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

(1)尺寸效应：制备175x175x80 （S型）、350x350x80 （M型）、700x700x80 （L型）3种不同尺寸的密实拉伸试件，考察试件尺寸对混凝土抗拉强度的影响。结果表明，与小尺寸试样相比，大尺寸试样的强度有所降低。当试件尺寸增加4倍时，混凝土强度降低12% ~ 16%。(2)断裂过程区特征：利用造影剂x射线技术检测到缺口尖端形成的细小裂纹。断裂过程区最大长度的增加速率大于试样尺寸比的增加速率。与试样尺寸比的增加相比，断裂过程区的最大宽度的增加速度非常缓慢。利用声发射三维定位方法对断裂过程区进行了检测。声发射法检测到的断裂过程区面积大于x射线法检测到的。(3)断裂能：在最大载荷下，尽管试样尺寸不同，但由受载面积-C.O.D曲线除以断裂过程区面积和体积计算得到的断裂能基本不变。

(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.