No abstract

The micro-cracks that commonly occur in concrete structures are a potential source of crack propagation which leads to the possibility of catastrophic failure. Concrete cracks that occur propagating mainly along the interface zone that significantly conditioned by aggregate characteristics. Aggregate characteristics as concrete fillers have a significant role as a strain energy release medium known as fracture energy. This research is using an experimental investigation about the fracture characteristics of concrete using different gradations with a maximum diameter of 25 mm and 20 mm. The experiment includes a compressive strength test and a fracture parameter test. Three-point bend test was selected based on RILEM recommendations to calculate fracture parameters. The result has shown that the aggregate gradations used in concrete mixtures should take into account the effect on compressive strength and total fracture energy. Uniform gradations with smaller maximum sizes have high compressive strength but low fracture energy.

Tekuk merupakan fenomena yang terjadi jika batang memperoleh gaya tekan. Tekuk perlu dihindari agar tidak terjadi kegagalan struktur bangunan. Rangka atap baja ringan merupakan salah satu struktur bangunan yang beresiko tinggi terjadinya tekuk, yang disebabkan karena material yang sangat tipis. Salah satu alternatif untuk meningkatkan tekuk pada rangka baja ringan adalah penggabungan material baru atau yang disebut material komposit. Aplus casting plaster salah satu alternatif material tambahan yang bisa meningkatkan batang kuat terhadap tekuk. Kandungan bahan yang ada pada material tersebut adalah calcium sulfate hemihidrate dan cristaline silica. Material ini bisa diperoleh dipasaran sebagai bahan pembuatan lis plafon. Pada penelitian ini ingin mengetahui beban maksimum  dan pola keruntuhan elemen batang komposit dan non komposit pada rangka baja ringan. Jumlah sample masing-masing 18 elemen batang komposit dan non komposit dengan panjang elemen batang  masing-masing 400mm, 600mm, 800mm, 1000mm, 1200mm dan 1400mm. Metoda analisis menggunakan SNI 7971-2013 untuk material non komposit dan SNI 1729-2015 untuk material komposit, sedangkan metoda eksperimental dilakukan dengan uji tekan menggunakan alat UTM (Universal Testing Material) dengan pembebanan bertahap sampai elemen batang mengalami keruntuhan. Hasil penelitian menunjukan bahwa elemen batang komposit memiliki kekuatan yang lebih tinggi dari elemen batang non komposit antara 48.35% sampai dengan 108.96% dengan pola keruntuhan yang terjadi tekuk lentur untuk semua elemen batang non komposit dan tekuk lokal pada sebagian elemen batang komposit kecuali pada panjang elemen batang  1200mm dan 1400mm terjadi tekuk lentur.

Concrete is brittle material which generally consists of many micro cracks which are a potential source of crack propagation which leads to possible catastrophic failure and resulting fracture of concrete structures under service loads. The relationship of fracture energy to material properties has not been clearly identified, with most studies showing a relative insensitivity to the water-cement ratio, and concrete cracks propagate mainly along the aggregate-cement interface. This research is an experiment about the effect of water-cement ratio on fracture energy based on the RILEM method. The fracture energy is measured by testing under three bend points with the notch depth ratio is 0.25 and loading rate is 0.05 mm/sec using a closed-loop testing machine to produce load-displacement curve. Concrete used crushed stones with a maximum size of 19 mm which was tested at 56 days of age and has a water-cement ratio (w/cm) of 0.30, 0.40 and 0.6. The correlation between fracture energy and water-cement ratio are insensitive to each other. This can be seen when concrete containing a lower water-cement ratio (0.3) tends to have increased compressive strength but decreases fracture energy.