Microstructural Evolution of Early Reaction Products in Alkali-Activated Slag Cement at Early Age
XIAO Jianmin
LI Hui
LEI Ruixin
Abstract：The microstructural evolution of early reaction products of alkali-activated slag(AAS)pastes was investigated by X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FTIR),27Al and 29Si magic-angle spinning solid-state nuclear magnetic resonance(MAS NMR)and 1H-29Si cross polarization magic-angle spinning solid-state nuclear magnetic resonance(1H-29Si CPMAS NMR).The results reveal that calcium aluminium silicate hydrate gel(C-A-S-H),hydrotalcite and single sulfur hydrated calcium sulfoaluminate(AFm)are found in AAS pastes in 3-28 d.The C-A-S-H gel is a complex structure of end chain tetrahedra(Q1),branching chain tetrahedra(Q2),Al-replacing chain tetrahedra(Q2(1Al))or Al-replacing layered tetrahedra(Q3(1Al)).The degree of reaction increases with prolongation of hydration time.The hydration degree of slag,Al/Si molar ratio and proportion of bridging tetrahedra that is occupied by Al increase with the early 24 h hydration reaction of AAS cement.Aluminum oxygen polyhedral of slag undergoes the process of structural depolymerization,the formation of layered crystals of hydrotalcite and AFm,and the formation of Q2(1Al).In the early 24 h of the reaction,Q2(1Al)develops rapidly and water molecules are crosslinked with silicon oxygen backbone;at the same time chemical combined water is formed,the layered tetrahedra(Q3)and Q3(1Al)structures with higher polymerization degree are not found.Consequently,the 0-24 h reaction stage is the C-A-S-H oligomer gel formation stage.
Keywords：alkali-activated slag cementmicrostructureearly hydration timeproduct evolution
Publication Date：2024-05-28
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：10( 381-390 )