The Table of Contents for this section is available.
The work covered by this section consists of the construction of a cement treated base composed of aggregate, portland cement, and water which are mixed at a central plant and placed on a prepared subgrade. The base shall be compacted, shaped, and cured to conform to the lines, grades, depths, and typical sections shown on the plans or established by the Engineer.
All materials shall meet the requirements of Division 10 shown below:
Aggregate Article 1010-5
Portland cement, Type I Article 1024-1
Water Article 1024-4
Cement treated base shall not be constructed from November 1 to March 31 inclusive. Base shall not be constructed when the air temperature is less than 40F in the shade nor when conditions indicate that the temperature may fall below 40F within 24 hours. No frozen materials shall be incorporated into the mixture and no material shall be placed on frozen subgrade. The base shall be protected from freezing for a period of 7 days after completion. Work shall be performed only during daylight hours unless otherwise provided by the provisions of the traffic control plans.
No cement treated base shall be placed that will not be covered with pavement by December 1 of that year. Failure of the Contractor to cover the cement treated base as required above will result in the Engineer notifying the Contractor in writing to cover the cement treated base with a sand seal. The sand seal shall be applied in accordance with the requirements of Section 660 except that Articles 6603, 66011, and 66012 will not apply. This work shall be performed by the Contractor at no cost to the Department. In the event the Contractor fails to apply the sand seal within 72 hours after receipt of such notice, the Engineer may proceed to have the work performed with other forces and equipment. The cost of such work performed by other forces will be deducted from monies due or to become due the Contractor. The application of the sand seal by the Contractor or other forces will in no way relieve the Contractor of the responsibility to maintain or repair the damaged base, no matter what the cause of damage, at no cost to the Department.
When the Contractor proposes to use quarry production as the source of aggregate and when that source is not documented by a currently approved job mix formula, the Contractor shall submit to the Department's Materials and Tests Unit, samples of all aggregates proposed for use at least 3 weeks prior to beginning production. The aggregate samples shall be taken by the Contractor in the presence of the Engineer. The Contractor shall also submit in writing the proposed gradation for the cement treated base material. The Department will then prepare a mix design based upon the samples submitted and the Contractor's stated proposed gradation.
A job mix formula will be established for the cement treated base material within the design limits indicated in Table 1010-4. The job mix formula shall remain in effect until modified in writing by the Engineer.
All cement treated base material mixtures shall conform to the job mix formula within the tolerance ranges specified in Table 540-1. In the event the Contractor is not able to maintain the production within the tolerance ranges specified in Table 540-1, production will cease until such time as a new mix design and job mix formula has been established and approved by the Engineer.
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540-5 CONSTRUCTION REQUIREMENTS.
(A) Preparation of Subgrade:
The subgrade shall be prepared in accordance with Section 500. The subgrade shall be firm and able to support without displacement the construction equipment and the compaction operations hereinafter specified. Soft or yielding subgrade will be corrected and made stable before construction proceeds. The subgrade shall be moistened as needed prior to spreading the base material.
(B) Mixing:
(1) General:
The quantity of cement to be added to the aggregate shall be as shown in the plans or as directed by the Engineer within the tolerance hereinafter specified.
The cement, aggregates, and water shall be thoroughly mixed in an approved central mixing plant. The mixer shall be a batch or continuous-flow type stationary mixer and shall be equipped with feeding and metering devices that will add aggregate, cement, and water into the mixer in the specified quantity. The batch weights or rates of feed of cement shall be within 0.3 percent of the quantity designated by the Engineer. The batch weights or rates of flow of the water shall be within a range of optimum to optimum plus 1.5 percent moisture. The batch weights or rates of feed of aggregate shall be within 5 percent of the amounts designated by the Engineer.
Mixing time, to assure a proper blend of materials, shall be a minimum of 20 seconds unless otherwise authorized by the Engineer.
(2) Batch Type Plant:
The mixer shall be equipped with a sufficient number of paddles of a type and arrangement to produce a uniformly mixed batch.
Water shall be added during the mixing operation as required to provide the quantity of moisture specified; however, water shall not be added to the mixture before the aggregate and cement have been mixed sufficiently to prevent the formation of cement balls.
The mixer shall be equipped with a timing device which will indicate by a definite audible or visual signal the expiration of the mixing period.
(3) Continuous Flow Type Plant:
Cement storage silos shall be calibrated and marked so that the amount of cement in the silo can be readily determined at any time. Feeders and/or meters for introducing the cement into the mixer shall be of such design that the amount of cement can be accurately determined before it is introduced into the mixer. The cement feeder shall use a variable speed motor which is regulated by a control mechanism indicating the speed of the motor in r.p.m. or equivalent measure. The indicator shall be of such design that it can be read in daylight from a point 4 feet from the indicator. The cement holding tank which is used in feeding cement shall be equipped with an air pressure gauge and air pressure regulating control such that air pressure can be regulated to a uniform flow.
The water shall be measured by a meter which determines flow in gallons per minute and shall be controlled by 2 valves. One valve shall be a variable flow valve which shall be used for controlling the rate of flow of the water only. The other shall be an on-off valve connected to the plant controls such that the water is turned on and/or off when the plant is started and stopped.
After the material has been processed by the pug mill, it shall be stored in a holding bin with the minimum capacity of 3 tons before discharging into trucks. Material shall be held in the holding bin for loading purposes only and shall not be stored for loading subsequent trucks. Loading trucks directly from a belt or auger box will not be permitted.
A satisfactory platform shall be available for obtaining samples from trucks. Provisions shall be made for calibrating the plant daily and at other times as deemed necessary by the Engineer.
On plants that are electronically controlled, manual calibration will be required to verify the electronic calibration and shall be performed at the beginning of a project. If the plant operation is interrupted by more than four (4) calendar days during an active project, the manual calibration process shall be performed again. Random manual calibrations shall also be performed at the direction of the Engineer.
(C) Hauling and Placing:
The mixed base material shall be hauled to the roadway in trucks with protective covers to avoid moisture loss. In no case shall the time between the loading of the haul trucks and the beginning of compaction exceed 1 hour.
Stringlines shall be placed by the Contractor for alignment control for placing a layer of base.
The base shall be placed in a uniform layer on the moistened, prepared subgrade to produce the depth required by the plans. To insure homogenous distribution of the base material in each layer, the material shall be placed using approved spreaders. The spreading operations shall be performed in such a manner as to eliminate pockets of material of non-uniform gradation resulting from segregation in the hauling or discharging operations. Each layer shall be spread so that compaction can be started without further shaping.
A single spreader may be used provided it is capable of placing a uniform, full-depth layer of material across the full width of the base in one pass. Otherwise, 2 or more spreaders will be required, and they shall be operated so that the spreading progresses along the full width of the base in a uniform manner unless otherwise approved by the Engineer.
Base placed on areas inaccessible to mechanical spreading equipment may be spread in one layer by methods approved by the Engineer. After spreading, the material shall be thoroughly compacted to the required lines, grades, typical sections by means of pneumatic tampers, or with other compaction equipment which will constantly obtain the degree of compaction required.
(D) Compaction:
Compaction shall begin immediately after the base has been placed on the prepared subgrade. The compacted thickness of any one layer of base shall not exceed 8 inches and shall not be less than 4 inches.
After spreading, the moisture content of the material shall be maintained within a range of optimum to optimum plus 1.5% moisture during compaction.
Compaction shall be accomplished by the use of approved self-propelled rollers except that a sheep-foot roller shall not be used for more than 2 passes. The base shall be compacted by the use of approved self-propelled rollers to a density equal to at least 97% of the maximum density 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 Tests Unit. The Engineer may, at his option, utilize nuclear methods as described in Article 52010 to determine the density of the base in lieu of the methods required above.
Final compaction, including that necessary due to correction of high or low areas, shall be completed within 3 hours after water has been added to the mixture. Any cement-aggregate mixture that has not been compacted and finished shall not remain undisturbed for more than 30 minutes. When rain causes excessive moisture, the entire section shall be reconstructed. When such reconstruction is necessary, the work of reconstruction and the cement required shall be furnished at no cost to the Department.
At the end of each day's construction, a straight transverse construction joint shall be formed by cutting back into the completed work to form a vertical face. The base for large, wide areas shall be built in a series of parallel lines of convenient length and width meeting the approval of the Engineer. Straight longitudinal joints shall be formed at the edge of each day's construction by cutting back into the completed work to form a vertical face free of loose or shattered materials. Where traffic considerations require that a longitudinal joint be exposed for an excessive length of time, the Engineer may require that it be covered with a curing seal in accordance with Section 543.
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.
After the cement treated base has been finished as specified herein, it shall be cured in accordance with Section 543.
(A) Approved Stockpile Production:
For approval, stockpiles shall be constructed and tested in accordance with Article 10105.
(B) Quarry Production:
If the average gradation test results for the lot are outside the limits established by Table 5402, Column B, but within the limits established by Column C, the lot will be accepted and an adjustment in unit price will be made by the following method:
The number of points shown in Column D, Table 5402, will be assigned to the lot on an accumulative basis for each percent the average gradation of the base materials are outside the limits of Column B, Table 5402, but within the limits of Column C, Table 5402. Price adjustments will be made by reducing the unit price of the lot by 2% for each point so assigned.
If the average gradation test results are outside the limits established by Column C, Table 5402, the Engineer will make a determination as to whether the base will serve the intended purpose. If the Engineer determines that the base will not serve the intended purpose, the base will be removed and replaced at no additional cost to the Department. If the Engineer determines that the base will serve the intended purpose it will be accepted in accordance with the provisions of Article 1053.
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Completed sections of the base may be opened when necessary to lightweight local traffic, provided the base has hardened sufficiently to prevent marring or distorting of the surface, and provided the curing is not impaired. Construction equipment shall not use the base except as necessary to discharge into the spreader during paving operations.
The Contractor shall maintain the base in an acceptable condition until final acceptance of the project. Maintenance shall include immediate repair of any defects or damage that may occur. This work shall be performed by the Contractor at not (See Standard Special Provisions) cost to the Department and shall be repeated as often as may be necessary to keep the base in an acceptable condition. Repairs to the base shall be performed by replacing the base for its full depth rather than by adding a thin layer of cement stabilized material to the existing layer of base.
The quantity of base course to be paid for will be the number of tons of base mixture which has been incorporated into the completed and accepted work. The quantity will be measured by weighing in trucks on certified platform scales or other certified weighing devices. No deduction will be made for any moisture contained in the base mixture at the time of weighting. Measuring will not be made of any base mixture added or replaced for corrective measures during construction or for repairing damaged areas.
The quantity of portland cement to be paid for will be the number of tons of cement that has been incorporated into the mix. When bulk cement is used, the quantity will be measured by weighing in trucks on certified platform scales or other certified weighing devices. Measurement will not be made of any cement added or replaced for corrective measures during construction or for repairing damaged areas.
The quantity of base course, measured as provided in Article 54012, will be paid for at the contract unit price per ton for "Plant Mixed Cement Treated Base Course".
The quantity of portland cement, measured as provided in Article 54012, will be paid for at the contract unit price per ton for "Portland Cement for Plant Mixed Cement Treated Base Course".
Asphalt curing seal will be paid for as provided in Article 5436.
Blotting sand will be paid for as provided in Article 8185.
The above prices and payments will be full compensation for all work covered by this section including but not limited to the furnishing of water and aggregate; the mixing, proportioning, hauling, and spreading of the materials; furnishing portland cement at the point where it is incorporated into the mix; manipulating, compacting, and finishing the base; maintaining the base; making repairs or corrections to the base; and applying sand seal in accordance with Article 5403.
Payment will be made under:
Plant Mixed Cement Treated Base Course Ton
Portland Cement for Plant Mixed Cement Treated Base Course Ton