Suggested operating instructions for the manufacture of polymer modified asphalt using Elvaloy® RET

This document describes equipment and procedures for modifying asphalt using DuPont Elvaloy® RET reactive elastomeric terpolymer.

DuPont Elvaloy® RET reacts with asphalt to improve its hot temperature properties. Base asphalt should be formulated to the desired cold weather properties. Then, by modifying with Elvaloy® RET, the asphalt's warm-weather properties can be enhanced. Typically, the hot SHRP numbers can be raised by 24°C with no change in cold SHRP properties.

The mixing tank should be approximately 16 ft high and 22 ft in diameter to ensure thorough mixing with a top-down mixer. (A taller tank can be used with two side-mounted propeller mixers, but they should have 20- to 30-hp motors and their placement is critical to ensure thorough mixing.)

The top-down mixer should have at least two sets of blades, four blades each, with a 10- to 15-hp motor. The bottom set of blades should be approximately 1.5 ft from the bottom of the tank, and the top set of blades should be about 4 ft below the liquid surface to ensure that the polymer, which will float on the surface of the asphalt, is drawn down into the asphalt.

The tank should be heated at all times, preferably with hot oil through a heating coil of adequate size to maintain an asphalt temperature of 385°F. Tank insulation is a must.

A recirculation line should be installed to circulate asphalt from the bottom of the tank to the top of the tank continuously during polymer loading, mixing, and acid addition.

A vapor recovery system for the mix tank may also be necessary. If so, a typical asphalt vent fan/filter package is sufficient. Asphalt modified with Elvaloy® RET does not emit any different vapors than standard asphalt heated to similar temperatures.

Elvaloy® RET addition system

Elvaloy® RET is available in either 1100-lb boxes, or in bulk shipment. Various types of solids conveyers can be used to transport the Elvaloy® RET to the top of the mixing tank. These include grain elevators, tube conveyors, pneumatic conveyors, or vacuum conveyors. Mechanical or vacuum conveying is preferred over air conveying because adding air to the mix tank can promote oxidation of the asphalt and will aggravate the emission of noxious fumes. Suggested conveyor systems are listed in Appendix A.

Critical solid handling design factors are as follows:

1. Solid polymer must not exceed 150°F at any point in the system, or polymer will melt.
2. Solid addition rate must be measurable, and should be adjustable.
3. Tank inlet connection should be designed to minimize melting/sticking of polymer.

For additional information on safety and handling of Elvaloy® RET, please read the Material Safety Data Sheet.

Entire mixing polymer addition system

Polymer addition and mixing systems are available for rent or purchase. One supplier is Reichel & Drews Inc., 1025 West Thorndale Ave., Itasca, IL 60143-1365 U.S.A, telephone (708) 773-2500¹.

Mixing Procedures

For plant setup similar to Figure 1 This procedure assumes that the plant setup is similar to Figure 1 and Example 1. Figure 2 and Example 2 describe the typical setup for using the Reichel & Drews addition system.
Figure 1 Click on the image below for a full view in a separate window	Reichel & Drews Addition System Click on the image below for a full view in a separate window

1. A lab mix study needs to be performed to determine optimum Elvaloy® RET level prior to producing commercial pounds of product. (Typical Elvaloy® RET levels range from 1.5 to 2.5 percent.) Do not increase polymer above laboratory levels without first running a lab test to see if PMA (polymer modified asphalt) will gel at the increased levels of polymer. DuPont has an asphalt lab that will perform initial screenings of this process on your asphalt, and will provide SHRP data for the asphalt.
2. The very first PMA production run should be a small-scale production. (~50 tons). This small run will be used to check the accuracy of the lab scale versus actual production scale.
3. Inspect the mix tank. Flush and empty if necessary before adding the PMA base stock.
4. Check that the PMA base stock meets all cold weather bid specifications. (Remember that Elvaloy® RET modifies the hot weather properties. The base stock must be formulated to meet the cold weather properties.)
5. Begin adding the PMA base stock to the tank. Heat the base stock up to 385 °F.
6. Sample the PMA base asphalt in the blend tank. Measure the viscosity at 140°F (60°C). Check other asphalt properties for baseline values.
7. Turn agitator and recirculation pump on. Check the top of the mix tank to assure tank is being vigorously agitated. (You should be able to see a vortex or rough churning on the surface of the asphalt.) Do not proceed if tank is not properly agitated.
8. Begin adding the Elvaloy® RET at a rate of 30 lb/min. Check the top of the tank periodically for polymer buildup (iceberg like lumps). If polymer buildup is encountered, shut down polymer addition and allow polymer to mix into the asphalt. After polymer is mixed in, restart polymer addition at a rate of 5 lb/min less than previous rate. Repeat this step until no polymer buildup is detected after one hour of continuous polymer addition.
9. If no polymer buildup is encountered at 30 lb/min for one hour, increase polymer addition rate by 10 lb/min and wait one hour. If there is no polymer buildup, increase the addition rate by another 10 lb/min. Repeat this step until polymer buildup occurs, or maximum polymer feeder rates are encountered. (Note: It is rare to be able to exceed 100 lb/min without having polymer buildup.) If a polymer buildup is detected, reduce feed rates back to the previous level that did not produce buildup. If the buildup continues, discontinue polymer addition until the buildup is gone.
10. Continue adding Elvaloy® RET until the desired amount has been added.
11. After the optimum polymer addition rate is determined, check this rate over the next few production runs to ensure there is no buildup on top of the tank.
12. Maintain tank temperature at 385°F.
13. Once all the Elvaloy® RET has been added, check the top of the tank to ensure all the polymer has been dissolved.
14. Sample tank and run the absolute viscosity at 140°F. The viscosity measurement will be used to monitor the rate of the reaction. Continue monitoring the viscosity every few hours.
15. When the viscosity has remained stable for 24 hrs, the reaction is complete. The PMA should be tested to ensure that it meets all the end-use specifications.
16. The PMA can now be pumped to a finished product storage tank and held at 325°F. The storage tank should have a gentle mixer (10-1 to 15-hp side mixer) at the bottom of the storage tank. The PMA will not separate or settle out of the asphalt, because the Elvaloy® RET is incorporated into the backbone of the asphalt molecule. If longer-term storage of the PMA is needed, the tank can be cooled and reheated.

Example 1 - Production Rate Calculation

Assumptions:

8:00 a.m. Tank has 348,000 lbs of base asphalt, heated to 385°F.

Tank has been sampled for cold SHRP properties, passed at -40.
Check viscosity is 120 cps.
Start tank agitator and recirculation.
Start polymer addition at 50 lb/min.

9:00 a.m. Check tank top for polymer mixing.

10:00 a.m. Check tank top for polymer mixing

11:00 a.m. Stop polymer addition, all 8,925 lbs have been added.

Check viscosity (~200 cps).
Leave agitator and recirculation on, hold tank at 385°F.
Begin sampling viscosity every hour to monitor reaction

11:00 a.m. (next day)

Sample viscosity is slightly above 800 cps and stops rising, reaction is complete. (Recheck viscosity after 24 hrs to make sure reaction is complete.)
Sample for all SHRP data.
Asphalt is ready to be pumped to finished product tank

For plant setup similar to Figure 2 Polymer is added continuously to the asphalt, while it is being pumped from the base asphalt tank to the product tank. Flow rates between the tanks depend on the system design.

Figure 2 Click on the image below for a full view in a separate window

Example 2 - Production Rate Calculation

Assumptions:

8:00 a.m. Base tank has 348,000 lbs of base asphalt, heated to 385°F.

Tank has been sampled for cold SHRP properties, passed at -40.
Check viscosity is 120 cps.
Start product tank's agitator and recirculation.
Start polymer addition at 30 lb/min, asphalt flow at 90,000 pph.

8:15 a.m. Sample product tank. Make sure all Elvaloy® RET is dissolved in asphalt.

Continue sampling product tank periodically.

Noon All polymer added, all asphalt is now in the product tank.

Check viscosity (~200 cps).

Noon (next day)

Sample viscosity is slightly above 800 cps and stops rising, reaction is complete. (Check viscosity after 24 hours to make sure reaction is complete.)
Sample for all SHRP data.

* Note: This list of conveyor suppliers is not a DuPont endorsement of any supplier or a DuPont non-endorsement of any supplier not on this list, nor does this list convey any DuPont warranty, express or implied, of merchantability or fitness for a particular use or any other warranty to user of any equipment listed.

Disclaimer: While DuPont believes that the procedure set forth in this publication can be used to safely and effectively modify asphalt, DuPont does not warrant or guarantee the completeness, efficacy or safety of the process or its use. The information contained herein is intended for use only by competent personnel in designing and operating a facility to modify asphalt, and the user of this information accepts full responsibility for its use. Consistent with the foregoing, anyone using this information shall indemnify and hold DuPont harmless from any loss, claim, damage, or injury to persons or property whatever the cause may be arising out of or pertaining to the use of the information, unless the same is shown by the user to have been caused directly by bad faith or willful misconduct on the part of DuPont. Furthermore this publication is not to be taken as a license to operate under, or a recommendation to infringe, any patents.