, fly ash fineness was found to be the best means of rapidly assessing its reactivity. Some of the other methods considered gave promising behaviour but require further refinements. Therefore, it is suggested that in addition to 45 µm sieve residue, other types of fineness measurement (e.g. sub 10 µm quantities, d50 and d90) can be considered suitable alternatives to activity index. Similarly, foam index tests with the automatic shaker or the AB80 test method could both be used as fly ash physical requirement tests, or in production control for air-entrained concrete.

This thesis deals with the study of cement – concrete coverings. The aim of the thesis is a summary of current knowledge of these constructions. The experimental part of this paper deals with the design of concrete for the lower layer of cement – concrete cover. Emphasis is placed on the elimination of microcracks and to increase the lifetime of these construction.

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This research aims to evaluate the tecniques for disposal of waste obtained from electrical insulators. These pieces are one of the supplies widely used for electric power generation, and become a waste due to their replacement for new ones after maintenance and expansion works, in places like substations, generating units, distribution networks, transmission lines and its own production process. In Brazil, it is possible to acumulate waste from these insulators in courtyards and waste areas, besides wastelands, impairing the environment. Thus, it is known that an alternative for treatment is needed and the lack of knowledge and techical safe forces the development of reasearches about this subject, what are still in the beggining. So, this study proposes the evaluation of potential use of such a porcelain in concrete, through the replacement of conventional aggregates and cement. The research was conducted with a careful characterization of the waste in different maximum dimension sizes, with physicochemical and mineralogical analysis obtained from X-Ray diffration and images from scanning eletronic microscopy, for example. Besides, tests of alkali-aggregate reaction were perfomed in order to assess the chemical stability of the waste in mortar. Regarding to viscoelastic and mechanical properties, the compressive strength, modulus of elasticity, water absorption, and abrasion/erosion were performed. The experimental program considered eleven different mixes of pumped concrete, take into account the following replacement rates: 8% replacement of cement; 50% and 100% replacement of fine aggregate; and 45% and 100% replacement of coarse aggregate. Some mixes were done with both replacement of fine and coarse aggregate. The investigation of mechanical strength, deformation and durability, in conditions aforementioned, demonstrates that concrete with replacement was statistically similar to concrete without any replacement by waste, resulting a suitable concrete with porcelain waste content. The efficiency of compressive strength ranged from 0,087 MPa/kg to 0,107 MPa/kg and the modulus of elasticity reached values up to 38 GPa, indicating expressive results for these properties. Lastly, in research is possible to observe the conclusions about reological characteristics of all concrete and the influence of these replacement on cement content.
A presente pesquisa aborda a temática da destinação do resíduo dos isoladores elétricos proveniente da cadeia geradora de energia elétrica, como as relacionadas às manutenções e ampliações das subestações, unidades geradoras, redes de distribuição, linhas de transmissão e do próprio processo de produção do isolador. No Brasil esta cadeia acumula progressivamente resíduos em pátios e áreas de descarte, e às vezes esses materiais são lançados por terceiros em locais como terrenos baldios, impactando no meio ambiente. Nesse contexto, uma alternativa seria sua utilização para outros fins, os quais, por falta de conhecimento e segurança técnica, ainda se encontram em fases iniciais de estudo. Diante disso, a presente pesquisa propõe a investigação do potencial de uso destas porcelanas no concreto, em substituição aos agregados convencionais e também ao cimento. Para tanto, conduziu-se incialmente uma caracterização minuciosa do resíduo nas suas diversas dimensões, por meio de análises químicas, físicas e mineralógicas utilizando diferentes métodos, como a difração de raios X e imagens por microscópico eletrônico de varredura, por exemplo. Na sequência foram realizados testes para verificar a estabilidade química do resíduo em argamassa para o desencadeamento de reações álcalis-agregado. Em relação à sua incorporação no concreto, foram realizados ensaios para aferição da resistência à compressão, módulo de elasticidade, absorção de água, abrasão e erosão. As análises foram realizadas em onze concretos estruturais bombeáveis com diferentes teores de substituição, que contemplaram adição de 8% em substituição ao cimento, no agregado miúdo com 50% e 100% de substituição, no agregado graúdo com 45% e 100%, e em algumas composições com substituições simultâneas no miúdo e graúdo. De posse dos resultados, foi traçado um perfil de resistência mecânica, deformabilidade e durabilidade que apresentaram para algumas substituições valores estatisticamente iguais ao concreto sem resíduo, tornando factível a utilização do concreto com porcelana. Eficiências para resistência à compressão variando de 0,087 MPa/kg a 0,107 MPa/kg, módulo de elasticidade com valores de até 38 GPa, são números significativos para as propriedades. Análises da reologia do concreto e impactos no consumo de cimento são aspectos também observados e discutidos no decorrer do trabalho.

O desenvolvimento do concreto de alta resistência - CAR foi um importante avanço na tecnologia de concreto, entretanto, a despeito de suas inúmeras vantagens como material estrutural, o seu emprego tem sido limitado, por ter se revelado mais susceptível à fissuração nas primeiras idades. Isto se deve à ocorrência do fenômeno da retração autógena, particularmente mais intenso nestes concretos que nos de resistência normal, uma vez que no CAR, há significativamente maior quantidade de material cimentício e menor quantidade de água, o que dá origem a uma estrutura porosa muito refinada logo nas primeiras idades, gerando altas magnitudes de tensões capilares. Além do estudo sobre o entendimento do fenômeno, as pesquisas atualmente têm buscado formas de mitigá-lo a fim de contribuir para estruturas mais duráveis. Diante do exposto, esta pesquisa investigou o comportamento do CAR, no tocante às propriedades mecânicas, elásticas e viscoelásticas e à durabilidade, quando empregado um aditivo redutor de retração - ARR que pode se configurar como estratégia mitigadora para a redução da retração autógena, bem como verificar a sua influência sobre a microestrutura e hidratação da pasta de cimento. Os resultados indicam que o ARR é eficaz na redução da retração autógena e retração por secagem, sem alterar de forma relevante as propriedades mecânicas e elásticas: a resistência à compressão sofre uma pequena queda de 5% com o uso de 2% de ARR em relação ao concreto referência, contudo, as demais propriedades não são alteradas com o uso do ARR. Quanto ao efeito sobre a fluência, não se obtiveram resultados conclusivos. A durabilidade, medida pelos ensaios de penetrabilidade a íons cloretos, permeabilidade à água, carbonatação natural e absorção capilar e por imersão, não é comprometida com a incorporação do aditivo redutor de retração. Do ponto de vista microestrutural, observou-se que o ARR altera o volume total de poros, embora de uma forma não muito expressiva; e ainda constatou-se que este aditivo afeta a velocidade de hidratação das pastas de cimento, e que possivelmente interage com compostos de hidratados da pasta, sem, no entanto, alterar as características macroestruturais do material.
The development of high strength concrete - HSC represented an important advance in concrete technology. However, even knowing that this kind of concrete has several advantages as a structural material, its application is limited by the early ages cracking. This occurrence is due to the autogenous shrinkage phenomenon, once HSC has a greater amount of cementitious material and a lower amount of water in relation to a normal-strength concrete. This condition implies in a greatly refinement of pore structure at early ages which lead to a higher magnitudes of capillary tension than the one observed in a normal-strength concrete. Beyond to study the phenomenon, much research has been conducted in many countries in order to reduce autogenous shrinkage and contribute to more durable structures. So, this research aims to investigate the effectiveness of shrinkage-reducing admixtures – SRA in decreasing the autogenous shrinkage of HSC, and mainly, verify its influence on viscoelastic, elastic and mechanicals properties and durability. The effect of SRA on microstructure and on the cement paste hydration was also investigated. The results show that SRA is effective in reducing the autogenous shrinkage and drying shrinkage without remarkable changes in elastic and mechanical properties. There were not conclusive results related to the creep property. The concrete durability under the action of aggressive agents (such as water, CO2 and chloride) was not influenced by the SRA, information provided by the results of chloride penetration, natural carbonation, water permeability, capillary absorption and absorption of water tests. In a microstructural point of view, it was observed that the addition of SRA results in a small rise in total pore volume. Besides, the results suggest that the SRA affects the rate of cement hydration and it can interact to the hydrated products of paste without implying in great influences on the macrostructural characteristics of the material.

La préservation des ressources naturelles et la limitation des émissions de CO2 sont une contribution au développement durable. Dans le cadre de la conception du béton, cette contribution consiste à utiliser des granulats locaux ou recyclés. Cependant, ces derniers peuvent être poreux et de faible qualité. La communauté scientifique est d'accord sur le fait que la porosité intrinsèque des granulats modifie les propriétés de transport du béton, mais dans quelle mesure reste une question. L'objectif de la thèse est d'analyser l'impact de la porosité intrinsèque des granulats grossiers, principalement sur les propriétés de durabilité du béton. Dans une compréhension préliminaire et en vue d'accentuer les phénomènes se produisant dans le béton, un programme expérimental est conçu pour le modèle élémentaire (EM), qui est composé de pâte et de gravier. L'impact de la nature des granulats (poreux et non poreux), de l'état d'humidité et du volume ainsi que de la nature du liant, est analysé sur i) la porosité de l'eau du modèle élémentaire, ii) la structuration de l'interface pâte-granulat. Ensuite, à l'échelle du béton, les matériaux ont été conçus avec le même squelette de granulats (même sable) et la même teneur équivalente en liant. Les conceptions variaient selon la nature des granulats, l'état d'humidité, la nature du liant, la variation du rapport eau/ciment et l'incorporation d'adjuvants chimiques (plastifiant ou superplastifiant). L'impact de la porosité des granulats grossiers sur les propriétés à l'état frais (affaissement, densité apparente et teneur en air emprisonné) et à l'état durci (résistance à la compression, porosité de l'eau, absorption d'eau, perméabilité aux gaz, migration des chlorures, carbonatation accélérée et teneur en portlandite) a été étudié. Les principaux résultats montrent que l'état d'humidité des agrégats et la nature du liant sont les premiers facteurs qui conditionnent la structuration de l'interface pâte/agrégats au sein du modèle élémentaire. La nécessité d'utiliser des agrégats poreux en surface saturée et sèche est particulièrement mise en évidence. À l'échelle du béton, les propriétés à l'état frais sont influencées par la porosité des granulats et le rapport eau/liant (W/B). Cependant, pour un rapport eau/liant fixe correspondant à une consistance fluide, les variations des propriétés à l'état frais mesurées lors de l'incorporation de granulats poreux ne dépendent pas de la nature du liant. Dans le béton durci, la porosité des granulats joue un rôle important dans la porosité de l'eau et la perméabilité à l'air du béton, quelle que soit la nature du liant. Pour les autres propriétés de durabilité (absorption d'eau, migration de Clo, carbonatation et résistance à la compression), la nature du liant l'emporte sur la porosité des granulats
The preservation of natural resources and the limitation of CO2 emissions are a contribution to sustainable development. In the context of the concrete design, this contribution consists in using local or recycled aggregates. However, local or recycled aggregates can be porous and of low quality.The scientific community agrees that the intrinsic porosity of aggregates changes the transport properties of concrete, but to what extent is still a question. The objective of the thesis is to analyze the impact of intrinsic coarse aggregate porosity on mainly the durability properties of concrete. In a preliminary understanding and with a view to accentuating phenomena occurring in the concrete, an experimental program is designed for elementary model (EM), which is composed of paste and gravel. The impact of the aggregate nature (porous and non-porous), moisture state and volume together with the binder nature, is analyzed on i) the water porosity of EM, ii) the structuration of the paste-aggregate interface. Next, at concrete scale, materials were designed with the same skeleton of aggregates (same sand) and the same equivalent binder content. The designs varied by the aggregate nature, moisture state, the binder nature, the variation of water/cement ratio and the incorporation of chemical admixtures (plasticizer or superplasticizer). The impact of coarse aggregate porosity on properties in the fresh state (slump, apparent density and entrapped air content) and in the hardened state (compressive strength, water porosity, water absorption, gas permeability, chloride migration, accelerated carbonation and Portlandite content) was studied. The main results show that the moisture state of aggregate and the binder nature are the first factors that condition the structuring of the paste/aggregate interface within the elementary model. The necessity to use porous aggregates in saturated surface dry is particularly highlighted. At the scale of concrete, the properties in the fresh state are influenced by the aggregate porosity and the water/binder (W/B) ratio. However, for a fixed W/B ratio corresponding to fluid consistency, the variations in the fresh properties measured when porous aggregates are incorporated do not depend on the binder nature. In hardened concrete, porosity of aggregate plays an important role in water porosity and air permeability of concrete whatever the nature of binder. For other durability properties (water absorption, Clo migration, carbonation and compressive strength), the nature of binder overcome leading in comparison to the porosity of aggregate

This diploma thesis focuses on the resistance of concrete to abrasion with regard to the raw materials used for their production. In the theoretical part of the thesis are described admixtures, different types of aggregate and aggregate composition which influence the resistance of concrete to abrasion. In the experimental part, 15 different C30 / 37, S4 concrete formulations were proposed. Different types of aggregates - fecal gravel (Žabčice), biotic granodiorite (Olbramovice) and amphibolite (Želešice) have always been used in the recipes. Fine ground limestone, micro-silica, high-temperature fly ash and finely ground slag were ingredients that were added to the proposed recipes. Consistency was determined by the method of cone seating and the density of fresh concrete. In the hardened state, concrete density, compressive strength, bending tensile strength, tensile strength, watertightness, concrete absorption, and abrasion resistance were determined using the Böhm method and wide wheel method. The test specimens were tested after 7, 28, and 90 days of maturation.

Fresh properties of mortars are important factors in altering the performance of self compacting concrete (SCC). Measurement of the rheological properties of the fine mortar part of concrete is generally used in the mix design of SCC. It can be stated that SCC rheology can be optimized if the fine mortar part of concrete is designed properly. However, measurement of the rheological properties is often impractical due to the need for complex equipment. Therefore, more practical methods of assessing mortar workability are often preferred. In this study, four mineral admixtures, three superplasticizers (SP) and two viscosity modifying admixtures (VMA) were used to prepare self compacting mortar (SCM). The mineral admixtures included fly-ash, brick powder, limestone powder, and kaolinite. Two of the SPs were polycarboxylate based and another one was melamine formaldehyde based. One of the viscosity modifying admixtures was based on an aqueous dispersion of microscopic silica and the other one was based on high molecular weight hydroxylated polymer. Within the scope of the experimental program, 43 mixes of SCM were prepared from different materials with keeping the amount of mixing water constant. Workability of the fresh mortar were determined using V - funnel and slump flow tests. The setting time of the mortars, were also determined. The hardened properties that were determined included the ultrasonic pulse velocity (UPV) and the strength which was determined at 7, 28, and 56 days. It was concluded that among the mineral admixtures used, only fly-ash and limestone powder increased the workability of the mixes. The two polycarboxylate based SPs yield approximately the same workability and the melamine formaldehyde based SP was not as effective as the other two.

This diploma thesis deals with the study of high-strength, high-volume fly ash concrete. The theoretical part of this thesis focuses on the detailed characteristic and main principles of high-strength concrete, high-volume fly ash concrete. In addition, according to the findings, the technology of high-strength and high-volume fly ash concrete, including principles of high strength, has been described. On the basis of the findings, high-strength, high-volume fly ash concrete for specific compressive strengths has been designed and created in the experimental section. These concretes were then subjected to a number of tests.

This dissertation presents a literature review of the state-of-practice for the use of IC in concrete mixtures and how structural engineers and construction engineers can adapt IC to their present and future work. Current high early strength concrete mixtures have natural cracking and shrinkage problems due to the high content of cementitious material or their chemical components. Using IC allows for early strength, enhanced durability, reduced shrinkage and a better curing by providing water that can be absorbed by the cement past after the final set. Rapid hydration and high early strength Portland cement and calcium sulfoaluminate (CSA) concretes are commonly used as pavement repair media. The fresh properties (slump, setting time), mechanical properties (elastic modulus, compressive and tensile strength), and volume stability (autogenous shrinkage, drying shrinkage, restrained ring shrinkage, and creep) of rapid repair media were evaluated with and without internal curing with saturated lightweight aggregate. Significant improvements in volume stability were also noted. Results indicate that internal curing can successfully improve volume stability and mitigate restrained shrinkage cracking in rapid repair media without compromising fresh properties or ultimate mechanical strength. Maturity was observed for CSA mixtures and exhibited a correlation with compressive strength development which could be beneficial for rapid repair media on the field.

U disertaciji su prikazani rezultati sopstvenog eksperimentalnog istraživanja na osnovu kojih je izvršena komparativna analiza uticaja različitih vrsta lakih agregata i vrste i količine cementa na osnovna fizičko-mehanička svojstva lakoagregatnih betona. Takođe, analizirana je i mogućnost zamene dela cementa mineralnim dodacima u cilju smanjenja negativnih uticaja proizvodnje betona na životnu sredinu. Rezultati su pokazali da je primenom svih analiziranih vrsta agregata moguće dobiti konstrukcijski lakoagregatni beton, čak i sa manjim količinama cementa, odnosno sa zamenom dela cementa mineralnim dodacima, kao i da je moguće uspostaviti pouzdane korelacione veze između pojedinih svojstava betona i primenjenih komponentnih materijala.
In dissertation are presented results of own experimental research of acomparative analysis of the impact of different types of lightweightaggregates and the type and quantity of cement on basic physical andmechanical properties of structural lightweight concrete. Also, the possibilityof replacing part of cement with mineral admixtures is analyzed in order toreduce the negative impact of concrete production on the environment. Theresults showed that it is possible to obtain structural lightweight aggregateconcrete with all types of lightweight aggregates and even with lowerquantities of cement or with a replacement of part of a cement with mineraladmixtures. Also, it is possible to establish a reliable correlation betweencertain properties of concrete and used component materials.

Estruturas de concreto mais arrojadas têm sido executadas ao longo das últimas décadas, utilizando-se de projetos e técnicas construtivas cada vez mais avançadas, às quais, por sua vez, procuram manter a qualidade na execução da obra e proporcionar maior durabilidade e rapidez na entrega do empreendimento. Dentro deste contexto evolutivo, também se enquadra a tecnologia do concreto, incluindo o estudo dos efeitos de seus materiais constituintes (agregados, aglomerantes, aditivos, adições, etc) sobre as mais diversas propriedades do concreto. Frente a este desafio, a tese se propõe a contribuir de maneira planejada na avaliação de como algumas adições minerais e os aditivos plastificantes podem afetar as propriedades do concreto, com ênfase dada à fluência nas primeiras idades de início de carregamento. A fluência além de ser de difícil obtenção de resultados em laboratório é uma propriedade que possui sua complexidade associada às diversas variáveis intervenientes no fenômeno e ainda ao seu mecanismo de atuação, o qual não é totalmente compreendido. A atual bibliografia sobre o assunto tem se mostrado incipiente e algumas vezes contraditória nos trabalhos disponíveis, principalmente quando se refere aos efeitos na fluência nas primeiras idades, apesar dos esforços depreendidos por pesquisadores consagrados desde a década de 30 do século passado. Assim, surgiu a necessidade de se delimitar a pesquisa a partir de um programa experimental capaz de avaliar, mesmo que ainda restrito a uma amostra de materiais e dosagem limitada, mas que permita uma visão geral de como as adições e os aditivos interagem no comportamento da fluência. O programa experimental compreenderá basicamente na avaliação matricial das possíveis combinações das adições minerais: metacaulim, escória de alto-forno e argila calcinada, associadas aos aditivos plastificantes, base lignossulfonato e naftaleno, sobre a fluência do concreto nas idades iniciais de carregamento de 1, 3 e 7 dias, e ainda sobre outras propriedades mecânicas, elásticas e térmicas, também nas idades de 14 e 28 dias. Os resultados demonstram que tanto as adições minerais estudadas como os aditivos plastificantes e suas combinações, avaliados por meio da análise estatística de variância, interferem decisivamente no comportamento da fluência, mesmo mantendo o proporcionamento dos materiais inalterados em relação à referência. A idéia é de que esta pesquisa contribua para a atualização dos padrões normativos atuais sobre o assunto, e que estimule futuras pesquisas para detalhar o efeito de outras adições e aditivos químicos sobre a fluência e também sobre uma série de traços de concreto e condições além das abordadas nesta tese.
Bolder concrete structures have been performed in the past decade. They use increasingly advanced building projects and techniques which, in turn, aim at keeping work quality and providing higher durability and quicker project completion. Concrete technology also has a role this evolutionary setting. It studies the effects of its component materials (aggregates, binders, chemical and mineral admixtures, etc.) on various concrete properties. In face of this challenge, this thesis aims at contributing to a planned assessment of how some mineral and chemical admixtures can affect concrete properties, mainly regarding creep at early ages at loading. Besides being difficult to assess through laboratorial testing, creep is a property whose complexity is associated to several intervening variables and to its working mechanisms, which are not fully understood. The current relevant literature has shown to be incipient and sometimes contradictory concerning the available studies, mainly those referring to the effects of creep at early ages, despite the efforts renowned researchers have made since the 1930s. This explains the need of limiting the investigations to an experimental program which is able to assess, even if restricted to a sample of materials and limited mix proportion, but also allow an overview of how mineral and chemical admixtures interact creep behavior. For assessing the possible mineral admixture combinations, this experimental program will comprise basically: metakaolin, blast furnace slag, and calcined clay associated to lignosulfonate and naphthalene-based admixtures on concrete creep at ages of loading 1, 3, and 7 days, as well as on other mechanical, elastic, and thermal properties, at ages 14 and 28 days. The results show that both mineral and chemical admixtures and their combinations, assessed in this study through statistical analysis of variance, significantly interfere in creep behavior, even though material proportion remains unchanged compared to the reference concrete mix. The idea is that this research can contribute to update the current standards in this field, and stimulate future studies detailing the effect of other mineral and chemical admixtures on creep and also on other concrete mixes and conditions that have not been approached in this study.

Etude des betons avec resistance a la rupture en compression simple entre 30 et 130 mpa a 28 jours, realises par introduction de fumee de silice condensee et de fluidifiant. Dosage optimal de la fumee de silice (autour de 10% du poids du liant); variation des proprietes mecaniques, plus forte pour la resistance a la compression, avec fragilisation. Influence du fluidifiant sur la faible resistance a la compression aux jeunes ages et sur le retrait (moindre retrait avec la fumee de silice qu'avec les betons classiques d'egale resistance, fortement doses en ciment et/ou fluidifiant)

Corrosion of reinforcing steel in concrete exposed to chloride-laden environments is a well-known and documented phenomenon. The need for cost effective systems for protection against corrosion has become increasingly clear since the first observations of severe corrosion damage to interstate bridges in the 1960's. As one potential solution to the mounting problem of corrosion deterioration of structures, corrosion-inhibiting admixtures have been researched and introduced into service. This report conveys the results of a three-part laboratory study of corrosion inhibiting admixtures in concrete. The commercial corrosion inhibiting admixtures for concrete have been analyzed by three evaluation methods, including: * Conventional concrete corrosion cell prisms under ponding, * Black steel reinforcing bars immersed in simulated concrete pore solutions, * Electrochemical screening tests of special carbon steel specimens in electrochemical corrosion cells containing filtered cement slurry solution. The purposes of the study include: * Determining the influence of a series of commercially available corrosion inhibiting admixtures on general concrete handling, performance and durability properties not related to corrosion. * Determining the effectiveness of corrosion inhibiting admixtures for reduction or prevention of corrosion of reinforcing steel in concrete, relative to untreated systems, under laboratory conditions. * Conducting a short-term pore solution immersion test for inhibitor performance and relating the results to those of the more conventional long-term corrosion monitoring techniques that employ admixtures in reinforced concrete prisms. * Determining whether instantaneous electrochemical techniques can be applied in screening potential inhibitor admixtures. Concrete properties under test included air content, slump, heat of hydration, compressive strength, and electrical indication of chloride permeability. Monitoring of concrete prism specimens included macro-cell corrosion current, mixed-cell corrosion activity as indicated by linear polarization, and ancillary temperature, relative humidity, and chloride concentration documentation. Simulated pore solution specimens were analyzed on the basis of weight loss and surface area corroded as a function of chloride exposure. Electrochemical screening involved polarization resistance of steel in solution. Results include corrosion potential, polarization resistance and corrosion current density.
Master of Science

Etude en vue de la realisation de murs legers, isolants, homogenes, l'anisotropie de structure pouvant augmenter la resistance vertical et diminuer la conductivite horizontale. Etude de l'effect d'un siliceux, poudre d'aluminium et eau, autoclave a 175**(o)c. Les resultats s'expliquent par la structure dissymetrique vis-a-vis de l'eau des molecules proteiques, hydrophobes d'un cote et hydrofuges de l'autre

Esta tesis tiene un enfoque cuantitativo, la cual propone evaluar la influencia de la permeabilidad en diseños de concreto con el uso de aditivos Sika WT – 100 y Sika WT – 200 en obras hidráulicas de Lima Metropolitana, debido a que estas estructuras almacenan y/o conducen grandes volúmenes de agua a una velocidad determinada, y éstas al tener contacto con el agua reducen su vida útil. Los objetivos de esta tesis son determinar la profundidad de penetración de agua bajo presión bajo la Norma Europea EN 12390 – 8 y la resistencia a la compresión bajo la Norma Técnica Peruana NTP 339.034; para finalmente, determinar la permeabilidad para diseños de concreto bajo la Norma Técnica Colombiana NTC 4483. Para lograr los objetivos mencionados, se diseñó y elaboró 144 probetas cilíndricas de concreto de 10 cm de diámetro y 20 cm de altura y 48 probetas cilíndricas de concreto de 15 cm de diámetro y de altura, de las cuales fueron 64 probetas de concreto patrón (sin uso de ningún aditivo), 64 probetas de concreto con aplicación de 2% de aditivo Sika WT – 100; y 64 probetas de concreto con aplicación de 1% de aditivo Sika WT – 200. Los resultados de los diseños de concreto patrón, WT – 100 y WT – 200 con una relación agua/cemento de 0.40, con respecto a la profundidad de penetración de agua bajo presión, fueron 40, 30 y 15 mm, respectivamente. Los resultados de los diseños de concreto patrón, WT – 100 y WT – 200, con respecto a la resistencia a la compresión a los 28 días con una relación agua/cemento de 0.40, fueron 637, 621 y 632 kg/cm2, respectivamente. Según la Norma Técnica Colombiana NTC 4483 y con los resultados obtenidos, se concluye que el diseño de concreto patrón y el diseño de concreto WT – 100 alcanzan una media permeabilidad y que el diseño de concreto WT – 200 alcanza una baja permeabilidad, con una relación agua/cemento de 0.40. This thesis has a quantitative focus, that propose to evaluate the influence of permeability concrete designs with the use of admixtures Sika WT – 100 and Sika WT – 200 in Metropolitan Lima waterworks, because these structures store and lead large volumes of water at a certain speed, and when these has contact with water reduces their useful life. The objectives of this thesis are to determine the depth of penetration of water under pressure under the European Norm EN 12390-8 and compressive strength under the Peruvian Technical Norm NTP 339.034; finally, determine the permeability of concrete designs under the Colombian Technical Norm NTC 4483. To achieve these objectives, we designed and developed 144 cylindrical concrete specimens 10 cm in diameter and 20 cm high and 48 cylindrical concrete specimens 15 cm in diameter and height, which were 64 concrete specimens pattern (without use of any admixture) concrete specimens 64 with application of 2% admixture Sika WT - 100; and 64 concrete specimens with application of 1% admixture Sika WT - 200. The results of pattern, WT – 100 and WT - 200 concrete designs with a water – cement ratio of 0.40, with respect to the depth of penetration of water under pressure, were 40, 30 and 15 mm, respectively. The results of pattern, WT – 100 and WT - 200 concrete designs with a water – cement ratio of 0.40, with respect to compressive strength at 28 days, were 637, 621 and 632 kg/cm2, respectively. According to the Colombian Technical Norm NTC 4483 and the obtained results, one can conclude that the pattern concrete design and WT - 100 concrete design reach a medium permeability and concrete design WT - 200 reaches a high permeability, with a water – cement ratio of 0.40.

Cement replacement materials are by-products used to produce high performance concrete. Published data on the effects of combinations of mineral admixtures in concrete on the microstructural and performance-related properties under different curing regimes are comparatively little. Further the correlation of strength of concrete to its permeability and pore structure is also not clear. The main objective of this research is to study the performance of various combinations of fly ash/silica fume and slag/silica fume concretes under three different curing regimes, viz. continuous moist curing, no moist curing after demolding and air drying after 7-days of initial moist curing. Six different concrete mixes were prepared with ordinary portland cement and a blend of portland cement and combinations of fly ash+silica fume and slag+silica fume The water-to-cementitious materials ratio of all the concrete mixtures was kept constant at 0.45. The properties investigated included workability of the fresh concrete, engineering properties such as cube and modified cube compressive strength, flexural strength, dynamic modulus of elasticity, pulse velocity, shrinkage and swelling, permeability and microstructural properties such as porosity and pore size distribution. The results show that prolonged dry curing results in lower strengths, higher porosity, coarser pore structure and more permeable concretes. It was found that the loss in early age compressive strength due to incorporation of fly ash or slag can be compensated for by the addition of small amounts of silica fume. The engineering and microstructural properties and permeability of concretes containing fly ash or slag appear to be more sensitive to poor curing than the control concrete, with the sensitivity increasing with increasing amounts of fly ash or slag in the mixtures. The incorporation of high volumes of slag in the concrete mixtures refined the pore structure and produced concretes with very low porosity and threshold diameters. The results emphasize that a minimum 7-day wet curing is needed for concrete with mineral admixtures to develop the full potential, and that continued exposure to a drying environment can have adverse effects on the long-term durability of inadequately cured slag or fly ash concretes. The results also confirm that compressive strength alone is not an adequate index to judge the performance of concrete, and the knowledge of the strength, pore structure and permeability are required for this purpose. Slag/silica fume concrete mixtures showed better performance than fly ash/silica fume concrete mixtures as regards the development of engineering and microstructural properties.

Los materiales autosanables son materiales con la capacidad de reparar sus daños de forma autónoma o con ayuda mínima de estímulos externos. En el campo de la construcción, el desarrollo de elementos autosanables aumentará la durabilidad de las estructuras y reducirá las acciones de mantenimiento y reparación. Los elementos de hormigón armado presentan frecuentemente pequeñas fisuras (< 0.3 mm), no relevantes mecánicamente, pero que pueden suponer un punto de entrada para agentes agresivos. El hormigón tiene una cierta capacidad de autosanación, capaz de cerrar pequeñas fisuras, producida principalmente por la hidratación continuada y la carbonatación. Estudios recientes han intentado mejorar dicha capacidad y diseñar productos específicos para conseguirla. Estos productos incluyen, entre otros, aditivos cristalinos, agentes micro o macroencapsulados, e incluso el uso de bacterias. Los aditivos cristalinos (CA) son un tipo de aditivo para hormigón que se considera que aporta propiedades de autosanación. No obstante, la falta de conocimiento sobre su comportamiento limita su uso. Además, los métodos para evaluar la autosanación en hormigones no están estandarizados todavía. Esto complica la realización de un análisis crítico de los diferentes productos y métodos de evaluación propuestos en la literatura. Para responder a esta falta de conocimiento, los objetivos de esta tesis son: 1) estudiar y proponer procedimientos experimentales para evaluar los fenómenos de autosanación en hormigón y, 2) evaluar experimentalmente las mejoras producidas al introducir aditivos cristalinos. Esta tesis incluye como ensayos para la determinación de la autosanación: la evaluación del cierre de fisuras, la permeabilidad al agua, flexión a tres puntos y absorción capilar. Además, se han realizado varias campañas experimentales para validar los ensayos propuestos. Posteriormente, estos ensayos se han utilizado para analizar la influencia de varios parámetros, incluyendo entre otros: presencia de aditivos cristalinos, nivel de daño, tiempo necesario para el sanado, composición del hormigón y condiciones de sanado. Finalmente, se analizan los efectos producidos al añadir aditivos cristalinos en hormigón en la fluidez, resistencia e hidratación. Los resultados muestran que el cierre de fisuras es un ensayo eficaz y sencillo para evaluar la autosanación. Sin embargo, la orientación de la fisura durante el sanado ha resultado ser de gran importancia, y no considerar este aspecto puede llevar a conclusiones engañosas. El ensayo de permeabilidad al agua propuesto en este trabajo presenta una buena estabilidad y es fácil de implementar en laboratorios. Además, las relaciones obtenidas entre los parámetros de fisura y la permeabilidad del agua han confirmado la relación cúbica indicada en la literatura. Este trabajo muestra que analizar la eficiencia de autosanado mediante el cierre de fisuras puede llevar a una sobreestimación de la capacidad de sanación, comparada con los resultados obtenidos mediante permeabilidad. Los ensayos de sorptividad resultaron fáciles de implementar, sin embargo, los resultados obtenidos mostraron una alta dispersión y sensibilidad a las variaciones en las fisuras producidas durante el proceso de prefisuración. En cuanto a la evaluación de la recuperación mecánica, los resultados muestran que la evolución de las propiedades del hormigón con el tiempo es un parámetro que debe considerarse, especialmente en fisuras de edades tempranas. En este trabajo se ha obtenido que los aditivos cristalinos potencian las reacciones de autosanación, pero tienen una capacidad limitada. La proximidad de los CA a la industria es un punto positivo para su inclusión como un nuevo tipo de aditivo de hormigón. Sin embargo, los resultados obtenidos en esta tesis indican que se necesitan más análisis para determinar sus efectos completos en hormigón, especialmente con respect
Self-healing materials are materials with the capability to repair their damage autonomously or with minimal help from an external stimulus. In the construction field, the development of self-healing elements will increase the durability of structures and reduce their maintenance and repair actions. Reinforced concrete elements frequently suffer small cracks (< 0.3 mm), not relevant mechanically, but they can be an entrance point for aggressive agents. Concrete has a natural self-healing capability able to seal small cracks, produced by the continuing hydration and carbonation processes. Recent studies have attempted to improve that healing capability and to design specific products to achieve it. These products include, among others: crystalline admixtures, micro- or macro-encapsulated agents, and even the use of bacteria. Crystalline admixtures (CA) are a concrete admixture that is claimed to provide self-healing properties. However, the lack of knowledge on their behavior and self-healing properties limits their usage. In addition, the methods to evaluate the self-healing capability of mortar and concrete are not standardized yet. This complicates the performance of a critical analysis of the different self-healing products and evaluation methods found in the literature. In order to answer to this lack of knowledge, the objectives of this thesis are: 1) to study and propose experimental procedures in order to evaluate self-healing in concrete and, 2) to evaluate experimentally the self-healing enhancements produced when introducing crystalline admixtures. This thesis includes the following tests for the determination of the self-healing: the evaluation of crack closing, water permeability, three point bending tests and capillary absorption test. In addition, several experimental campaigns have been performed with the objective of validating the proposed tests. Afterwards, these methods have been used to analyze the influence of several parameters, including among others: the presence of crystalline admixtures, the damage extent, healing time needed, concrete composition and healing conditions. Finally, the effects that crystalline admixtures produce in concrete are analyzed in terms of slump, strength and hydration. The results show that crack closing is an effective and simple method to evaluate self-healing. However, the orientation of the crack during healing is of great importance, and disregarding this aspect may lead to misleading conclusions. The water permeability method proposed in this work has good stability and it is easy to implement in concrete laboratories. Moreover, the relations obtained between crack parameters and water permeability confirmed the cubic relation, as reported in the literature. This work shows that analyzing healing efficiency by means of crack closing tends to overestimate self-healing if compared with the results obtained by means of water permeability. Sorptivity analysis tests were easy to implement, however, the results obtained in this work showed high dispersion and sensitivity to the variations of the cracks introduced during the precracking process. Regarding the evaluation of mechanical recoveries, the results show that the evolution of concrete properties with time is a parameter of importance that, therefore, should be considered, especially for early age cracks. In this work, crystalline admixtures have been reported as an enhancer of self-healing reactions, but with a limited capacity of enhancement. The proximity of CA to the industry is a positive point to their inclusion as a new type of admixture for concrete. However, the results obtained in this thesis indicate further analyses are needed to determine their full effects on concrete, especially regarding self-healing.
Els materials autosanables són materials amb la capacitat de reparar els seus danys de forma autònoma o amb ajuda mínima d'estímuls externs. En el camp de la construcció, el desenvolupament d'elements autosanables augmentarà la durabilitat de les estructures i reduirà les accions de manteniment i reparació. Els elements de formigó armat presenten freqüentment fissures menudes (< 0.3 mm), no rellevants des del punt de vista mecànic, però poden suposar un punt d'entrada per a agents agressius. El formigó té una capacitat de autosanació capaç de tancar fissures menudes, produïda principalment per la hidratació continuada i la carbonatació. Estudis recents han intentat millorar eixa capacitat i dissenyar productes específics per aconseguir-la. Aquests productes inclouen, entre d'altres, additius cristal·lins, agents micro- o macroencapsulats, i fins i tot l'ús de bacteris. Els additius cristal·lins (CA) són un tipus d'additiu reductor per formigó que es considera que proporciona propietats de autosanació. No obstant, la manca de coneixement sobre el seu comportament limita el seu ús. A més, els mètodes per avaluar la autosanació de formigons encara no estan estandarditzats. Açò complica la realització d'una anàlisi crítica dels diferents productes i mètodes d'avaluació proposats a la literatura. Per respondre a aquesta manca de coneixement, els objectius d'aquesta tesi són: 1) estudiar i proposar procediments experimentals per avaluar els fenòmens d'autosanació en formigó i, 2) avaluar experimentalment les millores produïdes en introduir additius cristal·lins. Aquesta tesi inclou com assajos per a la determinació de l'autosanació: l'avaluació del tancament de fissures, la permeabilitat a l'aigua, flexió a tres punts i absorció capil·lar. A més, s'han realitzat diverses campanyes experimentals per validar els assajos proposats. Posteriorment, aquests assajos s'han utilitzat per analitzar la influència de diversos paràmetres: presència d'additius cristal·lins, nivell de dany, temps necessari per a la sanació, composició del formigó i condicions de sanació. Finalment, s'analitzen els efectes produïts en afegir additius cristal·lins en formigó en fluïdesa, resistència i hidratació. Els resultats mostren que el tancament de fissures és un assaig eficaç i senzill per avaluar l'autosanació. No obstant això, l'orientació de la fissura durant la sanació ha resultat ser de gran importància, i no considerar aquest aspecte pot portar a conclusions enganyoses. L'assaig de permeabilitat a l'aigua proposat presenta una bona estabilitat i és fàcil d'implementar en laboratoris. A més, les relacions obtingudes entre els paràmetres de fissura i la permeabilitat a l'aigua han confirmat la relació cúbica de la literatura. Aquest treball mostra que analitzar l'eficiència de l'autosanació amb el tancament de fissures pot sobreestimar la capacitat de sanació, comparada amb els resultats obtinguts-dues mitjançant permeabilitat a l'aigua. Els assajos de sorptivitat van resultar fàcils d'implementar, però, els resultats obtinguts en aquest treball van mostrar una alta dispersió i sensibilitat a les variacions en les fissures produïdes durant el procés de prefissuració. Pel que fa a l'avaluació de la recuperació mecànica, els resultats mostren que l'evolució de les propietats del formigó amb el temps és un paràmetre d'importància que, per tant, s'ha de considerar, especialment per fissures primerenques. En aquest treball s'ha obtingut que els additius cristal·lins potencien les reaccions d'autosanació, però tenen una capacitat limitada. La proximitat dels CA a la indústria és un punt positiu per a la seva inclusió com un nou tipus d'additiu de formigó. Tanmateix, els resultats obtinguts en aquesta tesi indiquen que calen més anàlisis per determinar els seus efectes complets en formigó, especialment pel que fa a l'autosanació.
Roig Flores, M. (2018). Self-healing concrete: efficiency evaluation and enhancement with crystalline admixtures [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/100082
TESIS

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Increasing the durability of concrete structural elements is primordial, especially those related to power generation in eolic areas that are subjected to the phenomenon of reinforcement corrosion. In this context, this study aims to evaluate the overall protection ability of concrete to the phenomenon of reinforcement corrosion induced by chlorides. To this end, it was adopted a statistical program based on a fractional factorial design in which the variables studied were as follows: the water-binder ratio (0.35, 0.45 and 0.55), the type of mineral admixture (silica fume and blast furnace slag at specific levels), the type of corrosion inhibitor (calcium nitrite, sodium nitrite and amine) and the level of corrosion inhibitor (minimum and maximum recommended by each manufacturer). In the concrete investigations, the tests performed were corrosion potential, polarization resistance and electrochemical impedance. Throughout the experiments, it was possible to testify the beneficial effect of reducing the water-binder ratio. It was also possible to prove the very positive effect of the incorporation of mineral admixtures, especially of silica fume. The satisfactory performance of various inhibitors evaluated was also verified, specially when concrete contains mineral admixtures. A parallel study was conducted to make a comparative analysis of inhibitors at the same range of concentrations (at solid levels of 0.76%, 2.21% and 3.66% of the compound on the cement mass), nevertheless this study have demonstrated that fixing contents for all inhibitor is not appropriated, and the recommended dosages by the manufacturer is the best condition. As the levels recommended by manufacturers, it was found that the higher percentages have not worked well for sodium nitrite otherwise, for amine and nitrite calcium, the higher levels implied better results. Regarding the tannin inhibitor also assessed in the parallel study mentioned above (related to specific inhibitors), its good performance related to corrosion inhibition happened just for the content of 0.76% (the lowest levels). For the other contents, it was verified anomalous results. These results demonstrated that each type of corrosion inhibitor has its optimal concentration for use in concrete. Based on a cost-benefit analysis and evaluating the increase in the concrete value for cubic meter (in R$) in the presence of inhibitors at the same contents, it was verified a relative parity prices among the tested nitrites and an extremely high cost of amine. However, when performing the same analysis but using the levels recommended by the manufacturers for each inhibitor independent, it was found that the large disparity in prices between nitrite and amine was reduced considerably. An assessment of technical and economic feasibility was also performed based on the efficiency of corrosion inhibition and cost per cubic meter of concrete mixtures that did not show a typical depassivation of their stell bar up to the attack age evaluated
O aumento da durabilidade é um aspecto primordial para os elementos estruturais de concreto, em especial aqueles constituintes das estruturas de geração de energia em parques eólicos, sujeitos ao fenômeno de corrosão das armaduras. Nesse contexto, este trabalho tem como objetivo geral avaliar a capacidade de proteção de diferentes concretoS frente ao fenômeno da corrosão da armadura induzida por cloretos. Para tanto, foi adotado um planejamento estatístico baseado em um modelo fatorial fracionado em que as variáveis estudadas foram: a relação água/aglomerante (0,35; 0,45 e 0,55), o tipo de adição mineral (sílica ativa e escória de alto-forno, em teores específicos), o tipo de inibidor de corrosão (nitrito de cálcio, nitrito de sódio e amina) e o teor de inibidor de corrosão (mínimo e máximo recomendado por cada fabricante). Na avaliação dos concretos, foram realizados ensaios de potencial de corrosão, resistência de polarização e impedância eletroquímica. Ao longo de todo experimento foi possível constatar o efeito benéfico da redução da relação a/agl. Também foi possível verificar o efeito extremamente positivo da incorporação das adições minerais, em especial da sílica ativa. Constatou-se também o efeito positivo dos diversos inibidores avaliados, em seus teores mínimo e máximo, beneficio que se mostrou mais pronunciado quando da utilização conjunta com as adições minerais. Um estudo paralelo foi realizado para se fazer uma análise comparativa dos inibidores dentro da mesma faixa de teores empregados (teores de 0,76%; 2,21% e 3,66% de sólidos do aditivo em relação à massa de cimento), no qual se verificou que a utilização desses teores fixos para os diferentes tipos de inibidores não se mostrou tão eficiente quanto em relação à utilização dos aditivos na dosagem de recomendação do fabricante. Quanto a estes teores (recomendados pelos fabricantes), verificou-se que os percentuais mais altos não funcionaram bem para o nitrito de sódio, ao passo que para a amina e para o nitrito de cálcio os teores mais elevados resultaram em melhores resultados. Em relação ao tanino, inibidor que também foi avaliado no estudo paralelo referido anteriormente (específico sobre os inibidores), só houve algum resultado de inibição de corrosão para o teor de 0,76% (mais baixo dos teores), tendo-se obtido resultados anômalos para os outros 2 teores mais altos. Tais resultados permitiram constatar que cada tipo de inibidor de corrosão possui sua concentração ótima de utilização no concreto. Fazendo-se uma análise de custo e avaliando-se o acréscimo em Reais no valor do m3 do concreto proporcionado pelos diversos aditivos inibidores e nos teores de mesma faixa de emprego, verificou-se uma relativa paridade de preços entre os nitritos e um elevadíssimo custo da amina. No entanto, ao se realizar a mesma análise, mas utilizando os teores recomendados pelos fabricantes de cada inibidor, verificou-se que a grande disparidade de preços entre os nitritos e a amina foi reduzida de forma considerável. Uma avaliação da viabilidade técnico-econômica dos concretos também foi realizada, a partir dos dados de eficiência de inibição à corrosão e custo/m3 das misturas que não apresentaram comportamento típico de despassivação de suas armaduras até a idade de ataque considerada

Concrete experiences volume changes throughout its service life. When loaded, concrete experiences an instantaneous recoverable elastic deformation and a slow inelastic deformation called creep. Creep of concrete is composed of two components, basic creep, or deformation under load without moisture loss and drying creep, or deformation under drying conditions only. Deformation of concrete in the absence of applied load is often called shrinkage. The deformation due to creep is attributed to the movement of water between the different phases of the concrete. When an external load is applied, it changes the attraction forces between the cement gel particles. This change in the forces causes an imbalance in the attractive and disjoining forces. However, the imbalance is gradually eliminated by the transfer of moisture into the pores in cases of compression, and away from the pores in cases of tension. Designs typically use one of the two code models to estimate creep and shrinkage strain in concrete, ACI 209 model recommended by the American Concrete Institute or the CEB 90 Eurocode 2 model recommended by the Euro-International Committee. The ASSHTO LRFD is based on the ACI 209 model. Three other models are the B3 model, developed by Bazant; the GZ model, developed by Gardner; and the SAK model developed by Sakata. The development of concrete performance specifications that limit the amount of compressive creep of concrete mixtures used by the Virginia Department of Transportation, specifically concrete mixtures used for prestressed members (A-5 Concrete) were assessed, along with determining the accuracy and precision of the creep models presented in the literature. The CEB 90 Eurocode 2 model for creep and shrinkage is the most precise and accurate predictor. The total strain for the VDOT portland cement concrete mixtures discussed in this study were found to be between 1200 ± 110 microstrain at 28 days, and 1600 ± 110 microstrain at 97 days, at a five percent significant level.
Master of Science

L’objectif de cette thèse est d’étudier l’influence de la température sur la thixotropie des bétons autoplaçants (BAP). L’intérêt de ce travail s’inscrit dans la perspective d’optimiser les formulations des BAP dans une large gamme de température. Un plan factoriel composite centré a été adopté dans le but de minimiser le nombre d’essais tout en étudiant les effets des facteurs (température et dosage en agent de viscosité (AV)) et leurs interactions sur les propriétés rhéologiques des BAP.La première phase de l’étude consistait à quantifier la thixotropie du béton juste après le malaxage et durant la période dormante en fonction du dosage en AV à des températures comprises entre 11.3 et 30.7°C selon le protocole proposé par Wallevik sur le rhéomètre BML4. Les résultats ont montré que l’indice de thixotropie présente un minimum respectivement pour un dosage en AV de 0.28 % (par rapport à la masse d’eau) et une température de 24°C. Cependant, ce protocole ne permet pas d’étudier la déstructuration des BAP, facteur recherché par exemple dans les coulages multicouches. Nous avons donc été amenés à retenir un protocole utilisé dans les gels et appelé protocole Dolz. L’application de ce dernier aux pâtes de ciment et aux BAP a permis de mettre en évidence une nouvelle grandeur, le potentiel de déstructuration K. Les valeurs du potentiel K montrent qu’au delà d’un certain dosage en AV et d’une certaine température, apparaissent des phénomènes d’encombrement qui réduisent le potentiel K. Ainsi, le potentiel K apporte des informations complémentaires pour l’aide à la sélection de dosages adéquats du couple superplastifiant – agent de viscosité en fonction de la température de coulage
The aim of this thesis was to study the influence of the temperature on the thixotropy of self-consolidating concrete (SCC). The research significance comes within the perspective to optimize the design of SCC in a wide range temperature. A factorial composite experimental plan was carried out in order to minimize the total number of tests while studying the effects of factors (temperature and dosage of viscosity modifying admixture (VMA)) and their interactions on the rheological properties of SCC. The first phase of the study was to quantify the thixotropy of concrete proportioned with various dosage of VMA at different temperatures ranging from 11.3 to 30.7°C just after mixing and at different time during the dormant period using the protocol proposed by Wallevik in BML4 rheometer. The results indicated that the values of thixotropy index present a minimum respectively with a VMA dosage of 0.28 % (by mass of water) and a temperature of 24°C.On the other hand, this protocol does not allow studying the destructuration of SCC, useful factor needed for example in the multi-layer casting. We therefore had to retain a protocol used in gels and called Dolz protocol. The application of this last to cement pastes and SCC has revealed a new grandeur, the potential of destructuration K. The values of K show that beyond a certain dosage in VMA and a certain temperature, the congestion phenomena appear that reduce the potential K. In this case, the potential of destructuration provides complementary information to assist in the selection of appropriate dosages of couple superlasticizer-VMA whatever the casting temperature may be

Includes bibliographical references.
The deterioration of concrete in South Africa is becoming of major concern to the construction industry. The maintenance of reinforced concrete structures is an extremely expensive exercise and is a continuing necessity. Concrete curing is a practice that is understood to be a necessity within industry, but is often overlooked as a result of time and/or economic constraints. The objective of the study is to ascertain whether or not the implementation of better quality and alternative curing techniques will improve the durability properties of the concrete. Curing is defined as the maintenance of appropriate moisture and temperature conditions to permit the continuation of the hydration or pozzolanic reaction. The objective of curing is to ensure the progress of hydration reactions causing the filling and discontinuity of capillary voids by hydrated compounds in newly placed concrete. Modern curing methods are generally classified as wet or sealing. Wet methods include fogging, sprinkling, ponding, immersion and wet coverings. Sealing methods include plastic coverings and membrane forming curing compounds. Crystallising permeability reducing admixtures may be included in the concrete mix design in order to decrease the penetrability of concrete by decreasing the interconnectivity of the pore structure. Curing methods need to be employed in order to assure specified durability limits are acquired, as durability constraints are implemented in industry. Various methods of curing were tested in order to establish the effect of the techniques on the durability properties of concrete. Samples were placed in water and in winter (Western Cape, South Africa) and simulated summer environments. Various curing techniques were then employed within each of the exposure environments. The curing methods were damp hessian, cling wrap, two curing compounds and two crystallising permeability reducers (PRA's). Samples were also left untreated in each environment as reference samples. Compressive strength, oxygen permeability, water sorptivity, chloride conductivity, bulk diffusion and accelerated carbonation tests were conducted. The results obtained in the study concur with those presented in literature. Prolonged periods of moist curing are significantly beneficial to the compressive strength and durability properties of concrete , however, full water immersion is not a feasible alternative for large or insitu-cast concrete elements. Results of the study show that d amp hessian was the best method to ensure superior durability properties. The sealing of samples with curing compounds in a cool and wet environment (winter) is not recommended, whereas it is marginally beneficial, as was clingwrap, in a hot and dry environment (summer). The crystallising PRA's provided mixed results and were favourable where excess moisture was available and fairly ineffective in dry conditions. The durability properties of concrete are markedly affected by the curing technique implemented .

This dissertation presents the results of a study performed to investigate methods for increasing the damping capacity of concrete. A variety of additives, both particle and latex based, were added to standard concrete mixtures by replacing up to 20% of the fine aggregate to measure their effects on strength, stiffness, damping, and air content. The additives included rubber particles from recycled tires, calcium carbonate particles, styrene butadiene rubber (SBR) latex, and a commercially available product named ConcreDamp which contains vegetable gum suspended in styrene butadiene latex. An initial investigation resulted in the observation that all of the additives with the exception of the SBR latex would both increase air content and decrease compressive strength. As a result, combinations of additives were investigated to see if both the mechanical and dynamic properties could be improved. The addition of steel fibers to mixtures with ground rubber were found to significantly increase air content which offset any gains in compressive strength. The combination of ground rubber and latex was shown to improve both increase compressive strength and reduce air content. The study advanced to investigate the effects of rubber size on air content, strength, and damping. It was found that for the same volume of rubber, a larger rubber particle would decrease air content, decrease compressive strength, and improve damping. The results of this study show that the best performing additive was the vegetable gum latex which improved the concrete damping by a factor of 2 when added as 15% of the fine aggregate. Additionally, an equation is presented for calculating a strength reduction factor for concrete containing rubber particles of different sizes. Finally, two full scale footbridge laboratory specimens were tested to investigate the effect of increased material damping at the structural level. One footbridge was constructed using a base concrete mixture without damping admixtures. The second was constructed with a concrete mixture that contained a replacement of 15% of the fine aggregate with ground rubber. The results were used to create a finite element model in SAP2000 that was used to predict the effects that high damping concretes would have on the footbridge specimen.
Ph. D.

The application of a mineral admixture, or a corrosion inhibitor, or a combination of both are methods used for the corrosion protection for reinforced concrete bridges. The results of a study on evaluation of corrosion inhibitors from three different manufacturers and of concretes with fly ash, slag cement, and silica fume and a concrete with silica fume and a corrosion inhibitor are presented. The specimens were built to simulate four exposure conditions typical for concrete bridges located in the coastal region or inland where deicing salts are used. The exposure conditions were horizontal, vertical, tidal, and immersed zones. The specimens were kept inside the laboratory and were exposed to weekly ponding cycles of 6% (w/w) sodium chloride solution. In addition, cover depth measurements from 21 bridge decks and chloride data from 3 bridge decks were used, together with laboratory data, in modeling the service lives of the investigated corrosion protection methods. The methods used to assess the condition of the specimens included chloride concentration measurements, corrosion potentials, and corrosion rates (3LP). Additionally, visual observations were performed for identification of rust stains and cracking on concrete surfaces. Modeling the time as a function of probability of the end of functional service life (EFSL) is presented. It has been shown that the distributions of surface chloride concentration, C0, and diffusion coefficient, Dc, are key elements in the model. Model predictions show that the concretes with mineral admixtures provide much better level of protection against moisture and chlorides than the ordinary portland cement concrete alone. Application of a corrosion inhibitor causes an elevation of the chloride threshold resulting in an additional increase in time to EFSL. More field studies are needed to better estimate distributions of surface chloride concentration and diffusion coefficient of Virginia bridge decks, and to confirm predicted times to EFSL for low permeable (LP) concretes.
Ph. D.

Reinforced concrete exposed to chlorides is subject to rapid deterioration once the concentration of the chloride ion in the concrete reaches a critical level to cause corrosion of the reinforcing steel. The chloride ion diffuses through concrete according to Fick's Law, which is a function of time, a driving concentration, and a diffusion constant. The diffusion constant varies with temperature and the variety of concrete . The research included determination of diffusion constants for six types of concretes after 8 weeks and 16 weeks of ponding with an NaC1 solution. In addition, one set of these samples was subjected to the outside environment while the other was indoors under controlled conditions. The mixes included water to cement ratios of 0.35, 0.40, 0.45, and 0.50, and two water to cement ratios of 0.45 with 15% cement replacement with pozblan admixtures (silica fume and type'F flY ash). Thus, the effects of temperature, water to cement ratio, and pozzolanic admixtures in regard to the diffusion constant for concrete were found. The method by,which a diffusion constant was found is as 1)X3% solution of-NaC1 is ponded on top of a four inch thick 'specimen of concrete. 2) Powder samples of the paste are taken at specified time at depths of -0.5, 1.0 1,:5, and 2-.5 inches. 3) These samples are analyzed for chloride content by potentiometric titration. 4) The data is fit to Fick's Law by nonlinear regression and an effective diffusion constant determined.
Master of Science

The use of electromagnetic waves as a nondestructive evaluation technique to evaluate Portland cement concrete (PCC) structures is based on the principle that a change in the structure, composition, or properties of PCC results in a change in its dielectric properties. The coaxial transmission line is one of the few devices that can measure the dielectric properties of PCC at a frequency range of 100-1000 MHz. A coaxial transmission line developed at Virginia Tech was used to study the effect of moisture, type of aggregate, water/cement ratio, curing period, admixture type (microsilica, superplasticizer, and shrinkage admixture), and chloride content on the dielectric properties of PCC. Measurements were conducted in the time domain and converted to the frequency domain using Fast Fourier Transform. The research found that an increase in the moisture content of PCC resulted in an increase in the dielectric constant. Mixes containing limestone aggregate had a greater dielectric constant than those containing granite. The dielectric constant decreased with curing period due to the reduction in free water availability. Mixes containing higher water/cement ratios exhibited a higher dielectric constant, especially in the initial curing period. The admixtures did not significantly affect the dielectric constant after one day of curing. After 28 days of curing, however, all three admixtures had an effect on the measured dielectric constant as compared to control mixes. Chloride content had a significant effect on the loss part of the dielectric constant especially during early curing. A relationship was also established between the chloride permeability (based on conductance measurements) of PCC and its dielectric constant after 75 days of moist curing.
Master of Science

Abstract : It is well known that the winter in Quebec is particularly harsh and poses high demand on concrete performance, especially that used in infrastructure applications. Government agencies, in charge of repair and rehabilitation of such infrastructure, must work to restore the concrete and to extend the lifetime of structures. The objective of this research is to develop high-performance, self-consolidating concrete intended for repair applications that will facilitate the casting of slim and highly reinforced sections while ensuring adequate durability and service life. The performance of fresh concrete made with several Chemical admixture and hydraulic binder combinations has been evaluated. In total, five different brands of admixtures along with four binder types were used in this investigation. Two different approaches were used in proportioning the concrete to ensure proper stability: the use of low water-cementitious ratio, or the use of a moderate water-cementitious ratio (w/cm) with a Viscosity-Enhancing Agent (VEA) to enhance cohesiveness. Optimized mixtures were assessed for key workability characteristics, including: static stability, dynamic stability, and rheological parameters. The mixtures had initial slump flow of 660 ± 20 mm and maximum surface settlement of 0.5%. Some mixtures were made with synthetic fibres and initial slump flow of 700 ± 20 mm. // Résumé : Il est bien connu que l’hiver québécois est particulièrement agressif pour les ouvrages en béton. Les organismes publics doivent de plus en plus compter avec des travaux de réfection afin de réparer les structures existantes pour en prolonger la durée de vie. Le but de cette recherche est de développer un béton autoplaçant destiné aux travaux de réparation qui puisse faciliter la construction d’ouvrages minces et fortement renforcés. Cinq différents adjuvants et quatre différents liants hydrauliques ont été utilisés pour la fabrication d’un tel béton autoplaçant. Deux différentes approches ont été utilisées : l’une avec un faible rapport eau/liant sans agent colloïdal et l’autre avec un rapport eau/liant modéré avec agent colloïdal. La stabilité dynamique, la stabilité statique et les paramètres rhéologiques ont été mesurés lors des différents essais. Les propriétés du béton autoplaçant incluaient un étalement de 660 ± 20 mm et une stabilité statique limitée à une valeur maximale de 0,5%, mesurée avec une colonne de tassement de 700 mm. Des fibres ont été incorporées au béton autoplaçant et ses propriétés ont été améliorées jusqu’à un étalement de 700 ± 20 mm.

Cracked pavement slabs lead to uncomfortable and eventual unsafe driving conditions for motorists. Replacement of cracked pavement slabs can interrupt traffic flow in the form of lane closures. In Florida, the traffic demands are high and pavement repairs need to be carried out swiftly typically using concrete with high cement contents and accelerators to create rapid setting and strength gain. The concrete used in these pavement replacements is usually accompanied by a high temperature rise, making the replaced slabs susceptible to cracking. Cracking is a result of developed tensile stresses in the concrete, which exceed the concrete's tensile strength capacity. This research is being conducted to determine the risk of cracking for pavement slabs with varying dosages of chloride based accelerator used to promote high early strength. To analyze the effect of the accelerator, five different concrete mixtures including a control were assessed in a series of tests with varying accelerator dosages. Experiments included: mortar cube testing, concrete cylinder testing, autogenous deformation measured with a free-shrinkage frame, and restrained stress analysis using a rigid cracking frame. The findings indicate that accelerators are necessary to meet the strength requirements, and that the higher the accelerator dose, the higher the early shrinkage in the first 24 hours determined from the free shrinkage frame. Accidental overdose of the chloride-based accelerator results in the highest cracking potential and the highest shrinkage when tested under field generated temperature profiles.

Plasticizing and superplasticizing admixtures are the key components of nearly every concrete. These admixtures improve workability of mortar and fresh concrete which lead to facilitation of depositing and compaction. Adding of plasticizers or superplasticizers enables to change properties of fresh and hardened concrete, especially to reduce water-cement ratio, thereby increasing strength and durability of concrete or to improve other properties. The main aim of this thesis is to monitor the effect of plasticizing admixtures and their dosage on the rheology and hydration of concrete with emphasis on the development of hydration temperature. The other goal is to examine their strength qualities. Behaviour of plasticizing admixtures is analysed at first on cement pastes, as simple systems, and then verified on concrete.

The objective of this paper is to present the results of the connection between a substrate and self-compacting concrete with underwater launch simulating the repairs to concrete structures submerged in various applications. Therefore, we used samples of "old" concrete structures extracted from the Power Plant Itumbiara the state of Goiás, which was considered substrates. The concrete used in this work follows the parameters established strengths in the research completed in 2003 by the laboratory of Furnas Centrais Elétricas and has been adjusted to the materials (gravel and sand) found in the city of the Minas Gerais. The results are from the sample concrete of vertical and horizontal joints of the bodyspecimens prismatic concrete substrates and kept submerged and extracted after a year, so almost complete hydration. The analysis relating to the launch of concrete indicate that it is entirely feasible production for small applications. Visibility during the concreting was hampered by increased turbidity of the water produced by the concrete, so you must reduce the presence of a direct flow of water in concrete. The analysis was by comparing the results of the testimonies and bodies-of-proof. We observed an increase in strength in direct relation to the diameter of the testimony. In the samples concrete of 50 mm x 100 mm was obtained a coefficient of variation of 9.00% giving the concrete a low variability. The testimonies of concrete compounds and submerged concrete substrate (with seal inclined) had a resistance value 84% over the bodies-of-proof. The tensile strength by diametrical compression of the testimony amounted to 54% of the reference value. Can also check the interface between substrate concrete and after the break.
O objetivo deste trabalho é apresentar os resultados do estudo da ligação entre um substrato e o concreto auto-adensável com lançamento subaquático simulando a realização de reparos em estruturas de concreto submersas em diversas aplicações. Para tanto foram utilizadas amostras de concreto antigo provenientes de estruturas extraídas da Usina Hidrelétrica de Itumbiara no estado de Goiás, que foram considerados substratos, o concreto utilizado no presente trabalho segue os parâmetros de dosagens estabelecidos na pesquisa concluída em 2003 pelo laboratório de Furnas Centrais Elétricas e foi ajustado aos materiais (brita e areia) encontrados na região de Uberlândia do Estado de Minas Gerais. Os resultados obtidos são provenientes de testemunhos das juntas verticais e horizontais dos corpos-de-prova prismáticos concretados com substratos e mantidos submersos e extraídos após um ano, portanto, a hidratação quase completa. As análises relativas ao processo de lançamento do concreto indicam que é totalmente viável sua produção para pequenas aplicações. A visibilidade durante a concretagem foi dificultada pelo aumento de turbidez da água produzida pelo concreto, portanto deve-se diminuir a presença de um fluxo de água direto no concreto. As análises foram por comparação entre os resultados dos testemunhos e dos corpos-de-prova. Foi observado um aumento da resistência em relação direta ao diâmetro do testemunho. Nos testemunhos de 50 mm x 100 mm obteve-se um coeficiente de variação de 9% dando ao concreto uma variabilidade baixa. Os testemunhos compostos de concreto submerso e substrato de concreto (com junta inclinada) obtiveram uma resistência com valor 84% em relação os corpos-de-prova. A resistência à tração por compressão diametral dos testemunhos correspondeu a 54% do valor de referência. Também pode ser verificada a interface entre substrato e concreto após a ruptura.
Mestre em Engenharia Civil

A reação álcali-agregado no concreto é um fenômeno que tem como causa uma reação química que ocorre entre os hidróxidos alcalinos provenientes do cimento e alguns minerais reativos presentes no agregado. Esta reação pode causar a deterioração do concreto, pois os seus subprodutos podem tornar-se expansivos na presença de umidade, originando fissuração, diminuição da resistência, aumento da permeabilidade e, eventualmente, a ruptura da estrutura. O uso de adições minerais em concretos suscetíveis à reação álcali-agregado tem sido apontado como uma alternativa eficiente na prevenção da reação expansiva, juntamente com o uso de agregados não reativos e a limitação dos teores de álcalis no cimento ou concreto. Neste contexto, o presente trabalho teve como objetivo principal a investigação do processo de deterioração do concreto devido à reação álcali-sílica, principalmente no que se refere ao tipo ou mineralogia do agregado e à utilização de cinza de casca de arroz, como substituição parcial do cimento Portland. Desta forma, o programa de pesquisa compreendeu, a realização de ensaios de expansão acelerada em barras de argamassa (ASTM C1260/94) moldadas com cimento Portland tipo CP-I S 32, com teores de 12,5; 25 e 50% de dois tipos de cinza de casca de arroz, em substituição parcial ao cimento, e quatro diferentes tipos de agregados (basalto B, basalto BGO, granito e riodacito). A microestrutura dos materiais utilizados e das barras submetidas ao ensaio acelerado foi avaliada através de técnicas analíticas e experimentais, tais como, petrografia, difração de raios x, porosimetria por intrusão de mercúrio, microscopia eletrônica de varredura e de transmissão (MEV e MET), com microanálise por detecção de energia dispersiva (EDS). Os resultados obtidos no ensaio acelerado comprovaram a potencialidade reativa das rochas analisadas e identificaram uma correlação entre o tipo de rocha e o teor de cinza de casca de arroz. A análise da microestrutura indicou que existe uma reação química da CCA com o meio alcalino utilizado no ensaio que acaba interferindo na formação e na relação C/S dos produtos expansivos resultantes da reação álcali-sílica.
The alkali-aggregate reaction in concretes is a phenomenon caused by a chemical reaction that occurs between alkaline hydroxides from Portland cement and some reactive minerals from aggregates. Such reaction can cause severe concrete deterioration, as its by-products can become expansive in the presence of water, originating fissuration, strength reduction, permeability increase, and eventually, the failure of concrete structures. The use of mineral admixtures in concretes susceptible to the alkali-aggregate reaction has been pointed out as an efficient alternative to prevent concrete expansion, along with the use of non-reactive aggregates and the limitation of the alkali amount in cement or concrete composition. In this context, the main purpose of the present work was the investigation of concrete deterioration due to the alkali-silica reaction, focusing the aspects related to the type or mineralogy of the aggregate and the utilization of rice husk ash as partial substitution of Portland cement. The research program comprised initially accelerated expansion tests carried out in mortar bars (ASTM C 1260/94), which were molded using CP-I S 32 Portland cement, 12.5, 25, and 50% contents of two types of rice husk ash, as partial replacement to the cement, and four different types of rock aggregates (basalt B, Basalt BGO, granite, and rhyodacite). Also, the microstructure of the concrete mixtures investigated, after being submitted to expansion in the accelerated tests, were evaluated through experimental and analytical techniques such as petrography, mercury intrusion porosimetry, x-ray diffraction, scanning and transmission electron microscopy (SEM and TEM), and energy dispersive detection (EDS). The results obtained have proved the reactivity potential of the investigated rock aggregates and identified a correlation between type of aggregate and rice husk ash content. The microstructure analysis indicated that the occurrence of a chemical reaction involving the rice husk ash in the alkaline environment established in the tests, had a significant effect on the amount of expansive by-products as C/S relation resulting from alkali-silica reactions.

Three epoxy-coated reinforcing steel (ECR) types removed from job sites, one shipped directly from the coater's plant, three commercial corrosion inhibitors, and one ECR plus a corrosion inhibitor were evaluated as reinforcing steel corrosion protection systems against chloride induced corrosion. The three corrosion inhibitors were calcium nitrite, an aqueous mixture of esters and amines, and a mixture of alcohol and amine. The ECR was tested in two groups, 0% and 1% coating damage. Corrosion protection performance was evaluated by the amount of visually observed blister surface area, for the ECR, and corroded surface area, for the tested corrosion inhibitors. Results of the ECR testing demonstrated that coating debondment and corrosion of ECR is directly related to the amount of damage present in the coating, as well as coating thickness. For the bare steel tested with and without corrosion inhibitors, the results showed that corrosion increases with increasing chloride concentrations. Corrosion inhibition characteristics were demonstrated only by the calcium nitrite corrosion inhibitor. A corrosion protection evaluation test was developed for concrete corrosion inhibitor admixtures. The test solution is a simulated concrete pore water. Corrosion is accelerated by evaluating the temperature to field conditions of 40 C. The test consists of a 7 day pretreatment period followed by a 90 day test period. The corrosive sodium chloride is added to the solution containing the bare or epoxy-coated reinforcing steel specimens after the 7 day pretreatment period. In addition, the solution is periodically saturated with oxygen.
Master of Science

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES
The rheological properties...
As propriedades reológicas...