Abstract
Ordinary Portland cement (OPC) is widely used in the solidification/stabilization of Pb-contaminated soils. However, many studies have suggested that the high content of Pb would degrade the mechanical properties of OPC-solidified/stabilized soils. This paper presents a new binder, geopolymer fine aggregate (GFA), composed of ground granulated blast furnace slag, fly ash, CaO, and Na2SiO3. For comparison, OPC was used as a conventional binder. Mechanical properties and leaching characteristics are typically used to evaluate the effects of binders on solidified/stabilized soils. Nevertheless, limited information on the mechanical properties and leaching characteristics of the GFA-solidified/stabilized soils is available. This study thus investigated the mechanical properties and leaching characteristics of geopolymer-solidified/stabilized Pb-contaminated soil. Unconfined compressive strength test, permeability test, synthetic precipitation leaching procedure, simplified bioaccessibility extraction, phytoavailability extraction (with diethylene-triamine penta-acetic acid), sequential extraction procedure, mercury intrusion porosimetry, and scanning electron microscopy (SEM) were performed on OPC- and GFA-solidified/stabilized soil. The results showed that the GFA presented a better effect on the mechanical properties and leachability of the solidified/stabilized soils than the OPC-solidified/stabilized soils. The GFA-solidified/stabilized soil displayed considerably lower leachability, bioaccessibility, and phytoavailability of Pb and higher mechanical properties and chemical stability than the OPC counterpart. This study demonstrated that GFA had a better effect than OPC on the solidification/stabilization of Pb-contaminated soils.
Highlights
Pb-contaminated soil has become a severe problem in China due to improper waste disposal practices and accidental chemical spills [1]
When the binder dosage increased from 5% to 20%, the Unconfined compressive strength (UCS) of the Ordinary Portland cement (OPC)-solidi ed/stabilized soil was increased from 0.55 MPa to 3.12 MPa, whereas that of the geopolymer fine aggregate (GFA)-solidi ed/ stabilized soil was increased from 0.95 MPa to 4.35 MPa. e UCS of pastes with OPC was larger than that with GFA at the same dosage. e increased UCS of the Pb-contaminated soil solidi ed/stabilized by OPC was attributed to the large production of AFt or C-S-H
When the binder dosage increased from 5% to 20%, the hydraulic conductivity of the OPCsolidi ed/stabilized soil was decreased from 1.85 × 10−5 cm/s to 2.13 × 10−7 cm/s, whereas that of the GFA-solidi ed/ stabilized soil was decreased from 3.31 × 10−6 cm/s to 8.25 × 10−8 cm/s. e decreased trend of hydraulic conductivity was mainly due to the development of binder hydration
Summary
Pb-contaminated soil has become a severe problem in China due to improper waste disposal practices and accidental chemical spills [1]. Inorganic materials include calcined kaolin, ground granulated blast furnace slag (GGBS), fly ash (FA), and clay [7,8,9]. Among these inorganic materials, GGBS and FA are promising options to prepare geopolymers. Mechanical properties and leaching characteristics are widely used to evaluate the effects of binders on solidified/stabilized soils [1, 2, 5]. Limited information on the mechanical properties and leaching characteristics of GFA-solidified/stabilized soils is available. Is study aimed to investigate the mechanical properties and leaching characteristics of GFA-solidified/stabilized soils. Mercury injection porosimetry (MIP) and scanning electron microscopy (SEM) tests were conducted to reveal the microstructural characteristics of GFA-solidified/stabilized soils
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