Feasibility of Stabilized Zn and Pb Contaminated Soils as Roadway Subgrade Materials

Mingli Wei,Yuan Li,Shiji Zhou,Hao Ni,Gianfranco Carotenuto

doi:10.1155/2020/1025056

Abstract

The authors have developed a new binder, KMP, which is made from oxalic acid-activated phosphate rock, monopotassium phosphate (KH2PO4), and reactive magnesia (MgO). This study explores the acid neutralization capacity, strength characteristics, water-soaking durability, resilient modulus, and pore size distribution of KMP stabilized soils with individual Zn, Pb, or coexisting Zn and Pb contaminants. For comparison purpose, Portland cement (PC) is also tested. The results show that KMP stabilized soils have a higher acid buffering capacity than PC stabilized soils, regardless of the soil contamination conditions. The water stability coefficient and resilient modulus of the KMP stabilized soils are found to be higher than PC stabilized soils. The reasons for the differences in these properties between KMP and PC stabilized soils are interpreted based on the stability and dissolubility of the main hydration products of the KMP and PC stabilized soils, the soil pore distribution, and concentration of Mg or Ca leached from the KMP and PC stabilized soils obtained from the acid neutralization capacity tests. Overall, this study demonstrates that the KMP is effective in stabilizing soils that are contaminated with Zn or Pb alone and mixed Zn and Pb contaminants, and the KMP stabilized soils are better suited as roadway subgrade material.

Highlights

Large quantities of abandoned industrial sites, which may be contaminated by high concentrations of heavy metals, have been produced, caused by the rapid industrialization and urbanization in China for the last several decades [1]
The cement hydration products such as Ca(OH)2, CSH, and CAH have a relatively higher solubility and are more easy to dissolve under acidic condition [4, 29], and (2) Zn or Pb merely consumes a small amount of PO43− and hydroxyl ions (OH-), which results in a marginal impact on the formation of MgKPO4·6H2O and Mg3(PO4)2·8H2O in the KMP stabilized soils [3]
E water-soaking durability test and resilient modulus test results show that KMP stabilized contaminated soils possess higher qu′, Kr, and MR relative to the Portland cement (PC) stabilized contaminated soils, regardless of the initial soil contamination condition (Figures 4, 5, and 7). e phenomenon can be attributed to three causes: (1) the KMP stabilized dV/dlgD

Summary

Introduction

Large quantities of abandoned industrial sites, which may be contaminated by high concentrations of heavy metals, have been produced, caused by the rapid industrialization and urbanization in China for the last several decades [1]. The strength and modulus of cement stabilized soils decreased rapidly as Zn concentrations increased [5] For heavy metals such as Zn and Pb, a tremendous retardant effect on cement hydration has been proved to exist. Du et al [4] reported that the presence of Pb and Zn in the cement stabilized soils hinders the formation of Ca(OH)2/ CSH and thereby decreases the soil buffering capacity. In this case, the higher the concentration, the more intensive the retardant effect of heavy metals [4, 5]. The higher the concentration, the more intensive the retardant effect of heavy metals [4, 5]. erefore, it is necessary to develop alternative binders to stabilize soils that have relatively

Methods

Results

Conclusion