<p>Unused waste vehicle tires can be easily disintegrated into microplastics in landfills. The barrier performance of the liner material in a landfill plays a crucial role in terms of environmental protection. Furthermore, there is an eager need to make research on the engineering properties of soils that are contaminated with microplastics. In order to determine the compaction properties and plasticity characteristics of a sand-bentonite mixture that represented a barrier contaminated with tire wear microplastics, standard Proctor compaction, liquid and plastic limit tests were conducted on 0.05, 0.1, 0.2, 0.5, 1 and 2% tire wear microplastics-added sand-bentonite mixtures. Polyacrylamide (PAM) is a synthetic polymer that is typically used as a soil enhancer. The tests were repeated on anionic and cationic PAM-added sand-bentonite mixtures. Test results indicated that tire wear microplastics and also PAM addition caused decrease in the maximum dry unit weight (<i>Ɣ</i>_<i>dmax</i>), liquid limit (LL) and plastic limit (PL) and increase in the plasticity index (PI). The rates of decrease in Ɣ_dmax and increase in PI were even higher for the tire wear microplastics-added sand-bentonite mixtures. 2% tire wear addition caused <i>Ɣ</i>_<i>dmax</i> to decrease from 17.27 to 15.99 kN/m³ and PI to increase from 14 to 19%. According to these results, the decrease in compactibility and increase in plasticity of the sand-bentonite mixture might alter the barrier performance with a possible change in hydraulic conductivity, which is a critical parameter for the liner material in a landfill.</p>