Creep response of recycled asphalt shingles

Recycled asphalt shingles (RAS) mixed with granular materials or cementitiously stabilized to control their otherwise high compressibility provide a viable lightweight structural fill material in highway embankments or backfill behind retaining structures. In this research, deviator creep response of RAS mixed with bottom ash (BA) or stabilized with self-cementing fly ash (FA) was investigated. Systematic constant stress consolidated-drained triaxial tests were conducted on compacted RAS–BA and RAS–FA mixtures at ranges of confining pressures, deviator stresses, and temperatures expected in the field. Results showed that both compacted RAS–BA and RAS–FA mixtures represent classic creep response similar to soils. Creep rupture was observed at deviator stresses higher than 80% of deviator stress at failure. To prevent creep rupture, mobilized shear strength in the design of side slopes of highway embankments containing RAS should be limited to 80% of deviator stress at failure. Creep rate is affected by confining pressures. At a given stress level, the creep rate decreased and the time to creep rupture increased with increasing confining pressure. Temperature change also affects the creep strain and strain rate of compacted RAS–BA and RAS–FA mixtures. The strain rate of the compacted RAS–BA mixture exponentially increased with temperature. However, thermal pre-loading at summer field temperatures significantly reduced the strain rate of the compacted RAS–BA mixture from 64 × 10−6%/min to 3.6 × 10−6%/min and that of the RAS–FA mixture from 190 × 10−6%/min to 6.9 × 10−6%/min. To minimize creep strain and strain rate of structural fill materials containing RAS, construction is recommended during warm seasons. Creep models were developed to evaluate the time-dependent deformation of embankments constructed with RAS mixed with granular materials or stabilized with self-cementing fly ash.