open access publication

Article, 2024

Aqueous carbonation of aged blended Portland cement pastes: Impact of the Al/Si ratio on the structure of the alumina-silica gel

Cement and Concrete Research, ISSN 1873-3948, 0008-8846, Volume 177, Page 107428, 10.1016/j.cemconres.2024.107428

Contributors

Neto, Fábio Maia 0000-0002-0040-8140 [1] Snellings, Ruben 0000-0002-4354-4871 [2] [3] Skibsted, Jo Rgen 0000-0003-1534-4466 (Corresponding author) [1]

Affiliations

  1. [1] Aarhus University
    2. [NORA names: AU Aarhus University; University; Denmark; Europe, EU; Nordic; OECD];
  2. [2] Flemish Institute for Technological Research
    3. [NORA names: Belgium; Europe, EU; OECD];
  3. [3] KU Leuven
    4. [NORA names: Belgium; Europe, EU; OECD]

Abstract

Carbonation of recycled cement paste receives growing attention since it can carbonate end-of-life concrete at ambient conditions and chemically bind CO2 on a geological timescale. This work investigates aqueous carbonation of blended cement pastes, cured for 12–14 years and incorporating silica fume, fly ash, slags, and natural pozzolan as SCMs, using solid-state NMR, XRD, TGA and in-situ pH measurements. The carbonation products are calcite and an amorphous alumina-silica gel for all blends, where the initial calcium content governs the amount of calcite formed and, consequently, the CO2-uptake capacity. Aluminum is only present in tetrahedral coordination in the alumina-silica gel for all blends, where a higher aluminum content results in a reduced polymerization of the aluminosilicate network. A structural model for the alumina-silica gel is proposed, based on deconvolutions of the 29Si NMR spectra, which accounts for the Al/Si ratio and the reduced polymerization of silicate tetrahedra by the incorporated AlO4 units for the gels produced by carbonation of different blended cements.

Keywords

Al/Si ratio, AlO4, AlO4 units, CO2, CO2 uptake capacity, NMR, NMR spectra, SCM, TGA, XRD, alumina-silica gel, aluminosilicate, aluminosilicate network, aluminum, aluminum content, ambient conditions, amount, amount of calcite, aqueous carbonation, ash, attention, blended cement, blended cement paste, blends, calcite, calcium content, capacity, carbon, carbonate production, cement, cement paste, chemical, chemically bound CO2, concrete, conditions, content, coordination, deconvolution, fly ash, fume, gel, geological timescales, higher aluminum content, impact, in situ pH measurements, incorporating silica fume, initial calcium content, measurements, model, natural pozzolan, network, pH measurements, paste, polymerization, pozzolan, production, ratio, reduced polymerization, silica fume, silicate tetrahedra, slag, solid-state NMR, spectra, structural model, structure, tetrahedra, tetrahedral coordination, timescales, units, years

Funders

  • Danish Agency for Science and Higher Education

Data Provider: Digital Science

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