Evaluation of the indirect tensile strength of asphalt concrete containing reclaimed asphalt pavement and waste oils using response surface method

In spite of many environmental and economical advantages of using reclaimed asphalt pavement (RAP) in the production of asphalt mixtures, many technical issues remain not very well understood and require further investigation, including the interactions between RAP content, rejuvenator type and rejuvenator content, and their combined effects on engineering properties of the resultant asphalt mixtures. In this study, statistical modeling tools were utilized to gain greater insight into the aforementioned interactions. The indirect tensile strength (ITS), an important engineering property which is related to the resistance against cracking and rutting of asphalt mixtures, has been selected as the primary engineering characterization tool in this investigation. The ITS of asphalt concrete mixes containing RAP (at 25, 50 and 75% by weight of total aggregates) and incorporating waste engine oil (WEO) and waste cooking oil (WCO) as rejuvenating agents (at 5, 10 and 15% by weight of total binder) was investigated using response surface methodology (RSM). As expected, the ITS was found to increase with increasing RAP content and to decreases with increasing oil content. Results also revealed that incorporating WEO resulted in higher ITS of the asphalt mixes compared to WCO. Interaction plots of test results show that the increase of ITS with increasing RAP content depends on the oil content, with higher rate for mixtures with lower oil content, and is independent of oil type. Optimization of ITS in RSM reveals that using 75% of RAP and 5% of WEO results in the highest indirect tensile strength of the mixture.