CONCRETE WITH WASTE MATERIALS FOR CONSTRUCTION 3D PRINTING

Abstract

Recently in Singapore’s construction industry, concrete 3D printing (C3DP) has been gaining interest and traction. C3DP is a formwork less construction method that utilises a 3D printer to extrude mortar in layers vertically to form the component. The challenge is creating an optimal mix design so that the mortar is printable and buildable. Literature has shown that concrete is the most common construction material in the world. Cement is the key component in concrete and is the highest contributor to the carbon footprint in the production of concrete. An alternative material is needed to reduce the usage amount of cement. Therefore, this paper explores recycling waste material like fly ash and biochar in 3D printable mortar, to alter its rheological properties to improve buildability and make it a greener mortar by reducing the amount of cement for C3DP application.

In this research, 3 mix design are studied; 1) plain mortar, 2) fly ash mortar (15% cement by binder mass replaced with class F fly ash) and 3) biochar mortar (addition of 1% of cement weight of mixed wood saw dust biochar). Based on the portable vane (PV) test, biochar mortar had the highest static yield stress development, fly ash mortar had the second highest while plain mortar was the lowest. Fly ash and biochar influence the mortar by shortening the setting time. From the buildability test, plain mortar and fly ash mortar were successfully extruded by the 3D printer while biochar mortar was unsuccessful. However, plain mortar’s printed component did not achieve shape stability with deformation observed due to its low static yield stress with insufficient internal structural build-up. Fly ash mortar’s printed component achieved shape stability with minimal deformation due to its moderate static yield stress with sufficient internal structural build-up.

The results conclude that fly ash is a suitable waste material in altering the rheological properties which made the mortar more buildable for C3DP application.