Attachment 5 - SC HMA Division 300 - SOW.pdf

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May 2004 Bases and Subbases 300-i

Table of Contents Section Page

300 GENERAL GUIDELINES...........................................................................................300-1

300.1 INTRODUCTION...................................................................................................300-1

300.2 PAVEMENT CONSTRUCTION: OVERVIEW .......................................................300-1

300.2.1 Pavement Structure ......................................................................................300-1

300.2.2 Subgrade Foundation ...................................................................................300-2

300.2.3 Base Structure ..............................................................................................300-2

300.2.3.1 Subbase ...............................................................................................300-2

300.2.3.2 Base Course ........................................................................................300-2

300.2.4 Surface Structure..........................................................................................300-3

300.2.5 Geosynthetic Material Considerations ..........................................................300-3

300.3 SUMMARY OF INSPECTION DUTIES .................................................................300-3

301 CEMENT MODIFIED SUBBASE...............................................................................301-1

301.1 DESCRIPTION OF WORK....................................................................................301-1

301.2 PRECONSTRUCTION CONSIDERATIONS.........................................................301-1

301.2.1 Contract Document Review ..........................................................................301-1

301.2.2 Coordination of Project Personnel ................................................................301-2

301.2.3 Material Considerations ................................................................................301-2

301.2.3.1 Subgrade Material ................................................................................301-2

301.2.3.2 Portland Cement and Water.................................................................301-2

301.2.3.3 Asphalt Prime Coat ..............................................................................301-2

301.2.4 Weather Considerations ...............................................................................301-2

301.2.5 Sampling and Testing Considerations ..........................................................301-2

301.2.6 Subgrade Inspection and Approval...............................................................301-3

301.3 INSPECTION DURING CONSTRUCTION ...........................................................301-3

301.3.1 Scarification Operation .................................................................................301-3

301.3.2 Application of Portland Cement ....................................................................301-3

301.3.2.1 Moisture Content and Rate of Application............................................301-3

301.3.2.2 Spreading of Cement ...........................................................................301-4

301.3.3 Mixing Operation...........................................................................................301-4

301.3.3.1 Traveling Mixing Plant ..........................................................................301-4

301.3.3.2 Dry Mixing ............................................................................................301-4

300-ii Bases and Subbases May 2004

Table of Contents (continued)

301.3.3.3 Application of Water .............................................................................301-4

301.3.3.4 Wet Mixing ...........................................................................................301-4

301.3.3.5 Core Molding........................................................................................301-4

301.3.4 Compaction Operation..................................................................................301-5

301.3.4.1 Moisture Content ..................................................................................301-5

301.3.4.2 Density Testing ....................................................................................301-5

301.3.5 Finishing Operation.......................................................................................301-5

301.3.6 Curing Operation ..........................................................................................301-6

301.4 POST-CONSTRUCTION CONSIDERATIONS .....................................................301-6

301.4.1 Construction Joints .......................................................................................301-6

301.4.2 Checking Subbase Thickness ......................................................................301-6

301.4.3 Traffic and Maintenance Considerations ......................................................301-7

301.5 DOCUMENTATION AND PAYMENT CONSIDERATIONS ..................................301-7

302 SOIL-AGGREGATE SUBBASE................................................................................302-1

302.1 DESCRIPTION OF WORK....................................................................................302-1

302.2 PRECONSTRUCTION CONSIDERATIONS.........................................................302-1

302.2.1 Contract Document Review ..........................................................................302-1

302.2.2 Coordination of Project Personnel ................................................................302-1

302.2.3 Materials Considerations ..............................................................................302-1

302.2.4 Weather Considerations ...............................................................................302-2

302.2.5 Sampling and Testing Considerations ..........................................................302-2

302.2.6 Subgrade Inspection and Approval...............................................................302-2

302.3 INSPECTION DURING CONSTRUCTION ...........................................................302-2

302.3.1 Application of Aggregate Material .................................................................302-2

302.3.2 Mixing Operation...........................................................................................302-2

302.3.3 Compaction Operation..................................................................................302-3

302.3.4 Finishing Operation.......................................................................................302-3

302.3.5 Application of Asphalt Prime Coat ................................................................302-3

302.4 POST-CONSTRUCTION CONSIDERATIONS .....................................................302-3

302.5 DOCUMENTATION FOR PAYMENT....................................................................302-3

303 SAND-CLAY BASE COURSE...................................................................................303-1

303.1 DESCRIPTION OF WORK....................................................................................303-1

303.2 PRECONSTRUCTION CONSIDERATIONS.........................................................303-1

May 2004 Bases and Subbases 300-iii

303.2.1 Contract Document Review ..........................................................................303-1

303.2.2 Coordination of Project Personnel ................................................................303-1

303.2.3 Material Considerations ................................................................................303-1

303.2.3.1 Sand-Clay Material...............................................................................303-1

303.2.3.2 Asphalt Prime Coat ..............................................................................303-2

303.2.4 Weather Considerations ...............................................................................303-2

303.2.5 Sampling and Testing Considerations ..........................................................303-2

303.2.6 Subgrade / Subbase Inspection and Approval .............................................303-2

303.3 INSPECTION DURING CONSTRUCTION ...........................................................303-2

303.3.1 Hauling and Placement Operation................................................................303-2

303.3.2 Spreading Operation.....................................................................................303-3

303.3.2.1 Mixing and Shaping..............................................................................303-3

303.3.2.2 Sampling and Testing ..........................................................................303-3

303.3.3 Compaction Operation..................................................................................303-4

303.3.3.1 General ................................................................................................303-4

303.3.3.2 Moisture Content ..................................................................................303-4

303.3.3.3 Lift Thickness .......................................................................................303-4

303.3.3.4 Density Testing ....................................................................................303-4

303.3.4 Finishing Operation.......................................................................................303-5

303.3.5 Checking Base Course Thickness................................................................303-5

303.3.6 Application of Asphalt Prime Coat ................................................................303-5

303.4 POST-CONSTRUCTION CONSIDERATIONS .....................................................303-6

303.5 DOCUMENTATION AND PAYMENT CONSIDERATIONS ..................................303-6

304 COQUINA SHELL BASE COURSE ..........................................................................304-1

304.1 DESCRIPTION OF WORK....................................................................................304-1

304.2 PRECONSTRUCTION CONSIDERATIONS.........................................................304-1

304.2.1 Contract Document Review ..........................................................................304-1

304.2.2 Coordination of Project Personnel ................................................................304-1

304.2.3 Material Considerations ................................................................................304-2

304.2.3.1 Coquina Shell Material .........................................................................304-2

304.2.3.2 Asphalt Prime Coat ..............................................................................304-2

304.2.4 Weather Considerations ...............................................................................304-2

304.2.5 Sampling and Testing Considerations ..........................................................304-2

300-iv Bases and Subbases May 2004

304.2.6 Subgrade / Subbase Inspection and Approval .............................................304-2

304.3 INSPECTION DURING CONSTRUCTION ...........................................................304-2

304.3.1 Hauling and Placement Operation................................................................304-2

304.3.2 Spreading Operation.....................................................................................304-3

304.3.2.1 Mixing and Shaping..............................................................................304-3

304.3.2.2 Sampling and Testing ..........................................................................304-3

304.3.3 Compaction Operation..................................................................................304-3

304.3.3.1 General ................................................................................................304-3

304.3.3.2 Moisture Content ..................................................................................304-4

304.3.3.3 Lift Thickness .......................................................................................304-4

304.3.3.4 Density Testing ....................................................................................304-4

304.3.4 Finishing Operation.......................................................................................304-4

304.3.5 Checking Base Course Thickness................................................................304-5

304.3.6 Application of Asphalt Prime Coat ................................................................304-5

304.4 POST-CONSTRUCTION CONSIDERATIONS .....................................................304-5

304.5 DOCUMENTATION AND PAYMENT CONSIDERATIONS ..................................304-6

305 GRADED AGGREGATE BASE COURSE ................................................................305-1

305.1 DESCRIPTION OF WORK....................................................................................305-1

305.2 PRECONSTRUCTION CONSIDERATIONS.........................................................305-2

305.2.1 Contract Document Review ..........................................................................305-2

305.2.2 Coordination of Project Personnel ................................................................305-2

305.2.3 Material Considerations ................................................................................305-2

305.2.3.1 Graded Aggregate Material ..................................................................305-2

305.2.3.2 Asphalt Prime Coat ..............................................................................305-3

305.2.4 Weather Considerations ...............................................................................305-3

305.2.5 Sampling and Testing Considerations ..........................................................305-3

305.2.6 Subgrade/Subbase Inspection and Approval ...............................................305-3

305.3 INSPECTION DURING CONSTRUCTION ...........................................................305-3

305.3.1 Hauling and Placement Operation................................................................305-3

305.3.2 Spreading Operation.....................................................................................305-3

305.3.2.1 Mixing and Shaping..............................................................................305-3

305.3.2.2 Checking Rate of Application ...............................................................305-4

305.3.2.3 Sampling and Testing ..........................................................................305-4

May 2004 Bases and Subbases 300-v

305.3.3 Compaction Operation..................................................................................305-5

305.3.3.1 General ................................................................................................305-5

305.3.3.2 Moisture Content ..................................................................................305-5

305.3.3.3 Lift Thickness .......................................................................................305-5

305.3.3.4 Density Testing ....................................................................................305-6

305.3.4 Checking Surface Smoothness ....................................................................305-6

305.3.5 Checking Base Course Thickness................................................................305-6

305.3.6 Application of Asphalt Prime Coat ................................................................305-7

305.4 POST-CONSTRUCTION CONSIDERATIONS .....................................................305-7

305.5 DOCUMENTATION AND PAYMENT CONSIDERATIONS ..................................305-7

305.5.1 Graded Aggregate Base Course (Unit Area Basis) ......................................305-7

305.5.2 Graded Aggregate Base Course (Unit Weight Basis)...................................305-8

305.5.3 Asphalt Material for Prime Coat....................................................................305-8

306 RESERVED ...............................................................................................................306-1

307 CEMENT STABILIZED EARTH BASE COURSE .....................................................307-1

307.1 DESCRIPTION OF WORK....................................................................................307-1

307.2 PRECONSTRUCTION CONSIDERATIONS.........................................................307-1

307.2.1 Contract Document Review ..........................................................................307-1

307.2.2 Coordination of Project Personnel ................................................................307-1

307.2.3 Material Considerations ................................................................................307-1

307.2.3.1 Soil Material .........................................................................................307-1

307.2.3.2 Portland Cement and Water.................................................................307-1

307.2.3.3 Asphalt Prime Coat ..............................................................................307-2

307.2.4 Weather Considerations ...............................................................................307-2

307.2.5 Sampling and Testing Considerations ..........................................................307-2

307.2.6 Subgrade Inspection and Approval...............................................................307-2

307.3 INSPECTION DURING CONSTRUCTION ...........................................................307-2

307.3.1 Method and Timing of Operations ................................................................307-2

307.3.2 Stationary Plant Mixing Operations ..............................................................307-2

307.3.2.1 Soil-Cement Mixture Production...........................................................307-2

307.3.2.2 Hauling and Placement ........................................................................307-2

300-vi Bases and Subbases May 2004

307.3.3 Road Mixing Operations ...............................................................................307-3

307.3.3.1 Scarification and Pulverization Operation ............................................307-3

307.3.3.2 Spreading of Cement ...........................................................................307-3

307.3.3.3 Mixing and Shaping Operation.............................................................307-3

307.3.4 Compaction Operation..................................................................................307-4

307.3.4.1 Moisture Content ..................................................................................307-4

307.3.4.2 Density Testing ....................................................................................307-4

307.3.5 Finishing Operation.......................................................................................307-4

307.3.6 Curing Operation ..........................................................................................307-5

307.4 POST-CONSTRUCTION CONSIDERATIONS .....................................................307-5

307.4.1 Construction Joints .......................................................................................307-5

307.4.2 Checking Base Course Thickness................................................................307-5

307.4.3 Traffic and Maintenance Considerations ......................................................307-6

307.5 DOCUMENTATION AND PAYMENT CONSIDERATIONS ..................................307-6

308 CEMENT STABILIZED AGGREGATE BASE COURSE ..........................................308-1

308.1 DESCRIPTION OF WORK....................................................................................308-1

308.2 PRECONSTRUCTION CONSIDERATIONS.........................................................308-1

308.2.1 Contract Document Review ..........................................................................308-1

308.2.2 Coordination of Project Personnel ................................................................308-1

308.2.3 Material Considerations ................................................................................308-1

308.2.3.1 Graded Aggregate Material ..................................................................308-1

308.2.3.2 Portland Cement and Water.................................................................308-1

308.2.3.3 Asphalt Prime Coat ..............................................................................308-2

308.2.4 Weather Considerations ...............................................................................308-2

308.2.5 Sampling and Testing Considerations ..........................................................308-2

308.2.6 Subgrade/Subbase Inspection and Approval ...............................................308-2

308.3 INSPECTION DURING CONSTRUCTION ...........................................................308-2

308.3.1 Method and Timing of Operations ................................................................308-2

308.3.2 Aggregate-Cement Mixture Production ........................................................308-2

308.3.3 Hauling and Placement.................................................................................308-2

308.3.4 Compaction Operation..................................................................................308-3

308.3.4.1 General ................................................................................................308-3

308.3.4.2 Moisture Content ..................................................................................308-3

308.3.4.3 Density Testing ....................................................................................308-3

May 2004 Bases and Subbases 300-vii

308.3.5 Checking Surface Smoothness ....................................................................308-4

308.3.6 Curing Operation ..........................................................................................308-4

308.4 POST-CONSTRUCTION CONSIDERATIONS .....................................................308-4

308.4.1 Construction Joints .......................................................................................308-4

308.4.2 Checking Base Course Thickness................................................................308-5

308.4.3 Traffic and Maintenance Considerations ......................................................308-5

308.5 DOCUMENTATION AND PAYMENT CONSIDERATIONS ..................................308-5

309 HOT-MIX SAND ASPHALT BASE COURSE............................................................309-1

309.1 DESCRIPTION OF WORK....................................................................................309-1

309.2 PRECONSTRUCTION CONSIDERATIONS.........................................................309-1

309.2.1 Contract Document Review ..........................................................................309-1

309.2.2 Coordination of Project Personnel ................................................................309-1

309.2.3 Material Considerations ................................................................................309-2

309.2.3.1 Performance Graded Asphalt Binder ...................................................309-2

309.2.3.2 Aggregate Materials .............................................................................309-2

309.2.3.3 Hot-Mix Asphalt Mixture .......................................................................309-2

309.2.4 Weather Considerations ...............................................................................309-2

309.2.5 Sampling and Testing Considerations ..........................................................309-2

309.2.6 Subgrade/Subbase Inspection and Approval ...............................................309-3

309.3 INSPECTION DURING CONSTRUCTION ...........................................................309-3

309.3.1 General .........................................................................................................309-3

309.3.2 Application of Asphalt Tack Coat..................................................................309-4

309.4 POST-CONSTRUCTION CONSIDERATIONS .....................................................309-4

309.4.1 Construction Joints .......................................................................................309-4

309.4.2 Checking Base Course Thickness................................................................309-4

309.4.3 Traffic and Maintenance Considerations ......................................................309-4

309.5 DOCUMENTATION AND PAYMENT CONSIDERATIONS ..................................309-5

309.5.1 Hot-Mix Sand Asphalt Base Course (Unit Weight Basis) .............................309-5

309.5.2 Performance Graded Asphalt Binder (Unit Weight Basis) ............................309-5

309.5.3 Asphalt Material for Tack Coat .....................................................................309-5

310 HOT-MIX ASPHALT AGGREGATE BASE COURSE...............................................310-1

310.1 DESCRIPTION OF WORK....................................................................................310-1

300-viii Bases and Subbases May 2004

310.2 PRECONSTRUCTION CONSIDERATIONS.........................................................310-1

310.2.1 Contract Document Review ..........................................................................310-1

310.2.2 Coordination of Project Personnel ................................................................310-1

310.2.3 Material Considerations ................................................................................310-1

310.2.3.1 Performance Graded Asphalt Binder ...................................................310-1

310.2.3.2 Aggregate Materials .............................................................................310-1

310.2.3.3 Hot-Mix Asphalt Mixture .......................................................................310-2

310.2.4 Weather Considerations ...............................................................................310-2

310.2.5 Sampling and Testing Considerations ..........................................................310-2

310.2.6 Subgrade / Subbase Inspection and Approval .............................................310-2

310.3 INSPECTION DURING CONSTRUCTION ...........................................................310-2

310.4 POST-CONSTRUCTION CONSIDERATIONS .....................................................310-3

310.5 DOCUMENTATION AND PAYMENT CONSIDERATIONS ..................................310-3

310.5.1 Hot-mix Asphalt Aggregate Base Course .....................................................310-3

310.5.2 Performance Graded Asphalt Binder............................................................310-3

310.5.3 Asphalt Material for Tack Coat .....................................................................310-3

311 PERMEABLE ASPHALT BASE COURSE ...............................................................311-1

311.1 DESCRIPTION OF WORK....................................................................................311-1

311.2 PRECONSTRUCTION CONSIDERATIONS.........................................................311-1

311.2.1 Contract Document Review ..........................................................................311-1

311.2.2 Coordination of Project Personnel ................................................................311-1

311.2.3 Material Considerations ................................................................................311-1

311.2.3.1 Performance Graded Asphalt Binder ...................................................311-1

311.2.3.2 Aggregate Materials .............................................................................311-1

311.2.3.3 Hot-Mix Asphalt Mixture .......................................................................311-2

311.2.4 Weather Considerations ...............................................................................311-2

311.2.5 Sampling and Testing Considerations ..........................................................311-2

311.2.6 Subgrade / Subbase Inspection and Approval .............................................311-2

311.3 INSPECTION DURING CONSTRUCTION ...........................................................311-2

311.4 POST-CONSTRUCTION CONSIDERATIONS .....................................................311-3

311.5 DOCUMENTATION AND PAYMENT CONSIDERATIONS ..................................311-3

May 2004 Bases and Subbases 300-1

Section 300 General Guidelines

300.1 INTRODUCTION

To ensure good performance and longevity of a pavement structure, continuous and thorough inspection during the early stages of highway construction is critical. Pavement structure failures can often be traced to an improperly constructed subgrade, subbase, base course or drainage feature. Good field inspection will detect deficiencies early in the project, facilitating immediate corrective action and minimizing future pavement failures. Division 300 provides the SCDOT Inspector and Resident Construction Engineer with guidance that should be used in conjunction with sound engineering judgment and field experience to inspect the construction of highway pavement subbase and base courses.

300.2 PAVEMENT CONSTRUCTION: OVERVIEW

300.2.1 Pavement Structure

In general, a pavement structure is designed to carry the repetitive loads of projected vehicular traffic, taking into consideration the type of facility required, the number and type of vehicles that are expected to use the facility during its design life, the quality of materials available on the project and other design factors. The pavement structure itself consists of several layers of various material types and thicknesses, which are placed and compacted sequentially from the ground up. Each layer is designed to distribute the load it supports to the layer immediately below it, thus allowing the vehicular load directly supported by the surface courses to be uniformly distributed throughout the pavement structure to the subgrade foundation. This concept is illustrated in Figure 300A.

Vehicular Load

Surface Course(s) (Division 400 or 500) Intermediate Course (Division 400)

Surface Structure

Base Course(s) (Division 300) Subbase (Division 300)

Base Structure

Subgrade (Division 200) Undisturbed Soil

Distribution of Vehicular Load

TYPICAL PAVEMENT STRUCTURE

Figure 300A

300-2 Bases and Subbases May 2004

300.2.2 Subgrade Foundation

Earthwork must be completed and approved before initiating work on the subbase or any base course, including clearing and grubbing, roadway and drainage excavation, and embankment and subgrade construction (see Division 200). The subgrade is the foundation of the entire pavement structure; therefore, its construction must be closely inspected as discussed in Section 208. Once the subgrade has been approved by the District Construction Engineer, continue to monitor the subgrade for excessively wet areas, soft spots, ruts and grade deficiencies. Require the Contractor to correct such deficiencies in accordance with the provisions of the Contract before they are covered by a subsequent subbase or base course.

Additional drainage, grading and compaction rework may be required to bring the subgrade into compliance. As needed, seek assistance from the Resident Construction Engineer.

300.2.3 Base Structure

The base structure within the pavement structure includes base courses and may include a subbase course, as well. The primary functions of the subbase and base courses are to:

• provide uniform structural support of the pavement;

• prevent volume changes in the subgrade (i.e., shrink, swell);

• minimize damage due to pavement pumping; and

• distribute traffic loads to the subgrade.

300.2.3.1 Subbase

The construction of a subbase is sometimes necessary to provide additional support for the pavement structure. The need for a subbase will be determined during the design phase and is based on criteria such as projected vehicular traffic and the strength characteristics of the underlying subgrade material. If warranted, the subbase will be defined in the Contract Plans and Specifications. In general, the subbase may be either a special treatment of the upper layer of the subgrade (see Section 301) or a layer of inexpensive, locally available aggregate material (see Section 302). Because a base course will overlay the subbase, closely monitor construction for compliance and obtain final approval of the subbase from the Resident Construction Engineer before initiating work on the base course.

300.2.3.2 Base Course

The base course is a structural layer that directly supports the surface structure, as shown in Figure 300A. As such, the base course must be constructed of suitable, durable material to withstand the relatively higher stresses imposed upon it. The Contract Plans and Specifications will designate, as determined during design, the number and type of base courses required and whether the base will be laid over a subbase or directly on top of the subgrade. The major Sections in this Division discuss the types of base courses that are typically used by SCDOT.

Closely monitor construction for compliance and obtain final approval of each base course from the Resident Construction Engineer prior to initiating work on an overlying layer. The surface structure will be placed over the base structure.

May 2004 Bases and Subbases 300-3

300.2.4 Surface Structure

The surface structure, consisting of intermediate and surface courses as shown in Figure 300A, is the uppermost layer within the pavement structure. Because the surface structure directly bears the load of vehicular traffic, it must be constructed of the highest quality materials. The type of surface structure required for the project will be determined during the design phase and will be defined in the Contract Plans and Specifications. Closely monitor surface structure construction for compliance with respect to material quality, placement, consolidation, compaction, grade, cross slope, thickness and smoothness criteria. See Division 400 and Division 500, respectively, for additional information on the types of intermediate and surface courses that are typically constructed.

300.2.5 Geosynthetic Material Considerations

Geosynthetic materials (e.g., geotextiles, geocells, geogrids, geomembranes, geocomposites) are commonly used for various applications in highway construction. Section 815 discusses applications related to erosion and sediment control. Where geotextile fabric is used to separate layers within the pavement structure (e.g., subgrade, subbase, base course), the fabric allows the water to pass through the pavement structure without clogging. The water will be intercepted and carried away from the roadway by the underlying drainage structure. Such geosynthetic materials must be approved prior to installation. Obtain from the Contractor and submit to the Research and Materials Laboratory for approval the manufacturer’s certification document for the geosynthetic material, which should include the manufacturer’s name, fabric type or trade name, the project, the intended application on the project and the required test results (e.g., Minimum Average Roll Value). Verify that the material delivered to the project is labeled with the manufacturer’s name, fabric type or trade name, Lot Number and the quantity of shipment. Retain these labels in the project file, referencing the information on SCDOT Form

100.10 – Materials Certification Log. See the SCDOT Guide Instruction Manual for Inspectors of Earthwork and Base Course Construction for additional information.

300.3 SUMMARY OF INSPECTION DUTIES

Pavement construction is a sequenced operation. Construction of the base course cannot begin until the subgrade and subbase, if specified, have been completed and approved.

Similarly, construction of the surface course cannot begin until the base course has been completed and approved. Roadway longevity, in general, depends greatly on the quality of the work and materials that are incorporated into each of these pavement courses. Inspection must therefore be deliberate and thorough as each course is constructed, demonstrating acceptability prior to initiating construction of an overlying course. It is very difficult to assess, and possibly correct, a suspected deficiency in an underlying layer once covered by a subsequent layer. In addition, once the facility is opened to traffic, a deficiency in only one course, having gone undetected, can cause premature pavement failure. Consider the following guidelines during the early stages of pavement construction:

300-4 Bases and Subbases May 2004

• Review project documentation and become familiar with the requirements of the Contract, including plans, cross-sections, Standard Drawings, Standard Specifications, Supplemental Specifications and Special Provisions. Remember that the Contract Plans, Special Provisions and Supplemental Specifications take precedence over the Standard Specifications. See Section 105.04 of the Standard Specifications for information on the order of precedence of Contract documents.

• Review the meeting minutes from the Preconstruction Conference and understand any special requirements of the project. Know the conditions that exist within the limits of construction, paying particular attention to erosion and sediment control and to any areas where it may be difficult for construction equipment to access the project.

• Know the material requirements of the project and ensure that materials obtained from sources outside the right-of-way are obtained from approved sources. Verify that construction equipment and base plants have been properly calibrated.

• Become familiar with the sampling and testing procedures required for the project. Pay particular attention to the type and frequency of the Quality Control Samples and Tests and the Independent Assurance Samples and Tests required for component materials and Contract pay items.

• Verify that sufficient drainage has been provided and that the drainage features, such as underdrains, have been properly installed. Ensure that the Contractor corrects any soft spots or otherwise unstable areas before placing embankment, subgrade, subbase or base course materials. Obtain final approval of the subgrade from the District Construction Engineer.

• During placement of material requiring moisture conditioning, monitor the differences in moisture content, density, color and texture to ensure it is being maintained at or near optimum, as established by the Research and Materials Laboratory. A change in these properties is a good indicator that the material being hauled to the project has changed.

• Prior to initiating work on a subsequent course, ensure that each layer of material is compacted to target density and that the course complies with the thickness and smoothness criteria specified in the Contract. Check line, grade and cross-section to ensure that the requirements of the project have been met.

May 2004 Bases and Subbases 301-1

Section 301 Cement Modified Subbase

301.1 DESCRIPTION OF WORK

Where the underlying subgrade material is determined to be of poor quality and more suitable soil or aggregate materials are either unavailable or uneconomical, the Contract will typically require that the subgrade be improved with cement in accordance with Section 301 of the Standard Specifications. The SCDOT Inspector will be responsible for verifying that the Contractor treats the existing subgrade as specified and where designated in the Contract Plans and Specifications. In general, the Contractor will be required to:

• pulverize the existing subgrade soil to a specified depth;

• apply Portland cement and water at a specified rate;

• thoroughly and uniformly mix the pulverized soil, cement and water materials;

• compact the resultant mixture to a target density;

• shape the compacted surface to the designated grade and cross slope;

• apply an asphalt curing material at a specified rate; and

• maintain the subbase surface in an acceptable condition during the operation.

For the reconstruction of an existing roadway, the Contract may specify the construction of a cement modified recycled base. The construction of a cement modified recycled base is similar to that of a cement modified subbase; however, the Portland cement will be mixed with the scarified and pulverized material of the existing pavement. When specified, the exceptions to Section 301 will be specified in the Special Provisions. Pay particular attention to the Contractor’s sequence of operations, application rate of materials, depth and uniformity of mixing, moisture content during compaction, density obtained, curing period and the resultant thickness and smoothness of the completed subbase. Loose, segregated or rutted areas are unacceptable and will require immediate correction by the Contractor. After construction and prior to placement of any subsequent base course, obtain final approval of the subbase from the Resident Construction Engineer and verify compliance for all test results.

301.2 PRECONSTRUCTION CONSIDERATIONS

301.2.1 Contract Document Review

Review the Contract Plans and Specifications and the publication Guide Instruction Manual for Inspectors of Earthwork and Base Course Construction. Pay particular attention to the requirements of Supplemental Specifications and Special Provisions that take precedence over Standard Specifications. Specifically note the required cross-section (e.g., width, depth, cross slope). Become familiar with the required materials, equipment and construction methods, sequence of operations, sampling and testing procedures and acceptance criteria. Know the measurements required for payment, applicable payment adjustments and the SCDOT Construction Forms that will be needed to document the prosecution and progress of the work.

301-2 Bases and Subbases May 2004

301.2.2 Coordination of Project Personnel

Review the meeting minutes of the Preconstruction Conference. Meet with the Resident Construction Engineer and the Contractor Superintendent to ensure a complete and thorough understanding of inspection duties and to effectively communicate Contract requirements and any special directives to the Contractor.

301.2.3 Material Considerations

301.2.3.1 Subgrade Material

Additional sampling and testing of subgrade material is generally unnecessary at the time the subbase is to be constructed. See Section 301.2.6 for additional information.

301.2.3.2 Portland Cement and Water

Verify that Portland cement and water to be incorporated in the work conform to specified requirements and that quantities on the project are sufficient to ensure a continuous operation.

Ensure that the Portland cement is supplied from a manufacturer listed on SCDOT Approval Sheet 6. Application rates will be established by the Research and Materials Laboratory.

301.2.3.3 Asphalt Prime Coat

Verify that the asphalt material to be used as the asphalt prime coat is supplied from a manufacturer listed on SCDOT Approval Sheet 38 and is of the type specified for the project.

Several different types are generally acceptable; however, the Contract may specify the use of a particular type. If material type is optional, only one material type is to be used for curing; watch for evidence of cross-contamination with other asphalt materials used on the project. In addition, verify that the material is maintained in sufficient quantity to treat the surface area finished during the day’s operation. Prolonged exposure of the finished subbase surface without being properly treated with an asphalt prime coat should generally be avoided.

301.2.4 Weather Considerations

Pay particular attention to the weather forecast before work on the cement modified subbase begins or resumes. Check the temperature forecast for acceptability. Do not allow work to be performed on an excessively wet or frozen subgrade.

301.2.5 Sampling and Testing Considerations

Accurate and representative sampling of work and materials cannot be overemphasized. An improperly taken sample may not be truly representative; and if testing is performed on such a non-representative sample, the test results will be meaningless with respect to assessing quality and adherence to specified requirements. SCDOT and Contractor personnel who are responsible for sampling and testing must be certified by the Department. It is the responsibility

May 2004 Bases and Subbases 301-3 of the Resident Construction Engineer to ensure that each Inspector is properly certified for the type of sampling and testing to be performed. Review and understand the applicable criteria for the Quality Control Samples and Tests and the Independent Assurance Samples and Tests that are documented in Section 106. Review and understand the procedures, equipment, safety precautions and acceptance criteria for the applicable sampling and testing procedures that are documented in Appendix C. See Appendix B for information on sample identification cards.

301.2.6 Subgrade Inspection and Approval

The SCDOT Inspector is responsible for inspecting the subgrade with respect to materials, grade, width, thickness, cross slope, density and drainage, as discussed in Section 208. Prior to initiating work on the subbase, the subgrade must be approved by the District Construction Engineer. Therefore, at the time the subbase is to be constructed, additional sampling and testing of the subgrade material is generally unnecessary. However, it is good construction practice to continually monitor the subgrade for evidence of unacceptability (e.g., excessively wet areas, high or low spots, ruts, muck, loose or segregated material). Require that unsuitable soil material be removed and replaced with acceptable material. Underdrains or rework (e.g., additional grading and compaction) may also be required before proceeding with subbase construction. As needed, seek guidance from the Resident Construction Engineer.

301.3 INSPECTION DURING CONSTRUCTION

301.3.1 Scarification Operation

Check the depth of scarification of the subgrade for compliance. Verify that the Contractor is not blading into the subgrade too deeply. Perform the required sieve analyses to verify that the gradation of the pulverized material (i.e., soil, existing pavement material) is within acceptable limits.

301.3.2 Application of Portland Cement

301.3.2.1 Moisture Content and Rate of Application

The application rate of cement and the initial optimum moisture content of the soil-cement mixture will be established by the Research and Materials Engineer based on a representative sample of the subgrade material to be treated. The application rate of cement is typically specified as pounds per square yard and the optimum moisture content is typically specified as percent moisture in the soil-cement mixture. The optimum moisture content should be tested using SC-T-29 twice per day or if material changes. Excessively dry conditions may warrant the application of additional water. Sudden downpours and rainy conditions may require the Contractor to halt work. Contact the Research and Materials Engineer for any needed assistance. See Section 301.3.4.1 for additional information on moisture content.

301-4 Bases and Subbases May 2004

301.3.2.2 Spreading of Cement

Prior to the spreading of cement, verify that the Contractor has properly calibrated the spreader and closely monitor the rate of application to ensure that the cement is being spread uniformly across the entire width of the subgrade at a rate within ±5% of the pounds per square yard specified by the Research and Materials Engineer. Require the Contractor to recalibrate the spreader if necessary. The spreading operation must be continuous. Do not allow the Contractor to apply more cement along the length of the subgrade than can be completely processed in a single day’s operation. The mixing operation, in particular the application of water, must commence within three hours of the application of cement. Check the application rate using SC-T-141 (see Appendix C).

301.3.3 Mixing Operation

301.3.3.1 Traveling Mixing Plant

To thoroughly blend the cement and subgrade soil materials, the Contractor will be required to use either a single-pass or a multiple-pass traveling mixing plant, as specified.

301.3.3.2 Dry Mixing

Dry mixing is used to pulverize and combine the air-dry soil and cement materials sufficiently to prevent cement balls from forming when water is added. Verify that dry mixing is maintained at the proper depth. Mixing deeper than that specified will dilute the mixture and possibly reduce the strength of the subbase. Watch for unpulverized lumps and require pre-wetting if evident.

301.3.3.3 Application of Water

Verify that the spray bar evenly distributes the water across the full width of the subgrade.

Check the moisture content for acceptability and, if needed, require the rate of application to be adjusted. See Section 301.3.4.1 for additional information on moisture content.

301.3.3.4 Wet Mixing

After water has been introduced, the mixing of the moist soil and cement materials will continue until a uniform mixture has been obtained. At least twice daily, verify that 100% of the pulverized soil-cement mixture will pass a 2-inch sieve and at least 65% will pass a No. 4 sieve.

The traveling plant should leave the treated subgrade in a loose condition ready for immediate compaction. Compaction must commence within 30 minutes of wet mixing.

301.3.3.5 Core Molding

Prior to compaction, core molding of the soil-cement mixture is required. Ensure that one set of two cores is molded each work day. Each core will be molded at 100% maximum dry density, according to the Standard Proctor Test, using the following procedures:

May 2004 Bases and Subbases 301-5

1. Preparation. Use a 4-inch split mold, available from the Research and Materials…