Effect of mass ratio and milling on compressive strength and corrosion resistance of blast-furnace slag/fly ash geopolymer activated by solid alkali activator

Abstract

Fly ash and granulated blast-furnace slag can be considered "multifunctional waste." This study is focused on properties of a non-cement binder prepared from slag and fly ash activated by solid alkali activator. Fly ash was milled (2.5, 5.0, and 7.5 min) in order to increase its reactivity, and particle size distribution, specific surface area, and grain morphology were determined for all milled FA samples. Two GBFS +FA mixtures (70:30 and 85:15 w/w) were studied. Prepared mixtures were activated by solid alkali activator (Na2SiO3). Optimal weight ratios were calculated for CaO, SiO2, and Al2O3 components. Properties of the mixtures were studied in dependence on the GBFS:FA mass ratio and FA milling time (0-7.5 min). After 2 and 28 days of hydration, compressive strength of all mixtures exceeded 20 and 60 MPa, respectively. The 85:15 ratio led to generally higher compressive strength 108.3 MPa was reached after 90 days using FA milled for 7.5 min. Corrosion resistance was tested by exposing mixtures to distilled water, 0.5% HCl, and 3% Na2SO4 for 65 days, and evaluated by measuring changes in CS. Also the corrosion resistance was found higher (Na2SO4) than and comparable (HCl, water) to the 70:30 ratio. This study aims to show that GBFS +FA mixtures (70:30 and 85:15 w/w) activated by solid Na2SiO3 can achieve high CS and good corrosion resistance.