Factors such as water to cement ratio, moisture, mixture, presence and depth of rebar, and dimension of specimens, all of which affect apparent resistivity of concrete, were analyzed by experimental and modeling methods. Cylinder and rectangular prism concrete specimens were used in the experiments exposed in a high moisture room, laboratory room temperature, high humidity and outdoor weather environments. Single rebar and four rebar specimens were used to study the rebar effect on the apparent resistivity. Modeling analysis was employed to verify and explain the experimental results. Based on the results, concrete with fly ash showed higher resistivity than concrete with just ordinary Portland cement. Rebar presence had a significant effect on the measured apparent resistivity at some of the locations. The results could be used as a guide for field apparent resistivity measurements and provide a quick, more precise and easy way to estimate the concrete quality. / by Yanbo Liu. / Thesis (M.S.C.S.)--Florida Atlantic University, 2008. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2008. Mode of access: World Wide Web.

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy, Johannesburg, 2017 / Many reinforced concrete (RC) structures in inland environment deteriorate early due to carbonation-induced corrosion of their reinforcement. In some cases, the deterioration is visible within a few years of construction in the form of cover concrete cracking. This is widely accepted as one of the limit state indicators in defining the end of functional service life for existing RC structures undergoing corrosion. Many of the currently available service life prediction models are incapable of providing realistic service life estimates of RC structures beyond the corrosion initiation stage. Therefore, the need to incorporate the corrosion initiation and propagation stages in a comprehensive durability prediction approach has been receiving much research attention. In this research, empirical models were developed for predicting carbonation rate and the amount of steel radius loss required to initiate a first visible crack in concretes exposed to Johannesburg environment. The experimental data for the models were obtained from investigations of carbonation-induced reinforcement corrosion, which were explored in three phases; (i) concrete early-age durability and strength characteristics (ii) carbonation rate of different concrete mixes exposed to the natural inland environment (iii) amount of steel radius loss required to initiate the first visible crack on the pre-carbonated cover concretes exposed to an unsheltered environment. The experimental variables for the earlyage durability and strength tests were; water/binder ratio (w/b) and binder type; w/b, binder type, initial moist curing duration and exposure conditions are the experimental variables for the carbonation rate test. Cover depth, reinforcement diameter, binder type and w/b variables were considered for the corrosion cracking test. The results showed that an improvement in concrete quality (binder type, w/b ratio and extending the initial moist curing duration) and increment in cover thickness improved the durability of the RC structures exposed to the natural inland environment. Based on the trends in the observed experimental results, models to predict carbonation rate and the amount of steel radius loss required to initiate cover cracking in concrete were developed. The proposed models’ predictions are more closer to the measured values and compared well with the predictions of some previous models which indicate their respective predictive applications. They provide a general basis for durability analysis of RC structures in inland environment and can serve as basis for condition assessment of existing structures in the inland environment. Engineers can appreciate the consequences of design options on the service life of RC structures, while owners of RC structures can have information about how long their RC structures may last before any repair is envisaged / XL2018

A crescente utilização do concreto, que é o produto mais fabricado no mundo em termos de volume, somada à pressão do mercado por redução de custos com manutenção das exigências mínimas para segurança do projeto, tem impacto direto na importância e necessidade do controle de qualidade do material. Para concretos usinados, predominantes em grandes centros urbanos, as normas do país preconizam a não utilização dos 15% iniciais e finais do volume total de concreto do caminhão betoneira para fins de ensaio. No entanto, devido a maior facilidade e agilidade, é constatada como prática comum nos canteiros de obra da região a coleta de amostras logo da primeira porção de concreto descarregado. Considerando tal procedimento, fora do padrão preconizado por norma, somado à ausência de normatização para aferição da qualidade do misturador e uniformidade da mistura do concreto e a importância dos ensaios de controle de qualidade dos concretos perante a segurança das estruturas, a presente pesquisa tem como objetivo analisar as variações de resistência à compressão e de propriedades físicas do concreto ao longo da descarga da mistura em caminhão betoneira. A fim de atingir a meta proposta, realizaram-se coletas de amostras em cinco pontos distintos, ao longo da descarga do concreto do caminhão betoneira, para cada um dos 65 lotes (amassadas) avaliados, considerando três diferentes traços de concreto. Para cada ponto de coleta foram avaliados a resistência à compressão, o abatimento de tronco de cone e o teor de agregado graúdo. Estatisticamente, foi constatado que há amassadas em que a variação do ponto de coleta influencia na resistência à compressão, no entanto não se pode afirmar o mesmo considerando critérios da ABECE, adotados como parâmetro de análise na falta de normatização específica para o tema. Não houve a formação de um perfil representativo das variações de resistência conforme o ponto de coleta, diferentemente do teor de agregado graúdo, em que se pode visualizar claramente um perfil em que há concentração de brita nos pontos extremos, início e final da coleta. Em relação à consistência, de modo geral, houve uma redução do ponto inicial ao final, dentro dos limites de indicados por norma. / The crescent utilization of concrete which in terms of volume, is the most produced product in the world, added to the pressure of the market to reduce the costs and maintenance of the safety minimum requirements of a project, make a direct impact on the material quality control’s importance and necessity. For ready-mixed concrete, mostly seen in large urban centers, the initial and final 15% usage of its total volume is not recommended by the country standards for test purposes. However, due to the ease, it is a common practice in construction sites of the region to collect samples once the first portion of the concrete is unloaded. Taking into account such procedure, which does not meet the standards recommended, added to the lack of standardization to assess the quality of the concrete mixer, the uniformity of the concrete mixture and the importance of the quality control tests of concrete under the safety of structures, the purpose of this research is to analyze the variations of the concrete strength when compressed and its physical properties along the discharge of the mixture made in a mixer truck. In order to achieve the proposed goal, there were sampling carried out at five different points along the discharge from the concrete mixer truck, for each of the 65 lots (batches) analyzed, considering three different types of concrete. Each sampling collected was analyzed by going through a slump test, compression strength and granulometry analysis. Statistically, it was proven that the sample point collection variation of some of the batches influences the compression strength, on the other hand the same cannot be found considering the ABECE criteria, used as analysis parameter in the absence of specific regulations for the subject. No representative profile of resistance variations based on the sample collection point was formed, in contrast to the coarse aggregate content, in which profile can be clearly seen a concentration of gravels at the extreme points, at the commencement and the end of the sample collection. Regarding its consistency, on the whole, there was a reduction from the initial and to the end point, respecting the regulations standards.

A crescente utilização do concreto, que é o produto mais fabricado no mundo em termos de volume, somada à pressão do mercado por redução de custos com manutenção das exigências mínimas para segurança do projeto, tem impacto direto na importância e necessidade do controle de qualidade do material. Para concretos usinados, predominantes em grandes centros urbanos, as normas do país preconizam a não utilização dos 15% iniciais e finais do volume total de concreto do caminhão betoneira para fins de ensaio. No entanto, devido a maior facilidade e agilidade, é constatada como prática comum nos canteiros de obra da região a coleta de amostras logo da primeira porção de concreto descarregado. Considerando tal procedimento, fora do padrão preconizado por norma, somado à ausência de normatização para aferição da qualidade do misturador e uniformidade da mistura do concreto e a importância dos ensaios de controle de qualidade dos concretos perante a segurança das estruturas, a presente pesquisa tem como objetivo analisar as variações de resistência à compressão e de propriedades físicas do concreto ao longo da descarga da mistura em caminhão betoneira. A fim de atingir a meta proposta, realizaram-se coletas de amostras em cinco pontos distintos, ao longo da descarga do concreto do caminhão betoneira, para cada um dos 65 lotes (amassadas) avaliados, considerando três diferentes traços de concreto. Para cada ponto de coleta foram avaliados a resistência à compressão, o abatimento de tronco de cone e o teor de agregado graúdo. Estatisticamente, foi constatado que há amassadas em que a variação do ponto de coleta influencia na resistência à compressão, no entanto não se pode afirmar o mesmo considerando critérios da ABECE, adotados como parâmetro de análise na falta de normatização específica para o tema. Não houve a formação de um perfil representativo das variações de resistência conforme o ponto de coleta, diferentemente do teor de agregado graúdo, em que se pode visualizar claramente um perfil em que há concentração de brita nos pontos extremos, início e final da coleta. Em relação à consistência, de modo geral, houve uma redução do ponto inicial ao final, dentro dos limites de indicados por norma. / The crescent utilization of concrete which in terms of volume, is the most produced product in the world, added to the pressure of the market to reduce the costs and maintenance of the safety minimum requirements of a project, make a direct impact on the material quality control’s importance and necessity. For ready-mixed concrete, mostly seen in large urban centers, the initial and final 15% usage of its total volume is not recommended by the country standards for test purposes. However, due to the ease, it is a common practice in construction sites of the region to collect samples once the first portion of the concrete is unloaded. Taking into account such procedure, which does not meet the standards recommended, added to the lack of standardization to assess the quality of the concrete mixer, the uniformity of the concrete mixture and the importance of the quality control tests of concrete under the safety of structures, the purpose of this research is to analyze the variations of the concrete strength when compressed and its physical properties along the discharge of the mixture made in a mixer truck. In order to achieve the proposed goal, there were sampling carried out at five different points along the discharge from the concrete mixer truck, for each of the 65 lots (batches) analyzed, considering three different types of concrete. Each sampling collected was analyzed by going through a slump test, compression strength and granulometry analysis. Statistically, it was proven that the sample point collection variation of some of the batches influences the compression strength, on the other hand the same cannot be found considering the ABECE criteria, used as analysis parameter in the absence of specific regulations for the subject. No representative profile of resistance variations based on the sample collection point was formed, in contrast to the coarse aggregate content, in which profile can be clearly seen a concentration of gravels at the extreme points, at the commencement and the end of the sample collection. Regarding its consistency, on the whole, there was a reduction from the initial and to the end point, respecting the regulations standards.

A crescente utilização do concreto, que é o produto mais fabricado no mundo em termos de volume, somada à pressão do mercado por redução de custos com manutenção das exigências mínimas para segurança do projeto, tem impacto direto na importância e necessidade do controle de qualidade do material. Para concretos usinados, predominantes em grandes centros urbanos, as normas do país preconizam a não utilização dos 15% iniciais e finais do volume total de concreto do caminhão betoneira para fins de ensaio. No entanto, devido a maior facilidade e agilidade, é constatada como prática comum nos canteiros de obra da região a coleta de amostras logo da primeira porção de concreto descarregado. Considerando tal procedimento, fora do padrão preconizado por norma, somado à ausência de normatização para aferição da qualidade do misturador e uniformidade da mistura do concreto e a importância dos ensaios de controle de qualidade dos concretos perante a segurança das estruturas, a presente pesquisa tem como objetivo analisar as variações de resistência à compressão e de propriedades físicas do concreto ao longo da descarga da mistura em caminhão betoneira. A fim de atingir a meta proposta, realizaram-se coletas de amostras em cinco pontos distintos, ao longo da descarga do concreto do caminhão betoneira, para cada um dos 65 lotes (amassadas) avaliados, considerando três diferentes traços de concreto. Para cada ponto de coleta foram avaliados a resistência à compressão, o abatimento de tronco de cone e o teor de agregado graúdo. Estatisticamente, foi constatado que há amassadas em que a variação do ponto de coleta influencia na resistência à compressão, no entanto não se pode afirmar o mesmo considerando critérios da ABECE, adotados como parâmetro de análise na falta de normatização específica para o tema. Não houve a formação de um perfil representativo das variações de resistência conforme o ponto de coleta, diferentemente do teor de agregado graúdo, em que se pode visualizar claramente um perfil em que há concentração de brita nos pontos extremos, início e final da coleta. Em relação à consistência, de modo geral, houve uma redução do ponto inicial ao final, dentro dos limites de indicados por norma. / The crescent utilization of concrete which in terms of volume, is the most produced product in the world, added to the pressure of the market to reduce the costs and maintenance of the safety minimum requirements of a project, make a direct impact on the material quality control’s importance and necessity. For ready-mixed concrete, mostly seen in large urban centers, the initial and final 15% usage of its total volume is not recommended by the country standards for test purposes. However, due to the ease, it is a common practice in construction sites of the region to collect samples once the first portion of the concrete is unloaded. Taking into account such procedure, which does not meet the standards recommended, added to the lack of standardization to assess the quality of the concrete mixer, the uniformity of the concrete mixture and the importance of the quality control tests of concrete under the safety of structures, the purpose of this research is to analyze the variations of the concrete strength when compressed and its physical properties along the discharge of the mixture made in a mixer truck. In order to achieve the proposed goal, there were sampling carried out at five different points along the discharge from the concrete mixer truck, for each of the 65 lots (batches) analyzed, considering three different types of concrete. Each sampling collected was analyzed by going through a slump test, compression strength and granulometry analysis. Statistically, it was proven that the sample point collection variation of some of the batches influences the compression strength, on the other hand the same cannot be found considering the ABECE criteria, used as analysis parameter in the absence of specific regulations for the subject. No representative profile of resistance variations based on the sample collection point was formed, in contrast to the coarse aggregate content, in which profile can be clearly seen a concentration of gravels at the extreme points, at the commencement and the end of the sample collection. Regarding its consistency, on the whole, there was a reduction from the initial and to the end point, respecting the regulations standards.

M. Phil. / The purpose of this research is to see if on-site portable pull-out tests in South Africa on post-installed chemical and mechanical fixings can produce similar results to internationally laboratory tested fixings. The method used in the field study was to use typical South African 25 MPa, 75 mm slump ready mix concrete as supplied by a reputable supplier and to test several types of fixings in common situations, some covered in the European Technical Approval Guidelines (ETAG) and some not. The results were analyzed against published international values and theoretical calculations for the fixings. The findings showed that the results produced using the portable equipment can show values similar to the published and theoretical values. It was also shown that this methodology can be used as a diagnostic tool to reveal installation errors. The pull-out test operator needs to be skilled to ensure a satisfactory outcome of the tests. The implications of the findings have direct bearing on: The on-site pullout testing of post installed anchors in South Africa; The diagnosing of bad anchor installation. And secondarily bearing on: The education of post-installed fixing installers and designers; The lack of standards for post-installed anchors in South Africa; The transportability of data from international research to South African conditions.

No description available.

La presente investigación tiene como objetivo general determinar la calidad del concreto en obras de autoconstrucción de viviendas que se encontraban realizando en el Sector I del distrito de la Victoria y determinar si el concreto que se elabora en las obras cumplen con los requerimientos normativos. Dentro de esta investigación se desarrolló, analizando la calidad del concreto que se vinieron efectuando, evaluando así el día de los vaciados datos, a través de unas fichas, detallando los puntos de interés y tomando; así por cada obra se adquirió muestras de sus agregados y a su vez se realizaron 3 probetas en obra para conocer la resistencia diseñada de la estructura vaciada. Para el desarrollo de esta investigación se llevó a cabo un muestreo, en el cual fueron seleccionadas 10 obras que se encontraban en construcción. Se hizo una comparación entre los datos obtenidos en campo y el proceso constructivo que efectuaban los maestros para conocer si cumplían con los requisitos mínimos que nos da la Norma E 0.60. Finalmente, se llegó a la conclusión que el concreto que ejecutaban en el lugar de investigación no llega a la resistencia requerida de 210 kg/cm para elementos estructurales, debido a esto se propuso un diseño de mezcla con en volumen de baldes, así en basándonos en esa medida poder lograr obtener la resistencia requerida. Además de los errores que se encontraron en las construcciones, se efectuó una propuesta de guía donde indican los puntos clave para una correcta elaboración del concreto. / This research presents two general objectives: determining the quality of the concrete in selfbuild housing projects that were being carried out in Prolongación la Quintas, Zone I of La Victoria District, and checking if the concrete produced in these projects meet the regulatory requirements. On the one hand, in this study, a correct pouring evaluation on construction work was done through some forms that allowed detailing the points of interest, for instance, the dosage. On the other hand, samples of aggregates were acquired from each construction work, and in turn, 3 graduated cylinders were taken from it, which after being subjected to the respective tests, allowed to identify the designed resistance of the poured structure. For the development of this research, a sampling was performed in 10 previously selected construction works. Considering the E.060 standard, a data evaluation, obtained from the field research and the construction process executed by the master builders, was done in order to determine whether they meet the minimum requirements established in that standard. Finally, it was concluded that the concrete used at the research work site did not reach the required resistance for structural elements being 210 kg/cm2. Consequently, a mixing design was proposed, detailing the volume of buckets, to obtain the required resistance. Besides the malpractices found in the construction works, a guide proposal was made, in which key points for an adequate concrete fabrication are indicated.

Thesis (MEng)--Stellenbosch University, 2014. / ENGLISH ABSTRACT: Construction of structural concrete frames may take place by using either cast in-situ or precast methods. With the cast in-situ method, these elements are constructed on the construction site as needed. Precast construction on the other hand is more resembles a line. The elements are constructed in a precast yard in a systematic fashion and once completed, they are taken to the construction site where they are to be erected. This study identifies the aspects and attributes which influence the quality of concrete during the construction phase of these two construction methods. The study is independent from the conceptual or design phase. Information regarding these aspects and attributes were obtained from literature and from contractors in industry through interviews and site visits. The literature review also focuses on quality management techniques and factors that influence quality in the construction environment. The information obtained from the site visits and literature was used to design a survey which was sent out to a number of respondents. A comparison between in-situ and precast construction was made based on the results of the survey. The synthesis of the research findings can be used by project teams to help them decide on the choice between in-situ and precast construction. It was found that precast construction is better for durability, and fitness for purpose is less complex for the in-situ solution. Recommendations for future studies are provided at the end of the document. / AFRIKAANSE OPSOMMING: Konstruksie van beton struktuurrame kan plaasvind deur die gebruik van in-situ of voorafvervaardigde metodes. Met die in-situ metode, word hierdie elemente op die terrein gebou soos benodig. Tydens voorafvervaardigde konstruksie aan die ander kant is die konstruksie soortgelyk aan 'n produksielyn. Die elemente word gegiet in 'n voorafvervaardingsterrein in 'n sistematiese wyse, en sodra dit voltooi is, word dit na die konstruksie terrein geneem waar dit opgerig word. Hierdie studie identifiseer die aspekte en eienskappe wat 'n invloed op die kwaliteit van beton het tydens die konstruksiefase van hierdie twee konstruksie metodes. Die studie is onafhanklike van die konseptuele of ontwerp fases. Inligting rakende hierdie aspekte en eienskappe is verkry uit die literatuur en van kontrakteurs in die bedryf deur middel van onderhoude en besoeke. Die literatuur fokus ook op die gehalte, bestuurs-tegnieke en faktore van gehalte in die bou-omgewing. Die inligting is verkry deur ‘n vraelys wat aan 'n aantal respondente gestuur is. 'n Vergelyking tussen in-situ en voorafvervaardigde konstruksie is vervolgens gemaak op grond van die resultate van die opname. Die sintese van die bevindinge kan gebruik word deur projek spanne om hulle te help besluit oor die keuse tussen in-situ en voorafvervaardigde konstruksie. Die resultate dui daarop dat voorafvervaardigde konstruksie beter is vir duursaamheid, maar passing op terrein is minder kompleks vir die in-situ oplossing. Aanbevelings vir toekomstige ondersoeke word aan die einde van die studie gemaak.

Submitted by Silvana Teresinha Dornelles Studzinski (sstudzinski) on 2016-02-15T14:12:54Z No. of bitstreams: 1 Carlos Eduardo Braun_.pdf: 3816402 bytes, checksum: 868ecc968577b70b35d2cfde265248ec (MD5) / Made available in DSpace on 2016-02-15T14:12:54Z (GMT). No. of bitstreams: 1 Carlos Eduardo Braun_.pdf: 3816402 bytes, checksum: 868ecc968577b70b35d2cfde265248ec (MD5) Previous issue date: 2015-04-07 / CAPES - Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / PROSUP - Programa de Suporte à Pós-Gradução de Instituições de Ensino Particulares / Durante a execução de elementos de concreto no canteiro de obras, procedimentos de controle de qualidade do concreto são adotados com o objetivo de verificar se o material atende às características de projeto. Esta verificação também visa evitar falhas durante as etapas subsequentes da construção, que podem levar até à inviabilização do empreendimento. Estudos sobre métodos que têm como objetivo estimar a relação água/cimento (a/c) do concreto no estado fresco vêm recebendo maior atenção nos últimos tempos, devido à importância deste parâmetro sobre a resistência e durabilidade das estruturas de concreto, e por não existirem métodos práticos e precisos disponíveis até o momento, que permitam a sua determinação após a realização da mistura. Estudos sobre o método da resistividade elétrica apontam para uma forte correlação entre os valores de resistividade e a relação água/cimento do concreto no estado fresco, possibilitando a utilização do método como uma interessante alternativa para determinação da relação a/c. O presente estudo tem como objetivo apresentar uma análise do método da resistividade elétrica, aplicado à estimativa de valores de relação água/cimento de concretos no estado fresco, confeccionados com cimentos nacionais, além da estimativa de valores de resistência à compressão axial do concreto no estado endurecido. Foram realizados ensaios com concretos dosados a partir do método IPT/EPUSP para seis cimentos nacionais (CPV-ARI, CPIV-32, CPIII-40, CPII-Z-32, CPII-F-32 e CPII-E-40), variando-se a relação a/c (0,35, 0,45, 0,55 e 0,65), utilizando uma sonda aprimorada para realização dos testes, a qual foi desenvolvida neste estudo com base num protótipo já desenvolvido anteriormente. Os resultados obtidos apontam para uma forte correlação existente entre a resistividade elétrica do concreto no estado fresco e a relação a/c, com valores médios das estimativas para relação a/c dentro do intervalo de ±0,02, com relação aos valores efetivos das misturas testadas. A margem de erro média para as estimativas de relação a/c, considerando-se todos os cimentos testados, ficou no intervalo entre 2,25% e 9,38%. Foram obtidos coeficientes de determinação na ordem de 85,7% a 95,2% para as estimativas de resistência à compressão, mostrando que é possível determinar tanto a relação a/c quanto a resistência à compressão do concreto através do método da resistividade elétrica, quando o material encontra-se ainda no estado fresco. / During construction of concrete elements in the building site, quality control proceedings are adopted in order to verify if the concrete reaches its design specifications, which also avoids failures during the subsequent stages of the construction. Test methods used for the determination of the water-cement (w/c) ratio have received increased attention, due to the importance of this ratio for the concrete resistance and durability, and also because there isn’t any practical and sufficiently precise method available at the moment, which could be used for determining water-cement ration after mixing. Studies about the electrical resistivity method have shown a strong relationship between the measured resistivity values and water-cement ratio, for the fresh concrete, making this method an interesting alternative for determining w/c ratio. This study presents an analysis of the electrical resistivity method, applied to determine the water-cement ratio of several fresh concrete mixtures made with different types of Brazilian cements, in addition to estimates of compressive strength values of the hardened concretes. Concrete mixtures were made out of six cement types (CPV-ARI, CPIV-32, CPIII-40, CPII-Z-32, CPII-F-32 and CPII-E-40), dosed by the IPT/EPUSP method, and four water-cement ratios (0.35, 0.45, 0.55 and 0.65). Tests were performed using an improved probe, developed in this study, based in one prototype developed previously. Results shown a strong relationship between the electrical resistivity of fresh concrete and its water-cement ratio, with average estimated values within ±0,02 of the actual water-cement ratio values for the mixtures tested. The average error for the w/c ratio estimated values, considering all of the cements tested, was between 2,25% and 9,38%. The compressive strength estimates reached coefficients of determination between 85,7% and 95,2%, showing that it is possible to estimate both w/c ratio and compressive strength of concrete while still in the fresh state with the electrical resistivity method presented here.