Investigation of gap-graded concrete by nonlinear fracture mechanic principles

The concrete, as a quasi-brittle material, includes many cracks, and flaws. The Fracture Mechanics examine the failure conditions of materials by considering the structural damages and by analyzing the spread and growth conditions of notches, cracks and flaws developed on the body. Recently, the studies on mechanical behavior of cementitious materials have been increased. To analyse a cement-based material structure according to fracture mechanics, its fracture parameters are needed to be determined at first. The experimental studies revealed that the fracture parameters of concrete are particularly influenced by four material parameters: compressive strength, maximum aggregate size, water-cement ratio, and aggregate type. During the comprehensive experimental studies, the different combinations of the material parameters were used to investigate their effect on the fracture parameters; moreover, some formulas were suggested for normal concretes. In this study, it was not only focused on the improvement and the production of normal concrete properties, also hardened concrete properties of the gap-graded concrete. In addition, the gap-graded and continuously-graded concretes with 8 and 16 mm of maximum aggregate size were produced. The produced concrete specimens were classified as notched and un-notched. The fracture loads of the cubes obtained by split-tension tests were investigated according to the Bazant's Size Effect Law and the Carpinteri's Multi-fractal Size Effect Law approaches. On the other hand, the notched cubes and beams were analyzed according to the three most popular fracture mechanics model in concrete fracture: the Two-Parameter Model, the Size -Effect Model and the Double-K Model. Consequently, some statistical relationships between the concrete components and the fracture parameters of the concretes with continuously-graded and gap-graded were determined. In addition, it was concluded that the concrete with gap-graded is more ductile than the concrete with continuously-graded according to the concrete fracture mechanics. Keywords: Double-K model, Fracture mechanics, Multi-fractal size effect law, Size effect law, Size effect model, Two-parameter model.