In extrusion-based 3D concrete printing technology, a reinforcement method is required for the printed mortar because it generally has a low tensile strength and cannot be used alone for members subjected to tensile stress. In this study, a continuous fiber-reinforced mortar was fabricated by extruding a continuous reinforcing steel fiber simultaneously with mortar, producing beam specimens with axially oriented reinforcements. The structural performance of the specimens was investigated using bending tests, and the experimental results were compared with cross-sectional calculations to evaluate the reinforcing effect of the continuous fibers. The results indicated that mortar beams reinforced with continuous fibers exhibited flexural capacities comparable to the calculated values. This paper is an English translation of the authors’ previous work [Kitamura, Y., Sasaki, K., Ishizeki, Y., & Nakarai, K. (2025). Experimental study on flexural behavior of 3D printed mortar beam reinforced with continuous fiber. Concrete Research and Technology, 36, 71-81. (in Japanese)].

This paper investigates the interface between normal weight concrete (NWC) and lightweight aggregate concrete (LWAC) of different ages, focusing on shear resistance. The main parameters affecting bond strength and commonly used testing methods are analyzed. Design shear resistance is also reviewed according to different guidelines, including Eurocode 2 (EC 2), the second-generation (draft) of Eurocode 2 (prEC 2), ACI 318-19 and the fib Model Code 2010. Methods for determining friction coefficients and surface roughness parameters are presented, along with a description of several methods for measuring surface roughness. Experimental results from the literature are considered to assess the influence of key parameters. The paper also highlights limitations in current surface roughness characterization methods and the lack of standardized approaches for determining friction and cohesion parameters.