Recycled portland cement concrete (RPCC) aggregates are increasingly being considered for use in the U.S as an alternative to new aggregate materials for rigid pavement subbases. The four papers in this dissertation present results of studies that compared the strength/stiffness and permeability of RPCC subbases to crushed limestone subbases; employed scanning electron microscopy (SEM) and X-ray microanalysis to investigate RPCC aggregates and tufa precipitate; conducted spatial analysis of pH values in a flow channel and thermogravimetric analysis to examine the environmental impact of RPCC aggregate subbases; and monitored seasonal variations in temperature, moisture, frost depth, and ground water table in pavement foundation layers to document climate conditions. The findings from this research showed that although the RPCC subbases had generally lower permeability, they were much stiffer than values that are normally used for pavement design criteria and apparently provide adequate support for rigid pavements although RPCC aggregates potentially produces tufa.