309.01 252 SECTION 309 – AGGREGATE -CEMENT BASE COURSE
309.01 Description ................................ ................................ ................... 252
309.02 Materials ................................ ................................ ...................... 252
309.03 Equipm ent ................................ ................................ .................... 253
309.04 Limitations ................................ ................................ ................... 254
309.05 Preparing the Existing Subgrade ................................ .................. 254
309.06 Cement Application, Mixing, and Spreading ............................... 254
309.07 Compaction ................................ ................................ .................. 255
309.08 Finishing ................................ ................................ ...................... 256
309.09 Construction Joints ................................ ................................ ....... 256
309.10 Thickness and Surface Tolerances ................................ ............... 256
309.11 Curing ................................ ................................ .......................... 256
309.12 Traffic and Maintenance ................................ .............................. 256
309.13 Method of Measurement ................................ .............................. 257
309.14 Basis of Payment ................................ ................................ .......... 257
DESCRIPTION
309.01 Description
This work consists of constructing a base of mineral aggregate and Portland cement on a prepared surface. MATERIALS
309.02 Materials
Provide materials as specified in: Water ................................ ................................ .................. 302.03.B Portland Cement, Type I ................................ ........................ 901.01 Portland-Pozzolan Cement, Type IP ................................ ...... 901.01 Crushed Stone or Sla g, Grading D ................................ ................................ .......... 903.05 Aggregate, Crushed or Uncrushed Gravel or Chert ............... 903.15 309.03 253 Recycled Concrete Aggregate ................................ ............ 903.05.C Bituminous Material for Curing, Emulsified Asphalt, Types allowed for Tack Coat in 403 ............................... 904.03 Provide emulsified asphalt, of a type allowed for Tack Coat in 403, meeting the test requirements specified in Table 904.03-1. Submit a sample of the cement and aggregate to be used to the Materials and Tests Laboratory for approval at least 15 days before use. EQUIPMENT
309.03 Equipment
Provide a stationary mixing plant or mechanical road mixer(s).
A.Stationary Mixing Plant Provide an approved twin -shaft pugmill as specified in 303.06.A. The cement feeder shall include a surge tank between the cement supply and the pugmill. The feeder system shall be so designed that the aggregate feeder will not operate unless the cement feeder operates. During production of aggregate cement base, do not use the plant for other operations. The plant shall be capable of weighing each component and adjusting for moisture in the aggregates. Plants shall b e calibrated annually and in the presence of the Engineer if requested.
B.Mechanical Mixer (for Road Mixing) Provide pugmill or rotary type mechanical mixers capable of producing a uniform blend of all materials to the full depth of the course being placed. At least one mixer shall be capable of adding a regulated amount of water under pressure and uniformly mix ing it with the aggregate and cement. The mixers may be either self -propelled or trailer type. 309.04 254 CONSTRUCTION REQUIREMENTS
309.04 Limitations
Only process the amount of aggregate -cement base that will be covered with the succeeding stage of base or pavemen t construction during the same construction season. Do not process aggregate -cement base unless the ambient air temperature is at least 40 °F in the shade and rising. Only add cement to aggregate that is free of frost, whether the aggregate is stockpiled for plant mixing or spread for roadway mixing. For roadway mixing, limit application of cement to an area that will allow for continuous operations and for the completion of all but the final surface finish within 3 hours from the time cement is applied. When using a stationary mixing plant, spread the material, using approved mechanical spreaders, within 1 hour after being discharged from the mixer. Complete all operations except final surface finishing within 3 hours after the material is discharged fro m the mixer. Continue processing the uncompacted aggregate -cement mixture with no delay of more than 30 minutes. If the uncompacted aggregate -cement mixture is wetted by rain so that the average moisture content exceeds the specified tolerance, reconstruc t the section as specified in 304.13.
309.05 Preparing the Existing Subgrade
Before beginning other construction operations, prepare the subgrade as specified in 205, 207, or 302, whichever is applicable.
309.06 Cement Application , Mixing, and Spreading
The quantity of cement to be added to the aggregate shall range between 3% and 5%, by weight, of the dry material. The Engineer will establish the exact percentage of cement within the above range based on test results, provided by the Contractor, of the aggr egate selected for use on the project.
A.Roadway Mixing Spread the aggregate on the subgrade to the required thickness, width, and cross -section using an approved mechanical spreader. Uniformly apply the specified quantity of Portland cement over the spread 309.07 255 aggregate using an approved mechanical cement spreader. Do not apply cement if the moisture content of the aggregate exceeds by more than 4% the optimum moisture content specified by the Engineer for the aggregate -cement mixture. Replace spread cement t hat has been lost due to the Contractor’s negligence at no additional cost to the Department. Perform road mixing using mechanical mixer(s). At least one pass of the mixer may be required before adding water. When required, add water through the mixer o r by other approved methods to bring the mixture to the required moisture content. Continue mixing until a uniform mixture is obtained.
B.Stationary Mixing Plant If using a stationary plant, continue mixin g until a uniform and intimate mixture of cement, aggregate, and water has been obtained. All material fed into the plant shall travel the full length of the pugmill. Periodically check the quantity of cement expended by emptying the cement storage bin. Transport the mixture from the plant to the road in numbered trucks equipped with tight, metal, rear -end dump beds. Provide a sufficient number of trucks to ensure satisfactory progress of the construction operations. Use an approved mechanical spreader to spread the material. In mixing, handling, and placing the base material, take care to prevent segregation. Place shoulder material for a width of at least 3 feet before spreading the base material in order to confine the base material and allow satisf actory compaction along the edges of the base.
309.07 Compaction
The Contractor may use any type of compacting equipment that will produce the required result. At the start of compaction, the percentage of moisture in the mixture based on oven dry weight shall not vary more than 3% above or 1% below the specified optimum moisture. Extend rolling over the edges of the base material onto the shoulders. The Department will divide the completed base into lots of approxi mately 10,000 square yards for density testing purposes, and will perform five density tests on each lot. The average dry density of each lot shall be not less than 95% of maximum density as determined according to AASH TO T 134, and no individual test shall be less than 92% of maximum density. Rework or replace material not meeting the specified density at no additional cost to 309.08 256 the Department. At the beginning of a project or at any time it is deemed advisable, smaller lots may be considered to evaluate rolling procedures or for other reasons as approved or directed by the Engineer.
309.08 Finishing
Perform finishing operations in the same manner as specified for soil -cement base construction in 304.09.
309.09 Construction Joints
At the beginning of each day’s construction, form a straight transverse construction joint by cutting back into the completed work to form a true vertical face. Build aggregate -cement base for large, wide areas in a series of parallel lanes of convenient length and width meeting the approval of the Engineer. Form straight longitudinal joints at the edge of each day’s construction by cutting back into the completed work to form a true vertical face free of loose or shattered material.
309.10 Thickness and Surface Tolerances
The Department will determine the thickness of the base by measuring test holes dug at random locations. The measured thickness shall not deviate from that shown on the Plans by more than plus 1 -1/2 inches or min us ½ inch. Reconstruct or replace work found not to be within this tolerance as specified in 304.13. The surface of the completed base shall be in reasonably close conformity to the lines, grades, and cross -section shown on the Plans or established by the Engineer and shall have a satisfactorily smooth riding quality.
309.11 Curing
Perform curing of the finished base in the same manner as specified for soil - cement base construction in 304.12.
309.12 Traffic and Maintenance
The Contractor may open portions of completed base to traffic as specified in 304.14. 309.13 257 Maintain the completed base as specified in 304.15. COMPENSATION
309.13 Method of Measurement
The Department will m easure:
1.Mineral Aggregate for Aggregate -Cement Base Course by the ton in accordance with 109.
2.Earth moved to prepare the existing subgrade, in accordance with 309.05, as provided for under the appropriate provisions of 203 and 207.
3.Portland Cement incorporated in the work by the ton in accordance with 109.
4.Bituminous Material used for curing seal by the ton in accordance with 109.
5.Water used in mixing and finishing operations by the M.G. (1,000 gallons) using calibrated tanks or distributors, or accurate meters. The Department will deduct the weight of total moist ure, as determined by dry weights, of the base material at the time of weighing in excess of 3% of optimum moisture content. The Department will not measure or pay for water added to emulsified asphalt used for curing.
309.14 Basis of Payment
A.General The Department will pay for accepted quantities at the contract prices as follows: Item Pay Unit Mineral Aggregate Ton Portland Cement Ton 309.14 258 Bituminous Material Ton Water MG When mixing is performed in a stationary plant, the Department will not pay for wate r. When road mixing is performed, the Department will pay for water added to the material during mixing at the direction of the Engineer.
B.Adjustments Specific Gravity. In cases where the Bulk SSD specific gravity of the mineral aggregate exceeds 2.8 5, the Department will adjust the tonnage of mineral aggregate for payment by multiplying the tonnage of mineral aggregate used by a specific gravity of 2.8 5 and dividing by the higher specific gravity. 310.01 259 SECTION 310 – CONDITIONING MINERAL AGGREGATE BASE
310.01 Description ................................ ................................ ................... 259
310.02 Materials ................................ ................................ ...................... 259
310.03 Equipment ................................ ................................ .................... 259
310.04 Conditioning ................................ ................................ ................ 260
310.05 Surface Requirements ................................ ................................ .. 260
310.06 Method of Measurement ................................ .............................. 260
310.07 Basis of Pay ment ................................ ................................ .......... 261
DESCRIPTION
310.01 Description
This work consists of reshaping and compacting an existing mineral aggregate base or surface. MATERIA LS
310.02 Materials
Provide materials as specified in: Aggregate for Conditioning Base ................................ .......... 903.05 Calcium Chloride, Type 1, Type 2 or Calcium Chloride Liquor ................................ ................ 921.02 EQUIPMENT
310.03 Equipment
Provide motor graders and water distributors in the number necessary for satisfactory prosecution and completion of the work, as well as one or more rollers of a type and sufficient weight to obtain the required density and to seal the surface of the base course.
Source: Tennessee Standard Specifications for Road and Bridge Construction, 2021 Edition. Pages 261–267 of 1,072.