For those involved in oil and chip programs, there are several kinds of oil to consider. I am going to give an account of what our county uses, and the differences in the types of oil. We use either Rapid Set, High Float Emulsion, or High Float Polymer. Here in southern Illinois, we experience large temperature swings, as well as very high humidity in the summer. Oil and chip roads tend to bleed-the oil separates from the rock and comes to the top. This can be so bad at times, that the road is slick on hot humid days. I will go over the types of oil we have used, and how well they have performed for us.
RS-2 (Rapid set, 2 means high viscosity because they are stored at higher temperatures). This is the primary oil our county uses. We use this on roads whose average daily traffic (ADT) ranges from 300-1200. This seems small, but for our counties, the 1200 is a high number. Some of our townships may have ADTs as small as 25. Like the name says, this oil is rapid setting, and can be driven on pretty quickly. We use a rubber-tire roller to break down the emulsion. The emulsion is a mixture of water and oil held together with a surfacant. When the emulsion is broken down, the asphalt can then bind with the rock. We have had good luck with this oil, but bleeding is still an issue. For roads with over 1000 ADT, we may have to sprinkle aggregate on them during the first few hot humid days of the summer following the year they were oil and chipped to soak up the oil.
HFE-90, HFE-150 (High Float Emulsion, and the 90, 150, mean penetration ranges). We use primarily the HFE 150, and mostly when RS-2 is not available. We due tend to experience more bleed compared to RS-2. The HFE-90 is rapid setting, but tends to bleed more than the HFE-150. The HFE-150 forms a good adhesion to the aggregate, and is more flexible., but takes a little longer to set up. On occasion, we have had to re-sprinkle aggregate on roads in the fall that were treated with HFE in the late spring or early summer as they were oil and chipped.
HFP (High Float Polymer). We have just been experimenting with HFP during the last two seasons. The polymer is much more flexible and elastic compared to the emulsified asphalt. Early chip retention has also been much better. We have used the HFP on a couple of our roads with higher traffic (1000 ADT-high for us!) and a few roads with bleeding issues. We have been very satisfied. We may be able to seal these roads every third year instead of every other year. The drawbacks? Price of course. The price has been about $0.60 more per gallon. If we only have to use it every third year though, there is still a savings. Availability may be an issue as well. We are in a rural area with pretty much one supplier of road oil. They may not always be able to get the HFP when we need it, since we are one of the only agencies that has been using it so far.
When considering what oil to use, make sure to consider the charge in the oil and on the rock also. They can either be cationic (positive) or anionic (negative). Just make sure that they are of opposite charges; the same principles apply as in a magnet. Positive attracts negative. The theory is, a positive rock with bond better with a negative oil and vice-versa.
In review, we are very happy with the HFP, but at a higher initial cost. RS-2 and HFE-150 are almost interchangeable, with the edge going to the RS-2 for its quick set time, and slightly better adhesion than the HFE-150. The RS-2 and HFE-150 have been historically bid at the same price for us, so sometimes it is also an issue of availability over preference.