Biochar as additive for improved building performances and heavy metals solidification of sediment-based lightweight...

The sustainable disposal of large volumes of contaminated dredged river sediment has become a challenge for municipal management. In this study, a cutting-edge biochar application method was innovated, which converted the polluted dredged sediment into a low-carbon and environmentally friendly building material through an autoclave-free method. As the amount of biochar addition increased from 0 to 2% (w/w), the compressive strength of the dredged sediment-based lightweight concrete (DS-LC) increased from 3.92 to 4.61 MPa. Accordingly, the thermal conductivity decreased from 0.237 to 0.222 W/(m K), the water absorption decreased by 6%, and the water resistance coefficient increased by 33%. Results of X-ray diffraction (XRD) and thermogravimetric (TG) analysis showed that biochar promoted the hydration reaction and the carbonation process. Scanning electron microscopy (SEM) attached with energy-dispersive X-ray spectroscopy (EDX) showed that biochar addition changed the microstructure of the DS-LCs, which made the pore distribution more uniform and densified. Biochar addition also strengthened the immobilization of heavy metals (Cu, Zn, Cr, and As) by approximately 18-27% and combination of biochar and silica fume could increase the heavy metal immobilization by 28-44%. Compared with the traditional concrete material, the DS-LC with biochar addition could not only reduce the carbon emission but also has potential economic benefit for the treatment and utilization of dredged sediment.