Water loss and shrinkage prediction in 3D printed concrete with varying w/c and specimen sizes

• Published in: Cement & concrete composites 2024-05, Vol.149, p.105523, Article 105523
• Main Authors: Ma, Lei, Jia, Zijian, Chen, Yuning, Jiang, Yifan, Huet, Bruno, Delaplace, Arnaud, Zhang, Yamei, Zhang, Qing
• Format: Article
• Language: English
• Subjects: 3D printing; Shrinkage modeling; Surface to volume ratio; Water loss; Water to cement ratio
• ISSN: 0958-9465; 1873-393X
• DOI: 10.1016/j.cemconcomp.2024.105523

In 3D printed concrete (3DPC), the absence of formwork leads to increased shrinkage compared to traditional cast concrete which uses formwork. This increase in shrinkage is primarily due to the rapid evaporation of moisture during the early stages. Therefore, our research focused on how the initial water content and the exposed surface area affect the total shrinkage by varying water-to-cement ratio (w/c) and the surface-to-volume ratio (s/v). For 3DPC with high w/c, we used calcium formate (CaF) to improve its printability by increasing static yield stress. Dry environment makes the evaporation the predominant mode of water loss, significantly decelerating the hydration process in samples with fully exposed surfaces. At 28 d, the evaporated moisture in 3DPC is 2.8 times higher than the moisture consumed by hydration. A predictive model for the shrinkage properties of 3DPC has been developed by considering that 3DPC experiences both hydration and evaporation simultaneously from early stages on the basis of the water mass conservation principle. The predictions were found to align with actual shrinkage test results, as evidenced by quantitative analysis of parameters like internal RH, mass loss, degree of hydration, and porosity, thus validating the accuracy of the model. •Achieve the printability of 3D printed concrete with high w/c by the utilization of calcium formate.•Establish a linear relationship between capillary pore volume and shrinkage at 60% RH.•Quantitatively compare the loss of evaporated water and hydrated water in 3D printed concrete.•Develop a total shrinkage model for 3D printed concrete considering the feature of early exposure.