Sustainable conversion of contaminated dredged river sediment into eco-friendly foamed concrete

Large quantities of contaminated river sediment is dredged continuously worldwide, which is generally dumped in landfill areas resulting in land occupation and soil-groundwater pollution. An innovative approach is demonstrated in this study to transform contaminated sediment into eco-friendly foamed concrete by adding cement, foam and silica fume without heating and pressure. With the foam percent rising from 0% to 80% (v/v), the compressive strength and dry density of foamed concrete decreased from 18.8 to 2.1 MPa and from 1442 to 620.6 kg M-3, respectively. Accordingly, the thermal conductivity declined from 0.516 to 0.173 W m(-1). K-1, and water resistance coefficient decreased from 0.73 to 0.43. Dosage of 10% silica fume as substitution of part of cement exhibited a comprehensive optimization of the concrete properties because of its activity in the hydration reaction and pore-filling effect identified by X-ray fluorescence (XRF), X-ray diffraction (XRD) and scanning electron microscopy (SEM) attached with energy dispersive X-ray spectroscopy (EDX). It also narrowed the pore size distribution and made the pore structure more uniform and denser detected by optical microscope. Heavy metals in the sediment can be immobilized by 81.5-98.1% for As, Cr, Cu and Zn, even in an acidic environment. This study provides new opportunities for hazardous dredged river sediment recycling, which is prospective because it not only consumes a large amount of sediment but also avoids depletion of resources and creates profits. (C) 2019 Elsevier Ltd. All rights reserved.