Old concrete that have "reached the end of the road" can be recycled and used not only as aggregate for new concrete, but also for a number of other applications in construction. In the many countries, there are no longer any barriers to the use of recycled concrete as aggregate in new concrete.
Recycled concrete is simply old concrete that has been demolished and removed from pavements, bridges, foundations, or buildings and crushed into various sizes for reuse.

Advantages of Recycling Concrete:
Conserves natural resources,
Good for the environment,
Can be good business,
Expected to grow.
Use of Recycling Concrete:
Recycled concrete is being used to produce aggregates for

Many types of general bulk fills;
Base or fill for drainage structures;
Soil-cement pavement bases;
Pavement subbases;  
Bituminous concrete;
Lean-concrete or econocrete bases;
New concrete for pavements, shoulders, median barriers, sidewalks, curbs and gutters, building and bridge foundations, and even structural grade concrete.
Recycling Process of Old Concrete
Removal of Steel and other embedded items
Reinforcing steel and other embedded items, if any, must be removed, and care must be taken to prevent contamination by dirt or other wasted building materials, such as plaster or gypsum, or asphalt from pavements, which can be troublesome. It is advantageous if old concrete can be freed from foreign matter before demolition begins.

Demolition of Old Concrete
Use the concrete breaker to break the big concrete to concrete block.

Crushing of Concrete Block
Crushing Plants for production of recycled concrete are not much different from plants engaged in the production of conventional crushed stone plant. The two basic types of crushers are compression crushers and Impact crushers. Most crushing plants have both primary and secondary crushers, however, some plants produce aggregates by primary crushing only. In plants with both levels of crushing, the primary crusher normally reduces the material down to about 3/4 in. The material then passes through two screens that separate the aggregate into sizes, greater than and less than 3/8 in. The larger material is fed to the secondary crusher where the maximum desired coarse aggregate size is set.  Recyclers often prefer a Jaw crusher because it can handle large pieces of concrete; a Cone crusher, on the other hand, can handle fragments no bigger than 8 in.