3D打印粗骨料混凝土力学性能

Mechanical Properties of 3D Printed Concrete with Coarse Aggregates

研发了一种可以连续、稳定的打印最大粒径10mm的粗骨料混凝土3D打印系统。对比测试了3D打印粗骨料混凝土与浇筑混凝土的力学性能,发现3D打印粗骨料混凝土抗压强度呈现细微的各向异性特征(差异在5%以内),而抗折强度呈现显著的各向异性特征(差异在20%~25%之间);与浇筑混凝土相比其抗压强度降低10%~15%,垂直于打印方向的抗折强度(Fy与Fz)降低10%~15%,平行于打印方向的抗折强度(Fx)降低30%~35%。通过微观结构分析发现,3D打印粗骨料混凝土的总孔隙率与浇筑混凝土总孔隙率相近,但3D打印粗骨料混凝土存在明显的层间薄弱区,其灰度值比平均灰度值低25%,说明在层间薄弱区的孔隙分布更加密集,3D打印混凝土中体积在10mm3以上的大孔隙率较浇筑混凝土高出10.6%。特有的层间结构和较高的大孔隙率导致3D打印混凝土力学性能的各向异性特征和强度的降低。对比发现,3D打印粗骨料混凝土的水泥用量比以往研究中3D打印砂浆的水泥用量减少17.8%~49.6%。

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(Fy and Fz)is reduced by 10%~15%,and the flexural strength parallel to the printing direction(Fx)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.