307Lime Treated Subgrade

Lime Treated Subgrade

Description

307.01This work consists of treating the earth subgrade by combining lime and water with the

pulverized soil subgrade material to the specified depth and compaction requirements as shown on the plans.

Materials

307.02Lime. Lime for lime treated subgrade shall be applied in slurry form. Dry application

of lime will not be allowed unless otherwise approved by the Engineer. Commercial lime slurry shall be a pumpable suspension of solids in water. Lime for lime treated subgrade shall conform to the requirements of ASTM C977 and rate of slaking test for moderate reactivity per ASTM C110 and shall be the product of a high-calcium limestone as defined by ASTM C51.

307.03Water. Water used for mixing or curing shall be per subsection 712.01, with the

additional requirement that the sulfate content shall be less than 500 ppm.

Construction Requirements

307.04General. The Contractor shall construct one or more compacted courses of treated

material, to the depth specified in the Contract. The treated material shall be a uniform blend of soil, lime, and water, free from loose or segregated areas. It shall have uniform density and moisture content and be void of all vegetation and other organic or man-made material. The subgrade shall be well bound for its full depth and width with a smooth surface suitable for placing subsequent courses. The Contractor shall regulate the sequence of the work to accurately apply and uniformly blend the lime at the designated rate and rework the courses as necessary to meet the above requirements. The Contractor shall submit a mix design to the Engineer for approval, before constructing the test section.

The Contractor shall mix hydrated or quicklime with water to produce lime slurry at the job site with equipment specifically manufactured for this purpose.

Excessive aeration of lime slurry will not be permitted.

The lime-treated subgrade shall not be mixed when it is raining, or when the subgrade material is frozen. The lime-treated subgrade shall not be mixed or compacted if the temperature of the lime or soil is below 35 °F.

307.05Preparation of Subgrade. Before beginning any lime treatment, the subgrade shall be

constructed and finished to smooth and uniform surfaces conforming to the grades and typical sections specified. Variation from the subgrade plane elevations specified shall not be more than plus or minus 0.1 foot. The subgrade shall also be proof rolled per subsection 307.07. Soft or otherwise unsuitable subgrade disclosed by proof rolling shall be over-excavated and replaced to a compacted stable state. The in-place density shall be at least 95 percent of AASHTO T 99 density within 0-3 percent of optimum moisture content.

307.06

307.06Test Section. Before full-scale production, the Contractor shall construct a test

section to demonstrate, to the satisfaction of the Engineer, subgrade stabilization using the materials, equipment, and methods to be used in full-scale production. The test section shall be at least 100 feet long, two spreading and mixing lanes wide, and the same depth as the course represented in the plans. The test section shall be constructed at a location approved by the Engineer. The test section shall be tested per the same test requirements for the lime and soil design mix, and as determined by the Contractor. If the test section is unsatisfactory, the Contractor shall adjust the materials, equipment, and methods or combinations thereof as necessary to conform to the specifications. Additional test sections shall be constructed as required to produce a satisfactory test section before full-scale production. Unsatisfactory test sections shall be removed and replaced at the Contractor’s expense. Full production shall not begin until a satisfactory test section is completed and approved by the Engineer. Before start of work, the Contractor shall determine the lime application rate, and the maximum dry density and optimum moisture content of the material after it has been treated with lime. All tests shall be performed in the presence of the Engineer. These test results will be used to determine the Contract requirements for lime application.

307.07Proof Rolling. Both before and after the lime treatment, the Contractor shall

perform proof rolling per subsection 203.08, except that final proof rolling will take place a minimum of seven days after lime treatment, unless otherwise approved by the Engineer.

307.08Processing Materials. After the subgrade has been finished and approved as

specified, the subgrade shall then be cut and pulverized by a cutting and pulverizing machine to the depth and width shown on the plans. Precautions shall be taken to avoid forming furrows of loosened material below the depth specified for the lime-stabilized soil mixture. The machine shall uniformly cut and pulverize the loosened material to a depth not greater than 10 percent over the thickness of the lime-treated layer as specified in the Contract and shall have cutters that plane the base of the cut and pulverize zone to a smooth surface over the entire width of the cut. The machine must give visible indication at all times that it is cutting to the proper depth.

initial mixing operations can be completed during the same working day, and at the specified percentage of hydrated lime, by equipment capable of pumping and re- circulating the mixture while in transit. The slurry shall be applied through spray bars to assure a uniform flow and distribution.

lime, soil, and water shall be thoroughly mixed and blended by a self-propelled rotary type mixing machine, until a uniform mixture throughout the required depth and width is obtained and all clods and lumps are reduced to a maximum 2-inch diameter size. There shall be a minimum 6-inch overlap between passes to assure consistent mixing and breakdown. The mixing machine shall make at least of two passes to uniformly mix the lime, water, and soil to the full depth of the pulverized layer. Non-uniformity of color reaction, when the treated material is tested with the standard phenolphthalein alcohol indicator, will

307.09

be considered evidence of inadequate mixing. Streaks and pockets of lime will also be considered evidence of inadequate mixing and shall require additional mixing to correct. The moisture content of the mixture immediately following the blending of water, lime, and soil shall not be less than optimum as determined by AASHTO T 99, plus necessary hydration moisture. Hydration moisture will be considered as one percentage point for each percent of lime being added. When proper mixing has been accomplished, the mixture shall be cured for at least 48 hours. Light rolling to seal the surface of the mixture shall be required. The mixture shall be maintained in a moist condition throughout the entire curing period.

self-propelled rotary type mixing machine and maintained at approximate optimum moisture content as determined. If the lime stabilized soil mixture contains clods, they shall be reduced by approved pulverization so that the remainder of the material shall meet the gradation requirements of Table 307-1 when tested dry by laboratory sieves. If it is determined that additional lime needs to be added to the previously mixed subgrade, the total depth of the subgrade shall be mixed.

307.09Compaction

material shall be aerated or sprinkled as necessary to maintain the mixture within the specified moisture content limits during and following compaction. The field density for the compacted mixture shall be at least 95 percent of the maximum density of laboratory specimens prepared from samples taken from the lime soil material in place after curing and before compacting. The specimens will be compacted and tested per AASHTO T 99, and the in-place field density will be determined per CP 80. Any mixture that has not been compacted shall not be left undisturbed for more than 30 minutes. The moisture content of the mixture at the start of compaction shall be at 2 plus or minus 1 percent above the optimum moisture content. The optimum moisture content will be determined per AASHTO T 99.

specified. All irregularities, depressions, or weak spots, that develop, shall be corrected immediately by scarifying the areas affected, adding or removing material as required, and reshaping and re-compacting by sprinkling and rolling. The surface of the course shall be maintained in a smooth condition, free from undulations and ruts, until other work is placed or the work is accepted.

on the plans shall be compacted to the extent necessary to remain firm and stable under construction equipment. After each section is completed, the Engineer will conduct tests. If the material fails to meet the density and strength requirements per the lime and soil design mix, it shall be reworked to meet these requirements at the Contractor’s expense. Throughout this entire operation, the shape of the course shall be maintained by blading, and the surface upon completion shall be smooth and shall conform with the typical section shown on the plans and to the established lines and grades. Variation from the subgrade plan elevations specified shall not exceed 0.04 foot. Should the material, due to any reason or cause, lose the required stability, density, or finish, before the next course is placed or the work is accepted, it shall be recompacted and refinished at the Contractor’s expense.

307.10

307.10Finishing and Curing. When initial compaction of the top layer of the lime-

stabilized soil mixture is nearing completion, the surface shall be shaped to the required lines, grades, and cross section, and compaction continued until uniform and adequate compaction is obtained. The treated material shall be maintained at a moisture content satisfactory for proper curing by one of the following:

to 1) is applied per subsection 307.10, item (3) below.

immediately after the lime-treated subgrade has been finished. One application shall be made consisting of 0.20-gallon diluted mixture per square yard. The completed section shall be cured for a minimum of seven days before further courses are added or any traffic is permitted, unless otherwise directed by the engineer. Acceptable compressive strength test results shall be in a range from a minimum of 160 pounds per square inch to 500 pounds per square inch.

307.11Construction Joints. Construction joints are not required after each day’s work

unless there is a time lapse of seven days or more between the processing of adjacent sections. If construction joints are required, they shall be formed by cutting back into the completed work to form a vertical face. Damage to completed work shall be avoided.

307.12Thickness Acceptance. Lime treated subgrade will be accepted for minimum

thickness on a lot basis. A lot will consist of 1,500 square yards. One core shall be taken at random by the Contractor’s Process Control Inspector in each lot. When the measurement of the core from a lot is not deficient by more than 0.5 inch from the minimum plan thickness, full payment will be made. When such measurement is deficient by more than 0.5 inch and not more than 1.0 inch from the plan thickness, two additional cores shall be taken at random and used in determining the average thickness for that lot. The thickness of the core shall be determined by average caliper measurement of cores tested per ASTM C174. When the average measurement of the three cores is not deficient by more than 0.5 inch from the plan thickness, full payment will be made. If the average measurement of the three cores is deficient by more than 0.5 inch but less than 1.0 inch from the plan thickness, the entire lot may be left in place and a 10 percent price reduction to the contract unit price will be made. If the average measurement of the three cores is deficient more than 1.0 inch but less than 2.0 inches from the plan thickness, the entire lot may be left in place and a 50 percent price reduction to the contract unit price will be made. When the average thickness is deficient by more than 2.0 inches, the entire lot shall be replaced at the Contractor’s expense.

307.12

Table 307-1 Schedule for Minimum Sampling and Testing

Element and Process Acceptance Remarks Procedure Control pH 1/5000 sq yd pH will be determined after % lime has 1/10,000 sq ASTM C977 (App) (Design) or fraction been established based on unconfined yd or fraction ASTM G51 (Field) thereof compressive strength 1/5000 sq yd Atterburg Limits 1/10,000 sq or fraction Reduce by 1/2 original PI AASHTO T89, T90 yd or fraction thereof 1/5000 sq yd Swell Potential 1/10,000 sq 1/2% or less with 200 psf surcharge or fraction ASTM D4546 yd or fraction pressure thereof Determined by design plan criteria. Do 1/5000 sq yd Unconfined Compressive 1/10,000 sq not immerse in water after moist-cure or fraction Strength ASTM D5102 yd or fraction period. The tests shall be conducted on thereof (Procedure B) 1/soil type samples cured in a moist environment 1/soil type for 5 days @ 100 °F. A lot is defined as 1 When measurement is <0.5”, 2 Thickness Acceptance core per 1/3000 sq yd additional cores shall be taken in that ASTM C174 1500 sq yd or fraction lot and the average of 3 cores will or fraction determine the thickness of that lot thereof 1/5000 sq yd 1": 100% passing; Gradation 1/10,000 sq or fraction #4: 60% passing. AASHTO T11 and T27 yd or fraction thereof Dry sieving after final mixing Minimum 95% of maximum dry density Determining Percent 1/5000 sq yd 1/10,000 sq per AASHTO T 99. Moisture content of Relative Compaction or fraction yds or mixture at the start of compaction shall Soil-Aggregate by thereof fraction be at 2 ± 1% above optimum moisture Nuclear Method CP 80 content. Moisture Density Curve 1/soil type 1/soil type AASHTO T99

Water soluble sulfate content in soil Sulfate 1/soil type 1/soil type shall be less than 0.2% by dry soil CP-L 2103 weight.

307.13

Method of Measurement

307.13Hydrated lime will be measured by the ton. If quicklime is used the pay quantity will

be determined using the certified lime purity for each truckload as follows: Pure quicklime (CaO) • 1.32 = Hydrated Lime (Ca(OH)2) Quicklime delivered • % purity • 1.32 = A Quicklime delivered • % inert material = B A + B = total hydrated lime produced = pay quantity

Processing lime-treated subgrade will be measured by the square yard for the area completed and accepted. Overlap mixing will not be measured and paid for separately but shall be included in the work.

Basis of Payment

307.14The accepted quantities will be paid for at the contract unit price for each of the

pay items listed below that appear in the bid schedule. Payment shall include all processing materials, lime application and mixing, compaction, and materials used in curing. Payment will be made under: Pay Item Pay Unit Hydrated Lime Ton Processing Lime Treated Subgrade ( Inch) Square Yard

Test sections and coring will not be measured and paid for separately but shall be included in the work. All proof rolling will be measured and paid for per Section 203.

401.01