ITEM 206 CHEMICALLY STABILIZED SUBGRADE

206.01 Description

206.02 Materials

206.03 Limitations

206.04 Test Rolling

206.05 Construction

206.06 ContractorDesigned Chemically Stabilized Subgrade

206.07 Method of Measurement

206.08 Basis of Payment

 

206.01 Description. This work consists of constructing a chemically stabilized subgrade using the method specified, which will either be cement stabilized subgrade (CSS) or lime stabilized subgrade (LSS), including designing the percentage of chemical in the stabilized subgrade.

The Contract Documents will contain an estimated quantity for the specified chemical for the project, based on using 6 percent for cement and 5 percent hydrated lime, per dry unit weight of a soil weighing 110 pounds per cubic foot (1760 kg/m3).

206.02 Materials. When CSS is specified, furnish portland cement conforming to the requirements of 701.04.

When LSS is specified, furnish hydrated or quick lime conforming to 712.04.B.

Furnish water conforming to 499.02. Potable water is satisfactory.

For CuringCoat furnish 702.04 EmulsifiedAsphalts, Types RS-1 or RS-2, or the curing materials specified in 451.02.

206.03 Limitations. Perform chemical stabilization work when the air temperature is 40 F (5 C) or above and when the soil is not frozen.

Do not perform this work during wet or unsuitable weather.

206.04 Test Rolling. When specified, test roll prior to chemical stabilization with a proof roller conforming to 204.06.

206.05 Construction.

A. Spreading. Prepare a report denoting the type of equipment to be used, speed of the intended equipment usage, rate of application of the chemical, and calculations to produce the required percent of chemical. Submit this report 2 working days prior to the work for acceptance.

Shape the subgrade to the approximate profile grade prior to spreading the specified chemical so as to permit the construction of a uniform compacted course of chemically treated soil to the thickness shown on the plans. The addition of the specified chemical will raise the subgrade profile approximately 1 inch (25mm). Remove this excess material during the fine grading.

If a 206.06 ContractorDesigned Subgradeis not specified, use the following spreading percentage rates for the specified chemical. This percentage is based on a dry unit weight of soil of 110 pounds per cubic foot (1760 kg/m3):

Cement

6 percent

Lime - Hydrated

5 percent

Lime - Quick

4 percent

 

Spread the specified chemical uniformly on the subgrade using a mechanical spreader at the approved rate and at a constant slow rate of speed.

Use a distribution bar with a maximum height of 3 feet (1 meter) above the subgrade. Use a canvas shroud that surrounds the distribution bar and extends to the subgrade.

Minimize dusting when spreading the specified chemical.

Do not spread the specified chemical on standing water.

Do not apply the specified chemical if wind conditions are such that blowing cement or lime exceeds the limits in 107.19.

B. Mixing. Immediately after spreading the specified chemical, mix the soil and chemical, as follows.

1. CSS. Mix the cement and soil using a power driven transverse type mixer equipped with a computer controlled volumetric water read out. Continue mixing until the cement is thoroughly incorporated into the soil and is a uniform color.

Do not water during the initial mixing.

Complete the initial mixing, so that 80 percent of the soil cement mixture passes a No. 4 sieve (4.75 mm) and 100 percent passes the 1 inch sieve (25mm), exclusive of aggregate larger than the No. 4 sieve (4.75 mm) size.

Following the initial mixing, remix the soil and introduce water through the transverse mixer to bring the mixed material to at least optimum moisture. uniformly distribute the water in sufficient quantity to hydrate the cement.

If the cement can be mixed to the required gradation and the water can be added to the CSS to bring the CSS to the required moisture content, then one mixing of the soil, water and cement may be used.

Restrict the addition of water when moisture content of soil exceeds 3 percent above optimum. Add water to the mixed soil in less than 2 hours after the initial mixing.

Once the water is added to the mixture, complete the mixing, compacting, and shaping within 2 hours from start to finish.

2. LSS. Mix the lime and soil by using an approved power driven rotary type mixer. If necessary, add water to bring the mixed material to at least optimum moisture content for hydrated lime and to at least 3 percent above optimum for quick lime. Continue mixing until the lime is thoroughly incorporated into the soil, all soil clods are reduced to a maximum size of 2 inches (50 mm), and the mixture is a uniform color.

Following the initial mixing, lightly compact the material to seal it against rain or excessive drying by using a steel wheel or pneumatic tire roller.

Before final mixing, cure the initially-mixed, lightly-compacted material for a period of not less than 24 hours and not more than 7 days. Perform the initial cure with water. If conditions during construction are such that more than 7 days elapse between initial mixing and final mixing, add an additional 0.5 percent of lime during the final mixing. Furnish the additional lime at no cost to the Department unless the delay beyond the 7-day limit is caused by conditions beyond the Contractors control.

Perform the final mixing using an approved power-driven rotary-type equipment until the soil is completely pulverized with all clods reduced to a maximum size of 1 inch (25 mm) and at least 60 percent of the clods passing the No. 4 (4.75 mm) sieve, exclusive of aggregate larger than the No. 4 sieve (4.75 mm). Continue mixing until the lime is uniformly distributed throughout the pulverized soil.

During final mixing, return the mixture to the moisture contents stated above, then shape and compact the mixture.

3. Mixture Depth Check. Check the uniformity of the mix by digging trenches or a series of holes at regular intervals for the full depth of treatment and inspecting the color and depth of the exposed material. The Engineerwill use diluted hydrochloric acid or phenolphthalein to ensure that the specified chemical is mixed to the desired depth.

C. Compacting. Start compaction immediately after the shaping and final mixing.

Compact all chemically stabilized subgrade to the requirements in 204.03, except the Engineerwill use 98 percent of the maximum dry unit weight for acceptance.

The Engineerwill obtain the maximum dry density for acceptance by using the moisture density curves submitted by the geotechnical consultant, the Ohio Typical Density Curves, or the maximum dry density obtained by test section method.

When a test section method is used for compaction acceptance; use 98 percent of the test section maximum dry unit weight for acceptance of the production chemically stabilized subgrade construction. Use at least the same number of passes and compactive effort used to construct the test section in the production chemically stabilized subgrade areas.

Construct a new test section when the material, supporting foundation, or embankment changes.

Reduce the moisture content or number of passes, if the material becomes unstable.

Use a vibratory footed roller weighing at least 10 tons (9 metric tons).

Use the moisture controls according to 203.07.A, except ensure that the moisture content at time of compaction is at or above optimum.

Perform the final rolling using a steel-wheeled roller. Do not use vibration during the final rolling.

Shape the compacted chemically stabilized subgrade to approximately 1 inch (25mm) above the plan profile grade and typical sections.

Do not allow any mixture of chemically stabilized subgrade that has not been compacted and shaped to remain undisturbed for more than 30 minutes.

D. Curing. Immediately following the compaction and shaping of the chemically stabilized subgrade, cover the surface with Curing Coat for curing the chemically stabilized subgrade. Use a rate of 0.3 gallon per square yard (1.3 liters per square meter) for emulsions or a rate of 0.05 gallons per square yard (0.20 liters per square meter) when the curing materials in 451.02 are used.

Apply the CuringCoat prior to the surface drying out. If the Curing Coat is delayed or the surface starts to dry out, indicated by turning white, apply water for temporary curing until the Curing Coat can be applied. Do not apply the Curing Coat unless the Curing Coat can set up before it rains. When the application of Curing Coat must be delayed, keep the chemically stabilized subgrade wet by using water until the Curing Coat can be applied.

Cure the chemically stabilized subgrade for at least five days before the placement of the overlying course.

E. Proof Rolling. After the cure period, proof roll the chemically stabilized subgrade according to Item 204.

F. Fine Grading. Remove the excess material and fine grade the chemically stabilized subgrade to the profile grade and typical sections within the tolerances in 203.08. Perform this work after the curing and proof rolling.

G. Protection. Drain and maintain the work according to 203.04.A.

Do not operate any equipment on the chemically stabilized subgrade during the cure period.

Do not allow the chemically stabilized subgrade to freeze during the cure period.

Cover the completed chemically stabilized subgrade with the aggregate base within 60 calendar days.

206.06 ContractorDesigned Chemically Stabilized Subgrade. Perform design according to Supplement 1120, Mixture Design for Chemically Stabilized Soils.

206.07 Method of Measurement. The Department will measure CementStabilized Subgradeor Lime Stabilized Subgrade by the number of square yards (square meters) computed from the profile grade and typical sections accepted in place.

The Department will measure cement by the number of tons (metric tons) incorporated in the complete and accepted work.

The Department will measure lime by the number of tons (metric tons) incorporated in the complete and accepted work. The contract quantities contain the amount of hydrated lime estimated to complete the work. When the Contractoruses quick lime, the following equation is used to calculate the equivalent amount of hydrated lime incorporated in the completed and accepted work:

EHL = QL 1.32

 

Where:

EHL = quick lime equivalent in hydrated lime

QL = tons of quick lime

 

The Department will measure Test Rolling according to 204.08 as specified for Proof Rolling.

The Department will measure CuringCoat by the number of square yards (square meters) computed from the profile grade and typical sections accepted in place.

The Department will not measure ContractorDesigned Chemically Stabilized Subgrade.

206.08 Basis of Payment. The Department will pay lump sum for all work, labor, and equipment described in 206.06. The Department will pay one-third of the lump sum amount bid when the soil sampling and testing is complete and the report is accepted by the Department. The Department will pay one-third of the lump sum amount bid when the moisture density curves of the chemically stabilized subgrade are accepted by the Department. The Department will pay one-third of the lump sum amount bid when the chemically stabilized subgrade is completed and accepted by the Department.

The Department will pay for accepted quantities at the contract prices as follows:

Item unit Description

206 Square Yard CementStabilized Subgrade, __inches deep

(Square Meter)

206 Square Yard Lime Stabilized Subgrade, __ inches deep

(Square Meter)

206 Square Yard Lime Kiln Dust Stabilized

(Square Meter) Subgrade, __ inches deep

206 Square Yard Chemical Mixture Stabilized

(Square Meter) Subgrade, __ inches deep

206 Ton (Metric Ton) Cement

206 Ton (Metric Ton) Lime

206 Ton (Metric Ton) Lime Kiln Dust

206 Square Yard CuringCoat

(Square Meter)

206 Hour Test Rolling

206 Lump Sum ContractorDesigned Chemically Stabilized

Subgrade