Synthesis of clay geopolymers using olive pomace fly ash as an alternative activator. Influence of the additional commercial alkaline activator used

In this research, the use of olive pomacefly ash(OPFA) as an alkaline source for the activationof calcined clays (CC) from Bail en (Ja en, Spain) was studied. The optimal composition was obtained for 70 wt % CC and 30 wt % OPFA. The physical,mechanical and thermal properties of control geopolymers that usewater as a liquidmediumhave been studied and comparedwith geopolymers that use additional activating solutions as sodiumor potassiumhydroxide solutions (8M), or amixture of alkaline hydroxide and alkaline silicate solution (NaOHeNa2SiO3 or KOHeK2SiO3). The results showed that OPFA can be used as an alkaline activator, showing mechanical properties slightly lower than those obtained when additional alkaline hydroxide activating solutions were used. The best compressive strength was obtained for geopolymers that use alkaline silicates as an activating solution. However, the best thermal insulation properties were obtained for control geopolymers. The microstructural characteristics of the geopolymers were evaluated by means of X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and Scanning ElectronMicroscopy (SEM-EDS) that corroborate the formationof geopolymeric gel inall the specimens, beingthe amount of gel formed greater insamples using commercial potassiumactivating solutions. These results demonstrate the feasibility of using this type of waste, OPFA, as activating reagents in the manufacture of geopolymers or alkaline activated materials. The manufactured geopolymers can be used as compressed earth blocks for walls and partitions, since the specimens pursue mechanical properties that comply with current regulations, presenting better thermal insulation properties.Peer reviewe