5-10 (B) Shaping and Compaction
Shape the stabilized subgrade to the lines, grades and typic al sections shown on the plans. Compact the entire depth and width of the stabilized subgrade to a density equal to at least 100% of that obtained by compacting a sample of the material in accordance with AASHTO T 99 as modified by the Department. Copies of these modified testing procedures are available upon request from the Materials and Tests Unit. Compact the stabilized subgrade at a moisture content which is approximately that required to produce the maximum density indicated by the above test method. Dry or add moisture to the material as required to provide a uniformly compacted and acceptable subgrade.
510-4 Tolerance
A tolerance of ± 1/2 inch from the established grade will be permitted after the stabilized subgrade has been graded to a uniform surface. Perform gra ding of the subgrade such that the maximum differential between the established grade and the stabilized subgrade within any 100 f oot distance is 1/2 inch.
510-5 Protection
Protect the aggregate stabilized subgrade in accordance with Article 500- 4.
510-6 Measurement and Payment
Stabilizer Aggregate will be measured and paid as the actual number of tons of aggregate, exclusive of any corrective material, which has been mixed with the completed and accepted subgrade. This quantity will be measured as provided for in Article 520- 11. Payment will be made under : Pay Item Pay Unit Stabilizer Aggregate Ton
520-1 Description
Perform the work covered by this section including, but not limited to , constructing a base composed of an approved aggregate material hauled to the road, placed on the road, mixed, compacted and shaped in accordance with the lines, grades, depths and typical sections shown in the plans ; applying a sand seal in accordance wit h Article 520 -5; and maintaining the base.
520-2 Materials
Refer to Division 10. Item Section Aggregate Base Course 1005, 1006 and 1010
520-3 Methods of Production
Furnish aggregate upon which no restrictions are placed on the production or stockpiling, except as provided in Sections 1005, 1006 and 1010. Place a ggregates on the roadway which have been sampled, tested and approved in accordance with Article 520 -6.
520-4 Subgrade Preparation
Prepare the subgrade in accordance with Section 500 before placement of the base material.
5-11 520-5 Hauling and Placing Aggregate Base Material
Place the aggregate material on the subgrade with a mechanical spreader box capable of placing the material to a uniform loose depth and without segregation; except , for areas inaccessible to a mechanical spreader box, the aggregate material may be placed by other methods approved by the En gineer. In addition, as approved by the Engineer, place by end dumping aggregate on approved sandy subgrade soils to provide a working platform and reduce wheel rutting of the subgrade. When allowed, end dumping will be limited to a uniformly spread thic kness of 2 to 3 inches prior to placing the remaining aggregate thickness with a mechanical spreader box. Where the Contractor elects to use more than one source of aggregate as described in Section 1005, place the various types of aggregate used in an a pproved manner which will permit the sampling and testing required by Section 1006 and 1010. Where the required compacted thickness of base is 10 inches or less, the base material may be spread and compacted in one layer. Where the required compacted thic kness is more than 10 inches spread the base material and compact in 2 or more approximately equal layers. Compact the base material to a minimum thickness of approximately 4 inches for any one layer. Have each layer of material sampled, tested, compact ed and approved before placing succeeding layers of base material or pavement. Do not place base material on frozen subgrade or base. Base course that is in place on November 15 shall immediately be covered with a subsequent layer of pavement structure or with a sand seal. Base course that has been placed between November 16 and March 15 inclusive shall be covered within 7 calendar days with a subsequent layer of pavement structure or with a sand seal . Apply sand seal in accordance with Section 660, except Articles 660 -3 and 660- 12 will not apply. Failure by the Contractor to cover the base course as required above will result in the Engineer notifying the Contractor in writing to cover the base course with a sand seal and to suspend the operations of placing aggregate base course until such cover has been placed. I f the Contractor fails to apply the sand seal within 72 hours after receipt of such notice, the Engineer may proceed to have such work performed with other forces and equipment. The appli cation of the sand seal by the Contractor or by others will in no way relieve the Contractor of the responsibility to maintain or repair the damaged base or subgrade, no matter what the cause of damage. Do not allow traffic on the completed base course other than necessary local traffic and that developing from the operation of essential construction equipment as may be authorized by the Engineer. Repair any defects that develop in the completed base or any damage caused by local or construction traffic ac ceptably. Hauling equipment may be operated with the approval of the Engineer, over a lower layer of base, however, acceptably repair any rutting, weaving or soft areas that develop. Do not exceed 35 mph with hauling equipment traveling over any part of t he base. Use methods of handling, hauling and placing which will minimize segregation and contamination. If segregation occurs, the Engineer may require that changes to the Contractor's methods and may require mixing on the road to correct segregation. R emove and replace all aggregate which is contaminated with foreign materials to the extent that the base course will not adequately serve its intended use. The above requirements will be applicable regardless of the type of aggregate placed and regardless of prior acceptance.
520-6 Sampling, Testing and Acceptance
Perform sampling for the determination of gradation, LL and PI for the various types of aggregate, as defined in Se ction 1010.
5-12 Where visual observation indicates the need to do so, the Engineer may require the Contractor
to road mix areas of nonuniform gradation. The Engineer reserves the right to take samples in addition to the lot acceptance samples from within the lot in areas exhibiting nonuniform gradation. When the test results from such an additional sample is outside the gradation limits in Section 1010 and the nonuniformity cannot be corrected by road mixing, the aggregate base course represented by the sampl e will be rejected and replaced by the Contractor.
520-7 Shaping and Compaction
Machine and compact the layer of base within 48 hours after beginning the placing of a layer of the base. Maintain each layer to the required cross section during compaction and compact each layer to the required density before placing the next layer. Compact the base material at a moisture content which is approximately that required to produce a m aximum density. Dry or add moisture to the material when required to provide a uniformly compacted and acceptable base. If it is necessary to add water after the material is placed, scarify the material and add water uniformly throughout the full depth o f the layer of the base course material. Density determination will be based on Article 520 -9. Shape the final layer of base material in accordance with the lines, grades and typical section 16 as shown on the plans. Construct the base course so that it is smooth, hard, dense, unyielding and well bonded upon completion. A broom drag may be used in connection with the final finishing and conditioning of the surface of the base course.
520-8 Tolerances
After final shaping and compacting of the base, the Engineer will check the surface of the base for conformance to the grade and typical section and determine the base thickness. Construct the base so that the thickness of the base is within a tolerance of ± 1/2 inch of the base thickness required by the plans. When the base course will be used under concrete pavement, the tole rance will be ± 1/4 inch. Construct the base so that the maximum differential between the established grade and the base within any 100 feet section is 1/2 inch or 1/4 inch when used as a base course under concrete pavement .
520-9 Density Determination
The Engineer may us e nuclear or conventional means as described below to determine the density of selected base course materials required by Sections 520 and 540. The target density will be from the material’s most recent AASHTO T 180 test results, which may be obtained from the Materials and Tests Unit. A new target density is to be obtained when there is a change in the source of material, when a significant change occurs in th e composition of the materials from the same source or when determined necessary.
A.Conventional Method When electing to use conventional density test number 3 (ring test) to determine density, compact each layer of the base to a density equal to at least 10 0% of that obtained by compacting a sample of the material in accordance with AASHTO T 180 as modified by the Department. Information on these modified testing procedures are available in the NCDOT Conventional Density Operator’s Manual on line in the Mat erials and Tests Unit’s website.
B.Nuclear Method When electing to use a nuclear density gauge to determine density, compact each layer of the base to a density meeting requirements in the NCDOT Nuclear Density Testing
Source: North Carolina Standard Specifications for Roads and Structures, 2024 Edition. Pages 238–240 of 857.