Quantified research on the nonuniform distribution of expanded polystyrene beads in sandwich panels

Expanded polystyrene (EPS) concrete is a core material in sandwich panels, and EPS beads are widely believed to be nonuniformly distributed in the panels. However, the effectiveness of attempts to improve the homogeneity has been difficult to prove because of the lack of a direct method to quantitively evaluate a nonuniform distribution. Based on the application of picture recognition technology to surfaces cut from sandwich panels, a novel method for quantitatively evaluating the number and distribution of EPS beads was given. To verify this method, three commercial sandwich panels were cut into 345 specimens. Four cut surfaces of every specimen were photographed and recognized, and the distribution of some properties, including the number, area ratio, and equivalent diameter of beads, the area ratio of pores, and the density and compressive strength of concrete, were investigated and analyzed. The results showed that the area ratio of EPS beads in the cut surfaces and the density and compressive strength of EPS concrete had obvious linear relationships with the height within the panels. Based on the rules, normalized equations of the density and compressive strength with respect to the area ratio of EPS beads were promoted. This paper showed that the picture recognition of the cut surfaces method could quantitively and directly reveal the nonuniformity of not only EPS beads but also some properties caused by EPS beads in concrete. With this method, comparison and evaluation of the trials to improve the homogeneity of EPS concrete are possible. (C) 2020 Elsevier Ltd. All rights reserved.