Unveiling micro-chemo-mechanical properties of C-(A)-S-H and other phases in blended-cement pastes

Current demand for novel highly sustainable concrete urges improving the links between chemical and mechanical effects of supplementary cementitious materials (SCMs) on the microstructure of blended-cement pastes. In this work, coupled NanoIndentation and Quantitative Energy Dispersion Spectroscopy (NI-QEDS) was applied to disclose chemo-mechanical properties of microstructure phases in systems incorporating typical dosages of fly ash, slag, metakaolin, or glass powder. For a fixed water-to-binder ratio of 0.4, the C-(A)-S-H chemistry was significantly affected by the SCMs, while its average mechanical properties varied within the limited ranges M ≈ 25-27 GPa, H ≈ 0.7-0.8 GPa and C ≈ 180-230 GPa. The SCMs further changed the arrangement of anhydrous phases and minor hydrates embedded in the C-(A)-S-H matrix, which were also characterized (e.g., Portlandite, AFm such as carboaluminates, or an hydrotalcite-like phase). Finally, engineering properties of blended-cement matrices requires tailoring both the intermix of hydrates and the rigid anhydrous SCM inclusions.