Prediction of interfacial tensile bond strength in 3D printed concrete based on a closed-form fracture model

Abstract

Interfacial bond strengths in 3D printed concrete may affect the deformation compatibilities among the extruded filaments and the anisotropy of concrete. However, the previous predictions were size dependent inevitably based on the assumption of interfacial continuity and homogeneity. This work aims to propose a fracture model capable of predicting the realistic tensile bond strength (ft) and fracture toughness (KIC) of interfaces between filaments and layers in 3D printed concrete. To reflect the discontinuity and heterogeneity of interfaces, a discrete number (β) and a microstructure characteristic parameter (G) were proposed. A simple linear relationship of the maximum fracture load (Fmax) related to ft or KIC was established, and thus, the realistic interfacial ft and KIC can be determined after obtaining Fmax from the tests on the specimens with any sizes. Subsequently, three-point bending tests were performed to study the interfacial fracture properties of printed concrete with various contents of manufactured sand. The results show that the addition of manufactured sand improved the interfacial ft and KIC between filaments but had little effect on the interfacial fracture parameters between layers. The anisotropic behavior of the 3D printed concrete was clarified by evaluating the predicted ft and KIC along different directions. This research brings novel insights into the interfacial behaviors in 3D printed concrete.