Difference between revisions of "306 - Aggregate Surface Course"

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<center><span STYLE="font: 40pt arial;">'''Aggregate Surface Course'''</span></center>
 
<center><span STYLE="font: 40pt arial;">'''Aggregate Surface Course'''</span></center>
  
−
<center>[http://mdotcf.state.mi.us/public/specbook/files/2012/306%20Agg%20Surface%20Course.pdf 2012 STANDARD SPECIFICATIONS FOR CONSTRUCTION - SECTION 306]</center>
 
  
 +
==[[#GENERAL|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.
  
−
==[[#GENERAL|GENERAL]]==
+
'''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.
 +
 
 +
'''Fine-Graded Aggregate:''' Fine-graded aggregate is a mixture of aggregates with a uniform distribution of small size aggregate particles passing through a #4 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 ===
 +
Aggregate surface courses are primarily used for low volume roadways, driveways, or temporary roadway surfaces. Maintenance gravel is used for temporary access as well as to repair rutting, potholes, or similar deformities of an existing aggregate surface course. Natural or crushed aggregates are commonly used. Different areas of the state require different thicknesses.
  
−
Compliance with density requirements for aggregate surface course construction is just as important as for aggregate base construction. Poor compactive efforts and failure to adhere to placement guidelines will result in settlement and rutting. Rutting of the surface during construction and prior to final grading and shaping should be repaired by scarifying to a depth below the ruts and recompacting to 98 percent of the maximum unit weight. The filling in of ruts by just blading the surface is not an adequate repair and will only lead to segregation and further rutting.
 
  
 
{{top}}
 
{{top}}
  
 
==[[#MATERIALS|MATERIALS]]==
 
==[[#MATERIALS|MATERIALS]]==
 +
All materials must meet acceptance requirements in the [https://www.michigan.gov/mdot/Business/Construction/Materials-Source-Guide Materials Source Guide] and the [https://www.michigan.gov/mdot/-/media/Project/Websites/MDOT/Business/Construction/Standard-Specifications-Construction/CFS-Manuals/Procedures-Aggregate-Inspection.pdf?rev=e2f19aadca344460afca48b7b9ddb31e&hash=5D3CB25E2CD084FACCFD616004CCEB82 Procedures for Aggregate Inspection] and be listed on the Contractor-provided Material Source Lists in the project files. 
 +
 +
=== Description of Materials ===
 +
Material requirements are dependent on the final purpose of the roadway. In all cases, a dense graded material should be used. Gradation requirements can be found in [https://mdotwiki.state.mi.us/images_construction/9/95/2020-Standard-Specifications-Construction.pdf#page=816 Section 902 of the Standard Specifications for Construction].
 +
*  Roadways that WILL Receive a Paved Surface: Use 21A, 21AA, or 22A aggregates.
 +
*  Roadways that Will NOT Receive a Paved Surface: Use 23A or 23AA aggregates.
 +
*  Maintenance Gravel: Use 21A, 21AA, 22A, 23A, 23AA, or salvaged aggregates.
 +
 +
When crushed concrete is used for in the open-graded drainage course, it cannot be used within 100 feet of a waterbody. The contract documents typically have details in the Notice to Bidders for areas where the use of crushed concrete is restricted.
 +
 +
=== Pictures of Materials ===
 +
{|
 +
|+
 +
|-
 +
| [[File:305-002.jpg|200px|thumb|center|'''21AA Aggregate Pile (Limestone)''']] || [[File:208-2-2-3.jpg|200px|thumb|center|'''21AA Material''']]
 +
|-
 +
| [[File:306-001.jpg|200px|thumb|center|'''23A Aggregate Surface Course for a Roadway''']] || [[File:306-003.jpg|200px|thumb|center|'''Maintenance Gravel Placed for a Temporary Roadway''']]
 +
|}
 +
 +
 +
{{top}}
 +
 +
==[[#EQUIPMENT|EQUIPMENT]]==
 +
The following list of equipment can be used for aggregate surface course and maintenance gravel work:
 +
* Bulldozer
 +
* Grader
 +
* Excavator
 +
* Dump truck
 +
* Front end loader
 +
* Vibratory roller
 +
* Gas powered rammer tamping machine
 +
* Plate Compactor
 +
* Transit or laser level
 +
* Leveling/grade poles
 +
 +
=== Description of Equipment ===
 +
Aggregate surface course material is typically dumped on the grade by a truck and graded with a grader or bulldozer. Most equipment utilizes AMG to effectively shape the roadway. A vibratory roller is used to compact the aggregate after it is graded.
 +
 +
=== Pictures of Equipment ===
 +
{|
 +
|+
 +
|-
 +
| [[File:Smooth drum roller.jpg|200px|thumb|center|'''Smooth Drum Roller''']] || [[File:302-005.jpg|200px|thumb|center|'''Grader''']] || [[File:Laser transit.jpg|200px|thumb|center|'''Laser Transit''']]
 +
|}
 +
  
−
<span style="color: red"> -Reserved- </span>
+
{{top}}
 +
 
 +
==[[#PRECONSTRUCTION|PRECONSTRUCTION]]==
 +
Prior to the start of construction, the Inspector should perform the following:
 +
# Review the plans to verify the location of the work.
 +
#* Take note of areas where vibratory compaction use is excluded, if applicable.
 +
# 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.
 +
# Verify project control points are established and matching between the Contractor and the inspection staff.
 +
# 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.
 +
# Verify the subgrade and subbase are at the required elevation and the cross-slope is in accordance with the project specifications.
 +
# 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.
 +
# Verify all materials are approved for use and meet specifications, and verify that stockpiled materials are protected from weather and sunlight as required by the specifications and manufacturer recommendations.
 +
# Obtain photographs of material tickets, storage method, and location.
 +
# Review the Stockpile Management Plan if crushed concrete produced from an onsite crushing facility is used.
 +
# 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 local ordinances.
 +
#* Disposal of excavated 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.
  
 
{{top}}
 
{{top}}
  
 
==[[#CONSTRUCTION|CONSTRUCTION]]==
 
==[[#CONSTRUCTION|CONSTRUCTION]]==
 +
=== Aggregate Surface Course ===
 +
The subbase or subgrade must be free of rutting, potholes, and other irregularities. If deformities exist, they need to be bladed or scarified to a depth below the bottom of the irregularity and graded out before the aggregate surface course can be placed.
 +
 +
Installation of an aggregate surface source begins with placement of a dense graded aggregate on the grade by a truck, it is then pushed into place by a grader. If the required thickness exceeds 8 inches, multiple lifts will be required to reach the final thickness. Each lift requires a roller pattern to establish density of the material. Segregation can occur if material is handled too many times in the process of being placed. The aggregate surface should be graded within 1/2 inch of the crown and grades shown on the plans.
 +
 +
Poor compactive efforts and failure to adhere to placement guidelines will result in settlement and rutting. Rutting of the surface during construction and prior to final grading and shaping should be repaired by scarifying to a depth below the ruts and recompacting to 98% of the maximum unit weight. It is not adequate to only fill in ruts by blading the surface as this will just lead to segregation and further rutting.
 +
 +
=== Maintenance Gravel ===
 +
Maintenance gravel is used to repair irregularities in an aggregate surface course and for temporary access through driveways and intersections. Maintenance gravel must provide a flush transition to the road surface with positive drainage for all driveways, intersecting streets, and adjacent surfaces where traffic is maintained. Existing widths of all driveways and intersections must be maintained unless otherwise noted on the plans. During maintenance of an aggregate surface course, the existing approach width needs to be maintained in a smooth stable condition. If small spot repairs are performed, an excavator might take material directly from a truck and be used to grade the repaired areas. A plate compactor would be used to compact small, shallow repair areas. Compaction should be performed to a minimum 95% of the maximum unit weight.  Maintenance gravel should be removed the same day the area is paved.
 +
{|
 +
|+
 +
|-
 +
| [[File:306-007.jpg|200px|thumb|center|'''Maintenance Gravel for Temporary Access Driveway''']] || [[File:307-008.jpg|200px|thumb|center|'''Ensure Contractor Removes Traffic Control Devices Once Maintenance Gravel for Temporary Access Driveway has been Placed''']]
 +
|}
 +
 +
 +
{{top}}
 +
 +
==[[#INSPECTION & TESTING|INSPECTION & TESTING]]==
 +
=== Inspection ===
 +
The Inspector should utilize, at a minimum, the following tools to perform the required inspection:
 +
* 100-foot tape measure or longer
 +
* 25-foot tape measure
 +
* Measuring wheel
 +
* Chaining pin
 +
* 6-foot stick ruler
 +
* 4-foot level
 +
* Working plans
 +
* Survey rod
 +
* Camera
 +
* Hand auger
 +
Grade checks are required every 50 feet across the section to ensure all layers are within ±1/2-inch.
 +
The Inspector should obtain approved drawings and specifications for review. Lay out and discuss with the Contractor areas where crushed concrete is not permitted, if applicable.
 +
 +
=== Testing ===
 +
For evaluation of aggregate materials, use only certified aggregate sampling and testing technicians. Refer to the [https://www.michigan.gov/mdot/-/media/Project/Websites/MDOT/Business/Construction/Standard-Specifications-Construction/CFS-Manuals/Procedures-Aggregate-Inspection.pdf?rev=e2f19aadca344460afca48b7b9ddb31e&hash=5D3CB25E2CD084FACCFD616004CCEB82 Procedures for Aggregate Inspection] manual and project specifications for testing requirements and frequencies. The Engineer should coordinate with the region testing lab to ensure the required number of aggregate tests for the project are being completed.
 +
 +
For every new source, new day, or suspected change in material, a moisture check needs to be completed. Obtaining moisture readings from a nuclear density gauge is only an approximation and is often used as a guide in the field. Official determination of moisture content will be made from a field sample stored in a plastic bag with the moisture content checked for payment using the oven dry method only if it’s paid for by weight.
 +
 +
Density for each lift needs to be achieved before subsequent layers are built up. The maximum lift thickness permitted is 8 inches after compaction. If hot mix asphalt (HMA) will be placed over the aggregate surface course, density needs to achieve a minimum of 98% compaction. For all other cases, density needs to achieve a minimum of 95% compaction including applications where 3 inches or less are placed. The Inspector should ensure the minimum number of required density tests are being performed per the [https://www.michigan.gov/mdot/-/media/Project/Websites/MDOT/Business/Construction/Standard-Specifications-Construction/CFS-Manuals/Density-Testing-Inspection-Manual.pdf?rev=6ea61069b3b649e5bbd9362f000a4e0b&hash=44138356CA520616DF23E2E1D8E49AE0 Density Testing and Inspection Manual].
  
−
<span style="color: red"> -Reserved- </span>
+
{{top}}
 +
 
 +
==[[#MEASUREMENT, DOCUMENTATION & PAYMENT|MEASUREMENT, DOCUMENTATION & PAYMENT]]==
 +
=== Measurement and Payment ===
 +
Aggregate surface course and maintenance gravel can be paid by weight, area, volume, or per each area completed. Each load ticket must include the required information. Refer to [https://mdotwiki.state.mi.us/images_construction/9/95/2020-Standard-Specifications-Construction.pdf#page=198 Section 306.03.B of the Standard Specifications for Construction] for information required on each ticket.
 +
 
 +
* By weight: The scale weight of the material will be paid for. If the moisture content exceeds 8%, reductions to the load ticket to remove the excess moisture will need to be made. Final measurement will be in tons.
 +
* By area: The area will be measured by the length and width shown on the plans for the given thickness in square yards.
 +
* By volume: The volume will be measured based on plan dimensions for the aggregate surface course in cubic yards. If loose measure (LM) is noted in the pay item, the hauling units need to be counted, measured, and inspected.
 +
* By each: Typically, only driveways or intersections are paid by each. Count the total driveways or intersections where the aggregate surface course or maintenance gravel was installed.
 +
 
 +
==== Weighing Materials ====
 +
Materials paid for by weight are required to be weighed on an approved scale system. There are permanent and portable scale systems.
 +
 
 +
===== Permanent Scale System =====
 +
A permanent scale system is defined as a weighing device that has not been moved from a given location within the last six months. Scale inspections will be conducted by a private scale agency or the Michigan Department of Agriculture. These inspections are valid for one year. The scale owner will provide the Engineer and regional materials personnel written verification that the scale system has been inspected according to specifications.
 +
 
 +
===== Portable Scale System =====
 +
For portable scales, the Contractor will obtain scale approval from a local official sealer of weights and measures, or the Engineer may give approval based on verifying the results of the portable scales by passing the loads over another scale that has an official seal.
 +
 
 +
===== Platform Scales =====
 +
If the platform scales (permanent or portable) are observed in operation, the following are important:
 +
* The scales are operating freely.
 +
* The scales are reasonably clean.
 +
* The approaches are in relatively good condition.
 +
Platform scales need to be balanced at zero and should be periodically checked throughout the day. The Engineer will require a coupled vehicle to be reweighed with each unit being uncoupled at least monthly during its use on the project. The total weight of the uncoupled units must agree with the total weight of the coupled units within ±0.2%.
 +
 
 +
===== Tare Weights =====
 +
Tare weights should be recorded at least twice a day: once in the morning and once in the afternoon. It is good practice to ensure the hauling units are reasonably clean when performing this operation. Aggregates are weighed to the nearest 100 pounds.
 +
 
 +
=== Documentation ===
 +
The Daily Work Report (DWR) should show all computations, measurements, and supporting documentation needed to verify the quantity submitted for payment. Primary supporting documentation includes moisture and grade checks.
 +
[https://mdotjboss.state.mi.us/webforms/GetDocument.htm?fileName=1900.pdf Form 1900, Aggregate Inspection Daily Report], will need to be completed for every sublot of aggregate to track gradation acceptance.
 +
[https://mdotjboss.state.mi.us/webforms/GetDocument.htm?fileName=0582B.pdf Form 0582B, Moisture & Density Determination - Nuclear Method], is used to record density testing results.
 +
 
 +
{{top}
  
 +
==[[#LOCAL AGENCY PROJECTS|LOCAL AGENCY PROJECTS]]==
 +
Some local agencies have stricter gradation requirements than MDOT. Refer to the project specifications for aggregate surface course and maintenance gravel to ensure the proper material gradation is being followed.
 
{{top}}
 
{{top}}
  
−
==[[#MEASUREMENT AND PAYMENT|MEASUREMENT AND PAYMENT]]==
+
==[[#RAIL PROJECTS|RAIL PROJECTS]]==
  
 
<span style="color: red"> -Reserved- </span>
 
<span style="color: red"> -Reserved- </span>
  
 
{{top}}
 
{{top}}
 +
 +
  
 
[[Category:Construction Manual]]
 
[[Category:Construction Manual]]
 
[[Category:Division 3]]
 
[[Category:Division 3]]
 
[[Category:Section 306]]
 
[[Category:Section 306]]
 +
[[Category:New CM Format]]

Latest revision as of 14:47, 13 October 2025

306
Aggregate Surface Course


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.

Fine-Graded Aggregate: Fine-graded aggregate is a mixture of aggregates with a uniform distribution of small size aggregate particles passing through a #4 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

Aggregate surface courses are primarily used for low volume roadways, driveways, or temporary roadway surfaces. Maintenance gravel is used for temporary access as well as to repair rutting, potholes, or similar deformities of an existing aggregate surface course. Natural or crushed aggregates are commonly used. Different areas of the state require different thicknesses.


[top of page]

MATERIALS

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

Description of Materials

Material requirements are dependent on the final purpose of the roadway. In all cases, a dense graded material should be used. Gradation requirements can be found in Section 902 of the Standard Specifications for Construction.

  • Roadways that WILL Receive a Paved Surface: Use 21A, 21AA, or 22A aggregates.
  • Roadways that Will NOT Receive a Paved Surface: Use 23A or 23AA aggregates.
  • Maintenance Gravel: Use 21A, 21AA, 22A, 23A, 23AA, or salvaged aggregates.

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

Pictures of Materials

21AA Aggregate Pile (Limestone)
21AA Material
23A Aggregate Surface Course for a Roadway
Maintenance Gravel Placed for a Temporary Roadway


[top of page]

EQUIPMENT

The following list of equipment can be used for aggregate surface course and maintenance gravel work:

  • Bulldozer
  • Grader
  • Excavator
  • Dump truck
  • Front end loader
  • Vibratory roller
  • Gas powered rammer tamping machine
  • Plate Compactor
  • Transit or laser level
  • Leveling/grade poles

Description of Equipment

Aggregate surface course material is typically dumped on the grade by a truck and graded with a grader or bulldozer. Most equipment utilizes AMG to effectively shape the roadway. A vibratory roller is used to compact the aggregate after it is graded.

Pictures of Equipment

Smooth Drum Roller
Grader
Laser Transit


[top of page]

PRECONSTRUCTION

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

  1. Review the plans to verify the location of the work.
    • Take note of areas where vibratory compaction use is excluded, if applicable.
  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 and the cross-slope is in accordance with the project specifications.
  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 and sunlight 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 local ordinances.
    • Disposal of excavated 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.

[top of page]

CONSTRUCTION

Aggregate Surface Course

The subbase or subgrade must be free of rutting, potholes, and other irregularities. If deformities exist, they need to be bladed or scarified to a depth below the bottom of the irregularity and graded out before the aggregate surface course can be placed.

Installation of an aggregate surface source begins with placement of a dense graded aggregate on the grade by a truck, it is then pushed into place by a grader. If the required thickness exceeds 8 inches, multiple lifts will be required to reach the final thickness. Each lift requires a roller pattern to establish density of the material. Segregation can occur if material is handled too many times in the process of being placed. The aggregate surface should be graded within 1/2 inch of the crown and grades shown on the plans.

Poor compactive efforts and failure to adhere to placement guidelines will result in settlement and rutting. Rutting of the surface during construction and prior to final grading and shaping should be repaired by scarifying to a depth below the ruts and recompacting to 98% of the maximum unit weight. It is not adequate to only fill in ruts by blading the surface as this will just lead to segregation and further rutting.

Maintenance Gravel

Maintenance gravel is used to repair irregularities in an aggregate surface course and for temporary access through driveways and intersections. Maintenance gravel must provide a flush transition to the road surface with positive drainage for all driveways, intersecting streets, and adjacent surfaces where traffic is maintained. Existing widths of all driveways and intersections must be maintained unless otherwise noted on the plans. During maintenance of an aggregate surface course, the existing approach width needs to be maintained in a smooth stable condition. If small spot repairs are performed, an excavator might take material directly from a truck and be used to grade the repaired areas. A plate compactor would be used to compact small, shallow repair areas. Compaction should be performed to a minimum 95% of the maximum unit weight. Maintenance gravel should be removed the same day the area is paved.

Maintenance Gravel for Temporary Access Driveway
Ensure Contractor Removes Traffic Control Devices Once Maintenance Gravel for Temporary Access Driveway has been Placed


[top of page]

INSPECTION & TESTING

Inspection

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

  • 100-foot tape measure or longer
  • 25-foot tape measure
  • Measuring wheel
  • Chaining pin
  • 6-foot stick ruler
  • 4-foot level
  • Working plans
  • Survey rod
  • Camera
  • Hand auger

Grade checks are required every 50 feet across the section to ensure all layers are within ±1/2-inch. The Inspector should obtain approved drawings and specifications for review. Lay out and discuss with the Contractor areas where crushed concrete is not permitted, if applicable.

Testing

For evaluation of aggregate materials, use only certified aggregate sampling and testing technicians. Refer to the Procedures for Aggregate Inspection manual and project specifications for testing requirements and frequencies. The Engineer should coordinate with the region testing lab to ensure the required number of aggregate tests for the project are being completed.

For every new source, new day, or suspected change in material, a moisture check needs to be completed. Obtaining moisture readings from a nuclear density gauge is only an approximation and is often used as a guide in the field. Official determination of moisture content will be made from a field sample stored in a plastic bag with the moisture content checked for payment using the oven dry method only if it’s paid for by weight.

Density for each lift needs to be achieved before subsequent layers are built up. The maximum lift thickness permitted is 8 inches after compaction. If hot mix asphalt (HMA) will be placed over the aggregate surface course, density needs to achieve a minimum of 98% compaction. For all other cases, density needs to achieve a minimum of 95% compaction including applications where 3 inches or less are placed. The Inspector should ensure the minimum number of required density tests are being performed per the Density Testing and Inspection Manual.

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MEASUREMENT, DOCUMENTATION & PAYMENT

Measurement and Payment

Aggregate surface course and maintenance gravel can be paid by weight, area, volume, or per each area completed. Each load ticket must include the required information. Refer to Section 306.03.B of the Standard Specifications for Construction for information required on each ticket.

  • By weight: The scale weight of the material will be paid for. If the moisture content exceeds 8%, reductions to the load ticket to remove the excess moisture will need to be made. Final measurement will be in tons.
  • By area: The area will be measured by the length and width shown on the plans for the given thickness in square yards.
  • By volume: The volume will be measured based on plan dimensions for the aggregate surface course in cubic yards. If loose measure (LM) is noted in the pay item, the hauling units need to be counted, measured, and inspected.
  • By each: Typically, only driveways or intersections are paid by each. Count the total driveways or intersections where the aggregate surface course or maintenance gravel was installed.

Weighing Materials

Materials paid for by weight are required to be weighed on an approved scale system. There are permanent and portable scale systems.

Permanent Scale System

A permanent scale system is defined as a weighing device that has not been moved from a given location within the last six months. Scale inspections will be conducted by a private scale agency or the Michigan Department of Agriculture. These inspections are valid for one year. The scale owner will provide the Engineer and regional materials personnel written verification that the scale system has been inspected according to specifications.

Portable Scale System

For portable scales, the Contractor will obtain scale approval from a local official sealer of weights and measures, or the Engineer may give approval based on verifying the results of the portable scales by passing the loads over another scale that has an official seal.

Platform Scales

If the platform scales (permanent or portable) are observed in operation, the following are important:

  • The scales are operating freely.
  • The scales are reasonably clean.
  • The approaches are in relatively good condition.

Platform scales need to be balanced at zero and should be periodically checked throughout the day. The Engineer will require a coupled vehicle to be reweighed with each unit being uncoupled at least monthly during its use on the project. The total weight of the uncoupled units must agree with the total weight of the coupled units within ±0.2%.

Tare Weights

Tare weights should be recorded at least twice a day: once in the morning and once in the afternoon. It is good practice to ensure the hauling units are reasonably clean when performing this operation. Aggregates are weighed to the nearest 100 pounds.

Documentation

The Daily Work Report (DWR) should show all computations, measurements, and supporting documentation needed to verify the quantity submitted for payment. Primary supporting documentation includes moisture and grade checks. Form 1900, Aggregate Inspection Daily Report, will need to be completed for every sublot of aggregate to track gradation acceptance. Form 0582B, Moisture & Density Determination - Nuclear Method, is used to record density testing results.

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LOCAL AGENCY PROJECTS

Some local agencies have stricter gradation requirements than MDOT. Refer to the project specifications for aggregate surface course and maintenance gravel to ensure the proper material gradation is being followed.

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RAIL PROJECTS

-Reserved-

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