Jeremy Gregory, an engineer who studies the economic and environmental implications of materials, their recycling and end-of-life recovery, has been named executive director of the MIT Concrete Sustainability Hub, effective July 1. Gregory replaces Professor Hamlin Jennings, who is widely known for developing the first fully quantitative model of the nanostructure of the major component of hydrated cement. Concrete is the most widely used building material on Earth. The production of cement — its basic building block at the nanoscale — accounts for about 5 percent of the world’s total carbon dioxide emissions. The Concrete Sustainability Hub was established in 2009 with the goal of accelerating emerging breakthroughs in concrete science and swiftly transferring those research advances into industry. Read a news release.