Local structure and Ca/Si ratio in C-S-H gels from hydration of blends of tricalcium silicate and silica fume

Ana Cuesta,Isabel Santacruz,Angeles G De La Torre,Monica Dapiaggi,Jesus D Zea-Garcia,Miguel A.G Aranda

doi:10.1016/j.cemconres.2021.106405

Ana Cuesta, Isabel Santacruz + Show 4 more

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https://doi.org/10.1016/j.cemconres.2021.106405

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Abstract

At the microscale, C-S-H gels from alite, or neat Portland cements, has a Ca/Si ratio close to 1.80. At the nanoscale, C-S-H is described by a defective tobermorite structure which allows a maximum Ca/Si ratio close to 1.40. There is no agreement in the location of the extra 0.40 mol of Ca(OH)2 at the nanoscale. Atomistic modelling studies reported Ca(OH)2 species within the tobermorite interlayer space. Other works point toward a fine intermixing of defective tobermorite and nanoportlandite. Here, we have prepared a series of alite blended with silica fume and studied the pastes by several techniques including synchrotron pair distribution function (PDF). In the employed conditions, the C-S-H gel formed by the pozzolanic reaction has nearly the same local structure than the primary C-S-H gel. Furthermore, differential PDF points toward Ca(OH)2 excess having a local structure compatible with few-layer thick nanoparticles stretched along the c-axis.

Highlights

Cement industry can be considered one of the major contributors for greenhouse gases emissions because for every ton of type-I grey Portland cement (PC), ~0.95 CO2 tones are released into the atmosphere
Triclinic tricalcium silicate material had a BET specific surface area (SSA) of 1.9(1) m2 g− 1 and a dv,50 of 4.6 μm whose Particle size distribution (PSD) is shown in Fig. S1a (Supplementary information)
The multitechnique study, including synchrotron pair distribution function analysis, of the alite-silica fume blend series, complemented with hydrated belite, has allowed us to draw three main conclusions for the high-quality samples prepared by full consumption of silica fume without significant carbonation: (1) In the employed experimental conditions, the secondary C-S-H gel formed by the pozzolanic reaction has the same local structure as the primary C-S-H gel formed by the alite hydration

Summary

Introduction

Cement industry can be considered one of the major contributors for greenhouse gases emissions because for every ton of type-I grey Portland cement (PC), ~0.95 CO2 tones are released into the atmosphere. This translates into ~7% of the total anthropogenic CO2 emissions [1,2]. SCMs are reactive siliceous, aluminosiliceous, or calcium alumi nosiliceous materials with hydraulic or pozzolanic properties. Research on these systems is becoming increasingly important [5,6,7]. A wide va riety of materials are available to be used as SCMs [5], mainly silica fume, ground granulated blast furnace slag, fly ash, calcined natural minerals, biomass ashes and other industrial byproducts and wastes [7]

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