Influence of specimen geometry on fracture toughnesses of concrete based on boundary effect model

Abstract

This paper presents the effect of specimen geometry on fracture characteristics of concrete in terms of fracture toughness KIc and initial fracture toughness KIcini. Three commonly used specimen geometries in laboratory were adopted in the study, that is, three-point bending (TPB), compact tension (CT) and four-point bending (FPB) specimens. The Boundary Effect Model (BEM) was used to determine these two fracture parameters, where a new approach was proposed to derive KIcini. To do this, only the maximum aggregate size dmax, the maximum load Pmax and the initial crack length relative to the specimen depth α0 were required. Previous experiments from TPB, CT and FPB specimens were reutilized to acquire KIc and KIcini, and then the geometry influence on these two fracture toughnesses were investigated. The results show that the gained values of KIc and KIcini from TPB, CT, FPB separately or combined TPB + CT + FPB were rather close, meaning little influence from specimen geometry on fracture toughness. Additionally, the ratio of KIcini/KIc was almost the same regardless of specimen geometry shape and α0 when 0.2 ≤ α0 ≤ 0.8.