5-19 540-12 Maintenance
Maintain the base in an acceptable condition until final acceptance of the project. Include immediate repair of any d efects or damage that may occur in any maintenance operation. Perform this maintenance at no cost to the Department and repeat as often as may be necessary to keep the base in an acceptable condition. Perform repairs to the base 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.
540-13 Measurement and Payment
Aggregate for Cement -Treated Base Course will be measured and paid at the contract unit price per ton that 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 aggregate at the time of weighing. Measurement will not be made of any base mixture added or replaced for corrective measures during construction or for repairing damaged areas. Portland Cement for Cement -Treated Base Course will be measured and paid at the contract unit price per ton 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. When cement -treated base is produced at a commercial source for more than one project, the Engineer may elect to measure the cement based upon the cement content shown in the approved job mix formula. Measurement wil l not be made of any cement added or replaced for corrective measures during construction or for repairing damaged areas. Asphalt Curing Seal will be paid in accordance with Article 543 -5. Blotting Sand will be paid in accordance with Article 818 -4. The above prices and payments will be full compensation for all work covered by this section 25 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 542 — 3.
If the Contracto r fails to provide sand seal as required and the Engineer has the work performed by other forces, the cost of such work will be deducted from monies due or to become due to the Contractor. Payment will be made under Pay Item Pay Unit Aggregate for Cement -Treated Base Course Ton Portland Cement for Cement -Treated Base Course Ton SOIL -CEMENT BASE
542-1 Description
The work covered by this section consists of constructing and curing a soil -cement base by treating the subgrade, existing subbase or existing base, or any combination of these materials, by pulverizing, adding P ortland cement, adding aggregate when requir ed, mixing, wetting and compacting the mixture to the required density. Proportion, spread and mix the materials on the roadway; manipulate, compact and finish in accordance with the Standard Specifications and the lines, grades, depths and typical sections shown on the plans or established by the Engineer.
5-20 542-2 Materials
Refer to Division 10. Item Section Aggregate, ABC Table 1005 -1 Portland Cement, Type I 1024 -1 Water 1024 -4 Use soil material that consists of material existing in the area to be paved, approved borrow material or a combination of these materials proportioned as directed by the Engineer that is free from vegetation, roots or other objectionable matter; and does not contain aggregate or stone larger than 2 inches .
542-3 Limitations
Do not construct the soil -cement base when the air temperature is below 40 °F nor when conditions indicate that the temperature may fall below 40° F within 24 hours. Do not place or mix materials with frozen subgrade. Protect the base from freezing for 7 days after completion. Perform the work only during daylight hours except as otherwise provided in the contract. Do not construct soil -cement base that will not be covered with a layer of base or pavement by December 1 st of the same 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. Apply the sand seal in accordance with Section 660 except Articles 660 -3 and 660- 12 will not apply. I f 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 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.
542-4 Equipment
A.General Use any combination of mac hines or equipment that will produce the required results meeting the approval of the Engineer. Correct any leakage of fluids and/or materials promptly or the Engineer may order such equipment removed and replaced with satisfactory equipment. Use equipme nt and methods for applying cement, water, curing seal and blotting sand that will not damage the base and in accordance with Article 107 - 21.
B.Cement Spreaders Use mechanical spreaders that have an adjustable rate of flow and the capability of spreading the required amount of cement in one pass.
C.Water Distribution Equipment Add water to the soil with a pressure distributor or other suitable equipment capable of uniformly distributing the required amount.
D.Mixers Perform all mixing with a self -propelled rotary mixer. Disc harrows, motor graders and other equipment may be used only to supplement the mixing done by the rotary mixer. Use mixing equipment that is capable of mixing to a compacted depth of at least 10 inches .
5-21 (E) Compaction Equipment
Use self -propelled compaction equipment. Accomplish finish rolling with a pneumatic - tire roller or if permitted by the Engineer, a smooth steel -wheel roller.
F.Scarifying Equipment Use a grader -scarifier for the initial scarification of the soil. Use equipment capable of scarifying the soil to the full depth of the stabilized treatment. When required by the Engineer, use a weeder, spiketooth harrow or nail drag, followed by a broom drag when scarifying during finishing operations.
542-5 Preparation of Roadbed
Before the addition of any cement to the soil, grade and shape the area to be stabilized in accordance with the typical sections, lines and grades shown on the plans. Perform drying or addition of moisture where necessary before the application of cement. Create the subgrade so it is firm and able to support the construction equipment and compaction operations specified. Correct and make stable, soft or yielding subgrade before construction proceeds.
542-6 Scarifying
Scarify the soil in the area to be stabilized to the required depth and width before application of cement. Pulverizing with a rotary mixer will follow scarifying , except it may be deleted in areas where, if determined , the soil types or conditions make pulverizing with a rotary mixer impractical.
542-7 Application of Cement
When the Contractor has brought the subgrade to the elevation required by the plans, the Engineer will sample the soil to be stabilized in order to determine the quantity of cement to be incorporated. Incorporate 24 calendar days into the schedule to allow the Engineer sufficient time to perform the required sampling, testing and final design of the cement stabilization. Before spreading cement, aggregate shall be spread at the rate shown in the plans. Incorporate cement into the mix at the rate directed by the Engineer. Uniformly spread the quantity of cement required for the full depth of treatment over the surface in one pass. Do not apply cement on excessively wet grade or on windy days. Apply cement to the soil when the percentage of moisture in the soil material is the correct amount that assures a uniform mixtur e of soil material and cement during the mixing operation. Do not exceed the optimum moisture content established by the Engineer for the soil cement moisture except by permission. 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 accordanc e with standard test procedures used by the Department. Apply cement only to such an area that all operations shall be completed in the same day during daylight hours. Complete finishing the soil -cement mix within 4 hours of adding water to the soil- cemen t mixture. 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. Replace all spread cement that has been displaced before mixing is started.
542-8 Mixing
Immediately after the cement has been spread, mix it with the loosened soil material for the full depth of the treatment until a homogenous and uniform mixture is produced. M ixing will
5-22 be sufficient when 100% of the mixture passes a 1/2 inch sieve and at least 80% passes
a No. 4 sieve, exclusive of any aggregate. Immediately after mixing the soil and cement, add any additional water that is necessary to bring the moisture content between optimum and optimum plus 2% 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 w ithin the specified range. Avoid excessive concentrations of water as well as wet spots or streaks on or near the surface. After all mixing water has been applied, continue mixing until a uniform mixture is obtained at the required moisture content. Per form the operations of cement spreading, water application and mixing so that they result in a uniform soil, cement and water mixture for the full depth and width of the area being treated. Remix any soil and cement mixture that has not been compacted and finished within 30 minutes.
542-9 Compaction
Begin compaction of the mixture immediately after the mixing operation is completed. At the start of compaction, make sure that t he moisture in the mixture is no more than 2 % above or below the optimum moisture content and is less than the quantity which will cause the soil - cement mixture to become unstable during compaction and finishing. Compact the mixture to at least 97% of tha t obtained by a moisture -density test using AASHTO T 134 as modified by the Department. Copies of these modified testing procedures are available upon request from the Materials and Tests Unit. Before compaction, prepare the mixture in a loose condition f or its full depth. Compact the loose mixture uniformly to the specified density. During the compaction operations, initial shaping may be required to obtain uniform compaction and required grade and cross section.
542-10 Finishing
When initial compaction is nearing completion, shape the surface of the soil -cement to the required lines, grades and cross section. Maintain the moisture content of the surface material at optimum or higher during finishing operations. If necessary, lightly scarify the surface to remove any tire imprints or smooth surfaces left by equipment. Continue compaction until a unifo rm and adequate density is obtained. Perform the compaction and finishing to produce a dense surface free of compaction planes, cracks, ridges or loose material. When rain causes excessive moisture, reconstruct the entire section. Where such reconstructio n is necessary, furnish all work and cement required.
542-11 Thickness
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 f eet. Construct the soil -cement base so that the measured thickness does not deviate from that shown on the plans by more than + 1 inch or - 1/2 inch. Where the base is deficient in thickness by more than 1/2 inch, remove and replace the area of deficient base with base of the required thickness. 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 ar ea may, at the discretion of the Engineer, be left in place.
542-12 Curing
After the cement -treated base has been finished as specified herein, cure it in accordance with Section 543.
5-23 542-13 Construction Joints
Build soil- cement for large wide areas in a series of parallel l anes 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 completed work to form a true vertical face free of loose or shattered material. Constr uct joints 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 pr eviously constructed area during mixing operations. Set guide stakes for cement spreading and mixing if deemed necessary.
542-14 Traffic
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. Do not use construction equipment on the base for hauling except as necessary to discharge into the spreader during paving operations.
542-15 Maintenance
Maintain the soil cement base in an acceptable condition until final acceptance of the pro ject. Include , in maintenance operations , immediate repair of any defects or damage that may occur. Repeat as often as may be necessary to keep the base in an acceptable condition. Perform repairs to the base by replacing the base for its full depth rat her than by adding a thin layer of soil -cement mixture to the existing layer of base.
542-16 Measurement and Payment
Soil Cement Base will be measured and paid at the contract unit price per square yard that 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. Measurement will not be made of any base added or replaced for corrective measures during construction or for repairing damaged areas. Aggregate for Soil Cement Base will be measured and paid in tons at the contract unit price per ton. The aggregate will be measured by weighing in trucks or certified platform scales or other certified weighing devices. No deductions will be made for any moisture contained in the aggregate at the time of weig hing. Portland Cement for Soil Cement Base will be paid at the contract unit price per ton 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 certifi ed weighing devices. Measurement will not be made of any cement added or replaced for corrective measures during construction or for repairing damaged areas. Asphalt curing seal will be paid as provided in Article 543 -5. Blotting Sand will be paid as prov ided in Article 818 -4. If a layer of Soil Cement Base is deficient in thickness but has been permitted to be left in place in accordance with Article 5 42-11, payment for that Soil Cement Base will be made at 50% of the contract unit prices for Soil Cement Base . Sand seal applied due to the failure of the Contractor to cover the Soil Cement Base as required will be incidental to the work of this section. If the Contractor fails to provide sand seal as required and the Engineer has the work performed by othe r forces, the cost of such work will be deducted from monies due or to become due to the Contractor. Payment will be made under :
Source: North Carolina Standard Specifications for Roads and Structures, 2024 Edition. Pages 247–251 of 857.