Use of Recycled Materials

In addition to virgin aggregates, various recycled materials can be a good source of aggregate for base and subbase under a concrete pavement, especially when sustainability is of concern. Recycled concrete is the most frequently used recycled material (Figure 9) for use as unstabilized bases and as aggregates for cement-stabilized bases. The advantage of using recycled concrete is that almost any desired gradation can be achieved by crushing the recycled concrete, and most of the produced aggregates can easily meet the L.A. abrasion requirement of 50 percent or less. Some precautions that must be considered in using recycled concrete material include the following:

• Once crushed, recycled concrete materialbecomes very angular and may requiremore compaction effort than virginaggregates.
• Unless the source of the recycled concreteis known, the material should be tested forcontaminants such as soil, wood, plaster,gypsum, plastic, rubber, etc.

During crushing and sizing operations, a relatively small amount of fine particles may stick to the processed coarse aggregates. Although these fines do not create a serious problem, it is good practice to wash the processed aggregates to reduce potential for leaching and clogging of the drainage system. Use of these materials as aggregates for cement-treated base is also a good practice, if the material contains excessive fines or exhibits high plasticity for an unstabilized base.

Other recycled materials frequently used as unstabilized bases for rigid pavements include waste materials such as reclaimed asphalt pavement, mill tailings, and other waste rock materials. These materials must be processed in an appropriate manner, may need to be blended with other materials to meet the gradation requirements, and should be free of any reactive chemical components.