Everyone knows the value of RAP. But what is the best way to use it? Conventional wisdom suggests (AASHTO M 23) that one can use up to 15% RAP without changing the asphalt grade specified. When you want to use 15-25% RAP, it is suggested that you use one grade softer asphalt for your mix and when you use more than 25% RAP, detailed blending charts must be utilized. Sometimes, a RAP Rejuvenator like Sripath Technologies® ReLIXER™ is required. Keep in mind that all performance specifications (of the finished roadway and mix) must be met but a good rule of thumb is if you are outside of the above parameters, double check your design!!
RAP is RAP is RAP is RAP—NOT—-Knowing the quality of your RAP is of utmost importance and without getting into the myriad of details and in summary, one must measure the asphalt grade of the RAP to be used and select an asphalt (with a Rejuvenator if needed) so that when combined, the resultant asphalt grade meets the job specifications. Of course, the classification of the RAP must be understood too so that the resultant mix design meets gradation specifications. More next week!!