Effect of alkali hydroxide on calcium silicate hydrate (C-S-H)

TY - JOUR

T1 - Effect of alkali hydroxide on calcium silicate hydrate (C-S-H)

AU - Yan, Yiru

AU - Yang, Sheng Yu

AU - Miron, George D.

AU - Collings, Ines E.

AU - L'Hôpital, Emilie

AU - Skibsted, Jørgen

AU - Winnefeld, Frank

AU - Scrivener, Karen

AU - Lothenbach, Barbara

N1 - Publisher Copyright: © 2021 The Authors

PY - 2022/1

Y1 - 2022/1

N2 - This paper investigates the effect of KOH and NaOH on C-S-H structure and solubility. Both KOH and NaOH have a similar effect, they increase pH values and silicon concentrations, and decrease calcium concentrations. At higher alkali hydroxide concentrations, more portlandite precipitates, while amorphous silica dissolves. This increases the Ca/SiC-S-H at low Ca/Sitarget but lowers the maximum Ca/SiC-S-H from 1.5 to 1.2 in 1 M KOH/NaOH. The amount of alkalis bound in C-S-H increases with increasing alkali hydroxide concentrations and is higher at low Ca/SiC-S-H. KOH/NaOH lead to a structural rearrangement in C-S-H, increasing the interlayer distance, number of layers stacked in c direction and shortening the silica chains. The mean chain lengths (MCL) estimated from FTIR and Raman spectroscopy agree well with the trends from 29Si NMR. Comparison with the independently developed CASH+ thermodynamic model showed a good agreement between the observed and modelled changes, including the shortening of the MCL.

AB - This paper investigates the effect of KOH and NaOH on C-S-H structure and solubility. Both KOH and NaOH have a similar effect, they increase pH values and silicon concentrations, and decrease calcium concentrations. At higher alkali hydroxide concentrations, more portlandite precipitates, while amorphous silica dissolves. This increases the Ca/SiC-S-H at low Ca/Sitarget but lowers the maximum Ca/SiC-S-H from 1.5 to 1.2 in 1 M KOH/NaOH. The amount of alkalis bound in C-S-H increases with increasing alkali hydroxide concentrations and is higher at low Ca/SiC-S-H. KOH/NaOH lead to a structural rearrangement in C-S-H, increasing the interlayer distance, number of layers stacked in c direction and shortening the silica chains. The mean chain lengths (MCL) estimated from FTIR and Raman spectroscopy agree well with the trends from 29Si NMR. Comparison with the independently developed CASH+ thermodynamic model showed a good agreement between the observed and modelled changes, including the shortening of the MCL.

KW - Alkali hydroxide

KW - C-S-H

KW - Ca/Si ratio

KW - Cement

KW - Characterization

UR - http://www.scopus.com/inward/record.url?scp=85117216950&partnerID=8YFLogxK

U2 - 10.1016/j.cemconres.2021.106636

DO - 10.1016/j.cemconres.2021.106636

M3 - Journal article

AN - SCOPUS:85117216950

SN - 0008-8846

VL - 151

JO - Cement and Concrete Research

JF - Cement and Concrete Research

M1 - 106636

ER -