303 - Open Graded Drainage Course

303 Open-Graded Drainage Courses

GENERAL DESCRIPTION

Definitions of Terms

Aggregate: Aggregate refers to the material used as the foundation of infrastructure. It typically consists of sand, gravel, crushed stone, or recycled materials like crushed concrete.

Approach: An approach is the section of roadway leading up to a bridge, culvert, or a main roadway. It is designed to provide a smooth transition.

Automated Machine Guidance (AMG): Automated machine guidance is the process of automatically adjusting the motion of a machine with an onboard computer that obtains its position from global positioning systems, robotic total stations, lasers, or combinations of similar methods while referencing the Contractor’s model developed for the project.

Booking Grade: Booking grade is the process of documenting verification checks of the grade to ensure elevation and slope are within the project specifications.

Concrete Crushing Plant: A concrete crushing plant is a facility where concrete rubble is crushed and processed into aggregate for reuse in construction projects.

Dense-Graded Aggregate: Dense-graded aggregate is a mixture of aggregates with an even distribution of different size aggregates.

Geotextile: Geotextile is a specialized fabric with the capacity to filter, separate, reinforce, and facilitate drainage in roadway applications. Not all geotextile fabrics perform the same.

Loss by Wash: Loss by wash is the amount of material which is washed through a #200 sieve.

Open-Graded Aggregate: Open-graded aggregate is a type of aggregate material characterized by a high porosity and void content, allowing water to drain through freely. It is commonly used in drainage applications to prevent water accumulation on road surfaces.

Salvaged Aggregate: Salvaged aggregate refers to granular material salvaged from the project site. The material is tested to meet specific gradation requirements prior to re-use on the project.

Segregation: Segregation in construction refers to the separation of different sizes or types of aggregate particles within a mixture. It can occur during handling, transport, or placement of materials and can lead to inconsistencies in the composition and performance of the final product.

Shoulder: The shoulder is the portion of the roadway adjacent to the main driving lanes. It provides additional space for emergency stopping, vehicle breakdowns, and pedestrian use, and also helps to support the road edge.

Stone: Stone refers to a naturally occurring mineral material, typically used as aggregate in concrete, asphalt, and road base layers. Stones vary in size and composition, with common types including granite, limestone, and basalt.

Subbase: Subbase is a layer of material placed beneath the road surface or pavement layers and roadway base course. It provides additional support, drainage, and stability to the pavement structure, helping to distribute loads and prevent uneven settlement.

Subgrade: Subgrade is the existing ground or soil surface upon which the road or pavement section is constructed. It serves as the foundation for the road layers above and must be properly prepared and compacted to ensure stability and durability.

General Overview

Open-graded drainage course is used under concrete and hot mix asphalt pavements for support of the paved surface, to distribute traffic loads, to prevent damage of underlying layers, and for drainage into underdrains. It is a manufactured blend of aggregates. Natural aggregate, such as limestone, and recycled crushed concrete are the most common materials. The primary Michigan aggregate class used for open-graded drainage courses is 4G.

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MATERIALS

All materials must meet acceptance requirements in the Materials Source Guide and be listed on the Contractor-provided Material Source Lists in the project files.

Description of Materials

Open-graded aggregate meeting the gradation requirements noted in Section 902 of the Standard Specifications for Construction typically consists of the following:

• Natural aggregate: Limestone, basalt, granite, etc.
• Recycled concrete
• Slag aggregate

4G material used for OGDC has two different gradation requirements. The first gradation requirement is taken prior to placement and compaction. The second gradation requirement is taken after placement and compaction. The different requirements are to allow for some aggregate breakdown through the construction process. The percent passing on the 1/2-inch, #8, #30, and #200 sieves are increased to account for aggregate breakdown. Loss by wash is limited to 6% when tested prior to placement and compaction, and 8% after placement and compaction. Unlike dense-graded base gradations, there is not a minimum amount for the loss by wash.

When crushed concrete is used for in the open-graded drainage course, it cannot be used within 100 feet of a waterbody. Project documents typically have details in a Notice to Bidders for areas where the use of crushed concrete is restricted.

Materials must come from the qualified product list and are subject to onsite material testing to confirm the material meets the specifications.

The Contractor may elect to use an onsite crushing plant to recycle existing concrete pavement. If the Contractor requests this, coordination with the MDOT Region Lab and Construction Field Services Division is required to test the plant’s product.

Pictures of Materials

4G Aggregate Placed for Road Base

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EQUIPMENT

The following equipment is typically used for construction of an open graded drainage course:

• Bulldozer
• Grader
• Single or dual drum roller
• Trimmer
• Spreader
• Water truck
• Concrete crushing plant (potential on large projects)

Description of Equipment

Open-graded aggregate is typically dumped on the geotextile or dense graded aggregate base separator by a truck and pushed into place using a bulldozer. Spreaders may also be used. Fine grading is performed with a trimmer, bulldozer, or grader, which typically utilizes AMG to achieve the correct cross-section. The aggregate is then compacted with a roller to achieve the required density. A water truck is sometimes used to increase the moisture content of the aggregate during compaction.

Pictures of Equipment

Auto Trimmer Equipped with AMG	Bulldozer Placing Open-Graded Aggregate
Smooth Drum Roller	Open-Graded Aggregate Being Placed on Geofabric Separator

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PRECONSTRUCTION

Preconstruction meetings are held for the Engineer and Contractor to discuss and understand installation requirements, stockpile management, placement of the separator layer, placement of the open graded drainage course, and acceptance/payment.

Prior to the start of construction, the Inspector should perform the following:

1. Review the plans to verify the location of the work.
2. Verify the existing subgrade and/or sand subbase are in sound condition and have been accepted. A proof roll or geotechnical analysis may be conducted to determine condition of existing subgrade. If poor soils are encountered, coordinate with the Engineer for testing and/or removal of the soils.
3. Verify project control points are established and matching between the Contractor and the inspection staff.
4. Verify the AMG plan is in place and review the work with the Contractor.
   • If AMG is not used, verify a surveyor has provided grade stakes for the work.
5. Verify the subgrade and subbase are at the required elevation, the cross-slope is in accordance with the project specifications, and the separator layer has been placed.
6. Review the plans and the Special Provision for Maintenance of Traffic. There may be restrictions or staging requirements for the installation of the aggregate. Installation restrictions are typically associated with staging requirements on a project and access to side streets and driveways.
7. Verify all materials are approved for use and meet specifications, and verify that stockpiled materials are protected from weather as required by the specifications and manufacturer recommendations.
8. Obtain photographs of material tickets, storage method, and location.
9. Review the Stockpile Management Plan if crushed concrete produced from an onsite crushing facility is used.
10. Hold an onsite meeting with the Contractor to discuss:
    • The construction methods that will be used to complete the work.
    • Required traffic control measures, proximity of traffic to the work area, and maintaining driveways and other access points during construction.
    • Communication required if impacting residents or businesses during installation.
      • Residents and businesses should be contacted if there will be disruptions to services. Coordination by the Contractor with impacted users may be required if disruption is necessary.
    • Review of local ordinances.
    • Disposal of trimmed material and material stockpile locations. The Contractor should provide authorization letters to the Engineer noting material stockpile and disposal locations.
    • Soil erosion and sedimentation control measures that will be utilized to minimize soil erosion and subsequent sedimentation.
    • Methods for securing the site during work operations and at the end of each workday.

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CONSTRUCTION

The subbase or existing grade should be accepted prior to the aggregate base course being placed. The grade should not be frozen, soft, rutted, or generally unstable prior to placement of the aggregate base course. Due to the increased void space, a separator layer is needed between the OGDC and the layer of material below it to prevent intermixing and loss of support. Typically, either a dense graded aggregate layer or geotextile separator are installed to create a separation between the OGDC and the subbase or subgrade. Refer to Section 302 and Section 308 of the Standard Specifications for Construction for proper installation of aggregate base course and geotextile separator.

Control Strip

Prior to full production placement, a control strip is required to be constructed to verify methods for placement and compaction do not cause segregation or degradation and produce an open-graded drainage course meeting post-placement gradation requirements and appropriate consolidation. If the Contractor changes the source of the material, a new control strip is required. Control strip requirements include:

• Must be 600 to 1,000 feet in length.
• Means and methods of constructing the control strip, including the establishment of a roller pattern, must be documented and match the methods that will be used during full production placement.
• After compaction and final trimming, the Engineer will obtain in-place samples from the control strip to test for loss by wash and gradation per Table 902-1 of the Standard Specifications for Construction.
  • Per Subsection 303.03.D of the Standard Specifications for Construction, the Contractor is to provide mechanical assistance for sampling from the grade when the layer thickness is greater than 4 inches.
  • Sampling occurs in various locations throughout the test strip with samples from each location being blended together prior to gradation testing.
• Density will be verified by the MDOT representative to meet the requirement of 95% of the maximum unit weight with a moisture content of optimum or below.

General Construction

Open-graded aggregate is typically deposited on the separator-covered grade by a truck, then pushed into place by a bulldozer. If the cross-section calls for more than 8 inches of depth, the open-graded aggregate must be placed in two lifts. Each lift is required to follow the roller pattern established during the control strip to ensure density requirements are met and excessive crushing of the open-graded aggregate does not occur. Segregation can occur if material is handled too many times in the process of being placed.

If open-graded aggregate is to be used for a haul road, an additional 2-inch thickness above the plan cross-section is required to protect the OGDC from contamination and material breakdown. Subsequent removal of this additional material to reach the proposed cross-section and elevation is at no cost to the contract.

After final trimming to the proposed cross-section and elevation, excess material may be stockpiled and retested for gradation to be potentially re-incorporated back into the project.

Final grading is performed by a grader or a trimmer, generally equipped with AMG. During final grading, particularly when a grader is used, it is critical for sufficient moisture to be present to ensure the fine particles do not settle out and lead to excessive segregation.

The Contractor should perform the necessary compaction to meet the density requirements of the OGDC. If density testing continually fails due to a low moisture content, the Contractor is allowed to use a water truck to increase the moisture content of the aggregate up to, but not above, the optimum moisture content. A moisture content closer to optimum may improve the ability to obtain density. A change in rolling pattern or equipment are other means the Contractor can use to achieve density.

If concrete trucks are allowed on the open-graded aggregate for placement of concrete, it should only be to back onto the grade from the haul road, deposit the concrete on the grade, and then return to the haul road. Trimmed grade should not be used as a haul road for empty trucks, and excessive turning should be avoided to minimize damage to the OGDC surface. Frequent access points should be provided from the haul road to the grade and the wheel path of trucks should be varied to minimize the amount of loading that occurs in any single area of the final OGDC surface.

Rutted Grade Used as a Haul Road for Concrete Trucks

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INSPECTION & TESTING

The Inspector should utilize, at a minimum, the following tools to perform the required inspection:

• Measuring wheel
• 100-foot tape measure or longer
• 25-foot tape measure
• Chaining pin
• 6-foot stick ruler
• 4-foot level
• Working plans
• Total Station for documenting grade checks if AMG is used by the Contractor
• String line or laser level if traditional survey stakes are used
• Camera

The Inspector should take the following steps prior to the start of construction:

1. Obtain approved drawings and specifications for review. Lay out and discuss with the Contractor areas where crushed concrete is not permitted, if applicable.
2. Review the means and methods used for placement and compaction of the control strip.
3. Verify the source of the open-graded aggregate; if it is not from a prequalified pit, ensure required quality assurance testing is completed ahead of time.
4. If crushed concrete is being used from an onsite crushing facility, observe how it is being stockpiled off the crusher belt to ensure it is in conformance with the Contractor’s Stockpile Management Plan. Segregation may occur if material is not leveled off as the pile is being built. Use only certified aggregate samplers for evaluating aggregate stockpiles.

Stockpile of Crushed Aggregate Onsite

The Inspector should take the following steps during construction:

1. Observe delivery, placement, and compaction of the material for conformance to the approved method established during the control strip. The roller pattern established during the control strip should be adhered to.
   • When any of the following occurs during construction of the open-graded layer, a new test strip will be required:
     • Changes in Contractor’s placement procedures.
     • Changes to the equipment being used for placement.
     • Materials source changes or a blending of material sources.
   • If segregation, contamination, or excessive material degradation are observed, sampling and testing of the in-place materials may be warranted. The Contractor must be notified of the limits of the area where these concerns were observed. Paving operations should not be allowed to proceed on the questionable areas (stop paving a minimum of 500 feet prior to the area) and open-graded placement operations should stop.
2. Perform a moisture test on the aggregate material if payment is based on weight.
3. Complete the required daily verification of compaction efforts of either a proof roll or density testing, whichever was agreed to by the engineer. If density testing is the agreed upon method, 95% of the maximum unit weight with a moisture content not greater than optimum is required as established with:
   • The Michigan Cone if natural or slag aggregates are used; or
   • The AASHTO T-180 if crushed concrete is used as detailed in the Density Testing and Inspection Manual.
4. Review grade after trimming for areas of segregation. If there are areas of significant segregation, notify the Engineer and Contractor for a corrective action plan to be implemented. Areas of significant segregation can cause bigger issues when trucks are placed on the grade for paving material delivery.
5. Complete quality assurance verification of the trimmed grade and document results of these checks. Possible checks include:
   • Cross-section checks.
   • Top surface elevation checks.
     • If AMG is used by the Contractor, a surveyor with a Total Station should be utilized to check surface elevations of the open-graded drainage course.
   • Depth checks.

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MEASUREMENT, DOCUMENTATION & PAYMENT

Measurement and Payment

There are typically three pay items associated with open graded drainage course.

• Open-Graded Drainage Course _inch is paid by the square yard will be measured by length and width at the specified depth required.
• Open-Graded Drainage Course, CIP is paid by the plan volume in cubic yards as defined by the plan typical sections.
• Open-Graded Drainage Course, Shoulder can be paid by the square yard or ton. If paid by the ton, scale weights will be used for all material placed with additives at a moisture of 8% or below. If moisture contents are above 8%, the excess moisture will be deducted from the scale weight tickets.

Refer to Table 303-1 and Table 303-2 of the Standard Specifications for Construction for payment reduction factors for any in-place test results that do not meet gradation requirements.

Documentation

The primary report required for the payment of open-graded drainage course is the Daily Work Report (DWR). The Inspector should note in the remarks section of the report the condition of the base material during placement, material verification, and equipment and manpower used.

Sketches and calculations documenting the work completed is required and should include:

1. Station to station length and width of area being paid on this date.
2. Survey or other approved methods for verification the open-graded drainage course was constructed in conformance with proposed cross-sections and elevations.
3. Volume and tonnage of material placed.

Depth checks must be included with the DWR when the pay item is noted by the inch.

Ensure gradation forms are being filled out by the certified aggregate sampler.

Form 0582B, Moisture and Density Determination – Nuclear Method is used to record density testing results.

Delivery tickets must be verified for the source of material against the approved Material Source List. Each ticket must include the required information. Refer to Subsection 303.03 of the Standard Specifications for Construction for the information required on each ticket.

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LOCAL AGENCY PROJECTS

-Reserved-

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RAIL PROJECTS

-Reserved-

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