Using Calcium Oxide and Accelerator to Control the Initial Setting Time of Mortar in 3D Concrete Printing

In recent years, 3D printing has attracted a lot of attention in the construction industry. Compared with general concrete construction, 3D concrete printing has higher flexibility in creating concrete’s shape and design. 3D concrete printing requires the precise control of fresh concrete properties such as flowability, extrudability, and resistance to segregation during printing process. The initial setting time of the concrete also needs to be controlled as it needs to adhere to the next layer and then harden rapidly in order to support the upper layer. This study proposes a method to control the initial setting time of the concrete for the 3D printing process by using a mixture of calcium oxide powder and accelerators. The study showed that using 5–10% calcium oxide and 2–4% accelerator by mass of cement, the initial setting of the concrete can be varied. It is also shown that adding only accelerator prolongs the setting time of the mixture due to the plasticizer contained therein. By using calcium oxide power, the initial setting time of the concrete can be hastened and the combination of calcium oxide powder and accelerator can reduce the initial setting time while maintaining good workability of the mixture. The addition of accelerator also increases the early compressive strength of the concrete mixture.