Size Effect And Failure Characteristics On Splitting Tensile Strength Of Concrete

As quasi brittle material, concrete strength exhibits size effect. Thus its strength is not only determined by the material properties, but also varies with the specimen sizes, loading and boundary condition. Extensive studies on the factors influencing the size effect on splitting tensile strength of concrete and the size effect laws have been carried. However, controversies still exist with respect to experimental results and conclusions of splitting tensile strength of concrete. Based on available test data from previous research, expressions with better representing of size effect are unable to be distinguished.In order for a further investigation of size effect of concrete splitting tensile strength and splitting tensile failure of specimens, a series of cylinder specimens varying in diameters and heights were designed, and the size effect and failure characteristics of concrete splitting were studied. Research carried out in this thesis is as following:(1) Splitting tensile tests on concrete cylinders with different diameters and heights were conducted and the influence of diameters, heights, etc. on size effect were discussed. Based on the test results, the size effect laws proposed by Bazant, Kim and Carpinteri as well as size effect expressions based on the Weibull's theory in the form of splitting area and of highly stressed volume (HSV) were compared.(2) By using high frequency dynamic strain measurement and digital video recording technique, the splitting fracture and its development of specimens were monitored and recorded, and the cracking and failure characteristics were studied.(3) Based on the experimental studies in the thesis and test data collected from other researchers, a general expression in terms of splitting area for size effect on splitting tensile strength of concrete was proposed.It is shown that splitting tensile strength of concrete cylinders is not only affected by diameters but also by heights, and that for cylinders with constant heights and varying in diameters, the Carpinteri's size effect expression is best fit for the test data.For cylinders with different diameters and heights, ether splitting area or HSV can be used for depicting the decreasing of splitting tensile strength with increasing of cylinder sizes, and the expressions in the form of splitting area provides better results.Different failure modes were observed in the splitting tensile test, and the central fracture mode and secondary fracture mode are the two primary failure modes among others. Results from dynamic strain measuring and video recording show that in both the central fracture mode and the secondary fracture mode, cracking initiates form the center of cylinder section, however, strain distribution, cracking growth, failure and cracking patterns are different.