Category:621 Flowable Backfill

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To backfill is to refill an excavated area, often with the same soil as was originally removed. Soil characteristics such as shrinkage and swell factors (The ratio of the quantity of excavated material to the quantity of embankment that can be constructed from the same material) are important in typical backfill situations. Flowable backfill is used when ordinary soil compaction is not practical.

621.1 Construction Inspection Guidelines for Sec 621

Description (for Sec 621.1)

This item of work is used to backfill structures in locations where ordinary compaction methods are not practical. When correctly placed it is very stable and does not settle over time.

Consistency (for Sec 621.3.1)

The test method in the Standard Specifications should be used as a guideline. The intent of the specification is to attain a consistency that will flow freely but that will also hold the solids in suspension during placement.

Construction Requirements (for Sec 621.4)

Vibrators should not be used on flowable backfill because they will cause the solids to settle out. The mix proportions should be adjusted to produce a consistency that will flow freely. Care should be taken to plug all outlets including any drainage structures.

621.2 Material Inspection for Sec 621

This article establishes procedures for inspecting and acceptance of flowable backfill materials.

621.2.1 Procedure

The individual components to be used in flowable backfill as specified in Sec 621 are to be inspected and accepted in accordance with the applicable sections of the Engineering Policy Guide.

Approved commercial brand mixtures may be used in lieu of the mixture specified in the specifications. When approved commercial brand mixtures are used, the components specified to be specification materials shall be inspected and accepted in accordance with the Engineering Policy Guide. That normally includes all aggregates and cementitious materials. Commercial additives as approved for foaming do not require reporting, as that is implied in the commercial brand approval.

621.2.2 Commercial Brand Mixtures

Brand Name Approval. To obtain approval of a commercial brand mixture, the manufacturer shall submit to Construction and Materials a request accompanied with appropriate documents.

Documentation shall include a product data sheet, material safety data sheet and a certification showing the name of the manufacturer, name of product and specific test data showing compliance with the requirements of the specifications. The material batch proportions per unit volume and 28-day compressive strength shall be shown. Mixtures with a unit weight (mass) less than that of water will not normally be approved unless the project is specifically designed for its use.

Upon approval of the commercial mixture, the brand will be placed on a list of qualified commercial flowable backfill mixtures. The commercial mixtures are shown in Qualified Flowable Backfill Mixtures.

621.2.3 Report (Records)

Flowable backfill is to be reported using AASHTOWARE Project (AWP). The report shall show a Status of Accepted/Complete or Rejected/Fail. Appropriate remarks, as described in EPG 106.20 Reporting, are to be included in the report to clarify conditions of acceptance or rejection.

The individual components specified to comply with the specifications are to be reported through AWP in accordance with the applicable Engineering Policy Guide sections.