Interlayer bond strength models for three dimensional-printed mortar

Three-dimensional (3D) printing enables free-form construction without formwork; however, interlayer interfaces formed during layer-by-layer deposition act as weak planes that govern structural performance. This study presents a combined experimental and predictive investigation of interface normal and shear strengths of 3D-printed mortar under varying printing interval times and temperatures, considering compressive strength, age and initial setting time. Mortars with two strength classes were tested under normal and elevated temperature conditions. Results show that elevated temperature enhances early-age hydration and interface strength at short intervals but accelerates surface moisture loss and bond degradation at longer intervals. A key finding is that interlayer bond performance is governed by the printing interval relative to the initial setting time, providing a unified parameter for assessing interface quality. Based on regression analysis, empirical models are proposed to predict interface normal and shear strengths as functions of printing interval time, temperature, compressive strength, mortar age and initial setting time. The proposed models show good agreement with experimental results and provide a practical design-oriented framework for evaluating interlayer bond performance of 3D-printed mortar structures.