Development of a material recycling process for waste concrete is an urgent issue. This paper summarizes the current situation of the issue, and introduces new waste concrete recycling processes via carbonic acid treatment. In the processes, alkaline calcium compounds in the hydrated cement part of waste concrete are extracted and precipitated as calcium carbonate (CaCO(3)). By utilizing this reaction, CaCO(3) and clay alternative material can be produced from waste cement particles. Furthermore, combined use of the carbonic acid treatment and conventional mechanical grinding allows fine aggregates to be recycled from waste concrete. The process does not need any additional materials except water and carbon dioxide (CO(2)). The process is considered to be a promising option for waste concrete recycling.