Section 213 — Subgrade Stabilization
Description
213.01This work consists of processing and incorporating stabilizing additives into the upper layer of subgrade.
Material
213.02Conform to the following Subsections: Chemical admixtures 711.03 Fly ash 701.03(a) Hydraulic cement 701.01 Lime for soil stabilization 725.03(b) Water for construction 725.01(c)
Construction Requirements
213.03Proportioning. Submit a subgrade stabilization mix design at least 30 days before production. Include compressive strength values for at least three application rates with at least one app lication rate above and one below the strength shown in Table 213-1. Table 213-1 Subgrade Stabilization Compressive Strength Requirements Stabilization Mixture Test Procedure Average Unconfined Compressive Strength (3 specimens minimum) Lime -Soil ASTM D5102, Procedure B 100 psi minimum(1) Lime -Fly ash -Soil ASTM D5102, Procedure B 150 psi minimum(1)
Cement -Soil,
Cement -Fly ash -Soil,
or Fly ash -Soil ASTM D1633, Method A 200 psi minimum(2)
(1)At 7-day cure at 105 °F.
(2)At 7-day cure. Include the following with the mix design as applicable:
(a)Source of each component material;
(b)Results of the applicable tests including optimum moisture content (after treatment), hydration moisture rate, maximum dry density (after treatment), Atterberg limits (before and after treatment), and recommended application rates of stabilizing material; and
(c)If requested:
(1)200-pound sample of the subgrade soil;
(2)25-pound sample of the fly ash;
(3)25-pound sample of the lime;
(4)25-pound sample of the cement; and
(5)2-pound sample of each chemical admixture. Start production after the mix design is approved. Provide a new mix design if there is a material source change.
213.04Production Start -Up Procedur es. Conduct a pre -stabilization preparatory phase meeting at least 7 days before the start of stabilizing operations according to Subsection 153.06(a) . Notify the CO at least 7 days before starting operations.
213.05General. Store stabilizing additives and chemical admixtures in closed, weatherproof containers. Recondition the subgrade according to Subsection 303.06. Scarify or pulverize the subgrade to the required depth. Use a rotar y mixer with direct water injection capabilities to adequately blend the material and to produce a homogeneous mixture within 2 percent of the optimum moisture content. At the end of each production day, shape the subgrade surface to provide positive drainage. Provide a construction joint according to Subsection 305.11 for tying into existing stabilized subgrade.
213.06Application. Do not apply stabilizing additives when weather conditions cause excessive material loss or when the air temperature may fall below 32 °F within 48 hours. Apply stabilizing additives when the prepared subgrade surface temperature is at least 40 °F. Adjust the subgrade material moisture content to 2 to 3 percent above optimum. Apply fly ash by the dry method. Apply lime and cement by either the dry or slurry method.
(a)Dry method. Uniformly apply the stabilizers using an approved metered spreader. Apply water using approved methods to obtain the proper moisture content for mixing and compaction. If qu icklime and fly ash are pre- blended, limit the maximum particle size of the quicklime to ⅛ inch to avoid segregation.
(b)Slurry method. Mix material with water. Report the percent solids in the slurry to the CO for each production day. Apply the slurry using either trucks with approved distributors or rotary mixers. Equip the distributor truck or rotary mixer tank with an agitator to keep the stabilizers suspended in water. Make successive passes over the material to obtain the proper moisture and additive con tent.
213.07Mixing. Keep traffic, except mixing equipment, off the spread material. Use a rotary mixer.
(a)Lime mixtures.
(1)Preliminary mixing. Adjust the moisture content of the mixture to optimum plus necessary hydration moisture. Use the mix design hydration moisture rate. Thoroughly mix the lime, soil, and water to obtain a homogeneous friable mixture. Complete the mixing on the same day lime is applied. Check to ensure lime is fully hydrated and add additional water if necessary. Mellow the mixture for 1 to 4 days at a moisture content of 2 to 3 percent above optimum as directed.
(2)Final mixing. Remix until 95 percent of the mixture, except hard and durable particles, passes a 1½- inch sieve and at least 50 percent of the soil portion of the mixture passes a No. 4 sieve when tested according to AASHTO T 27 in the non-dried condition.
(b)Lime/fly ash mixtures. Mix according to Subsection 213.07(a)(1) . Use either a pre-blended lime/fly ash mixture or mix the lime and fly a sh in separate operations. If the lime and fly ash are mixed separately, mix the lime first and mix the fly ash within 2 days of lime mixing. Adjust the moisture content of the lime/fly ash mixture to 2 to 3 percent above optimum. Mix the material to prevent formation of fly ash balls. Complete the mixing within 2 hours after adding the fly ash.
(c)Cement, fly ash, or cement/fly ash mixtures. Add water to adjust the moisture content of the mixture to 2 to 3 percent above optimum. Mix the material until 95 percent of the mixture, except hard and durable particles, passes a 1½ -inch sieve and at least 50 percent of the soil portion of the mixture passes a No. 4 sieve when tested according to AASHTO T 27 in the non- dried condition. Complete the mixing within 2 hours after the cement, fly ash, or both are added.
213.08Compacting and Finishing. Immediately after final mixing, spread and compact the mixture. Use a vibratory sheepsfoot roller to achieve compaction. Use pneumatic- tire and steel drum rollers for finish rolling. Compact the mixture to at least 95 percent of maximum dry density from the approved mix design. Complete compaction operations within 2 hours of completion of mixing. Finish the compacted subgrade to within ±0.10 foot of the staked line, grade, and cross -section. Check the surface with a 10 -foot metal straightedge. Add or remove material to correct surface deviations more than ¾ inch in 10 feet between two contacts of the straightedge with the surface. When adding material, scarify the subgrade to at least 6 inches. Remix according to Subsection 213.07 and recompact the area to restore the required density and strength.
213.09Curing. Keep the subgrade continuously moist and within 3 percent of optimum moisture content until the next course is placed. Apply water under pressure through a spray bar equipped with nozzles, which produce a fine, uniform spray. Place the next course within 14 days after compacting and finishing. If the subgrade deforms, loses density, or ravels before placement of the next course; correct the damaged subgrade. Traffic may be allowed on the stabilized subgrade 24 hours after compaction and finishing if approved. 213.10 Acceptance . See Table 213-2 for sampling, tes ting, and acceptance requirements. Material for subgrade stabilization stabilizing additives will be evaluated under Subsections 106.02 and 106.03. Subgrade stabilization work will be evaluated under Subsections 106.02 and 106.04. Construction joints will be evaluated under Section 305. Reconditioning of subgrade will be evaluated under Section 303.
Measurement
213.11Measure the Section 213 pay items listed in the bid schedule according to Subsection 109.02 and the following as applicable: When measuring subgrade stabilization by the square yard, measure the length horizontally along the centerline of the roadway and the width horizontally to include the top of the subgrade stabilization width, including widenings.
Payment
213.12The accepted quantities will be paid at the contract price per unit of measurement for the Section 213 pay items listed in the bid schedule. Payment will be full compensation for the work prescribed in this Section. See Subsection 109.05 . Table 213-2 Sampling, Testing, and Acceptance Requirements
Material or
Product Type of
Acceptance
(Subsection) Characteristic Category Test Methods
Specifications Sampling
Frequency Point of
Sampling Split
Sample Reporting
Time Remarks
Mix Design
Subgrade
stabilization Measured & tested for conformance (106.04) Proportioning − Subsection
213.031 per submitted mix design Existing roadbed or subgrade If requested 30 days before production −
Production
Stabilized
material Measured & tested for conformance (106.04 ) Moisture - density − AASHTO T 99, Method C(1) 1 per soil type but not less than 1 for each day of production Processed material behind mixer If requested Before using in work − Gradation − AASHTO T 27 & T 11 1 per 3500 yd2 but not less than 1 per layer " " " − Density − AASHTO T 310 or other approved procedures " In-place No Before placing next layer −
Compressive
strength (7-day cure) − ASTM D5102,(2) D1633(3) as applicable " Processed material behind mixer " " −
(1)At least 5 points per proctor.
(2)At 7-day cure at 105° F. Compact sampled material immediately according to Procedure B. Do not complete the proportioning and mixing of Sections 10.2 and 10.3. Report average unconfined compressive strength from at least three specimens.
(3)At 7-day cure. Report average unconfined compressive strength from at least three specimens. DIVISION 250 EARTH RETAINING