Abstract This paper aims to investigate the fundamental properties of bituminous plug expansion joint filling mixtures containing high content of rubber granules. Rubber granules were added by replacement of part of stone aggregates. Dynamic response, creep, relaxation and flexibility tests were carried out. The test results showed that the addition of rubber granules allowed preparing low modulus joint filling materials. Rubber granules had a great influence on complex modulus, but a limited effect on phase angle. The modified Huet–Sayegh (HS) model was well capable to simulate the rheological properties in a wide range of frequency and temperature. Permanent deformation resistance of joint mixtures was susceptible to the large amount of rubber granules. The slope of relaxation modulus over time on a log–log scale can be used as a reliable indicator to evaluate the relaxation behavior. The replacement of stone aggregates by rubber granules formed a new and soft stone–rubber skeleton, which allowed preparing joint mixtures with a better flexibility at low temperature.