Cold recycling mix design

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. 

The other difference with hot recycling mix design is the pre-mix moisture content and final moisture content of the recycled mixture. Moisture content determination is important in cold recycling mix design because it affects the workability of the material and can control the degree of compaction achieved. 

In general, the steps of a cold recycling mix design consist of the following  

There are various cold recycling mix design methods. Stroup-Gardiner (2011) provides statistical information and other details related to the cold recycling mix designs used in the United States. 

One of the cold recycling mix design methods is described in detail in the ARRA manual (ARRA2001). 

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The downflow fixed-bed reactor has been used widely for hydrodesulfurization processes and is so called because of the feedstock entry at the top of the reactor while the product stream is discharged from the base of the reactor (Figure 5-6). The catalyst is contained in the reactor as stationary beds with the feedstock and hydrogen passing through the bed in a downward direction. The exothermic nature of the reaction and the subsequent marked temperature rise from the inlet to the outlet of each catalyst bed require that the reaction mix be quenched by cold recycle gas at various points in the reactor. Hence the incorporation of separate catalyst beds as part of the reactor design. 

The recycling agent is bitumen emulsion with the addition of a very small amount of cement or lime. The type, grade and rate of bitumen emulsion and the amount of cement or lime are determined through evaluation of the RA and cold mix design process. The mix design process may dictate the addition and use of new aggregates. 

The current US practices on hot mix designs and other matters related to in-place cold recycling have been reported in a National Cooperative Highway Research Program (NCHRP) report (Stroup-Gardiner 2011). 

Another mix design procedure of cold recycled material produced in situ including full-depth cold recycling (FDR) or in-plant (ex situ) using a wide range of binders and binder blends is also provided by Merrill et al. (2004). 

The reader can also find very useful information regarding laboratory tests related to mix design of cold in situ recycling (FDR) and recommendations needed for test methods to make them applicable for the design of FDR materials in a Federal Highway Administration report (Bang et al. 2011). 

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