Chapter 3: Key Findings

The countries visited were thorough in their preparations for the scanning team's visit and were generous in sharing their experience and expertise. Based on discussions with experts in the countries visited, the team documented several key findings, or actions taken that have had a marked impact on pavement preservation activities and program success. These key findings are categorized in the same topic areas as the amplifying questions sent to the host agencies before the team's visit. They are outlined below by topic area and country.

MANAGEMENT PERSPECTIVE AND POLICIES

All the countries visited have made a commitment to designing and building long-lasting structural pavement sections on their national roadway networks. This decision has caused all of these nations to focus maintenance activities on surface courses to preserve the large investment in the underlying layers. This, in turn, promotes the use of relatively low-cost seals and thin overlays as the primary maintenance techniques, instead of more costly types of rehabilitation.

France

• As noted above, the French government has made a conscious decision to design and build extremely durable, long-lasting structural pavement sections - which include surfacing, base, and subbase materials - on the Motorway system.
  
  
• Every five years, a comprehensive road investment plan is developed for France's entire road system.
  

South Africa

• The South Africans, like the French, also build robust structural sections with a long service life into their national network. The methodology used, however, is quite different. In South Africa, roadway sections are constructed of cement-treated subbase covered by a high-quality crushed aggregate base course. The total thickness of these layers is typically 450 millimeters (subbase and base) in a total pavement structure thickness of 1 to 1.2 meters. The final layer is a thin asphalt section of 30 to 50 millimeters. In France, the bituminous layers are considerably thicker.
  
  
• A rolling five-year road improvement plan is developed each year using pavement management system data and funding optimization strategies. Consequences of various funding scenarios are evaluated and a program is selected that maximizes road conditions at a total program cost within the budget available. Potential savings for vehicle operating costs are also included in the optimization analysis, but user costs are not.
  
  
• The pavement management system has been used effectively to justify increased funding for road maintenance and preservation. Simple but clear presentations of network analyses and maintenance needs have been made to local and national politicians. These presentations have been successful in obtaining additional pavement preservation funds.

Australia

• Australia uses long-term (10-year) maintenance contracts to turn over total control and responsibility for roadway system maintenance, rehabilitation, and capital improvements to private contractors. These contracts are performance based and require contractors to meet a set of standards. Standards include roughness, texture, rutting, skid resistance, and remaining service life. These standards are measured and established at the beginning of the contract and monitored during the contract. Contractors are prequalified before they submit a contract proposal.
  
  
• Asset management programs for pavements have been used as effective methods for determining maintenance needs and increasing funding. Australian states have realized the importance of asset management for two reasons. First, asset management provides information and data that enable state transportation authorities to better manage their systems. Second, it provides a means to demonstrate to management the importance of additional funding for road assets.
  

RESOURCE COMMITMENT AND COST-EFFECTIVENESS

France

• Maintenance focus is on the wearing course. Providing initially high structural capacity enables officials to emphasize protecting the structure with relatively low-cost seals and thin overlays on a seven-to-10-year cycle. This also allows for a focus on maintaining good surface characteristics, such as high grip (skid resistance) and reduced noise.

South Africa

• Distress definitions for pavement management systems are conservative (i.e., severe crack threshold above three millimeters). This focuses maintenance intervention early in the pavement life cycle. In so doing, the South Africans use a higher percentage of relatively inexpensive techniques to keep water from the base structure.
  
  
• The South Africans schedule a high percentage of pavement management system-selected projects for implementation, including 80 to 90 percent for the national system. This is achievable because pavement management is accepted at the national level and by some maintenance communities at the provincial levels. This allows for network conditions to be optimized to as high a degree as funding will permit.
  

Australia

• Australia has tried to maximize operational efficiency and cost-effectiveness in the execution and implementation of maintenance works. This was initiated in part because of national policy requirements that mandate competitive procedures. This is accomplished differently in some states. Queensland, New South Wales, and Victoria have retained some in-house maintenance capabilities, but they have complied with the national policy by requiring their own forces to meet competitive requirements, such as prequalification of skills or tendering offers to perform work. In Western Australia, maintenance operations are competitively negotiated with private contractors. This has resulted in seven-to-17-percent savings for performing maintenance activities compared to benchmark estimates. Estimates assume that work will be performed at or above current standards. Ten-year contracts have just been initiated.
  
  
• Pavement management strategies for allocating maintenance resources vary by state, according to state perception of user needs. In more urbanized areas, roughness and functional considerations, such as ride and noise abatement, drive project selection in the pavement management systems employed. In more rural areas, structural considerations are emphasized. In Queensland in particular, the age of surface seals is modeled in the pavement management system and used as the primary predictive trigger for reseal applications. Modeling is based on both empirical and mechanistic analysis.
  
  
• For most states, rehabilitation is a minor part of the maintenance program and pavement preservation techniques are emphasized. This is partially because of budget constraints that require low-cost treatments in the early stages of pavement life. In Victoria, for example, it is typical for 90 percent of the annual maintenance budget to be committed to preservation, while 10 percent is committed to rehabilitation.
  
  
• Operating costs for vehicles are used in cost modeling for pavement management systems in most states. This drives treatment selection toward measures that reduce operating costs, such as improved smoothness.
  

TREATMENTS, TECHNIQUES, AND PERFORMANCE

All three countries use only quality materials for both bitumen and aggregate.

Generally, crushed granite and proven polymer-modified asphalt binders are used. This is ensured through the use of rigorous specifications. Materials sources are specified and there is no inhibition to using sources a great distance from the project site.

France

• The primary preservation treatment on high-volume roadways is mill and inlay. Often, a high modulus asphalt mix that has proven to be rut resistant (limited to a 10/20 penetration grade) is incorporated into the projects.
  
  
• Cold asphalt concrete has been used extensively with good success on low-volume roads as a riding surface (75 to 100 millimeters). The cold asphalt concrete mix process focuses on achieving good coating of the aggregates and is preferred over hot-mix asphalt for low-volume roads.
  

South Africa

• South Africa makes extensive use of chip seals. Well-established and standardized guidelines based on research and practical experience are used. Chip seals are routinely used on routes with 50,000 equivalent vehicle units (EVU) or higher. The pavement management system has verified that surface seals are effective treatments for preserving pavement life.

• In some instances, hot-mix asphalt overlays are covered immediately with chip seals to provide sufficient surface friction and, at the same time, ensure a system
  more impervious to water.

Australia

• 
  Figure 5. Australia uses a technique of pre-coating aggregates for chip seals to reduce aggregate loss.

  All the states visited use a treatment called geotextile-reinforced sprayed seal. The construction sequence involves spraying a tack coat, placing the geotextile, and then applying a chip seal on top. Information was presented showing that this treatment reduced reflective cracking. In Victoria, 12 to 15 years of performance is expected from this treatment. Typically, a crumb-rubber bitumen or conventional bitumen is used for these seals.
  
  
• The technique of pre-coating aggregates for chip seals is used throughout Australia. This practice prevents or reduces the loss of aggregates on chip seals.
  
  
• All the Australian states make extensive use of polymerized asphalts. Considering the heavy and large amounts of trucks using rural roads, states believe there is a need for the best-performing bitumen possible. Styrene butadiene styrenetype polymers are predominately used in their bitumens (at twice the rate used in the United States) for both hot-mix asphalt and chip seal applications.
  
  
• Crumb rubber modifier (15 to 20 percent) is used in bitumen for chip seals. This has been effective in reducing reflecting cracking.
  
  
• Even when using full-depth hot-mix asphalt pavements, a chip seal is placed on the base material (or subbase) before the asphalt layers are placed. This prevents moisture infiltration or capillary action.
  
  
• New South Wales has been successful in placing thin (40-to-60-millimeter) asphalt overlays on existing concrete pavements by placing hydrocarbon curing and a tack coat before placing the overlay on the concrete. The overlays on more recent plain concrete pavements are done primarily for noise control, while those on older jointed reinforced concrete pavements are done for ride quality when large-scale diamond grinding equipment is not available. There are also economic benefits, as well as benefits in locations where there are level constraints but maintenance of reflective cracking is necessary.

• A chip seal system incorporating glass fibers is used in New South Wales to prevent reflective cracking. The process involves spraying a coat of polymer-modified bitumen emulsion, followed by blowing chopped fibers on the surface and spraying a second coat of polymer-modified bitumen emulsion, all in one operation. As with all emulsion seals, control of early trafficking is needed until a degree of curing (evaporation of water as opposed to breaking of emulsion) has occurred.
  

INNOVATIVE METHODS, PRACTICES, AND PROCEDURES

France

• Four-year warranties are used in contracts when applying preventive maintenance techniques. The functional properties warranted are friction, rutting, and smoothness. The responsibility of the contractor for the repair of non-compliant sections reduces with time and traffic. A secondary effect of the application of warranties has been the innovation of materials and mixtures by contractors and material suppliers. In most instances, contractors are vertically integrated so the innovation takes place within the company.
  
  
• Under a system called the Charter of Innovation, the government and industry share in the risk of experiments to develop new and innovative products. Requests for proposals are issued annually for new products and test sections are constructed. The company and government share in the cost of conducting surveys. Successful products are then accepted nationally for inclusion in the preventive maintenance program.
  
  
• A process has been developed by a contracting firm that incorporates vegetable oil in a 70-100 penetration grade bitumen, some of which has been modified. This is called a bio-binder. The objective has been to produce an emulsion that is safe (handling temperatures), environmentally friendly (non-solvent-based renewable resource), and has the necessary technical properties to perform. The first experimental section was built in 1997 and seven million square meters were placed in 2000.
  

South Africa

• A stress-in-motion device to measure contact stresses in vehicles has been developed and is in regular use.
  
  
• A crack activity meter has been developed to measure reflective cracking potential and the need to restore the surface before placing an overlay. The meter can measure both horizontal and vertical movement simultaneously and fits between the dual wheels of a test vehicle. Data is captured and processed electronically.
  
  
• SANRAL has developed a fitness-for-purpose certification system for bituminous products that allows for the early implementation of innovative and proprietary products not covered by existing standards. The program provides potential users with a scientifically sound basis for their decisions on whether a product is fit for its intended purpose.

Australia

• In New South Wales, sandwich seals with two-coat geotextile reinforced treatment have resulted in an acceptable performance (no reflective cracking) for 11 years on roadways with traffic volumes of 1,200 vehicles per lane per day.
  
  
• In New South Wales, a pavement condition survey vehicle called Road Crackä has been developed to detect cracking on the pavement surface. This vehicle measures the full lane width at 80 kilometers per hour with real-time processing, measuring cracks down to a millimeter and classifying them as longitudinal, transverse, and crocodile. Sawn joints are identified. Alternatively, at lower speeds, a full digital image of the road surface can be retained. Funding is being sought to develop and market this vehicle.