Evaluation of Self-Compacting Concrete Strength with Non-Destructive Tests for Concrete Structures

Self-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.info:eu-repo/semantics/publishedVersio

Evaluation of In-place Concrete Strength by Near-to-surface Tests

The near-to-surface tests, as described by British Standard BS 1881: Part 207: 1992, comprises different techniques which were developed to evaluate in-situ strength of concrete, and it includes: internal fracture, pull-out, pull-off, penetration resistance and break-off tests. Since these tests measure only a property of concrete close to the surface, the evaluation of in-situ strength of concrete mass has to be obtain by a experimentally correlation between the near-to surface test results and the compressive strength of concrete mass. This paper discusses the reliability of two of this techniques, penetration resistance test and pull-out tests, as a construction tool for the evaluation of the in-place concrete strength both in normal and high strength concrete. For penetration resistance test applied to high-strength concrete an alternative firing apparatus to the standard apparatus, Windsor Probe Test System, is used. The obtained correlations are also presented and compared to those obtain by other research works.info:eu-repo/semantics/publishedVersio

A Comparative Study of Penetration Resistance Apparatus on Concrete

The existence of a relationship between the compressive strength of a given concrete and its resistance to penetration by a steel probe fired into the concrete is well known; the depth of penetration will be inversely proportional to the compressive strength. A test apparatus, designed for this purpose, using a special probe and standardised powder charge, was developed in the USA during the 1960s’ and is known as Windsor Probe Test and covered by the ASTM Standards (ASTM-C803-90). In Europe, similar standards are the British Standards (BS 1881: Part 207: 1992). The aim of this work is to perform studies concerning to a new apparatus application in comparison with the WPT System, which was called Alternative Firing Apparatus (AFA). Five different mix proportions were produced in order to obtain five sets of specimens with five different classes of compressive strength. The tests with the two described systems were performed at 28 days age for each set of specimens. The obtained results show that the Alternative Firing Apparatus could be a suitable mean for the assessment of in-place strength. The main physical limitation of penetration resistance tests is the surface damage and the danger of splitting of members, which limits the zones of testing. However, it was found that the Alternative Firing Apparatus causes less damage than WPT System. Consequently, minor distances between probes are possible.info:eu-repo/semantics/publishedVersio

Non-destructive Tests on Concrete

Concrete 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).info:eu-repo/semantics/publishedVersio

Analysis of Within-Test Variability of Non-Destructive Test Methods to Evaluate Compressive Strength of Normal Vibrated and Self-Compacting Concretes

Non-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.info:eu-repo/semantics/publishedVersio

Non-Destructive Tests on Normal and High Strength Concrete

One 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.info:eu-repo/semantics/publishedVersio

Metodologia para a composição de betões auto-compactáveis

No presente trabalho são revistos alguns dos principais métodos de estudo da composição de betões auto-compactáveis, com especial incidência nos métodos propostos por Okamura et al., pela JSCE, pelo CBI e pelo LCPC. São também abordados os aspectos relativos ao desenvolvimento, aos materiais constituintes, às propriedades do betão fresco e endurecido e ainda à produção e manuseamento do material. A revisão efectuada permitiu observar que os métodos propostos por Okamura et al. e pela JSCE são os mais generalizados pela sua simplicidade, mas apresentam algumas limitações inerentes, associadas à dificuldade em optimizar e modelar as misturas com vista à obtenção de um qualquer valor médio especificado para a resistência à compressão do betão na fase de estudo da composição. Em resultado da apreciação efectuada, entendeuse adequado investigar a possibilidade de se delinear uma nova abordagem ou introduzir novos parâmetros para o cálculo da composição dos betões auto-compactáveis que permitissem responder a algumas dessas limitações, admitindo como ponto de partida o método proposto por Okamura et al.. A proposta a desenvolver deveria assentar em procedimentos de cálculo expeditos, cuja primeira e fundamental abordagem seria suportada por ensaios em argamassas, como propôs Okamura. Analisadas as propostas de diferentes autores, foi definido um intervalo de variação para cada um dos parâmetros que caracterizam o escoamento das argamassas (Gm e Rm), conducente à obtenção de betões auto-compactáveis. Para cada família de materiais finos (i.e., para cada associação de materiais finos), as dosagens de superplastificante e de água de amassadura que conduziram aos parâmetros Gm e Rm pretendidos, foram determinados por estudos experimentais em argamassas adoptando uma metodologia que difere ligeiramente daquela proposta por Okamura et al.. Foram introduzidos novos parâmetros para quantificar as dosagens de agregados finos (Vp/Vs) nas argamassas e de agregados grossos (Vm/Vg) nos betões e fizeram-se variar estes parâmetros abaixo e acima dos valores correspondentes propostos por Okamura et al., por forma a avaliar uma possível optimização das misturas, principalmente através da redução do volume de pasta. Finalmente, foram analisados os parâmetros que melhor se adequaram ao controlo da resistência à compressão das argamassas e, indirectamente, ao controlo da resistência dos betões. A análise efectuada foi direccionada unicamente para os betões do tipo finos (solução mais corrente) e apenas foram avaliados os aspectos físicos e mecânicos do seu comportamento. Foram efectuados estudos em argamassas e betões utilizando associações binárias e ternárias de materiais finos, que combinaram dois tipos de cimentos (CEM I 42,5R e CEM II/B-L 32,5N) e quatro adições: fíler calcário, cinzas volantes, sílica de fumo e fíler granítico. O fíler granítico utilizado, proveniente de desperdícios industriais, foi testado a título experimental como adição, com resultados promissores. Sob condições idênticas de escoamento, o fíler granítico revelou consumos de superplastificante idênticos àqueles obtidos com as cinzas volantes e fíler calcário (reconhecidamente úteis na produção de betões auto-compactáveis), enquanto que a sílica de fumo revelou consumos excessivos de superplastificante, quer em termos absolutos, quer comparativamente às restantes adições. Os resultados obtidos foram satisfatórios e culminaram com a apresentação de uma proposta para o estudo do betão auto-compactável do tipo finos, a qual facilita a optimização da mistura e permite estimar, na fase de estudo da composição, a resistência à compressão do betão.Some of the main methods for self-compacting concrete mix design are reviewed in the present research work, with special focus on those proposed by Okamura research group, JSCE, CBI and LCPC. The aspects concerning to development, constituent materials, properties of fresh and hardened concrete and furthermore the production and handling of the material are also reviewed. The bibliographic review have indicated that the methods proposed by Okamura research group and JSCE are the most generalized due to its simplicity, but they present some inherent limitations, associated to its difficulty on optimizing and modelling concrete mixtures in order to achieve a specified mean value for compressive strength defined on the mix design phase. As a result of that appreciation, it was considered adequate to investigate the possibility of outline a new approach or to introduce new parameters for the selfcompacting concrete mix design that allow finding the answer for such limitations, considering, as a start point, the method proposed by Okamura research group. The new proposal should lay on an easy and swift procedure, which, for a start, should be supported by tests on mortar mixes, as proposed by Okamura research group. After the examination of proposals by different authors, an interval of variation was defined for each of the parameters that characterized the flow behaviour of mortars (Gm and Rm), leading to self-compacting concrete mixes. For each family of fine particles, the proportions of superplasticizer and water content which lead to the wanted Gm and Rm parameters were determined by trial mixtures of mortar using a methodology that slightly differ from that proposed by Okamura research group. New parameters were introduced to quantify the proportions of fine aggregate (Vp/Vs) on mortars and to quantify the proportions of coarse aggregate (Vm/Vg) on concretes. Such parameters were changed to values lower and higher than those proposed by Okamura research group, in order to achieve an optimized mixture, namely by reducing the paste volume. Finally, the parameters that better evaluate the mortars compressive strength and, indirectly, the concrete compressive strength were analysed. The analysis done was directed to the powder type self-compacting concrete (the most common solution) and only the physical and mechanical aspects of its behaviour were analysed. Studies on mortar and concrete mixes were made using binary and ternary associations of powder materials which combine two types of cements (CEM I 42,5R and CEM II/B-L 32,5N) and four mineral additions: limestone powder, fly ash, silica fume and granite filer. The granite filer that was used here, originating from a by-product of industry, was tested experimentally as a mineral addition, with promising results. Under identical flow behaviour properties, the granite filer has revealed identical needs of superplasticizer dosages as those of fly ash and limestone powder additions (recognised as advantageous for self-compacting concrete), while the silica fume has revealed overmuch needs of superplasticizer, either in absolute volume, or comparatively with other additions used. The results obtained were satisfactory and ended with the presentation of a proposal for mix design of the type powder self-compacting concrete. This enables the optimization of mixes and, on the mix design phase, allows the estimation of the compressive strength of concrete.Financiada pelo subprograma Educação PRODEP III (Medida n.º 5/ Acção n.º 5.3 – Acções de Doutoramento, Ref. 5.3/C/185.009/01)

A comparison between on-site measured and estimated based adjustment factor values used to calculate heat losses to unconditioned spaces in dwellings

Steady-state methods have been widely used in Europe to analyse the energy performance of low-energy buildings. The accuracy of such methods depends on the assumptions regarding the compensation of non-stationary effects but also on the input design data, such as the temperature of unconditioned spaces (UnSp). This temperature depends mainly on the thermal characteristics of UnSp envelope, air ventilation rate, temperature of the conditioned spaces, and the external environment. External environment varies over time, daily and seasonally, making it difficult to accurately estimate UnSp temperature. European Union (EU) directives stated that the UnSp temperature can be evaluated by the adjustment factor (b) set by EN ISO 13789. However, each Member State may adjust procedures, by proposing simplified approaches, either for new or existing buildings. In this paper the b-values measured on-site in three dwellings were compared to those calculated by EN ISO 13789, as well as those estimated based on simplified procedures, allowed in the regulatory framework of some EU Member States, namely Ireland, Portugal, Spain, France, and Italy. The study allowed to conclude that EN ISO 13789 and Irish BR 443 provided similar values. However, if the purpose is to simplify procedures and reduce computation effort, French RE2020 proved to be very effective. The thermal characteristics of the UnSp envelope and air ventilation rate were identified as the parameters that most affect the estimation of the b-value, while thermal losses through linear thermal bridges and the ground do not seem to have a significant impact.info:eu-repo/semantics/publishedVersio

Neutral Axis Depth versus Ductility and Plastic Rotation Capacity on Bending in Lightweight-Aggregate Concrete Beams

This article presents an experimental study on the evolution of the neutral axis depth at failure in the critical section with the flexural ductility and plastic rotation capacity of reinforced concrete (RC) lightweight-aggregate concrete (LWAC) beams. For this, the results of a previous experimental program involving RC LWAC beams tested in flexure until failure are used. The variable studies were the concrete compressive strength (between 22.0 and 60.4 MPa and dry density between 1651 and 1953 kg/m3) and the longitudinal tensile reinforcement ratio (between 0.13% and 2.69%). The flexural ductility and the plastic rotation capacity of the RC LWAC beams are characterized by a ductility index and a plastic trend parameter, respectively. The influence of the variable studies, as well as the relation of the flexural ductility and plastic rotation capacity with the values for the neutral axis depth at failure are analyzed and discussed. Some conclusions are drawn which can be useful for the design of RC LWAC beams for flexure. In particular, it is shown that the practical rule of limiting the neutral axis depth at failure to ensure ductile behavior, as used in normal-weight aggregate concrete beams, is also valid for RC LWAC beams.info:eu-repo/semantics/publishedVersio

Comparison between the human reactions in a simulacrum and in a real fire situation

Human reaction to a fire situation in buildings depends on the characteristics of each individual, of the building and the actual emergency situation. To minimize the consequences of an emergency fire situation in a building, it is important to have a safe, orderly and rapid evacuation. For this purpose the occupants should be trained to respond in an appropriate way. Therefore, it is necessary to assess whether simulacrums or fire drills are effective or not. In recent years, in Portugal, the number of fire simulacrums in office buildings, schools and hotels, among others, have increased. Taking as reference the Portuguese population, this article presents the results of an ongoing research project that compares the human behavior in a real fire situation with that observed in a fire simulacrum. The study was supported by a significant number of surveys conducted to the occupants who were involved in one of the two previous mentioned situations. The comparison between the actions undertaken by the occupants in both situations allows understanding if human behavior in a simulacrum reflects human behavior in a real fire situation.info:eu-repo/semantics/publishedVersio