On the significance of interfacial chemistry on the strength of fly ash-cement composites

• Published in: Cement and concrete research 2022-01, Vol.151, p.106619, Article 106619
• Main Authors: Shishehbor, M., Sakaniwa, D., Stefaniuk, D., Krakowiak, K.J., Abdolhosseini Qomi, M.J.
• Format: Article
• Language: English
• Subjects: Calcium silicate hydrate; Cement hydrates; Chemical composition; Composite materials; Compressive strength; Fly ash; Interfacial chemistry; Interfacial properties; Mechanical properties; Multiscale modeling
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2021.106619

Despite the large number of studies on supplementary cementitious materials, the underlying physicochemical interfacial processes that govern their strength remain obscure. To address this knowledge gap, this paper strives to establish a relation between the chemical composition of fly ash (FA) at the molecular level and the macroscopic compressive strength in cement hydrates-FA composites. We develop a multiscale modeling framework that links the fundamental physicochemical attributes of calcium silicate hydrate (C-S-H)-FA interfaces across molecular (~1 nm), mesoscopic (~100 nm), and microscopic (~10 μm) length scales. We observe that FA's chemical composition affects the interfacial properties across all scales. FAs with higher network-modifier cation concentration show stronger molecular and mesoscale interfacial properties and statistically significant higher macroscopic compressive strength. This is particularly interesting for Class F FA, where early-age reactivity is negligible.