Introducing magnesium oxide into 3D printed concrete to mitigate dry-shrinkage

Concrete 3D printing has gained significant attention in recent years as an innovative method for construction. However, 3D printed concrete (3DPC) faces greater shrinkage challenges compared to conventional concrete due to several factors, including the absence of coarse aggregates, a higher proportion of cementitious materials, and the lack of formwork. Magnesium oxide (MgO), known for its water-expanding properties, can be incorporated into the concrete mix to address shrinkage issues, mitigating cracking and promoting a zero-shrinkage outcome for 3DPC. This research explores the role of MgO as an expansion agent to counteract the shrinkage of 3DPC, aiming to improve its shrinkage-related properties. In the study, different concentrations of magnesium oxide, specifically 0 %, 3 %, 6 %, and 9 %, were tested to formulate 3DPC mixtures. The study assesses the impact of varying MgO contents on the material's flowability, rapid solidification, and printability. Experiments have shown that when the MgO content increases from 0 % to 9 %, the flowability of concrete decreases by 250 %, the 12-h penetration resistance decreases by 450 %, and it cannot be effectively formed. After 90 days, the compressive and flexural strengths decreased by 20 % and 15 % respectively, but the MgO expansion effect significantly alleviated the drying shrinkage problem, indicating that although high content improved crack resistance, it seriously damaged the mechanical and construction properties. After completing the test process, the microstructure of the sample was analyzed by SEM to assess the impact of different MgO contents. Based on the examination results, the optimal dosage of MgO was determined, which significantly contributed to improving the material properties.