Modification effect of nanosilica and polypropylene fiber for extrusion-based 3D printing concrete: Printability and mechanical anisotropy

Recently cement-based 3D printing (3DP) technology has been broadly adopted in civil engineering, and its printability is an important factor for its further application. Taking cement, fine sand and thickener as the basic formula, hybrid nanosilica (NS) and polypropylene (PP) fibers with different dosages are tested to comparing their modification effects on 3DP concrete's printability and mechanical anisotropy. The mortar flowability, printability, physical-mechanical properties and microstructure of these modified 3DP concretes are tested. The results demonstrated that both NS and PP fibers can accelerate the setting time of mortar, reduce its paste fluidity and slump, and improve its printability and homogeneity. But its density and compressive strength are reduced. Specifically, adding 1% NS and 0.2% PP fibers to 3DP concrete can improve its buildability by more than 67%, reduce the deformation rate up to 46% and the anisotropy of compressive strength up to 64%. These additive material also make the structure change from brittle failure to ductile failure, which is beneficial to structural safety. The microstructure analysis of these presented 3DP concrete shows that the NS can increase the number of concrete's micro pores and improve both its pore structure and the cementation property between layers, which can enhance the cementation between PP fibers and cement paste. These results can enrich the 3D-printed cement construction in additive manufacturing.

Automated summary

The effects of adding hybrid nanosilica (NS) and polypropylene (PP) fibers on the printability and mechanical anisotropy of 3D printed concrete were studied. The results showed that adding 1% NS and 0.2% PP fibers improved the buildability of the concrete and reduced deformation rate. These additives also improved the microstructure of the concrete and enhanced its structural safety.