Influence of Temperature and Humidity on Mechanical Properties of Calcined Oyster-Shell Powder-Modified 3D-Printed Concrete

Calcined oyster-shell-powder-modified concrete (CS), developed by our research group, is an ecological quick-setting concrete suitable for 3D printing technology. It has been discovered that the material's formability is obviously affected by ambient temperature and humidity after the 3D printing process, and this phenomenon also occurs in other 3D-printed concrete materials. To figure out the influence laws of temperature and humidity on the mechanical properties of CS-modified 3D-printed concrete during the curing time, the methods of both microanalysis and macro testing are applied. The molecular dynamics method is used to reveal the effects of temperature and humidity on the material's mechanical parameters, including elastic modulus, bulk modulus, and shear modulus. The macroscopic compressive strength and flexural strength of the 3D-printed concrete are measured to validate microanalysis findings. Results show the most suitable curing conditions for improving the mechanical properties of CS-modified 3D-printed concrete are the ambient temperature of 20 ± 1 °C and the relative humidity of 80-95%. Under this curing condition, the 28 day flexural strength of CS-modified 3D-printed concrete can reach 14 MPa, and the compressive strength can reach 44 MPa, which significantly improves the strength of printed samples.