502 SOIL-CEMENT BASE COURSE

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502.01 DESCRIPTION.
Construct soil-cement base course using a combination of soil and portland cement, uniformly mixed, moistened, compacted, shaped, and sealed. Unless otherwise specified, the soil, cement, and water may be either plant mixed or mixed in place.
502.02 MATERIALS.
Portland Cement       902.03
Emulsified Asphalts       904.03
Production Plant       915
Soil       916.01.01 or 916.01.02
Water       921.01
502.03 CONSTRUCTION.
At least 30 days prior to the start of constructing the base course, submit the proposed production plants, location of plants with respect to project site, equipment, and material sources for approval.
Protect the subgrade and base against damage from all causes. Repair or replace damaged subgrade and base.
502.03.01 EquipmentAll machinery, tools, and apparatus necessary for the proper construction and acceptable completion of the work, together with the necessary supplies for upkeep and maintenance.. All equipment, including the production plant and on-site equipment, is subject to approval. Have the production plant ready for inspection at least 48 hours before the start of construction operations.
502.03.02 Weather Restrictions.
(a) Temperature and Surface Conditions. Place soil-cement base course when the ambient air and surface temperatures are at least 40 F and rising. Do not place material on a frozen subgrade.
(b) Cold Weather Protection. Protect the completed base from freezing during the seven-day curing period.
(c) Precipitation. Do not place material during precipitation. When precipitation has occurred during the previous 24 hours, the EngineerAny person designated by the Administrator or the procurement officer, acting directly or through his duly authorized representative, such representative acting within the scope of the particular duties assigned to him or of the authority given him. will determine if the subgrade is sufficiently dry. If precipitation occurs during placement, placement of material en route from the plant to the job site shall be at the ContractorAny person having a Contract with a procurement agency. Contractor does not include an employee with an employment Contract, or an employee organization with a collective bargaining agreement.’s risk.
502.03.03 SubgradeThe top surface of a roadbed upon which the pavement structure, shoulders, and curbs are constructed. Preparation. Complete the subgrade to final line and grade at least 500 ft ahead before beginning base course construction.
Construct the foundation as specified in Sections 204 and 208. If traffic, including construction equipment, is allowed to use the subgrade foundation or preceding layer, distribute the loading over the entire width of the course to aid in obtaining uniform and thorough compaction. Remove rutting by reshaping and recompacting the affected area as specified in Section 204.
502.03.04 Design Mix. At least 45 days prior to the start of constructing the base course, submit samples of the soil and portland cement from the proposed material sources. Sample the materials as specified in the Materials Manual. The EngineerAny person designated by the Administrator or the procurement officer, acting directly or through his duly authorized representative, such representative acting within the scope of the particular duties assigned to him or of the authority given him. will determine the exact proportions of soil and portland cement, and the optimum moisture content based on these samples. Proportions may be revised during construction to provide for changing conditions as directed. Plant mixed material shall be sampled at the plant. Mixed in place material shall be sampled from a 100 ft long control strip constructed on the site.
502.03.05 Transportation. Handle and transport mixed materials in a manner that minimizes segregation and loss of moisture. Cover all loads in accordance with State laws, unless hauling is off road and approved. Unless approved, do not dump material into piles, haul over the completed base course, or stockpile the material on the job site.
502.03.06 Spreading of Plant Mix Material. Spread the base material uniformly in layers of approximately equal thickness, to provide the specified planned depth. Avoid segregation of coarse and fine particles. Build shoulders or berms at least 2 ft wide on each side of the base and to the top elevation of each uncompacted layer, except when placing the base against concrete curbs or gutters.
502.03.07 Mixed In Place Construction. Pulverize the soil base material to ensure that, at the completion of moist mixing, 100 percent passes a 1 in. sieve and at least 80 percent passes a No. 4 sieve. Limit any variation in the moisture content of the soil at the time of cement application to 2 percent from optimum. Then spread portland cement on the soil at the approved spread rate. In the presence of the EngineerAny person designated by the Administrator or the procurement officer, acting directly or through his duly authorized representative, such representative acting within the scope of the particular duties assigned to him or of the authority given him., use an accurate scale to verify the spread rate. Then thoroughly mix the pulverized soil and cement. Immediately after completing the mixing operation, use a pressurized distributor to spray water on the mixture at the approved rate. Mix the soil/cement/water combination until it is uniform.
502.03.08 Grade or Finished Surface Control. Shape the surface of the base material to the specified line, grade, and cross section. Set grades longitudinally and transversely with fixed controls spaced no more than 25 ft. Compact and smooth the surface over its full width using a smooth faced steel-wheeled roller, or if rolling is not feasible, by mechanical tampers and vibratory compactors, as approved. Maintain the finished grade within 1/2 in. from the established grade.
502.03.09 Finishing. Shape the surface of the base material to the specified line, grade, and cross section.
502.03.10 Compaction. Immediately after placement, compact the soil-cement base to a density of at least 100 percent of the maximum density as determined by T 134. Measure the in place density per MSMT 350. Furnish a compaction block as specified in 204.03.04.
At the start of compaction, maintain the moisture in the mixture to within 2 percent of the specified optimum moisture. Begin compaction operations, except on superelevated curves, at the sides of the course. Overlap the shoulder or berm at least 1 ft and progress toward the center parallel to the center line of the roadway. On superelevated curves, begin compaction at the low side and progress toward the high side. Continue compaction operations until all compaction marks are removed.
502.03.11 Construction Joints. At the end of each day’s construction, create a straight transverse construction joint by cutting back into the completed work to form a vertical face. Build the base for large, wide areas as a series of parallel lanes of convenient length and width, complete with longitudinal joints, as approved.
502.03.12 Protection and Curing. Complete all spreading, compacting, and shaping within three hours after the mixing water, cement, and soil come in contact. Reconstruct any section not meeting these requirements. Maintain the surface of the base course in a moist condition until the emulsified asphalt is applied. Use distributing equipment conforming to 503.03.01 to apply the emulsified asphalt at the rate of 0.2 gal/yd2. Avoid ponding of the emulsified asphalt. If ponding occurs, use a sand blotter or an equivalent method as approved.
Allow the soil cement base course to cure for a period of seven days. During this period, close the base course to all traffic. Repair damaged areas.
502.03.13 Maintenance. During construction and after completion of the base course, maintain the base course until the surface course is placed. When unacceptable work cannot be repaired, replace it for the full depth of the base.
502.04 MEASUREMENT AND PAYMENT.
The payment will be full compensation for control strip, and for all material, labor, equipment, tools, and incidentals necessary to complete the work.
502.04.01  Soil-Cement Base CourseThe one or more layers of specified material and thickness placed on a subbase or a subgrade to support a surface course. will be measured and paid for at the Contract unit price per square yard.
Surface area measurements will be based on the specified width of the base and the actual length measured along the center line of the base surface.
502.04.02  Portland Cement for Soil-Cement Base CourseThe one or more layers of specified material and thickness placed on a subbase or a subgrade to support a surface course. will be measured and paid for at the Contract unit price per ton.