501 AGGREGATE BASE COURSES
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- Construct base courses using one of the following:
- (a) Graded aggregate without a stabilizing agent.
- (b) Plant mixed graded aggregate with a Portland cement stabilizing agent.
- (c) Bank run gravel.
- (d) Sand aggregate.
Graded Aggregate for Base Course 901.01 Bank Run Gravel for Base Course 901.01 Sand Aggregate Base Course Coarse Aggregate 901.01, Size No. 57 Fine Aggregate Section 916, Select Borrow Portland Cement 902 Type I or IA Emulsified Asphalt 904.03 Production Plant Section 915 Water 921.01 Moisture and Dust Control Agents 921.02
- At least 30 days prior to the start of constructing the base course, submit the proposed plants, equipment, and material sources for approval.
- Protect the subgrade and base against damage from all causes. Repair or replace damaged areas.
- Limit excavation for widening to an area that can be backfilled the same working day using graded aggregate base. Refer to Standard No. 104.01-28 for the area to be backfilled. Maintain the temporary graded aggregate base wedge with a 4:1 or flatter fill slope. Compact the material as directed. Leave the graded aggregate base wedge in place until placement of the asphalt mix base.
- 501.03.01 Equipment. All equipment, including the production plant and on-site equipment, is subject to approval. Have the plant ready for inspection at least 48 hours prior to the start of construction operations.
- 501.03.02 Weather Restrictions.
- (a) Temperature and Surface Conditions. Place graded aggregate stabilized with Portland cement when the ambient air and surface temperatures are at least 40 F and rising. Place graded aggregate, bank run gravel, and sand aggregate base when the ambient air and surface temperatures are at least 32 F and rising. Do not place material on a frozen subgrade.
- (b) Cold Weather Protection. Protect the plant mixed graded aggregate stabilized 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 Engineer 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 Contractor’s risk.
- 501.03.03 Subgrade Preparation. Before beginning base course construction, complete the approved subgrade to final line and grade at least 500 ft ahead. 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.
- 501.03.04 Stabilized Graded Aggregate Base Mix. Use the amount of Portland cement determined according to T 180, Method D, with oversize particle correction applied.
- 501.03.05 Bank Run Gravel Base Mix. Mixing or blending of materials using approved chemical additives will be permitted.
- 501.03.06 Sand Aggregate Base Mix. Provide a mixture containing 35 percent to 40 percent coarse material as measured by dry weight of the total mix.
- 501.03.07 Transportation. Handle and transport mixed base 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 is approved. Unless approved, do not dump material into piles, haul over the completed base course, or stockpile the material on the job site.
- 501.03.08 Spreading. Spread the base material uniformly and 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.
- 501.03.09 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 greater 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.
- 501.03.10 Compaction. Immediately after placement, compact the material to the required density. During compaction operations, maintain the moisture content of the material to within 2 percent of optimum moisture. Determine the optimum moisture content and maximum dry density as follows:
- (a) Graded Aggregate Base, Sand Aggregate Base, and Bank Run Gravel Base according to T 180 with oversize particle correction applied.
- (b) Graded Stabilized Aggregate Base according to T 134.
- Compact graded aggregate base, bank run gravel base, and sand aggregate base to at least 97 percent of the maximum dry density. Compact graded stabilized aggregate base to at least 95 percent of the maximum dry density. Measure in place density per MSMT 350 or 352.
- 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.
- 501.03.11 Graded Stabilized Aggregate Base Protection and Curing. Complete the spreading, compacting, and shaping within three hours after the mixing water, cement, and aggregate come in contact. Reconstruct any section not conforming to these requirements. Maintain the surface in a moist condition until the emulsified asphalt seal coat is applied. Apply the emulsified asphalt using distributing equipment as specified in 503.03.01 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 material to cure for a period of seven days. During this period, close the base course to all traffic. Repair damaged portions of the base course seal coat.
- 501.03.12 Moisture and Dust Control Agents. When specified, add calcium or magnesium chloride at the plant or apply it to the surface of the material at the project site. Apply calcium chloride at the rate of 1 lb/yd2. Apply magnesium chloride at the rate of 1 lb/yd2 or as a solution at the rate of 1/2 gal/yd2.
- 501.03.13 Maintenance. During construction and after completion of the base course, maintain the base until the surface course is placed. When unacceptable work cannot be repaired, replace it for the full depth of the base.
501.04 MEASUREMENT AND PAYMENT.
- The payment will be full compensation for all aggregate, furnishing, hauling, placing, curing, and for all material, labor, equipment, tools, and incidentals necessary to complete the work.
- 501.04.01 Graded Aggregate Base Course, Graded Aggregate Base Course Stabilized with Cement, Bank Run Gravel Base Course, and Sand Aggregate Base 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.
- The temporary graded aggregate base wedge constructed in conformance with Standard No. MD 104.01-28, maintaining the 4:1 or flatter slope, compaction, and removal of the material, will not be measured but the cost will be incidental to the Graded Aggregate Base Course item.
- 501.04.02 The Portland cement stabilizing agent and the emulsified asphalt for seal coat will not be measured but the cost will be incidental to the Graded Aggregate Base Course Stabilized with Cement item.
- 501.04.03 Bank Run Gravel Base. Material manipulation or addition of chemical additives will not be measured but the cost will be incidental to the Bank Run Gravel Base Course item.
- 501.04.04 Calcium or Magnesium Chloride will be measured and paid for at the Contract unit price per square yard or per ton as specified.