Hempcrete is a carbon-negative building material made from hemp shives and lime binders, but low compressive strength has kept it out of most construction jobs. New research from Cape Peninsula University of Technology shows that replacing 3% of the binder with potassium sulphate raises compressive strength by around 65% at 28 days while barely changing the material's density or its ability to sequester carbon. The activated mix reached 0.681 MPa versus 0.413 MPa for the control, and net emissions stayed roughly 0.47 kg CO2e per test specimen, nearly identical to the reference mix. The additive also cut drying shrinkage and helped the material retain strength after oven drying. The trade-off is small, but durability data like freeze-thaw behavior and end-of-life carbon release are still missing before hempcrete can scale in real buildings.
