The shear strength of the interface between artificial rock and printed concrete at super-early ages

Abstract

3D concrete printing has the potential to replace shotcrete for construction of linings of tunnels in hard rock. The shear strength of the interface between rock and printed concrete is vital, especially at super-early ages. However, traditional methods for testing the shear strength of the interface, e.g., the direct shear test, are time-consuming and result in a high variability for fast-hardening printed concrete. In this paper, a new fast bond shear test is proposed. Each test can be completed in 1 min, with another 2 min for preparing the next test. The influence of the matrix composition, the age of the printed matrices, and the interface roughness of the artificial rock substrate on the shear strength of the interface was experimentally studied. The tests were conducted at the age of the matrices at the 1st, the 4th, the 8th, the 16th, the 32nd, and the 64th min after its final setting. A dimensionless formula was established to calculate the shear strength, accounting for the age of the printed matrices, the interface roughness, and the shear failure modes. It was validated by comparing the calculated results and the experimental results of one group of samples.

Graphical abstract

Keywords

rock tunnel / printed concrete / interface / fast bond shear test / shear strength

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Acknowledgements

Financial support by the Ministry of Science and Technology of China (No. 2021YFE0114100) and by the Federal Ministry of Education, Science and Research (BMBWF) of Austria (No. CN11/2021), jointly provided for the project ‘Intense Upgrades of the New Austrian Tunnelling Method (NATM) and Demonstration of its Applicability to High-Quality Urban Development’, is gratefully acknowledged. The work was supported by the Science and Technology Commission of Shanghai Municipality (No. 21DZ1203505). In addition, the authors are indebted to the National Natural Science Foundation of China (Grant Nos. 51908424 and U1934210), Shanghai Rising-Star Program (No. 22QB1405000), and Jiangxi Province Department of Transportation Key Engineering Project (No. 2021C0008). The second author acknowledges the financial support provided by the Chinese Scholarship Council (CSC, No. 202006260198).

Competing interests

The authors declare that they have no competing interests.

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