Review of Standards for Lightweight Aggregate Application as Backfill Material

Lightweight aggregates such as expanded shale, clay, and slate have proven to meet design criteria for backfill applications.  The low density of these aggregates significantly reduces the earth pressures behind bridge abutments and other retaining structures.  In addition, the lower density reduces the transportation cost, and thus, the overall cost of the project.  Further, the high permeability of the aggregate allows for proper drainage in the backfill and internal curing when mixed in concrete.  Moreover, manufactured and recycled lightweight aggregates have lower environmental impacts in comparison with conventional aggregates and their cementitious products.  Despite these advantages, current standards generally address backfill applications using weight-based methods, which is only appropriate for most conventional normal-weight aggregates. Therefore, the low density of lightweight aggregates is an obstacle in the implementation of these standards.  Public and private entities are thus reluctant to use these alternative materials, unless they can afford to develop special specifications.  Modification of weight-based standards and implementing volume-based procedures will allow various stakeholders to incorporate lightweight aggregates in projects. The aim of this research is to gather information on current standards and specifications within local, state, federal, and international jurisdictions.  Further, this project will develop and illustrate a methodology for testing materials using a volume-based approach in comparison to a weight-based approach.  The literature study also covers current in-progress efforts by entities such as ASTM, DOT, and Eurocode, towards the development of new standards for lightweight aggregates.