301Subgrade Modification

- SUBGRADE MODIFICATION SUBGRADE MODIFICATION

301.1DESCRIPTION

Modify the subgrade using the materials and methods shown in the Contract Documents. When the Contract Documents specify, realign the s houlders and clean and reshape the ditches. B I D I T E M S U N I T S Manipulation for Aggregate Subgrade Modification (*)(**) Square Yard Manipulation for In-Place Material Subgrade Modification (**) Square Yard Aggregate for Subgrade Modification (*) Cubic Yard C a l c i u m C h l o r i d e T o n C e m e n t T o n F l y A s h T o n Water (Subgrade Modification) (Set Price) M Gallon * Type, typically Rock, Silt or Millings **Calcium Chloride, Cement or Fly Ash

301.2MATERIALS

Provide materials that comply with the applicable requirements. Aggregate for Subgrade Modification… ................................................................ DIVISION 1100 Emulsified Asphalt (SS-1H or CSS-1H) ............................................................... DIVISION 1200 Medium Cure Cutback Asphalt (MC-250) ............................................................ DIVISION 1200 Calcium Chloride .................................................................................................. DIVISION 1700 Portland Cement / Blended Hydraulic Cement ..................................................... DIVISION 2000 Fly Ash .................................................................................................................. DIVISION 2000 Water for Subgrade Modification .......................................................................... DIVISION 2400 Admixtures / Retarders .......................................................................................... DIVISION 1400 Provide silt for subgrade modification that complies with TABLE 301-1. TABLE 301-1: SILT FOR SUBGRADE MODIFICATION % Retained - Square Mesh Sieve P.I.

0-5 0-50 12 In-place material may be existing rock surfacing or milled pavement. When pavement millings are provided, the maximum size shall be 1½ inches.

301.3CONSTRUCTION REQUIREMENTS

and compact the materials as specified in the Contract Documents. Do not perform subgrade modification on frozen subgrade. Do not incorporate calcium chloride, cement or fly ash if air temperatures are expected below 32ºF during the first 24 hours after compaction.

Documents to provide the binder material. When the Cont ract Documents specify, provide binder material from the shoulder slopes, ditches and back slopes.

until no more than 5% of the material is retained on a 2-inch sieve. - SUBGRADE MODIFICATION If silt is the specified aggregate, a maximum of 20% by weight, minus No. 200 sieve material, is allowed in the combined mixture.

in the subgrade, blade the roadway to allow uniform distribution of the additive. On projects having more than 20,000 square yards of manipulation, use equipment with a recycling or mixing drum and with an automatic water proportioning system to incorporate the additive and water into the subgrade to the specified depth. This system may be pressurized or mechanical in nature, utilizing vane or augers feeding cement or fly ash through a funnel or hood at a controlled rate. On projects having less than 20,000 square yards of manipulation, and in irregular areas, submit a plan to the Engineer for approval that includes equipment and procedures that address subgrade preparation and application process to spread the cement or fly ash at the specified rate. On projects having more than 20,000 square yards of manipulation, and consisting of multi-phased construction, contact the District Office for approval to waive the use of the controlled application system. Consideration will be based on the Contractor’s proposed alternate method of applying the cement or fly ash, the square yards of manipulation in each phase, and the size of individual areas within each phase. The Engineer will conduct laboratory tests on site ma terials and the specified additive content to establish the optimum moisture content. Distribute the additive in a manner that minimizes loss of the material. Do not apply the additive if conditions are such that the material is lost due to the wi nd or rain. Do not use an additive that was not properly handled and stored in weatherproof containers. When sp ecified, apply a uniform covera ge of a retarder to the additive, immediately following the spreading of the additive. If the moisture content of the pulverized subgrade will accommodate additional moisture, the retarder may be diluted with water to obtain a uniform application. Mix the subgrade, additive and water. Continue mixing until a homogeneous, friable mixture that complies with TABLE 301-2 is obtained. TABLE 301-2: CALCIUM CHLORIDE, CEMENT OR FLY ASH MODIFIED SUBGRADE % Retained - Square Mesh Sieves 1 ½-inch ½-inch 0 50, maximum Complete the mixing within 30 minutes of adding the water to the additive and the subgrade. The uniform moisture content of the mixture immediately before being compacted shall be within ±3% of the optimum moisture content. If the moisture content of the mixture exceeds the opti mum moisture content, add additional cement or fly ash to lower the moisture content. Distribute the mixture as needed to maintain the optimum moisture content during the compaction operations.

centrifugal force of 24 tons for the initial compaction of the mixture. Use a rubber-tired or smooth-wheeled roller to complete the compaction of the surface. Compact the modi fied subgrade to a minimu m of 95% of the combined materials dry density, as determined in Part V. The co mpacted subgrade shall have uniform density and remain stable under construction traffic. Complete the compacti on operations within 2 hours of incorporating the additive into the subgrade. If any of these requirements are not satisfied, reprocess, recompact and refinish the deficient areas.

On projects having more than 20,000 square yards of manipulation, use automatic grade controlled equipment to trim the compacted modified subgrade. In irregular areas, trim the subgrade by wetting, blading and rolling. Compact the trimmed surface of the modified subg rade with a smooth-wheel or a pneumat ic-tire roller. If necessary during the final rolling, lightly scarify and blade the surface to eliminate equipment imprints.

the subgrade within 2 ½ hours of the time the wate r and cementing agent is added to the subgrade. Compact the trimmed surface of the treated subgrade with a smooth-wheel or a pneumatic-tire roller. Lightly scarify and blade the surface to eliminate equipment imprints while performing final rolling. - SUBGRADE MODIFICATION

subgrade after 2 ½ hours of the time the water and cementing agent is added to the subgrade. Compact the trimmed surface of the treated subgrade with a smoot h-wheel or a pneumatic-tire roller. Remove loose trimmed material from any low spots and fill with the next course of material at the Contractor’s expense. Clean and dress the shoulders and shoulder slopes. Remove all excess material and debris.

the subgrade is covered with base or surfacing if covered before 7 days. Protect the finished subgrade from drying by spraying with water to maintain a continuous moist condition. The Contractor may apply an asphalt prime coat instead of keeping the finished surface moist with water during the curing period. If this option is chosen, apply SS- 1H, CSS-1H or MC-250 at the rate of 0.22 gallons per square yard to achieve a minimum of 0.13 gallons per square yard residue. Multiple light applications may be necessary to obtain the specified rate of application without runoff.

the Contract Documents. Construct the subgrade modified w ith in-place materials according to subsection 301.3a. , using the specified in-place material for the aggregate.

subgrade has cured and can withstand the loads without damaging the subgrade. If the subgrade deforms under the construction loads and cannot return back to its original condition, or if it deflects more than 1 inch, allow the subgrade additional curing time before operating equipment on the subgrade. Repair any damaged subgrade.

base before it is subjected to freezing. If the finished treated subgrade is not covered with a lift of HMA or aggregate base and is subjected to freezing, the Engineer will determine when the subgrade needs to be reworked. KDOT will not pay for the replacement a nd refinishing of the treated subgrade if the material loses the required stability, density or finish before the next course is placed.

301.4MEASUREMENT AND PAYMENT

The Engineer will measure aggregate for subgrade m odification and silt for subgrade modification by the cubic yard by vehicle measurement at the place of unloading. If weight is converted to cubic yards for payment, the moisture in the aggregate is not measured for payment. The Engineer will measure water used for modified subgrade by the M Gallon using calibrated tanks or water meters. The Engineer will measure water used for subgrade preparation and mi xing, compacting and curing the modified subgrade. The Engineer will not measure water used for dust control, water wasted through the Contractor’s negligence or water in excess of the quantity required for mixing and compacting the modified subgrade. If the Contractor opts to use asphalt material to cure the modified subgrade, the Engineer will not measure the asphalt material for payment. The Engineer will measure calcium chloride, cement and fly ash by the ton. The Engineer will not measure additional cement or fly ash added to the mixture to reduce moisture content. The Engineer will measure the various types of subgrade manipulation by the square yard. Payment for "Manipulation for Ag gregate Subgrade Modification", "M anipulation for In-Place Material Subgrade Modification", "Aggregate for Subgrade Modification", "Calcium Chloride", "Cement" and "Fly Ash" at the contract unit prices and "Water (S ubgrade Modification) (Set Price)" at the contract set unit price is full compensation for the specified work.