Study of the Hydraulic Behavior of Steel Slag and CDW Recycled Aggregates to MSW Landfill Leachate

Abstract

Laboratório Nacional de Engenharia Civil (National Laboratory for Civil Engineering), in partnership with Faculdade de Ciencias e Tecnologia da Universidade Nova de Lisboa (Faculty of Sciences and Technology, NOVA University of Lisbon), have studied the technical feasibility of applying two recycled aggregates, one processed from electrical arc furnace steel slag and the other from concrete of construction and demolition waste (CDW), in the construction of the leachate collection and removal layer (LCRL) of municipal solid waste (MSW) landfills. In the paper is presented and discussed the hydraulic behaviour of these materials based on results obtained in permeability tests carried out on specimens prepared from grain-size in the ranges 0.25-2.0mm and 2.0-20.0mm, given that, in Portugal, the LCRL is composed by an upper layer of 0.2m thickness constructed with particles in the range of sand and a lower layer of 0.3m thickness constructed with particles in the range of fine gravel. Aiming to test their hydraulic behaviour to more aggressive conditions than those observed in MSW landfills, the leachate used in permeability tests, which was collected at a Portuguese MSW landfill, was acidified with hydrochloric acid to decrease the initial pH from 8.2 to 5.5. As a reference for the results obtained with the recycled materials in contact with the leachate, the same permeability tests were performed with tap water. In general, the hydraulic conductivity of tested materials was higher than the minimum (1x10-4m/s) required by Portuguese decree-law in force. Therefore, the results obtained suggest the possibility of applying both recycled aggregates in the construction of the LCRL of landfills.