How asphalt works

Prior to the deveopment of the Strategic Highway Research Program (SHRP) there was a meeting in Dallas to discuss the concepts. At that meeting it was stated that the goal was to make an asphalt that could correct any flaws that might be found in pavements. Unfortunately there is still a remnant of that opinion. Asphalt , even when modified, is a liquid. Its function is to waterproof and glue stuff together. (An additional function is to tar and feather,  however that generally is not considered a good construction practice unless things are really going bad.) This is an understanding I learned many years ago sharing an office at Shell Development with Ray Griffith, the inventor of the sliding plate microviscometer. The solution to rutting and tenderness is not asphalt modification but aggregate gradation, although modifying the asphalt can slow down rutting. The importance of gradation is something I learned from Vaughn Marker when he was the Asphalt Institute engineer in California.  The prime reason to polymer modify asphalt is to change the temperature susceptibility to combat non-load associated cracking. It is vital that the binder remains a liquid so that it can relax thermal stresses faster than they can build up. Thus trying to modify asphalt to combat load associated cracking is blowing in the wind. Load associated damage is caused by lack of adequate structural strength (or studded tires if you live where I do!). Lack of protection of the mix from water damage accelerates damage. I will discuss water damage later.
 

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