Title
Mineral Binders: chemical and physical challenges in cement and concrete
Abstract
Concrete is generally considered to be the most widely-used manufactured material on Earth. Global demand is now of the order of 10 cubic km per year. This requires the manufacture of about 4 Giga- tonnes of cement per year, accounting for about 8% of global anthropogenic CO2 emissions, despite the fact that concrete is probably the most eco-efficient of all man-made construction materials. Evidently, even small improvements in cement and concrete technology can have a significant effect on global CO2 emissions as well as on other globally-important sustainability indices.
Hydraulic cements are so called because they react with water to form stable hydrated compounds capable of bonding under wet conditions. Almost all modern concrete construction is made using hydraulic cements in which the main ingredient is a man-made mineral called “Portland cement clinker” (PCC). The most important components of PCC are calcium silicates which hydrate to give a poorly-crystalline calcium silicate hydrate referred to as C-S-H. This complex solid-solution phase constitutes the main binder in ordinary concretes, and has the great advantage of low cost; but its chemical and physical properties are complex and still rather poorly understood due to its poor crystallinity and the difficulty in analyzing its complex structure on the atomic-, nano- and meso-scale. Some recent novel hypotheses about its formation and structure will be discussed.
Many other mineral-based binders are possible, and some may be almost as inexpensive to make as C-S-H but with a lower carbon footprint. So a better general understanding of the way such materials form and bond to each other could help us better predict critical phenomena such as volume change, creep and permeability, which can strongly influence the durability of concrete structures. Some examples will be presented to illustrate the scientific challenges. Ultimately, solution of such challenges might allow us to develop a wide range of useful alternative mineral binder technologies.
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