220FLOWABLE BACKFILL

220.1DESCRIPTION—This work is furnishing, transporting, and placing flowable backfill. Flowable backfill

may be a mixture of coarse aggregate, fine aggregate, water , and air entraining agents, either cement or supplementary cementitious material, or a combination of both, and may or may not include bottom ash, or other admixtures. The three types of flowable backfill are as follows:

trenches, pipe trenches, bridge abutments, and around box or arch culverts.

soils below structure foundations, filling abandoned conduits, tunnels and mines, and backfilling around pipe culverts where extra strength is required.

abutments over highly deformable soils, backfilling retaining walls, filling vaults, and backfilling on top of buried structures.

220.2MATERIAL—

design as necessary. If using Type IS cement, adjust the quantity of slag cement in the design as necessary. From a source listed in Bulletin 15.

• Flyash. conforming to AASHTO M 295 (or ASTM C618) Table 1 requirements except maximum loss on ignition is 16%, and excluding the requirements of Table 1A, 2, or 2A.

From a source listed in Bulletin 15 or tested and approved before incorporating into the flowable backfill mix.

Soundness Test, PTM No. 510. The fine aggregate may be natural sand, manufactured sand, or foundry sand meeting Section 703.1. From a source listed in Bulletin 14.

finer than the No. 200 sieve. From a source listed in Bulletin 14.

Soundness Test, PTM No. 510, and conforming to the following dry sieve gradation requirements:

Sieve Size % Passing 1/2-inch 100 No. 200 0-10

backfill.

the Representative, at least 3 weeks before construction. Alkali-Silica remediation is not required regardless of the expansion value of the aggregates used in the mix design. Use Table A as a guideline for the mix design or submit an alternate design based on density guidelines and conforming to the strength requirements of Table A. Base the submitted mix design on an absolute volume of 1 cubic yard.

TABLE A Mix Design Properties & Criteria Type B Type C Type D Mix Design ( /CY) Cement (lbs)* Supplementary Cementitious Material (lbs)* Bottom ash (lbs)* or Coarse Aggregate or Fine Aggregate Air Generating Admixture*

** Slump (inches) AASHTO T 119, ASTM C136 7 min **** 7 min **** 7 min **** Density (pcf) AASHTO T 121, ASTM C136

N/A

N/A 30-70 or as specified *** Water Absorption of Aggregate AASHTO T 85 -- -- 20% max Compressive Strength (psi) PTM No. 604 28 Days

125 max

800 min

*Quantities may be varied or alternate designs submitted to adapt mix to conform to density and strength requirements or to adapt to specific site conditions. **Requires using a suitable lightweight aggregate or air entraining admixture. Provide a mix design that achieves the specified strength and density requirements. ***Approximate Value. Use of air entraining agent may reduce these values. ****Some applications may require containing flowable backfill by constructing dikes from the mix by using less water to produce a 3-inch minimum slump, if approved by the Representative. Thickening of the mix in other areas is allowed if approved by the Representative.

Provide mix designs that conform to specific density requirements, if specified. If source of material is changed, submit a revised mix design before using material. Conduct design mix testing at the highest flowability or slump being used for the project. If applications involve exposed metal or metal coated with a layer of thin concrete (< 1/2 inch), test the design mixes for corrosion resistance as follows:

Resistivity, AASHTO T 288, 60 day cure > 2000 ohm-centimeters pH of pulverized flowable backfill 5.0 to 9.5 Chlorides of pulverized backfill after cure < 200 ppm Sulfates of pulverized backfill after cure < 1000 ppm Sulfides of pulverized backfill after cure < 200 ppm

220.3CONSTRUCTION—

backfill to contact aluminized materials or compounds.

Produce and transport as specified in Section 704, excluding maximum temperature range of 90F, or by other approved methods from a facility accepted by the Department. The Contractor may adjust the mix in the field provided it achieves the criteria specified in Table A.

design the forms to sustain lateral fluid pressure equal to total weight of unhardened flowable backfill with a minimum 1.3 factor of safety. Construct formwork as specified in Section 1001.3(a). Do not place flowable backfill through flowing water. Remove and replace flowable backfill damaged by rain or flowing water. If excavation cannot be dewatered, place flowable backfill by a tremie procedure approved by the Representative. Break up lumps by remixing or other approved methods. Ensure that base drain outlets do not intersect areas where placing flowable backfill. Furnish solid base drain outlet pipes in areas intersecting the flowable backfill. Do not place flowable backfill at a material temperature below 50F or if the temperature of either the air or the surface that the flowable backfill is placed on is 40F or lower. Maintain the temperature of the in - place flowable backfill at no less than 50F for a minimum of 24 hours or until the next lift is placed. Do not place additional lifts until surface bleed water dissipates or the preceding lift hardens sufficiently to support foot traffic or both. Protect finished surface from frost, erosion, and damage with suitable covers of soil, aggregate, concrete, pavement, or other material approved by the Representative. If required, contain flowable backfill by constructing dikes from the mix. For the mix for dikes use less water to produce a 3-inch minimum slump, as directed by the Representative. Dikes will remain an integral part of completed flowable backfill. The Con tractor may thicken the mix in other areas if allowed by the Representative.

exceeding resisting capacity of structure. Do not place lifts that exceed 4 -foot, unless approved by the Representative. Protect structure foundation drains from intrusion and contamination of flowable backfill by using a separation membrane of Class 4, Type A geotextile. During placement of flowable backfill, protect existing structures, drainage facilities, utilities, etc., that are to remain within the fill area from movement or floating, damage, or misalignment. Repair or replace any damaged items, as directed by the Representative, at no additional cost to the Department. Provide preformed drain, no more than 2 inches thick, between the wall and the flowable fill and provide outlets at not more than 15 feet through the wall, or as directed by the Representative.

Standard Drawings. Place adequate support to provide the minimum required bedding from trench bottom to bottom of pipe, and protect pipe from damage, movement, floating and improper alignment. Protect pipe from intrusion of flowable backfill. If shown, place Class 4, Type A geotextile membrane around pipe. Prevent floating of pipe by placing flowable backfill in lifts or use sandbags or other weights to ballast pipe until lift is set. Place the backfill evenly on both sides of the trench to avoid overstressing the pipe. Monitor pipe alignment according to Section 601.3(c).

prevent floating. Protect utilities from damage and movement. Maintain proper alignment of conduits during placement of flowable backfill. Perform all utility work according to the permit requirements.

Test flowable backfill slump, according to AASHTO T 119, test air content according to AASHTO T 152 (do not apply an aggregate correction factor) or T 196, and for yield, according to AASHTO T 121, ASTM C136, as part of the QC Plan. Test flowable backfill for proper flowability using the slump cone. Conduct slump tests as often as necessary (at least once daily or every 200 cubic yard) to maintain the correct flowability at placement and if requested by the Representative. The Contractor may add water on-site to maintain flowability as needed. Test flowable backfill for yield at least once daily, or one test for every 200 cubic yard of material. Record all test results and submit to the Representative.

Mold 4-inch by 8-inch cylinders according to PTM No. 611, except specimens will remain in the mold until just before testing. Mold cylinders from the sample obtained for testing material flowability. Test for compressive strength according to PTM No. 604, except use neoprene caps. Ensure the Inspector witnesses compressive strength tests. Remove material that does not conform to Table A strength requirements. The Representative may allow the material to remain in place with liquidated damages assessed at $25/cubic yard per lot of deficient flowable fill.

hour after the surface bleed water has dissipated and as allowed by the Representative. Open flowable backfill Type D to traffic when directed by the Representative.

220.4MEASUREMENT AND PAYMENT—

If using flowable backfill in place of a material incidental to another item of work, then the flowable backfill is also incidental.