This Recycled Concrete Structural Backfill technical note addresses structural competency.

This Tech Sheet provides guidance for the acceptability of recycled crushed concrete and limestone as competent structural foundation (bedding) and embedment materials for StormTech chambers. It is possible that some materials that are found to be competent may contribute to occlusion of separation fabrics or blocking of infiltration / exfiltration surfaces such as the case of Tufa precipitate from unhydrated cement. It may also be appropriate to consider other criteria such as chemical content, alkalinity and potential toxicity. The project engineer may choose to establish additional criteria that may be appropriate for the application.

The following are specifications that StormTech recommends for the acceptance of reclaimed crushed concrete based on criteria for structural integrity: The gradation shall meet AASHTO M43 gradations as listed in the “Acceptable Fill Materials Table” in the StormTech Design Manual. The material shall meet ASTM D2488 angular or subangular classification. Deleterious materials shall be limited to: a) maximum 20% reclaimed pavement materials and b)maximum 0.15% building materials. For material hardness – Maximum loss of 40% in the LA Abrasion test (AASHTO T96). Freeze-Thaw Resistance – Maximum 12% loss after 5 cycles in magnesium sulfate solution (AASHTO T104).

The design shall be in accordance with the StormTech Design Manual and Installation shall be in accordance with the StormTech Installation Instructions.

The structural integrity of buried flexible structures is dependent upon both the strength of the flexible structure and the strength of the surrounding soils. The StormTech Design Manual provides a list of “Acceptable Fill Materials” that have been found to provide proper structural support for StormTech chambers. A cross section of the StormTech Chamber system surrounded by foundation and embedment stone is provided.