Olive biomass ash as an alternative activator in geopolymer formation: A study of strength, radiology and leaching behaviour

Chemical, physical, mineralogical and radiological characterization of olive biomass fly ash (OBFA) and bottom ash (OBBA) was main objective to determine their potential use as alkaline activators in the preparation of alkali-activated materials or geopolymers. Water solubility tests showed that they released K and Na ions, affording a high pH and alkaline content. Pastes made with 70 wt% vitreous blast furnace slag (SL) and 30 wt% of OBFA or OBBA yielded alkali-activated materials with 28 days mechanical strength of 33 to 18 MPa. In pastes prepared with 30 wt% OBFA, strength values were comparable to those developed by slag pastes activated with a commercial KOH. However, the pastes made with 70 wt% coal fly ash and 30 wt% OBFA or OBBA proved to be inviable because the pH reached was not high enough to activate the precursor. The radiological calculations of OBFA- and OBBA-SL bearing pastes would conform to European legislation on protection against exposure to ionising radiation, for the activity concentration index (ACI) found in the final product was less than 1 in all cases. The pastes leached primarily K. The presence of elements such as Po-210 and Pb-210 at the end of the decay chain in the eluates would not limit the use of biomass ash and slag blends. These findings have confirmed the feasibility of using olive oil biomass ashes as an alternative alkaline activator in blast furnace slag systems to produce alkali-activated materials or geopolymers, with properties that make them apt for use as building materials.