Evaluating the printability and mechanical performance of low impact concrete with slag and waste limestone for 3D printing

Abstract

Additive manufacturing of concrete has addressed several challenges associated with traditional casting methods by reducing the need for formwork, reducing labour costs and enabling complex architectural designs. The rheological properties of 3D printed concrete particularly flowability, extrudability and buildability are important to ensure quality. These printability requirements are often achieved by significantly increasing the cement content in the mix. However, such an approach raises critical concerns regarding the environmental sustainability of 3D concrete printing (3DCP). This research explores the feasibility of using ground granulated blast furnace slag and globigerina limestone waste as partial replacement of ordinary Portland cement to develop low-carbon concrete mixes for 3DCP. Five different mix compositions were developed: a control mix containing 100% Portland cement (CEM I 52.5R), and mixes with partial cement replacement; 20% slag and three additional mixes incorporating 20% slag combined with 10%, 15%, and 20% limestone. Experimental investigations were conducted to evaluate the fresh and hardened properties of the developed mixes. Fresh-state tests covered flowability, extrudability, buildability and open time, while hardened-state tests examined compressive strength, and flexural strength with emphasis on anisotropic behaviour under different loading orientations. Comparisons between cast and printed specimens were carried out to assess anisotropy for the printed specimens. The results show that GGBFS enhances the mix's flowability while the inclusion of limestone waste reduces it. Therefore, an appropriate balance between slag and limestone is essential to achieve optimal flowability and ensure printability. Incorporation of a high proportion of limestone negatively influences the mechanical performance and reduces the printability of the mix. Cast specimens exhibited higher compressive strength than 3D printed concrete, the latter showing anisotropy with lower strength in the Z-direction. GGBFS and limestone waste were effectively used to produce low carbon 3D printed concrete with sufficient rheological and mechanical properties, thereby reducing the environmental impact of 3D Printing of concrete.