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Laboratory Study of Feasibility of Stabilizing Zinc Clinker and Road Millings To Produce Low-Permeability Pavement Material

An international mining company has funded research to develop a lowpermeability pavement material by stabilizing on-site waste materials (zinc clinker and road millings) at a zinc processing plant in the mid-western United States. The need for development of this material has arisen from concerns of the state environmental protection agency (EPA) that rain is leaching zinc from stockpiles of clinker, thereby contaminating the surface soils, drainage ditches, and groundwater on the site. The desired engineering properties of the stabilized material are as follows: (a) the material must have sufficiently low permeability to act as an “impermeable” liner, (b) the material must bind the zinc to the clinker so that it does not leach out, and (c) the material must be stiff and strong enough to serve as a pavement base course and wearing surface. Laboratory tests were conducted with various stabilized combinations of asphaltic road millings, zinc clinker, and local clay from a zinc processing plant in the midwestern United States to determine whether a lowpermeability pavement material could be produced. Two methods of stabilization were studied: (a) one with portland cement and (b) one with a combination of three cold-mix additives (a binder, a stabilizer, and a sealant). The primary types of laboratory tests conducted were unconfined compression tests with cement-stabilized materials, Marshall stability tests with cold-mix-stabilized materials, and leachate-permeability tests with both types of stabilized materials. A design mixture was produced by the addition to the waste materials of the three proprietary coldmix additives (a binder, a stabilizer, and a sealant) and a local clay that meets all three requirements in tests with laboratory-prepared specimens. Field tests are needed to verify that these attributes can be produced by full-scale construction techniques. In addition, laboratory and field tests are needed to determine the durabilities of these stability materials for the repetitive traffic loads and environmental conditions to which pavement systems are subjected.