13C, 27Al and 29Si NMR Investigation of the Hydration Kinetics of Portland-Limestone Cement Pastes Containing CH3-COO--R+ (R=H or Na) Additives.

Anton Mazur,Konstantinos Sotiriadis,Peter Tolstoy

doi:10.3390/ma15062004

Abstract

The hydration kinetics of Portland-limestone cement pastes with organic additives in the form of acetic acid and sodium acetate were studied by using solid-state 13C, 27Al and 29Si NMR spectroscopy. The evolution of the relative content of various phases was monitored over the period of one month: amorphous and crystalline calcite (in 13C spectra), ettringite, aluminum in C-S-H gel, calcium aluminates and calcium hydroaluminates (in 27Al spectra), as well as alite, belite and silicon in C-S-H gel (in 29Si spectra). The retarding effect of the additives on cement hydration at early age was demonstrated. We show that the kinetics of phase assemblage formation is influenced by the acetate ion adsorption on the surface of the anhydrous cement components and hydrated phases. The kinetics of formation of ettringite in the cement paste, depending on the addition of acetic and or sodium acetate, is discussed in the context of potential thaumasite sulfate attack.

Highlights

Cement-based building materials are among the most used in modern construction. Despite their widespread application and the large amount of information regarding the chemistry of cement pastes [1,2], several issues regarding their properties during the hydration process and the effect of various environmental factors on the hardened material are still not clear
One of these factors is the chemical sulfate attack, which might occur in the form of conventional or thaumasite sulfate attack (TSA) [3,4]
As more silicon is available for the formation of thaumasite during TSA, which is derived from the continuously deteriorating calcium silicate hydrate phase, cement paste gradually transforms into a non-cohesive mass, further contributing to the destruction of building structures

Summary

Introduction

Cement-based building materials are among the most used in modern construction Despite their widespread application and the large amount of information regarding the chemistry of cement pastes [1,2], several issues regarding their properties during the hydration process and the effect of various environmental factors on the hardened material are still not clear. One of these factors is the chemical sulfate attack, which might occur in the form of conventional (ettringite or gypsum formation) or thaumasite sulfate attack (TSA) [3,4]. TSA is dangerous for Portland-limestone cement materials, because the presence of calcium carbonate facilitates this type of chemical attack

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Conclusion