Mechanical Performance of Commercially Available Premix UHPC-Based 3D Printable Concrete

3D printable concrete is gaining attention as a promising construction material. Prior research has shown that printable cementitious mixtures are often tailored for specific printing systems. No prior work had resolved how to adapt commercially available ultra-high-performance concrete (UHPC) for 3D printing. This gap motivated the current investigation into modifying UHPC for printing suitability. Established knowledge includes the importance of superplasticizer in concrete workability. However, adapting UHPC for extrudability remains uncertain. This paper's contribution is in evaluating UHPC for 3DCP without requiring custom formulations. The study focuses on fresh and hardened properties to assess printability. It also compares printed UHPC to mold-cast UHPC in mechanical performance.

This study aimed to evaluate the suitability of a commercial UHPC material for 3D concrete printing. The specific problem addressed is the lack of general-purpose printable UHPC formulations. The motivation is to adapt existing materials rather than developing new ones. The researchers tested UHPC with different superplasticizer percentages to find a printable mix. They focused on properties like extrudability, shape retention, and green strength. The study also aimed to assess mechanical performance in hardened state. The goal was to determine if commercial UHPC could meet printing requirements. The results were intended to guide future applications of UHPC in 3D printing.

The study used a commercial UHPC material modified with varying superplasticizer percentages. Four levels of superplasticizer (100%, 94%, 88%, 82%) were tested to find the optimal printable mix. Fresh-state properties like shape retention and green strength were measured. Hardened-state properties included compressive and flexural strength in three directions. The interlayer bond strength was also evaluated. Experimental methods included extrusion tests and mechanical loading. The printing requirements tested were extrudability, buildability, and shape retention. The comparison was made between printed and mold-cast UHPC samples.

The optimal superplasticizer level was found to be 88%, which met printing requirements. Printed UHPC showed superior flexural performance compared to mold-cast UHPC (15-18% higher). However, compressive strength was reduced by 32-56% in printed UHPC. The interlayer bond strength was also assessed as part of the hardened properties. The UHPC met criteria for extrudability, buildability, and shape retention. The anisotropic effects were observed in mechanical performance across loading directions. The study demonstrated that commercial UHPC can be modified for 3D printing. The results suggest that printed UHPC has potential for structural applications.

The authors concluded that commercial UHPC can be adapted for 3D printing with appropriate superplasticizer adjustments. The 88% superplasticizer level was sufficient for printability requirements. The printed UHPC showed improved flexural performance but reduced compressive strength. The interlayer bond strength was an important factor in hardened properties. The anisotropic effects were confirmed through mechanical testing. The study supports the feasibility of using commercial UHPC for 3D concrete printing. The results suggest that printed UHPC has potential for structural applications. The findings are specific to the tested UHPC formulation and printing conditions.