Effective Properties of Textile Composites: Application of the Mori-Tanaka Method

An efficient approach to the evaluation of effective elastic properties of carbon-carbon plain weave textile composites using the Mori-Tanaka method is presented. The method proves its potential even if applied to real material systems with various types of imperfections including the non-uniform waviness of the fiber-tow paths, both along its longitudinal direction and through the laminate thickness. Influence of the remaining geometrical parameters is accounted for by optimal calibration of the shape of the equivalent ellipsoidal inclusion. An application of the method to a particular sample of the carbon-carbon composite laminate demonstrates not only its applicability but also its efficiency particularly when compared to finite element simulations.Comment: 18 pages, 6 figure

Effect of cyclic freezing and thawing on the microstructure of composite cements

Mixed performance of composite cements exposed to freeze-thaw has been reported. A detailed understanding of the degradation mechanism is also lacking. This study investigates the microstructure of composite slag cements with and without limestone subjected to cyclic freezing and thawing. Freeze-thaw was assessed on concrete samples in accordance with CEN/TR 15177 but with a modified temperature profile. Microstructure was characterized by SEM and thermogravimetric analysis. The results indicate decalcification through carbonation and then leaching as dominant degradation mechanisms. This has implications on the pore structure and hence the water suction capacity and progression of the ice-front in concrete

Private Öffentlichkeit oder öffentliche Privatheit

Das Medium Fernsehen ist aus der privaten, sowie auch aus der öffentlichen Sphäre nicht mehr wegzudenken. Es hat in der zeitgenössischen Gesellschaft deutlich an Relevanz gewonnen und ist im Alltag jedes Einzelnen unverzichtbar. Nicht nur die Positionierung des Mediums in privaten Haushalten, sondern auch die Inszenierung privater Alltage darin spiegelt die gesellschaftliche Relevanz des und das Verhältnis von Fernsehen und Gesellschaft wider. Die Selbstdarstellung der Menschen kann sich im Rahmen des Mediums und in Formaten wie „Big Brother“ breitenwirksam realisieren. Durch historische und mediale Entwicklungen veränderten sich Relationen und Konnotationen der Begriffe „Öffentlichkeit und „Privatheit“. Die medial dargestellte „Privatheit“ unterscheidet sich von der Privatheit im Alltag dadurch, dass die MitspielerInnen Rollen annehmen und durch das Format fremdgesteuert werden. Die Inszenierungsstrategien der Sendung und die Rollengestaltungen der Teilnehmenden stehen im Verdacht, gesellschaftliche Normen umzuwerten. Ein Gefahrenpotential wird einerseits durch die Verdrängung der öffentlichen Sphäre und andererseits durch die freiwillige Aufgabe der Autonomie mit der Teilnahme an der Sendung befürchtet. Mithilfe von Sennetts „Verfall und Ende des öffentlichen Lebens: Die Tyrannei der Intimität“ und Rösslers „Der Wert des Privaten“ wird die aktuelle Bedeutung des Fernsehformats „Big Brother“ für den Diskurs um Privatheit und Öffentlichkeit untersucht

Effect of sulfate additions on hydration and performance of ternary slag-limestone composite cements

The global cement industry is striving to reduce its carbon footprint. Common approaches have included reduced clinker factors by blending cement clinker with supplementary cementitious materials (SCM). However supplies of SCMs are not sufficient to achieve replacement above about 30 %. Limestone ternary cements offer the opportunity to reduce the clinker factor of cements while maximizing the efficiency of SCMs. In these cements, calcite from limestone reacts with dissolved aluminates to form carboaluminate and in the process influence hydration of other constituents. However, sulfates which are conventionally added to regulate the early reactions in cement also compete for aluminates. Here we have used complementary techniques to investigate the effects of calcium sulfate additions on hydration, microstructure and performance of composite Portland clinker-slag-limestone cements. The results show that the presence of sulfate influenced the early-age reaction kinetics of the clinker phases and supplementary cementitious materials. However, even after sulfate depletion, the course of hydration and microstructures formed were significantly influenced. Increasing the sulfate level resulted in a gradual increase of the fraction of ettringite over AFm phases, coarser porosity and lower water content of the C-S-H. These microstructural changes impact the total porosity and hence cement strength in opposing ways, namely porosity is reduced with increasing ettringite fraction while the space filling capacity of the C-S-H is also reduced due to the lower water content of the C-S-H. These findings have important implications for optimizing the mechanical properties and durability of ternary blends