Mix Design Of Cold Recycled Bituminous Mixture Lab Report

6. Results and Discussion
6.1. Mix Design of Cold Recycled Bituminous Mixture Compaction characteristics of untreated bitumen mixes according to Modified Proctor Test is shown in Figure 6. When the RAP content increased, it resulted in reduction of MDD and the corresponding increase in OMC. The decreased MDD is obtained due to the weak bond between RAP and the virgin material and also due to less fine material that plugs the voids to produce denser mix. The corresponding increase in OMC is observed with increase in RAP content. Thus as the surface area of the particles increases with increase in RAP content more water is required to lubricate the whole mixture. Water is also consumed in cement hydration reaction to enhance compaction.
The values of accumulated permanent strain of cold recycled bituminous mixtures, without and with addition of varying percentage of RAP, at the end of 10000 cycles are shown in Figure 12. Based on data analysis at all temperatures, decreasing trend in accumulated permanent strain values is observed from 0% RAP to 60% RAP. However, no significant difference was found between the 50% RAP and 80% RAP mixtures, as supported by the overlapped error bars. This lack of a trend indicates that increase in RAP content does not significantly affect the performance related to permanent deformation. It can be seen that samples containing RAP showed better creep performance in terms of reduced accumulated permanent strain. This indicates that the RAP incorporated mixes becomes stiffer and thus has more potential to resist permanent deformation than when compared to the conventional mix. However, increased accumulated permanent strain showed decreasing trend of creep stiffness as the temperature increases. It was also observed that foamed asphalt mixes performed better in creep strength when compared with HMA. In foam mixtures, 60% RAP showed lower accumulated permanent strain statistically when compared with all
The fatigue life in terms of number of cycles obtained for mixes with and without RAP is shown in Figure 14. Based on data analysis, increased trend in fatigue values is observed in 50% RAP and 60% RAP mixtures at all microstrains. Fatigue life in all these mixtures is statistically significant due to the variability in test results as exhibited by error bars. The RAP mixes become stiffer compared to the mix without RAP and thus have better resistance to fatigue failure. A slight increase in stiffness can result in an exponential increase in fatigue life of the recycled mixture (Viet Hung Nguyen. 2009). Therefore, the increased fatigue life implies that the mix prepared with addition of RAP is more durable than the mix without RAP. As observed, resistance to fatigue failure is less in foamed mixes; this could be due to less bitumen content of lower viscosity. The increase in fatigue life of the mixes containing 50% RAP was found to be 9 and 7 times more when compared to the mix without RAP at 400 and 500 respectively. Also these cold recycled mixtures showed least resistance to fatigue failure at 500 microstrain indicating that these mixtures should be laid in lower layers of pavement. The test results of beam fatigue are given in Table