213FLOWABLE BACKFILL

213.01Description

This work shall consist of placing flowable backfill in trenches for pipe structures, culverts, utility cuts, other work extending under pavement locations, cavities beneath slopewalls and other locations in accordance with 105.03.

Flowable backfill will be classified as either removable or non-removable. Wherever Type 5, non-removable flowable backfill is specified, Type 4, flowable removable backfill may be used as a substitution, following notification to the 10 Engineer.

MATERIALS

213.02Materials

Materials shall be in acco rdance with the following:

Concrete Admixtures* ................................................. 912.03 Fine Aggregate ............................................................ 904.02(a) Fly Ash ........................................................................ 901.02 20 Portland Ceme nt .......................................................... 901.01(b) Water ........................................................................... 913.01

* Other admixtures that increase flowability may be used as approved by the Engineer. 213.02

The supplier may elect to use nominal size No. 23 and No. 24 gradations in accordance with 904.02(h) or may propos e the use of alternate gradations. The alternate gradation and proposed tolerances of material passing each sieve shall be included in the flowable backfill mix design.

213.03Flowable Backfill Mix Design

The Contractor may either design their own flowable backfill mix or may choose to use one of the four standard mix designs shown in 213.03(a).

If the flowable backfill is being placed around a pipe, the mix shall contain a minimum of 150 lb/cu yd of fly ash.

The following two Type 4, removable flowable backfill mixes and two Type 5, non-removable flowable backfill mixes may be used. The final mix results may vary 40 due to variations in cement and other mate rials. The Contractor shall be responsible for the performance of the flowable backfill and the mix shall meet the mix criteria in accordance with 213.04, and the minimum spread and blow counts in accordance with

213.07. The mix design shall be submitted to the DTE a minimum of seven days prior

to use and shall include the following:

Removable Non-Removable Component Type 4-1 Type 4-2 Type 5-1 Type 5-2 Cement Content, lb/cu yd 50 50 85 100 Fly Ash, lb/cu yd 0 150 0 150 Fine Aggregate, lb/cu yd 2,900 2,125 2,870 2,085 Water, lb/cu yd 500 400 500 400 Entrained Air, % 0 - 10 15 - 35 0 - 10 15 - 35

The Contractor shall submit a flowable backfill mix design, FBMD, to the DTE a minimum of seven days prior to the trial batch. The FBMD will be accepted in accordance with 213.04. The FBMD shall be submitted in a format acceptable to the DTE and shall include the following:

213.03

An FBMD in accordance with this section, which has been accepted for use on a previous contract, may be submitted to the DTE for consideration for use on the current contract. The submittal shall include copies of test results in accordance with 213.04 and 213.05. 70

Changes in the FBMD will not be allowed except for adjustments to compensate for routine moisture fluctuations or a change in sand source in accordance with 213.05 based on the dry flow determined from the trial batch testing. All other changes will require a new FBMD.

213.04Flowable Backfill Mix Criteria

The FBMD shall produce a workable mixture with the following properties:

Flow consistency will be measured in accordance with ASTM D6103. The diameter of the spread shall be at least 8 in.

A lightweight dynamic cone penetration test will be performed in accordance with ITM 216 after the flowable backfill mix has cured for three days. The average penetration resistance blow count number for removable flowable backfill shall not be less than 12 or greater than 30. Non-removable flowable backfill mixes shall have an average penetration resistance blow count greater than 30.

The removability modulus, RM, will be determined for the FBMD by the formula as follows:

RM = 0.000104 (U w)1.5 ඥ1.72N14 - 15.64

where:

N 14 = average lightweight dynamic cone penetration blow count after 14 days in accordance with ITM 216. 100

U w = dry unit weight, lb/cu ft, of flowable backfill after 14 days in accordance with ITM 218.

The RM shall be 1.0 or less for removable flowable backfill.

213.04

After all test results have been reviewed for compliance with the specifications, a mixture number will be assigned by the DTE.

213.05Flowable Backfill Trial Batch 110

If one of the four standard flowable backfill mix designs in 213.03(a) is used, a trial batch will not be required. The Contractor may still choose to perform a trial batch in accordance with 213.05(b), if desired.

A trial batch shall be produced by the Contractor and will be tested by the Department to verify that the FBMD meets the flowable backfill mix criteria. The Department will verify the classification of the mix as either removable or 120 non-removable from the results of the tria l batch. The flowable backfill shall be batched within the proportioning tolerances of 508.02(b). The Department will determine the test results and provide them to the Contractor. The trial batch shall be of sufficient quantity to allow the Department to perform all required tests from the same batch.

The Department will obtain a sample of the fine aggregate and fly ash described in the FBMD. The Department will test the dry flow in accordance with ITM 217 and record the results on the FBMD.

If the Contractor requests to change the source of the fine aggregate identified in a previously accepted FBMD the Contractor shall submit a revised FBMD to the DTE. The Department will obtain a sample of the new fine aggregate and, if applicable, a sample of the fly ash as identified in the previously accepted FBMD. Dry flow will be tested in accordance with IT M 217. If the test result is within ± 2.0 s of the value shown on the previously accepted FBMD, the revised FBMD will be accepted and a new trial batch will not be required. Failure to meet the dry flow test requirement will require the Contractor to submit a new FBMD and perform a new trial batch using the proposed new fine aggregate.

213.06Mixing Equipment

The mixing equipment shall be in accordance with the applicable requirements of 702 or 722.

CONSTRUCTION REQUIREMENTS

Placement

The flowable backfill shall not be placed on frozen ground. Flowable backfill shall be protected from freezing for 72 hr. Flowable backfill shall not be placed into or through standing water unless approved by the Engineer in writing. 150

The diameter of the flowable backfill spread shall be at least 8 in. at time of 213.05

placement. Water may be adjusted from the FBMD to meet the minimum spread requirement if the initial measured spread is between 7 and 8 in.

If using mixing equipment in accordance wi th 722, the yield will be checked using the 1/4 cu yd box method as follows:

surface to receive the discharged flowable backfill. 160

indicates that 1/4 cu yd of flowable backfill has been yielded.

box is not full, the gates shall be adjusted and the procedure shall be repeated until the actual and calculated volumes of flowable backfill agree.

load per truck thereafter. Additional yield tests will be required after making any adjustments.

The flowable backfill shall be brought up uniformly to the fill line as shown on the plans or as directed. When used as structure backfill, flowable backfill shall be placed uniformly so as not to induce unbalanced loading on any part of a structure.

The flowable backfill shall not be subjected to load or disturbed by construction activities until a lightweight dynamic cone penetration test has produced a minimum blow count. The minimum blow count shall be as follows: 180

213.08Method of Measurement

Flowable backfill will be measured by the cubic yard of the type specified as computed from the neat line limits shown on the plans. If neat line limits are not shown on the plans, the volume in cubic yards of flowable backfill furnished and placed will be computed from the nominal volume of each batch and a count of the batches. Unused and wasted flowable backfill will be estimated and deducted. Drilled holes 190 will be measured by the number of holes drilled.

If removable flowable backfill is approved for use in lieu of non-removable flowable backfill, it will be measured by the cubic yard as non-removable flowable backfill.

213.09Basis of Payment

The accepted quantities of flowable backfill will be paid for at the contract unit 213.09

price per cubic yard for the type specified, furnished and placed. Holes drilled in the pavement will be paid for at the contract unit price per each. 200

If removable flowable backfill is approved for use in lieu of non-removable flowable backfill shown on the plans, it will be paid for as non-removable flowable backfill. Substitutions by the Contractor shall be at no additional cost to the Department.

Payment will be made under:

Pay Item Pay Unit Symbol

Drilled Hole for Flowable Backfill ............................................ EACH Flowable Backfill, Non-Removable .......................................... CYS Flowable Backfill, Removable .................................................. CYS