Can 3-D Printed Gypsum Samples Replicate Natural Rocks? An Experimental Study

3D printing is an emerging technology which can offer valuable insight into rock characterization and theoretical model verification due to the sample reproducibility. Also, it will allow for the samples to be built at various scales with controlled geometries and specification to facilitate different types of analysis. In this study, gypsum powder was used for printing blindly to evaluate if mechanical and pore network characteristics of the specimens would resemble a natural rock. For this purpose, cylindrical specimens with different sizes were manufactured without inputting any pore network CT digital image of a natural rock. The objective was to study mechanical properties and deformation behavior of such samples by conducting a series of uniaxial compressive strength tests. Scanning electron microscope was utilized to characterize the microstructures of rock matrix prior to and after the experiments were performed. By determining the representative element area and image processing techniques, the surface porosity of 3-D printed samples was measured to be 5.8%. The analysis of pore size and shape distribution demonstrated the dominance of intermediate pore size as the main feature. This study enabled us to propose a new classification criterion for the pore shape based on printing procedures. Additional microstructural elements, micro-fractures, in particular, were identified, analyzed and classified into three separate categories, including intrapore micro-fracture, interpore micro-fracture and micro-fracture perforating pores. Finally, this study compared the mechanical properties and microstructure of 3D printed gypsum samples with typical natural rocks, also revealed the limitations in 3-D printing and suggested printing materials should be chosen, specific to the goal of the research study.