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The behaviour of concrete under sudden impact loads is complex. Moreover, very little is known about the impact behaviour of high-performance fibre-reinforced concretes (HPFRCs). To account for this, nanomodified deflection-hardening HPFRC mixtures incorporating coarse aggregates were produced with three ratios of fly ash to Portland cement (0·0, 0·2 and 0·4), three nanomaterials (nanosilica, nano-alumina and nanocalcite) and two hybridised fibre combinations (hooked-end steel with polyvinyl alcohol, or hooked-end steel with brass-coated microsteel) and tested for basic mechanical properties and flexural impact resistance. After experimental testing, beams used in impact testing were modelled using Abaqus. Cubic compressive strength did not change significantly with the differences in mixture parameters, although this was not the case for flexural parameters. For a given fly ash/Portland cement ratio and nanomaterial type, mixtures with hooked-end steel and polyvinyl alcohol fibres exhibited higher displacement and lower flexural strength capacity than those with hooked-end steel and brass-coated microsteel fibres. Nano-alumina contributed best to the development of mechanical properties and impact resistance of HPFRCs, followed by nanosilica and nanocalcite. Results validate the idea that costly polyvinyl alcohol fibres can be fully replaced with brass-coated microsteel fibres without risking mechanical properties and impact resistance, as long as matrix properties are properly controlled.

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In this study, an experimental program is conducted to understand the effect of the limestone powder (LSP) content replaced by silica sand on the composite properties. For this purpose, five different engineered cementitious composite (ECC) mixtures were adopted: ECC mixture with only silica sand (SS) for control purposes and four ECC mixtures in which SS is partially replaced by four levels of replacements (25%, 50%, 75%, and 100% by weight of total SS) of LSP. The properties of ECC mixtures produced were investigated for the ages of 3, 28, and 90 days. It was concluded that the mechanical properties of the ECC mixtures with LSP were in general higher than the reference mixture with only SS for all curing ages. Increase in the LSP content had a positive effect on the performance of the compressive strength, fracture toughness, and flexural strength at the ages of 3 and 28 days while this was not valid at the age of 90 days when compared to the reference mixture. Also, the ductility of the ECC beams strongly depends on the LSP content and specimen age.Résumé : Le présent article traite d'un programme expérimental réalisé pour comprendre l'effet du remplacement du contenu en poudre de chaux par du sable de silice sur les propriétés des composites. À cette fin, cinq mélanges différents de composites cimentaires techniques (ECC) ont été sélectionnés : un mélange d'ECC ne contenant que du sable de silice aux fins de contrôle, et quatre mélanges d'ECC dans lesquels le sable de silice est partiellement remplacé par quatre teneurs de poudre de chaux (25 %, 50 %, 75 % et 100 %). Les propriétés des mélanges d'ECC produits ont été examinées après 3, 28 et 90 jours. Il a été constaté que les propriétés mécaniques des mélanges d'ECC avec de la poudre de chaux étaient en général supérieures, pour tous les temps de cure, à celles du mélange de référence ne contenant que du sable de silice. L'augmentation du contenu en poudre de chaux a eu un effet positif sur le rendement en résistance à la compression, en ténacité et en résistance à la flexion après 3 et 28 jours de cure alors qu'il n'a eu aucun effet après 90 jours de cure par rapport au mélange de contrôle. De plus, la ductilité des poutres en ECC est grandement fonction du contenu en poudre de chaux et de l'âge de l'échantillon. [Traduit par la Rédaction]

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Bu çalışmada ISO/ITU H264/AVC video kodlaması kullanılarak kodlanmış bir video dizisinde makro-öbek bileşenleri çeşitleri analiz edilerek ani ve dereceli sahne kesikleri kestirimi uygulamaları için metodlar önerilmiştir. Sıkıştırılmış sahada yapılan analiz, video dizisinin tamamen sıkıştırmayı çözme sürecine gerek duyulmadan sahne geçişlerininin sezimini gerçeklestirmistir. Önerilen algoritmayi gerçeklemek için çesitli test video dizileri ISO/ITU H264/AVC kodlanarak QCIF çözünürlüğüne indirgenip, kodlanmistir ve kısmi sıkıştırmayı çözme işlemi gerçekleştirilerek makro-öbek tipleri istatistikleri incelenmistir. Video dizisinin kod çözümü sırasında, ISO/ITU H264/AVC standardının ayrıştırma, kısmi kod çözme süreçleri, sözdizim ve anlambilimsel özellikleri kullanilmiş ve önerilen metodlar referans yazılım üzerinde uygulanmistir. Uygulama ISO/ITU H264/AVC kodlanmış sayısal video kütüphanelerinde video özetleme, soyutlama uygulamalarını hedef alan alt seviye araçlar oluşturabilir.