Aggregate size effects on fracture behavior of concrete SCB specimens

Rashid Afshar ^a, Lohrasb Faramarzi ^a,*, Mirmilad Mirsayar ^b, Behnam J. Ebrahimi ^c

^a Rock Mechanics, Isfahan University of Technology, Department of Mining Engineering, Iran

^b Department of Aerospace, Physics, and Space Sciences, Florida Institute of Technology, USA

^c Department of Civil Engineering, Isfahan University of Technology, Isfahan, Iran

Doi:10.1016/j.conbuildmat.2023.131628

A B S T R A C T

Fracture in concrete and rock-like materials is the result of applying external loads, initiation, and propagation of
the cracks, and finally, creating the failure surface in the material. The most common type of fractures in solid  materials are usually formed under combined tensile/shear loading conditions. The stress intensity factors KI and KII, corresponding to opening and sliding modes (I and II), are the main fracture parameters, and their critical values (i.e., fracture toughness) show the material’s resistance against the initiation and propagation of cracks. In this paper, the fracture toughness of concrete specimens is determined by considering different aggregate sizes and using the three-point bending test on semi-circular bend (SCB) specimen. The fracture toughness parameters have been determined by different fracture criteria and compared with the values obtained in the laboratory on concrete specimens. The effect of aggregate size on fracture parameters and crack propagation path has been evaluated. To predict the crack initiation angle and fracture toughness values, the modified maximum tangential stress (MMTS) and extended maximum tangential strain (EMTSN) criteria along with conventional fracture criteria were used. The results showed, that with the increase in aggregate size, the fracture toughness value under mode I, II, and mixed-mode (I-II) has increased. The laboratory results showed that specimens with aggregate sizes of 0–19 mm have the highest fracture load, and specimens with the aggregate sizes of 0–5 mm have the lowest fracture load.

Keywords: Fracture toughness, Stress intensity factors, Semi-circular bend specimen, Aggregate size, Crack propagation angle