ASPHALTopics | Summer 2014 | VOL 27 | NO3

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The effect of polymer modification of asphalt cement was studied in a report published by the Asphalt Institute – Quantification of the Effects of Polymer-Modified Asphalt for Reducing Pavement Distress – ER 215 (also available in abbreviated form as IS 215). The study quantified the performance benefits of polymer modified asphalt (PMA) pavements and overlays using field data from controlled experiments across the U.S. and Canada. The distresses included in the study’s performance predictions and comparisons were rutting, fatigue cracking and transverse cracking. This study was carried out using mechanistic empirical distress prediction models that now form AASHTOWare Pavements-ME pavement design software. Mechanistic-empirical (M-E) distress prediction models were used to compare the performance of test sections to quantify the improvement in pavement life or reduction in surface distress by using PMA, as compared to conventional unmodified HMA mixtures. The report summary concluded that ”… the use of PMA mixtures result in less cracking and rutting – extending the service life of flexible pavements and overlays ...” PMA wearing and binder (intermediate) mixtures exhibited about half the cracking and about 40 percent of the rutting measured on comparison projects. It was found that “…PMA mixtures provide on the average about a 25 percent or a 2- to 10-year increase in service life …” Additionally, it was concluded that PMA could reduce maintenance costs and the number of maintenance operations. Why do we need a new test anyway? Let’s make this clear – this is not about different types of asphalt cement or different methods of carrying out modifications. The difference is in how you test the asphalt binder to determine if it has been modified correctly to ensure the level of performance that you require for the pavement you are designing. AASHTO M320 was intended to be blind to modification method. It was designed to be that way and the test procedure determines fundamental properties that relate directly to performance. Both of the new methodologies are not blind to modification method. The only way the specifications can be met is if an elastomeric polymer is used. This is a departure from the concept of the AASHTO M320 test procedure, but it is a good one. Highway agencies have recognized the benefits of using modified asphalts to reduce the amount and severity of pavement distresses and to increase service life. However, there hasn’t been an Ontario test methodology to ensure that the asphalt binder had been effectively modified with an elastomer – until now. Now there are two with no technical agreement on which to select. How do you solve this type of impasse? The only way, as suggested by industry, is to do a trial of the different test methodologies and see which is better at reducing distress. And that’s what MTO did – with over 1 million tonnes of hot mix over a three year period. The study is unprecedented in size – about one half of what MTO would pave in a single year. Now we have to monitor the pavements to find out what distress we get and we won’t have the start of good information until early next year and it will be another 3 or 4 years to complete the study. But why do we have this technical disagreement? If it’s just the test method, what’s the big deal? The big deal is how long it takes to do the testing and accuracy of the tests themselves. The ExBBR procedure takes about 120 g of conditioned binder, which is about ten times that required for the standard test, and you have to do 24 individual BBR tests with each sample tested three times at different ages. For the DENT test you need 150 g of conditioned binder to carry out six more tests (three tests in duplicate). All this to qualify one sample. That’s a lot of work and it takes about 7 days to complete. If we contrast that with the MSCR test procedure, there is an amazing difference. The test requires no additional material and only takes about 20 to 30 extra minutes at the end of the standard testing to complete. It uses existing equipment and, once the testing machine has the proper script installed, you only need to push a button. So one procedure is much simpler and faster, but is it as accurate (see tables)? I have attached a number of tables that present the results of the MTO semi-annual round robin binder testing. I’ve gone back to 2012, the year after the DENT test became an acceptance test for MTO. Two samples are sent out for each round of testing and the first thing you’ll notice is that some rounds only show a single result for each sample and some show two (a and b). When a round robin program administrator looks at the results, there may be ›› 58 OHMPA | ASPHALTOPICS
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FALL 2014 | VOL27 | NO3 th Annivers
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WE DARE TO BE DIFFERENT, SO YOU CAN
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Congratulations on 40 years of comm
Page 8 and 9: WE KNOW THE ROAD. WE’VE BEEN ON I
Page 10 and 11: THE STRAIGHT GOODS 10 OHMPA | ASPHA
Page 12 and 13: For approximately 30 years, Vacuum
Page 14 and 15: that there was no real difference i
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Page 18 and 19: For the last 15 years, consumers ha
Page 20 and 21: “When you don’t have to stop fo
Page 22 and 23: An all-Canadian connected car is un
Page 24 and 25: Ladies on a paver. Undated photo fr
Page 26 and 27: 26 OHMPA | ASPHALTOPICS HMA plant f
Page 28 and 29: Multiple Stress Creep Recovery proc
Page 30 and 31: The MSCR test uses the creep and re
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Page 34 and 35: Only Astec has the patented Double
Page 36 and 37: Pennsylvania State Route 462 in Lan
Page 38 and 39: The Ohio Department of Transportati
Page 40 and 41: One of OHMPA’s most significant c
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Page 44 and 45: 1998 1999 2000 2001 1998 Teri McKib
Page 46 and 47: 2007 2008 2009 2010 2011 2012 2013
Page 48 and 49: Asphalt Cement Specifications in On
Page 50 and 51: currently known. It has been adopte
Page 52 and 53: Special Profile Eddie DeToro, found
Page 54 and 55: 50 stability machines. Call, write,
Page 56 and 57: Albarrie’s Door Seals & Dryer/Dru
Page 60 and 61: occasions when the results for one
Page 62 and 63: ENVIRONMENT COMMITTEE A commitment
Page 64 and 65: Why OHMPA? We asked some of our mem
Page 66: THE LAST WORD by Gerry Chaput Succe
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ASPHALTopics | Summer 2014 | VOL 27 | NO3

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