Upcycling waste concrete powder into cement-free construction materials through low-dosage micron-sized polyethylene and hot-pressing

Massive quantities of concrete waste and polyethylene (PE) waste are generated annually, yet both remain underutilized. Previous studies showed that carbonation-induced CaCO 3 crystal bridges enhanced interparticle bonding and strength of compacted recycled concrete material, but carbonatable phases were exhausted after one carbonation cycle and the water absorption remained high. This study introduced micron-sized PE as hydrophobic-adhesive phases, considering the effects of PE size, PE content and carbonation. Results showed that the addition of 5 wt% PE achieved 6.4% water absorption, 47 MPa compressive strength, 10.2 MPa flexural strength and a 991% increase in toughness. Under pressure, molten PE remained confined within the concrete skeleton rather than extensively flowing into pores. Matrix bonding was governed by geometrical anchorage, PE-induced interfacial bonding, and short-range PE infiltration. This work offers a designable route to low-carbon building materials that reduces dependence on the intrinsic properties of waste concrete and enables multi-cycle recycling.