Homogeneously bloated aggregates formed by sintering at rising temperatures require higher temperature than aggregate bloated by the black core mechanism. Much liquid can be produced on the aggregate surfaces and induce sticking between the aggregates. In this study, highly refractory oxides, Al2O3 and SiO2, were coated onto the aggregate surfaces in order to control sticking. The degree of sticking was analyzed by identifying the phases formed and measuring the neck length (2x) of two aggregates (radius = r) stuck together. As the amount of coating increases, the (x/r) ratio decreases, indicating that the degree of sticking was reduced. For the Al2O3 coating, a smaller particle size of the coating powder leads to a greater aggregate surface area that can be coated, which prevents sticking between the aggregates. For the SiO2 coating, increasing the particle size of the coating powder decreased the (x/r) ratio in the 1 ~ 2 wt% coating, while the ratio increased for coating above 3 wt% due to the lower melting temperature of amorphous silica and the generation of β-cristobalite. The proper amounts and suitable particle size of the Al2O3 and SiO2 coating materials were obtained for manufacturing homogeneously bloated aggregates using 100% reject ash. These results could be used as basic data for the development of a mass-production process using a rotary kiln.

Keywords: Artificial aggregates, Reject ash, Sticking phenomenon, Oxide coating, Alumina, Silica, Neck length