Development of a Lightweight Pavement Block with Extremely High Permeability Using the Volcanic Pumice Bora

Bora is a granular volcanic pumice with a certain degree of hardness. In this study, we investigated the possibility of using fired Bora as a substitute for fine sand in mortar. The objective was to develop a lightweight pavement block with extremely high permeability using fired Bora. Initially, the changes in hardness and density of Bora particles fired at different temperatures were examined. The bending strength of mortar containing fired Bora as a fine aggregate was also evaluated. Subsequently, we fabricated a permeable pavement block with a hybrid structure, comprising a mortar containing the fired Bora and a porous material with large-sized Bora particles bonded using cement paste. We examined its bending strength and permeability and performed a quantitative analysis of the bending stress distribution on the block using the finite element method. The hardness of Bora significantly increased when fired at temperatures exceeding 900 °C; hence, Bora fired at 1100 °C can be used as an effective substitute for crushed sand in mortar. Furthermore, the results confirmed that the use of fired Bora enabled the production of lightweight pavement blocks with extremely high permeability that satisfied the bending strength criterion.