High modulus asphalt concrete (HMAC) mixtures are produced using hard grade binders or modified bitumen and are known to have exceptional resistance towards rutting and fatigue. Due to the similarity between hard binder and aged reclaimed asphalt (RA) binder, HMAC mixtures have great potential to incorporate higher percentages of RA material. Here we present a study evaluating the performance of HMAC mixtures incorporating high content of RA material. Both hard grade binder and polymer modified bitumen (PMB) were used for all the mixtures with RA content varying from 0% to 70%. The laboratory performance of mixtures was examined using wheel tracking test, semi-circular bend test, thermal stress restrained specimen test, water sensitivity test and four-point bending test. The results demonstrated that it is possible to develop HMAC mixtures with satisfactory performance using RA content up to 70%, by using PMB binder. The mixtures produced using PMB binder outperformed conventional hard grade binder mixtures especially for use in regions with extremely cold winters.

Reclaimed asphalt (RA) and Warm mix asphalt (WMA) are two widely used environmentally friendly mixtures in the paving industry. This study compares the laboratory performance of conventional hot mix asphalt (HMA) with virgin WMA, and WMA containing 60% RA content, using thermal stress restrained specimen test, wheel tracking test, and indirect tensile strength test. Based on test results, a reduction of 15 °C in mixing temperature was achieved for WMA mixtures compared to HMA using the given chemical additive. The virgin WMA mixture showed superior cracking resistance but lower rutting resistance than HMA, and incorporation of RA material without any further modification in the binder, deteriorated both cracking and rutting performance of WMA. It was also shown that laboratory short-term aging can significantly affect the performance of the mixtures.

Recycling of asphalt pavements gained popularity in 1970s due to the rapidly increasing cost and reducing supply of oil and hence - bitumen. However, presently there are other reasons to develop this technology, the main being the ability to utilize non-renewable resources. Sustainability of asphalt pavement construction can only be ensured if we are able to utilize the available reclaimed asphalt pavement (RAP) material completely in the new construction. Another potential advantage is the mutual benefit of using RAP in conjunction with warm mix asphalt (WMA). This is due to compensation of hardened binder from RAP with softer binder of WMA. For such mixes, significant energy savings can be realized due to the lower mixing and compaction temperature as well as due to lesser efforts required for compaction. This paper summarises several approaches that can be adopted to maximize the amount of RAP material in asphalt mixtures. In addition, the current recycling practices implemented in the industry are discussed to identify the main reason behind the lacking confidence in using high RAP content in mixes. The environmental and economical benefits of high rate of recycling are also discussed. Finally, the possible research directions that will allow to incorporate high proportion of RAP without compromising the performance of pavement are discussed.

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