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In a book published in 1906, Richard Meade outlined the history of portland cement up to that point1. Since then there has been great progress in portland cement-based construction materials technologies brought about by advances in the materials science of composites and the development of chemical additives (admixtures) for applications. The resulting functionalities, together with its economy and the sheer abundance of its raw materials, have elevated ordinary portland cement (OPC) concrete to the status of most used synthetic material on Earth. While the 20th century was characterized by the emergence of computer technology, computational science and engineering, and instrumental analysis, the fundamental composition of portland cement has remained surprisingly constant. And, although our understanding of ordinary portland cement (OPC) chemistry has grown tremendously, the intermediate steps in hydration and the nature of calcium silicate hydrate (C-S-H)*, the major product of OPC hydration, remain clouded in uncertainty. Nonetheless, the century also witnessed great advances in the materials technology of cement despite the uncertain understanding of its most fundamental components. Unfortunately, OPC also has a tremendous consumption-based environmental impact, and concrete made from OPC has a poor strength-to-weight ratio. If these challenges are not addressed, the dominance of OPC could wane over the next 100 years. With this in mind, this paper envisions what the 21st century holds in store for OPC in terms of the driving forces that will shape our continued use of this material. Will a new material replace OPC, and concrete as we know it today, as the preeminent infrastructure construction material?

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The reaction of one-to-one molar carbon/silica powder mixtures was studied using simultaneous thermogravimetric analysis and mass spectroscopy with crystalline and amorphous silica. Reaction proceeded via a two-stage path in which there are at least three identifiable competing global reactions. During the first stage, silicon carbide is formed along with small amounts of silicon monoxide. The most likely reaction path during this stage is the following: SiO,(s) + C(s) -+ SiO(g) + CO(g); SiO(g) + 2C(s) + SiC(s) + CO(g). The second stage consists of reactions between silica with silicon carbide which form silicon monoxide and, where conditions permit, may also form silicon metal. The major reaction during this stage is tSiO,(g) + SiC(s) + 3SiO(g) + CO(g).

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