Adding limestone powder to "green" concrete mixtures - those containing substantial amounts of fly ash, a byproduct of coal-burning power plants - can significantly improve performance, report researchers from the National Institutes of Standards (NIST) and the Federal Highway Administration (FHWA). The promising laboratory results suggest a path to greatly increasing the use of fly ash in concrete, leading to sizable reductions in greenhouse gas emissions, energy use, construction costs and landfill volumes. Global production of cement for concrete accounts for 5 to 8% of human-caused greenhouse gas emissions.