Pav i ng t he W ay f or a Mor e S u s t ai nabl e C onc r et e I nf r as t r u c t u r e A V i s i o n f o r D e v e l o p i n g a C o m p r e h e n s i v e D e s c r i p t i o n o f C e m e n t H y d r a t i o n K i n e t i c s National Institute of Standards and Technology Patrick D. Gallagher, Under Secretary of Commerce for Standards and Technology and DirectorCertain commercial entities, equipment, or materials may be identified in this document in order to describe an experimental procedure or concept adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the entities, materials, or equipment are necessarily the best available for the purpose. iii iv National Institute of Standards and Technology ForewordConcrete is far and away the most abundantly used man--made material on the planet. As a construction material, it is unique in its capacity to be formed and finished into an almost unlimited variety of shapes, textures, and colors. It can be made on demand with portland cement and inexpensive local materials. With correct placement and use, concrete can have a service life of 50 years to more than 200 years. Improving the proper and efficient use of concrete and portland cement requires better understanding of the chemical process of hydration, and how that process can be characterized and modeled -both for pure portland systems and for those containing admixtures and supplemental cementitious materials such as fly ash, slag cement, and others. Having interactive computer models, based on sound experimental data, for the chemical and physical interaction of cementing compounds, molecules, and ions in the concrete pore--water solutions will help both to improve cement manufacture and to optimize sustainable concrete mixtures.Importantly, concrete has the lowest embodied CO 2 content of any major material used in construction, including glass, steel, and wood. But so much concrete is produced annually that it still accounts for about 8 of industrial CO 2 production. Therefore, reducing both the CO 2 contribution and embodied energy of concrete is a societal challenge that must be addressed to ensure a sustainable built environment and transportation infrastructure. One way to reduce concrete's CO 2 contribution is to lower its embodied CO 2 and energy content and even further, typically by both more efficient production of cement binder and partial replacement with supplementary cementitious materials or fine mineral fillers. This approach is already being used, but often with uncertainty in the way the binder will perform. Concrete is typically overdesigned by at least 10 % because of the inability to ensure the exact performance of the binder material. Therefore, the ability to accurately model cement hydration kinetics and predict and improve the performance of concrete as it hydrates could lead to a 1 % reduction in the mass of cement and concrete used each year and significantly reduc...