Design and Evaluation of Sustainable Structural Lightweight Concrete Using Recycled Pet as Aggregates

<ns3:p> Background The accumulation of polyethylene terephthalate (PET) plastic waste poses environmental and sustainability challenges due to its non-biodegradable nature and limited disposal options. Repurposing PET as aggregates in structural lightweight concrete (SLWC) offers a dual benefit of waste valorisation and conservation of natural resources, while supporting circular economy objectives. Methods Eight experimental mix proportions of SLWC were developed using a factorial design approach, with water–to–cement ratios ranging from 0.40 to 0.45. PET aggregates were produced via thermal–mechanical processing and subjected to calcium hypochlorite treatment to improve surface bonding with cement paste. Standard tests were conducted to determine workability (Vebe time), fresh and dry densities, compressive strength, splitting tensile strength, and water absorption. Structural efficiency was also computed as a strength-to-weight performance indicator. Results The fresh and dry densities of the PET-based SLWC ranged from 1455–1515 kg/m <ns3:sup>3</ns3:sup> and 1490–1537 kg/m <ns3:sup>3</ns3:sup> , respectively, corresponding to category D1.6 lightweight concrete. Compressive strengths ranged between 14.1 and 16.5 MPa, fulfilling the LC13 classification for structural applications. Splitting tensile strengths were between 0.84 and 1.4 MPa, with several mixes achieving minimum thresholds for structural performance. Water absorption values ranged from 4.66% to 10.16%, remaining within international standards for lightweight concrete durability. Workability was low (Vebe times 13–40 s), attributed to the angular and hydrophobic properties of PET aggregates. Structural efficiency values of 9.5–10.9 kPa·m <ns3:sup>3</ns3:sup> /kg exceeded minimum international requirements. Conclusions This study confirms that PET aggregates can be successfully utilised to produce structurally viable and durable lightweight concrete. Although workability is reduced, the compressive strength, tensile strength, density, and durability criteria align with international standards. These results demonstrate a sustainable strategy for PET waste valorisation in construction, contributing to resource conservation, reduced environmental burden, and advancement of circular economy goals. </ns3:p>