Introduction

Structural fill is typically a screened earthen material used to create a strong, stable base. For example, the native soil at a site may be too weak to support a structure, so the native soil is replaced by compacted structural fill to provide the needed bearing capacity. Another common application is the filling of trenches and other excavations that will support roadways or other structures when completed. Structural fills are constructed by compacting earthen materials in place, so the compaction properties (optimum water content and maximum dry density) of the material are very important to the performance. The compressibility and shear strength are also important measures of the compacted material. Traditionally, fill materials have been composed of soil and natural aggregates. However, a number of IRC byproduct materials have been used successfully as high quality, cost effective substitutes for natural materials in this application.

 

Working materials will also apply to foundry sands, which means no special equipment is required. Similarly, the use of coal fly ash in embankments and fills is actually the second highest use of this material, with more than 7 million tons placed in 2006. The ash behaves like a fine sand or silt material but has a lower density.  Structural fills and embankments are also the highest use application of coal bottom ash, which is coarser than the fly ash and behaves more like sand. Air cooled and expanded blast furnace slags have been used in several large volume projects. Steel slags have been used in fill applications where expansion is not an issue.  Exposure to moisture may lead to chemical reactions, so care should be used when considering using steel slags under pavements or foundations where expansion may lead to poor performance. Tire shreds provide an excellent low density fill material, typically one-third the weight of Air cooled and expanded blast furnace slags have been used in several large volume projects. Steel slags have been used in fill applications where expansion is not an issue.  Exposure to moisture may lead to chemical reactions, so care should be used when considering using steel slags under pavements or foundations where expansion may lead to poor performance.

Benefits

The use of IRC materials in high volume applications like structural fills reduces the need for mining virgin aggregate and the associated use of water and fuel, reduces carbon dioxide emissions, and saves valuable landfill space.  At the same time, the use of these materials is as good or better than virgin materials, which provides added value to the project because of reduced costs.