Sodium aluminate activated waste glass: Reduced efflorescence behavior by C(N)−A−S−H transformation

Waste glass has been highly used in alkali activated materials, but the efflorescence behavior remains an intractable issue. This study investigates the effect of sodium aluminate as an activator to activate waste glass with the aim to mitigate the efflorescence behavior, and blast furnace slag is used as calcium source as well as to promote the early age strength. The gel structure (reaction product) was characterized by ²⁹Si and ²⁷Al NMR, subsequently the efflorescence behavior was investigated. Results show that sodium aluminate provides more AlOH₄⁻, which acts as cross-linking agents, linking silicate tetrahedra to form a three-dimensional gel network. A longer mean chain length of gels increases hydrogen sites at end-chain Q¹ silicate species, which can be replaced by cations along the silicate chain. The promoted formation of C(N)−A−S−H gel captures more Na⁺ in the pore solution, contributing to a limited Na⁺ leaching and higher resistance towards efflorescence.