Thomas Kang
Seoul National University
Department of Architecture and Architecture Engineering
Professor
The 5th Construction Element – Recycled Plastics
Throughout human history, only four primary materials—wood, stone (masonry), cementitious materials, and steel—have defined construction. While fibers, polymers, and alloys have found partial use, they’ve never reached the scale or structural significance of these traditional four. In this talk, we propose a paradigm shift with the introduction of a new material: recycled plastic blocks, which we believe represent the fifth construction element.
These blocks are made from mixed waste plastics—collected from oceans, rivers, and land—without the need for complex separation processes. The plastics are melted at temperatures up to 250 °C and cast into interlocking blocks. Despite their simple processing, these blocks achieve remarkable performance: a compressive strength of 24 MPa (comparable to concrete) and a tensile strength of 10 MPa (4–5 times greater than concrete), allowing them to function as a structural replacement for reinforced concrete.
Designed for use in retaining walls, erosion control structures, seawalls, and embankments, these blocks are not only robust and cost-effective, but also environmentally transformative. They sequester carbon, clean up plastic waste without incineration or landfilling, and offer the potential for future reprocessing with improved chemical treatments.
Drawing inspiration from the idea of a long-awaited “fifth element,” this innovation may be the sustainable, abundant, and resilient building material the world has been waiting for.
Yes.