This paper presents a numerical model for the simulation of the hydration process and the development of the microstructure on Selfcompacting cement paste (SCC) containing limestone powder as filler. Based on a series of experimental results, e.g. thermometric isothermal conduction calorimetry tests, environmental scanning electron microscopy (ESEM) image analysis, thermogravimetric analysis (TGA) and the derivative thermogravimetric analysis (DTG) measurements, the hydration process, the solid phase distribution, total porosity and pore size distribution have been determined at different hydration stages.Based on the hydration chemistry, the stoichiometry and the hydration kinetics of cement with limestone, an analytical hydration model and a microstructural model of self-compacting cement paste are proposed. Two SCC mixtures with w/c 0.41 and w/c 0.48, both with water/ powder ratio (w/p) 0.27, were simulated and compared to a traditional cement paste (TC) with w/c 0.48. The simulation results were discussed and validated against experimental measurements.Ré sumé Cet article présente un modèle numéri-que qui réalise une simulation du processus d'hydratation et le développement de la microstructure de la pâte de ciment auto-compactante (SCC) contenant comme filler de la poudre calcaire. Sur base d'une série de résultats expérimentaux-par exemple~: tests de calorimétrie par conduction thermométrique isotherme, analyse d'images par microscopie électronique environnementale (ESEM), analyse thermogravimétrique (TGA), analyse thermogravimétrique dérivée (DTG)-, le processus d'hydratation, la distribution de la phase solide, la porosité totale et la distribution de la taille des pores ont été déterminés à différentes étapes de l'hydratation.Sur base de la chimie et de la stoechiométrie de l'hydratation et de la cinétique de l'hydratation du ciment en présence de calcaire, un modèle analytique d'hydratation ainsi qu'un modèle de la microstructure de la pâte de ciment auto-compactante sont proposés. Des simulations concernant deux mélanges de SCC avec un rapport E/C de, respectivement, 0,41 et 0,48 et un rapport eau / poudre (W/P) de 0,27 ont été menées. Les résultats ont été comparés avec ceux d'une pâte de ciment traditionnelle (TC) dont le rapport E/C vaut 0,48. Les résultats de la simulation ont été discutés et validés en les comparant avec des mesures expérimentales.
High plasma levels of homocysteine (Hcy) promote the progression of neurodegenerative
diseases. However, the mechanism by which Hcy mediates neurotoxicity has not been
elucidated. We observed that upon incubation with Hcy, the viability of a
neuroblastoma cell line Neuro2a declined in a dose-dependent manner, and apoptosis
was induced within 48 h. The median effective concentration (EC50) of Hcy
was approximately 5 mM. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) nuclear
translocation and acylation has been implicated in the regulation of apoptosis. We
found that nuclear translocation and acetylation of GAPDH increased in the presence
of 5 mM Hcy and that higher levels of acetyltransferase p300/CBP were detected in
Neuro2a cells. These findings implicate the involvement of GAPDH in the mechanism
whereby Hcy induces apoptosis in neurons. This study highlights a potentially
important pathway in neurodegenerative disorders, and a novel target pathway for
neuroprotective therapy.
The mechanical behavior of hardening concrete is to a large extent determined by the evolving microstructure as a result of the hydration process. For traditional binder systems, consisting of Portland cement or blast furnace slag cement, the degree of hydration is known to be a fundamental parameter in this respect, enabling a detailed study and accurate prediction of the early-age mechanical behavior, including basic creep. Nowadays, in view of improved sustainability of cementitious materials, binder systems tend to become more complex, consisting of a blend of different powders. As the hydration process and microstructure development are influenced by the inclusion of powders into the binder, the question is raised whether the degree of hydration concept is still applicable to concrete based on complex blended binder systems. In this paper, some experimental results are summarized and the application to real structures is illustrated. Basic creep of hardening concrete with complex blended binders can still be modeled following the degree of hydration concept.
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