The Table of Contents for this section is available.
The work covered by this section consists of constructing and curing a soil-cement base by treating the subgrade, existing subbase, existing base, or any combination of these materials, by pulverizing, adding portland cement, mixing, wetting, compacting and finishing the mixture to the required density. This treatment may be applied to natural ground, embankment, or an existing pavement structure. The work shall be constructed in conformity with the typical sections, lines, and grades shown on the plans or as established by the Engineer, and in accordance with these specifications.
All materials shall meet the requirements of Division 10 shown below:
Portland cement, Type I Article 1024-1
Water Article 1024-4
Soil material shall consist of the material existing in the area to be paved, of approved borrow material, or of a combination of these materials proportioned as directed by the Engineer. The soil shall be free from vegetation, roots, or other objectionable matter, and shall not contain aggregate or stone larger than 2 inches.
The soil-cement base shall not be constructed from November 1 to March 31. Soil-cement base shall not be constructed when the air temperature is below 40F in the shade nor when conditions indicate that the temperature may fall below 40F within 24 hours. No materials shall be placed on or mixed with frozen subgrade. The base shall be protected from freezing for a period of 6 (See Standard Special Provisions) days after completion. The work shall be performed only during daylight hours except as otherwise provided in the special provisions or the traffic control plans.
No soil-cement base shall be constructed that will not be covered with a layer of base or pavement by December 1 of that year. Failure of the Contractor to cover the soil-cement base as required above will result in the Engineer notifying the Contractor in writing to cover the soil-cement 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 a 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.
(A) General:
Any combination of machines or equipment that are in good safe working condition that will produce the required results may be used upon approval of the Engineer, except where certain types of equipment are specified in the project special provisions. Equipment necessary for the proper prosecution of the work shall be on the project and have been approved by the Engineer prior to its use in the construction operations. The machines and equipment shall be maintained in a satisfactory operating condition at all times during use. Leakage of water, oil, grease, or other objectionable material shall be corrected promptly or the Engineer may order such equipment removed from the work and replaced with satisfactory equipment. Equipment used to apply water, curing seal, and blotting sand shall be of such type and weight that it will not damage the base.
(B) Cement Spreaders:
A mechanical spreader shall be used which has an adjustable rate of flow and the capability of spreading the required amount of cement in one pass.
(C) Water Distribution Equipment:
Water shall be added to the soil with a pressure distributor or other suitable equipment capable of uniformly distributing the required amount.
(D) Mixers:
All mixing shall be done with a self-propelled rotary mixer, except that disc harrows, motor graders, and other equipment may be used only to supplement the mixing done by the rotary mixer.
All mixing equipment shall be capable of mixing to a compacted depth of at least 10 inches.
(E) Compaction Equipment:
All compaction equipment shall be self-propelled. Finish rolling shall be accomplished with a pneumatic-tire roller or if permitted by the Engineer, a smooth steel-wheel roller.
(F) Scarifying Equipment:
A grader-scarifier shall be used for the initial scarification of the soil. The equipment shall be capable of scarifying the soil to the full depth of the stabilized treatment. When required by the Engineer, scarifying during finishing operations shall be done with a weeder, spiketooth harrow, or nail drag, followed by a broom drag.
Prior to the addition of any cement to the soil, the area to be stabilized shall be graded and shaped in close conformity to the typical sections, lines, and grades shown on the plans or established by the Engineer. Drying or addition of moisture shall be done where necessary prior to the application of cement. The subgrade shall be firm and able to support the construction equipment and the compaction operations specified. Soft or yielding subgrade shall be corrected and made stable before construction proceeds.
The soil in the area to be stabilized shall be scarified to the required depth and width prior to application of cement. Pulverizing with a rotary mixer will follow scarifying except that it may be deleted in areas where, if determined by the Engineer, the soil types or conditions make pulverizing with a rotary mixer impractical.
When the Contractor has brought the subgrade to the elevation required by the plans or as directed by the Engineer, the Engineer will sample the soil to be stabilized in order to determine the quantity of cement to be incorporated. The Contractor shall incorporate 45 days in his schedule to allow the Engineer sufficient time to perform the required sampling, testing, and final design of the cement stabilization.
Cement shall be incorporated into the mix at the rate shown on the plans or as designated by the Engineer. The quantity of cement required for the full depth of treatment shall be uniformly spread over the surface in one pass. Cement shall not be applied on excessively wet grade or on windy days.
The percentage of moisture in the soil material, at the time of cement application, shall be the amount that assures a uniform mixture of soil material and cement during the mixing operation. It shall not exceed the optimum moisture content established by the Engineer for the soil-cement mixture except by permission of the Engineer.
The optimum moisture content and density will be determined in the field by a moisture-density test on representative samples of soil-cement mixture; however, preliminary moisture-density values may be determined by laboratory tests using soils from the project. Moisture content will be determined by the Engineer in accordance with standard test procedures used by the Department.
Cement shall be applied only to such an area that all operations shall be completed in the same day during daylight hours. The total elapsed time between the addition of water to the soil-cement mixture and the completion of finishing shall not exceed 4 hours. No equipment, except that used in spreading and mixing, will be allowed to pass over the freshly spread cement until it is mixed with the soil. Spread cement that has been displaced shall be replaced before mixing is started at no cost to the Department.
Immediately after the cement has been spread, it shall be mixed with the loosened soil material for the full depth of the treatment until a homogenous and uniform mixture is produced. Mixing will be considered sufficient when 100% of the mixture passes a 1/2 inch sieve and a minimum of 80% passes a No. 4 sieve, exclusive of any aggregate.
Immediately after mixing the soil and cement, any additional water that is necessary shall then be added to bring the moisture content to not below or more than 2 percentage points above the optimum moisture content as determined by the Engineer. If moisture content exceeds the specified range, the soil-cement mixture may, if approved by the Engineer, be manipulated by remixing or blading to reduce the moisture content to within the specified range. Excessive concentrations of water as well as wet spots or streaks on or near the surface shall be avoided. After all mixing water has been applied, mixing shall continue until a uniform mixture is obtained at the required moisture content. Operations of cement spreading, water application, and mixing shall result in a uniform soil, cement, and water mixture for the full depth and width of the area being treated. Any soil and cement mixture that has not been compacted and finished shall not remain undisturbed for more than 30 minutes.
Compaction of the mixture shall begin immediately after the mixing operation is completed. At the start of compaction, the percentage of moisture in the mixture shall not be below or more than 2 percentage points above the optimum moisture content, and shall be less than the quantity which will cause the soil-cement mixture to become unstable during compaction and finishing. The mixture shall be compacted to at least 97% of that obtained by a moisture-density test using AASHTO T134 as modified by the Department. Copies of these modified testing procedures are available upon request from the Materials and Tests Unit.
Prior to compaction, the mixture shall be in a loose condition for its full depth. The loose mixture shall then be compacted uniformly to the specified density. During the compaction operations, initial shaping may be required to obtain uniform compaction and required grade and cross-section.
When initial compaction is nearing completion, the surface of the soil-cement shall be shaped to the required lines, grades, and cross-section. The moisture content of the surface material shall be maintained at not less than optimum during finishing operations.
If necessary, the surface shall be lightly scarified to remove any tire imprints or smooth surfaces left by equipment. Compaction shall then be continued until uniform and adequate density is obtained.
Compaction and finishing shall be done in such a manner as to produce a dense surface free of compaction planes, cracks, ridges, or loose material.
When rain causes excessive moisture, the entire section shall be reconstructed. Where such reconstruction is necessary, all work and cement required shall be furnished at no cost to the Department.
The compacted thickness of the completed soil-cement base will be determined by measurements made in test holes located at random intervals not to exceed 500 feet. The measured thickness shall not deviate from that shown on the plans or established by the Engineer by more than plus 1 inch or minus 1/2 inch.
Where the base is deficient in thickness by more than 1/2 inch, the area of deficient base shall be removed and replaced by base of the required thickness at no cost to the Department.
As an exception to the above, if the deficiency is not considered sufficient to seriously impair the required strength of the soil-cement base, the deficient area may, at the discretion of the Engineer, be left in place. However, only 50% payment will be made for the base and the theoretical amount of cement used.
After the cement treated base has been finished as specified herein, it shall be cured in accordance with Section 543.
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 true vertical face.
Soil-cement for large wide areas shall be built in a series of parallel lanes 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 completed work to form a true vertical face free of loose or shattered material.
Joints shall be constructed to provide a vertical joint having adequately mixed properly compacted material immediately adjacent to the joint. A longitudinal joint adjacent to partially hardened soil-cement built the preceding day may be formed by cutting back into the previously constructed area during mixing operations. Guide stakes shall be set for cement spreading and mixing if deemed necessary by the Engineer.
Completed sections of the base may be opened when necessary to light-weight 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 for hauling except as necessary to discharge into the spreader during paving operations.
The Contractor shall maintain the soil-cement 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 no 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 soil-cement mixture to the existing layer of base.
The quantity of base to be paid for will be the number of square yards of base which has been completed and accepted. In measuring this quantity, the width of the base will be measured across the top surface of the base. The length will be the actual length constructed, measured along the centerline of the surface of the base.
The quantity of portland cement to be paid for will be the number of tons of cement which 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, measured as provided in Article 54216, will be paid for at the contract unit price per square yard for "Soil-Cement Base."
The quantity of portland cement, measured as provided in Article 54216, will be paid for at the contract unit price per ton for "Portland Cement for Soil-Cement Base."
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 cement and water; preparation of the roadbed; the hauling, proportioning, spreading, and mixing of the materials; furnishing portland cement at the point where it is proportioned and incorporated into the mix; manipulating, compacting, and finishing the base; maintaining the base; making repairs for corrections to the base; and applying sand seal in accordance with Article 5423.
Payment will be made under:
Soil-Cement Base Square Yard
Portland Cement for Soil-Cement Base Ton