Cement is one of the most-consumed materials on Earth — second only to water — and it accounts for a whopping eight percent of the world's carbon pollution. What if we could turn this climate villain into a hero? Clean tech innovator and serial entrepreneur Ryan Gilliam reveals his company's surprisingly simple process for transforming waste from the cement-making process back into limestone using existing infrastructure, creating a competitive and eco-friendly product that could pave the way for gigaton-scale climate solutions.