Alkaline activation via in-situ caustification of one-part binders of composite precursors of waste glass and limestone

Abstract

Mixtures of powders of waste glass (WG), limestone (LS), Na₂CO₃ and CaO were used to formulate novel one-part in situ alkali-activated cement (WG-AAC). The in-situ interaction Na₂CO₃-CaO-H₂O promoted the formation of CaCO₃ and NaOH, which promoted the WG and LS dissolution and influenced the micro- and molecular features of the resulting cementitious products. Pastes and mortars developed 1-year strengths of up to 29 MPa and were stable underwater. Characterization by XRD, SEM, EDS, and ²⁹Si-NMR indicated that a Na₂CO₃:CaO ratio close to 1:1 resulted in polymerized C-S-H, CaCO₃, silica gel, and Ca-modified silica gel, which were intimately intermixed and possibly crosslinked through Q³ bonds. Such phases interacted synergistically improving the underwater stability of the WG-AAC, indicating that in-situ caustification is a suitable and practical alkaline activation for SiO₂-rich precursors.