1. Preparation: Ensure the aggregate gradation and binder content are correct and the materials are properly heated.
2. Mixing: Prepare the mix with PMB 82 E-10 and aggregates in the asphalt plant.
3. Transporting: Transport the mix to the site while maintaining the correct temperature.
4. Paving: Lay the mix uniformly with a paver and begin rolling immediately after laydown.
5. Compaction: Use breakdown, intermediate, and finish rollers to achieve the target density.
6. Surface Finishing: Ensure the final surface meets skid resistance and smoothness criteria.
7. Quality Control: Perform regular quality checks on mix, binder content, gradation, and compaction.
8. Cooling and Maintenance: Allow the mix to cool and periodically inspect the pavement after construction for long-term performance.

Step-by-Step Procedure for Laying SMA with PMB 82 E-10

1. Material Selection and Preparation

1.1 Aggregate Selection

• Coarse Aggregates: Select angular, durable aggregates to ensure proper stone-on-stone contact, which is crucial for SMA performance. The coarse aggregates should have a high-strength index.
• Fine Aggregates: The fine aggregates should complement the coarse aggregates, ensuring the right gradation for SMA’s open-graded structure.
• Filler Material: Use stone dust or hydrated lime as a filler to improve binder-aggregate adhesion and prevent stripping under wet conditions.

1.2 PMB 82 E-10 Binder Selection

• PMB 82 E-10 is a high-performance polymer-modified bitumen, specifically designed to improve high-temperature stability, elasticity, and fatigue resistance.
• The binder’s softening point and viscosity need to be within the range suitable for the climate and traffic conditions.
• For SMA, PMB 82 E-10 typically has a binder content between 5% to 7% of the total mix, depending on the traffic loading and climatic conditions.

2. Mix Design and Optimization

2.1 Aggregate Gradation

• Follow the SMA gradation specifications for coarse and fine aggregates. The gradation typically has a higher percentage of larger aggregates compared to regular hot-mix asphalt.
• The Void in the Mineral Aggregate (VMA) should be high (around 18-22%) to accommodate the higher binder content used in SMA.
• Ensure that the aggregates are well distributed to achieve good void-filling with the binder.

2.2 Binder Optimization

• Trial Mixes: Prepare different trial mixes to determine the optimum binder content (OBC) for the mix.
• Perform laboratory tests (e.g., Marshall Stability, Flow, and Compaction Tests) to find the binder content that gives:
  • Good cohesion between aggregates.
  • Adequate resistance to rutting.
  • Workability suitable for paving and compaction.
• Performance Testing:
  • Dynamic Shear Rheometer (DSR) tests for viscosity and elasticity.
  • Fatigue testing to ensure the mix can handle repeated loading without cracking.

3. Asphalt Mixing Plant Preparation

3.1 Heating of Materials

• Binder (PMB 82 E-10): Heat the polymer-modified bitumen to the recommended temperature, typically around 160°C to 180°C. Ensure that the binder is kept at a consistent temperature during the mixing process to prevent segregation.
• Aggregates: Pre-heat the aggregates to 150°C to 170°C to ensure proper coating of the binder. Overheating the aggregates should be avoided to preserve the characteristics of the PMB binder.

3.2 Mixing in the Plant

• In the mixing plant, ensure that the PMB 82 E-10 binder is thoroughly mixed with the preheated aggregates. The mixing time should be sufficient to achieve a uniform distribution of the binder around each aggregate particle.
• The mix should be consistent and homogeneous, with the binder adequately coating the aggregate surface. The polymer-modified binder improves adhesion, thus providing better cohesion and reducing the chances of stripping.

4. Transportation and Paving

4.1 Transporting the Mix

• Truck Transport: After mixing, transport the SMA mix in asphalt transport vehicles that are capable of maintaining the desired temperature.
• Temperature Control: The mix temperature during transport should remain between 140°C to 160°C to ensure the binder doesn’t harden prematurely, which could affect the workability of the mix.
• Use insulated covers or thermal blankets to maintain the temperature during transportation if the distance is long.

4.2 Paving the Mix

• Paver Setup: Use a paver to lay the SMA mix in uniform layers. Ensure the paving machine is calibrated to lay the mix at the specified thickness (usually 30 mm to 50 mm, depending on design requirements).
• Laydown Speed: Ensure the paving speed is controlled to allow for uniform distribution of the mix.
• Initial Compaction: Immediately after laying, begin initial compaction using a vibratory roller to prevent the mix from cooling too quickly and to achieve proper stone-on-stone contact.

5. Compaction

5.1 Breakdown Rolling

• Use a steel-wheel roller (static or vibratory) for initial breakdown rolling immediately after the mix is laid. This step helps compact the mix and reduce the air voids.
• Perform gentle rolling to avoid pushing the mix and causing segregation.

5.2 Intermediate Rolling

• Once the initial rolling is complete, use a rubber-tired roller for intermediate compaction. This type of roller helps achieve better surface texture and further compacts the mix without causing segregation.

5.3 Finish Rolling

• Final compaction should be done with a static steel-wheel roller or a rubber-tired roller, ensuring that the surface is compacted to the desired density (typically 96%-98% of theoretical maximum density (Gmm)).
• Ensure no over-compaction, as this may damage the mix and lead to premature failure.

5.4 Compaction Temperature

• Maintain a compaction temperature between 140°C to 160°C. The cooler the mix gets, the harder it becomes to compact, so ensure adequate compaction before the mix temperature drops below this range.

6. Surface Finishing and Quality Control

6.1 Surface Texture

• Check the surface texture to ensure skid resistance and smoothness. The SMA mix, due to its open gradation, may provide a slightly rough texture, but it should meet the required skid resistance criteria.

6.2 Smoothness Testing

• Perform a profilograph test or use a stringline to ensure the surface meets the required smoothness tolerance.

6.3 Quality Assurance

• Throughout the process, perform quality control (QC) checks such as:
  • Binder content checks to ensure it is within the specified range.
  • Aggregate gradation to confirm it meets the SMA specifications.
  • Compaction checks to ensure the density is within the acceptable limits.

7. Post-Construction Monitoring and Maintenance

7.1 Cooling and Curing

• Allow the surface to cool and cure gradually. PMB 82 E-10 will take a little longer to cool compared to conventional binders, so it’s important to prevent traffic on the surface until it’s fully cooled and has sufficient strength.

7.2 Periodic Inspection

• After the pavement is open to traffic, regular inspections should be carried out to check for signs of distress like cracking, rutting, or fatigue failure. SMA with PMB 82 E-10 should perform well under heavy traffic and adverse conditions, but early detection of any issues can help with timely maintenance.

7.3 Maintenance

• Periodic maintenance may include crack sealing or surface treatments to keep the surface in good condition for the design life of the pavement.