Mehmet Ali TAŞDEMİR, Fikret BAYRAMOV, Canan TAŞDEMİR

Çimento esaslı kompozit malzemelerin optimum tasarımı

Bu çalışmada, çelik tel narinliği ve içeriğinin eğilme halinde Çelik Tel Donatılı Betonun kırılma parametrelerine etkisi araştırılmakta ve bu parametreler optimize edilerek daha sünek ve daha düşük maliyetli beton elde edilmektedir. Optimum tasarım için, üç-düzeyli iki faktörlü tam deneysel tasarım, Tepki Yüzey Yöntemi ve çok amaçlı sayısal optimizasyon teknikleri kullanılmaktadır. Çelik telin narinliği ve içeriğinin özgül kırılma enerjisi ve karakteristik boya etkisinin belirgin olduğu sonucuna varılmaktadır. Daha sonra, agrega konsantrasyonunun betonun kırılma ve mekanik özeliklerine etkisi incelenmektedir. Kırılma enerjisinin belirlenmesi için RILEM TC 50-FMC standardına göre çentikli kirişler üzerinde üç noktalı eğilme deneyi yapılmıştır. Betonda agrega konsantrasyonunun artımı kırılma enerjisi ve karakteristik boy gibi kırılma özeliklerini belirgin biçimde iyileştirmektedir.

Optimum desing of cement-based composite materials

In this study, the main objective is to optimise the fracture parameters of Steel Fibre Reinforced Concretes for obtaining a more ductile behaviour than that of plain concrete. The effects of the aspect ratio and volume content of steel fibre on fracture properties of concrete in bending were investigated by measuring the specific fracture energy and characteristic length. For the optimum design, three-level full factorial experimental design, Response Surface Method and numerical optimisation techniques were used. The results show that the effects of fibre volume content and aspect ratio on specific fracture energy and characteristic length are significant. On the other hand, the effect of aggregate concentration on the fracture and mechanical behaviour of plain concrete under bending was investigated. For the determination of the fracture energy the three-point bending test was performed on notched beams according to the recommendation of the RILEM 50-FMC Technical Committee. Six control mixes ranging from hardened cement paste (hcp) to normal concrete were prepared in which the aggregate grading, water/cement ratio (w/c=0.316), and maximum aggregate size were kept constant, but the volume fraction of aggregate was changed as: 0.00 (hcp); 0.15; 0.30; 0.45; 0.60 and 0.68 m3/m3 (real concrete). Experimental results shows that modulus of elasticity, splitting tensile strength, net bending strength, fracture energy and characteristic length increases significantly with increasing aggregate concentration.

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