Volumetric changes of the 3D printable cementitious material

Abstract

Shrinkage and volume changes in cementitious materials are critical factors in their performance, particularly in advanced applications like 3D concrete printing, where dimensional stability is paramount. This study investigates the volume changes of fine-grained cementitious mixtures specifically designed for 3D printing and evaluates the impact of setting accelerators and steel fibers under laboratory and water storage conditions. Measurements were performed according to ČSN 73 1320 and Schleibinger Shrinkage measurement. The results reveal that setting accelerators significantly increase early-age shrinkage, with values up to 2.6 times greater than non-accelerated mixes within the first 24 hours. Over time, the rate of shrinkage progression decreases, aligning longterm trends between accelerated and non-accelerated mixes. Laboratory conditions amplify shrinkage compared to submerged conditions, where water storage mitigates shrinkage, resulting in stable or minor dimensional changes. Steel fibers marginally reduce shrinkage but cannot offset the effects of accelerators. Measured shrinkage values consistently exceeded the predictions of second generation of Eurocode FprEN 1992-1-1:2022, with deviations ranging from 1.4 to 1.6 in long-term assessments. This highlights the need for adjustments to Eurocode models to account for material properties of modern cementitious materials, including finer particle sizes and accelerated hydration kinetics. These findings emphasize the importance of optimizing mix designs and standards for 3D printing applications to achieve long-term dimensional stability.