Stylink® Technology is the SemMaterials process for making polymer modified asphalt binder. We manufacture it at our plants by chemically reacting a Styrene-Butadiene (SB) block copolymer in the base asphalt cement. When we ship Stylink® polymer modified asphalt, it is ready to use in the hot mix plant with little, if any, special care. To make sure that Hot Mix Asphalt (HMA) made from Stylink® binder meets expectations for handling and performance, it’s important to follow normal good practices and workmanship, as with any asphalt. It’s just common sense, but normal care on any project means you will avoid down time and have the best quality finished job.
We supply several different grades of polymer modified asphalt using Stylink® technology. Each grade is engineered for specific local conditions and specifications, and some of the cautions listed below may not apply. Consult your local SemMaterials representative for more specific information on the product you are using.
Delivery and Storage
When we ship Stylink® polymer modified asphalt, it is ready-to-use in your hot mix plant.
Shipped ready-to-use in same vehicles as liquid asphalt cement. Stylink® polymer asphalt is normally delivered to the hot mix plant between 310 and 350°F (154-177°C). It can be shipped in the same vehicles used to transport conventional liquid asphalt cement. Compatible with unmodified asphalt tank bottoms. While there is no problem using existing asphalt tanks for Stylink® polymer modified asphalt, the tank should be empty so you don’t dilute the polymer and lose some of its high performance properties. Mixing unmodified asphalt cement with Stylink® PMAC is normally not a problem, except large quantities will understandably dilute the polymer concentration, and will probably bring the material out of specification. Very small quantities in the bottom of the asphalt tank will have little, if any, effect on the operation or the concentration.
Agitation not needed. Stylink® polymer asphalt is a homogeneous material which can be safely stored without worry of polymer separation when normal care is taken. It doesn’t need agitation. But if the Stylink® polymer modified asphalt is cooled and reheated, normal circulation of the tank is recommended to evenly distribute the temperature.
Long term storage below 300°F, don’t heat above 350°F. If the project (and the hot mix production) is delayed, the Stylink® polymer asphalt should be stored below 300°F (150°C) to prevent degradation. When SBS modified asphalts are held much above 300°F for extended periods of time (several weeks or longer) the polymer may begin to break down. If there will be a long delay (more than three or four weeks), it’s best to turn off the heat completely or keep it set below 275°F (135°C). Stylink asphalt can be heated to 350°F for a short period of time if needed for specific projects. See the temperature guideline table for more information.
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 (see Table), 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 SemMaterials 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. (See table.)
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 SemMaterials product used in conjunction with your operation.