Moisture Sensitivity of Asphalt Pavements (2003)

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111 TOPIC 3 Questions and Answers MANSOUR SOLAIMANIAN Pennsylvania State University, Speaker Q1—John D’Angelo, Federal Highway Administration I will agree with you. I think one of the big things we have to do in any of this testing is try and simulate what’s happening in the field. But as I went through all the testing you showed here, you always talked about making specimens in the 7% range, plus or minus. I am really a believer that we’re not even close to what’s going on in the field. I think a lot of what we see in the field is actually much higher air voids, and that’s a big problem in that it’s not being recognized yet. How can we get a lab test to correlate to the field when the lab voids aren’t even close to what’s going on in the field? Have you looked at all at trying to address some of these issues, particularly about what’s really happening in the field and what level of compaction we really have out there? I’ll let you go from there. A—Mansour Solaimanian Thank you, John. I do agree with you. The construction air void has a major effect, and that needs to be looked at very closely. It’s not just a matter of stripping when you talk about the air void effect. It’s also considering the effect of air voids on rutting. You do your mix design, and then you make your specimens at 7% air voids, for example, for performance testing. Then you make your prediction of the performance of the mix and you wonder how this correlates with the field air voids. So that is a very general question. It’s not just for stripping, it’s for rutting and fatigue and other properties that you try to simulate or predict in the laboratory. So as part of this project, one of the things that we plan to do is to consider the air void effects in these tests and get them to the typical acceptable levels in the field. I think most states don’t accept a mix if the density is under 90%. Maybe we should take the air voids to the lowest acceptable level even though a penalty might be applied. We should then see how the results compare in terms of your failure and success with a 7% or any other air void level we are currently working on. Right now, we have only been looking at a typical level of air voids that has been used in T283 and other test procedures. Q2—Dale Rand, Texas Department of Transportation On the slide that showed the percentage of success, can you elaborate on the criteria used on the percentage of success? Was that an opinion or was that based on something else? It kind of implies that the test correlates with something. A—Mansour Solaimanian You notice that at the bottom of the slide, I had Kiggundu and Roberts. I took the data directly from their interpretation of failure and success, and I believe they looked at the mixes that had stripped and the mixes that did not strip or were considered good. I do not know what exactly their criteria have been on deciding which one had been a stripping mix in the field and which one not. They looked at the laboratory results and made a comparison against the field data.

112 Moisture Sensitivity of Asphalt Pavements: A National Seminar They decided which ones correlated well with the stripping ones and which ones did not. This way, they came up with percentages to indicate rate of success in prediction. For example, if a material is stripped in the field, and the lab criterion is 70% on TSR while we get 60%, then we consider this a successful prediction. On the other hand, if a mix had stripped and we had a TSR of 90%, then the prediction was not successful. Q3—Gayle King, Koch Pavement Solutions Mansour, great presentation. I find it interesting that you emphasize the methylene blue test but don’t talk about sand equivalency. My own prejudice lies in that same direction. A French sabbatical gave me a strong appreciation for the surface activity of fines, particularly as related to moisture damage in mixes. Of course methylene blue is now part of ISSA microsurfacing specifications, because fines also have a strong impact on emulsion break. Studies by Tim Aschenbrener and Ken Kandhal showed similar correlations between methylene blue and Hamburg. Although correlations weren’t perfect, Hamburg consistently failed when methylene blue was high. The entire experimental scatter fell in the region where methylene blue was low, because mixes will strip in the Hamburg for reasons other than surface-active fines. The message was clear, mixes consistently stripped when methylene blue was high. Do we get that same information from sand equivalency? Or should we replace sand equivalency with methylene blue? A—Mansour Solaimanian I am not sure I can answer your question but I will try. I do agree with you that methylene blue is a very good test. In terms of how good the r2 was in every case, I was just reporting what I noticed from Ken’s work. I suppose the r2 values were around 70%. But again, this is just based on his data. On replacing SE with MB, I am not sure you will be capturing the same thing because when you do the methylene blue, you are doing it on –200 material in the mix, and when you do your sand equivalency, you are basically doing it on material passing the No. 4 sieve. You do have an amount of fines in your mix that you need to watch out, regardless of your testing. You might have 4% of –200 material, but you should watch out that this material might contain a lot of bad clay. You still need to look at your sand equivalency to make sure your material passing the No. 4 sieve is OK. I may not have answered your question very clearly. Q4—Jack Van Kirk, Basic Resources, Inc. I have two questions. One is that after SHRP, you said a lot of the states switched over, and a total of 30 are now using T283. The first question is, Why did a lot of those states change over? What convinced them? The second question is, How much variability is in the parameters or the criteria they are using to run the test? Everything from voids in the specimens to saturation levels to compaction method can introduce differences between states and variability within a state. A—Mansour Solaimanian Why so many states picked it up, you want to answer that, Gary? I don’t know. I guess because it became a part of the Superpave Design System. With regard to your second question on variability, there is variability between technicians in a given state, and between different states depending on where you are in terms of your air voids and your testing procedures. It is a big deal.

Solaimanian, Harvey, Tahmoressi, and Tandon 113 Q5—Dick Root, Root Pavement Technology, Inc. Maybe a couple of comments on the procedure itself and maybe why it was adopted indirectly. I was a little bit confused by a couple of your comments, so maybe you can help clear me up on this. First of all, T283 and ASTM D4867 are the same test. One was performed or put together by a research team, and the other was put together by a committee, so they got a little bit deviant in the committee aspect of it. The control of air voids and saturation levels, you made an indication, or at least I perceive, that would affect the test results or maybe cause errors in it. There were several studies done during the original research and follow-up studies by Irv Dukatz at Vulcan Materials that showed that with a range of air voids at 6–8 and with the saturation levels of 55–80, you essentially get the same results for a ratio of strengths, not individual strength. Obviously, the PSI would be different at 6% voids than 8%, but when you start looking at ratios, that narrowed the data down to very, very close. I think the reason for the adoption of it is simple. It can be run in the field and it was reasonably an advancement over what we were running previous to that, boiling water tests and emergent compression tests. A—Mansour Solaimanian Yes, ASTM D4876 and AASHTO T283 I think are essentially the same, but if you look at the procedures, there is a 16-hour curing in AASHTO T283 that does not exist in ASTM D4867. Other than that, you are right. Curing is very different between the two procedures. I would be interested in seeing that data that you mentioned in terms of essentially getting the same ratio and see how big the database or what kind of data has been used in there. Q6—Carl Monismith, University of California, Berkeley I think that your answer why T283 was adopted is correct because many states, immediately after the completion of SHRP, adopted the Superpave method of mix design, and T283 is a part of the methodology. The other thing I wanted to mention is this matter of the sand equivalent and methylene blue tests. The sand equivalent test was developed circa 1950; information regarding the test was published by the Highway (now Transportation) Research Board by F. N. Hveem in 1952. The primary purpose of the test is to eliminate the potential for detrimental clay coatings on aggregate particles, coatings that could result from improper processing of aggregates obtained from alluvial deposits. I would argue that it would be extremely imprudent to replace the sand equivalent test with the methylene blue test; the sand equivalent test is a very important test for the control of fines. If pavement technologists want to look at the nature of these fines, methylene blue is a useful additional test. As noted above, to replace one with the other would be unwise. A—Mansour Solaimanian I agree, Carl.

TOPIC 4 Treatments