Abstract
Systematic investigation of filtrates and filter residues resulting from a 24 h treatment of metakaolin in different alkaline solutions were performed. On filtered metakaolin particles, inductively coupled plasma-optical emission spectrometry (ICP-OES) measurements reveal an enrichment of iron and titanium, which suggests an inhomogeneous distribution of these cations. Since the SiO2/Al2O3 ratio remains constant in all filter residues examined, the dissolution of the Si and Al monomers is congruent. Structural differences, identified by attenuated total reflection–Fourier transform infrared spectroscopy (ATR-FTIR) as a consequence of alkali uptake, influence the X-ray scattering contribution of metakaolin, and thus quantifications with the partial or no known crystal structure (PONKCS) method. This leads to deviations between the degree of reaction calculated from Si and Al solubility from filtrate and that quantified by quantitative powder X-ray diffraction (QPXRD) using the filter residue. Nevertheless, the described changes do not cause a shift in the X-ray amorphous hump in case of congruent dissolution, and thus allow the quantification of the metakaolin before and after dissolution with the same hkl-phase model.
Highlights
In recent years, the pozzolanic reactivity of calcined clays has increasingly moved into the focus of research
Their use as a supplementary cementitious material (SCM) could be a component to achieve the goal of more ecological concretes, since the replacement of cement by SCM offers one of the greatest opportunities to reduce CO2 emission in the production of concrete
Various scientists were investigating the question of a test method suitable for assessing the pozzolanic reactivity of different SCM directly from the respective SCM [9,10,11,12,13,14,15,16,17,18]
Summary
The pozzolanic reactivity of calcined clays has increasingly moved into the focus of research. Various scientists were investigating the question of a test method suitable for assessing the pozzolanic reactivity of different SCM directly from the respective SCM [9,10,11,12,13,14,15,16,17,18] Another approach is the determination of the reaction degree of SCM in cementitious systems [19,20,21,22,23,24,25,26,27,28,29,30].
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