Recycled Concrete MSE Wall-ERS

A Mechanically Stabilized Earth (MSE) wall is a vertical or near vertical earth retaining structure consisting of three major components: a facing panel, earth reinforcement, and reinforced select backfill. Backfill materials behind MSE walls must fulfill several engineering functions. They are required: (i) to have adequate shear strength to ensure stability within the backfill and interaction with the reinforcement (pullout resistance), (ii) to provide free drainage to reduce hydrostatic pore water pressure, (iii) to have adequate compaction characteristics to ensure minimal compressibility, (iv) to have satisfactory long-term (creep) characteristics to minimize excessive deformations, and (v) to be minimally corrosive to ensure the long-term integrity of reinforcement materials. For these reasons, coarse-grained soils are generally favored for MSE construction because they can provide free drainage (when the amount of fines is small), have greater friction angles than fine-grained soils, and tend to yield smaller deformations when correctly compacted. This limitation on material type, however, can significantly increase the cost of construction on some projects because of the cost of transporting select material to the construction site when local select fill is not available. In most cases, the cost of select backfill material dominates the total cost of MSE wall construction.

At the same time, industrial operations and construction activities create granular materials that must be disposed.  Producers of such materials must pay transportation costs, as well as disposal fees, to discard these materials. One solution is to recycle these materials and use them as alternative reinforced backfill. Throughout the U.S., substantial amounts of recycled asphalt pavement (RAP) and recycled concrete aggregate (RCA) are being produced through reconstruction activities. Granular industrial byproducts such as foundry sand/slag, bottom ash, and iron/steel slag are also produced in large quantities. If these materials were used as reinforced backfill for MSE walls, transportation and disposal costs associated with construction could be greatly reduced, translating into significant savings for state departments of transportation. Furthermore, such activities would promote sustainable construction, preserve natural resources, and reduce the carbon footprint and need for landfill disposal in highway construction.

This research project is a joint effort between Dr. William Likos from University of Wisconsin, Dr. Ahmet Aydilek from University of Maryland, and Dr. Burak Tanyu from George Mason University, where the researchers are evaluating the suitability of predominantly RCA and RAP to be considered as a backfill for MSE walls. In Phase 2 of this research project, the team will work on constructing a full scale MSE wall in laboratory condition to evaluate properties associated with constructability, drainage, and long-term performance with one of the recycled material selected from the on-going project.

For related publications see: Soleimanbeigi et al. (2019)