Bio-derived sodium silicate for the manufacture of alkali activated binders: use of bamboo leaf ash as silicate source

Abstract

Alkali activated binders are promising alternative to the use of Portland cement in the manufacture of concrete for curbing CO2 emissions. Novel sources of silicates have been investigated in the recent years for reducing cost and environmental impacts associated with the use of chemical activators. This study describes the production of solid sodium silicate activating powder from bamboo leaf ash (BLA). Bamboo leaves were calcined at 550-800 ºC, mixed with NaOH pellets and heated in an oven at 300 ºC. The obtained silicate powder was used for activating blended fly ash/slag samples. Mechanical and microstructural properties of BLA-based samples were compared to those of samples made with commercially available chemicals. The strength of BLA-activated mortars matched the commercially-sourced activators, being 25-30 MPa at 7 days and exceeding 40 MPa at 28 days. The microstructural analysis suggested that BLA-based sodium silicate showed a lesser degree of dissolution of precursors at 7 days, but the quality of the matrix was higher than that of NaOH-activated samples. These results confirmed that the reactivity of BLA-silicate powder was similar to that of commercial sodium silicate solutions, and show the potential valorisation of future biomass renewable waste in the production of low carbon, alkali-activated concretes.