Western Research Institute performed rheological tests and water sensitivity tests on asphalt cements that had been modified with carbonous residues obtained from the pyrolysis of scrap tires and waste motor oil. These tests are part of an ongoing program at the University of Wyoming Chemical Engineering Department to evaluate, as asphalt additives, solid carbonous products recovered from the scrap tire and waste motor oil pyrolysis experiments conducted at the University. The tests showed that carbonous residues increased the viscosity and decreased the elasticity of AC-10 and AC-20 asphalts. The tests also indicatedthat asphalt cements modified with carbonous residues were less sensitive to water damage and age embrittlement than unmodified asphalt cements.