In situ full-depth cold recycling

In situ full-depth cold recycling, also known as FDR or structural road recycling, is a cold recycling method where all asphalt layers and, in some cases, a predetermined portion of the underlying base material are uniformly pulverised and usually mixed with stabilising additives to produce a stabilised base course material. The pulverised reclaimed material may also be used as it is untreated for unbound base course material. 

The stabilising additives, in dry or liquid form, can basically be ordinary Portland cement (OPC), lime, fly ash, cement kiln dust (dry of slurry), bitumen emulsion, foamed asphalt or combinations of two or more of these additives. 

The treatment depths vary depending on the thickness of the existing structure, which generally ranges between 100 and 300 mm (ARRA 2001 Kandhal and Mallick 1997). 

FDR is an in-place rehabilitation process that can be used for reconstruction, lane widening, minor profile improvements and increased structural capacity by addressing the full range of pavement distresses (Stroup-Gardiner 2011). 

The main steps of FDR are pulverisation, introduction of additive, addition of new aggregate (when necessary), shaping, compaction and application of a wearing course. 

---