Alkali activated composite binders of waste silica soda lime glass and blast furnace slag: Strength as a function of the composition

• Composite binders of urban waste glass and blast furnace slag were studied.
• The Taguchi method was useful to optimize the formulation of the composites.
• The addition of Na2CO3 promoted high dissolution of glass particles.
• The reaction products were C–S–H and silica gel.
• Glass is a promising addition to alkaline slag cements.

Composite binders of urban waste glass/blastfurnace slag activated by NaOH and NaOH/Na2CO3 were studied using statistical methods (Taguchi); the factors were: %glass, curing temperature, %Na2O and ratio of alkalis; the compressive strength was the response variable. The optimal levels at 28 days were %0glass-60 °C-6%Na2O using 2Na2CO3/NaOH; after 90 days these changed to 100%glass-60 °C-10%Na2O using Na2CO3. The microstructure and composition of the hydration products varied depending on the glass content. The reaction mechanism was mainly of dissolution-precipitation of reaction products, in some cases rims of reaction products formed around the slag particles. The confirmation experiments matched the statistical predictions.