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- 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).
- Parameters for Self-compacting Concrete Mortar PhasePublication . Nepomuceno, Miguel; Oliveira, Luiz Antonio Pereira deThis paper reports an experimental study on the mortar phase for self-compacting concrete. A series of mortars were produced with similar flow properties, measured by spread and v-funnel tests, adequate to produce self-compacting concrete. The water content and the modified carboxylic superplasticizer dosage were determined experimentally for each mortar. Different percentages of cement replacement materials were used in binary blends, each one combining one of the two types of cement with one of the three mineral additions selected: limestone powder, granite filler and fly ash. Each of the binary blends of powders was combined in five different proportions in volume with the fine aggregate (Vp/Vs). Mortars were tested for compressive strength at 28 days age and this value was related to the water/cement ratio, the percentage of replacement materials, and Vp/Vs parameter. The analysis revealed the possibility of establishing adequate mortar parameters to obtain simultaneously the self-compactability and the required compressive strength of self-compacting concrete.
- Ensaios não destrutivos em betãoPublication . Nepomuceno, MiguelNo presente trabalho são passados em revista os principais métodos de ensaio não destrutivos, destinados a avaliar as diferentes propriedades do betão “in situ” e são tecidas a este respeito algumas considerações de âmbito geral. Segue-se uma extensa revisão bibliográfica, retratando o atual estado do conhecimento de um conjunto de ensaios não destrutivos selecionados por terem uma vasta aplicação em betões da gama de resistência normal e/ou por serem fáceis de operar e relativamente económicos ao ponto de justificar a sua aplicação corrente. Os ensaios estudados no presente trabalho são os seguintes: o ensaio de dureza superficial, utilizando o esclerómetro de Schmidt Tipo N; o ensaio de medição da velocidade de propagação de ultrassons, utilizando o aparelho “Pundit”; o ensaio da resistência à penetração, utilizando a Pistola de Windsor e uma Máquina Alternativa de Ensaio (testada para este efeito pela primeira vez); o ensaio da força de arranque, utilizando o sistema “Capo-test” e, ainda, o ensaio da tensão de tração direta, utilizando o sistema “Bond-test”. À revisão bibliográfica segue-se a descrição de um programa de ensaios experimental, que inclui: a aplicação de todos os ensaios acima listados em 11 lajes com betões de resistências à compressão que variaram desde os 17 MPa até aos 82 MPa; o ensaio à compressão de cubos de 150 mm de aresta curados juntamente com as lajes; a estimativa da resistência equivalente em cubos obtida de carotes extraídas dessas lajes e, ainda, o ensaio à compressão aos 28 dias de cubos padrão sujeitos a cura normalizada. A variabilidade dos próprios ensaios é avaliada em pormenor; são apresentadas as correlações obtidas com a resistência à compressão; são avaliados e apresentados os limites de confiança de 95% para essas correlações; são discutidos os resultados obtidos, comparando-os com trabalhos similares observados na bibliografia consultada. Finalmente, são apresentadas as conclusões finais e sugeridos futuros trabalhos nesta área.
- 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.
- Parameters for Self-compacting Concrete Mortar PhasePublication . Oliveira, Luiz António Pereira de; Nepomuceno, MiguelThis paper reports an experimental study on the mortar phase for selfcompacting concrete. A series of mortars were produced with similar flow properties, measured by spread and v-funnel tests, adequate to produce self-compacting concrete. The water content and the modified carboxylic superplasticizer dosage were determined experimentally for each mortar. Different percentages of cement replacement materials were used in binary blends, each one combining one of the two types of cement with one of the three mineral additions selected: limestone powder, granite filler and fly ash. Each of the binary blends of powders was combined in five different proportions in volume with the fine aggregate (Vp/Vs). Mortars were tested for compressive strength at 28 days age and this value was related to the water/cement ratio, the percentage of replacement materials, and Vp/Vs parameter. The analysis revealed the possibility of establishing adequate mortar parameters to obtain simultaneously the self-compactability and the required compressive strength of self-compacting concrete.
- 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.
- Evaluation of Self-Compacting Concrete Strength with Non-Destructive Tests for Concrete StructuresPublication . Nepomuceno, Miguel; Bernardo, LuísSelf-compacting concrete (SCC) shows to have some specificities when compared to normal vibrated concrete (NVC), namely higher cement paste dosage and smaller volume of coarse aggregates. In addition, the maximum size of coarse aggregates is also reduced in SCC to prevent blocking effect. Such specificities are likely to affect the results of non-destructive tests when compared to those obtained in NVC with similar compressive strength and materials. This study evaluates the applicability of some non-destructive tests to estimate the compressive strength of SCC. Selected tests included the ultrasonic pulse velocity test (PUNDIT), the surface hardness test (Schmidt rebound hammer type N), the pull-out test (Lok-test), and the concrete maturity test (COMA-meter). Seven sets of SCC specimens were produced in the laboratory from a single mixture and subjected to standard curing. The tests were applied at different ages, namely: 1, 2, 3, 7, 14, 28, and 94 days. The concrete compressive strength ranged from 45 MPa (at 24 h) to 97 MPa (at 94 days). Correlations were established between the non-destructive test results and the concrete compressive strength. A test variability analysis was performed and the 95% confidence limits for the obtained correlations were computed. The obtained results for SCC showed good correlations between the concrete compressive strength and the non-destructive tests results, although some differences exist when compared to the correlations obtained for NVC.
- Experimental evaluation of cement mortars with phase change material incorporated via lightweight expanded clay aggregatePublication . Nepomuceno, Miguel; Silva, Pedro Dinho daAn experimental evaluation on cement mortars with phase change material (PCM) incorporated via lightweight aggregate (LWA) is reported. Three groups of LWA mortars were produced: one with pre-soaked LWA and the others with PCM-filled LWA combining two different impregnation processes and PCM dosages of 50, 75 and 100 kg/m3 corresponding to the LWA contents of 242, 354 and 481 kg/m3, respectively. Mechanical and thermophysical properties were evaluated. The results showed that high thermal inertia and low mass are compatible in PCM-filled LWA mortars and that the thermal response increases with the PCM to a certain limit and then decrease.