The Table of Contents for this section is available.
The work covered by this section consists of the construction of a base composed of an approved aggregate material hauled to the road, placed on the road, compacted, and shaped to conform to the lines, grades, depths, and typical sections shown in the plans or established by the Engineer.
All materials shall meet the requirements of Division 10 shown below:
Aggregate base course Articles 1010-1, 1010-2, and 1010-3
(A) General:
The Contractor may, at his option, furnish aggregate base course material produced by any of the methods described below unless otherwise specified in the special provisions.
(B) Type A Aggregate:
Aggregate upon which no restrictions are placed on the production or stockpiling except as provided in Section 1005.
(C) Type B Aggregate:
Aggregates from an approved stockpile which has been constructed, tested, and approved in accordance with the provisions of Subarticle 5206(C)(2); and which have been placed on the roadway, sampled, tested, and approved in accordance with the provisions of Subarticle 5206(C)(3).
The subgrade shall be prepared in accordance with Section 500 prior to placement of the base material.
520-5 HAULING AND PLACING AGGREGATE BASE MATERIAL.
The aggregate material shall be placed on the subgrade with a mechanical spreader capable of placing the material to a uniform loose depth and without segregation except that for areas inaccessible to a mechanical spreader, the aggregate material may be placed by other methods approved by the Engineer.
Where the Contractor elects to use more than one type of aggregate as described in Article 5203, the placing of the various types used shall be done in an approved manner which will permit the sampling and testing required by Article 5206.
Where the required compacted thickness of base is 8 inches or less, the base material may be spread and compacted in one layer. Where the required compacted thickness is more than 8 inches, the base material shall be spread and compacted in 2 or more approximately equal layers. The minimum compacted thickness of any one layer shall be approximately 4 inches.
Each layer of material shall have been sampled, tested, compacted, and approved prior to placing succeeding layers of base material or pavement.
No base material shall be placed on frozen subgrade or base.
Base course which is in place on November 15 shall have been covered with a subsequent layer of pavement structure or with a sand seal. Base course which 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.
Sand seal shall be applied in accordance with the requirements of Section 660 except that Articles 6603, 66011, and 66012 will not apply.
Failure of 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. This work shall be performed by the Contractor at no cost to the Department. In the event that 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 cost of such work performed by the Department will be deducted from monies due or to become due the Contractor. The application 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, at no cost to the Department.
No traffic shall be allowed 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. Any defects that develop in the completed base or any damage caused by local or construction traffic shall be acceptably repaired at no cost to the Department. Hauling equipment may be operated with the approval of the Engineer, over a lower layer of base, however, any rutting, weaving, or soft areas that develop shall be acceptably repaired at no cost to the Department.
The maximum speed of hauling equipment traveling over any part of the base shall be as directed by the Engineer, but in no case shall it exceed 35 miles per hour.
The Contractor shall utilize methods of handling, hauling, and placing which will minimize segregation and contamination. If segregation occurs, the Engineer may require that changes be made in the Contractor's methods to minimize segregation, and may also require mixing on the road which may be necessary to correct any segregation. No additional compensation will be allowed for the work of road mixing as may be required under this provision. Aggregate which is contaminated with foreign materials to the extent that the base course will not adequately serve its intended use shall be removed and replaced by the Contractor at no additional cost to the Department. The above requirements will be applicable regardless of the type of aggregate placed and regardless of prior acceptance.
520-6 SAMPLING, TESTING, AND ACCEPTANCE.
(A) General:
Sampling for the determination of gradation, liquid limit, and plasticity index for the various types of aggregate, as defined in Article 5203, will be performed as outlined below in (B) and (C). Acceptance of the applicable type of aggregate will also be based upon the requirements listed below. Testing of all samples shall be in accordance with Subarticle 5206(D).
(B) Type A Aggregate:
For sampling and acceptance purposes, a lot will be considered to be 1000 tons or fraction thereof.
For each lot of aggregate placed on the road, 2 samples will be taken at random locations on the road prior to compaction.
To be acceptable, the average test results shall meet the gradation requirements shown in Column B of Table 5201 and the range between the test results of the 2 samples shall not exceed the requirements of Column D of Table 5201. When the average test result exceeds the gradation limits given in Column B but fails within the limits given in Column C, the lot shall be rejected and shall be removed and replaced by the contractor, or at the option of the Contractor, the lot may be left in place and the material will be considered as being reasonably acceptable in accordance with the provisions of Article 1053, and an adjustment in contract unit price will be made as follows:
The number of points shown in Column E of Table 5201 will be assigned to the lot involved on an accumulative basis for each percent that the base material is outside the gradation range shown in Column B. Price adjustments will be made by reducing the contract unit price by 2 percent for each point assigned.
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| Column E | |||||
| 1 1/2" | ||||||||
| 1" | ||||||||
| 1/2" | ||||||||
| # 4 | ||||||||
| # 10 | ||||||||
| # 40 | ||||||||
| # 200a | ||||||||
| # 200b | ||||||||
a This requirement will be applicable unless otherwise specified in the special provisions.
b This requirement will be applicable only when specified in the special provisions.
When the test results for a lot exceed the gradation shown in Column C of Table 5201, the lot will be rejected and shall be removed and replaced by the Contractor at no cost to the Department. When so rejected, the Contractor may request the Engineer to take and test additional samples from within the lot. The Engineer will take 2 additional random samples from within the lot. When the average test results of the additional samples fall within the gradation limits as shown in Column B of Table 5201 and the range between the test results of the two samples does not exceed that given by Column D of Table 5201, the lot shall be acceptable. If, however, the average gradation of the 2 additional examples exceeds the limits of Column B but falls within the limits established by Column C, the lot shall be rejected and shall be removed and replaced by the Contractor, or at the option of the Contractor, the lot may be left in place and the material will be considered as being reasonably acceptable in accordance with the provisions of Article 1053 and an adjustment in contract unit price will be made as indicated above.
When the test results for the 2 samples used to determine the average test result for acceptance exceed the range established by Column D of Table 5201, the lot will be judged to be nonuniform and acceptance will be made in accordance with Article 1053 and an adjustment in contract unit price will be made as follows:
The number of points shown in Column E of Table 5201 will be assigned to the lot involved on an accumulative basis for each percent that the range between the test results of the 2 samples exceeds those values given in Column D. Price adjustments will be made by reducing the contract unit price by 2 percent for each point assigned. The unit price adjustment for nonuniform base material will be in addition to any price adjustment determined necessary for average gradation.
Any lot having an assigned accumulative gradation and range total of 50 or more points will be rejected and shall be replaced by the Contractor at no cost to the Department, unless otherwise approved by the Engineer.
Where visual observation indicates the need to do so, the Engineer may require the Contractor to road mix areas of nonuniform gradation at no additional cost to the Department. 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 given in Column C of Table 5201 and the nonuniformity cannot be corrected by road mixing, the aggregate base course represented by the sample will be rejected and replaced by the Contractor at no cost to the Department.
When the test results for either the lot or additional samples taken within the lot indicate the material is to be rejected and removed by the Contractor, and the test results can be corrected by the addition of fine aggregate, the Engineer may allow the material to be corrected provided there is no cost to the Department for furnishing, remixing, reshaping, and recompacting of the base material. The average test result of the corrected material shall be within the gradation limits shown in Column B of Table 5201 and the range between the test results shall not exceed the requirements of Column D of Table 5201, otherwise the base material will be rejected and shall be replaced at no additional cost to the Department, unless otherwise determined by the Engineer.
In addition to the gradation acceptance requirements listed in Table 5201, the material passing the No. 40 sieve shall not have a liquid limit in excess of 30 nor a plasticity index in excess of 5. (See Standard Special Provisions) If any individual test results indicates values exceeding these, the Engineer may reject the entire lot.
(C) Type B Aggregate:
(1) General:
To be acceptable, the material shall have been stockpiled, sampled, tested, and approved in accordance with the provisions of Subarticle 5206(C)(2) and subsequently placed on the roadway, sampled, tested, and approved in accordance with the provisions of Subarticle 5206(C)(3).
(2) Stockpile:
A stockpile sampling unit shall consist of approximately 2000 tons of base material in a layer of approximately 2 feet in thickness which has been constructed in thoroughly mixed sublayers of approximately 8 inches of thickness. The acceptance lot size shall be the entire stockpile subject to the provisions of this article.
The base material shall contain approximate optimum moisture when placed in the stockpile. When more than 2000 tons of base material is to be placed in a stockpile layer, the layers shall be divided into sections of approximately 2000 tons and each section identified by properly maintained corner stakes as the work proceeds.
For each sampling unit, 2 random samples shall be taken. The gradation test results of these samples shall be averaged and the average shall be used to determine the acceptability of the unit.
Where a unit fails to meet the specification requirements of Article 10103(B) the unit represented shall be removed from the stockpile or covered by spreading the required amount of corrective material over the surface of the unit. Correction will not be allowed when the amount of corrective material required exceeds 5 inches (See Standard Special Provisions) in depth in which case the unit will be rejected and shall be removed from the stockpile.
In addition to the gradation acceptance requirements listed in Table 10102, the material passing the No. 40 sieve shall not have a liquid limit in excess of 30 nor a plasticity index in excess of 6. If any individual test results indicates values exceeding these, the Engineer may reject the entire lot.
Sampling of a replaced unit will be performed in the same manner as the original sampling. Resampling of a corrected unit will be done in accordance with procedures established by the Department. Copies of these procedures are available upon request from the Materials and Tests unit.
The completed stockpile will be approved only when the average of all the individual unit gradation test results meet the requirements for Subarticle 10103(B) for a completed stockpile.
The minimum height of an approved stockpile layer shall not be less than 5 layers. The material shall be removed from the stockpile by loading from the bottom edge of the pile.
No additional material shall be placed on a stockpile which has been completed and approved.
Where more than one stockpile is constructed for a project, they shall not overlap and proper identification shall be maintained on each stockpile at all times.
(3) Roadway:
For sampling and acceptance purposes, a lot shall consist of 20,000 tons of ABC material or fraction thereof.
The sampling procedure shall consist of randomly selecting 1000 tons of base from the first 5000 tons of material placed, excluding the first 1000 tons, and taking 2 samples from the selected 1000 tons at random locations.
The gradation test results of the 2 samples will be averaged and the average will be used to determine the acceptability of the lot.
The gradation indicated in Table 5201, Column C, will be used for determining acceptance of the ABC Type B material. When the average gradation test results fall within the limits of Column C, the entire 20,000 ton lot will be accepted.
When the average gradation test results fall outside the limits of Column C, the following steps will be followed:
1. Additional sampling of the 5000 tons of material shall be in order to isolate the unacceptable material. The procedure for this additional sampling shall consist of dividing the 5000 tons of material into two 2500 ton sub-lots and taking 2 samples at random locations from each of these two sub-lots. The gradation results of the 2 samples shall be averaged and this average shall be used to determine the acceptance of each of the sub-lots.
When the average gradation test results for a sub-lot is within the limits shown in Table 5201, Column C, the sub-lot will be considered acceptable.
When the average gradation test results for a sub-lot exceeds any of the limits shown in Table 5201, Column C, and the sub-lot cannot be corrected by the addition of fine aggregate or when the average gradation of a corrected sub-lot exceeds any of the limits of Table 5201, Column B, the sublot will be rejected and shall be removed and replaced at no additional cost to the Department unless otherwise approved by the Engineer. The replacement material shall meet the specification requirements for Type A aggregate or Type B aggregate depending on the source of the material.
When the average gradation test results for a sub-lot exceeds any of the limits shown in Table 5201, Column C, and the test results indicate the material can be corrected by the additional of fine aggregate, the Engineer may allow the material to be corrected provided there is no additional cost to the Department for furnishing, adding, remixing, reshaping, and recompacting of the added material. When the average gradation test results of the corrected sub-lot are within the limits shown in Table 5201, Column B, the sub-lot will be considered acceptable.
2. A new lot, comprising 20,000 tons of ABC or fraction thereof placed after the 5000 tons addressed in Step No. 1 above, will be designated and the sampling procedure of Subarticle 5206(C)(3) shall be followed.
In the event of failures of 2 consecutive lots, the Department will withdraw its approval of Type B ABC and the material will be sampled, tested, and accepted in accordance with the provisions of Subarticle 5206(B) for Type A aggregate.
(D) TESTING.
Testing will be performed at the Department laboratory, except where the Contractor has requested and the Engineer has agreed to perform on site testing. The Contractor shall make available, a laboratory meeting the requirements of Article 5207, and samples may be tested at the Contractor's laboratory.
520-7 CONTRACTOR FURNISHED LABORATORY.
Laboratories and equipment furnished by the Contractor for on site testing in accordance with the provisions of Subarticle 5206(D) for the use of Department personnel in testing aggregate material shall meet the approval of the Engineer. The laboratory shall have a minimum floor space of approximately 160 square feet and a minimum interior height of approximately 7 feet. The laboratory shall have facilities for proper heating and ventilation, and shall be provided with electricity and a water supply.
A list of the testing equipment required will be furnished by the Materials and Tests Unit.
The Contractor shall maintain the laboratory and testing equipment in a satisfactory condition.
The laboratory shall be used exclusively for testing purposes by the Engineer.
Within 48 hours after beginning the placing of a layer of the base, the Contractor shall begin machining and compacting of the layer. Each layer shall be maintained to the required cross section during compaction and each layer be compacted to the required density prior to placing the next layer.
Each layer of the base shall be compacted to a density equal to at least 100% of that obtained by compacting a sample of the material in accordance with AASHTO T180 as modified by the Department. Copies of these modified testing procedures are available upon request from the Materials and Test Unit.
Where the Engineer elects to use nuclear methods to determine the density, the requirements for density shall be as specified in Article 52010.
The base material shall be compacted at a moisture content which is approximately that required to produce a maximum density indicated by the above test method. The Contractor shall dry or add moisture to the material when required to provide a uniformly compacted and acceptable base.
The final layer of base material shall be shaped to conform to the lines, grades, and typical as shown on the plans or established by the Engineer. When completed, the base course shall be smooth, hard, dense, unyielding, and well bonded. A broom drag may be used in connection with the final finishing and conditioning of the surface of the base course.
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.
The thickness of the base shall be within a tolerance of plus or minus 1/2 inch of the base thickness required by the plans.
The maximum differential between the established grade and the base within any 100 foot section shall be 1/2 inch.
520-10 DENSITY DETERMINATION BY NUCLEAR METHODS
(A) Application:
The Engineer may, at his option, utilize nuclear methods as described below to determine the density of selected base course materials required by Sections 520, 540, and 541. The use of nuclear methods will include the establishment of the required density through the use of control strips constructed from materials actually being used on the project, and the determination of the density being obtained in test sections located throughout the project.
Testing will be performed in the direct transmission mode on all aggregate base course. Additional information on testing is provided in the N.C.D.O.T. Nuclear Gauge Operators Manual. Copies are available upon request from the Materials and Tests Unit.
(B) Control Strip:
(1) General:
A control strip is a section of material being tested having a minimum area of 400 square yards unless otherwise approved by the Engineer; and a layer depth not greater than the layer depth shown in the plans or required by the Specifications, whichever is less. Roadway control strips may be used to determine required density for shoulder material when approved by the Engineer. When shoulder control strips are deemed necessary by the Engineer, they shall be constructed to the full shoulder width. The location of a control strip shall be as directed by the Engineer. The material used in constructing the control strip shall consist of material from the same source and shall be of the same type of material being tested. Each control strip is to remain in place and become a portion of the completed project. At least one control strip shall be constructed when a change is made of the source of materials, when a significant change occurs in the composition of the materials from the same source, or when deemed necessary by the Engineer.
(2) Equipment:
Equipment used in compaction of control strips shall have been approved by the Engineer prior to use. Where uniform density is not being obtained throughout the depth of the layer of material being tested, the type and/or weight of the compaction equipment shall be changed as necessary to achieve uniform density even though such equipment has been previously approved by the Engineer.
When aggregate base course material is involved, at least one of the rollers shall be a steel wheel vibratory roller weighing not less than 6 tons.
(3) Compaction:
After the material in a control strip is spread and shaped to the required width and depth, the compaction of the material shall begin. Compaction shall be carried out in such a manner as to obtain uniform maximum density over the entire control strip.
When aggregate base course material is being compacted, it shall have a moisture content satisfactory to the Engineer immediately before compaction. If it is necessary to add water after the material is placed, the material shall be scarified and the water added uniformly throughout the full depth of the layer of the base course material.
(4) Target Density:
After the Contractor has completed compaction of the control strip, the Engineer will conduct 10 density tests at random locations within 10 equal segments of the control strip. The surface of the material being tested shall be smooth prior to any tests being performed. The results of the 10 tests will be averaged and the resulting average density will be the target density for all test sections being constructed in conjunction with a particular control strip. The required density will be expressed as a percentage of the target density.
When aggregate base course control strips are being constructed, the 10 random tests will not be made when the surface of the aggregate base course contains free moisture. In addition to determining the nuclear target density, a conventional density test No. 3 (ring test) will be performed in the control strip to assure the final density of the control strip is at least equal to 100% of that obtained by compacting a sample of the material in accordance with AASHTO T180 as modified by the Department. Copies of these modified testing procedures and conventional density test No. 3 procedures are available upon request from the Materials and Test Unit. If the density as determined by conventional density test No. 3 meets the required density, the control strip will be accepted for use. If it fails to meet the required density, additional compactive effort shall be expended by the Contractor on the strip or a new control strip shall be constructed. No aggregate base course density tests will be performed until an acceptable control strip has been constructed.
(C) Test Sections:
(1) General:
A test section is the testing unit for compaction. The material used in a test section shall be from the same source and shall be of the same type as the material used in the application control strip. The depth of a test section shall be equal to that of the control strip previously constructed for use with the test section involved except in cases where roadway for control strips are used to determine required density for shoulder material. The length of a test section shall be determined by the width as shown in the Nuclear Gauge Operator's Manual. Copies of this manual may be obtained from the Materials and Tests Unit.
(2) Acceptance Requirements:
The required density for aggregate base course shall be 98% of the nuclear target density. In addition, the nuclear density at any test location shall be at least 95% of the nuclear target density. Density tests will not be made when the surface of an aggregate base course contains free moisture.
The required density will be determined by the average of 5 nuclear density tests made at random locations within 5 equal segments of the test section.
Where the base material is placed in a trench section, the Contractor shall provide adequate drainage through the shoulders to protect the subgrade and base until such time as the shoulders are completed.
The Contractor shall maintain the surface of the base by watering, machining, and rolling or dragging when necessary to prevent damage to the base by weather or traffic.
Where the base or subgrade is damaged, the Contractor shall repair the damaged area; reshape the base to required lines, grades, and typical sections; and recompact the base to the required density at no cost to the Department.
The quantity of aggregate base course to be paid for will be the actual number of tons of aggregate which has been incorporated into the completed and accepted work.
The aggregate will be measured by being weighed in trucks on certified platform scales or other certified weighing devices. If permitted by the special provisions, the weight of base course material shipped by barge may be determined from water displacement measurements.
No deductions will be made for any moisture contained in the aggregate at the time of weighing.
The above prices and payments will be full compensation for all work covered by this section including but not limited to furnishing aggregate and water, mixing, hauling, spreading materials, compacting, shaping, applying a sand seal in accordance with the provisions of Article 5205, and maintaining the base.
Payment will be made under:
Aggregate Base Course Ton