Safe and economic disposal of water treatment residuals by reusing it as a substitution layer in roads construction (spectroscopic and geotechnical study).

Abstract

Cost-effective construction techniques, such as reusing waste materials, play important role in dramatically reduce costs. In recent years, sludges have gained considerable attention as a geotechnical material. Increase in the demand of drinking water from purification plants produces a huge amount of water treatment residuals (WTRs). The disposal of such residues can be considered problematic issue. In this study, innovate and economic method to disposal of WTRs was presented. Comprehensive experimental investigations have been done to determine the effect of utilizing WTRs as a substitution layer in collapsing soil through roads construction processes. The investigations extended to the geotechnical and spectroscopic properties. Tests were carried out on the soil sample mixing with 0, 4, 8, 12, and 16% of WTRs. The samples morphology and composition are characterized by scanning electron microscopy (SEM) and the energy dispersive spectroscope analyzer (EDS). The microstructure and organic constituents are analyzed by X-ray diffraction (XRD) and the Fourier transform infrared (FTIR). The geotechnical measurements include particle size distribution (PSD), single odometer test (SOT), modified proctor test, and the California bearing ratio (CBR). The microstructure analysis confirms that WTRs acted as a pore filler to decrease in porosity and create a denser and solidified structure which reduces the suction and maximum collapse potential. Mineralogical analyses implied that the soil with WTRs turns into a rich medium with metal cations and organic matters that react with minerals to form binding materials. From the geotechnical point of view, WTRs can be safely deposed by mixing with collapsing soil as a subgrade of road construction up to a value of 10% without any impact or reduction on CBR values. The reduction in the required amount of subgrade required by 10% effectively decreases the cost of road construction. Moreover, the results illustrate the remarkable improvement in the collapse potential of the soil, which is reduced by about 24.7% by mixing it with 10% WTRs.