613.01  Description

613.02  Materials

613.03  Mix Proportioning

613.04  Mix Adjustment

613.05  Alternate Mixes

613.06  Mixing Equipment

613.07  Mixing the Materials

613.08  Placing Mortar

613.09  Method of Measurement

613.10  Basis of Payment


613.01  Description.  This work consists of placing a low strength mortar backfill around conduits and at other locations.  Perform the work for this item according to Items 603 and 499, except as modified below.

613.02  Materials.  Furnish materials conforming to:

Cement.................................................... 701.01 or 701.04

Fly Ash.................................................................... 701.13


Furnish fine aggregate consisting of foundry sand, natural sand, sand manufactured from stone, gravel, or air-cooled blast furnace slag.  Conform to the fine aggregate gradation requirements of 703.05.  Use fine aggregate that is fine enough to stay in suspension in the mixture to ensure proper flow.

Furnish an air-entraining admixture that is designed for use in low strength mortar mixtures (also called controlled density fill or flowable fill).

613.03  Mix Proportioning.  Furnish a low strength mortar mixture listed below or provide an alternate mix conforming to 613.05.


Type 1[1]

Type 2

Type 3














Fly Ash, Class F







Fly Ash, Class C[4]







Fine Aggregate [3]







Water (Target)







[1]  The Contractor may add an air-entraining agent specifically designed for the use in the low strength mortar mixture.

[2]  Entrained air is substituted for fly ash in this mix. (Approximately 25 percent)

[3]  Saturated Surface Dry

[4]  Class C Fly Ash may be substituted for Class F Fly ash in Type 1 mixes with an approved mix design meeting the alternate mix design criteria of this specification.


These mixtures of materials are expected to yield approximately 1 cubic yard (1 m3) of material of a flowable consistency.  Make small adjustments, as necessary, in the amounts of the materials in a mix to achieve the final product.

613.04  Mix Adjustment.  Make one or more 1 cubic yard (1 m3) trial batches at different water contents to ensure a flowable material.  The mixture is too dry if cracks develop in the mixture as it flows into place.

Adjust the proportions to maintain the total absolute volume.  For large adjustments, see 613.05.

In order to expedite the settlement of a Type 1 mixture without entrained air, bleed water may appear on the surface immediately after the material is struck off.  A delay in bleeding indicates there are too many fines in the mixture.  The Contractor may reduce the fly ash quantity in increments of 50 pounds (30 kg) until the mixture is bleeding freely.  Add approximately 60 pounds (36 kg) of sand to replace each 50 pounds (30 kg) increment of fly ash to maintain the original yield.

613.05  Alternate Mixes.  The Contractor may submit alternate mixes for approval.  Furnish the mix design and test data from an independent test laboratory 30 days before the intended usage for approval.

Submit an alternate mix design for all mixes that:

A.      Vary more than 300 pounds (178 kg) in fine aggregate, 100 pounds (59 kg) in water, 20 pounds (12 kg) in cement, or 200 pounds (119 kg) in fly ash from the 613.03 mixes.  These are considered large adjustments.

B.      Have less than 50 pounds (30 kg) of cement in the Type 1 mixes or less than 100 pounds (59 kg) of cement in the Type 2 mixes.

C.      Use alternate materials.

D.      Contain foundry sand.

E.      Contain fly ash not conforming to 701.13.

F.      Use fine aggregate gradations other than 703.05.

The Contractor may use foundry sand if it meets the requirements of the Division of Surface Water Policy 400.007 “Beneficial Use of Non-Toxic Bottom Ash, Fly Ash and Spent Foundry Sand and Other Exempt Wastes,” and all other regulations.  Ten days before using a mixture containing foundry sand on the project, submit written permission from the Ohio EPA to the Engineer.  The Contractor may elect to have an independent ODOT consultant pre-qualified in remedial design environmental site assessment review the proposed usage.  The consultant will provide all documentation utilized to ensure that the proposed usage obeys all Ohio EPA regulations.  The consultant shall coordinate all EPA required meetings, documentation, and testing requirements.  The consultant shall certify the report or reports to the Department.

Provide alternate mixes with an unconfined compressive strength between 50 and 100 pounds per square inch (345 and 689 kPa) at 28 days when tested according to ASTM D 4832.  Ensure that the long term (12-month) unconfined compressive strength is less than 100 pounds per square inch (689 kPa).

Ensure that the final mix has the required strength, fills the voids of the intended usages and sets up within 12 hours (4 hours for Type 3 or Type 3 alternate mixes).  The proportioning, yield, consistency, workability, compressive strength, and all other requirements are the sole responsibility of the Contractor.

613.06  Mixing Equipment.  Provide the mixing capacity and delivery equipment to place the material without interruption as much as practical.  Deliver and place Type 1 and 2 mixes or Type 1 and 2 alternate mixes from ready mixed concrete trucks, or deliver them from a batch plant.

Deliver and place Type 3 mix using volumetric mobile mixers.  Calibrate volumetric mixers properly and sufficiently mix the materials in the mixer to produce a uniform material.

613.07  Mixing the Materials.  Discharge the mixture within 2.5 hours after adding water.

613.08  Placing Mortar.  Unless specifically shown on the plans, do not place the mortar within 3 (1 m) feet of the subgrade elevation.  Discharge the flowable material from the mixer by any reasonable means into the space of the plan intended usage.  Bring the fill material up uniformly to the fill line shown on the plans.  The Contractor may begin placing the other fill material over low strength mortar backfill material as soon as the surface water is gone.  The Engineer reserves the right to reject the mix if a flowable mixture is not produced.

Before placing the low strength mortar backfill as backfill for 603 Conduit, secure the conduit to prevent it from floating during placement of the flowable material.

613.09  Method of Measurement.  The Department will measure Low Strength Mortar Backfill by the number of cubic yards (cubic meters) completed and accepted in place, computed from the plan lines.  The Department will not pay additional compensation for over excavated areas or for a change in the material blends.

613.10  Basis of Payment.  The Department will pay for accepted quantities at the contract prices as follows:

Item           Unit                                Description

613             Cubic Yard                      Low Strength Mortar Backfill
                       (Cubic Meter)

613             Cubic Yard                      Low Strength Mortar Backfill
                       (Cubic Meter)                  (Type ___)