Chemo-Mechanical Properties of Cement Matrices with Fly Ash and Slag

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Title: Chemo-Mechanical Properties of Cement Matrices with Fly Ash and Slag

Author(s): William Wilson, Luca Sorelli, and Arezki Tagnit-Hamou

Publication: Special Publication

Volume: 320

Issue:

Appears on pages(s): 29.1-29.14

Keywords: calcium-aluminum-silicate-hydrates (C-A-S-H); calcium-silicate-hydrates (C-S-H); fly ash (FA); ground granulated blast-furnace slag (S); microstructure; nanoindentation; SEM-EDS; statistical deconvolution; supplementary cementitious materials (SCMs)

Date: 8/1/2017

Abstract:
A better understanding of the microstructural features of cement matrices incorporating supplementary cementitious materials (SCMs) represents key knowledge for engineering more sustainable concrete infrastructures. By fostering the coupling of nanoindentation techniques with quantitative energy-dispersive Xray spectroscopy (NI-QEDS), this work aims at disclosing the effects of substituting Portland cement by 30% fly ash or 50% slag on hydrous and anhydrous phases. Notably, after one year of hydration, measurements attributed to calcium-(aluminum)-silicate-hydrates, C-(A)-S-H, showed average Ca/(Si+Al) ratios < 1.5 for the pastes with SCMs, compared to Ca/(Si+Al) 1.9 for a Portland-cement-only paste. Interestingly, an intermix of C-(A)-S-H and hydrotalcite-like phases was also found in the slag-containing system. Nevertheless, similar micro-mechanical properties were found for these different C-(A)-S-H (modulus M 26–29 GPa [3770–4205 ksi] and hardness H 0.8–0.9 GPa [115–130 ksi]), which indicate that C-A-S-H formed by fly ash or slag reaction may replace Portland-cement C-S-H with equivalent mechanical properties at the micrometer scale.