Intrinsic differences in atomic ordering of calcium (alumino)silicate hydrates in conventional and alkali-activated cements

• Published in: Cement and concrete research 2015-01, Vol.67, p.66-73
• Main Authors: White, Claire E., Daemen, Luke L., Hartl, Monika, Page, Katharine
• Format: Article
• Language: English
• Subjects: Alkali-activated cement; Amorphous material (B); Calcium; Calcium silicate hydrate; Calcium–silicate–hydrate (C–S–H) (B); Cements; Gels; Hydrates; Nanostructure; Order disorder; Portland cement (D); Slags; Tricalcium silicate; X-ray diffraction (B)
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2014.08.006

The atomic structures of calcium silicate hydrate (C–S–H) and calcium (–sodium) aluminosilicate hydrate (C–(N)–A–S–H) gels, and their presence in conventional and blended cement systems, have been the topic of significant debate over recent decades. Previous investigations have revealed that synthetic C–S–H gel is nanocrystalline and due to the chemical similarities between ordinary Portland cement (OPC)-based systems and low-CO2 alkali-activated slags, researchers have inferred that the atomic ordering in alkali-activated slag is the same as in OPC–slag cements. Here, X-ray total scattering is used to determine the local bonding environment and nanostructure of C(–A)–S–H gels present in hydrated tricalcium silicate (C3S), blended C3S–slag and alkali-activated slag, revealing the large intrinsic differences in the extent of nanoscale ordering between C–S–H derived from C3S and alkali-activated slag systems, which may have a significant influence on thermodynamic stability, and material properties at higher length scales, including long term durability of alkali-activated cements.