Alternatives to Traditional Backfill

Association of Construction and Development
December 28, 2012 — 1,778 views  

There are many alternatives to traditional backfill that engineers and construction professionals should become familiar with. With green alternatives being a main focus of many environmentally conscious clients, alternative backfill materials like CSLM, recycled aggregates, and reclaimed backfill are options that should be employed by construction professionals and engineers. There can be some potential issues when using these materials, however, careful planning by a qualified professional can result in the proper implementation.

Controlled low-strength material, or CLSM, is a composite of fly ash, cement, water, and sand. Since fly ash is the waste product of burning coal for energy, the CLSM is a type of recycled material. Some considerations when using CSLM is the chemical composition and high pH. Both parameters can vary due to differences in the sources of the fly ash.

One of the most cost effective solutions using green materials is recycled aggregate. The recycled aggregate is composed of crushed up chunks of asphalt and concrete. If the construction site is located on a previous structure or paved lot, this may be one of the least expensive backfill materials available. There are two way of obtaining the recycled aggregate. The first is to haul, or contract a company to haul, the asphalt and concrete from the construction site to a plant which can process the large pieces into smaller usable pieces. The second is to use a machine on-site to crush the concrete or asphalt waste into aggregate. The second option is typically only feasible if there is a large amount of debris to process. Another consideration when selecting either option is space. If the site is small, the second option may not be feasible. The benefit to using the recycled aggregate is that it can usually be processed into the required size. The application of recycled aggregate is typically as road base.

Reclaimed backfill is the byproduct of processing. One type is slag which is the left-over rock from blasting activities. Another is bottom ash which is the remains at the bottom of a boiler that have been collected to be reused as backfill. The particle sizes of both types are generally acceptable for most construction however some consideration should be paid to the chemical composition of the debris. Some chemicals, especially sulfates, may have deleterious effects when placed near metals. However, an added bonus of using these materials is that they typically exceed standards on hardness tests.


Association of Construction and Development