Item 314 and various one-time use special specifications allow the use of these additives. These treatment procedures are all intended for reclamation of in-place pavement structures. Application is typically accomplished using a reclaimer/recycler coupled to one or more bulk tankers that supply the liquid treatment agents. Recycling machines have become increasingly sophisticated and more powerful over the years; up to 12-in. of existing pavement depth can be processed with much improved distribution and uniformity of water and bituminous treatment agents. The emulsion content is typically below 4.0%, with the residual typically around 2.5%. Small percentages of lime or cement (typically ≤ 1.5%), when required by the mix design, are usually spread on the surface of the existing roadway ahead of the recycling machine. These additives are lifted and mixed together with the reclaimed roadway materials and liquid agents in the on-board mixing drum in a single pass. The lime or cement additives serve the following functions ( , 2012):

Alternately, a lime or cement slurry can be injected into the recycler mixing chamber through a separate spray bar attachment. These processes result in a product that locks up finer particles by encapsulating them in bitumen, causing them to adhere to larger particles that are not coated. The result is a material that remains more flexible than other chemically-treated materials, but significantly reduces the moisture sensitivity. A limitation for using these treatment methods is the lack of knowledge and experience for many in the mixture design and placement operations of these materials. Designing a foamed asphalt mixture requires a specialized laboratory foaming unit. Contact CST’s Geotechnical, Soils and Aggregates Branch for assistance.

A significant precaution for these types of treatment options is dredging up high PI subgrade material and mixing it with the reclaimed pavement materials. The high PI materials will not disperse properly and cannot be adequately coated with bitumen; hence the material will remain moisture susceptible and prone to permanent deformation (rutting). This is more likely to occur with thin existing structures and structures with highly variable sectional thickness/composition along the project. Where this condition is anticipated and high PI soils are likely, the design process should include a preliminary recycling pass using lime, or install a lift of flexible base before the recycling pass to include this better material into the mix and to avoid dredging up the subgrade material. Curing emulsion treated layers to achieve strength and stability in a timely manner may be problematic where moisture loss is delayed by environmental conditions, such as high humidity or unanticipated high in-place moisture contents. On the other hand, curing foamed asphalt treated layers can often be achieved in approximately 2 hours, and the roadway can be reopened to traffic.