Stylink® PMAC Temperature Guidelines
| Recommended Temperature Ranges | |
|---|---|
| Short Term Storage | 300 - 340 °F (149-171°C) |
| Long Term (up to 3 weeks) | 260 - 290 °F (127-143°C) |
| Extended Term (> 3 wks) | No Heat |
| Shipping to Job Site | 310 - 350 °F (154-177°C) |
| Job Site Storage | 300 - 350 °F (149-177°C) |
| Stylink® Grade* | Typical* Mix Temperature | Typical* Compaction Temperature |
|---|---|---|
| PG 58-34 PG 58-40 |
270 to 300°F (132-149°C) | 230 to 260°F (121-127°C) |
| PMAC Type IB PG 64-34 PG 64-28 |
290 to 310°F (143-155°C) | 250 to 270°F (121-132°C) |
| PMAC Type IC PG 70-22 PG 70-28 |
310 to 320°F (154-160°C) | 260 to 290°F (127-143°C) |
| PMAC Type ID PG 76-22 PG 76-28 PG 82-22 PG 82-28 |
300 to 350°F (149-177°C) | 275 to 300°F (135-149°C) |
|
*NOTES: Mixing and Compaction temperatures are given for dense graded mixtures. These are general guidelines; Stylink® products are formulated locally to meet local specifications and performance needs. Contact your local SemMaterials representative for specific recommendations on the product you are using. Mixing temperatures may be adjusted to compensate for loss of temperature during transport or extremes in ambient temperature, but care should be taken not to heat low temperature grades (-34 and -40) higher than necessary. Click for a handling checklist with guidelines for shipping, storing, manufacturing, hauling, laying and compacting Styling modified asphalt. |
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Prevent localized overheating. If reheating is required, it should be done gently, with care taken not to locally overheat the modified asphalt. Hot oil heating systems are preferred to prevent localized overheating, and recirculating the material in the tank helps distribute the heat. Of course, hot oil heating coils and recirculation during heating are good practice with any asphalt materials.
HMA Plant Production
Stylink® PMAC needs no special equipment during production. Stylink® PMAC can be used in batch or drum mix plants without any special equipment, alterations or additions to the plant. The production of Stylink® hot mix is not much different from normal mixtures. There are some subtle differences, however, which should be taken into consideration to get the most benefit from the enhanced properties. The cautions below may not apply to all grades.
Pumps and meters correctly sized and calibrated. Stylink® PMAC has a higher viscosity and, therefore, you may find the pumping speed is slower. This usually happens when the temperature drops below the recommended mixing temperature, or a very heavy duty grade (PG 76-22 or higher) is used. In extreme cases this may lower the AC content of the mix if it’s not carefully monitored. To prevent any problems the pump should be correctly sized, and mass flow meters should be calibrated using the correct material and temperature.
Controls on weigh buckets may need adjustment. The increased viscosity may also cause the batch plant weigh bucket to empty more slowly. If this should happen, you may need to adjust the weight controls. (This problem doesn’t occur very often, and is mainly seen with the very heavy duty grades, or when the temperature is below the recommendation.) Clean plant with hot aggregate. If you use fuel oil for cleaning, be sure to run clean hot aggregate through the equipment shortly after the oiling operation. Better yet, just use hot aggregate without fuel oil for clean-up.
Correct temperatures are the key to success. Standard procedures for predicting conventional HMA mixing and compaction temperatures using viscosities do not work with Stylink® modified asphalt. Stylink® PMAC’s special properties were not considered when these were developed. To get the best results, the temperature of the mix as it is being laid is the most important. So that the temperature at the time of construction is optimal, the plant mix temperature should be adjusted as necessary, taking into consideration such things as the climate, distance of haul, etc. Care should be taken that very low temperature grades (-34, -40) are not heated higher than necessary. The table gives very general guidelines for recommended Road Science™ Stylink® specifications.
HMA Transport
The polymer may cause the Stylink® modified hot mixture to be “stickier”. This reduces the chance for draindown to occur. However, if the mixing temperature is too high, draindown may cause problems in the truck bed. Our customers have found that when the recommended mix temperature is used, there is practically never a draindown problem.
Release Agents prevent problems. If you have a problem with buildup in the truckbed, there are several possible release methods that you can use and several preventative measures to take. Many states have approved lists of release agents. Using dry detergent powder in addition to the soapy slip agent has helped in some cases, especially with open graded mixtures. Clean truckbeds prevent build-up and sticking. The truck beds should be cleaned at the end of each load. Material in the bed increases the probability of the next load sticking. If the truck beds are not maintained during the hauling operation, there may be major problems getting them cleaned up after they cool.
Truck liners may help. Some of our customers have had excellent results by placing wooden liners on the bottom of the truck beds, or by using polymer truck bed liners. The wooden liners absorb the release agent, extending its effectiveness.
Avoid cooling the material; tarping helps. If there is material sticking to the truckbed, the problem will be made worse if liquid soap agent is sprayed on top, cooling down the truck bed. If the truck bed is kept warm, it will clean itself. Tarping the truck will also keep the mix hot during transport, and is strongly recommended.
Some agencies suggest silicone. In some states, 1½ ounces of liquid silicone is used routinely in each tanker load of modified asphalt delivered. The mixture flows better under the paver screed. Silicone, however, can affect the binder testing of the modified asphalt, giving false results. Silicone can also irreversibly damage test equipment. If silicone is used, testing samples should be taken before the silicone is added.
Laydown
The Stylink® modified asphalt mixtures are laid with normal paving equipment, so specialized machinery isn’t needed. The equipment clean-up may be a little more difficult, but you can use standard clean-up methods.
Uniform, continuous paver operation produces the highest quality pavement. It’s always a good idea to coordinate plant production and paving operations so there is a continuous flow of mix supplied to the paver. This is particularly true with Stylink® modified hot mix. Continuous delivery to the laydown operation prevents the mix from prematurely cooling. The polymer modified liquid binder has an absolute viscosity two to four times greater than conventional AC’s, and may be difficult to handle if it is allowed to cool.
Preheated screed prevents problems. The screed heater on the laydown machine should be used to preheat the screed plate at the start of each new paving operation. A cold screed may cause the Stylink® modified mix to tear, resulting in an open, course texture. You can let the first truckload of mix help heat the screed by first conveying the mix to the screed, then waiting for a little bit before continuing with the laydown. We’ve seen very good results when this technique is used.
Prevent sticking with correct temperatures. The Stylink® technology makes the mix a little stickier than unmodified HMA. The workers may complain about the stickiness when working the mixture by hand. The problem can be avoided if the mixture is delivered to the jobsite at the recommended temperature.
Surface temperatures. Most specifications require the temperature of the surface on which hot mix is to be placed be at least 50°F (10°C) for lift thicknesses less than 1 1/2 inches. Polymer modified asphalt mixes may cool somewhat differently than conventional mixes (usually more slowly), but experience has shown that a minimum surface temperature of 50°F for all compacted lift thickness gives the best results.
Air temperatures. If the air temperature is lower than 50°F (10°C), the mix temperature may need to be adjusted slightly higher than normally recommended for that grade. The higher temperature allows more time for proper placing and compaction of the mixture, thus providing the workability and results you want. If greater lift thicknesses are to be placed (more than 3” compacted), you probably will not need the higher temperature.
Cool before return to traffic. Rubber tires have a natural attraction to the polymer modified mix while it is still hot. To prevent the mix from sticking to tires, avoid letting motor vehicles drive on the fresh Stylink® HMA pavement until it has had a chance to cool.
The Rolling Process
Stylink® HMA presents no special problems for achieving density. You can use your customary rolling operations with Stylink® modified HMA. Three rollers are normally used: 1) a breakdown roller; 2) a secondary roller; and 3) a finishing roller. For breakdown rolling, it is desirable to use a steel wheel vibratory roller operated at high frequency and at an amplitude suitable for the mix being placed. Under most conditions, a static steel wheel roller is also suitable.
Compact at the right temperature. The compaction procedures for Stylink® mixes are essentially the same as for conventional mixes. Stylink® mixes cool a little more slowly than conventional mixes, however, so there is somewhat more time to achieve the densities that are required. Guidelines for breakdown temperatures are given in the table. The finish rolling should be completed by the time the mix temperature has reached 200°F (93°C).
The roller train should be close to the paver. The breakdown roller should be kept as close behind the paver as possible, without causing excessive horizontal displacement. Compaction with a vibratory roller should be tailored to suit the mix. Normally the secondary roller should follow the breakdown as closely as possible.
Amplitude adjustments. You may need to make amplitude adjustments on a vibratory roller to suit the mix being placed. Such things as mix stability, temperature, gradation and lift thickness should be taken into consideration.
Finishing. Finish rolling is normally done with a static steel wheel tandem roller or with a vibratory roller operating in the static mode. The finish roller should complete the compaction at the time when all marks can be rolled out without making any new marks.
Treated roller water prevents sticking. A capful or two of laundry fabric softener or dishwashing liquid in the water tank of the steel wheel roller will help prevent sticking. The roller should also have a constant water supply.
Pneumatic tired rollers may be used. Pneumatic tired rollers can be used on Stylink® modified asphalt mixes. As with conventional mixes, it is necessary for the tires to be heated to prevent pick up of the mix. Once the tires have heated up, crumbs of the mix will no longer pick up.
- Tires should be heated gradually. A good practice is to heat the tires by starting the roller on a mix that has partially cooled, and then gradually getting onto the hotter mix.
- Skirts help retain the heat. Use of skirts will help the roller stay heated.
- A steel wheel roller for insurance. Having a steel wheel roller available is a good idea in case there should be problems with the pneumatic roller. In any case, finishing should be done with a static steel roller.
Good compaction gives good results. If standard good practice rolling procedures are followed, no compaction problems should be encountered, and the result will be the high quality pavement expected from a Road Science™ product used in conjunction with your operation.