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Chapter 5
Pavement, Materials, and Recycling
5.3. Flexible Pavement/Asphalt

Flexible pavement (asphalt) maintenance activities provide public safety, protect personal property, preserve the state's capital investment, and maintain a riding quality that is satisfactory to the traveling public. Road surface maintenance typically involves the use of asphalt and other materials to create impervious surface areas or to repair existing road surfaces. Surface and inlay repair includes all repairs of road bases, surface, and shoulder irregularities, including asphalt and concrete surfaces. Asphalt plant production includes production of asphalt for patching materials, staging, moving, stockpiling and setup of asphalt plants.

The basic input materials used in asphalt preparation are hot liquid asphalt and aggregates, such as sand and gravel. Some smaller quantities of recycled asphalt pavement, sulphur, rubber, lime and foundry sands may also be incorporated into the mix. The type of process technology used is important because it also effects quantity and quality of resulting air and waterborne contaminants. Air emissions from these mixing operations are a concern primarily because of high hydrocarbon, nitrous oxides, sulphur dioxide, carbon monoxide and particulate concentrations. Waterborne contaminants originate in aggregate storage areas, air scrubbers, and vehicle wash-down areas. Airborne contaminants are typically removed using filtering baghouses, while waterborne contaminants are usually removed in large settling ponds. Stormwater collected from aggregate storage areas and wastewater from the spraying down of HMA transport vehicles should be directed to a contaminated water treatment area. Treatment may consist of catchment basins and or settling ponds and oil-water separators. Treated water should then be discharged to local storm sewers or to a nearby river. Settled fines in the catchment basins should be removed and landfilled after being left to dry out as much as possible. [N]

A pollution prevention plan can encourage examination of existing process and pollution prevention technologies and consideration of upgrades or equipment improvements. Management practices play a key role in pollution prevention. Opportunities for pollution prevention through management, such as installing hot liquid asphalt storage tank high-level alarms, using soap instead of diesel for washing down trucks, and partially or completely containing raw aggregate storage areas, are suggested. Waste materials such as used baghouse socks, collected dust materials and dried sludge from settling ponds should be treated and recycled where possible. If there are no other alternatives, the materials should be disposed of in an environmentally responsible manner.

There are opportunities for changes on the most basic level in the asphalt production industry, namely changes to the input materials and products made. Because of the strict specifications and gradations required for quality HMA production, certain sands and gravels are required as the bulk of aggregate materials. However, other materials can be added to the basic aggregates without compromising the final HMA quality. Such materials are broken asphalt (taken from a road that has been ripped up), sulphur, rubber and foundry sands. Broken asphalt, known in the industry as RAP (recycled asphalt pavement), can almost always be incorporated into HMA and meet the required gradation.

 

5.3.1 Asphalt Cement Crack and Joint Grinding and Digouts/Structural Repair
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Flexible pavement is susceptible to cracking, and the cracks should be repaired to prevent the entrance of moisture into the subgrade. In some instances, cracks need to be cleaned prior to filling. A stiff broom, compressed air, or a gouge-type tool or mechanical router are typically used to clean the cracks. Cracks are then filled with rubberized sealant, emulsion or liquid asphalt. Fine sand may be applied to the surface of the crack after it has been filled. The repair of slippage cracks requires the removal of the surface layer prior to patching with mixed asphaltic concrete. Other subtasks associated with this activity include vehicle operation, disposal of removed material and grindings, and post-sweeping.

Structural pavement failure (digouts), pavement grinding and paving applies to significant repairs to structural pavement that require removal of the roadway surface using graders and grinders. Subtasks associated with this activity include vehicle operation, asphalt removal, disposal of removed material and grindings, pre- and post-sweeping.

Pollutant sources associated with this work include leaks, spills, dust and grinding can result in release of fuel, asphalt release agents, hydraulic fluid, oil, sediment, aggregate material and asphalt grindings. Water may be applied during grinding or post-sweeping operations. Recommended environmental stewardship practices to control and minimize pollution include standard best management practices (BMPs) such as illicit connection/illicit discharge reporting and removal, scheduling and planning, illegal spill discharge control, vehicle and equipment fueling, vehicle and equipment maintenance, solid waste management, hazardous waste management, liquid waste management, sanitary/septic waste management, safer alternative products, spill prevention and control, and sweeping and vacuuming. [N]

 

5.3.2 Asphalt Paving
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Asphalt work involves the patching or resurfacing of the roadbed with a mixture of mineral aggregate and bituminous binder. The purpose is to repair degraded asphalt surfaces. The primary subtasks include equipment operation, pre- and post-sweeping, asphalt application, binder application (tack coating), pavement application and compaction roller operation. Pollution may occur from leaks, spills and stockpiled material from sweeping. Potential pollutants may include: fuel, asphalt release agents, hydraulic fluid, oil, sediment, asphalt and petroleum-based binders. The use of water during sweeping, asphalt application, binder application, compaction roller operation and evaporative cooling must be controlled to prevent unpermitted non-stormwater discharges. Recommended environmental stewardship practices include: illicit connection/illicit discharge reporting and removal, scheduling and planning, illegal spill discharge control, vehicle and equipment fueling, vehicle and equipment maintenance, solid waste management, hazardous waste management, liquid waste management, sanitary/septic waste management, material use, safer alternative products, paving operations procedures, spill prevention and control, sweeping and vacuuming and water conservation practices. [N]

The asphalt plant and other facilities should be operated in such a manner so as to safeguard the air and water resources by controlling or mitigating environmental pollution in accordance with all Environmental legislation. Additional environmental stewardship practices that can minimize environmental impacts from paving operations include the following:

  • Ensure that contractors and/or staff who fuel and operate asphalt plants have an adequate spill plan and materials for spill containment.
  • Establish mixing plants outside of riparian corridors, site location to be approved by the Region Environmentalist/ Biologist and/or resource agencies.
  • Use commercial asphalt plants for asphalt supply, where economically feasible.
  • Provide areas for truck chute cleanout with proper containment of wet concrete.
  • Protect inlets and catchments from fresh concrete during inclement weather.
  • Where possible, perform surface work in dry weather, to minimize any runoff of potentially hazardous material.
  • Do not use volatile organic compounds (VOCs) to liquefy asphalt except for asphalt used in:
  • Long-life stockpile material for patching and repair.
  • Low temperature applications from October 16 to May 1.
  • Penetrating prime coat for preparing an untreated absorbent surface to receive asphalt.
  • Pre-treat all grader blades, truck beds, tires, asphalt distributors, or other equipment and tools with vegetable oil or other approved proprietary product as a release agent for asphalt. Hand sprayers can be used to apply vegetable oil.

 

5.3.3 Emergency Pothole Repairs
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Emergency pothole repairs are unscheduled, emergency repairs necessary for the protection of the traveling public. Pothole repairs involve the filling and resurfacing of potholes along flexible pavement portions of roadways and highways to eliminate holes and cuts in the pavement. Because of the unscheduled nature of the repairs, the applicability of BMPs is limited to planning measures that facilitate emergency response in an environmentally sound manner.

The potential for spilled patch material should be managed through safer alternative products when available, and appropriate vehicle and equipment maintenance and fueling practices. [N]

 

5.3.4 Sealing Operations
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Seal coats may be required for asphalt pavement due to erosion or oxidation of the roadway surface. Coatings may also be used to reduce the permeability of the surface or to reduce slipperiness. Seal coats include fog seal (emulsion and water), sand seal (asphalt and sand), chip seal (emulsion and rock screenings) and slurry seal (emulsion, additives, water and aggregate). Chip sealing provides a bituminous surface treatment (BST) to maintain and extend longevity for roads, and underlies many other maintenance and operations activities, such as shoulder rehabilitation, vegetation and shoulder projects. Crack sealing and surface treatments can extend the useful life of a pavement and delay the need for more costly or environmentally intrusive repairs. When crack densities are low to moderate, crack sealing is effective; however, as densities progress from moderate to high, surface treatments such as chip sealing are more effective.

Primary subtasks include pre- and post-cleaning, seal application, sand or aggregate application and compaction roller application. Associated subtasks include equipment operation. Potential pollutant sources include leaks, spills, dust, material tracking and excess release agent. These pollutants can release fuel, asphalt release agents, hydraulic fluid, oil, sediment, aggregate material and asphalt emulsion. Water may be applied during post-sweeping operations and needs to be managed to prevent polluted discharge.

Much research has been performed in the United States and abroad on the materials, design, construction techniques, and effectiveness of chip seals in practice. Louisiana Department of Transportation and Development chip seal practice research was completed in 1998, South Dakota completed research on chip seal best practices in 2000; and Oregon DOT chip seal research; however, environmental stewardship recommendations particular to this paving practice have not been explicitly addressed. Research is being summarized through a survey of BMPs and a research synthesis, started in fall 2003 with anticipated publication in 2005. According to the Project Investigator, the only environmental practice found was wetting the aggregate to reduce dust; however, this practice may not be included in the synthesis as wetting the aggregate can degrade adhesion. [N]

DOTs have employed the following environmental stewardship practices primarily to control water related discharges: illicit connection/illicit discharge reporting and removal, scheduling and planning, illegal spill discharge control, vehicle and equipment fueling, vehicle and equipment maintenance, solid waste management, hazardous waste management, liquid waste management, sanitary/septic waste management, material use, paving operations procedures, safer alternative products, spill prevention and control, sweeping and vacuuming and water conservation practices. [N]

The Montana Department of Transportation (MDT) developed the following Sanding and Chip Seal Material Specifications for PM-10 Nonattainment Areas, to control air quality: [N]

  • Furnish aggregate surfacing materials free of deleterious material except as permitted.
  • Do not use scoria (fired clay commonly found in conjunction with burned coal in the lignite fields of the state) as aggregate to be bituminized.
  • Ensure no combination of shale, clay, coal, and soft particles exceed 3.5 percent.
  • Ensure the aggregate is free of wood and other plant material.

For Crushed Top Surfacing Type "Washed Sand," MDT meets the following requirements for crushed top surfacing type "A", including added binder or blending material: [N]

  • Dust Ratio: Ensure that portion passing the No. 200 sieve does not exceed two-thirds of the portion passing the No. 40 sieve.
  • Ensure the maximum liquid limit and plasticity index for the material passing the No. 40 sieve is 25 and 6 respectively.
  • Ensure the composite aggregate is free of adherent films of clay and other matter that prevents the aggregates thorough coating with bituminous material. Ensure the bituminous material adheres to the material upon contact with water.
  • Ensure that when the aggregate is to be bituminized, both the material source and the composite aggregate have a volume swell not exceeding 10 percent and not showing cracking or disintegration.
  • Do not remove intermediate sizes from the material during production, unless authorized in writing.
  • Ensure the aggregate has a wear factor not exceeding 50 percent at 500 revolutions.
  • Ensure at least 35 percent by weight of the aggregate retained on the No. 4 sieve has at least one mechanically fractured face.

For cover material, MDT: [N]

  • Ensures the material for Grades 1A through 4A are non-plastic. For Grade 5A the liquid limit and plasticity index for the material passing the No. 40 sieve cannot exceed 25 and 6 respectively.
  • Ensures the composite aggregate is free of adherent films of clay, vegetable matter, frozen lumps, and other extraneous matter that prevents thorough coating with bituminous material. Ensure the bituminous material adheres to the material upon contact with water. Ensure no combination of shale, clay, coal, and soft particles exceed 1.5 percent.
  • Ensures the aggregate has a wear factor not exceeding 30 percent at 500 revolutions.
  • Ensures at least 70 percent by weight of the coarse aggregate for Grades 1A through 4A have at least one fractured face. Ensure at least 50 percent by weight of the coarse aggregate for Grade 5A has at least one fractured face.

 

5.3.5 Asphalt Equipment Cleaning
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Diesel fuel used to be the product of choice to clean and pretreat equipment when working with bituminous pavement; however, environmental regulations prohibit dumping or spilling diesel or asphalt. The following policy is the best known management practice when asphalt cleaning is necessary. [N]

  • Eliminate diesel as a releasing or cleaning agent and use environmentally sensitive cleaning and releasing agents.
  • Spray the beds down with vegetable oil after each load using just a thin stream at the top of the bed, it will run down and coat the entire side, then put one coat on the floor. Spray once as needed. At the end of the day there may be some mix on the tailgate, spray a thin bead around the top; the next day the mix should remain soft and come off with the first load.
  • Spray vegetable oil on the grader blades once a day or as needed.
  • Spray it down with the vegetable oil during the day, then clean it with a citrus based cleaner in the evening only as needed.
  • The asphalt distributor bar may need to be coated with vegetable oil after every spray.
  • Using vegetable oil on tools such as rakes and shovels works well, the mix does not build up on them, and what does remain can be easily tapped off.
  • Carry adequate erosion control supplies (diapers, kitty litter, shovels, etc.) to keep materials out of water bodies.
  • Use heat sources to heat and clean tack nozzles during operations.
  • Contain all products (including the cleaning product and the contaminated asphalt residue cleaned from the equipment) during cleaning using tarps, sand pads, pails or other collection methods to avoid spillage or accidental release of cleaning products.
  • When cleaning the distributor bar, always catch any diesel or asphalt. Use a tray and recycle the diesel or asphalt into the tank, then reverse the pump to clean out the piping and snivies or reverse the pump to suck all the asphalt and diesel back into the tank. Consult the asphalt distributor's operations manual for the correct method to reverse suction.
  • Do not clean equipment or tools near streams, ponds, or drainage structures.
  • Remove pieces of asphalt by scraping or other mechanical means, if possible, prior to application of a cleaning agent. Asphalt removed solely by mechanical methods is disposed of as construction and demolition debris.
  • Use a minimal amount when a petroleum product is used for cleaning and recover all of the cleaning product.
  • Use hand sprayers or other similar devices to minimize the amount of petroleum product applied.
  • Report releases of petroleum products.

 

5.3.6 Pavement Disposal
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Pavement should be recycled whenever possible.

Contaminated sand, soil, asphalt pavement residue, and other debris containing petroleum products resulting from activities such as paver cleaning with petroleum products should be handled as petroleum contaminated soil/debris and should be disposed at an authorized disposal site.

Recognizable uncontaminated broken concrete and asphalt from demolition activities or excess material from a project should be taken to an off-site disposal facility or to a construction and demolition waste processing facility and/or not disposed of within 30 meters (100 feet) of wetlands, archaeological sites or other sensitive environmental areas.

 

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Continue to Section 5.4»
 
Table of Contents
 
Chapter 5
Pavement, Materials, and Recycling
5.1 Preventative Maintenance and Pavement Management Systems
5.2 Stormwater Management in Paving Operations, Grinding, and Pavement Maintenance
5.3 Flexible Pavement/Asphalt
5.4 Concrete Installation and Repair
5.5 Pavement Marking
5.6 Curb and Sidewalk Repair
5.7 Recycling in Pavement and Roadside Appurtenances
5.8 Maintenance of Dirt and Gravel Roads
   
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