The principles of ReLIXER asphalt rejuvenator / recycling agent work equally well with Dense Graded and Gap Graded (including SMA) Mixes. We have experienced successes with all types, provided the mix design is appropriate. The rejuvenation is concerned only with restoring the balance of properties in the aged bitumen in RAP, and making the RAP bitumen contribute meaningfully to the total liquids. The other key issue in RAP mixes is ensuring that the particle size gradation (RAP + Aggregate) is within the prescribed specifications.
Frequently Asked Questions about Asphalt Rejuvenation with ReLIXER™
A good rejuvenator / recycling agent must bring about several benefits (attributes) to the mix. First, it must be capable of penetrating the RAP particle quickly and work, within the time-frames of normal mix production and silo storage (Rapid Diffusivity). It must also restore the balance of properties to the aged bitumen, so that the RAP bitumen contributes to the total liquids content in the mix (hence reducing virgin bitumen addition). It must provide stiffness reduction to High RAP mixes (ensuring easy laydown & compaction). It must also not endanger the future recyclability of the RAP. Finally, it must do all of the above and contribute to the long-term durability of the roadway. Even though one common measure of rejuvenation is softening of the bitumen, this is only one facet, a well-designed rejuvenator will do all of these.
The principles of Rejuvenation with ReLIXER work equally well with Dense Graded and Gap Graded (including SMA) Mixes. We have experienced successes with all types, provided the mix design is appropriate. The rejuvenation is concerned only with restoring the balance of properties in the aged bitumen in RAP, and making the RAP bitumen contribute meaningfully to the total liquids. The other key issue in RAP mixes is ensuring that the particle size gradation (RAP + Aggregate) is within the prescribed specifications. To this end, it is always helpful to classify the RAP into Coarse / Medium / Fine grades; this helps increased amounts of RAP that can be included in the Mix Design.
As mentioned in the preliminary Business Case outline, several types of Rejuvenators have been tried.
- Hydrocarbon oils – These work by softening the base bitumen, and were popular in the past (particularly at lower levels of RAP). These oils suffer from some drawbacks – non-green chemistry, many are hazardous chemicals, they lack rejuvenation and dosage efficiency (particularly for High RAP mixes may not be economic) and are susceptible to accelerated aging effects.
- REOBS (Engine Oil Bottoms) – whether refined, or unrefined, these suffer from some of the same drawbacks as mentioned above (the refined versions are better than the unrefined ones). Many US (& Canadian) states have banned their use, following a rash of (not completely substantiated) roadway failures.
- Softer Bitumens – again, in the past, particularly at lower percentages of RAP in mixes, softer bitumens were employed. These are effective only up to a point, as the RAP content is increased, and cannot be used in the case of 100 % RAP mixes. Depending on how the softening has been achieved, these may also be vulnerable to aging effects.
- Bio Oil Blends – these are emerging as the top choice in a wide variety of settings. They are easy to use (do not require heated storage), compatible with a wide variety of bitumens, are dosage efficient, can be engineered to provide good balance of properties in the mix and confer adequate aging resistance. These are based on sustainable, safe and green chemistry. ReLIXER is a product of years of development and has been deployed in roadways in several continents over the past 5 years.
What are the key properties which manufacturer’s value and properties road authorities need to be aware of?
In general, manufacturers of Rejuvenators / recycling agents have hewed to the outlines of performance important to Road Authorities. The key issue that must be recognized, is that formulaic approaches provided historically by Departments of Transportations do not work in High RAP mixes, and the Authorities are increasingly becoming aware of, and adopting different approaches to Mix design with RAP. For example, specifying that the bitumen shall be of a certain viscosity, or Pen/SP or PG Grade does not work well. Instead what is increasingly being used is Balanced Mix design for High RAP mixes. In Balanced Mix design, one is seeking to balance contrasting properties important on the Roadway and seeking to optimize them to achieve a good balance of properties needed on the Roadway. These involve Rutting and Fracture Testing (resistance to Cracking Failure / Fatigue). If a Mix is too stiff, the Rutting resistance is excellent, but the Crack Resistance is poor. If the mix is too soft, then Crack Failure is prevented, at the expense of early onset Rutting. Rutting and Fracture Toughness are measured by various tests throughout the world, and Sripath has data on a wide variety of Mixes on ReLIXER dosed mixes. In addition to Rutting and Fracture Toughness, some agencies also seek Aging test results, either on extracted bitumen from the mix, or on the mix itself, and again, Sripath has abundant aging data on ReLIXER dosed mixes. Finally, some Authorities/Customers also look at Moisture Susceptibility (Hot-Wet Strength tests), and we have data in these situations as well.
Other than chemistry, dosage & performance-related issues, none. However, this cannot be said of other types of rejuvenators. ReLIXER can be used in many settings : 25 – 100 % RAP Hot Mixes, Emulsion, Patching Materials, PMB mixes etc.
In general, no. ReLIXER has been used in conjunction with several common additives – WMA, Anti-Strip, Fibers etc. Some other rejuvenators have faced challenges in certain bitumens. Off course, Mix producers have to check against specific standards and requirements in their jurisdiction
Selection of appropriate rejuvenating oils for use in dense graded asphalt containing high RAP content?
Typically, selection and dosage is based on the bitumen in the RAP – bitumen content and bitumen age (& properties). ReLIXER enjoys wide-ranging compatibility in most bitumens. Most customers typically create Blending Charts based on RAP content and use these charts to adjust dosage based on the specific mix they are producing that given day.
What testing should road authorities be undertaking on the rejuvenating oil additives prior to incorporating into dense graded asphalt?
As mentioned above, these may include : Grade modification & Aging Characteristics in Virgin & Extracted Bitumen, Rutting, Fracture/fatigue Tests, Loose Mix Aging tests, Moisture Damage Tests etc. Not all jurisdictions use all these tests, typically it is based on local circumstances and experience.
Limits on incorporation of additives (either on its own or in conjunction with use of softer grade binders)?
This depends on type of rejuvenator / recycling agent used. Some oils face restrictions on dosage (due to properties, or economics). ReLIXER has not encountered any limits in systems we have encountered so far.
Different methodologies for incorporation of rejuvenating oils into asphalt (what is and is not suitable and does this depend on the level of RAP in the mix)
ReLIXER enjoys some natural advantages here. It is free-flowing & easy to use under most ambient conditions, and does not require heating to dispense. It is safe chemistry, with no known association with health hazards. It has a very high Flash Point. It has a very low odor, either in the mix tank, or in the mix. It can be deployed in bulk, or in totes/drums, with no special handling/storage issues. Published shelf-life is one year. All these advantages cannot be claimed by many agents mentioned above.
ReLIXER is dosage-efficient, and can be used in RAP mixes ranging from 25 – 100 %. It has been used in both Base Course and Wear Layer Course. Possessing a high Flash Point, it can be safely used in Production and Laydown of Mixes. When mixed with the base binder, it can be used in emulsions for Fog / Chip / Slurry Seals.
As for actual use, ReLIXER can be used in many different ways : addition to the virgin bitumen tank, co-injection with the bitumen at the drum, addition to Batch mixer either with the bitumen, or sprayed separately, or by spraying directly on to the RAP (for 100 % RAP mixes)
Health, safety and environmental concerns surrounding the use of rejuvenating oils into dense graded asphalt?
Another key area of advantage for ReLIXER. Some oils face restrictions/challenges based on hazardous labeling/effects (as noted on their MSDS sheets). ReLIXER is non hazardous, safe, green chemistry that faces no health, safety and environmental restrictions. It does not also require any special labeling for transport and storage.
Any additional auditing and compliance considerations which the road authorities should be mindful of ?
This is based on reporting requirements for individual jurisdictions. Typically, most mix producers do routine Q/C tests (mix &/or bitumen), which they provide to the Regulating Authorities. In addition, Sripath routinely monitors (and occasionally tests) mix properties of their customers, world-wide, and provides input for dosage, or other adjustments.
Not any with ReLIXER. As noted above, some oils cannot be used above a certain threshold, either due to dosage/performance issues, health/safety issues, or economic issues
This is typically determined by Production Mix testing (or by monitoring ReLIXER usage in Manufacturing Plant setting)
Easiest is by noting tank/tote level of ReLIXER and correlating it with Production tonnage. Secondarily, most customers do Mix Testing on Production batches to ensure compliance with properties of interest to them.
What is the shelf life of the rejuvenating agent? What about the asphalt mix, when stored in hot bins?
Published shelf-life of ReLIXER, under normal storage conditions, is one year. Storage Stability of material stored in Hot Bins, or in Hot Bitumen tanks is dictated by the properties of the materials themselves, not of the ReLIXER component.
What is the expected life of the rejuvenated surface (i.e. surface treated with rejuvenating agent)?
This depends on the requirements of the Regulating Authorities. Typically lab testing, either on the bitumen (Delta Tc, PAV aging etc) or on the Mix (loose Mix aging followed by prescribed testing) is used to determine this.
How long can the asphalt treated with rejuvenating / recycling agents be stockpiled before becoming ineffective?
I assume you are talking about Cold Patch Mixes. This is more a function of the formula, rather than of ReLIXER. The role of ReLIXER is only to activate the bitumen in the RAP (usually 100 %). The stability/usability of the resultant Mix is determined by method of manufacture (Hot mix, versus Cold Mix), ingredients (eg Anti-Strip, bitumen content, if any etc), storage conditions of the Mix and Ambient conditions.