A comparative assessment of the bearing capacity of unselected construction and demolition waste aggregates in unbound and cement-stabilised pavement subbases

• Widespread scepticism limits the use of UCDW aggregates in subbase pavement layers. • Unbound UCDW has a higher bearing capacity than natural aggregates. • Cement-stabilised UCDW aggregate has a slightly lower bearing capacity than natural aggregates. • Stabilised UCDW has a higher resilient modulus than stabilised natural aggregates. • UCDW aggregates are cheaper and meet sustainability requirements for road construction. Using unselected construction and demolition waste (UCDW) aggregate helps the road construction industry to meet sustainability requirements. Although the use of recycled UCDW aggregates is increasingly recognised and adopted in practice, there remains limited field evidence directly comparing their performance with that of natural (NAT) aggregates in unbound and cement-stabilised subbases. This study compared the bearing capacity of four 30-cm subbases (unbound and 3% cement-stabilised NAT and UCDW) using lightweight deflectometer and plate loading tests on an experimental road. The study was complemented by laboratory resilient modulus and indirect tensile strength measurements on specimens compacted during the construction activities. On average, the surface modulus of unbound UCDW materials was 16% higher than that of natural aggregates. Stabilisation with 3% cement significantly increased the bearing capacity sevenfold for UCDW materials and tenfold for NAT materials. After three days of curing, the average surface modulus increased from 112.3–126.6 MPa for unbound UCDW and 95.2–111.6 MPa for unbound NAT, to 884.7–1024.6 MPa for cement-stabilised UCDW and 1064.3–1198.1 MPa for cement-stabilised NAT. Unlike the field tests, where cement-stabilised NAT performed slightly better than cement-stabilised UCDW, the laboratory tests showed that cement-stabilised UCDW mixtures had a higher resilient modulus than cement-stabilised natural ones. These results demonstrate that UCDW aggregates can effectively replace natural ones in the formation of unbound or cement–stabilised road subbase layers.