Even after more than 25 years of research in the field of fracture mechanics applied to concrete, the influences of specimen shape, specimen size and with and without initial notch on fracture process in concrete are still not fully understood and quantified. Therefore further more experiments and theoretical studies on this field should be progressed extensively. Hereupon, this experiment was performed to investigate the influences of specimen size and with and without initial notch on tensile strength, fracture toughness $K_{Ic}$, fracture energy $G_f$, and notch sensitivity of concrete.
Tensile strength can be measured in three ways: direct tensile, splitting tensile, and flexural tensile tests. Because the cylindrical specimens are easier to handle and test, we selected cylindrical specimen and splitting tensile test in this work. The specimens were tested for diameters of 10, 20, 40, 80, and 160 cm with the same width of 20 cm. The ASTM standard test method (C 496), "splitting tensile strength of cylindrical concrete specimens", was followed as closely as possible.
The results show that size effect appears conspicuously. As the specimen sizes increase, the splitting tensile strength of the specimen without initial crack and the net stress at failure of the specimen with initial crack decrease. As compressive strength is very important parameter in strength criterion, so fracture energy is very important parameter in energy criterion. Fracture energy was calculated by BKP (Bazant-Kim-Pfeiffer) method. The fracture toughness which is the critical value of stress intensity factor is more and more large as the specimen sizes increase.
