Concrete blocks are famously strong and are used the world over, but there are major downsides to the material. It takes a lot of energy to create concrete—the process contributes to an estimated five percent of the world’s CO2 emissions, and that’s why startup Watershed Materials has been working for the past four years to develop an alternative that is not only better for the environment but also stronger than what it's replacing.

To reduce the high carbon footprint of Portland cement (one of the primary ingredients in concrete), Watershed Materials, with funding from the National Science Foundation, is developing a way to turn a mixture of natural clay materials into durable masonry. The clay’s chemical structure is altered in a geopolymerization process (bone up on the science here), resulting in a weather-resistant material with a high-compressive strength. Geopolymers already exist, but they rely on fly ash (which in turn relies on coal-burning energy). This new, in-development method eliminates fly ash from the process.

The mineral-based geopolymer mix cuts the use of cement and provides a reduction in “embodied energy,” which is the sum of the energy required to mine, produce, and transport the cement. With further development, these geopolymer blocks could help start the process of replacing cement for good.

Correction: This piece has been updated to reflect the difference between Watershed Blocks (which are already on the market) and the geopolymer blocks that are in development.