Recycle of inorganic wastes by hydrothermal technology

In order to build up a sustainable society, the authors have investigated the recycling technology of inorganic wastes with low energy consumption. Sewage sludge ash, concrete waste, and construction sludge were used as raw materials. These waste were mixed with Ca(OH)
2
and formed by uniaxial pressing. The specimens were autoclaved for 6 h at 180 °C under saturated steam pressure. The flexural strength of the specimens varied from 3.2 to 9.4 MPa with the bulk density of 1200 to 1550 kg/m
³
. The strength development was caused by filling of the initial void among the particles with tobermorite (Ca
5
(Si
6
O
18
H
2
)·4H
2
O) and hydrogarnet (Ca
3
Al
2
(SiO
4
)(OH)
8
) formed by hydrothermal treatment. To apply these solidified inorganic waste to paving tile, we determined that Ca(OH)
2
/wastes mass ratio is 15/85 for plant production condition. The paving tile had comparable performance with brick, block and concrete pavement.