The Experts below are selected from a list of 1548 Experts worldwide ranked by ideXlab platform
Zoubir Mehdi Sbartai - One of the best experts on this subject based on the ideXlab platform.
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Recommendation of RILEM TC249-ISC on non destructive in situ strength assessment of concrete
Materials and Structures, 2019Co-Authors: Denys Breysse, Michael Grantham, Jean-paul Balayssac, Samuele Biondi, David Corbett, Arlindo Goncalves, Vincenza A. M. Luprano, Angelo Masi, Andre Valente Monteiro, Zoubir Mehdi SbartaiAbstract:This recommendation is written to improve the assessment of the in situ. Compressive strength of concrete in existing structures by combining core strength values and non-destructive measurements. Both average strength and its scatter are considered. Deriving a characteristic strength from the assessment results is not considered here. The recommendation applies for most common techniques (ultrasonic pulse velocity, Rebound Hammer, pull-out) but also for less common techniques (penetration test, etc.). The recommendation does not apply to situations in which no core has been taken from the existing structure and is limited to situations where NDT is combined with cores. The recommendation introduces the concept of Estimation Quality Level, corresponding to the target of assessment, and which is put in relation with the means and strategy developed for assessing concrete. The text details all steps that must be followed from the data gathering to the checking of the quality of the final estimations. For more clarity, an illustrative example is described for each step of the assessment process.
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non destructive assessment of both mean strength and variability of concrete a new bi objective approach
Construction and Building Materials, 2016Co-Authors: Maitham Alwash, Zoubir Mehdi Sbartai, Denys BreysseAbstract:Abstract Using non-destructive techniques (NDT) like Rebound Hammer in combination with destructive techniques (DT) like core test is a common practice. Two approaches are widely used to produce a model for assessing the concrete strength. The first approach consists in fitting a specific model between NDT measurements and cores using the regression analysis. The second approach uses a prior model which is calibrated according to measured core strengths. The EN 13791 and ACI standards require a large number of cores to estimate mean concrete strength and concrete strength variability and consequently to calculate the characteristic strength value which depends on these two inputs. In this work, we propose a new approach for identifying the models based on NDT and DT tests in order to capture both mean strength and concrete strength variability. This approach is first illustrated by synthetic simulations which are a good way to study a problem having many degrees of freedom. The proposed approach is then tested on a real data set. In both cases, it is confirmed that the common approaches are able to estimate the mean strength but they fail, even with a large number of cores, to accurately estimate the concrete variability and hence the characteristic strength. Reversely, the new approach shows its high efficiency in capturing the concrete variability (in addition to the mean strength) with a number of cores lower than that prescribed by the standards.
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non destructive strength evaluation of concrete analysis of some key factors using synthetic simulations
Construction and Building Materials, 2015Co-Authors: Denys Breysse, Maitham Alwash, Zoubir Mehdi SbartaiAbstract:Abstract Non-destructive techniques (NDT) like Rebound Hammer (RH) and ultrasonic pulse velocity (UPV) are widely used in conjunction with destructive techniques (core tests) for assessing the concrete strength in existing buildings. The methodology consists in fitting regression models between NDT techniques and destructive tests on a limited number of cores. The quality of the model is affected by many influencing factors such as: the number of cores, the quality of NDT measurements, the variability in concrete strength, the existence and magnitude of possible uncontrolled factors (like saturation rate) and the combination of techniques. In this paper, the effects of these factors are studied using a synthetic simulation approach in order to well understand them and consequently to develop a methodology for improving the quality of strength assessment. In order to assess the quality of fitted model and its ability to estimate strength, RMSE and r 2 errors are calculated and it is found that the calculation of r 2 alone may give misleading indication since r 2 is very sensitive to the scattering of the explanatory variable. Another important result of the present study is that there is a critical minimal number of cores which makes the combination efficient while for a lower number the use of single technique is preferable. This number depends on the qualities of the two techniques to be combined.
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assessing the spatial variability of concrete structures using ndt techniques laboratory tests and case study
Construction and Building Materials, 2013Co-Authors: Ngoc Tan Nguyen, Denys Breysse, Zoubir Mehdi Sbartai, Jeanfrancois Lataste, Frederic BosAbstract:Abstract Spatial variability of concrete is an important characteristic, which qualifies the non-homogeneity of mechanical and physical properties on structural components. Assessing it can be of great interest for either locating potential damaged areas in an existing structure, or reliability analysis. A two-stage experimental program was carried out using non-destructive testing (NDT) on laboratory concrete slabs in outdoor environment and on an existing bridge. The spatial variability was assessed at three scales: point (repeatability), local and global, for several NDT techniques (ultrasonic, electrical resistivity, radar and Rebound Hammer). The experimental results were analyzed using statistical and geostatistical tools (descriptive and spatial statistics). In this study, the methodology consists of performing statistical analysis for assessing the spatial variability and estimating the required minimal number of NDT measurements. The spatial correlation of NDT measurements is studied with variographic analysis. Some correlation lengths were identified ranging 40–60 cm for the laboratory slab and the investigated bridge pier. Kriging method was used as a robust geostatistical tool, which allows the representation of the spatial variability of concrete structures.
Denys Breysse - One of the best experts on this subject based on the ideXlab platform.
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Recommendation of RILEM TC249-ISC on non destructive in situ strength assessment of concrete
Materials and Structures, 2019Co-Authors: Denys Breysse, Michael Grantham, Jean-paul Balayssac, Samuele Biondi, David Corbett, Arlindo Goncalves, Vincenza A. M. Luprano, Angelo Masi, Andre Valente Monteiro, Zoubir Mehdi SbartaiAbstract:This recommendation is written to improve the assessment of the in situ. Compressive strength of concrete in existing structures by combining core strength values and non-destructive measurements. Both average strength and its scatter are considered. Deriving a characteristic strength from the assessment results is not considered here. The recommendation applies for most common techniques (ultrasonic pulse velocity, Rebound Hammer, pull-out) but also for less common techniques (penetration test, etc.). The recommendation does not apply to situations in which no core has been taken from the existing structure and is limited to situations where NDT is combined with cores. The recommendation introduces the concept of Estimation Quality Level, corresponding to the target of assessment, and which is put in relation with the means and strategy developed for assessing concrete. The text details all steps that must be followed from the data gathering to the checking of the quality of the final estimations. For more clarity, an illustrative example is described for each step of the assessment process.
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non destructive assessment of both mean strength and variability of concrete a new bi objective approach
Construction and Building Materials, 2016Co-Authors: Maitham Alwash, Zoubir Mehdi Sbartai, Denys BreysseAbstract:Abstract Using non-destructive techniques (NDT) like Rebound Hammer in combination with destructive techniques (DT) like core test is a common practice. Two approaches are widely used to produce a model for assessing the concrete strength. The first approach consists in fitting a specific model between NDT measurements and cores using the regression analysis. The second approach uses a prior model which is calibrated according to measured core strengths. The EN 13791 and ACI standards require a large number of cores to estimate mean concrete strength and concrete strength variability and consequently to calculate the characteristic strength value which depends on these two inputs. In this work, we propose a new approach for identifying the models based on NDT and DT tests in order to capture both mean strength and concrete strength variability. This approach is first illustrated by synthetic simulations which are a good way to study a problem having many degrees of freedom. The proposed approach is then tested on a real data set. In both cases, it is confirmed that the common approaches are able to estimate the mean strength but they fail, even with a large number of cores, to accurately estimate the concrete variability and hence the characteristic strength. Reversely, the new approach shows its high efficiency in capturing the concrete variability (in addition to the mean strength) with a number of cores lower than that prescribed by the standards.
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non destructive strength evaluation of concrete analysis of some key factors using synthetic simulations
Construction and Building Materials, 2015Co-Authors: Denys Breysse, Maitham Alwash, Zoubir Mehdi SbartaiAbstract:Abstract Non-destructive techniques (NDT) like Rebound Hammer (RH) and ultrasonic pulse velocity (UPV) are widely used in conjunction with destructive techniques (core tests) for assessing the concrete strength in existing buildings. The methodology consists in fitting regression models between NDT techniques and destructive tests on a limited number of cores. The quality of the model is affected by many influencing factors such as: the number of cores, the quality of NDT measurements, the variability in concrete strength, the existence and magnitude of possible uncontrolled factors (like saturation rate) and the combination of techniques. In this paper, the effects of these factors are studied using a synthetic simulation approach in order to well understand them and consequently to develop a methodology for improving the quality of strength assessment. In order to assess the quality of fitted model and its ability to estimate strength, RMSE and r 2 errors are calculated and it is found that the calculation of r 2 alone may give misleading indication since r 2 is very sensitive to the scattering of the explanatory variable. Another important result of the present study is that there is a critical minimal number of cores which makes the combination efficient while for a lower number the use of single technique is preferable. This number depends on the qualities of the two techniques to be combined.
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assessing the spatial variability of concrete structures using ndt techniques laboratory tests and case study
Construction and Building Materials, 2013Co-Authors: Ngoc Tan Nguyen, Denys Breysse, Zoubir Mehdi Sbartai, Jeanfrancois Lataste, Frederic BosAbstract:Abstract Spatial variability of concrete is an important characteristic, which qualifies the non-homogeneity of mechanical and physical properties on structural components. Assessing it can be of great interest for either locating potential damaged areas in an existing structure, or reliability analysis. A two-stage experimental program was carried out using non-destructive testing (NDT) on laboratory concrete slabs in outdoor environment and on an existing bridge. The spatial variability was assessed at three scales: point (repeatability), local and global, for several NDT techniques (ultrasonic, electrical resistivity, radar and Rebound Hammer). The experimental results were analyzed using statistical and geostatistical tools (descriptive and spatial statistics). In this study, the methodology consists of performing statistical analysis for assessing the spatial variability and estimating the required minimal number of NDT measurements. The spatial correlation of NDT measurements is studied with variographic analysis. Some correlation lengths were identified ranging 40–60 cm for the laboratory slab and the investigated bridge pier. Kriging method was used as a robust geostatistical tool, which allows the representation of the spatial variability of concrete structures.
Spyridon A Paschalis - One of the best experts on this subject based on the ideXlab platform.
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combined non destructive testing ndt method for the evaluation of the mechanical characteristics of ultra high performance fibre reinforced concrete uhpfrc
Construction and Building Materials, 2017Co-Authors: Ourania Tsioulou, Andreas Lampropoulos, Spyridon A PaschalisAbstract:Abstract Ultra-High Performance Fibre Reinforced Concrete is a material which is becoming increasingly popular in structural applications, mainly due to its superior mechanical characteristics. The mechanical properties of this material are of high importance and the development of non-destructive techniques is vital for the evaluation of the mechanical characteristics of existing structures. In the current study, Ultra-High Performance Fibre Reinforced Concrete with different amounts of steel fibres has been examined. Compressive and tensile tests have been conducted alongside with Ultrasonic Pulse Velocity and Rebound Hammer measurements and the development of appropriate empirical non-destructive models has been examined.
K Sivaraman - One of the best experts on this subject based on the ideXlab platform.
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the effect of controlled permeable formwork liner on the mechanical and durability properties of self compacting concrete
Construction and Building Materials, 2016Co-Authors: S. Kothandaraman, S. Kandasamy, K SivaramanAbstract:Abstract The quality of the surface zone of concrete is a crucial factor for durable concrete structures, as it is the first line of resistance to penetration of aggressive agencies. Use of controlled permeable formwork (CPF) liner is one of the techniques employed to improve the quality of the surface zone of concrete. CPF liner drains mix water and entrapped air from the near surface of concrete while retaining cement and other fine particles. This helps to reduce water-cement ratio, increase cement content and decrease surface pores in the surface zone of concrete. It is postulated that CPF drains air and water, which migrate towards the formwork due to vibration caused while compacting concrete and hydrostatic pressure. In the present investigation, an experimental study was carried out to verify the performance and efficiency of CPF liner against self-compacting concrete (SCC). Suitable size specimens were prepared using impermeable formwork (IMF) and CPF liner as well. Tests were carried out to check compressive, split tensile strength and flexural strength; ultrasonic pulse velocity and Rebound Hammer; abrasion resistance, sorptivity and water absorption. The test results reveal that CPF liner performs equally well with SCC. Vibration/hydrostatic pressure may not play significant role in draining the interface water through CPF liner.
S. Kothandaraman - One of the best experts on this subject based on the ideXlab platform.
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The effect of controlled permeable formwork liner on the mechanical properties of concrete
Materials and Structures, 2016Co-Authors: S. Kothandaraman, S. KandasamyAbstract:Controlled permeable formwork (CPF) liner was developed primarily to improve the surface quality of concrete and thereby its durability. CPF liner allows air and water to escape from the surface adjacent to the formwork. This paper reports an experimental study carried out to investigate the influence of CPF liner on the strength and certain mechanical properties of concrete with three different water–cement (w–c) ratios. The specimens were prepared against CPF liner and impermeable steel formwork (IMF) and tested at various ages starting from 7 to 365 days. Various tests were conducted to assess surface quality; compressive, split tensile and flexural strengths, Rebound Hammer and abrasion resistance of concrete. The results indicate that CPF concrete performed better than IMF concrete in all aspects. The present investigation reveals that the use of CPF liner has significantly improved the tensile strength (say, 20 %) of concrete and the abrasion resistance has been enhanced to a remarkable level (50–80 %). Further, the surface quality is very essential to assess the cube strength of concrete and the existing testing method slightly underestimates the cube strength.
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the effect of controlled permeable formwork liner on the mechanical and durability properties of self compacting concrete
Construction and Building Materials, 2016Co-Authors: S. Kothandaraman, S. Kandasamy, K SivaramanAbstract:Abstract The quality of the surface zone of concrete is a crucial factor for durable concrete structures, as it is the first line of resistance to penetration of aggressive agencies. Use of controlled permeable formwork (CPF) liner is one of the techniques employed to improve the quality of the surface zone of concrete. CPF liner drains mix water and entrapped air from the near surface of concrete while retaining cement and other fine particles. This helps to reduce water-cement ratio, increase cement content and decrease surface pores in the surface zone of concrete. It is postulated that CPF drains air and water, which migrate towards the formwork due to vibration caused while compacting concrete and hydrostatic pressure. In the present investigation, an experimental study was carried out to verify the performance and efficiency of CPF liner against self-compacting concrete (SCC). Suitable size specimens were prepared using impermeable formwork (IMF) and CPF liner as well. Tests were carried out to check compressive, split tensile strength and flexural strength; ultrasonic pulse velocity and Rebound Hammer; abrasion resistance, sorptivity and water absorption. The test results reveal that CPF liner performs equally well with SCC. Vibration/hydrostatic pressure may not play significant role in draining the interface water through CPF liner.
