2520Lean Mix Backfill

2520.1DESCRIPTION

This Work consists of placing a lean cementitious, controlled-density backfill into utility and Culvert trenches, or other excavations, where the use of conventional compacting E quipment is impractical.

2520.2MATERIALS

The Department will provide mix proportions for lean mix backfill in accordance with 2461, “Structural Concrete.” Submit mix designs in accordance with 2461.2E.2, “Concrete Mix Design Requirements.”

2520.3CONSTRUCTION REQUIREMENTS

A Job Mix Proportioning After adding the specified quantities of cement, fly ash, and water, provide the remaining volume consisting of fine Aggregate and coarse Aggregate. The Contractor may use admixtures in accordance with 2461.2D, “Concrete Admixtures.” Adjust the mix at any time to maintain the consistency and strengths specified in Table 2461.2-5. The Engineer will base final approval for payment on satisfactory field placement and performance. B Batching and Mixing Requirements Provide ready-mixed lean mix backfill in accordance with 2461, “Structural Concrete,” except replace the word “concrete” with “lean mix.” C Lean Mix Backfill Placement Plug openings below the level of the desired backfill that would allow the mix to escape . Place the lean mix so that it flows around and beneath footings, foundations, walls, pipes, or otherS tructures that it was designed to support. The Department will not require compaction or mechanical vibration

when lean mix backfill is placed as approved by the Engineer. Vent or eliminate air pockets that water would normally fill to preclude voids remaining in the completed backfill. D Curing and Protection Maintain the air in contact with lean mix backfill surfaces at temperatures above freezing for at least 72 hours. The Department will not require additional curing after the evaporation of the substantial water gain on the surface.

2520.4METHOD OF MEASUREMENT

If the Contract specifies Lean mix backfill as a Contract Item, the Engineer will measure Lean mix backfill as the computed, theoretical volume based on the weight of the individual batch ingredients . The Engineer will deduct the volume of accountable waste from the measurement of L ean mix backfill.

2520.5BASIS OF PAYMENT

The Department will include the cost of Lean mix backfill and common backfill with other relevant Contract Items unless otherwise shown on the Plans. The Contract cubic yard price for Lean mix backfill includes the cost of providing the Lean mix backfill and the cost of forming, plugging, placing, venting, and protecting. The Department will pay for Lean mix backfill on the basis of the following schedule: Item No. Item Unit

2520.507 Lean Mix Backfill cubic yard