Cement: a two thousand year old nano-colloid

Since Roman times, cement is one of the synthetic materials with the largest production and usage by mankind. Its properties allowed the expansion of the Roman Empire and the building of still fascinating works. In spite of the diverse use of cement and the abundant literature accumulated during a century of systematic scientific research on this material, the understanding of its properties is still far from complete. Several issues are still open, ranging from the understanding of the hydration kinetics and the influence of the modern industrial additives, to the deep comprehension of the atomic arrangement and nanostructure of disordered hydrated calcium silicate phase (C-S-H) formed by hydration. This feature article briefly summarizes recent results in the field, highlighting the necessity for a colloidal model of the cement microstructure that, combined with the layer-like structure of the colloidal units, is the most effective approach to fully describe the characteristics of this peculiar material.