TY - JOUR

T1 - Impact of sulphate source on the hydration of ternary pastes of Portland cement, calcium aluminate cement and calcium sulphate

AU - Qoku, Elsa

AU - Bier, Thomas A.

AU - Schmidt, Gert

AU - Skibsted, Jørgen

N1 - Publisher Copyright: © 2022 Elsevier Ltd

PY - 2022/8

Y1 - 2022/8

N2 - The present work investigates the hydration and evolution of solid phase assemblage as a function of sulphate source in ternary Portland cement (PC), calcium aluminate cement (CAC) and calcium sulphate (CS¯HX) cement pastes. Two binders are compared, a PC‒rich and a CAC ‒ CS¯Hx ‒rich paste, containing gypsum and anhydrite as sulphate carrier, using a multi-method approach including calorimetry, XRD, TGA, MAS NMR spectroscopy, microscopy and thermodynamic modelling. The overall phase assemblage is very similar for the two-sulphate source in both PC-rich and CAC ‒ CS¯Hx−rich systems. However, the quantitative X-ray analysis, TGA and the 27Al, 29Si NMR show that the amounts of the crystalline hydrates and X-ray amorphous phases are influenced by the type of sulphate. In the long-term hydration, the anhydrite-bearing formulations exhibit the highest amount of ettringite, whereas the gypsum-containing samples develop a higher fraction of AFm phases and X-ray amorphous hydrates. This difference may relate to faster dissolution kinetics of gypsum compared to anhydrite in the studied ternary blends. For the CAC ‒ CS¯Hx −rich pastes, gehlenite from CAC (C2AS) shows hydraulic activity, which primarily results in the precipitation of strätlingite. Higher amounts of strätlingite are identified in the gypsum bearing samples, suggesting that the type of sulphate source impacts the hydration of silicate-bearing phases. Finally, the phase assemblages from thermodynamic modelling (using the GEMS software) are found to be in good agreement with those observed experimentally, although some differences occur as a result of kinetic effects.

AB - The present work investigates the hydration and evolution of solid phase assemblage as a function of sulphate source in ternary Portland cement (PC), calcium aluminate cement (CAC) and calcium sulphate (CS¯HX) cement pastes. Two binders are compared, a PC‒rich and a CAC ‒ CS¯Hx ‒rich paste, containing gypsum and anhydrite as sulphate carrier, using a multi-method approach including calorimetry, XRD, TGA, MAS NMR spectroscopy, microscopy and thermodynamic modelling. The overall phase assemblage is very similar for the two-sulphate source in both PC-rich and CAC ‒ CS¯Hx−rich systems. However, the quantitative X-ray analysis, TGA and the 27Al, 29Si NMR show that the amounts of the crystalline hydrates and X-ray amorphous phases are influenced by the type of sulphate. In the long-term hydration, the anhydrite-bearing formulations exhibit the highest amount of ettringite, whereas the gypsum-containing samples develop a higher fraction of AFm phases and X-ray amorphous hydrates. This difference may relate to faster dissolution kinetics of gypsum compared to anhydrite in the studied ternary blends. For the CAC ‒ CS¯Hx −rich pastes, gehlenite from CAC (C2AS) shows hydraulic activity, which primarily results in the precipitation of strätlingite. Higher amounts of strätlingite are identified in the gypsum bearing samples, suggesting that the type of sulphate source impacts the hydration of silicate-bearing phases. Finally, the phase assemblages from thermodynamic modelling (using the GEMS software) are found to be in good agreement with those observed experimentally, although some differences occur as a result of kinetic effects.

KW - Amorphous phases

KW - Anhydrite

KW - Calcium aluminate cement

KW - Gypsum

KW - Hydrate phase assemblages

KW - Portland cement

KW - Sulphate ternary binders

UR - http://www.scopus.com/inward/record.url?scp=85129937471&partnerID=8YFLogxK

U2 - 10.1016/j.cemconcomp.2022.104502

DO - 10.1016/j.cemconcomp.2022.104502

M3 - Journal article

AN - SCOPUS:85129937471

VL - 131

JO - Cement and Concrete Composites

JF - Cement and Concrete Composites

SN - 0958-9465

M1 - 104502

ER -