Effect of Limestone Powder Substitution on Fresh and Hardened Properties of 3D Printable Mortar

Abstract

Great progress has been made in 3D concrete printing (3DCP) in the past few years. The unique advantages of 3DCP over conventional concrete construction may include saving costs and labor, eliminating formwork, reducing the construction time, as well as increasing flexibility in architectural design. To satisfy the printing requirements, a high amount of binders is used for 3DCP. Among all the binders, ordinary Portland cement (OPC) is the most commonly used binder for 3DCP. However, producing OPC consumes high amounts of energy and exhausts high amounts of greenhouse gases. Therefore, with a high amount of OPC, 3DCP cannot be treated as a sustainable and environmental friendly construction method. Partially replacing OPC by supplementary cementitious materials (SCMs) might be a proper solution to make the 3D printable concrete sustainable. Limestone powder (LP) is one of the SCMs with the advantage of wide availability and low cost. This study analyzed the impact of substituting OPC by LP on the fresh and hardened properties of 3D printable mortar. Six mixtures with three LP substitution rates (0%, 25%, and 50% by volume of OPC) were designed. In the fresh stage, a squeeze flow test was used for evaluating the shape stability. In the hardened stage, drying shrinkage and mechanical properties were investigated. The results showed that a high amount of LP substitution had negative effects on both fresh properties and hardened properties. However, for a lower replacement percentage (i.e. a 25% replacement rate), the strength loss is still within reasonable limits.