Mitigation of autogenous shrinkage in alkali-activated slag (AAS) using doped diatomaceous earth (DE)

Large autogenous shrinkage of alkali-activated slag (AAS) cementitious materials and the potential high early cracking risk is a critical issue for their practical application. This study explores the use of doped diatomaceous earth (DE) to mitigate autogenous shrinkage in AAS systems. By partially replacing ground granulated blast-furnace slag (GGBFS) with calcined DE, the research evaluates shrinkage mitigation across various DE dosages and alkali equivalents. The hydration process and the phase compositions of AAS with doped DE were also experimentally investigated via multiple microscopic technique including scanning electron microscopy (SEM), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). Test results show that DE significantly reduces autogenous and chemical shrinkage, with a 25% DE replacement achieving reductions of 53.1% and 28.4%, respectively. The primary mechanism for shrinkage suppression is attributed to DE's relatively lower reactivity, which induces dilution effects, slowing the hydration reaction of GGBFS and reducing the formation of shrinkage-inducing compounds like C-(N)-A-S-H gel and hydrotalcite-like compounds. nuclear magnetic resonance (NMR) analysis further reveals that DE increases the mean chain length of C-A-S-H gel, hindering gel recombination and rearrangement and contributing to reduce autogenous shrinkage by other way. This work also highlights that the shrinkage mitigation effect varies with alkalinity levels, with optimal results achieved at alkali equivalents between 5% and 6%. Importantly, DE dosages up to 20% do not compromise the workability or mechanical properties of AAS materials. This research demonstrates that doped DE is an effective technique for reducing autogenous shrinkage of AAS materials with ensured flowability and strength.