3D numerical models of plaster-styrofoam specimens: Substantiating the variation of elastic modulus

Macroporous material reacts differently to stress than rock lacking voids visible to the naked eye. While it is generally understood that greater macroporosity negatively impacts strength and elastic modulus, this paper endeavors to quantify the effect of increasing macroporosity through numerical modeling. Macroporous rocks, such as lithophysal tuff, vesicular basalt and macroporous chalk occur often in nature. Man-made materials such as mine stope backfill and draincrete behave similarly to macroporous rocks. Linear elastic models were created as 5.1cm (2 inch) by 10.2cm (4 inch) right cylinders utilizing plaster properties with Itasca's FLAC3D and TNO Diana. Spherical voids were created with three diameter sizes - 3mm, 12.7mm (0.5 inch) and 25.4mm (1 inch). Porosity levels ranged from zero to thirty percent. Numerical data were compared to laboratory testing data from plaster specimens of the same size with Styrofoam inclusions of the same size and shape. Numerical models were found to yield significantly higher elastic moduli than the laboratory data. While the numerical data produce quite linear relationships, there is greater scatter within the data for the larger voids. This could be a result of clustering of voids or stress field interaction; however further testing is needed to verify these hypotheses.