SIZE EFFECT IN STRENGTH OF CONCRETE STRUCTURES AND PROPERTIES OF FRACTURE PROCESS ZONE

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(1) Size effect :Compact tension specimens of three different sizes, 175x175x80 (S type), 350x350x80 (M type), 700x700x80 (L type), were prepared to examine the effect of specimen size on the tensile strength of concrete. It was observed that the strength of the larger size specimen decrease compared to that of the smaller size specimen. When the specimen size increased by 4 times the strength of the concrete decreased by 12 to 16 %.(2) Properties of the fracture process zone :Fine cracks forming from the tip of the notch were detected by X-ray technique using contrast medium. The rate of increase in the maximum length of the fracture process zone was larger than the ratio representing increase in the specimen size ratio. The maximum width of the fracture process zone increased at a very slow rate compared to the increase in the specimen size ratio.Fracture process zone was also detected by AE three dimensional positioning method. The area of fracture process zone which was detected by AE method was larger than that detected by the x-ray method.(3) Fracture energy :At the maximum load, the fracture energy which was calculated from the area under load -C.O.D curve divided by the area and volume of fracture process zone was almost constant in spite of the differences of specimen size.