yes / Test results of nine recycled aggregate concretes and a control concrete using only natural aggregates are reported. The recycled aggregates used were classified into three different types according to their measured specific gravity and water absorption, namely, RG I for recycled coarse aggregate having a specific gravity of 2.53 and water absorption of 1.9%; RG III for recycled coarse aggregate having a specific gravity of 2.4 and water absorption of 6.2%; and RS II for recycled fine aggregate having a specific gravity of 2.36 and water absorption of 5.4%. The replacement levels of both recycled coarse and fine aggregates were 30, 50, and 100% in separate mixtures. Slump loss and the amount of bleeding with time were recorded for fresh concrete. Compressive and tensile strengths, moduli of rupture and elasticity, and unrestrained shrinkage strain were also measured for hardened concrete. The properties of fresh and hardened concrete tested, together with a comprehensive database reported in the literature, were evaluated with respect to the relative water absorption of aggregates combining the quality and volume of recycled aggregates used. In addition, the properties of hardened concrete with different replacement levels and quality of recycled aggregates were compared with the design equations of ACI 318-05 and empirical equations proposed by Oluokun for natural aggregate concrete, whenever possible. Test results clearly showed that the properties of fresh and hardened concrete containing recycled aggregates were dependent on the relative water absorption of aggregates. In addition, the moduli of rupture and elasticity of recycled aggregate concrete were lower than the design equations specified in ACI 318-05, when the relative water absorption of aggregates is above 2.5% and 3.0%, respectively.

An experimental program was conducted to establish a better understanding of the effect of Portland cement concrete's (PCC' s) basic properties on its dielectric properties over a wideband of frequency (0.1 MHz-10 GHz). Other parameters that may influence measured dielectric properties were investigated. These include chlorides presence in PCC, deterioration (due to alkali silica reaction [ASR] and freezing and thawing [Fff] damage), delamination, and segregation. In addition, the effect of different sizes of delaminated areas (filled with water) was evaluated using measured dielectric properties and waveform amplitude. Three different electromagnetic wave (EM) setups were used to conduct those measurements: parallel plate capacitor (0.1-40 MHz), coaxial transmission line (100 MHz to 1 GHz), and TEM antenna (0.5-10 GHz). The setups were designed and built by engineers from the Civil and Electrical Engineering Departments at Virginia Tech as a part of the overall research study. Testing results indicated the feasibility of using EM to detect changes in the basic properties of PCC over low RF using the parallel plate capacitor. This included the effect of curing time, water to cement (w/c) ratio, aggregate type, cement type, and air entrainment. The effect of curing time on the complex dielectric constant of PCC was quantitatively determined. However, the success in detecting changes in the PCC basic properties was limited at the microwave frequency range of 100 MHz to 10 GHz. Changes in the complex dielectric constant due to chloride intrusion into PCC were quantitatively significant only over the low radio wave frequency. The ASR in PCC was successfully identified by measured complex dielectric constant over the low RF, especially less than 20 MHz. Insignificant changes in the complex dielectric constant over the frequency range of 0.1 MHz to 1 GHz was noted when PCC was exposed to FIT cycles. Complex dielectric constant and waveform amplitude measurements of pce slabs over frequency range of 1 to 10 GHz showed significant changes with water content (in PCC); due to further hydration or injecting of water into empty delaminated areas. Waveform amplitude showed significant sensitivity to delamination and chlorides and low sensitivity to segregation. After testing several mixture theories to identify the most appropriate theory that is capable of predicting the dielectric constant of PCC (based on the dielectric properties of its components), Bruggemenn mixture theory was found to be the most feasible. / Ph. D.

FundaÃÃo de Amparo à Pesquisa do Estado do Cearà / Departamento Nacional de ProduÃÃo Mineral / The natural sand used in civil construction has become scarce due to the exhaustion of natural reserves and environmental constraints imposed by the regulatory agencies. Consequently, the prices of those inputs are likely to increase, burdening the consumer. In search of alternatives, sustainable and economical, this study proposes characterize crushed sand from quarries in the Fortaleza metropolitan region (RMF) and evaluate its implementation, as fine aggregate, in conventional concrete, as a replacement for natural sand. The experimental study is divided into two stages. The first one is the characterization of the physical, chemical and petrographical properties of eight kinds of crushed sand from RMF through the grading, density, water absorption, pulverulent material content, bulk density, grain shape analysis, alkali-aggregate reaction, petrographic analysis, X-ray fluorescence spectrometry (XRF) and X-ray diffraction (XRD) tests. The second step is the properties evaluation of the concretes produced with crushed sand incorporation. The tool "design and analysis of experiments" was used. The crushed sands were rated into three groups and a representative sand for each group was used in the concrete production, where two independent factors (water/cement ratio and crushed sand replacement content) were determined by ranging in three levels each one of them. The measurement variables analyzed were the additive consumption, compressive strength, diametral tensile strength, shrinkage, water absorption, void ratios, density and natural carbonation. The results suggest the viability of using crushed sand to replace natural sand in conventional concrete by 75%, given that the workability can be achieved with the use of plasticizing additives, and in general, there is an increase in the compression resistance, reduced water absorption and void ratios, in other properties the crushed sand incorporation produces no significant effects, therefore their use is considered to be technically feasible. / A areia natural utilizada na construÃÃo civil tem se tornado escassa devido ao esgotamento de reservas naturais e Ãs restriÃÃes ambientais impostas pelos ÃrgÃos fiscalizadores. Por consequÃncia, os preÃos desse insumo tendem a aumentar, onerando o consumidor final. Em busca de alternativas, sustentÃveis e econÃmicas, propÃe-se neste estudo caracterizar areias de britagem provenientes de pedreiras da RegiÃo Metropolitana de Fortaleza (RMF) e avaliar sua aplicaÃÃo, como agregado miÃdo, em concreto convencional, em substituiÃÃo à areia natural. O trabalho experimental està dividido em duas etapas. A primeira à a caracterizaÃÃo das propriedades fÃsicas, quÃmicas e petrogrÃficas de oitos tipos de areia de britagem da RMF, atravÃs dos ensaios de granulometria, massa especÃfica, absorÃÃo de Ãgua, teor de material pulverulento, massa unitÃria, anÃlise de forma dos grÃos, reaÃÃo Ãlcali-agregado, anÃlise petrogrÃfica, espectometria de fluorescÃncia de raios X (FRX) e difraÃÃo de raios X (DRX). A segunda etapa à a avaliaÃÃo das propriedades dos concretos produzidos com a incorporaÃÃo de areia de britagem. Utilizou-se a ferramenta âplanejamento de experimentosâ. Classificou-se as areias de britagem em trÃs grupos, sendo utilizada uma areia representante para cada grupo na produÃÃo dos concretos, onde se determinou dois fatores independentes (relaÃÃo Ãgua/cimento e teor de substituiÃÃo de areia de britagem) variando em trÃs nÃveis cada. As variÃveis de resposta analisadas foram: consumo de aditivo, resistÃncia à compressÃo, resistÃncia à traÃÃo diametral, retraÃÃo por secagem, absorÃÃo de Ãgua, Ãndices de vazios, massa especÃfica e carbonataÃÃo natural. Os resultados apontam a viabilidade da utilizaÃÃo de areia de britagem em substituiÃÃo à areia natural em concretos convencionais em atà 75%, tendo em vista que a trabalhabilidade pode ser alcanÃada com a utilizaÃÃo de aditivos plastificantes, e de modo geral, observa-se um incremento na resistÃncia à compressÃo, reduÃÃo da absorÃÃo de Ãgua e Ãndices de vazios, nas demais propriedades a incorporaÃÃo de areia de britagem nÃo produz efeitos significativos, portanto, sua utilizaÃÃo à considerado tecnicamente viÃvel.

Vários são os processos de deterioração do concreto e a reação álcali-agregado (RAA) se agrupa na categoria de degradação por processo químico. Como resultado da reação e em presença de umidade, são formados produtos que se expandem, podendo provocar a fissuração, perda de resistência, aumento da deformação, perda de funcionalidade, redução da durabilidade da estrutura, dentre outros. Pode-se dizer que o conhecimento quanto à prevenção da reação é vasto, porém o mesmo não pode ser dito sobre o seu mecanismo. Uma vez existindo a reação, ainda não se conhece uma maneira adequada para evitar sua continuidade. O trabalho consistiu no estudo de casos de concretos afetados pela reação álcaliagregado nas cinco usinas hidrelétricas que compõem o Complexo Hidrelétrico Paulo Afonso, de responsabilidade da Companhia Hidro Elétrica do São Francisco CHESF, subsidiária das Centrais Elétricas Brasileiras S/A ELETROBRÁS e responsável por gerar e transmitir energia elétrica para a região nordeste do Brasil. Os concretos das usinas possuem idades variando entre 20 e 50 anos. Foram avaliadas algumas propriedades físicas, químicas, mineralógicas, mecânicas e elásticas dos concretos, como: reatividade potencial, teor de álcalis do concreto, índice de deterioração, massa específica, resistência à compressão, resistência à tração por compressão diametral, módulo de elasticidade, coeficiente de Poisson e fluência. O principal interesse deste estudo é verificar se algumas das características dos concretos das usinas são afetadas devido à reação álcali-agregado. Os resultados indicam que, apesar dos concretos terem sido fabricados há décadas, seu potencial reativo ainda é bastante elevado, mas que as estruturas de concreto se apresentam pouco deterioradas quando comparadas a outras estruturas. Com relação às propriedades mecânicas, não foi observada redução significativa das resistências à compressão, tração e fluência, tendo sido o módulo de elasticidade a propriedade mais sensível aos efeitos da RAA. / Several are the concrete deterioration processes and the alkali-aggregate reaction (AAR) is classified as a chemical deterioration process. As a reaction result and in an umid environment expansion products are formed, being able to cause cracking, loss of strength, increase of deformation, loss of functionality, reduction of the durability of the structure, amongst others. The knowledge of reaction prevention is vast, but the same cannot be said about its mechanism. Once the reaction exists, there is not yet a way to avoid its continuity. The study was carried out in five hydroelectric plants of the Paulo Afonso Hydroelectric System, whose concrete was affeted by AAR. These dams are responsable for generating energy for the northeast of Brazil. The ages of the concretes are between 20 to 50 years. Some physical, chemical, mineralogical, mechanical and elastic properties of the concrete were evaluated, such as: potential reactivity, alkali content, deterioration index, bulk density, compressive strength, tensile strength, modulus of elasticity, Poissons ratio and creep. The main objective of this study is to evaluate if some of the characteristics of the concretes are affected by the AAR. The results indicate that, although the concretes have been manufactured decades ago, the potential reactivity is still high, but the concrete structures are not much deteriorated. With regard to the mechanical properties, it was not observed significant reduction on the compressive strength, tensile strength, creep, but the modulus of elasticity was the most sensible concrete characteristic affected by the AAR.

Vários são os processos de deterioração do concreto e a reação álcali-agregado (RAA) se agrupa na categoria de degradação por processo químico. Como resultado da reação e em presença de umidade, são formados produtos que se expandem, podendo provocar a fissuração, perda de resistência, aumento da deformação, perda de funcionalidade, redução da durabilidade da estrutura, dentre outros. Pode-se dizer que o conhecimento quanto à prevenção da reação é vasto, porém o mesmo não pode ser dito sobre o seu mecanismo. Uma vez existindo a reação, ainda não se conhece uma maneira adequada para evitar sua continuidade. O trabalho consistiu no estudo de casos de concretos afetados pela reação álcaliagregado nas cinco usinas hidrelétricas que compõem o Complexo Hidrelétrico Paulo Afonso, de responsabilidade da Companhia Hidro Elétrica do São Francisco CHESF, subsidiária das Centrais Elétricas Brasileiras S/A ELETROBRÁS e responsável por gerar e transmitir energia elétrica para a região nordeste do Brasil. Os concretos das usinas possuem idades variando entre 20 e 50 anos. Foram avaliadas algumas propriedades físicas, químicas, mineralógicas, mecânicas e elásticas dos concretos, como: reatividade potencial, teor de álcalis do concreto, índice de deterioração, massa específica, resistência à compressão, resistência à tração por compressão diametral, módulo de elasticidade, coeficiente de Poisson e fluência. O principal interesse deste estudo é verificar se algumas das características dos concretos das usinas são afetadas devido à reação álcali-agregado. Os resultados indicam que, apesar dos concretos terem sido fabricados há décadas, seu potencial reativo ainda é bastante elevado, mas que as estruturas de concreto se apresentam pouco deterioradas quando comparadas a outras estruturas. Com relação às propriedades mecânicas, não foi observada redução significativa das resistências à compressão, tração e fluência, tendo sido o módulo de elasticidade a propriedade mais sensível aos efeitos da RAA. / Several are the concrete deterioration processes and the alkali-aggregate reaction (AAR) is classified as a chemical deterioration process. As a reaction result and in an umid environment expansion products are formed, being able to cause cracking, loss of strength, increase of deformation, loss of functionality, reduction of the durability of the structure, amongst others. The knowledge of reaction prevention is vast, but the same cannot be said about its mechanism. Once the reaction exists, there is not yet a way to avoid its continuity. The study was carried out in five hydroelectric plants of the Paulo Afonso Hydroelectric System, whose concrete was affeted by AAR. These dams are responsable for generating energy for the northeast of Brazil. The ages of the concretes are between 20 to 50 years. Some physical, chemical, mineralogical, mechanical and elastic properties of the concrete were evaluated, such as: potential reactivity, alkali content, deterioration index, bulk density, compressive strength, tensile strength, modulus of elasticity, Poissons ratio and creep. The main objective of this study is to evaluate if some of the characteristics of the concretes are affected by the AAR. The results indicate that, although the concretes have been manufactured decades ago, the potential reactivity is still high, but the concrete structures are not much deteriorated. With regard to the mechanical properties, it was not observed significant reduction on the compressive strength, tensile strength, creep, but the modulus of elasticity was the most sensible concrete characteristic affected by the AAR.

Liquefied natural gas (LNG) is stored at a cryogenic temperatures ≤ -160°C and around atmospheric pressure to insure the minimum storage volume in tanks. The demand for LNG has been increasing as a primary source of energy. Therefore, there is significant interest in the construction of LNG tanks to achieve low cost and safe storage. Three systems are typically used to store LNG: single containment, double containment, and full containment. Concrete is used in these containment systems, and consequently, understanding concrete behavior and properties at cryogenic temperatures is important. The research documented in this thesis deals with computational analysis of the behavior of concrete subjected to cryogenic temperatures. The analysis focuses on the effect of aggregate sizes, coefficient of thermal expansion, volume fraction, and the shape of aggregate on damage of concrete subjected to cryogenic temperatures. The analysis is performed by developing a computational model using the finite element software ABAQUS. In this model, concrete is considered as a 3- phase composite material in a meso-scale structure: mortar matrix, aggregate, and interfacial transmission zone (ITZ). The Concrete Damage Plasticity model in ABAQUS is used to represent the mortar and ITZ phases of concrete. This model has the advantage of accounting for the effect of temperature on material properties. The aggregate phase is modeled as a linear-elastic material. The model parameters are selected based on comprehensive literature review of material properties at different temperatures. The finite element results provide very useful insight on the effects of concrete mixture design and properties on resistance to damage. The most important factor that affected damage development was the difference in the coefficient of thermal expansion between the mortar and aggregates. Models in which the mortar and aggregate had close values of positive coefficients experienced less damage. The model with irregular shape particles experienced more localized damage than the model with circular shape particles. The model was successful in demonstrating the effect of using air entrained concrete in reducing damage. The damage results predicted by the model for air entrained and non-air entrained concrete are validated by comparing them with experimental data from the literature. The analysis validated the capabilities of the mode in simulating the effect of reduction in temperature on damage. The modeling results and the findings from the literature review were used to put forward recommendations regarding the characteristics of concrete used in LNG storage.

The Soil Water Retention Curve (SWRC) of different soils has been researched thoroughly by multiple Geotechnical Engineers. The interpretation of the SWRC for a specific soil leads to the identification of certain properties of the soil. The SWRC typically involves a plot of suction measurements (on a logarithmic scale) against the volumetric water content or degree of saturation of the soil. This project aims to determine a manner in which concrete properties (such as durability, porosity, shrinkage, strength and stiffness) can be estimated through suction measurements. The Dew Point PotentiaMeter (WP4C) apparatus was used to measure the suctions of different concrete mixtures, as well as to derive the water retention curve of concrete. A cement paste study was first conducted to determine whether this apparatus is able to deliver representative results, which it is. It was discovered that the water retention curve of concrete is similar to a bimodal SWRC identified by Geotechnical Engineers. Thereafter, a mortar study was completed to determine if the water retention curves can be used to estimate different concrete properties. Three different porosity tests were investigated during this research study, namely the X-ray test, the Mercury Intrusion Porosimetry (MIP) test and a simple test method described in the durability index testing procedure manual assembled by University of Cape Town, University of the Witwatersrand and CoMSIRU. It was concluded that the MIP test and the simple test method described in the durability index testing procedure manual gave the most comparable results with regards to literature. The shrinkage of the concrete mixture was investigated to determine a relationship between the suctions and the shrinkage of the concrete. Different strength tests of all the concrete mixtures were also investigated, namely the flexural test, the compressive test, the splitting cylinder test and the E-value test (stiffness). It was concluded that there was a definite trend between the suction measurements and the specific concrete properties tested. The water retention curve has the potential to describe various properties of different concrete mixtures. / Dissertation (MEng (Structural Engineering))--University of Pretoria, 2020. / Civil Engineering / MEng (Structural Engineering) / Unrestricted

No description available.

La investigación actual se enfoca en evaluar cómo afecta el uso de Nanotubos de Grafeno y el Sistema SNS 360 al concreto estructural con resistencia de 21Mpa. Utilizamos una metodología cuantitativa de carácter experimental, considerando como variables independientes a los Nanotubos de Grafeno y el Sistema SNS 360, y como variables intervinientes las propiedades constituyentes propias del concreto. La muestra analizada incluye una mezcla de concreto estándar y otra con nano-adiciones, sumando un total de 160 prototipos: 140 cilíndricos y 20 prismáticos. Los ensayos realizados abarcan determinación del f’c, tracción y flexión en distintos intervalos: 3, 7, 14 y 28 días. Se experimentó con dosificaciones de MWCNT de 0.10%, 0.25% y 0.05%, añadiendo 1% y 2% de SNS 360 en cada caso. Los resultados indican que la dosificación de 0.05% de MWCNT combinado con 2% NPF ofrece las mejores prestaciones en el concreto. Algunos parámetros obtenidos son: asentamiento de 3.8”, peso unitario de 2321 kg/cm3, contenido de aire del 1.8%, y tiempo de fraguado de 125 min. A los 28 días, el f’c alcanzó 330 kg/cm2, la tracción fue de 27 kg/cm2, y la flexión llegó a 64 kg/cm2. En cuanto al desgaste, superó en 0.078% al diseño estándar, y la permeabilidad mostró una penetración máxima de 19.29 mm. El costo por m³ es de S/ 991.71, indica un aumento del 33.4% en relación con el concreto convencional. / The current research focuses on evaluating how the use of Graphene Nanotubes and the SNS 360 System affects structural concrete with a strength of 21 MPa. We use a quantitative methodology of an experimental nature, considering as independent variables the Graphene Nanotubes and the SNS 360 System, and as intervening variables the intrinsic constituent properties of the concrete. The analyzed sample comprises a standard concrete mix and another with nano-additives, totaling 160 prototypes: 140 cylindrical and 20 prismatic. Tests were conducted on compression, tension, and bending resistance at different intervals: 3, 7, 14, and 28 days. We experimented with MWCNT dosages of 0.10%, 0.25%, and 0.05%, adding 1% and 2% of SNS 360 in each instance. The findings suggest that a dosage of 0.05% MWCNT combined with 2% NPF provides the best performance in concrete. Notable data includes a settlement of 3.8”, a unit weight of 2321 kg/cm3, an air content of 1.8%, and a setting time of 125 min. At 28 days, the compression strength reached 330 kg/cm2, tension stood at 27 kg/cm2, and bending achieved 64 kg/cm2. Regarding wear, it exceeded the standard design by 0.078%, and permeability showed a maximum penetration of 19.29 mm. The cost per m³ is S/ 991.71, marking an increase of 33.4% compared to conventional concrete.

Made available in DSpace on 2014-12-17T14:07:19Z (GMT). No. of bitstreams: 1 DianaCSL.pdf: 800391 bytes, checksum: c85f3fef7e600f91edb93d3096219c80 (MD5) Previous issue date: 2005-11-25 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / The addition of active silica potentially improves the quality of concrete due to its high reactivity and pore refinement effect. The reactivity of silica is likely related to its charge density. Variations in surface charge alter the reactivity of the material consequently affecting the properties of concrete. The present study aimed at investigating variations in the charge density of silica as a function of acid treatments using nitric or phosphoric acid and different pH values (2.0, 4.0 and 6.0). Effects on concrete properties including slump, mechanical strength, permeability and chloride corrosion were evaluated. To that end, a statistical analysis was carried out and empirical models that correlate studied parameters (pH, acid and cement) with concrete properties were established. The quality of the models was tested by variance analysis. The results revealed that the addition of silica was efficiency in improving the properties of concrete, especially the electrochemical parameters. The addition of silica treated using nitric acid at pH = 4.0 displayed the best cement performance including highest strength, reduced permeability and lowest corrosion current / A adi??o da s?lica ativa ao concreto melhora a qualidade deste material, amplamente utilizado na Constru??o Civil, devido ? a??o dos efeitos: alta reatividade e refinamento dos poros. Acreditando-se que a reatividade da s?lica est? relacionada ? sua densidade de carga, uma varia??o da carga superficial modifica a reatividade do material, e consequentemente as propriedades do concreto. Assim, este trabalho objetiva estudar o efeito da varia??o da densidade de carga superficial da s?lica tratada com solu??es de ?cidos n?trico e fosf?rico a diferentes pHs: 2,0; 4,0 e 6,0 em propriedades do concreto: abatimento, resist?ncia ? compress?o, permeabilidade e par?metros indicativos do processo de corros?o por cloreto. Para tanto, realizou-se um planejamento experimental com a finalidade de obter modelos emp?ricos que relacionam as propriedades e par?metros avaliados com as vari?veis em estudo: pH, tipo de ?cido e tipo de cimento, bem como a an?lise de vari?ncia indicativa da qualidade do modelo proposto em rela??o ?s observa??es experimentais. Os resultados comprovaram a efic?cia da adi??o de s?lica ativa na mistura de concreto ?s propriedades estudadas. Indicam que uma varia??o na densidade de carga superficial da s?lica usada na confec??o de corpos de prova de concreto modifica as propriedades e par?metros eletroqu?micos estudados e que, o concreto com uso de s?lica tratada com solu??o de ?cido n?trico de pH 4,0, apresentou melhor qualidade: maior resist?ncia ? compress?o, menor permeabilidade e menor corrente de corros?o, quando tomados em rela??o aos demais