Early-age monitoring of fresh cementitious material by acoustic emission

Concrete properties are mainly affected by the fresh state since it has a significant impact on the long-term concrete performance. In this study, acoustic emission (AE) was applied to monitor the behavior of fresh cement paste. AE is based on the detection of high-frequency elastic waves originating from different material sources. This highly sensitive technique provides data that contribute to a deeper understanding of the different ongoing processes for fresh concrete, as the possible AE sources are many. Characterization of each different source type is difficult and therefore, a combined methodology of AE, capillary pressure in the matrix and specimen deformation was applied to monitor the fresh cement paste

Monitoring early-age acoustic emission of cement paste and fly ash paste

In this study, a combined approach of several monitoring techniques was applied to allow correlations between the AE activity and related processes such as shrinkage and settlement evolution, capillary pressure and temperature development in fresh cementitious media. AE parameters related to frequency, energy, and cumulative activity which exhibit sensitivity to the particle size distribution of cement paste are compared with inert fly ash (FA) leading to isolation of the mechanical sources from the chemical ones. Characterization of the origin of different processes occurring in cement paste during hydration is complex. Although acoustic emission (AE) monitoring has been used before, a qualitative relation between the microstructural formation or other early-age processes and the number or parameters of AE signals has not been established. The high sensitivity of AE enables the recording of elastic waves within the cementitious material, allowing the detection of even low-intensity activities

Monitoring of fresh concrete curing by combined NDT techniques

Ensuring the quality of fresh concrete and suitable curing conditions substantially reduces the possibility of future failure to perform as designed. However, the most reliable examination for concrete is mechanical testing after hardening. In order to obtain better control on the process from very early age, this study describes a combined approach of several monitoring techniques. Acoustic emission is used to record the numerous events occurring during the first hours when concrete is in liquid form as well as later when hardening takes place and drying shrinkage cracking is exhibited. In addition, pressure sensors follow the development of capillary pressure in the matrix and indicate the moment of air entry into the system. Settlement and shrinkage, measured both non-contact by digital image correlation and conventionally, as well as temperature shed light into the complex processes occurring into fresh concrete and help to verify the sources of AE. The final aim is to develop a methodology to assess the quality of the fresh concrete from an early age, to possibly project to the final mechanical properties and to ensure a proper service life

Damage classification in reinforced concrete beam by acoustic emission signal analysis

Acoustic Emission (AE) is a non-destructive testing technique which can be used to identify both the damage level and the nature of that damage such as tensile cracks and shear movements at critical zones within a structure. In this work, the acoustic emission parameters of amplitude, rise time, average frequency and signal strength were used to classify the damage and to determine the damage level. Laboratory experiments were performed on a beam (150 x 250 x 1900 mm). The acoustic emission analysis was successfully used to determine crack movements and classify damage levels in accordance with the observations made during an increasing loading cycle

System-Level Modeling, Analysis and Code Generation: Object Recognition Case Study

International audienceOne of the most important challenges in complex embedded systems design is developing methods and tools for modeling and analyzing the behavior of application software running on multi-processor platforms. We propose a tool-supported flow for systematic and compositional construction of mixed software/hardware system models. These models are intended to represent, in an operational way, the set of timed executions of parallel application software statically mapped on a multi-processor platform. As such, system models will be used for performance analysis using simulation-based techniques as well as for code generation on specific platforms. The construction of the system model proceeds in two steps. In the first step, an abstract system model is obtained by composition and specific transformations of (1) the (untimed) model of the application software, (2) the model of the platform and (3) the mapping between them. In the second step, the abstract system model is refined into concrete system model, by including specific timing constraints for execution of the application software, according to chosen mapping on the platform. We illustrate the system model construction method and its use for performance analysis and code generation on an object recognition application provided by Hellenic Airspace Industry. This case study is build upon the HMAX models algorithm [RP99] and is looking at significant speedup factors. This paper reports results obtained on different system model configurations and used to determine the optimal implementation strategy in accordance to hardware resources

Monitoring the reduction in shrinkage cracking of mortars containing superabsorbent polymers

Ultra-high performance concrete (UHPC) is characterized by a low water-to-cement ratio, leading to improved durability and mechanical properties. However, the risk for autogenous shrinkage and cracking due to restrained shrinkage increases, which may affect the durability of UHPC as cracks form pathways for ingress of aggressive liquids and gases. These negative features can be prevented by the use of superabsorbent polymers (SAPs) in the mixture. SAPs reduce autogenous shrinkage by means of internal curing: they will absorb water during the hydration process and release it again to the cementitious matrix when water shortage arises. In this way, hydration can continue and shrinkage is diminished

Localisation de l'acide gamma linolénique dans les mycéliums et dans les spores chez deux mucorales

En vue d'expliquer le rôle que pourrait jouer l'acide gamma linolénique dans la croissance des microorganismes, la localisation de cet acide est étudiée chez deux souches de Mucor au niveau des lipides membranaires d'une part, et au niveau des lipides de réserves des mycéliums et des spores d'autre part. Les compositions en acides gras de ces différents constituants sont comparées et une hypothèse sur la migration des lipides de réserves et avancée pour comprendre le fonctionnement de la croissance des mycélium

A Location Privacy Extension for DVB-RCS

In this paper we studied the DVB-RCS (Return Channel through Satellite) standard from a privacy perspective and proposed an approach to incorporate a location privacy enhancing mechanism into the standard. Offering location based privacy in DVB-RCS communication is a challenge as the location of a satellite terminal must be revealed to the network operator of the DVB-RCS network for technical and administrative reasons. We proposed an approach of cloaking the location by intentionally compromising its accuracy whilst maintaining the operability and integrity of the communications system. In addition we implemented a proof of concept technique utilizing the theoretical findings of this work on a real DVB-RCS system, presenting the methodology along with the tools used and the experimental results

Acoustic emission behavior of steel fibre reinforced concrete under bending

The present paper describes the acoustic emission (AE) behavior of concrete under four-point bending. Steel fibres of varying content were used as reinforcement in concrete slabs and their influence on the fracture process and the acoustic activity was investigated. The total acoustic emission (AE) activity was found to be directly proportional to the fibre content. Analysis revealed that particular AE parameters change monotonically with the progress of damage and can be used for the characterization of the failure process

Possibilité de production d'acide gamma linolénique par culture de Mucor circinelloïdes CBS 172-27 sur quelques huiles végétales

L'acide gamma linolénique (GLA) est un acide gras polyinsaturé, utilisé en pharmacie et en cosmétique dont les champignons Phycomycètes sont l'une des sources potentielles. Dans ce travail, on étudie les possibilités de produire le GLA par biotransformation de l'acide linoléique de quelques huiles végétales à l'aide d'une souche de Mucor (M. circillenoïdes CBS 172-27). Dans ce but, on détermine la composition des glycérides cellulaires de cette souche au cours des différentes cultures effectuées sur des huiles contenant différentes proportions d'acide linoléique et d'acide alpha-linolénique. Le champignon, cultivé sur les différentes huiles, produit des quantités variables de GLA. La production de cet acide dépend de la richesse en acide linoléique du milieu de culture et est indépendante de la présence de l'acide alpha-linolénique. Le mycélium du champignon cultivé sur huile de tournesol contient plus de 65 % d'une huile à 17,4 % de GL