Drainage Characteristics of Recycled Materials for Mechanically Stabilized Earth Walls
With the expansion of transport, commercial, and residential infrastructure to support the needs of a growing populous, greater amounts of construction materials are required. These aspects place increased amounts of stress on natural resources. While this demand for aggregate material continues to increase, construction and demolition waste generated from industrial operations and construction activities, such as crushed concrete from demolition, continue to increase as well. Much of the waste produced is either concrete demolition or asphalt concrete demolition, representing a large potential source of aggregate for infrastructure projects such as MSE walls. Although showing solid strength and stiffness properties, utilization of recycled concrete and asphalt aggregate is limited due to drainage complications and corrosive leachate. The objective of this study was to evaluate the drainage capability of concrete and asphalt aggregates, evaluate clogging potential associated with each aggregate, and to evaluate the corrosivity of the leachate produced from each aggregate. Laboratory experiments utilized to complete these objectives include particle breakage evaluation, rigid and flexible wall saturated column testing, calcareous tufa precipitation via a seepage cell, ionic concentration evaluation, scanning electron microscope spectroscopy, geotextile permittivity testing, pH testing of aggregate slurries, and electrical resistivity testing. Computer modeling was utilized as well with the support of laboratory data. Numerical variable saturated flow models were developed to understand the drainage capabilities of the recycled aggregates to a greater degree using simple MSE wall geometry. Geochemical block modeling was utilized to understand the saturation of calcite in the leachate solution and to model the maximum precipitation potential of the leachate. Results of the testing help to provide additional information regarding the drainage capabilities of recycled materials as well as the corrosivity of the leachate produced. From particle breakage testing, it was found that recycled aggregate broke more easily compared to dolomitic virgin aggregate counterparts. However, this difference is small (1.5 %) and may be irrelevant depending on material. Column testing and variable saturated flow modeling showed recycled concrete aggregates classified as fair to very poor draining materials at tested gradations. Cleaner recycled asphalt aggregates were found to be excellent to good draining materials, highlighting the importance of minimizing fines and fine sand to ensure capable drainage performance. Tufa precipitation testing and modeling showed that leachate from concrete aggregate possesses high potential for tufa precipitation over extended periods and multiple drainage cycles. However, blending of concrete and granite aggregate assists in lowering this potential. Furthermore, permittivity testing of geotextiles show that tufa possesses as more of a clogging problem over mechanical blockage over an infrastructure’s lifetime. Corrosivity testing showed that concrete aggregate struggled to meet both pH and electrical resistivity standards per WisDOT. Asphalt aggregate was better able to meet these standards. However, with the combination of concrete carbonation and aggregated blending, concrete aggregate was able to meet corrosivity standards as defined by WisDOT.