Novel one-part alkali-activated binder produced with coffee husk ash

•One-part alkali-activated binders (OP-AAB) were produced with coffee husk ash (CHA)•CHA was produced in different temperatures/times to act effectively as alkaline activator.•Full physicochemical characterization of CHA showed high soluble K2CO3 content.•Application of CHA in pastes of OP-AAB based on blast-furnace slag was carried out.•Microstructural results showed positive influence of CHA in OP-AAB. New alkaline activators to generate alkali-activated binders (AAB) are being studied to reduce common use of sodium hydroxide and sodium silicate due to environmental and safety problems. In this context, a new alkaline activator is proposed from coffee wastes: coffee husk ash (CHA). Coffee husk was calcined at different temperatures (600, 700 and 800 °C) and times (1–10 h) to determine the CHA with best properties for alkaline activator: high alkali content, low organic matter content, and high solubility/pH in water. Results showed that optimum calcination time and temperature were 6 h at 700 °C. Produced CHA presented high K2O content in the form of K2CO3, and CHA generated at 700 °C presented highest solubility/pH in water. This high activity was confirmed in mixtures of CHA with blast-furnace slag (BFS) in one-part AAB, in which hydrated products were detected in pastes through microstructural tests; and compressive strength of mortars yielded 16.4 MPa after 1 day at 60 °C.