ITEM 207 – PORTLAND CEMENT TREATED PLANT MIX BASE COURSE

207.1 Description

This item shall consist of a foundation for surface course composed of aggregate, Portland cement and water in proper proportions, mix by a travel plant or in a central plant, spread and compacted on a prepared subgrade/subbase in one or more layers, in accordance with this Specification and the lines, grades, thickness and typical cross-sections shown on the Plans or as established by the Engineer.

207.2 Material Requirements

207.3 Construction Requirements

207.3.1 Weather Limitations

Portland Cement shall not be applied during windy, rainy or impending bad weather. In the event rain occurs during the operations, work shall be promptly stopped and the entire section shall be reconstructed in accordance with this Specification.

207.3.2 Travel Plant Method

The salvaged or new soil-aggregate shall be pulverized until at least 80 mass percent of all material other than stone or gravel will pass a 4.75 mm (No. 4) sieve.

Any material retained on a 50 mm sieve and other unsuitable material shall be removed. If additional material is specified, it shall be blended with existing material. All butt joints at existing pavements or other structures shall be cleaned prior to mixing.

The subgrade/subbase shall support all equipment required in the construction of the base course. Soft or yielding areas shall be corrected prior to mixing.

The soil-aggregate to be treated shall be placed in uniform windrow and spread to a uniform thickness to the required width. The specified quantity of Portland Cement shall be applied uniformly in a trench on top of the windrows or spread uniformly over the soil-aggregate. Spread cement that has been lost shall be replaced, without additional compensation, before mixing is started.

Mixing shall be accomplished by means of a mixer that will thoroughly blend the cement with the soil-aggregate. The mixer shall be equipped with a water metering device that will introduce the required quantity of water during the mixing cycle. The cement soil-aggregate mixture shall be sufficiently bended to prevent the formation of cement balls when water is applied.

A maximum time of 2 hours shall be permitted for wet mixing, laydown, and finishing when this method is used.

207.3.3 Central Plant Method

The soil-aggregate shall be proportioned and mixed with cement and water in a central mixing plant. The plant shall be equipped with feeding and metering devices which will introduce the cement, soil-aggregate and water into the mixer in the quantities specified. Mixing shall continue until a uniform mixture has been obtained.

207.3.4 Spreading, Compacting and Finishing

The mixture shall be spread on a prepared and moistened subgrade/subbase in a uniform layer by an approved equipment. Not more than 60 minutes shall elapse between the start of mixing and the time of starting compaction of the spread mixture.

After spreading, the mixture shall be compacted and finished conforming to the procedures/requirements specified under Subsections 203.3.6, Spreading, Compacting and Finishing.

The compaction and finishing shall be completed within 2 hours of the time water is added to the mixture.

207.3.5 Protection, Curing and Maintenance

The completed cement treated base shall be cured with a bituminous curing seal applied as soon as possible after the completion of final rolling. The surface shall be kept moist until the seal is applied.

The rate of application shall be between 0.5 L/m2 to 1.00 L/m2 of surface. The exact rate will be determined by the Engineer. Curing seal will be applied in sufficient quantity to provide a continuous film over the base. The film shall be maintained at least 5 days unless the treated base is protected by a subsequent course.

The Contractor shall be responsible for adequate maintenance of the base at all times as specified under Subsection 203.3.7, Protection, Curing and Maintenance.

207.3.6 Trial Sections

Same as Subsection 203.3.8.

207.3.7 Tolerances

Same as Subsection 203.3.9.

207.3.8 Traffic

Same as Subsection 203.3.10.

207.4 Method of Measurement

Portland Cement Treated Plant Mix Base Course will be measured by the cubic meter (m3). The quantity to be paid for shall be the design volume compacted in-place as shown on the Plans, accepted in the completed course. No allowance shall be given for materials placed outside the design limits shown on the cross-sections. Trial sections shall not be measured separately but shall be included in the quantity of Portland Cement Treated Plant Mix Base Course.

207.5 Basis of Payment

The accepted quantities, measured as prescribed in Section 207.4, shall be paid for at the contract unit price for Portland Cement Treated Plant Mix Base Course which price and payment shall be full compensation for furnishing and placing all materials, including all labor, equipment, tools and incidentals necessary to complete the work prescribed in this Item.

Payment will be made under:

Pay  Item Number	Description	Unit of Measurement
207	Portland Cement Treated Plant Mix Base Course, (New or Salvaged) Soil-Aggregate	Cubic Meter