Hot in situ recycling

Hot in-central plant As in hot in situ recycling Increases transport cost of... 

Hot recycling may be carried out in situ or in a central mixing plant (in-plant). Hot in situ recycling is distinguished into repave, remix and reshape procedures. The basic steps followed in all versions of hot recycling are shown in Figure 18.4. 

Hot in situ recycling is a quite common form of recycling in which the recycling processes of the RA are completed on site. The process consists of heating the pavement to a temperature such that the top asphalt layer can be scarified (or rotary milled) to the specific depth. The loosened asphalt is then mixed, placed and compacted. Depending on the procedure followed, new asphalt material may or may not be added prior to compaction. 

The hot in situ recycling process requires the use of a number of equipment including preheaters, heaters, scarifiers, mixers, pavers and compactors. 

In hot in situ recycling, it is vital to examine the old asphalt mix before commencing the work by taking representative samples to establish the areas where the composition of the existing material varies. 

Remix is the hot in situ recycling process in which the pavement surface is heated, scarified and mixed a rejuvenating agent is added if required new hot asphalt material is added ... 

Figure 18.12 Comprehensive mix design flow chart of hot in situ recycled (HIR) asphalt mixture. (From ARRA, Basic Asphalt Recycling Manual. Asphalt Recycling Reclaiming Association. Annapolis, MD ARRA. 2001.)...

A recent study found that 33.273 MJ/km of energy is required for the reconstruction of a 7 cm thick asphalt layer when cold in situ recycling is used, while 120.351 MJ/m of energy is required when the conventional technique, that is, hot mix asphalt, is used (Mauduit et al. 2011). 

Figure 18.4 Methods and basic steps for hot in situ and in-central plant recycling.

It may also be economical to remove the inhibitory product directly from the ongoing fermentation by extraction, membranes, or sorption. The use of sorption with simultaneous fermentation and separation for succinic acid has not been investigated. Separation has been used to enhance other organic acid fermentations through in situ separation or separation from a recycled side stream. Solid sorbents have been added directly to batch fermentations (18,19). Seevarantnam et al. (20) tested a sorbent in the solvent phase to enhance recovery of lactic acid from free cell batch culture. A sorption column was also used to remove lactate from a recycled side stream in a free-cell continuously stirred tank reactor (21). Continuous sorption for in situ separation in a biparticle fermentor was successful in enhancing the production of lactic acid (16,22). Recovery in this system was tested with hot water (16). 

Pavement recycling methods differ from the flexible to the rigid type of pavement. In flexible pavements, two basic methods are distinguished hot recycling (HR) and cold recycling (CR). Each one is further distinguished into in situ (or in-place) and in-plant (central plant) recycling. 

Hot recycling in flexible pavements consists of removing the existing asphalt layer to a determined depth and replacing it with hot asphalt resulting from the same reclaimed material, with the possible addition of new material, that is, mixed in situ or new/recycled asphalt mixed in a central plant. 

The repave process offers perhaps the ultimate rehabilitation/hot recycling results compared to the other two hot recycling in situ processes. In particular, its advantages over the other two in situ processes are as follows (a) complete restoration of surface skid resistance since new asphalt material is used, (b) strengthening of the pavement to a certain extent and (c) minimisation of smoke emission. 

The mix design procedure of cold recycled asphalts produced in situ (except full reclamation) or in a central plant is similar to and perhaps simpler than the one followed in hot mix recycling. 

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