Abstract
Cement solidification/stabilization is widely used towards contaminated soil since it has a low price and significant improvement for the structural capacity of soil. To increase the usage of the solidified matrix, cement-solidified contaminated soil was used as road subgrade material. In this study, carbonation effect that reflected the durability on strength characteristics of cement-solidified contaminated soil and the settlement of pavement were evaluated through experimental and numerical analysis, respectively. According to results, compressive strengths of specimens with 1% Pb(II) under carbonation and standard curing range from 0.44 MPa to 1.17 MPa and 0.14 MPa to 2.67 MPa, respectively. The relatively low strengths were attributed to immobilization of heavy metal, which consumed part of SiO2, Al2O3, and CaO components in the cement or kaolin and reduced the hydration and pozzolanic reaction materials. This phenomenon further decreased the strength of solidified soils. The carbonation depth of 1% Cu(II) or Zn(II) contaminated soils was 18 mm, which significantly increased with the increase of curing time and contamination concentration. Furthermore, the finite element calculation results showed that surface settlements decreased with the increase of modulus of subgrade and the distance away from the center. At the center, the pavement settlement was proportional to the level of traffic load.
Highlights
Background value in soilMetal content Pb Cu Zn
The commercially available ordinary Portland cement (OPC) P·O42.5 was prepared, which consisted of 6%–15% active additive and 85%–94% cement. e natural moisture content of kaolin and sand was measured according to JIS A 1203
Considering the existence of Na(I) and Fe shown by Inductive Coupled Plasma Emission Spectrometer (ICP) results, the characteristic peaks at 2θ 26.73 and 20.43° indicate the presence of sodium phosphate hydrate (Na6P6O18·6H2O) and iron silicon carbide (Fe-Si-C)
Summary
E heavy metal-contaminated soils were prepared artificially by adding Pb(NO3), Zn(NO3)2·6H2O, and Cu(NO3) (Analytical reagent, Sinopharm, China) as a source of pollutant. Ird, based on the mixture proportion shown, the heavy metal solutions were prepared artificially by adding Pb(NO3), Zn(NO3)2·6H2O, and Cu(NO3) (Analytical reagent, Sinopharm, China). On the basis of Tang et al (2017)’s research, the cement-fly ash mixtures were demoulded and placed in a carbonation testing apparatus containing CO2 gas concentration of 20 ± 3%, relative humidity of 70 ± 2%, and temperature of 20 ± 2°C for 7, 14, and 28 days, which in accordance with the experimental scheme in this study [34]. E pavement structure comprised various layers including 18 cm asphalt layer, 40 cm cement treated base layer, and 242 cm cementsolidified contaminated soil layer. Bulk density (kN/m3) Elasticity modulus (MPa) Cohesive force (kPa) Internal friction angle (°) Poisson’s ration
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