Expansive Cementitious Materials to Improve Micro-Cable-Reinforcement Bond in 3D Concrete Printing (2021-10)¶

Microcable reinforcement has been demonstrated as a promising solution for enhancing the mechanical properties of three-dimensional (3D) printed concrete. Generally, inadequate interfacial bonding between simultaneously entrained microcables and concrete matrix limits the general application of microcable reinforcement. This paper proposes a method of automatically including expansive cementitious materials (ECMs) in the cable–concrete interface in the printing process to improve the cable bond in 3D concrete printing to improve cracking resistance. A pull-out device is designed and developed in the lab to assess the cable–matrix bonding properties with respect to different bond lengths. Four-point bending tests of a microcable-reinforced beam are also conducted. The crack evolution during these tests is monitored by digital image correlation. The test data are compared with calculated cracking and ultimate loads, crack spacing, and crack width, and a small difference of 15% is found. The experimental results exhibit a 44%–67% increase in the bond strength and a 30%–50% reduction in crack width, demonstrating the effectiveness of the currently proposed method in improving both the cable bond and cracking resistance. Scanning electron microscopy observations reveal that the improvements can be attributed to the lowered porosity or denser microstructure at the cable–ECM interface realized by the addition of the ECMs.