Mechanical Properties of 3D Printed Concrete with Coarse Aggregates

Abstract:

This paper developed a 3D printing system which could continuously and stably print concrete with an aggregate size up to 10 mm. Then， it tested and compared the mechanical properties of 3D printed concrete and cast concrete. It is found that the compressive strength of 3D printed concrete is slightly anisotropic with a difference of 5%. The flexural strength shows significant anisotropy with a difference of 20%~25%. Compared with the cast concrete， the compressive strength of 3D printed concrete is reduced by 10%~15%， the flexural strength perpendicular to the printing direction （F_y and F_z） is reduced by 10%~15%， and the flexural strength parallel to the printing direction （F_x） is reduced by 30%~35%. The microstructure analysis indicates that there is little difference between the total porosity of 3D printed concrete and the total porosity of cast one， but there are obvious interlayers in 3D printed concrete， where the gray value is about 25% lower than the average gray value， indicating that the pore distribution of the interlayer is denser. Therefore， the proportion of pores with a volume bigger than 10 mm³ in 3D printed concrete is 10.6% higher than that of cast specimen， which explains the reduction of the compressive strength and flexural strength of 3D printed concrete. It is concluded that the cement content of 3D printing coarse aggregate concrete is 17.8%~49.6% lower than that of 3D printing mortar in the previous study.