Loading...
8 results
Search Results
Now showing 1 - 8 of 8
- Non-destructive Tests on ConcretePublication . Nepomuceno, Miguel; Lopes, Sérgio Manuel RodriguesConcrete compressive strength of standard samples curing under standard conditions are of outmost importance for quality control of concrete as it is produced. However, those values can only be accepted as indicating the “potential strength” of concrete and may differ from the actual in-situ concrete compressive strength. The knowledge, as close as possible, of the in-situ concrete compressive strength is, in some situations, necessary in order to estimate, for instance: the time when precast concrete members can be moved and transported, the time of prestress, removal of moulds or propping, etc. Non-destructive tests (NDT) have been increasingly used in the last decades for this purpose, i. e., the assessment of in-situ quality and integrity of concrete elements, especially for estimation of the in-situ concrete compressive strength. The use of NDT methods on normal and high strength concrete elements will be evaluated on this paper qualitatively, taking as reference five different test methods, which imply the measurement of other five different properties. Such properties include the measurement of the surface hardness, ultra-sonic pulse velocity, penetration resistance, pull-out force and direct tensile strength (pull-off test).
- Parâmetros para a composição de betões auto-compactáveisPublication . Nepomuceno, Miguel; Oliveira, Luiz Antonio Pereira de; Lopes, Sérgio Manuel RodriguesO artigo descreve a segunda etapa de um estudo mais alargado relativo à metodologia da composição de betões auto-compactáveis. Na primeira etapa produziu-se um número significativo de argamassas com propriedades reológicas adequadas à obtenção de BAC e resistências à compressão entre os 25 MPa e os 95 MPa. As argamassas diferiram entre si pelo facto de possuírem diferentes razões entre os volumes absolutos de materiais finos e de agregados finos (Vp/Vs) e por conterem misturas binárias de materiais finos que combinaram os cimentos (CEM I 42,5R e CEM II/B-L32,5N) com as adições (cinzas volantes, fíler calcário e fíler granítico) em diferentes percentagens de substituição. Em comum, as argamassas apresentavam aproximadamente o mesmo comportamento no estado fresco, avaliado em termos de área de espalhamento relativa (Gm) e velocidade relativa de escoamento (Rm). Na segunda etapa produziram-se 60 betões utilizando diferentes razões entre os volumes absolutos de argamassa e de agregados grossos (Vm/Vg) e foram avaliadas as suas propriedades no estado fresco e no estado endurecido. Os resultados obtidos permitiram avaliar a relação entre os parâmetros de cálculo da mistura, a reologia (avaliada pelos ensaios de espalhamento e de fluidez), a auto-compactabilidade (avaliada pela Caixa-L) e a resistência à compressão dos betões auto-compactáveis.
- Estudo comparativo de adições para betões auto-compactáveisPublication . Nepomuceno, Miguel; Oliveira, Luiz Antonio Pereira de; Lopes, Sérgio Manuel RodriguesO artigo descreve a análise comparativa dos resultados obtidos em argamassas adequadas à produção de betões auto-compactáveis quando se utilizaram associações binárias e ternárias de materiais finos, que combinaram, em diferentes percentagens de substituição, dois cimentos e quatro adições: fíler calcário, cinzas volantes, sílica de fumo e fíler granítico. As misturas binárias de materiais finos combinaram os cimentos (CEM I 42,5R e CEM II/B-L32,5N) com as adições de cinzas volantes, fíler calcário e fíler granítico. As misturas ternárias de materiais finos combinaram a microssílica com cada uma das restantes adições e com o cimento (CEM I 42,5R). Para cada mistura de materiais finos foram produzidas argamassas com diferentes razões entre os volumes absolutos de materiais finos e de agregados finos (Vp/Vs). As dosagens de água (Vw/Vp) e de superplastificante (Sp/p%) foram ajustadas experimentalmente até que todas as argamassas apresentassem aproximadamente o mesmo comportamento reológico, avaliado em termos de área de espalhamento relativa (Gm) e velocidade relativa de escoamento (Rm). O estudo permitiu avaliar a influência das adições nas dosagens de água e superplastificante necessárias à obtenção das propriedades reológicas adequadas. Adicionalmente, foi possível correlacionar, para diferentes razões Vp/Vs, a resistência à compressão das argamassas com a razão água/cimento e a percentagem de substituição do cimento pela adição.
- Maximum coarse aggregate’s volume fraction in self-compacting concrete for different flow restrictionsPublication . Nepomuceno, Miguel; Oliveira, Luiz Antonio Pereira de; Lopes, Sérgio Manuel Rodrigues; Franco, Rui Miguel CalaçaThe volume of coarse aggregates (Vg) in self-compacting concrete (SCC) is usually conditioned to the passing ability (PA) in an L-box test. Some mix design methods use the three bar test results in L-box for proportioning SCC. However, in real structures, gaps can differ from those of L-box. By increasing the gaps, the Vg value can be increased and, consequently, the mortar phase volume can be decreased. In this study, the model proposed by Nepomuceno et al. (2014) to quantify the Vg value was modified to allow the introduction of an additional parameter that takes account for different gaps. Four SCC mixtures with different Vg values and the same mortar phase were produced and the PA value measured in the L-box test for different sizes of gaps: R1 (34 mm), R2 (64 mm), R3 (94 mm) and R4 (no restrictions). The results showed that for less demanding gaps it is possible to increase the Vg value of SCC and comply with the PA value in L-box test (H2/H1≥0.80).
- Methodology for the mix design of self-compacting concrete using different mineral additions in binary blends of powdersPublication . Nepomuceno, Miguel; Oliveira, Luiz Antonio Pereira de; Lopes, Sérgio Manuel RodriguesInteraction between the coarse aggregates and the mortar phase of self-compacting concrete (SCC) was evaluated in a two phase program. In the first phase, 74 mortars suitable for SCC were produced, combining different volumetric ratios between powders and fine aggregates and different binary blends of powders. In the second phase, 60 concretes were produced with different volumetric ratios between the mortar phase and the coarse aggregates, and their fresh and hardened properties were evaluated. Based on this study, correlations between mix design parameters, fresh and hardened properties were obtained and a methodology was proposed for the mix design of SCC.
- Non-Destructive Tests on Normal and High Strength ConcretePublication . Lopes, Sérgio Manuel Rodrigues; Nepomuceno, MiguelOne of the most important concrete properties for structural concrete design or re-design is the compressive strength. Furthermore, other important concrete properties can be derived from the compressive strength. This property is typically obtained by standardised crushing tests on cast cubes or cylinders. However, cast cubes or cylinders may not be available for testing and, therefore, alternative tests need to be considered. The most reliable alternative test is the core test, which needs specimens extracted from the structure. Obviously, this is a very destructive test and other less destructive tests have been developed and deserve some attention. Some of non-destructive or partially destructive tests were carried out by the authors on normal and high strength concrete and compared with cube/cylinder common tests and also with core tests. This paper presents results from this study. Test procedures and reliability of non-destructive tests are analysed and discussed. Conclusions are presented.
- Methodology for mix design of the mortar phase of self-compacting concrete using different mineral additions in binary blends of powdersPublication . Nepomuceno, Miguel; Oliveira, Luiz Antonio Pereira de; Lopes, Sérgio Manuel RodriguesThis paper details a comparative analysis of the results obtained in tests on mortars suitable for self-compacting concrete (SCC). The binary and ternary blends of powder materials used were combinations of two cements with four additions in different percentages: limestone powder, fly ash, granite filler and microsilica. The correlations between the mix design parameters of the mortar phase and the flow properties and compressive strength were evaluated. As a result of this evaluation, a simple methodology was proposed for the mix design of the mortar phase in binary blends of powder with the aim of simultaneously obtaining both adequate flow properties and the necessary compressive strength of the mortar.
- Analysis of Within-Test Variability of Non-Destructive Test Methods to Evaluate Compressive Strength of Normal Vibrated and Self-Compacting ConcretesPublication . Nepomuceno, Miguel; Lopes, Sérgio Manuel RodriguesNon-destructive tests (NDT) have been used in the last decades for the assessment of in-situ quality and integrity of concrete elements. An important step in the application of NDT methods concerns to the interpretation and validation of the test results. In general, interpretation of NDT results should involve three distinct phases leading to the development of conclusions: processing of collected data, analysis of within-test variability and quantitative evaluation of property under investigation. The analysis of within-test variability can provide valuable information, since this can be compared with that of within-test variability associated with the NDT method in use, either to provide a measure of the quality control or to detect the presence of abnormal circumstances during the in-situ application. This paper reports the analysis of the experimental results of within-test variability of NDT obtained for normal vibrated concrete and self-compacting concrete. The NDT reported includes the surface hardness test, ultrasonic pulse velocity test, penetration resistance test, pull-off test, pull-out test and maturity test. The obtained results are discussed and conclusions are presented.