Synergistic approach to enhancing interlayer bonding in 3D printed concrete via water to binder ratio and water retention addition

The process of printing in layers stacked on top of each other without the need for formwork in three-dimensional concrete printing makes the bonding at the interlayer interface very important, as it governs the structural performance and long-term durability of additively manufactured concrete elements. Weakening of the adhesive bond can lead to structural failure, reduced durability, and the risk of collapse. Bonding behavior at layer interfaces is influenced by several factors, including printing parameters, the printability of the material, water retention, and the shrinkage behavior of the 3D printable concrete material. This study investigates improving the adhesive bond between 3D printed concrete layers on a rectangular block of size 400 × 400x180 mm which were printed with various concrete mixtures. The concrete used in this research includes Ordinary Portland cement, limestone powder, river sand, water, and superplasticizer. Water-to-binder proportions of 0.30, 0.34, and 0.40 were adopted; superplasticizer content was various as 0.22%, 0.16%, and 0.10% respectively by the weight of cement. Experimental findings indicate that the block printed with the concrete having a water-to-binder ratio of 0.30 and superplasticizer content of 0.22% achieved the best improvement in the adhesive bond between the printed layers. Moreover, incorporating limestone powder at levels up to 10% by cement mass enhances water retention in the fresh mixture, mitigates shrinkage, and strengthens bonding at the interfaces of additively manufactured concrete layers. Especially, the adhesive bond between printed layers of the block was enhance by a combination of addition of limestone powder to concrete mix with a low water-to-binder proportion containing superplasticizer. Additionally, there was a linear relationship between printed height layer and the quality of layer interface bonding.