The recycling of debris, is considered as one of the most important resources for constructing base &subbase road layers in many countries. There are two problems for RCA: first, the considerable size it takes up when collected and second, its low technical properties. The second problem appears in countries which don't have natural quarries and they have to use RCA in certain fields (concrete mixes, asphalt mixes, granular road layers). This research discuses preparing RCA aggregates, by recycling the concrete waste, which comes from Al-Sallima landfill, near to Damascus city. Then many tests are carried out to study the effect of changing the aggregate's size on their mechanical & physical properties, and also to study the possibility of using these aggregates in constructing base &subbase road layers. As a result, it has been found that we can use RCA for constructing unbound base &subbase road layers, and the mechanical & physical properties of these RCA get better when the aggregate's size gets smaller, except in Proctor test. In this test, Proctor density and optimum moisture content get better when aggregate's size gets bigger.