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

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

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

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

Damage detection and healing performance monitoring using embedded piezoelectric transducers in large-scale concrete structures

Concrete keeps being the leading structural material due to its low production cost and its great structural design flexibility. However, concrete is prone to various ambient and operational loads which are responsible for crack initiation and extension, leading to decrease of its anticipated operational service life. The current study is focusing on the use of ultrasonic wave propagation techniques based on low-cost and aggregate-size embedded piezoelectric transducers for the online monitoring of the damage state and the healing performance in concrete structures with an autonomous healing system in the form of encapsulated polyurethane-based healing agent embedded in the matrix of concrete. The crack formation triggers the autonomous healing mechanism which promises material recovery and extension of the operational service life. The proposed technique is applied on large-scale, steel reinforced, concrete beams (150mm × 250 mm × 3000 mm), subjected to four-point bending. After the capsules are broken and the healing agent is released, which results in filling of the crack void, and polymerized, the concrete beams are reloaded. The results demonstrate the ability of the monitoring system to detect the initiation and propagation of the cracking as well as to assess the performance of the self-healing system

Experimental techniques synergy towards the design of a sensing tool for autonomously healed concrete

The first-generation of autonomously healed concrete elements is under construction: beams (SIM-SECEMIN project, Flanders Belgium), one-way flat slabs (MeMC, VUB, Belgium) and wall panels (Materials4Life project, UK) are designed with the embedment of encapsulated repair agent. In the presence of cracks, capsules rupture releasing the agent that fills the crack void. The released agent seals and mechanically restores the crack discontinuity. This automatic process can be repeatable using vascular networks that carry the agent and release it at different locations into concrete. The innovative design is built up following several series of laboratory-scale beam tests configured over the last decade. This paper discusses the application of numerous experimental techniques that assess the mechanical performance of autonomously healed concrete: Acoustic Emission, Ultrasound Pulse Velocity, Optical Microscopy, Digital Image Correlation, Capillary Water Absorption, Computed Tomography. The study focuses on the performance and efficiency of each method on laboratory and real-scale tests. The techniques with the most promising output are selected and combined in order to design a sensing tool that evaluates healing on real applications

Etude de l'influence des conditions de culture sur la teneur en acide gamma linolénique de souches de Mucor

L'acide gamma linolénique (GLA) est un acide gras très recherché à cause de ses propriétés biologiques. Mucor circinelloïdes CBS 172-27 et Mucor rouxianus CBS 120-08 sont deux mucorales dont les huiles sont riches en cet acide gras. Ces deux souches ont été cultivées sur différents milieux et certains paramètres de croissance ainsi que la composition en acides gras des triglycérides cellulaires ont été étudiés. La concentration et le type d'azote ainsi que la concentration en glucose dans le milieu de culture influencent de façon importante les compositions des deux souches. Les biomasses obtenues sont d'autant plus pauvres en protéines et riches en matières grasses que le milieu de culture est plus pauvre en azote. La composition générale des huiles est relativement constante, peu dépendante du milieu de culture; il semble par contre que les deux souches produisent des huiles plus concentrées en GLA dans les cas où les biomasses sont plus pauvres en matières grasses. L'étude de la composition minérale des souches a été effectuée et un milieu optimum a été mis au point. A partir de ce milieu, de bons rendements en matière sèche ainsi qu'une bonne production en GLA ont été obtenu

Production d'huiles riches en acide gamma linolénique par diverses souches de phycomycètes

Parallèlement à l'important effort agronomique actuel en vue d'intensifier la production d'huiles riches en acide gamma linolénique, la recherche de nouvelles sources d'acide gamma linolénique issu de la croissance de microorganismes a été mise au point par le biais de la biotechnologie. La croissance de diverses souches de Phycomycètes a été testée sur différents milieux de cultures. Une première étape de sélection sur des milieux organique s naturels a permis de mettre en évidence l'aptitude des différentes souches à produire une biomasse riche en huile à teneur élevée en acide gamma linolénique. La seconde phase de l'étude, effectuée sur un milieu minéral vitaminé, plus conforme aux exigences économiques de rentabilité industrielle, a démontré que les souches de Mucor rouxianus CBS 120-08 et Mucor circinell oides CBS 172-27 sont les microorganismes les plus performants. La phase de développement et de production plus intensive pourra être abordée sur ces deux souche

Rhodosporidium toruloides cultivated in NaCl-enriched glucose-based media: adaptation dynamics and lipid production

In the present report and for the first time in the international literature, the impact of the addition of NaCl upon growth and lipid production on the oleaginous yeast Rhodosporidium toruloides was studied. Moreover, equally for first time, lipid production by R. toruloides was performed under non-aseptic conditions. Therefore, the potentiality of R. toruloides DSM 4444 to produce lipid in media containing several initial concentrations of NaCl with glucose employed as carbon source was studied. Preliminary batch-flask trials with increasing amounts of NaCl revealed the tolerance of the strain against NaCl content up to 6.0% (w/v). However, 4.0% (w/v) of NaCl stimulated lipid accumulation for this strain, by enhancing lipid production up to 71.3% (w/w) per dry cell weight. The same amount of NaCl was employed in pasteurized batch-flask cultures in order to investigate the role of the salt as bacterial inhibiting agent. The combination of NaCl and high glucose concentrations was found to satisfactorily suppress bacterial contamination of R. toruloides cultures under these conditions. Batch-bioreactor trials of the yeast in the same media with high glucose content (up to 150 g/L) resulted in satisfactory substrate assimilation, with almost linear kinetic profile for lipid production, regardless of the initial glucose concentration imposed. Finally, fed-batch bioreactor cultures led to the production of 37.2 g/L of biomass, accompanied by 64.5% (w/w) of lipid yield. Lipid yield per unit of glucose consumed received the very satisfactory value of 0.21 g/g, a value amongst the highest ones in the literature. The yeast lipid produced contained mainly oleic acid and to lesser extent palmitic and stearic acids, thus constituting a perfect starting material for “second generation” biodiese