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http://dx.doi.org/10.14190/JRCR.2021.9.2.167

Statistical Evaluation of Moisture Resistance by Mixing Method of Recycled Asphalt Mixtures  

Kim, Sungun (Advanced Construction Research Center, Kangwon National University)
Kim, Yeongsam (Department of Regional Infrastructure Engineering, Kangwon National University)
Jo, Youngjin (Daegu & Gyeongbuk Branch, Korea Conformity Laboratories)
Kim, Kwangwoo (Department of Regional Infrastructure Engineering, Kangwon National University)
Publication Information
Journal of the Korean Recycled Construction Resources Institute / v.9, no.2, 2021 , pp. 167-176 More about this Journal
Abstract
When producing recycled asphalt mix, it is important that the old binder of reclaimed asphalt pavement(RAP) should be well melted during blending in the mixer. The recycled asphalt mix is produced by instant mixing(IM) of all materials(RAP, virgin asphalt and new aggregates) all together in the mixer. However, in the same recycled mix, the binder around RAP aggregate was found to show higher oxidation level than the binder coated around the virgin aggregate because the old binder of RAP was not rejuvenated properly while instant mixing. The partially-rejuvenated RAP binder is assumed to be a high stiffness point in IM recycled mix. In this study, the stage mixing(SM) method was introduced; blending RAP and virgin asphalt for the first stage, and then mixing all together with hot new aggregates for the second stage. To compare the effect of the two mixing methods on moisture resistance of recycled mixes, a statistical t-test was performed between SM and IM using indirect tensile strength(ITS) and tensile strength ratio(TSR). Three conditioning methods were used; a 16-h freezing and then 24-h submerging, 48-h submerging, and 72-h submerging in 60℃ water. It was found that the TSR(=ITSwet/ITSdry) values of the mixes prepared by SM was clearly higher than the IM mixes, and coefficients of variation of SM mixes were lower than the IM mixes. It was also observed that the ITSWET of SM was significantly different from the IM at α=0.05 level by statistical t-test. The ITSWET of SM mix was reduced less than the IM mix in severer conditioned mixes. Therefore, it was concluded that the stage mixing method was an important blending technique for producing better-quality of recycled asphalt mixes, which would show higher moisture resistance than the recycled mixes produced by conventional instant mixing.
Keywords
Reclaimed asphalt pavement(RAP); Recycled asphalt mixture; Moisture resistance; Stage mixing; Instant mixing;
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