IntroductionThe rapid adoption of 3D printed cement-based materials (3DPC) in construction industry, particularly in sustainable buildings, highlights a critical importance of understanding its shrinkage characteristics. Different from conventional concrete, 3DPC is characterized due to the absence of coarse aggregates, the lack of templates support during printing, and immediately exposure to environmental conditions, which make it more susceptible to shrinkage-induced cracking. Shrinkage in cement-based materials leads to internal stresses and potential durability issues, affecting a long-term structural integrity. It is thus to investigate the shrinkage behavior of 3DPC. In particular, the effect of material compositions (i.e., water-binder ratio (W/B), sand-binder ratio (S/B), and supplementary cementitious materials such as fly ash (FA) and ground granulated blast furnace slag (GGBS)) on the shrinkage (total shrinkage, autogenous shrinkage, and drying shrinkage) is not fully clarified. This study was to investigate the shrinkage characteristics of 3DPC and compare it with other cement-based materials (i.e., UHPC and cast mortar).MethodsTo investigate the impact of material composition on 3DPC shrinkage, a series of laboratory experiments were conducted by a standardized contact shrinkage testing method. Four key factors evaluated were W/B, S/B, FA replacement ratio, and GGBS replacement ratio. These material variables were selected based on their known influence on the microstructure and shrinkage behavior of traditional cement-based materials.Total shrinkage (TS), autogenous shrinkage (AS), and drying shrinkage (DS) were measured at specific intervals to capture early-age shrinkage behavior in 14 d. TS was calculated as a sum of AS and DS to represent the overall dimensional changes of the material for over time. The degree of influence of each material factor on the shrinkage was determined by grey relational analysis (GRA). GRA is a statistical method that enables the quantification of the relationship between multiple variables in complex systems, making it particularly suitable for determining the relative significance of material compositions in the context of 3DPC shrinkage.For comparative purposes, the shrinkage characteristics of conventional cast mortar and UHPC were also analyzed under identical conditions, enabling a comprehensive evaluation of the shrinkage performance of 3DPC.Result and discussionThe results reveal the distinct shrinkage patterns based on the material composition of 3DPC. Increasing the W/B can significantly reduce AS. However, the influence of W/B on DS is less than that on AS. Also, the S/B has a measurable effect on drying shrinkage. After an initial curing period of 3 d, a higher S/B ratio leads to a marked reduction in DS likely due to the presence of fine sand particles, which restricts the movement of water within the matrix and limit capillary stresses.Besides, the replacement of cement with FA has a beneficial effect on shrinkage reduction. The 14 d AS and DS both are significantly lower in 30% FA-modified 3DPC, compared to the control sample. Also, the incorporation of FA reduces the 14 d autogenous shrinkage and drying shrinkage of 3DPC in the same proportion. In contrast, the use of GGBS has a more complex influence on shrinkage. While GGBS replacement increases AS after 2 d, it reduced drying shrinkage before 5 d. The TS of 3DPC firstly decreases and then increases with the increase of GGBS dosage, and the TS of 3DPC is the minimum value when the dosage of GGBS is 10%.The grey relational analysis shows the factors influencing 3DPC shrinkage in an order of significance, i.e., W/B, S/B, GGBS and FA. This highlights a predominant role of water content in governing both autogenous and drying shrinkage in 3DPC systems, which is consistent with those in other cement-based materials. However, the relative importance of sand and supplementary materials indicates that a further optimization of the mix design can lead to an improved shrinkage performance. Comparing the shrinkage behavior of 3DPC with that of UHPC and cast mortar, the shrinkage magnitudes of 3DPC are generally higher. These results indicate a necessity of tailored shrinkage control strategies in 3DPC, especially in large-scale applications where cracking risk is a major concern.ConclusionsThis study provided a comprehensive evaluation of the shrinkage behavior of 3D printed cementitious materials, especially the influence of material compositions such as W/B, S/B, FA, and GGBS. Increasing the W/B of 3DPC significantly reduced AS more than DS. The DS decreased with increasing S/B after 3 d. The replacement of FA proportionately decreased the 14 d AS and DS of 3DPC, whereas the replacement of GGBS replacement ratios increased AS after 2 d and DS before 5 d. The influence of material composition on 3DPC shrinkage was ranked in a decreasing order of W/B, S/B, GGBS, and FA. Compared to other cement-based materials like UHPC and cast mortar, 3DPC exhibited a higher shrinkage, indicating the need for more focused research and innovation in shrinkage reduction techniques for 3DPC. These findings contributed to a deeper understanding of the material behavior and provided a foundation for a future work on optimizing 3DPC for large-scale and crack-resistant applications.