# Evaluation of Mechanical Properties of Recycled Material for Utilization in Asphalt Mixtures
## 4 Conclusions  
Since the coarse aggregate properties are identified by current research as the second most important parameter after gradation for the performance of HMA [49], therefore, in this research, attempts were made to assess the properties of RCA for use in asphalt mixture as coarse aggregate, and this paper presented the summary results of a comprehensive set of preliminary tests on RCA, RAP and basalt as well as different mixes of these aggregates to evaluate their basic mechanical and physical properties. It was argued that information on these fundamental properties were paramount in designing a durable and sustainable asphalt mixtures. To this end, different aggregate and aggregate mixes containing different percentages of RCA, RAP, and basalt were investigated in this research to assess its suitability as coarse aggregate in asphalt. This paper presented the results of this experimental work conducted as a component of a broader research project for designing an asphalt mixture. Based on this research, it was concluded that:  
1. RCA has lower value of flaky and misshapen particles in comparison with RAP and basalt. This implies that asphalt mixtures containing a certain amount of RCA can have better workability, deformation resistance and compaction.
2. RCA exhibits comparatively more absorption and wet/dry strength variation than conventional aggregate and RAP, while the results of other tests show that RCA still meets the requirements for aggregate in asphalt mixtures. Cracks and adhering mortar and cement paste can be significant reasons for the high water absorbtion of RCA which needs to be compensated for during mix design.
3. The results of water absorption and particle density test on different mix of coarse aggregates revealed that RCA increase will increase water absorption of the mixture. Therefore, the selection of optimum combination of RCA and other aggregates is required to satisfy the relevant standards requirements.
4. Regression analysis applied to the results of water absorption test on different combination of RCA and basalt, as illustrated in Figures 16 and 17, indicates that mixing of almost 8% of RCA with natural aggregates will provide the standard water absorption limit of 2%.
5. Since, according to Austroads (2014), the aggregates with water absorption of between 2% and 4% of their mass should be carefully examined by other tests [59]. This standard limit will allow further investigation of the application of up to 50% of RCA in mixtures because based on the water absorption results, it can be observed that the combination of 25% RCA and 75% basalt would provide water absorption of 2.93%, and the combination of 50% RCA and 50% basalt would provide water absorption of 3.71%, which are still in the range of aggregates that require further research for their water absorption properties.  
**Acknowledgments:** The authors would like to acknowledge Boral Asphalt Company for providing part of materials required for the research work.  
**Author Contributions:** [PERSON] is the main author and researcher conducting this research as the main component of her PhD studies, [PERSON] has directed and coordinated the project in a supervisory capacity, [PERSON] and [PERSON] have been consultants to the project providing valuable insights into behavior of aggregates and asphalt.  
**Conflicts of Interest:** The authors declare no conflict of interest.