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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 deterioration induced by alkali-silica reaction (ASR) is initiated by complicated heterogeneous chemical reactions. This study describes the experimental results obtained from the model reactant experiments focused on the kinetics of physical and chemical changes in the reactive aggregate-simulated pore solution system undergoing ASR. Specifically, the study investigated the products formed by exposing reactive silica mineral (a-cristobalite) to two alkali solutions in the presence of solid calcium hydroxide [Ca(OH) 2 ]. The experimental results showed that, as long as the Ca(OH) 2 remains in the system, the dissolution of the silica mineral proceeds at a constant rate and the only reaction product formed is the tobermorite-type C-S-H. However, once the supply of Ca(OH) 2 in the system is exhausted, the level of dissolved silica ions starts to increase. At the same time, the previously formed C-S-H changes in composition by incorporating silicon and alkali ions from the solution. Continuous increase in the concentration of silica leads to formation of the ASR gel as a result of interaction between silica and alkali ions.L. Struble-contributing editor Manuscript No. 33308.

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