Editing Bitumen (section)

== Recycling ==
Bitumen is a commonly recycled material in the construction industry. The two most common recycled materials that contain bitumen are reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS). RAP is recycled at a greater rate than any other material in the United States,<ref>{{Cite report |last1=Williams|first1=Brett A.|last2=J. Richard Willis|date=September 2020|title=Asphalt Pavement Industry Survey on Recycled Materials and Warm-Mix Asphalt Usage 2019 (Information Series 138) 10th Annual Survey |language=en|doi=10.13140/RG.2.2.21946.82888 |doi-access=free |via=ResearchGate |id=IS138(10e)}}</ref> and typically contains approximately 5–6% bitumen binder. Asphalt shingles typically contain 20–40% bitumen binder.<ref>{{Cite journal|date=1 April 2020|title=Recycled asphalt shingle modified asphalt mixture design and performance evaluation|journal=Journal of Traffic and Transportation Engineering (English Edition)|language=en|volume=7|issue=2|pages=205–214|doi=10.1016/j.jtte.2019.09.004|issn=2095-7564|doi-access=free|last1=Wang|first1=He|last2=Rath|first2=Punyaslok|last3=Buttlar|first3=William G.}}</ref>

Bitumen naturally becomes stiffer over time due to oxidation, evaporation, exudation, and physical hardening.<ref>{{Cite journal|last1=Karlsson|first1=Robert|last2=Isacsson|first2=Ulf|date=1 February 2006|title=Material-Related Aspects of Asphalt Recycling – State-of-the-Art|journal=Journal of Materials in Civil Engineering|volume=18|issue=1|pages=81–92|doi=10.1061/(asce)0899-1561(2006)18:1(81)|issn=0899-1561}}</ref> For this reason, recycled asphalt is typically combined with virgin asphalt, softening agents, and/or rejuvenating additives to restore its physical and chemical properties.<ref>{{cite report |last1=Al-Qadi |first1=Imad L. |last2=Elseifi |first2=Mostafa |last3=Carpenter |first3=Samuel H. |title=Reclaimed Asphalt Pavement – A Literature Review |date=March 2007 |hdl=2142/46007 |hdl-access=free |citeseerx=10.1.1.390.3460}}</ref>