A new concrete alternative made of pumice and seashells

There are certain materials we just can't go without, and one of them is concrete. Unfortunately, the production of cement leaves a large carbon footprint - it's estimated it's responsible for between 5 an 8 percent of global CO2 emissions. That's why my next guest has spent nearly 7 years trying to develop a sustainable alternative, and to do it, he's combining materials and practices traditional in both Roman and Maori engineering. Dr Enrique del Rey Castillo is a lecturer at the University of Auckland's faculty of Engineering and Design.