Enhancing the Buildability of CSA Cement/OPC-Blended Mortar in 3D Printing: Optimizing CSA Cement and Water Contents Using a Statistical Approach

This study examined the influence of the water–binder ratio and calcium sulfoaluminate (CSA) cement replacement on the properties of fresh three-dimensional concrete printing (3DCP) materials and identified optimized mix proportions to enhance buildability. Experimental analyses included flowability tests, setting time evaluations, green strength assessments, extrusion pressure measurements, and printing tests. Buildability was evaluated using layer strain and interlayer bonding performance as key indicators, while statistical techniques were applied to develop a mixture design that maximized buildability and minimized the number of printing tests required. The experimental results showed that layer strain increased with a higher water–binder ratio and a lower CSA cement replacement ratio, and a similar trend was observed for interlayer bonding performance. The optimized mixture was determined using response surface methodology based on 13 experimental runs, yielding a water–binder ratio of 0.297 and a CSA cement replacement ratio of 3.88%. Verification results indicated that the optimized mixture exhibited superior buildability, with a mean relative error of 7.55% between the measured and predicted values, demonstrating close agreement between actual performance and predicted outcomes. These findings confirmed that the optimization process was effective and practically sound for enhancing the buildability of 3DCP materials.